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Acute Health Effects of the
Cantara Metam Sodium Spill
An Epidemiologic Assessment
C A L I F O R N I A D E P A R T M E N T O F H E A L T H S E R V I C E S
Environmental Epidemiology & Toxicology Program
JUNE 1992
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E X E C U T I V E S U M M A R Y
On July 14, 1991, a major pesticide spill occurred in a remote area of Northern California near the
town of Dunsmuir. Due to a train derailment, 19,000 gallons of the herbicide metam sodium were
released into the Sacramento River. Nearly all aquatic life in a 45-mile segment of the river from the spill
site to Lake Shasta was killed as the chemical flowed downstream. Individuals near the river reported a
variety of symptoms from exposure to vapors released by the decomposing chemical. This report,
prepared by the California Department of Health Services (DHS) Environmental Epidemiology and
Toxicology Program (EETP), examines health effects of the spill reported to the local medical community
from July 14 to August 16,1991.
F I N D I N G S
Sourccs of information for this investigation included area hospital records, pesticide illness
reports filed by private physicians, and questionnaires completed by individuals using the temporary
evacuation and triage center in Dunsmuir. Cases were defined as anyone who sought evaluation at one
of these three sources of information for symptoms they felt were spill-related.
During the one-month period of study, 705 cases were identified. These individuals accounted
for a total of 848 medical visits. The number of medical evaluations was approximately equally
distributed between the hospital emergency rooms, private physicians, and triage center. Most of the
cases were from Dunsmuir (70.6%), Mt. Shasta (7.2%) and Castel la (6.4%) which were the three
communities closest to the spill site. By age distribution, the largest number of cases were in the 30-39
age group. Relatively few cases were recorded for ages 50 and over. For each age group, more females
than males reported symptoms.
A wide range of symptoms were recorded. Overall, the most common symptoms were headache
(63.8%), eye irritation (48.5%), nausea (46.2%), throat irritation (42.0%), dizziness (29.6%), shortness of
breath (27.1%), diarrhea (25.3%), nasal irritation (23.1%), and chest tightness (22.4%). The types of
symptoms reported varied little by gender and age. However, there were significantly fewer symptoms
per person on average for those less than 20 and those greater than 69 years of age. Odors were reported
by 35% of the cases. The most common odor reported was a sulfur/rotten egg smell. Symptoms did not
differ significantly between those reporting an odor and those who reported no odor. Smokers appeared
to have more symptoms and higher frequency rates for nearly all symptoms than those identified as non-
smokers. However, data on odor detection and smoking history was missing for a large number of cases.
Many people reported symptoms more than one week after the spill. The types of symptoms
reported were similar although a significantly higher percentage of weakness, diarrhea, cough, and rash
were recorded among those reporting symptoms a week or more later. Most exposure and symptom
onsets appeared to occur within the first two days after the spill. However, nearly one-quarter of the
cases in which initial exposure and symptom onset dates were known app>eared to delay evaluation for
seven or more days after symptom onset.
Seven hospitalizations were recorded. There were four respiratory-related admissions, two cases
of possible syncope (fainting), and one case of a cardiac arrhythmia in a person involved in initial clean
up activities. All were discharged by July 28. There were no fatalities.
Eight women who were pregnant at the time of the spill were identified through the
investigation. No adverse pregnancy outcomes were identified although two women did obtain
therapeutic abortions in part because of concerns over exposure effects.
An analysis of Dunsmuir cases suggested that nearly 14% of the population within the city limits
sought medical evaluation. Within the Dunsmuir area, it appeared that exposures occurred on both sides
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of the river at distances of up to 1500 feet away from the river. In an analysis using serial 300 foot zones
away from each side of the river, symptom rates appeared highest among the population who lived
within 300 feet of the river (21.2%), decreased and remained relatively constant at 12-15% for the
population living within 301-600, 601-900, and 901-1200 feet from the river, and increased to 19.8% for
those living between 1201-1500 feet from the river.
C O N C L U S I O N S
The Cantara incident had an undeniably devastating environmental impact on the affected
portion of the Sacramcnto River. The full extent of health effects has not been determined. The data in
this report was observational, uncontrolled, and subject to many types of bias. It can not support absolute
cause and effect relationships. However, several important points can be made.
Approximately 700 individuals sought medical attention for symptoms they believed were
related to the spill-a highly significant finding given the sparse population of the area. The finding that
14% of Dunsmuir city residents sought mcdical care is quite striking. However, the study did not include
those who did not seek care. It is likely the number of cases included in this investigation is an
underestimate of the true number of people affected. Symptoms were consistent with exposure to irritant
gases. Irritation of the eyes, gastrointestinal tract, respiratory tract and skin occurred. Non-specific
neurologic complaints also were common. Gender, age, and smoking status were factors which appeared
to affect symptom reporting.
Exposure assessment is limited by a lack of environmental data for the first two days after the
spill. The exact types and concentrations of substances which were present is not known. Because metam
sodium decomp>oscs rapidly upon dilution in water, exposure-related symptoms are believed to be
secondary to its volatile breakdown products of which the most likely is methyl isothiocyanate (MITC).
Some symptoms probably occurrcd at chemical concentrations below odor thresholds which is consistent
with MITC toxicology. Based on odor reports, exposure to hydrogen sulfide also occurred although its
significance in producing symptoms is unknown. Because there were no fatalities and few
hospitalizations, it is unlikely that prolonged, high-level exposures occurred.
Although most exposure and symptom onsets appeared to occur within the first two days after
the spill, symptoms unexpectedly were being reported many days after the spill. Later symptom reports
may be due to: delays in seeking medical evaluation; attributing non-spill-related symptoms to the
incident; psychologically mediated symptoms similar to that seen with post-traumatic stress disorder;
slowly resolving or chronic health problems related to exposure; or unrecognized or underestimated
toxicologic properties of the spilled chemical such as persistence in the environment and sensitization of
certain individuals to the chcmicals. The long-term health effects of exposure, including effects on the
reproductive system remain to be determined.
R E C O M M E N D A T I O N S
The incident has raised questions regarding the lack of a hazardous material classification for
transportation of metam sodium, the overall safety and toxicology of metam sodium, the effectiveness
and efficiency of the emergency response of public health agencies, and health care access in a crisis
situation. Specific DHS follow-up activities which are currently in progress to address these concerns
i n c l u d e :
Follow-up Investigation of the Affected Population: DHS-EETP recently conducted a door-to-
door survey in the city of Dunsmuir to determine the extent of symptoms experienced and further define
exjx)sure effects. The investigation includes individuals not seen by health care providers and will also
address health care access in the area. Results wil l be released at a later date.
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Birth Defects Monitoring: DHS is monitoring prcgnancy and birth outcomes in the affected area
through the DHS Genetic Disease Branch and its Birth Defects Monitoring Program. An interim report is
exp>ected by Fall, 1992.
Characterization of Metam Sodium: Staff from DHS laboratories are characterizing metam
sodium and its breakdown products more precisely in order to improve exposure modelling. Improved
methods of measuring metam sodium and other environmental contaminants are being investigated
(metam sodium toxicology has been extensively reviewed and will be discussed in an upcoming
document produced by Cal-EPA).
Emergency Response Capability Improvement: DHS has collaborated with other agencies to
improve the emergency response for railroad chemical spills. Staff currently participate on the Railroad
Accident Prevention and Immediate Deployment Force (RAPID) which recently was established through
State Senate Bill 48. DHS also is evaluating its internal emergency response procedures and methods of
improvement. Field communications equipment is being upgraded. Simulated mock emergencies
similar to the Cantara incident are planned periodically as a training tool for DHS staff.
Communication of Risks and Results: DHS will maintain a strong presence in Dunsmuir for the
next several months to communicate with community members and physicians about health concerns.
Collaboration with Other State and Federal Agencies: DHS will continue to work with other
public health agencies to support tighter regulations which protect public health in the areas of chemical
classification, transportation, and marketing.
A C K N O W L E D G M E N T S
This document was produced by the California Department of Health Services (DHS)
Environmental Epidemiology and Toxicology Program (EETP), Lynn Goldman, Chief. David Hewitt
(DHS-EETP) and Richard Kreutzer (DHS-EETP) were the authors. The report would not have been
possible without the generous assistance of Terri Barber (Siskiyou County Environmental Health
Department) and many other county health department staff.
Co-investigators of the incident included; Dennis Shusterman, California Environmental
Protection Agency (Cal-EPA), who was first on the scene and produced the initial surveillance forms;
Richard Sun (DHS Infectious Disease Branch); Dena Mangiamele (DHS Veterinary Public Health Unit)
Lynn Goldman (DHS-EETP) and Richard Jackson (Cal-EPA). Additional support with data abstraction
and analysis was provided by Glen Ikawa (DHS Epidemiology and Disease Prevention Section (EDPS),
Jennifer Mann (Cal-EPA), Theresa Saunders (DHS-EETP), and Joanne Siebles (DHS-EDPS).
