Concepts and Terminology of Health Risk...

3_Exposure_Risk Introduction

Concepts and Terminology of Health Risk Assessment

Mustafa M. Aral

MESL @CEE,GThttp://mesl.ce.gatech.edu/[email protected]

Health Risk Assessment process:

� Hazard identification;

� Exposure-dose assessment;

� Dose-response assessment; and,

� Risk characterization.


Steps Involved in HRA.


Exposure Assessment

1

2 3

4

5

Environmental Health Continuum

Pathway Transport

Epi studies


Continuum For Relating Environmental Contamination With Clinical Disease

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ARLY

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(After Lioy, 1990; Johnson and Jones, 1992)

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Framework for Exposure Assessment


Exposure Assessment Risk Evaluation Process:

Contaminant SourceSource Identification

Environmental ConcentrationAir, surface water and groundwater

ExposureDermal, Ingestion, Inhalation

Exposure Dose

Exposure Risk

Multipathway fate and

transport processes

Multipathway fate and

transport modeling

Human activities and

contactExposure modeling

Intake and uptake Kinetic models

Dose to risk analysisMechanistic, statistical

and uncertainty models


Source to Population Risk Man.

CONTAMINANT

SOURCE

ADVECTIVE ANDDIFFUSIVE

TRANSPORT

CHEMICAL,BIOLOGICAL AND

PHYSICAL FATEPROCESSES

POPULATIONRECEPTORS

Physical Removal

Chemical Removal

Biological Removal

REMEDIATION

Physical Containment

PATHWAY CONTROL

Chemical Containment

Biologic Containment

Risk Assessment

Risk Communication

Exposure-DoseAnalysis

RISK MANAGEMENT

Out flux Prevention

Recycling

Out flux Minimization

SOURCE MANAGEMENT


Exposure Assessment:Historical Perspectives-1

� About 3200 B.C.: The Asipu, a group of priests in the Tigris-Euphrates Valley establish a methodology:

� Hazard identification;

� Generation of alternatives;

� Data collection (including signs from the gods) and analysis;

� Report creation and documentation.



� King Edward II had to deal with the problem of smoke in London:

� 1285: Established a commission to study the problem.

� 1298: Commission called for voluntary reductions in the use of soft coal.

� 1307: Royal proclamation banned soft coal, followed by a second commission to study why the proclamation was not being followed.



� London cholera epidemic of 1854

� 2,050 people died in one week.

� Method of cholera transmission unknown.

� Exposure assessment method

� Dr. John Snow’s cholera map

� Relation of cholera cases (deaths) to water supply.


Dr. John Snow’s cholera map


Defining Exposure

� Contact of a chemical, physical, or biological agent with the outer boundary of an organism.


Defining Dose

� Dose is the amount of a substance available for interaction with metabolic processes or biologically significant receptors aftercrossing the outer boundary of an organism

� Exposure is external

� Dose is internal


Exposure / Dose


Exposure

Dose

Quantifying Exposure:

� Exposure is quantified as the concentration of the agent in the medium in contact, integrated over the time duration of contact

1

0

( , ) ( )t T

t TE c t C t dt

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= ∫

This

Course


Quantifying Dose:

� Potential dose for an intake process (dermal, inhalation and ingestion) is the integration of the chemical intake rate (concentration of the chemical in the medium times the intake rate of the medium, C times IR) over time

D C t IR t dtpot

t

t

= ∫ ( ) ( )

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This Course


� Present exposure

� Environmental and biologic measurements

� Past exposure

� Data if available in conjunction with computational models



RI/FS

Epidemiologic investigation

Time Present-day

Con

tam

inatio

n

Exposure

Relationship of epidemiologic investigations to remediation activities (RI/FS)


Approaches to Quantification of Exposure

� Exposure can also be estimated from dose, which in turn can be reconstructed through internal indicators (biomarkers, body burden, excretion levels, etc.) after the exposure has taken place (reconstruction)


Approaches to Quantification of Exposure

� Measure at point of contact while it is taking place, measuring both exposure and time of contact and integrating them (point- of-contact measurement)

� Estimated by separately evaluating exposure concentration and time of contact, and then combining the information (scenario evaluation)



Typical ConditionDesired Condition



� Screening level models

� ACTS, ISCPC

� Complex environmental systems

� Groundwater flow and transport models

� Water-distribution system models

� Atmospheric dispersion models

� Uncertainty analysis

� Monte Carlo simulation


Dose Terminology

� Potential dose

� Amount available for ingestion, inhalation, or skin absorption.

� Applied dose

� Amount of a substance presented to an absorption barrier and available for absorption.


Dose Terminology--continued

� Absorbed dose

� Amount crossing a specific absorption barrier (exchange boundaries of skin, lung, digestive tract, etc. )

� Internal dose

� Amount absorbed and associated with internal adverse effect (a more general term )


Toxicology

� Zero contaminant discharge in an industrial society is not possible;

� It is safe to say that we are being constantly exposed to natural or synthetic chemicals in our ambient environment;

� The task of the environmental health scientists is to ensure that the public health is not adversely affected by exposure to these chemicals.


