Ebook Use of Traditional Foods in a Healthy Diet in Alaska: Risks in Perspective
Mercury occurs naturally in the earth’s crust, is ubiquitous in the environment, and is a component of freshwater and marine fish and mammals. Human industrial activities such as coal burning contribute to the global distribution of mercury in the environment. Global mercury emissions have increased since the 1700s. Currently, known man-made emissions of mercury roughly equal known natural emissions. Mercury has many chemical forms that occur naturally in the environment. From a public health standpoint, methyl mercury is the most important.
Alaskans are exposed to methylmercury primarily from ingestion of fish and marine mammals. Methylmercury concentrations in the most frequently consumed fish (e.g., salmon, cod, halibut, pollock, sole, and herring) are very low, consistently below 0.2 ?g/g [parts per million, ppm, wet weight (all tissue concentrations are wet weight unless noted otherwise)]. This is one-fifth of the Food and Drug Administration (FDA) action level for commercial sale of seafood of 1 ppm. Alaska salmon average 0.05 ppm of methylmercury. Similarly for marine mammals, except for some beluga whale tissues, average methylmercury concentrations are below 0.2 ppm. Bowhead whale tissues (e.g., muscle, blubber, epidermis, liver and kidney) contain very low methylmercury concentrations (<0.02 ppm). Older fish and marine mammals that are higher on the food chain have higher concentrations of methylmercury.
Currently, there is scientific and public health agreement regarding safe levels of dietary methylmercury intake for adults. The World Health Organization (WHO) developed guidelines based upon the Minimata and Niigata, Japan poisoning outbreaks associated with heavily industrial methylmercury olluted fish, and on an Iraqi mercury-poisoning outbreak, where grain treated with a mercury-containing fungicide intended for crops was instead used to bake bread. The WHO relied heavily upon data from these tragedies to develop a provisional tolerable weekly intake (PTWI) for methylmercury of 230 µg, and for total mercury of 300 µg. This weekly intake corresponds to a daily dose of 0.5 µg/kg/day.
Scientists, medical, and public health professionals do not agree on safe levels of dietary intake of methyl mercury to protect the developing fetus. Two large-scale, rigorous, epidemiologic studies were designed to to determine if subtle neurodevelopmental effects could be associated with chronic low-level in utero exposures. One study was conducted in the Faroe Islands; the other was conducted in the Seychelles Islands. These studies produced different results.
In the Faroe Islands study, no clinical or neurophysiological methylmercury elated abnormalities were noted in 917 children evaluated at 7 years of age. However, subtle decreases in some neurodevelopmental test results were found to be associated with low-level mercury exposure, although most test scores of highly exposed children were normal. The median maternal hair mercury concentration was 4.5 ppm. Methylmercury exposure in this cohort occurred primarily through the consumption of pilot whale meat (1-2 meals a week; average methylmercury concentration detected in pilot whale meat was 1.6 ppm) which also contained polychlorinated biphenyls (PCBs). PCBs are suspected to cause similar subtle neurodevelopmental effects. Therefore, in this cohort, it is not possible to separate the contributions of PCBs and methylmercury, or their potential interaction, to the subtle decreases noted in the neurodevelopmental tests. Nevertheless, the U.S. Environmental Protection Agency (USEPA) chose to base its recommendations for dietary exposure primarily upon the data from the Faroe Islands study.
In the Seychelles Islands study no neurodevelopmental effects were detected in 643 children. The median maternal hair mercury concentration was 6.6 ppm, an exposure higher than the Faroe Islands. Over 75% of the mothers reported eating 10-14 fish meals per week. Average fish concentrations of methylmercury were approximately 0.3 ppm. In contrast to the Faroe Islands study, exposure to PCBs or other potential neurotoxins were extremely low in the Seychelles Islands.
In 2001, the USEPA developed a new reference dose (RfD) (the safe dose that can be consumed every day over a lifetime of 70 years without any ill effects), relying on the Faroe Islands study, for methylmercury that is 0.1 µg/kg/day. In developing their new RfD, the USEPA made a decision to dismiss the results of the Seychelles Islands study. The EPA also made a decision not to take into account the well-known health benefits of fish consumption or to assess the risks associated with loss of nutrients from the diet.
Contents
Executive Summary
Introduction
Background
- Mercury in the Environment
Mercury in Humans-Historical Evidence
Methylmercury Concentrations in Alaskan Fish
Methylmercury Concentrations in Alaskan Shellfish
Methylmercury Concentrations in Alaskan Marine Mammals
Human Health Effects of Methylmercury
- Methylmercury Poisoning
Biochemical Mechanisms of Methylmercury Toxicity
Epidemiologic Studies of Chronic Low Level Methylmercury Exposure
Potential Cardiovascular Effects from Low-Level Mercury Exposure
Risk Assessment Food Consumption Guidelines
- World Health Organization (WHO)
Food and Drug Administration (FDA)
Agency for Toxic Substances and Disease Registry (ATSDR)
United States Environmental Protection Agency (USEPA)
Health Canada
Arctic Monitoring and Assessment Programme
Dietary Intake of Methylmercury in Alaska
- Exposure Estimates
Factors that May Modify Possible Methylmercury Toxicity
Selenium and Methylmercury Exposure
Selenium Concentrations in the Environment
Inorganic vs. Organic Mercury in Liver and Kidney Tissues
Methylmercury Levels in Alaskans
Alaska’s Perspective on USEPA and FDA National Fish Advisories
Summary
Recommendations
Tables
Figures
References
Units of Measurement
Download
PDF Ebook Use of Traditional Foods in a Healthy Diet in Alaska: Risks in Perspective
Posted in :
