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MERCURY POLLUTION

• Extent of pollution? • Chemistry of Mercury • Production and Uses • Mercury emissions and deposition • Mercury cycling, stores and fluxes • Methylation of mercury • Methylmercury from flooding • Methylmercury in food chain and bioaccumulation • Indicators of mercury sensitivity • Effects of mercury on wildlife • Human effects of mercury consumption/exposure • Acceptable levels of mercury

Sources of these notes – Driscoll et al., 2007 – BioScience (required reading) Aquatic pollution (2000, third edition) by Edward Laws And some other sources…..

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MERCURY POLLUTION – THE EXTENT OF THE PROBLEM? Across the nation • Mercury had the highest number of fish consumption

advisories across the nation! 2011 Advisories for all pollutants

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2011 Fish consumption advisories

• Advisories based on the more than allowable concentration of

Mercury measured in fish (varies with states, for NY = 1ppm, FDA action limit; Michigan ~ 0.5 ppm)

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Delaware fish consumption advisory: http://www.dnrec.delaware.gov/fw/Fisheries/Documents/2015-16_Delaware_Fish_Consumption_Advisories.pdf PCBs seem to be high for DE. Although current advisories in the United States have been issued for 34 different pollutants, most advisories involve five primary bioaccumulative contaminants: • Mercury—3921 advisories active in 2011 • PCBs—1102 advisories active in 2011 • Chlordane—60 advisories active in 2011 • Dioxins—129 advisories active in 2011 • DDT and metabolites—67 advisories active in 2011

Source: http://www.epa.gov/sites/production/files/2015-06/documents/maps-and-graphics-2011.pdf An increase in advisories issued by the states generally reflects an increase in the number of assessments of contaminants in fish and wildlife tissues. **** In the US, mercury only a problem with respect to fish. Direct exposure to air and water not an issue.

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• Bioaccumulation – net accumulation of contaminants in an organism from all routes of exposure (water, sediment, food, air..)

• Bioconcentration – accumulation in organism directly

from water • Biomagnification – increase in contaminant concentrations

at higher levels in the food chain o Mercury biomagnification ~ 10,000,000

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Mercury – the chemistry

• Mercury – heavy silvery white liquid metal – only common

metal which is in liquid form at ordinary temperatures • High vapor pressure and low solubility • Mercury vaporizes readily under ambient conditions • Its saturation vapor pressure of 14 mg/m3 greatly exceeds the

average permissible concentrations for occupational (0.05 mg/m3) or continuous environmental exposure (0.015mg/ m3) --- which mean air saturated with mercury vapors can be extremely hazardous to human health!!

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Three oxidation states of Inorganic Mercury:

1. Hg 0 – elemental, or metallic mercury 2. Hg2 +2 – mercurous ion, a divalent mercury form --- also

indicated as -- Hg(I) 3. Hg +2 – mercury II, the mercuric ion, a divalent ion – also

indicated as – Hg(II)

Mercurous and mercuric forms can form numerous inorganic and organic compounds, but mercurous ion is rarely stable under ordinary environmental conditions. Organic Forms:

1. Phenyl Hg (phenylmercuric acetate or PMA) 2. Methoxy Hg (methoxyethyl mercury acetate) 3. Alkyl Hg (methylmercuric acetate)

The compounds most likely to be found under environmental conditions are: • Mercuric salts HgCl2, Hg(OH) 2 and HgS; • Methylmercury compounds, methylmercuric chloride (CH3

HgCl) and methylmercuric hydroxide (CH3 HgOH); • organomercurics C-Hg covalent bond (i.e., dimethylmercury

and phenylmercury). Only Hg(II) can be converted to Methyl Mercury Hg0 and Hg(I) cannot be transformed directly to Methyl Mercury [they have to be first converted to Hg(II)]

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Three most common forms of Mercury:

1. Elemental Mercury – Hg0 2. Inorganic Mercury --- Divalent Mercuric Ion 3. Organic Mercury form -- Methyl Mercury

• Most of the Atmospheric Mercury - Hg0 • Most of the Mercury in soil, water, sediments – Inorganic

