Effect of deep-frying fish on risk from mercury

The U.S. Environmental Protection Agency (EPA) and many states have issued advisories to limit or avoid the consumption of certain fish or fish from certain waters, particularly by pregnant women and young children or even women of childbearing age. Typically, risk is calculated by multiplying contaminant concentrations in fish tissue, frequency of meals, and meal size, compared to some criterion, usually the U.S. EPA reference dose (RfD). Site-specific data on mercury concentrations, meal size, and consumption frequency by fishermen were used to determine how frying fish affected risk estimates. In consumption studies fishermen typically estimate the size of portions as they appear on the plate (i.e., cooked), yet assessors calculate risk based on contaminant levels in uncooked fish. Largemouth bass (Micropterus salmoides, n = 39) were collected from the contaminated L Lake on the Savannah River Site, South Carolina. Fillets from the opposite sides of the same fish were divided and randomly assigned to a raw or fried treatment (the commonly used local cooking method). The fried fillet was further divided in half for a breaded or nonbreaded treatment. Mercury averaged 0.44 mug/g (ppm, wet weight) in raw fish, 0.63 mug/g in fried and breaded fish, and 0.76 mug/g in fried, unbreaded fish. The maximum concentration was 1.5 mug/g in raw fish (1.9 mug/g in cooked fish). Deep-frying with and without breading resulted in weight loss of 25% and 39%, while mercury levels increased by 45% and 75%, perhaps due to the breading and absorption of oil. At the mean fish consumption rate of people fishing locally, mercury intake exceeded the U.S. EPA RfD of 0.1 mug/kg/d for all except white females. Thus consumption of fish from this lake would exceed acceptable levels. Risk assessments should be conducted with site-specific data on contaminants and consumption of cooked fish and consumption studies should specify whether portion size was pre- or postpreparation. Fishermen estimate the amounts of fish they eat based on a meat size (usually cooked), while risk assessors determine mercury levels in raw fish. A conversion factor of about 2 for mercury increase during cooking is reasonable and conservative.