Biotransport of mercury and human methylmercury exposure through crabs in China – A life cycle-based analysis

Highlights: • Domestic crabs in China have high MeHg levels close to those of marine fish species. • The annual MeHg output from crab harvesting has increased rapidly in the past decade. • A total of 6.8% of the land area in China contributes 71% of the crab MeHg output. • Interregional trade of crabs has dramatic impacts on inhabitant MeHg exposure. • Inhabitants face underestimated exposure risk to MeHg during crab market seasons. Exposure to methylmercury (MeHg) has various toxic effects on humans. The evaluation of human MeHg exposure has previously focused on fish consumption. However, in this study, we found that MeHg levels in domestic crabs in China were also relatively high (range: 50–1400 ng/g, dry weight). The high MeHg levels in crabs and their high consumption do not match the risk assessment of MeHg, indicating an underestimated exposure risk, especially in MeHg-sensitive groups such as pregnant women. The annual crab MeHg content output in China was estimated to be 30 ± 27 kg. A total of 6.8% of the country's land area contributes 71% of the MeHg output. However, 66% of the output is redistributed to non-crab-producing regions via interregional food trade, posing risks to the population on a national scale. The daily intake of MeHg from crabs could easily exceed the reference dose (0.1 µg/kg of body weight per day) suggested by the United States Environmental Protection Agency with consideration of coexposure from fish, rice, and other food sources. We suggest that future MeHg exposure analysis includes crab MeHg as a coexposure pathway to estimate the dietary MeHg limit accurately and emphasize the influence of interregional food trade on MeHg exposure.