Toxicologic support and advice were provided by Michael DiBartolomeis (Cal-EPA), Asa
Bradman (DHS-EETP), Robert Howd (Cal-EPA), and Richard Lam (Cal-EPA). Geographic and population
data were provided by Robert Sellman (Planning Director, Siskiyou County). Maps were produced by
Tim Lomas (DHS-EETP) and Rachel Broadwin (DHS-EETP). Peer review and suggestions were provided
by Amy Casey (DHS-EETP), Lynn Goldman (DHS-EETP) Martin Kharrazi (DHS-EETP), Denise Koo
(DHS-EETP), Daniel Smith (DHS-EETP), and Suzanne Teran (DHS-EETP). David Simmons and Theresa
Saunders (DHS-EETP) formatted and assembled the report.
Special thanks goes to the Mt. Shasta Mercy Hospital, the Redding Medical Center and Redding
Mercy Hospital medical records staffs for their assistance in this investigation.
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Table o f Contents
L I S T O F T A B L E S A N D H G U R E S v
B A C K G R O U N D 6
D e s c r i p t i o n o f t h e I n c i d e n t 6
T o x i c o l o g y o f M e t a m S o d i u m a n d B y p r o d u c t s 8
D H S - E E T P R e s p o n s e t o t h e I n c i d e n t 1 0
M E T H O D S 1 1
D a t a C o l l e c t i o n I n s t r u m e n t s 1 1
D a t a S o u r c e s 1 2
D a t a A n a l y s i s 1 2
R E S U L T S 1 4
D a t a S o u r c e s 1 4
C l i n i c a l M a n i f e s t a t i o n s o f E x p o s u r e 1 6
H o s p i t a l i z a t i o n s 2 5
P r e g n a n c i e s 2 5
H e a l t h I m p a c t o f t h e S p i l l o n D u n s r n u i r 2 5
D I S C U S S I O N ^
L i m i t a t i o n s o f T h i s S t u d y 2 9
M a j o r F i n d i n g s 2 9
C O N C L U S I O N S 3 1
R E C O M M E N D A T I O N S 3 ] _
G e n e r a l R e c o m m e n d a t i o n s 3 1
S p e c i fi c F o l l o w - u p A c t i v i t i e s I n P r o g r e s s 3 3
R E F E R E N C E S 3 5
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List of Tables and Figures
TABLES
1 . O d o r a n d I r r i t a n t T h r e s h o l d s o f M e t a m S o d i u m B r e a k d o w n P r o d u c t s 9
2 . S i t e o f S p i l l - R e l a t e d M e d i c a l E v a l u a t i o n 1 4
3 . C i t y o f R e s i d e n c e f o r C a s e s 1 4
4 . O d o r s R e p o r t e d b y C a s e s 1 6
5 . N u m b e r ( P e r c e n t ) o f C a s e s R e p o r t i n g S e l e c t e d S y m p t o m s 1 8
6 . Num ber ( Pe r cen t ) o f Cases Repor t i ng Se lec t ed Sym pt om s by G ender 19
7. Percent of Cases Repor t ing Selected Symptoms by 10-year Age Groups 20
8. Number (Percent) of Cases Reporting Selected Symptoms by Odor Detection Status 21
9. Number (Percent) of Cases Reporting Selected Symptoms by Smoking Status 22
10. Number (Percent) of All Visits in Which Selected Symptoms arc Rep>orted by Date Evaluated 23
1 1 . I n i t i a l E x p o s u r e b y I n i t i a l S y m p t o m O n s e t D a t e 2 4
1 2 . I n i t i a l S y m p t o m O n s e t b y I n i t i a l M e d i c a l E v a l u a t i o n D a t e 2 4
1 3 . S p i l l - R e l a t e d H o s p i t a l A d m i s s i o n s 2 5
14. Dunsmuir City Population and Number (Percent) Reporting Symptoms by Gender and Age 28
15. Dunsmuir Area Population and Number (Percent) Reporting Symptoms by Distance of
H o m e f r o m t h e S a c r a m e n t o R i v e r 2 8
FIGURES
1 . M a p o f A f f e c t e d A r e a 7
2 . A g e a n d G e n d e r D i s t r i b u t i o n o f C a s e s 1 5
3 . D a t e a n d S i t e o f S p i l l - R e l a t e d M e d i c a l E v a l u a t i o n s 1 6
4 . R e s i d e n c e L o c a t i o n o f D u n s m u i r A r e a C a s e s 2 7
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Acute Health Effects of the
Cantara Metam Sodium Spill
An Epidemiologic Assessment
On the evening of July 14, 1991, 19,000 gallons of the herbicide metam sodium were spilled into
the Sacramento River in Northern California as the result of a train derailment. As the chemical travelled
downstream, it killed nearly all aquatic life in its path over an approximately 45-mile segment of the river.
Individuals near the river experienced a variety of symptoms related to exposure to the vapors released
by the chemical. The purpose of this report is to describe health effects of the spill reported to the local
mcdical community for an approximately one-month period immediately following the spill. Public
health implications of the incident and recommendations for further study are also addressed.
B A C K G R O U N D
Description of the Incident
The Sacramento River in Northern California has long been renowned for its beauty and excellent
trout fishing. Originating near Mt. Shasta, it flows southward to Lake Shasta (Figure 1). Human
population along this segment of the river is generally sparse.
On July 14, 1991, at 21:40 hours, a Southern Pacific railroad train consisting of 97 cars and four
locomotives derailed on a tight bridge curve spanning the Sacramento River in a remote area known as
the "Cantara Loop," located approximately six miles north of the town of Dunsmuir. A locomotive, six
empty freight cars, and an unlabeled tank car left the tracks. The tank car fell from the bridge into the
river and came to rest in a partially inverted position in the shallows directly beneath the bridge.
Although the exact cause of the derailment has not been determined, one proposed theory is that
the train may have derailed when one or more of the lead engines momentarily lost and then regained
traction causing a sudden surge. The portion of the train on the curve then may have been pulled tight or
straight with the cars behind it and derailed-a phenomenon termed "stringlining" or "bowstringing."^ It
has also been theorized that the make-up of the train alone (i.e., the order in which cars were linked) may
have been sufficient to cause the bowstringing.
Crew members reported odors coming from the derailed cars shortly after the derailment. By
approximately 21:51, the Dunsmuir clerk and railroad dispatcher's office in Roseville, California had been
a d v i s e d o f t h e d e r a i l m e n t . C r e w m e m b e r s r e v i e w e d t h e t r a i n m a n i f e s t t o d e t e r m i n e t h e c o n t e n t s o f t h e
derailed cars. The tank car, a U.S. Department of Transportation (DOT) 111-A, which has a single 7/16
inch thick steel wall and is the most common type of tank car in use, was not placarded as carrying a
haza rdous subs tance . C on ten ts w e re l i s ted i n the t ra i n man i fes t as " w eed k i l l e r " and i den t i fied an hou r o r
more later as metam sodium.^ The Material Safety Data Sheet (MSDS)^ for the substance was reviewed
and listed the contents as 32.7% metam sodium and 67.3% proprietary or nonhazardous ingredients.
There was little information in the MSDS on procedures for dealing with the release of a large amount of
the substance. Because metam sodium was not officially classified as a hazardous material by the DOT at
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the time of the spill, the manifest contained no specific toxicologic information or recommendations in the
event of an accidental release as is required for hazardous materials.
At approximately 04:30 on July 15, Southern Pacific staff who had inspected the site reported a
three by four inch hole in the derailed tank car above the water line which was not leaking. It was
estimated that approximately 1500 gallons of metam sodium might have leaked into the river. As reports
of health effects and dead fish downstream became available later that morning, the extent of the spill
was reevaluated. Reexamination of the tank car revealed two submerged holes in the car at the point
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where it was resting on the river bed.^ At approximately noon on July 15, the extent of the spill was
upgraded to 19,500 gallons, the entire capacity of the tank car.
Because a small amount of metam sodium mixed with river water remained in the tank car at the
time it was pulled from the river on July 16, at 16:30, final estimates have placed the amount of material
actually released into the Sacramento River to be approximately 19,000 gallons of a 32.7% concentrated
solution of metam sodium in water with no other constituents. It is believed that nearly all of the metam
sodium was released during the first hour after the derailment.^
The spilled material was noted to travel en masse southward at approximately 0.5-1.0 mph until
it reached Lake Shasta, 45 miles from the spill site, in the early hours of July 17. Aquatic life along this
section of the river was severely affected. California Department of Fish and Game biologists reported
fish k i l l s in the hundreds o f thousands.
Once the plume entered Lake Shasta, it appeared to remain in a stationary, unbroken mass (it is
not known how much metam sodium remained in this plume). Southern Pacific, hoping to hasten the
dispersal and degradation of the chemical, implemented a previously untested aeration procedure on July
20, which continued through July 30.^ While the effectiveness of the procedure remains unknown, levels
of the primary metam sodium breakdown product in lake water samples were below detection levels by
July 29.
The largest population center on the affected segment of the river is the town of Dunsmuir
(population 2129, 1990 census)" , located six miles downstream from the spill (Figure 1). Several much
smaller communities (Castella, Sweetbrier, La Moine, Pollard Flats, Delta, and Lakehead) are located
farther downstream. In addition, there are several campgrounds located along this segment of the river.
