US EPA warns rising mercury levels in the Pacific Ocean could have implications for fish and human health

The US plans to ramp up collaborative efforts with international partners to curb global mercury pollution, following new findings that mercury levels in the North Pacific Ocean have climbed approximately 30 per cent over the last 14 years. The jump is largely due to global increases in atmospheric mercury emissions, though the Asian coast has been highlighted as a particular offender. 

The US Geological Survey (USGS) study documents for the first time the process in which increased mercury emissions from human sources enter the North Pacific Ocean and go on to contaminate seafood. The authors note that much of the mercury comes from the atmosphere, and predict an additional 50 per cent increase in Pacific Ocean mercury levels  by 2050.

Such increases, the US Environmental Protection Agency (EPA) warns, could have implications for resulting levels of methylmercury (a highly toxic form of mercury) in Pacific Ocean fish. Methylmercury quickly accumulates in the food chain, and human exposure has been associated with negative effects on foetal brain development and other health problems.

More than 90 per cent of human methylmercury exposure in the US is attributable to ocean fish and shellfish consumption, according to the USGS.

’This study gives us a better understanding of how dangerous levels of mercury move into our air, our water, and the food we eat, and shines new light on a major health threat to Americans and people all across the world,’ says the EPA’s administrator, Lisa Jackson.

Eastward transport

’Mercury researchers typically look skyward to find a mercury source from the atmosphere due to emissions from land-based combustion facilities,’ says USGS’ David Krabbenhoft. ’In this study, however, the pathway of the mercury was a little different. It appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts. The mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents.’

The USGS scientists sampled Pacific Ocean water from 16 different sites and used computer models to predict future ocean mercury concentrations.

The EPA says the USGS findings should be used to help make informed decisions about atmospheric mercury emissions and potential human exposure to methylmercury from fish consumption.

While environmental advocates have praised the EPA’s aggressive response to the report, others see it as an over-reaction.

The study deserves ’hard scrutiny,’ says Mary Anne Hansan of the National Fisheries Institute, a US trade group representing the seafood industry. She insists that existing, peer-reviewed research shows no mercury increase in ocean-going fish over the last 30 years, and emphasises that the USGS researchers did not test levels of mercury absorption in fish. 

Hansan and others suggest that any conclusions or predictions about seafood based on these research findings are inappropriate. ’How can a study that didn’t test any fish draw conclusions about ’the food we eat’? Last time we checked, people don’t drink ocean water any more often than they eat the soil that crops grow in,’ says The Center for Consumer Freedom, a Washington, DC-based non-profit organisation reportedly funded by restaurants and food companies.

Rebecca Trager, US correspondent for Research Europe