Mercuric compounds • Most of the Mercury in animal tissue – Methylmercury

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PRODUCTION & USES

• Hg in most soils and rocks is low ~ 60ppb • Highest conc. in Ore – Cinnabar – HgS – mercuric sulfide

• HgS production peak in 1970s ~ 10,000 tons/yr • Currently ~ 3000 t/yr

What is it used for? • Used in Chlor-alkali plants for the production of Cl2 and

NaOH Discharges from chlor-alkali plants were significant point sources of Hg

• Hg Dry Cell Batteries

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• Toxic qualities of Hg – antifouling and mildew proofing

paints o Use in former banned in 1972 under FIFRA (Federal

insecticides, fungicides, and rodenticides act) • Use in electrical apparatus – neon lights, switches, …….

• Thermometers, manometers, barometers,…..

• Each year up to 100 million dental fillings in the US –

amalgam – in combination with silver and tin and other metals o Only 50% of that prepared is actually used – some

wastage

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• Hg used as catalyst in various processes – PVC, synthetic acetate fiber

• Used to coat seeds, Hg-based fungicides

o Restricted under Federal Insecticide, Fungicide, and

Rodenticide Act (FIFRA) since 1970 and 1972 o Impacts on seed-eating birds o 1969 case in New Mexico – farmer fed grain to pigs

and then ate the pigs! o 1972 Iraq – bread prepared from treated wheat – 450

people died! • Used in mining industry to purify metal through the

amalgamation process – Silver in Mexico, Gold in Brazil and Peru

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MERCURY EMISSIONS AND DEPOSITION Atmospheric emissions and deposition – primary nonpoint source of Hg • Globally, 6600 metric tons of Hg emitted to the

atmosphere • 2/3rd of this – direct or remitted anthropogenic sources

(1/3rd new, 1/3rd old recycled emissions) • Coal powered plants – 50-60% of all anthropogenic – 1450

metric tons. • Anthropogenic Hg emissions in the US = 103 tons.

• Hg emissions in US from medical waste and municipal

incinerators have declined

• Hg emissions from coal power plants have declined since CAA o Mercury content in coal ~ 0.1 to 0.24 ppm

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Hg forms in emissions (1999, in the northeast) – • Hg0 = 57% • Reactive gaseous mercury (RGM) = 33% • Particulate mercury (PM) = 10%

Residence time and transport potential of Hg forms – • Hg0 – 0.5 to 2 years – tens of thousands of kilometers • RGM – 0.5 to 2 days – tens to a few hundred kilometers • PM – 0.5 to 3 days – tens to hundred kilometers • Hg0 can be oxidized to Hg(II) (by Ozone); Similarly Hg(II)

can be reduced by sulfides back to Hg0 Clean Air Mercury Rule (CAMR) – May 2005 USEPA • 70% reductions in Hg by 2025 from Coal-fired power

plants. • Allows a “cap-and-trade” approach.

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Atmospheric Deposition • Direct absorption of Hg0 by vegetative surfaces – through

stomatal exchange!! o Mosses and lichens serve as a good indicator of this

type of source! • Wet & Dry deposition

• Peak deposition in the 70s and 80s???? – as indicated by

Hg concentrations in lake sediments Figure 1 from Driscoll et al 2007

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• Current US deposition levels = 52 metric tons annually.

2014 Mercury deposition Map – Mercury Deposition Network (MDN)

Highest deposition in the South east US! http://nadp.sws.uiuc.edu/MDN/annualmdnmaps.aspx

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• Northeast US deposition – from US (local/regional) sources

– coal power plants, etc. • Southeast US deposition – from Global Mercury pool

(Hg0)

• Greater precipitation in the southeast and how mercury is scavenged from the atmosphere

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MERCURY CYCLING AND STORES Main Stores of Mercury: 1. Atmosphere 2. Soils 3. Water 4. Sediments Mercury in the Soil • Largest store of mercury (90% or more of the terrestrial

portion) – even if all mercury emissions were stopped today – the soil store would continue to maintain current pollution levels for at least 50 years!!!!

