It has long been known that mercury levels in seafood can prove poisonous to humans. Methylmercury, an especially toxic form of mercury, can lead to kidney dysfunction and neurological disorders.
Pregnant women in particular are told to be careful because dietary exposure to methylmercury can lead to birth defects in infants.
Now a new study suggests that humans need to be more wary of saltwater fish like tuna, mackerel and sharks than of freshwater fish. Although seawater has lower concentrations of mercury than freshwater, mercury in seawater is more likely to stay in its toxic form, researchers report in a recent issue of Nature Geoscience.