By 06:00 on July 15, the county health department had logged complaints from Dunsmuir
residents of irritated eyes and unpleasant odors from the river. The tail-end of a light yellow green plume
was reported to pass through Dunsmuir around 07:45.^ Mt. Shasta Mercy Hospital, located a few miles to
the north of the spill site, began seeing exposure-related illnesses in its emergency room by 11:(X) on July
15 .
At approximately 11:30 on July 15, the city manager of Dunsmuir ordered the Dunsmuir Police
Department to begin a mandatory evacuation of the town. This was downgraded to a voluntary
evacuation order approximately one hour later and remained in effect until July 19. At 14:00 on July 15, a
temporary shelter for voluntary evacuees was established at the Dunsmuir High School, located on a hill
approximately 1500 feet from the river. The shelter remained open until 20:(X) on July 20. Paramedics
were stationed at the shelter to assess, treat, and triage health complaints.
Toxicology of Metam Sodium and Byproducts
D E S C R I P T I O N O F C O M P O U N D A N D B Y P R O D U C T S
Metam sodium (also known as sodium methyldithiocarbamate), molecular formula C2H4NS2Na,
is most commonly used as a soil fumigant which is added to fields as an aqueous solution prior to
planting crops in order to control nematodes, soil fungi, weeds, weed seeds, and soil insects. Agricultural
use of metam sodium has increased dramatically in recent years since other previously used fumigants,
such as 1,3 dichloroprof)ene (Telone), were removed from the market because of health concerns. An
estimated 7 to 12 million pounds of metam sodium are used annually in the U.S.; among the 50 states,
California accounts for the largest percentage of use.^'^ It is typically applied to soil at rates of up to 300
lbs per acre. Because pure metam sodium in white crystalline solid form is unstable, it is normally
transported in a concentrated solution in water for commercial use.^
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Metam sodium in this form is essentially non-volatile. Upon further dilution with water, (as
would occur when applied to moist soil), it is believed to rapidly decompose to the volatile compounds,
methyl isothiocyanate (MITC), which is the major biocidal byproduct, and hydrogen sulfide (H2S). Other
potential, albeit less common, byproducts include methylamine and carbon disulfide. '
MITC is expected to volatilize completely from treated soil within two to three weeks after appli
cation. Because MITC is highly water soluble, it has the potential to leach into groundwater. In aquatic
environments, it is not expected to bio-concentrate in aquatic organisms or adsorb to sediment or
suspended organic matter.
E X P O S U R E E F F E C T S
Acute effects: Given metam sodium's rapid decomposition upon dilution with water, the
potential for exposure to the parent comp>ound was expected to be minimal. Both MITC and H2S, the two
main byproduct gases, are chemical irritants. For H2S, a gas which can occur naturally, exfxjsure effects
are better known. Low concentrations of H2S in the range of 10 - 200 parts per million (ppm) can cause
localized eye and respiratory tract irritation. Higher concentrations may produce systemic symptoms
such as nausea, vomiting, diarrhea, headache, dizziness, confusion, weakness, tachypnea, tachycardia,
cardiac arrhythmia and sweating.^ MITC is known to be extremely irritating to skin and mucous mem
branes and at much lower concentrations than Although other acute health effects of MITC
exposure in humans are less well described, the health effects would appear to be similar to those seen
with H2S exposure based on limited data from animal studies and case reports of occupational
exposure.' Metam sodium is a thiocarbamate and, unlike carbamate and organophosphate pesticides,
does not significantly inhibit cholinesterase.
An important difference between the two compounds is the relationship between their odor and
irritant threshold concentrations as shown in Tabic 1. MITC can cause symptoms at concentrations not
normally detected by the sense of smell. In contrast, H2S can be smelled at levels much less than those
necessary to produce irritant symptoms.
MITC should not be confused with methyl isocyanate (MIC), the substance released during a
1984 industrial accident in Bhopal, India, in which over 2000 deaths and 200,000 injuries were reported.
Although MITC and MIC are structurally related and both are chemical irritants, they are distinct
chemicals with different toxicologic properties. Also, toxicologic evidence suggests MIC concentrations
were several thousand times higher in Bhopal than expected MITC concentrations from the Cantara
incident. Thus, observed exposure effects in Bhopal can not be directly translated to MITC.
TABLE 1. odor and I r r i tan t Thresho lds o f Metam Sodium Breakdown
P r o d u c t s
C O M P O U N D
C H A R A C T E R I S T I C M I T C H 2 S R e f e r e n c e s
O d o r h o r s e r a d i s h r o t t e n e g g s 1 0 , 1 1
O d o r t h r e s h o l d * l O O p p b 1 p p b 1 1 , 1 2
I r r i t a n t t h r e s h o l d * 7 0 p p b 1 0 , 0 0 0 p p b 7 , 1 2
* Lowest reported valuesthresholds may vary considerably from person to person.
ppb = parts per billion
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Chronic Effects: Other health effects from exposure to metam sodium or MITC have not been
well-defined. Because a number of required laboratory animal studies have not yet been completed,
specific data on carcinogenic, reproductive, and other chronic effects are incomplete. '* Information which
i s k n o w n i s s u m m a r i z e d b e l o w :
Carcinogenicity: Studies of MITC for carcinogenicity in rats and mice have been negative.
Metam sodium itself has not been examined in a long-term study for cancer end-p>oints.'
Teratogenicity: Based on published data by the California Department of Food and Agriculture
(CDFA), it was initially believed that there were no teratogenic effects from exposure to metam sodium or
its byproducts. However, further review of information contained in CDFA's proprietary data files by
California Environmental Protection Agency (Cal-EPA) staff indicated that metam sodium may be a
teratogen, producing neural tube defects in rats and rabbits at high doses. At levels which showed
minimal maternal toxicity, MITC administration was associated with fetal growth retardation in rabbits.
Effects on humans are unknown. MITC is currently being tested for teratogenicity.
Chronic respiratory effects: Individuals exposed to irritant gases similar to MITC occasionally
have been shown to develop prolonged bronchial hyper-responsiveness (i.e., reactive airway dysfunction
syndrome or RADS) following an initial chemical bronchitis.^^
DHS-EETP Response to the Incident
I N I T I A L R E S P O N S E
Both Siskiyou and Shasta Counties were affected by the spill since the county line crosses the
affected river segment just south of Dunsmuir. There were considerable challenges in coordinating the
emergency response across both counties. A command post was established at the Siskiyou County
Sheriffs Department substation in the city of Mt. Shasta, less than five miles north of the spill site. Central
management operations, which included most state agency representatives, were located at the California
Department of Forestry (CDF) Ranger Office in Redding, approximately 60 miles south of the spill site.
The California Department of Fish and Game (CDFG) was the lead agency in responding to the incident.
Over 50 federal, state, county, and local agencies ultimately became involved at some point in the first
week following the incident.
The California Department of Health Services (DHS) became aware of the incident at
approximately 08:00 on July 15. Later that afternoon, staff from the DHS Hazard Identification and Risk
Assessment Branch (HIRAB) were dispatched to the incident site to provide medical, toxicologic, and
epidemiologic support to the local health departments and to document the event (HIRAB officially
became part of the newly-formed Cal-EPA on July 17,1991). On July 17, as the magnitude of the incident
became more apparent, additional staff from the DHS Environmental Epidemiology and Toxicology
Program (EETP) and physicians from the DHS Preventive Medicine Residency Program were sent to aid
in the epidemiologic investigation and remained through July 20.
EPIDEMIOLOGIC INVESTIGATION OBJECTIVES
In the early phases of the incident, several unknown variables complicated predicting the
potential health effects of the spill. The exact composition of the tank car contents, including the
possibility of unidentified toxic constituents in the metam sodium solution, was not immediately known.
Although prior laboratory data and limited occupational rep>orts provided an indication of the probable
environmental fate and potential health effects, the chemical behavior of such a large quantity of metam
sodium in a dynamic, non-laboratory environment could not be predicted with certainty. There were no
pre-established "off-the-shelf" guidelines for measuring metam sodium or MITC in the environment.
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Reliable MITC air sampling methods and equipment, which could quantify the exposures that were
occurring, were not in place until July 17, more than two days after the spill. Furthermore, there was a
one to three day turn-around time for laboratory reports on MITC air levels.
Therefore, the first objective of the epidemiologic investigation was to quickly determine the
immediate risk to public health and the extent of health effects from the spill. Activities in this area have
been described previously. To briefly summarize, telephone calls and on-site visits to area hospitals
and the shelter facility were made from July 15 to July 20. Health care providers at these sites were
interviewed regarding the number of spill-related patients evaluated and the types and severity of
symptoms they had seen. Patient medical charts were reviewed. Reported symptoms were assessed for
consistency with known toxicologic end-points of metam sodium and were examined for evidence of
exposure to unexpected substances. This rapid assessment indicated that: 1) a substantial number of
individuals reported symptoms from the spillmost of which did not require hospitalization; 2) there
were no fatalities as a result of the spill; and 3) reported symptoms were generally consistent with
exposure to irritant vapors such as those expected to be produced from decomposition of metam sodium.
