Methylmercury

1. Methylmercury Current Issues, Regulatory Problems R.O. Manning PHRM 8930

3. Mercury in Watersheds In 1998, of 21,800 impaired waterbodies 33 states listed at least one mercury impairment 5.6 million impaired acres of Lakes, Estuaries, Wetlands ~43,500 Hg impaired miles of Stream/River/Coastal ~4,000 were listed for metals (including mercury) ~1,100 were listed specifically for mercury ~8 states listed atmospheric deposition as source ~650 segments impaired by atmospheric deposition

4. 4 144 Mg (158 tons) Hg / yr emitted from U.S. anthropogenic sources 87% from combustion point sources 10% from manufacturing point sources 2% from area sources 1% miscellaneous sources Data from 1994-1995, MSRC

5. 80% of Hg from combustion is from 4 sources Coal-fired utility boilers -- 33% Municipal waste combustion -- 19% Commercial / industrial boilers -- 18% Medical waste incinerators -- 10% MSRC, 1997

6. Today’s News

7. NAS Report, Public Health “ The population at highest risk is the children of women who consumed large amounts of fish and seafood during pregnancy. … the risk to that population is likely to be sufficient to result in an increase in the number of children who have to struggle to keep up in school and who might require remedial classes or special education.”

8. NAS Report -- “…the risk of adverse effects from the current MeHg exposures in the majority of the population is low. However, individuals with high MeHg exposures from frequent fish consumption might have little or no margin of safety ( i.e. , exposures of high-end consumers are close to those with observable effects).”

9. CDC MMWR MMWR, March 2, 2001/Vol. 50/No. 8 Blood and Hair Mercury Levels in Young Children and Women of Childbearing Age – United States, 1999

10. CDC Study Presents preliminary estimates of blood and hair Hg levels from the 1999 National Health and Nutrition Examination Survey (NHANES 1999) and compares them with a recent toxicologic review by the National Research Council (NRC).

11. CDC Findings The findings suggest that Hg levels in young children and women of childbearing age generally are below those considered hazardous.

12. CDC Findings Preliminary estimates show that approximately 10% of women have Hg levels within one tenth of potentially hazardous levels indicating a narrow margin of safety for some women and supporting efforts to reduce methyl mercury exposure

18. RfD Definition An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious health effect during a lifetime.

20. Toxicity Indices U.S. EPA - RfD - 0.1 ?g/kg - day ATSDR - MRL - 0.3 ?g/kg - day these are both daily doses that can be used to calculate “safe” levels in fish tissue U.S. FDA - tolerance - 1.0 mg/kg

21. RfD 2001 RfD = 0.1?g/kg/day Based on NRC and external scientific input BMDL of 1.0 ?g/kg/day -- from neuropsychological effects in Faroese children exposed in utero through maternal seafood consumption No data to support separate RfD for children Applicable to lifetime daily exposure for all populations including sensitive subgroups; not restricted to pregnancy or developmental periods

22. Hg toxicity Non cancer High dose Mental retardation, cerebral palsy, deafness, blindness, paresthesia Low dose (prenatal) Poor performance on neurobehavioral tests, fine-motor function, language, visual-spatial abilities, and verbal memory

23. Hg toxicity Three large epidemiological studies Faroe Islands (+) Seychelles Islands (-) New Zealand (+) NAS – neurodevelopmental deficits most sensitive, well-documented

24. Hg in adults Fish-eating populations in the Amazon decreased manual dexterity, muscular fatigue reduced color discrimination, near visual contrast sensitivity, peripheral vision

25. Effects in adults -- 2 Cardiovascular effects 1833 Finnish men Over 7 year period men with hair Hg of 2 ppm or higher had 2 fold greater risk of acute myocardial infarction

26. Effects in adults -- 3 Minamata population deficits in “acts of daily living”; prevalence relatively greater in Minamata group compared with appropriate age control group increased symptoms in Hg area adults (not MD patients) Heart palpitation, staggering, hand tremors, dizziness, pain in legs and hands

27. Support from animal studies Newland & Rasmussen (2000) postpartum exposure in rats led to decline in motor performance task Rice et al (3 studies) – accelerated aging of sensory system function in monkeys exposed developmentally.

28. Uses of RfD Criterion development – published 1/01 Other EPA regulatory or risk management activities Basis for fish advisories

29. Why Fish Consumption Advisories? Protect Public Health Promote Best Use of Resource Focus Attention on Problem Areas

30. Why Mercury? Fish accumulate organic or methyl mercury in muscle methyl mercury is neurotoxic can pass through placenta and blood:brain barrier developing fetus and children most sensitive

31. Assessing Risk “The Dose Makes The Poison” Toxicity and Exposure yields Risk Information on both equally important

32. Toxicity For non-carcinogens like mercury, evaluated using a threshold approach How much can one be exposed to on a regular basis without appreciable risk of a detrimental effect occurring

33. Exposure Toxicity X Dose (exposure) = Risk How much do people eat (meal sizes, frequencies) Different groups of people (sport anglers vs subsistence fishers vs pregnant women, nursing mothers, young children, developing fetus)

34. Risk-Based Fish Consumption Limits Limits are intended to protect human health by limiting exposure to chemical contaminants in fish tissue Provide guidance on the maximum number of meals of fish from a defined area that can be eaten, over a specified time period, by defined groups of consumers.

35. Calculation of Safe Consumption Limits

38. National Freshwater Fish Advice -- 1 Developed in concert with FDA Released 12/00; revised 3/01 Target -- women who are Pregnant Could become pregnant Nursing Feeding a young child

39. National Freshwater Fish Advice -- 2 Limit consumption of freshwater fish One meal /week Meal Adult -- 6 ounces cooked, 8 ounces uncooked Child --2 ounces cooked, 3 ounces uncooked Check with state or local health department for advice on waters where friends /family fish Follow FDA advice for ocean, commercial

44. State Approaches AL – FDA based – tiered – 1 ppm FL – Risk based – tiered - 0.5, 1.5 ppm GA - Risk based - tiered - 0.23, 0.7, 2.0 ppm LA – Risk based – tiered – 0.5 ppm MS – FDA based – tiered – 1 ppm SC – Risk based – tiered – 0.1(0.25), 0.6, 3.0 ppm

45. State Approaches (cont.) Trigger levels (0.2 ? 1.0 ppm) Toxicology – close Regulatory (bright-line) – far apart In range measured in environment