Mercury pollution in marine ecosystems from sources to seafood

Mercury pollution in the surface ocean has doubled over the past century while more than 90 percent of mercury exposure in the U.S. and in many regions of the world comes from this consumption of estuarine and marine fish. The Coastal and Marine Mercury Ecosystem Research Collaborative (C-MERC), comprised of more than 70 scientists and policy experts, recently published a series of 11 papers and produced a synthesis report, “Sources to Seafood: Mercury Pollution in the Marine Environment”. The main objective of this collaborative effort was to inform policies and management actions currently under consideration at the local, national and international level to limit mercury pollution. Four major findings emerged from the C-MERC synthesis: 1. Mercury pollution contaminates commonly consumed marine fish at levels that exceed human health guidelines, and mercury pollution continues to rise. 2. Mercury pollution enters the marine environment along distinct pathways that are linked to different mercury sources. Atmospheric inputs from global sources of mercury emissions dominate in the open ocean and in coastal systems strongly influenced by ocean currents. Riverine mercury inputs dominate coastal waters that are receiving bodies of watersheds. Some coastal waters receive multiple inputs from both the atmosphere and rivers. 3. Most seafood consumers are “general consumers” whose methylmercury exposure comes from fish typically harvested from the open oceans while “local consumers” generally eat seafood from nearby coastal waters. 4. Methylmercury concentrations in marine fish will decline roughly in proportion to decreases in mercury inputs, though the timing of the response will vary. Methylmercury in open ocean fish will begin to decrease within many years to decades after emissions controls. In contrast, methylmercury in fish from coastal systems contaminated by legacy mercury may take many decades, or even centuries, to fully reflect the declines in inputs.