A second objective of the investigation was to more formally document and analyze spill-related
health effects reported to the local medical community and occurring within the first month after the
incident. Information from such a study could be used to define better the toxicology of this relatively
unstudied chemical and more fully gauge the total acute health impact of the incident. Methods and
findings of this analysis are described below.
M E T H O D S
We examined spill-related health effects reported from July 14 through August 16, 1991, from
either the temporary evacuation and triage shelter in Dunsmuir, private physicians in the Dunsmuir/Mt.
Shasta region, or area hospitals. For each of these information sources, cases were defined as persons
reporting symptoms during the period of study which they believed were secondary to the spill.
Exposure was based on self-report. Cases could potentially include area residents, tourists, or individuals
traveling through the affected area who sought medical evaluation at one of the information sources.
D a t a C o l l e c t i o n I n s t r u m e n t s
A one-page, self-administered questionnaire for patients was designed by DHS staff and
distributed to both the shelter and the Mount Shasta emergency room on July 15. In addition to name,
gender, age, address, and date completed, the questionnaire contained a list of possible symptoms based
on known metam sodium toxicology which could be checked or circled. A space to write in any other
symptoms which may have been experienced was provided. The questionnaire also asked respondents
to describe any odors they smelled and the location, time, and duration of their exposure. The original
questionnaire form was revised slightly during the first week after the spill to include a more complete
list of possible symptoms and facilitate easier completion by respondents.
Pesticide Illness Reports (PlR's) were a second data collection instrument. These are one-page
forms which must be completed by any California physician who examines a patient with health
problems suspected to be pesticide related. The forms are submitted to both the County Health Officer
and the State. Items on the form include the patient's name, gender, age, and address, date of evaluation,
and date, time, location, and route of exposure. Physicians are also asked to briefly describe symptoms,
physical findings, treatment, and indicate if the patient was pregnant at the time of exposure.
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A single abstraction form was designed to extract data from the questionnaires, PIR's and
hospital patient records. Information which could be captured by the abstraction form included patient
demographics, symptoms, physical findings, test results, treatment, and exposure history. The
abstraction form was prepared in an Epi Info computer database for direct key entry of records when
possible. The procedures for obtaining the information from each of the three sources are described
b e l o w .
D a t a S o u r c e s
1. Dunsmuir Shelter: Individuals using the Dunsmuir shelter triage facility during its period of
operation from July 15-20, were encouraged by shelter staff to complete the questionnaire. Parents were
asked to complete the questionnaire for young children. Questionnaires were collected by shelter staff
and later returned to DHS. In addition, DHS was permitted to review a separate index card file which
shelter paramedics had maintained for all patient contacts. Questionnaires were supplemented with
paramedic data when possible to complete the case profile.
2. Local Physicians: DHS obtained copies of all spill-related PIR's for the study period which had
been received by the Siskiyou County Environmental Health Department through September, 1991.
3. Hospital data: Three hospitals (Mercy Hospital in Mt. Shasta, Mercy Hospital in Redding, and
the Redding Medical Center) were identified within 25 miles of the affected river segment and thus were
presumed most likely to see spill-related illnesses. On July 15 and 16, DHS contacted each hospital by
telephone regarding spill-related patient contacts. DHS requested access to all emergency room and
inpatient medical records of patients identified by hospital staff as being spill-related. Mt. Shasta Mercy
Hospital staff agreed to distribute and collect questionnaire forms identical to those distributed at the
shelter. Patients voluntarily completed the questionnaire while waiting for evaluation. If completed,
questionnaires were included in the patient's permanent medical record and used by abstractors to
supplement information provided by the attending physician. Two-person teams abstracted records on-
site at each of the three hospitals during the first week after the spill.
Once the field investigation team left on July 20, Mt. Shasta Mercy Hospital was contacted daily
by telephone through August 16 to monitor the number of spill-related patients being seen. Because the
two hospitals in Redding reported very few spill-related patient contacts during the first week after the
spill, they were not surveyed after July 19. The remaining spill-related patient charts for the study period
from Mt. Shasta Mercy Hospital were abstracted on-site in August.
Data Analysis
Once all records were entered into a single Epi Info database, they were reviewed for duplicates.
Some individuals had records abstracted from multiple sources. If the recorded visits for the same person
occurred on different days, they were considered separate records regardless of the reporting source. If
the visits to different reporting sources occurred on the same day, it was usually the result of paramedics
at the shelter triaging patients to either local physicians' offices or to the Mount Shasta emergency room.
Thus, these visits were considered to represent a theoretical single visit for which information provided
by paramedics and attending nurses and physicians was combined. Any discrepancies in the information
provided by the different reporting sources were individually inspected, resolved where the correct
information was clear (e.g, key entry error) and, in the few cases of continued confusion, resolved in favor
of the emergency room or private physician record.
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Data were analyzed by date and site of evaluation, age, gender, and city of residence.
Frequencies of reported odors and symptoms were calculated. Symptoms were stratified by age, sex,
evaluation site, date of evaluation, odor detection, and smoking history. A one-way analysis of variance
or Student's t-test was used to determine whether the average number of symptoms reported per case
differed for any of the stratified variables. Relation of symptom onset to exposure date and evaluation
da te w as a l so exami ned .
All hospitalizations and pregnancies identified through the surveillance were reviewed. In
October, DHS staff conducted a telephone follow-up survey of women identified as pregnant at the time
of the spill. This survey included questions on past pregnancy history, number of weeks pregnant at the
time of the spill, progress of pregnancy since the spill, and pregnancy outcome.
An exposure assessment analysis of cases reporting their city of residence as Dunsmuir was
performed because: 1) Dunsmuir was the largest community affected by the spill; 2) it was located
closest to the spill and therefore, presumably had the highest contaminant levels; 3) it straddles the
Sacramento River so that nearly all residents are located within a short distance of the river and were
theoretically at risk of exposure; 4) its location 6 miles from the spill site meant that the leading edge of
the spill plume would have reached the city sometime in the early morning of July 15-a time when most
residents would be expected to be at home; and 5) 1990 census data gives a relatively current estimate of
the population at risk so that rates of illness could be calculated.
Exposure assessment for individual cases was limited by the absence of environmental
monitoring data for the first 2 days after the spill. As a surrogate for exposure, distance of the exposure
site from the river was examined in relation to symptom reporting and attack rates for Dunsmuir
residents. The primary exposures for Dunsmuir residents were assumed to have occurred at home on the
morning of July 15.
A map of the Dunsmuir area showing the location of city limits, major streets and highways, and
the Sacramento River, was produced using the computer program ARC/lnfo.^^ Home addresses of cases
listing their city of residence as Dunsmuir were determined using database information. For those cases
in which a street address was not given (i.e. missing or P.O. Box), a 1991 telephone directory of the area
was consulted. As a final method of determining home address, the Dunsmuir post office was contacted
to provide a street address. Cases in which the street address could not be located were excluded. Case
residences then were geo-coded and plotted on the Dunsmuir map.
Rates of illness were calculated for the Dunsmuir population and stratified by age and gender
using only those cases who actually lived within the city limits as the numerator and 1990 census data as
t h e d e n o m i n a t o r .
To examine the association between residential distance from the river and symptom reporting,
we created 300 foot concentric regions or zones around the river. Because of the irregular city
boundaries, the zones included some areas outside the city limits. Zones were also extended
approximately one-half mile past the southern city boundary to include those cases who reported their
city of residence as Dunsmuir but lived just south of the city limits. Populations of each zone were
determined from census block data. Where a block crossed two or more zones, the proportion of the
block population in the zone was presumed equal to the proportion of the block's housing units located
wi th in that zone. Rates o f i l l ness were ca lcu la ted and contrasted for each zone.
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R E S U L T S
D a t a S o u r c e s
Information was obtained for 848 medical visits that were related to the spill from July 15 through
August 16,1991. There were a total of 705 separate individuals with 115 seeking medical attention more
than once (89 seen twice, 24 seen three times, and 2 seen four times). The number of medical evaluations
were approximately equally distributed between the triage center, physicians' offices and emergency
rooms (Table 2).
Of the 278 emergency room visits recorded, 257 (92.4%) occurred at Mt. Shasta Mercy Hospital;
13 (4.7%) occurred at the Redding Medical Center; and 8 (2.9%) occurred at Redding Mercy Hospital.
Information from 223 visits to private physicians in the area was primarily obtained from pesticide illness
reports which were received from 17 different providers.
The total number of shelter evaluations (361) is slightly lower than that previously reported by
shelter staff. Data arc missing for those individuals who did not complete questionnaires. A total of 23
individuals evaluated at the shelter sought additional evaluation from emergency rooms or private
physicians.
TABLE 2. Site of Spill-Related Medical Evaluation
N U M B E R O F E V A L U A T I O N S
Emergency Room
M D O f fi c e
Shelter Only
U n k n o w n
R e p e a t
Includes 19 initially seen at shelter.