• Most of the Mercury in the soil – Inorganic forms of Hg(II) –

nearly 97 to 99% - HgCl2, Hg(OH)2, HgS • Inorganic Hg(II) forms complexes/sorption with organic

matter (fulvic and humic acids) and mineral matter --- resulting in reduced mobility of mercury

• Some of the Hg(II) may complex with DOC and thus leach

out - strong correlation of Hg with DOC in uplands draining to surface waters – especially with the aromatic fractions of DOC

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o Strong relationship with specific UV absorbance metric (SUVA) for DOC

• Sorption affected by – type of soil, dissolved organic carbon,

and species like S- and Cl-

• Biomass or organic matter burning, forest fires, etc. can lead to release and oxidation of Hg to the atmosphere!

• The other form of Hg in soil -- methylmercury – CH3Hg+–

formed due to the process of methylation of Hg(II) • CH3Hg – typically less than 3% of the total mercury soil pool

– but very potent! Mercury Uptake by Plant and Animals Plant uptake of Mercury although possible is very small under normal environmental conditions – which means that plants as a mercury source to animals or other consumers can be neglected • Mercury in foliage – mostly from atmosphere – stomatal

exchange • Mercury in roots – uptake from soil

Mercury not a concern along the terrestrial chain as it is for the aquatic food chain!

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Mercury in Freshwater Ecosystems

Pathways of entry: • Hg(II) and CH3Hg+ from dry and wet deposition • Hg(II) and CH3Hg+ with runoff – dissolved or bound to

sediment or attached to DOC

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o Surface and near surface flow paths carry greater

amounts of Hg o Strong correlation with DOC

• Hg(II) and CH3Hg+ from groundwater flow A significant amount of Hg(II) may partition to the water column, especially if there is a high concentration of suspended material in the water column. Most of the mercury in the water column will be bound to organic matter, either to –

• dissolved organic carbon (DOC; consisting of fulvic and humic acids, carbohydrates, carboxylic acids, amino acids and hydrocarbons; or to

• suspended particulate matter. • 25 to 60% of the organic-complexes of mercury in the

water column – may be particulate bound, rest is the dissolved-DOC phase

• Hg0 concentrations in the water column are very low – Hg0 may be formed due to reduction of Hg(II) which may then be lost via volatilization.

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• Most of the volatilization losses from water and soils – recent mercury deposition – referred to as “prompt recycling”

• Methylmercury in the water column – less than 25% of the total mercury, typically less than 10%

• Studies have shown that total and methylmercury concentrations have a positive correlation with the DOC of the waters – work by Driscoll at Syracuse U.

• Methylmercury losses may occur to – volatilization, runoff, biotic uptake, or demethylation to Hg0.

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METHYLATION OF MERCURY • A very important process – with regards to the potential of

mercury as a toxic substance! • Conversion of Inorganic Mercury to MethylMercury

(MeHg) • Mono-methylmercury - CH3Hg+ (CH3HgOH or CH3HgCl) or

di-methylmercury could be formed – (CH3)2Hg

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• Di-methylmercury (CH3)2Hg volatilizes from surface water

and is generally not persistent in aquatic environments • Mercury methylation is brought about by sulfate-reducing

bacteria (SRB) and certain molds typically under anaerobic environments (could also occur under aerobic conditions)

• Higher MeHg concentrations during late summer (in

wetlands)– warmer temps cause higher rate of microbial activity

Factors affecting Methylation: 1. Availability of Hg(II) 2. Oxygen concentration

• Although methylation may occur under aerobic conditions – the process is much more accelerated under anaerobic conditions.

• Methylation will be greatest at the sediment-water interface as opposed to in the water column

3. pH

• low pH – favors generation of methylmercury – essentially releasing Inorganic mercury from complexes – greater availability of inorganic mercury

*** unexpected consequences of acid deposition!

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4. Redox potential 5. Presence of sulfate and sulfide • In presence of high pH and sulfide – mercury will be

precipitated as mercuric sulfide and will not be available for methylation, --- If the sulfide is oxidized to sulfate mercury will be released and be available for methylation.

• Sulfate may also stimulate SRB production and hence the

methylation process.

