Mercury rises alarmingly in marine predatory fish
doi:10.1038/nindia.2019.106 Published online 8 August 2019
Ocean warming and dietary shifts due to overfishing may increase the levels of methylmercury (MeHg) in some fish consumed by humans, researchers have revealed1.
Most of the inorganic mercury from natural and human sources is deposited in the ocean, where microorganisms convert it into MeHg. Fish are the predominant source of human exposure to MeHg, a potent neurotoxin.
However, the Minamata Convention on Mercury, a global treaty to reduce man-made mercury emissions, didn’t consider how ongoing changes to marine ecosystems might affect the accumulation of MeHg in fish.
To throw light on this, an international research team, including Asif Qureshi, a scientist from the Indian Institute of Technology in Hyderabad, analysed 30 years of data on ecosystem, sediment and seawater MeHg concentrations from the Gulf of Maine, a marginal sea in the northwestern Atlantic Ocean.
The researchers found that concentrations of MeHg in the tissue of Atlantic cod had increased by up to 23 per cent between the 1970s and 2000s. They attribute these changes to shifts in diet as a result of overfishing, with cod having a greater reliance on prey, such as larger herring and lobster, that have higher concentrations of MeHg than other prey fish consumed in the 1970s.
They also found that the effects of seawater temperature rises could have contributed to an estimated 56 per cent increase in MeHg concentrations in Atlantic bluefin tuna.
Climate change, the researchers note, is likely to exacerbate human exposure to MeHg through marine fish, suggesting that stronger regulations are needed to protect ecosystems and human health.
1. Schartup, A. T. et al. Climate change and overfishing increase neurotoxicant in marine predators. Nature (2019) doi:10.1038/s41586-019-1468-9