Includes 4 initially seen at shelter.
TABLE 3. City of Res-idence for Cases
N U MB E R O F C A S E S
D u n s m u i r
M t . S h a s t a
C a s t e l l a
L a k e h e a d
Other (
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Characteristics of Cases
As shown in Table 3, the majority of individuals who sought medical attention were from the
communities of Dunsmuir (70.6%), Mt. Shasta (7.2%), and Castella (6.4%), which were the three
communities closest to the spill site. The age and gender distribution of those reporting symptoms are
shown in Figure 2. For each age group, more females than males reported symptoms, particularly for
those between age 20 and 39. Overall, 54.3% of the individuals reporting symptoms were female. Of
individuals reporting symptoms, the largest numbers were seen in the 30-39 age group.
Figure 3 shows the number of spill-related medical visits by both date and site of evaluation. The
number of visits remained relatively constant from July 15 to 19, decreased sharply on Saturday, July 20,
and gradually tapered off during the second post-spill week. A small increase in the number of visits was
noted on Monday, July 29. There were 28 additional visits from August 1 to 16.
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S Y M P T O M S
Symptoms most commonly reported at first evaluation by individuals seeking medical attention
are shown for each evaluation site in Table 5. The symptoms reported at each site were generally similar.
Overall, the most common symptom reported was headache (63.8%); nearly half of the individuals
evaluated complained of eye irritation and/or nausea. Symptoms represented in the "other" category
included: depression, disorientation, drowsiness, dry mouth, earache, fatigue, fever, hot flashes,
irritability, memory reduction, nose bleed, numbness, pain in the arms or legs, ringing in the ears, and
sweating. Each of these symptoms was reported by fewer than 5% of the cases.
A significantly (p < .05) higher percentage of emergency room patients reported dizziness,
weakness, eye irritation, nausea, vomiting, respiratory symptoms (shortness of breath, chest tightness,
cough and wheeze), metallic taste, nervousness, flushing and chills. The average number of symptoms
reported by each case was also significantly higher for emergency room patients than for private
physician or shelter patients.
As shown in Table 6, the distribution of symptoms varied little by gender. Females reported a
significantly higher percentage of diarrhea and nervousness. There was not a significant difference
between males and females in the mean number of symptoms reported per case.
Types of symptoms reported by age groups are shown in Table 7. Distribution of symptoms was
generally similar for each age group. There were significantly fewer symptoms per person on average for
those less than 20 and greater than 69 years of age.
Table 8 compares the types of symptoms reported for cases 10 years of age or older based on
whether an odor was reported. A total of 227 cases reported smelling an odor while 49 reported smelling
no odor. A large number of cases (282) did not have any data regarding odor detection. The frequency of
headache was significantly higher among those reporting an odor; the frequency of weakness,
nervousness, and flushing was significantly higher among those reporting no odor. Otherwise, the
distribution of symptoms was generally similar. The mean number of symptoms p>cr case was not
significantly different based on odor detection status.
Table 9 compares the type of symptoms reported by smoking status. Data on smoking status was
limited. A total of 75 cases were recorded as current smokers while 48 specifically reported they did not
smoke. There were 435 cases in which this data was missing. The distribution of symptoms was similar
based on smoking status although, for nearly all symptoms, the frequencies were lower in the non-
smokers. The only symptom in which this difference was statistically significant was shortness of breath.
The mean number of symptoms per case was higher for smokers but not statistically significant.
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TABLE 5. Number (Percent) of Cases Reporting Selected Symptoms
S I T E
Emergency Room
Private Physician S h e l t e r
T o t a l
S Y M P T O M n = 2 1 9
n = 171 n = 30 7
p-va lue
N = 697
N e u r o l o g i c
h e a d a c h e 1 3 5 ( 6 1 . 6 ) 104 (60.8) 206 (67.1) 0 . 2 7
445 (63.8)
d i z z i n e s s 8 6 ( 3 9 . 3 ) 31 (18.1) 89 (29.0) < 0 . 0 1
206 (29.6)
w e a k n e s s 5 0 ( 2 2 . 8 ) 6 (3.5)
25 (8.1) < 0 . 0 1 81 (11.6)
M u c o m e m b r a n o u s I r r i t a t i o n
e y e 1 2 3 ( 5 6 . 2 )
77 (45.0)
138 (45.0) 0 . 0 2 338 (48.5)
t h r o a t 1 0 4 ( 4 7 . 5 ) 68 (39.8) 121 (39.4) 0 . 1 4 293 (42.0)
n a s a l 5 1 ( 2 3 . 3 ) 37 (21.6) 73 (23.8) 0 . 8 7 161 (23.1)
G a s t r o i n t e s t i n a l
n a u s e a 1 1 6 ( 5 3 . 0 )
84 (49.1) 122 (39.7) 0 . 0 1 322 (46.2)
d i a r r h e a 5 5 ( 2 5 . 1 )
51 (29.8) 70 (22.8) 0 . 2 4 176 (25.3)
a b d o m i n a l p a i n 4 8 ( 2 1 . 9 )
37 (21.6) 46 (15.0) 0 . 0 7 131 (18.8)
v o m i t i n g 4 9 ( 2 2 . 4 )
26 (15.2) 29 (9.4) < 0 . 0 1
104 (14.9)
R e s p i r a t o r y
s h o r t n e s s o f b r e a t h 7 7 ( 3 5 . 2 ) 30 (17.5) 82 (26.7)
< 0 . 0 1
189 (27.1)
c h e s t t i g h t n e s s 6 7 ( 3 0 . 6 ) 26 (15.2) 63 (20.5) < 0 . 0 1
156 (22.4)
c o u g h 6 7 ( 3 0 . 6 )
13 (7.6) 17 (5.5) < 0 . 0 1
97 (13.9)
w h e e z e 3 2 ( 1 4 . 6 ) 17 (9.9) 32 (10.4)
< 0 . 0 1 81 (11.6)
D e r m a t o l o g i c
r a s h 3 0 ( 1 3 . 7 ) 32 (18.7) 33 (10.7) 0 . 0 5
95 (13.6)
i t c h i n g 3 2 ( 1 4 . 6 )
14 (08.2)
32(10.4)
0 . 1 2 78 (11.2)
M i s c e l l a n e o u s
m e t a l l i c / o d d t a s t e 3 2 ( 1 4 . 6 ) 2 (1.2)
16 (5.2) < 0 . 0 1 50 (7.2)
n e r v o u s 1 7 ( 1 7 . 8 ) 5 (2.9)
11 (3.6) 0 . 0 4 33 (4.7)
fl u s h i n g 2 1 ( 9 . 6 )
1 (0.6) 9 (2.9) < 0 . 0 1
31 (4.4)
c h i l l s 1 4 ( 6 . 4 ) 4 (2.3) 4 (1.3) < 0 . 0 1 22 (3.2)
o t h e r 8 9 ( 4 0 . 6 ) 84 (49.1) 91 (29.6) < 0 . 0 1 264 (37.9)
Mean number of
s y m p t o m s p e r c a s e 5 . 9
4 . 4 4 . 3 < 0 . 0 1 4 . 8
A Pearson chi square was used to compare proportions of patients reporting symptoms by sites; an
analysis of variance was used to compare mean number of symptoms by site.
' S i te i nde te rmina te fo r 8 cases .
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Number (Percent) of Cases Reporting Selected
Symptoms by Gender
GENDER*
SYMPTOM
N e u r o l o g i c
h e a d a c h e
dizz iness
w e a k n e s s
M u c o m e m b r a n o u s I r r i t a t i o n
G a s t r o i n t e s t i n a l
d i a r rhea
abdominal pain
vomiting
R e s p i r a t o r y
s h o r t n e s s o f b r e a t h
chest tightness
cough
w h e e z e
D e r m a t o l o g i c
itching
M i s c e l l a n e o u s
metal l ic/odd taste
lushing
F e m a l e
n = 379
250 (66.0)
124 (32.7)
41 (10.8)
182 (48.0)
170 (44.9)
91 (24.0)
184 (48.5)
113(29.8)
74(19.5)
63 (16.6)
100 (26.4)
90 (23.7)
51 (13.5)
42 (11.1)
50 (13.2)
47(12.4)
31 (8.2)
13 (3.4)
19 (5.0)
12 (3.2)
150 (39.6)
n = 319
198 (62.1)
85 (26.6)
40 (12.5)
160 (50.2)
126 (39.5)
75 (23.5)
140 (43.9)
66 (20.7)
57(17.9)
41 (12.9)
91 (28.3)
68 (21.3)
46 (14.4)
42 (13.2)
47 (14.3)
31 (9.7)
20 (6.3)
21 (6.6)
12 (3.8)
10 (3.1)
116(36.4)
p-value~
Mean number ot
s y m p t o m s p e r c a s e 5 ^ 0 4 7 0 . 2 2
Gender unknown for 7 cases.
^ A Pearson chi square was used to compare proportions of patients reporting
symptoms by gender; a Student t-test was used to compare the mean number of
symptoms by sex.
