Methylmercury, fish consumption, and the precautionary principle

Area of Science:

• Environmental Science
• Public Health
• Toxicology

Background:

• Assessing the benefits of mercury (Hg) emission reductions from U.S. coal-fired power plants is complex.
• Epidemiology studies on methylmercury health effects provide data, but safe exposure levels remain uncertain.
• Dietary factors, such as co-contamination with polychlorinated biphenyls (PCBs) in seafood, complicate exposure assessments.

Purpose of the Study:

• To probabilistically assess the public health benefits of curtailing mercury emissions from U.S. coal-fired power plants.
• To evaluate U.S. population exposure to mercury on a national scale.
• To address uncertainties in epidemiological data and the relative importance of local versus national mercury deposition.

Main Methods:

• Literature review of recent studies on mercury health effects and exposure.
• Analysis of epidemiological data, focusing on cross-study comparisons of mean exposures.
• Consideration of national-scale exposure patterns and potential confounding dietary factors.

Main Results:

• U.S. population exposures to mercury are generally below levels associated with reported adverse health effects.
• Uncertainties persist regarding safe mercury exposure levels due to confounding dietary factors in study populations.
• The relative importance of local airborne mercury deposition versus broader exposure pathways requires further investigation.

Conclusions:

• Unilateral reduction of mercury emissions from U.S. coal-fired power plants alone is unlikely to yield substantial public health benefits.
• Further research is needed to clarify safe mercury exposure thresholds and the impact of co-contaminants.
• A comprehensive approach considering multiple exposure sources and confounding factors is essential for accurate health benefit assessments.