• Increased sulfate deposition with acid rain will increase mercury release

6. Complexing inorganic and organic agents • Greater amounts of humic/fulvic acids mean greater sites

for mercury binding – but in low pH conditions mercury releases will occur from these sites.

• Aluminum may compete with mercury for DOC sorption sites

7. Salinity

• There appears to be a negative correlation between the rate of methylmercury formation and salinity in estuarine sediments. The rate is lower in more saline environments because the bicarbonate component of

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seawater slows methylation of Hg [II] under both aerobic and anaerobic conditions.

8. Organic carbon

• DOC may actually bind up free mercuric ion and thus

reduce methylation. However in freshwater lakes, DOC and pH may interact in such a way that less mercuric ion will be bound to DOC and more will be available for methylation.

• Nutrients and organic matter can stimulate the

bacterial growth rates. Decaying matter can create anaerobic environments – which may increase the methylation process.

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METHYLMERCURY RELEASE DUE TO FLOODING CAUSED BY HYDRO-ELECTRIC PROJECTS IN CANADA

• Mercury stored in soils in inorganic form is released as MeHg

following flooding. • Flooded soils provide the anaerobic environments favorable

for release of MeHg • Alternating cycles of flooding may enhance MeHg

methylation

Research on methylmercury release being performed at the Environmental Lakes Area – Manitoba http://www.umanitoba.ca/institutes/fisheries/index.html http://www.umanitoba.ca/institutes/fisheries/fludex.html

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MERCURY IN THE FOOD CHAIN AND BIOACCUMULATION

(trophic transfer)

Definitions – Bioaccumulation – the net accumulation of contaminant by an organism due to uptake by all routes (water, sediment, food, air) Bioconcentration – net accumulation of contaminants by organisms by uptake from water Biomagnification – tendency of contaminant to accumulate at higher concentrations at higher levels in the food web due to dietary uptake

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• Both Inorganic and Methylmercury are taken up directly from

water and food (or ingested sediment) – but it is the MeHg that bioaccumulates and biomagnifies and is toxic

• Elemental and inorganic forms of mercury are poorly

absorbed in the organisms (a large portion of what is consumed is excreted)

• Very large amounts of inorganic mercury are required for it to

be toxic – because of its low bioassimilation

o A person can swallow upto ½ kg of metallic Hg and show no adverse effects

o 98% of the Hg is excreted with urine and feces o Inorganic (solid or liquid) Hg does not penetrate the

blood-brain barrier o Hg vapor may be more toxic – problems in felt hat

industry! – mad hatter disease! o Inorganic Hg may get methylated by microbes within

the bodies of some birds and fish • In contrast, Methylmercury is readily transferred across

biological membranes – and is strongly bound to sulfhydryl groups on proteins of tissue such as muscle – disrupt the cell membranes and destroy the cells

• The problem is that Mercury binds with muscle as

opposed to other toxics that bind with fatty tissues or skin tissues – this means Mercury cannot be filleted out or cooked

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out of consumable fish -- actually, mercury concentrations increase after cooking because moisture is lost.

******??? which other toxics are unlike mercury in this regard? • Trophic transfer – greatest jump in bioaccumulation occurs

from water to phytoplankton (algae) – 105 to 106 ****Figure 3 from Driscoll et al. 2007

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• MeHg continues to increase up the food chain -- Top aquatic predators such as freshwater largemouth bass, pike and walleye and marine fish such as king mackerel, sharks, and swordfish may contain concentrations of mercury 10,000 to 100,000 times greater than that found in the surrounding water

***Fish Hg concentrations -

• Positively correlated with lake or watershed drainage area

• Negatively correlated with – pH, ANC, nutrient

concentrations, zooplankton density, and human land use *** Why is phytoplankton or fish Hg negatively correlated with high nutrient concentrations (nutrient enrichment)?????? • Within fish populations – Hg concentrations or burdens

increase with size and age of populations – slower rates of elimination, longer exposure, feeding habits at higher trophic levels

• Greater than 90% of the bioaccumulated Mercury is MeHg

that’s why EPA recommends determination of total mercury as a measure of MeHg (MeHg measurements are much more expensive that total mercury)