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Table 7. Percent of Cases Reporting Selected Symptoms by 10-year Age Groups
AGE (years)*
0 - 9 1 0 - 1 9 2 0 - 2 9 3 0 - 3 9 4 0 - 4 9 5 0 - 5 9 6 0 - 6 9 70 +
n = 1 0 1 n = 1 0 2
n = 8 1 n = 1 4 7 n = 1 1 6 n = 5 2 n = 3 9
n = 2 1
S Y M P T O M
(%) (%) (%) (%) (%) (%) (%) (%)
p-value"'"
N e u r o l o g i c
h e a d a c h e 3 2 . 7 6 4 . 7 7 7 . 8 7 4 . 1
7 7 . 6
5 7 . 7 6 9 . 2
4 7 . 6 < 0 . 0 1
d i zz i ness
9 . 9 2 1 . 6 3 9 . 5
3 8 . 1 3 9 . 7 3 4 . 6 2 3 . 1
3 3 . 3 < 0 . 0 1
w e a k n e s s 7 . 9 6 . 9
1 8 . 5 1 0 . 9
1 2 . 9
1 3 . 5 2 0 . 5 1 4 . 3
0 . 1 6
M u c om e m br a n ou s I r r i t a t i o n
eye
3 8 . 6
4 7 . 1 5 1 . 9 4 9 . 0 5 1 . 7 4 8 . 1
6 6 . 7
5 2 . 4 0 . 1 8
t h r o a t
2 3 . 8 3 2 . 4 5 3 . 1 5 3 . 7 4 9 . 1 5 1 . 9 4 6 . 2 2 8 . 6 < 0 . 0 1
n a s a l
1 7 . 8 2 5 . 6 2 5 . 9 2 9 . 3 2 6 . 7 2 6 . 9 2 5 . 6 1 9 . 0 0 . 5 4
G a s t r o i n t e s t i n a l
n a u s e a
2 9 . 7 4 6 . 1 5 8 . 0 5 1 . 0 5 1 . 7 5 0 . 0 4 3 . 6 1 4 . 3 < 0 . 0 1
d i a r r h e a 2 7 . 7 1 7 . 6 2 7 . 2 3 4 . 7 3 1 . 9 2 3 . 1 1 7 . 9 4 . 8 0 . 0 1
abdominal pain 1 6 . 8
2 0 . 6 2 3 . 5 1 6 . 3 1 3 . 8 2 3 . 1 1 5 . 4 9 . 5 0 . 3 6
vomiting
1 5 . 8 7 . 8 2 3 . 5 1 6 . 3 1 3 . 8 2 1 . 2 1 0 . 3 0 . 0 0 . 0 4
R e s p i r a t o r y
s h o r t n e s s
o f b r e a t h
7 . 9 1 1 . 8 3 3 . 3 3 3 . 3 3 5 . 3 5 0 . 0 3 5 . 9 2 3 . 8 < 0 . 0 1
chest tightness
4 . 0 1 2 . 7 3 0 . 9 2 7 . 2 3 2 . 8 3 2 . 7 3 0 . 8 2 3 . 8 < 0 . 0 1
cough
1 4 . 9 8 . 8 1 9 . 8 1 3 . 6 1 3 . 8 1 5 . 4 2 8 . 2 4 , 8 0 . 1 0
w h e e z e 7 . 9 3 . 9
1 6 . 0 1 7 . 0 1 4 . 7 1 9 . 2 1 7 . 9 0 . 0
0 . 0 1
D e r m a t o l o g i c
r a s h 1 2 . 9 1 3 . 7 1 4 . 8
1 5 . 0 1 2 . 9 1 3 . 5 1 2 . 8
1 9 . 0 0 . 9 9
itching
5 . 9 8 . 8 1 4 . 8 1 1 . 6 12.9 17.3 1 0 . 3 9 . 5 0 . 4 4
M i s c e l l a n e o u s
m e t a l l i c / o d d
t a s t e 1 . 0 1 . 0 9 . 9 8 . 8 1 1 . 2 1 1 . 5 1 7 . 9 4 . 8 < 0 . 0 1
n e r v o u s
3 . 0 1 . 0 3 . 7 6 . 8
6 . 9 3 . 8
1 5 . 4 4 . 8 0 . 0 4
flushing
3 . 0 1 . 0 6 . 2 4 . 1 4 . 3 3 . 8 1 2 . 8 4 . 8 0 . 2 0
c h i l l s 2 . 0 0 . 0 4 . 9
5 . 4 1 . 7 5 . 8 5 . 1 0 . 0 0 . 1 8
o t h e r 3 7 . 6 1 9 . 6
3 7 . 0 4 2 . 9 4 8 . 3 4 4 . 2 4 1 . 0 5 2 . 4 < 0 . 0 1
Mean number
of symptoms
p e r c a s e
3 . 2 3 . 7 6 . 0 5 . 7 5 . 7 5 . 7 5 . 8 3 . 8 < 0 . 0 1
* Age unknown for 46 cases.
A Pearson chi square was used to compare proportion of patients reporting symptoms by age; an analysis of variance was
used to compare the mean number of symptoms by age group
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TABLE 8. Number (Percent) of Cases Reporting Selected Symptoms by
Odor Detec t ion S ta tus
O D O R D E T E C T I O N S T A T U S
SYMPTOM
N e u r o l o g i c
h e a d a c h e
dizz iness
w e a k n e s s
M u c o m e m b r a n o u s I r r i t a t i o n
G a s t r o i n t e s t i n a l
n a u s e a
d i a r rhea
abdominal pain
vomiting
R e s p i r a t o r y
s h o r t n e s s o f b r e a t h
chest tightness
cough
w h e e z e
Dermatol OGic
r a s h
itching
M i s c e l l a n e o u s
metal l ic/odd taste
n e r v o u s
flushing
M e a n n u m b e r o f
s y m p t o m s p e r c a s e
n = 227
191 (84.1)
109 (48.0)
41 (18.1)
155 (68.3)
142 (62.6)
101 (44.5)
135 (59.5)
86 (37.9)
61 (26.9)
40(17.6)
92 (40.5)
81 (35.7)
39 (17.2)
49 (21.6)
37 (16.3)
28 (12.3)
34 (15.0)
16 (7.0)
15 (6.6)
10 (4.4)
97 (42.7)
n = 4 9
33 (67.3)
22 (44.9)
20 (40.8)
30 (61.2)
26 (53.1)
19 (38.8)
30 (61.2)
13 (26.5)
14(28.6)
8 (16.3)
22 (44.9)
17(34.7)
13 (26.5)
12 (24.5)
9(18.4)
11 (22.4)
7(14.3)
11 (22.4)
9 (18.4)
4 (8.2)
17(34.7)
p -va l ue '
Excludes cases
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T A B L E 1 0 .
Number (Percent) of All Visits in Which Selected Symptoms are
Reported by Date Evaluated
DATE SEEN
SYMPTOM
N e u r o l c x s i c
h e a d a c h e
d i z z i n e s s
w e a k n e s s
M u c o m e m b r a n o u s I r r i t a t i o n
G a s t r o i n t e s t i n a l
d i a r r h e a
abdominal pain
vomiting
R e s p i r a t o r y
s h o r t n e s s o f b r e a t h
chest tightness
cough
w h e e z e
Dermatol oGic
itching
M i s c e l l a n e o u s
m e t a l l i c / o d d t a s t e
n = 564
364 (64.5)
177 (31.4)
58 (10.3)
272 (48.2)
224 (39.7)
123 (21.8)
254 (45.0)
138 (24.5)
105 (18.6)
80(14.2)
163 (28.9)
143 (25.4)
72 (12.8)
64(11.3)
72 (12.8)
63 (11.2)
33 (6.2)
30 (5.3)
27 (4.8)
19 (3.4)
193 (34.2)
7 / 2 2 - 8 / 1 6
n = 247
163 (66.0)
64 (25.9)
39 (15.8)
120 (48.6)
108 (43.7)
56 (22.7)
120 (48.6)
84 (34.0)
60 (24.3)
46 (18.6)
65 (26.3)
54 (21.9)
49 (19.8)
39(15.8)
50 (20.2)
25 (10.1)
24 (9.7)
14 (5.7)
14 (5.7)
8 (3.2)
131 (53.0)
fl u s h i n g 2 7 ( 4 . 8 ) 1 4 ( 5 . 7 ) 0 . 6 0
c h i l l s 1 9 ( 3 . 4 ) 8 ( 3 . 2 ) 0 . 9 2
o t h e r 1 9 3 ( 3 4 . 2 ) 1 3 1 ( 5 3 . 0 ) < 0 . 0 1
Mean Number of
s y m p t o m s p e r v i s i t 4 8 5 4 0 . 0 1
Evaluation date unknown for 37 cases.
A Pearson chi square was used to compare the proportion of patients reporting symptoms by date
seen; a Student t-test was used to compare the mean number of symptoms by date.