Toxicology

� Exposure aspects of environmental health effect studies are commonly considered in epidemiologic investigations.

� Adversity or other measures of the effect of exposure is studied in the field of toxicology.

� Scientist, who conduct laboratory studies on animals to understand, quantify and estimate health effects of a wide range of toxic substances, are referred to as toxicologist.

� Their work traditionally consists of quantifying the effects of one toxicant to a single or multiple animal species.


Toxicology� Descriptive toxicology: In this group, scientist’s work primarily focuses

on the toxicity testing of chemicals. The studies performed in this category are designed to generate toxicity information that can be used to identify the various organ toxicities that the test agent is capable of inducing under a wide range of exposure conditions;

� Research/mechanistic toxicology: Under this category, scientists study the toxicant in more detail for the purpose of gaining an understanding of how the toxicant initiates those biochemical orphysiological changes within the cell or tissue that results in toxicity. Thus, the goal here is to understand the chain of biologic or biochemical events a toxicant triggers in a cell to create a toxic outcome; and,

� Environmental/applied toxicology: The studies described in the two categories given above are conducted in a laboratory setting. In the applied toxicology category scientist’s focus is on the chemicals in the ambient environment. The purpose of the studies under this category is more on the use of descriptive and mechanistic toxicology results to identify some measure of safe dose of the toxicant through risk assessment methods.


Environmental Epidemiology

� Epidemiology is a field of science in which scientists seek to understand the links between infectious diseases and the manner it may spread in a community or population.


A case study:

Importance

� Definition of pollution/contamination.

� Lack of knowledge.

� Limited evaluation may lead to disaster.


BANGLADESH

Arsenic Problem


Problem

� Tens of millions of persons in many districts are drinking ground water with arsenic concentrations far above acceptable levels.

� Thousands of people have already been diagnosed with poisoning symptoms, even though much of the at-risk population has not yet been assessed for arsenic-related health problems.


Number of people drinking water with arsenic levels >50 micrograms per liter

1. Argentina

2. Australia

3. Austria

4. Bangladesh (30,000,000)

5. Canada

6. Chile

7. China

8. Germany

9. India

10. Inner Mongolia (300,000)

11. Jamaica

12. Japan

13. Mexico

14. New Zealand

15. Sweden

16. Taiwan

17. Thailand (2,000)

18. USA (~300)

19. Vietnam

20. Yugoslavia3_Exposure_Risk Introduction

Root of the Problem


Drilling a Tube Well:


Root of the problem:

� The problem go back to the early 1970s when most Bangladeshis living in the countryside relied on surface ponds and rivers for their drinking water.

� Sewage bacteria, unleashed a battery of water-borne disease which killed a quarter of a million children each year, according to the World Bank.

� Thus UNICEF sought to solve the problem by initiating a massive tube well project to tap into underground water sources, despite warnings by some local people that they were pumping the “devil’s water.”


Bangladesh’s arsenic poisoning: Who is to blame?

� In the 1970s, international agencies headed by the United Nations Children’s Fund (UNICEF) began pumping millions of dollars of aid money into Bangladesh for tube wells to provide “clean” drinking water.

� According to the World Health Organization, the direct result has been the biggest outbreak of mass poisoning in history.

� Up to half the country’s tube wells, now estimated to number 10 million, are poisoned.

� Why? Because nobody tested for the natural poison, arsenic, widely found in underground water.

� And when the link is found, the results were swiftly buried so that nobody made the connection.

� Even now as the scale of the calamity emerges, nobody is admitting culpability. Not UNICEF, which initiated the tube wells program and paid for the first 900,000 wells, nor the World Bank, a fellow sponsor. Not the Bangladeshi government, or the foreign engineers and public health scientists who did not think to test the water for so long.


Where does arsenic come from:

� The arsenic probably originates in the Himalayan headwaters of the Ganges and Brahmaputra rivers, and has lain undisturbed beneath the surface of the region’s deltas for thousands of years in thick layers of fine alluvial mud smeared across the area by the rivers.

� The mud in Bangladesh lies thicker, wider and flatter than almost anywhere on Earth. It can take hundreds or thousands of years for underground water to percolate through the mud before reaching the sea. All the while it is absorbing arsenic.

� The arsenic concentration in the soil is not extraordinary. Time is the culprit.

� Arsenic in Bangladesh drinking wells may be linked to crop irrigation, MIT study finds.

� The contaminated wells almost all take water from a depth of 20 to 100 m.

� Shallower wells are clean because they contain mostly recent rainwater or water flowing swiftly through the sediments.

� Deeper wells tap water in older sediments which have by now been flushed clean of arsenic.


Suggested steps towards the solution?

� In the first step of the mammoth task of testing the country’s tube wells, volunteers, aid workers and officials paint the dangerous ones red, which should only be used for washing.

� The villagers are supposed to use the safe wells exclusively for drinking, but that’s not easy when the lucky one is found in someone else’s backyard.