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INDICATORS OF MERCURY SENSITIVITY Fish Hg concentrations related to water parameters (Chen et al., 2005)– • DOC • ANC • pH • total phosphorus Driscoll et al 2007 tested these indicators for northeastern lakes Using the 0.3 ppm MeHg USEPA criterion for yellow perch ******Figure 4 from Driscoll et al. 2007

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Lakes with MeHg levels greater than 0.3 ppm in yellow perch had significantly

- higher DOC - lower pH - lower total phosphorus

than lakes with levels less than 0.3 ppm. Potential thresholds for elevated fish Hg from Figure above – • Total P < 30 ug/L • pH < 6 • DOC > 4 mg/L • ANC < 100 ueq/L

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EFFECTS OF MERCURY ON WILDLIFE SPECIES • Deformities • Carcinogenic effects • Reproductive failure

Impacts on Adirondack Loons:

• 105 loons found dead or debilitated in the state between 1972

and 1999 • Mercury was found in the liver of 83 loons • Mercury interferes with the bird’s ability to raise offsprings

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• Mercury will interfere with muscle coordination and vision

making it harder for the loon to feed itself and its young Mercury Impacts on Livestock • In cattle and sheep, dietary intake of 0.2 mg/kg mercury will

cause uncoordination, unsteady gait, and eventual death. • Mortality in poultry begins with mercury levels of 5.0 ppm.

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ACCEPTABLE LEVELS OF MERCURY EXPOSURE Human body burden of – 25-30 mg of MeHg is dangerous. Other viewpoint – no Hg is best – because any Hg will damage cells – at the cellular level there is no threshold! • EPA criteria for fish consumption – not exceed 0.3 mg/kg

of MeHg or 0.3 ppm MeHg. Based on a total fish and shellfish consumption-weighted rate of 0.0175 kg fish/day.

• FDA action level for mercury = 1.0 ppm of MeHg

Background level in food = 0.02-0.05 ppm. Meat and fish have higher levels • Pork & beef = 0.1 ppm • Fish = 0.2 ppm • Tuna = 0.21 • Swordfish = 0.95 • Sharks = 1.33 ppm

Drinking water standard = 2µg L-1 Acute and chronic levels for aquatic organisms – table 12.8

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OSHA limit in workplace = 0.1 mg/m3

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HUMAN EFFECTS OF MERCURY CONSUMPTION • Highest MeHg levels are generally found in human kidneys. • MeHg readily crosses the placental and the blood/brain

barriers • Pregnant women may discharge the Hg from their body into

the fetus! • Estimates of half-life in human body 44 to 80 days • Excretion of MeHg occurs via – feces, urine, breastmilk • MeHg – may cause daughter cells to get unequal numbers of

chromosomes – genetic impacts • Mercury vapor – inflammation of the gums, metallic taste,

diarrhea, mental instability, and tremors

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Acute Toxicity Lethal dose – 10 to 60 mg/kg High Doses of MeHg may cause – • Impaired central nervous system • Kidney damage and failure • Gastro-intestinal damage • Cardiovascular collapse, shock and death Chronic Toxicity • Deterioration of the nervous system • Impairment of hearing, speech, vision and gait • Involuntary muscle movement • Corrosion of skin and mucous membranes • Difficulty in chewing and swallowing Largest and most classic case of human mercury poisoning – Minamata Bay, Japan. Chisso Co. started using the bay in 1932 for dumping mercury waste – continued till 1968! Dumped wastewater contaminated with MeHg More than 900 dead, 12,615 affected. 26 yr ban on fishing.

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Residents who ate the fish displayed numbness, tunnel vision, slurred speech, spasms. Many suffered violent convulsions -- a strange dance of death -- before going mad and dying. “Dancing cat disease”! CONCENTRATIONS IN PPM !

Fish & Shellfish Cats Humans

oyster 5.6 control 0.9-3.66 control less than 3.0

gray mullet 10.6 kidney 12.2-

36.1 kidney 3.1-

144.0 short-necked clam

20.0 liver 37-145.5 liver 0.3-70.5

china fish 24.1 brain 8-18 brain 0.1-24.8

crab 35.7 hair 21-70 hair 96-705