C H R O N O L O G Y O F S Y M P T O M S
An unexpected finding was the continued reporting of health complaints a week or more after
the spill. Table 10 compares the types of symptoms reported during the first week after the spill to those
reported a week or more later. Significantly higher percentages of weakness, diarrhea, cough, rash, and
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other symptoms were reported among those seen later. The remaining symptoms showed little
difference in distribution between the two groups.
Table 11 compares initial exposure and symptom onset date. For those cases in which exposure
and symptom onset date were known, 212 (57.8%) of individuals reported initial symptoms and exposure
occurred July 15. A total of 314 (85.6%) reported symptom onset within one day after exposure, 24 (6.5%)
reported symptom onset two days after exposure, and 29 (7.9%) reported symptom onset three or more
days after exposure.
Table 12 compares the initial symptom onset date to the date of first evaluation. For those in
which this information was complete, 130 (27.9%) sought evaluation within one day of symptom onset
while 113 (24.3%) delayed evaluation for seven or more days after symptom onset.
Table 11. Initial Exposure by Initial Symptom Onset Date
EXPOSURE DATE (July)
S Y M P T O M
DATE (July) 1 4
1 5 1 6
1 4 7
1 5 2 8 2 1 2
1 6 1 3 3 1 3
1 7 2 1 3 2
1 8 1 8 4
1 9 0 8 0
2 0 0
1
0
2 1 0 2 0
2 2 - 2 5 1 4
2
T o t a l 4 0 2 8 1 2 1
Exposure date not given for 127 cases. Symptom onset date not given for 45 cases. Neither exposure nor symptom
onset date given for 166 cases.
Table 12. Initial Symptom Onset by Initial Medical Evaluation Date
SYMPTOM DATE (July)
EVALUATION
D A T E ( J u l v ) 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1
1 4 0
7 / 2 2 - 8 / 1 6
1 5 0 4 7 4 7
1 6 0 2 1 4 2 5
1 7 1 3 3 1 1 8 5 3
1 8 1 3 7 1 0 4 5 5 7
1 9 1 4 0 9 1 2 6 1 2 8 0
2 0 0 1 9
5
4
4
4
2
3 8
2 1 1
5 4 1 2 2 1 0 1 6
7 /22 -8 /16 6 8 8 1 6 5 3 4 8 3 1 5 1 4 8
Tota l 1 0 2 9 1 5 9 3 4 2 0 2 2 11 1 8 1 5 465'
Symptom onset not given for 202 cases. Evaluation date not given for 29 cases, Neitfier symptom onset nor
evaluation date given for 9 cases.
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Hospitalizations
A total of seven individuals were admitted to Mt. Shasta Mercy Hospital during the first week
after the spill for possible exposure related illness. A summary of these patients is shown in Table 13.
There were four respiratory-related admissions, and two cases of possible syncope (fainting). Cardiac
arrhythmia (bigeminy) and disorientation were noted in one individual who probably received a
particularly intense exposure through involvement in initial clean-up activities at the spill site . All
patients were discharged by July 28. There were no other known spill-related hospital admissions in the
area. There were no human fatalities due to the spill.
TABLE 13. Spill-Related Hospital Admissions (Mt. Shasta Mercy Hospital)
A D M I T D I S C H A R G E
C A S E / S E X / A G E
1 / F / 3 4
2 / M / 3 6
D I S C H A R G E D I A G N O S E S
Syncope, headache, light headedness,
abdominal cramps with nausea and
vomiting
PVO's* with bigeminy, respiratory
distress, probable mucosal irritation,
h e a d a c h e
3 / F / 4 2
Asthma exacerbat ion
4 / M / 3 4
5 / M / 6 3
Asthma exacerbat ion
COPD exacerbation
6 / M / 5 5
7 / M / 4 6
PVC = premature ventricular contraction.
COPD = chronic obstructive pulmonary disease.
Syncope-unexplained, chronic alcohol
use, COPD
Acute bronchospasm and subsequent
p n e u m o n i a
Pregtiancies
Eight women who were pregnant and in the spill area were identified during the surveillance. A
follow-up survey of pregnancy outcomes in October, 1991, found that two of the women who were in the
first trimester of prcgnancy elected to have a therapeutic abortion. Four women who were in the second
trimester of pregnancy at the time of the spill reported symptoms immediately following the spill
including headache, eye irritation, nausea, and rash. All women expressed concern over the possible
effects exposure might have on their developing child. Their physicians have told them their pregnancies
appear to be progressing normally. The remaining two women could not be contacted.
Health Impact of the Spill on Dunsmuir
A total of 498 (70.6%) of the 705 cases listed their city of residence as Dunsmuir. Of these, 391
(78.5%) had home addresses which could be located within or directly adjacent to the Dunsmuir city
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limits (Figure 4). For the 107 remaining cases, a street address could not be identified or, in a few isolated
cases, the address was much farther south or north of the city limits.
Rates of symptom reporting for cases living within the Dunsmuir city limits are shown in Table
14. A total of 290 cases, or approximately 13.6% of the Dunsmuir city population based on 1990 census
data, sought medical evaluation for symptoms attributed to the spill during the first month after the
incident. Rates of symptom reporting appeared slightly higher among females than males (14.57o vs
12.4%). Larger differences were seen based on age group. Approximately 20% of the 20 to 29 and 30 to 39
age group population reported symptoms while less than 10% of those in the 60 to 69 and over 70 age
groups reported symptoms.
Rates of symptom reporting for each 300 foot zone away from the Sacramento River are shown in
Table 15. Total population included in the analysis (2539) is higher than the Dunsmuir city population
because the analysis includes census blocks adjacent to the Dunsmuir city limits. Overall, 391 (15.4%) of
the Dunsmuir area population rep>orted symptoms based on 1990 census block data. Rates were highest
in the 0-300 foot zone (21.2%), decreased and remained relatively constant at 12-15% for the 301-600, 601-
900 and 901-1200 foot zones, and increased again to 19.8% for the 1201-1500 foot zone. There was no
significant change in distribution when attack rates were stratified by initial symptom onset date (results
not shown). Rates based on age and gender distribution could not be calculated because distribution of
t hese va r i ab l es w i th i n the i nd i v i dua l census b l ocks w as no t ava i l ab l e .
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Figure 4. Residence Location of Dunsmuir Area Cases *
i I ' a 1
' t / ' U ^ ' J
: / / ///,' A n/
\ ' '7/ / /=// I
" I '( ' vlY \
' V \ \ V\\ ^ J O X I
^ \ \ V ' = ^ 1 X
I ^ > a
\ \
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' / V ^ ^ -i ' ' I
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' ' ; ' '11 ' '' '7
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\ \ M a \ Y \ \
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[ a l m U l e 5 \ \ \ V ^
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SacramenU Rirer
[almUle 5
Citr Limits
Sovnheni Pacific Railroad
= 5 f-dse
= 7 Cdsa
= 3 Caia
= 9 Case
i n r m m i s M M ^ ^ \ ^ ^ ^
Sovnheni Pacific Railroad A A i J ' ' ' '
100 ?ool latenraJs ."rom Ritct f \ P t j i
T'= y'}t p'< ' :'
/ I 7 a ' ^ 5 n J ^ V ' 1 > '
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= Kds (SHELTER) rf'? | , i/;fi.' ,[ / / /
= 4 Cases /I ' i 'a*l|a< il ' ^ ^
f ^ i t " i * ^ 1 ' ' ' ^
yc '=* iA*. 1 ', ', ;
\ 1 ^ t a v i r | . J I < .
f I I i I glT ^ I I ' ' '
J D S-Ho'l: ,, 1 ' ' '
f fl / ' I I ' ' '
' .' ' ^ ///S i 7^ -' /
,7/ ///*,i // .''/
r # 1 ^ ' I t i t ' ' f
M l l i l l B m
(=^7 ' ^' //r' I -'''
^J ; ; ; ; ;
' ' / f t
/ / / ' ^ / S / / J f : > t
y / / / ^ / - ' ' / ' ' '
f Z / v / W y y / /
For purposes of presentation, the
northern city limit boundary, which
extends for approximately 2 more
miles, is not shown. No cases
were located in this essential ly
undeveloped, non-residential area.
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Table 14. Dunsmuir City Population and Number (Percent)
Reporting Symptoms by Gender and Age
F e m a l e
D U N S M U I R
p o p u l a t i o n '
1990 census figures.
Only cases in which home located within city limits.
Gender not given for 3 Dunsmuir cases.
Age not given for 15 Dunsmuir cases
Table 15. Dunsmuir Area Population and Number (Percent)
Reporting Symptoms by Distance of Home from
t h e S a c r a m e n t o R i v e r
D U N S M U I R
p o p u l a t i o n '
D U N S M U I R
C A S E S
Distance from River (feet)
3 0 1 - 6 0 0
6 0 1 - 9 0 0
9 0 1 - 1 2 0 0
1 2 0 1 - 1 5 0 0
86 (21.2)
87(13.6)
99 (14.4)
76 (12.9)
43 (19.8)
391 (15.4)
Based on 1990 census block figures, includes areas surrounding city limits (see
Figure 4).