� In the long run, part of the answer lies in sinking deeper wells to tap cleaner water. Or develop new shallow wells.

� But it will take millions of dollars to install these wells in addition to the needed surface tanks and distribution pipes.

� Also some deep tube wells in West Bengal have started bringing up arsenic months or years after they were opened.

� Another idea is to adopt traditional methods such as ponds and tanks to “harvest” rainwater. This will work in some places, but “there is not enough rain all year for that to be feasible as the main strategy.”

� Water supply from water distribution systems?


Summary of Arsenic Poisoning in Bangladesh

� Population of Bangladesh: 125 million

� Total population in regions where some wells are known to be contaminated: 35–77 million

� Maximum concentration of arsenic permitted in drinking-water according to WHO recommendations: 10 mg/l

� Maximum concentration allowed in Bangladesh: 50 mg/l (similar to many countries worldwide)

� Number of tube-wells sampled by the British Geological Survey (1998): 2022

– Proportion of wells with arsenic concentrations >50 mg/l: 35%

– Proportion of wells with arsenic concentrations >300 mg/l: 8.4%


Health Effects

� Skin lesions, Skin cancer

� Internal cancers (Bladder, Kidney, Lung)

� Neurological effects

� Hypertension and cardiovascular disease

� Pulmonary disease

� Peripheral vascular disease

� Diabetes mellitus


Solution

� In contrast to diseases like malaria, cholera and tuberculosis, which require a more complex public health response, the response to arsenic contamination is clear-cut.

� PROVIDE ARSENIC FREE WATER.Piped Water Supply System launched at Duptara Village


Water Treatment

� One method Berkeley Lab scientists have developed involves coating particles of coal ash with ferric hydroxide. In water, the arsenic binds to the resulting dark red powder and can be filtered out with the coated ash.

� Sold for around $2 per person for a year's supply, this low cost powder (Arsenic Removal Using Bottom Ash — ARUBA) is affordable to low-income villagers while allowing the factory and local distributors to make a small profit.

� The process is now available for licensing from Berkeley Lab and a number of companies have applied for exclusive rights.


Emergency Response Initiated� The core activity of an emergency action plan for this threat to human health should be rapid

case ascertainment and immediate provision of arsenic free water. � The objectives of such a plan should be as follows:

(1)to identify all cases of arsenicosis in Bangladesh; (2)the immediate identification of an interim source of arsenic-free water and commencement of implementation of the long-term solution; (3)to monitor patients’ progress and compliance with interim water treatment until a long-term water source has been identified and made available; and,(4)to provide care for patients, including vitamin supplementation, lotions for patients with keratoses and treatment of infections.

� Strategies to reduce exposure A short-term strategy might include five responses.(1) Identify nearby tube-wells that have water with a low arsenic content. (2) Provide a water filter for each household. A candle filtration system is available. It is easy to use and maintain, and this contributes to good compliance. The disadvantage is that the arsenic-loaded candles must be disposed of but this should not be a problem if the filter is used as an interim solution for a few months only. Units designed to be attached to tube-wells to remove arsenic are being tested and may prove to be an effective short-term alternative. (3) Provide chemicals to be used daily to remove arsenic from household drinking-water. The small packet of chemicals that can be mixed in water and left to stand overnight is very cheap and is simple to transport. The disadvantages of this strategy include the need for daily or close to daily use and the need to dispose of the sludge after each treatment. Whether people will use these chemicals needs to be evaluated. (4) Use surface water sources that have been treated by filtration and chlorination. (5) Close highly contaminated wells when a temporary water source has been identified.

� Field kits should be used if they can detect contamination of water containing 100 mg/l or more of arsenic. It would be better still if they could reliably detect 50 mg/l. Since WHO’s recommended maximum concentration of 10 mg/l cannot be accurately measured with a field kit, it has been proposed that samples should be sent to laboratories for testing. However, sending samples to a laboratory can cause delays to program in the affected communities. In contrast, using field kits that can measure concentrations of 50 mg/l provides instantaneous results and facilitates prompt action to find an alternative water source if needed.3_Exposure_Risk Introduction

Summary

� Arsenic exposure in Bangladesh is widespread and involves thousands of wells

� Estimates indicate that at least 100 000 cases of skin lesions caused by arsenic have occurred and there may be many more. If exposure continues, skin lesions will continue to occur.

� Skin lesions are occurring in children aged 10 years and younger

� Large numbers of cancers are predicted to occur in the future, including fatal internal cancers

� The cause is known: each day of continued exposure increases the risk of morbidity and death.

� Sustained drinking of water containing 500 mg/l of arsenic may result in 1 in 10 people dying from arsenic-related cancers

� Unlike other major health problems experienced in Bangladesh, arsenic-caused diseases can be eradicated at relatively low cost


Distributed Source (Oil transport routes and oil pollution)

From OECD, The State of the Environment, Paris, 1985


Distributed source (Global Distribution of Acidity from Precipitation)


to be continued…


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