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D I S C U S S I O N
Limitations of This Study
Because this investigation represents only individuals who actively sought medical evaluation, it
is probable that the number of people who exp>erienced health effects from the spill is higher. Those who
experienced milder symptoms may not have associated them with the spill or considered them serious
enough to seek medical evaluation. Others may have left the area temporarily. Tourists and campcrs
may have returned home rather than be evaluated. Several shelter evacuees told us of frustration over
long waits and leaving without being seen at the suddenly overwhelmed emergency room. Anecdotal
reports from residents have indicated that the spill exaggerated preexisting problems in health care access
in the impacted area. However, although some individuals who experienced symptoms were
undoubtedly missed by this investigation, the data presented should provide a reasonable estimate of the
range and severity of symptoms experienced. In addition, because the data represent health effects
reported as they occurred, the study is less likely than subsequent retrospective studies to be affected by
reca l l b ias .
A second major limitation is that we do not know exactly what substances were responsible for
the observed health cffects, although based on known toxicology, MITC is the most likely candidate.
Since reliable air sampling data are not available for the first two days after the spill, we cannot determine
the type and concentration of metam sodium byproducts to which individuals may have been exposed.
Also, there are no current laboratory tests which can specifically identify the presence of these substances
in the body. Therefore, exposure is based on self-report, and dose cannot be classified as to severity.
Because few individuals reported the characteristic horseradish odor of MITC, it would appear
that MITC levels causing symptoms were probably below the MITC odor threshold which has been
reported from one study as 100 ppb. Odor reports suggest that H2S exposure also occurred. Whether
H2S was present in concentrations high enough to produce irritative symptoms is impossible to
determine. However, given that H2S was expected to be present at lower concentrations than MITC,
H2S is a less potent irritant than MITC, and H2S's irritant threshold is almost ten thousand times higher
than its odor threshold, it app>ears reasonable to assume that most symptoms were secondary to MITC
e x p o s u r e .
Major Findings
In this investigation, self-reported exposure to vapors released by metam sodium was most
commonly associated with non-specific neurologic complaints (headache, dizziness) and irritation of the
eye, respiratory tract, gastrointestinal tract, and skin. Although the three sources of information used in
this study represented both self-reported data (questionnaires) and observer-reported data (PIR's and
medical charts), the relative frequency and distribution of symptoms reported were similar regardless of
source. A significantly higher number of symptoms reported by individuals evaluated at the ER may
indicate that this group had the most severe health effects.
Symptoms in nearly all cases were not severe enough to require hospitalization. Of the seven
people hospitalized, four had pre-existing respiratory disease. Exposure effects on pregnant women
remain to be determined. While this study found no cases of spontaneous abortions or birth
abnormalities, the spill may have played a role in two womens' decision to obtain a therapeutic abortion.
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Because this report includes only symptomatic persons who sought medical care, the actual
symptom rate is probably higher. Even so, the finding that over 15% of Dunsmuir area residents sought
care is quite striking. It was p)0ssible to identify several risk factors. Males and females reported a similar
number of symptoms although the proportion of those reporting symptoms appeared to be slightly
higher for females. Older and very young individuals appeared less likely to report symptoms.
Explanations for the age differences in symptom reporting could include increased tolerance to irritant
effects among older individuals, differences in the degree of exposure among different age groups, or
differences in the ability or willingness to seek care among different age groups.
Our limited geographic analysis suggests a dose-distance relationship. The symptom attack rate
in the 0-300 foot zone was markedly elevated compared to more distant zones. The plateau in attack rates
over the 301-600, 601-900 and 901-1200 foot zones suggest that a clear-cut distance-symptom relationship
might be demonstrated within the 0-300 foot zone. The elevated attack rate in the 1201-1500 foot zone is
inconsistent with our presumed distance-dose symptom relationship. Thus distance from the river of
case homes, as a proxy for exposure, was only somewhat predictive of symptoms. Primary site of
exposure may not correlate well with place of residence, particularly for residences farthest from the
river. Contaminants may have moved in a more complex way than simple dispersal.
Of significance is the finding that symptoms among those rep)orting an odor were nearly identical
to those who did not report an odor. While odor detection data was missing for a high number of cases,
this finding suggests symptoms occurred at chemical concentrations below the odor threshold which
would be consistent with known MITC toxicology. Although detecting an odor could theoretically
indicate a higher level of exposure, this could not be substantiated by the data available.
For the limited number of individuals in whom smoking history was known, smokers tended to
have higher individual symptom rates and a higher number of symptoms overall. This may indicate
smokers were more susceptible to irritant effects of exposure or an unknown interaction exists between
exposure and smoking.
Perhaps the most unexpected finding of the investigation was the occurrence of symptom
reporting days and even weeks after the spill when the possibility of exposure to metam sodium
byproducts was presumed to be minimal. There have been several anecdotal reports of individuals who
left the area after the spill, returned when metam-related chemical levels were not detectable and then
had a recurrence of their symptoms. Others have reported a recurrence of symptoms following
rainstorms two to three months after the spill.
Reasons for the prolonged health effects are unclear. Although initial exposure/symptom onset
information was given for only a little over half of the cases, it appears that most initial exposures and
symptoms occurred within two days after the spill. Symptoms being reported a week or more after the
spill did not appear to differ substantially from those reported initially except that there was a
significantly higher proportion among late symptom reporters of weakness, diarrhea, cough and rash.
There are several possible explanations for the late symptom reports. First, either because of
worry or because of an interest in formally documenting their symptoms for legal purposes, many of the
later medical visits may have represented follow-up visits for initial symptoms which were resolving.
Second, residents may have attributed the development of new health problems which were unrelated to
the spill to the incident. Third, some of the late symptoms could be attributed to psychological trauma,
similar to that seen with post-traumatic stress disorder.^^ Certainly, as a result of the spill, area residents
were subjected to numerous potential stressors such as fear of unknown health effects from exposure,
sudden evacuation from their home, and helplessness in watching the destruction of a once thriving river
which may have been their source of economic livelihood. These stressors could theoretically manifest
themselves as depression, irritability, difficulty concentrating, sleep disturbances and fatigue, etc. Fourth,
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later symptom reports could also represent either slowly resolving or chronic problems related to the
spill. Finally, there could be previously unrecognized or underestimated toxicologic properties of metam
sodium and its byproducts (e.g., persistence in the environment) or sensitization of certain individuals to
these chemicals. Low levels of MITC were reported in vegetation samples taken by the Department of
Fish and Game near Dunsmuir as late as August. Although unlikely, re-exposure to metam sodium
byproducts weeks after the spill cannot be entirely discounted.
C O N C L U S I O N S
The Cantara incident had an undeniably devastating environmental impact on the affected
portion of the Sacramento River. Unfortunately, the full extent of human health effects has not been
determined. The suddenness and resulting chaos of the event made systematic study difficult. The data
in this report is observational, uncontrolled, and subject to several types of biases. Information was
obtained from different sources. Because of the primary need to treat and triage cases, responding
medical personnel could not always obtain or record information for each case in the same manner or to
the same level of completeness.
While the investigation can not conclude causc and effect relationships on a strictly scientific
level, several important points can be made regarding the health effects of the incident. Over 700
individuals sought medical attention for symptoms they believed were related to exposure to the spilled
chemicals--a highly significant finding given the relatively low population of the area. Those who may
have been affected but did not or could not seek medical care were not included in this investigation.
Therefore, it is likely that the number of cases included in this investigation is an underestimate of the
total number of individuals affccted. Symptoms were consistent with exposure to irritant gases.
Irritation of the eyes, gastrointestinal tract, respiratory tract, and skin occurred. Non-specific neurologic
complaints such as headache and dizziness were common. Seven hospitalizations were recorded. No
fatalities or adverse pregnancy outcomes were observed. Gender, age, and smoking status were factors
which appeared to affect symptom reporting.
Some symptoms probably occurred at chemical concentrations below odor thresholds. In the
Dunsmuir area, exposures appeared to occur on either side of the river at distances of up to a quarter-
mile from the river. The exact types and concentrations of substances which were present is not known.
Because there were no fatalities and few hospitalizations, it is unlikely that high-level exposures occurred.
Most exposure and symptom onsets appeared to occur within the first two days after the spill.
However, symptoms were unexpectedly reported many days and weeks after the spill. Reasons are
unknown. Long-term health effects of exposure, including effects on the reproductive system, are
u n k n o w n .
R E C O M M E N D A T I O N S
Genera l Recom m enda t i ons
The public health implications of this incident are far reaching. However, it is beyond the scope
of this report to make specific recommendations within the entire arena of affected institutions and
agencies. Major concerns raised by the incident are addressed below.
H A Z A R D O U S M A T E R I A L C L A S S I F I C A T I O N A N D T R A N S P O R T A T I O N
Although metam sodium is a biocide, which by definition is a threat to the environment if used
incorrectly, it was not classified as a hazardous material by the US DOT. As a result, the herbicide was
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shipp)ed in a standard non-puncture resistant tank car which neither was placarded nor carried specific
toxicologic information and recommendations regarding accidental release. Whether a different type of
rail car would have prevented the spill is unknown. However, procedures for
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