article · Environmental Science & Technology Letters
Human exposure to toxic methylmercury occurs predominantly through the consumption of marine fish. Although international efforts focus on lowering mercury emissions to safeguard public health, the precise effects of these interventions on marine life have remained uncertain. An assessment of global tropical tuna data collected between 1971 and 2022 reveals that, despite an overall decrease in worldwide human-driven mercury emissions since the 1970s, tuna mercury concentrations have remained largely stable over the long term. A notable exception occurred in the northwestern Pacific during the late 1990s, where skipjack mercury levels rose in tandem with increasing regional emissions. Computer modelling indicates that legacy mercury stored in the subsurface ocean over centuries continues to feed surface waters, creating significant environmental inertia. Consequently, substantial reductions in emissions alongside persistent biomonitoring are required to decrease mercury levels in pelagic fish.
Methylmercury in consumed seafood poses significant risks to human health. Because historic mercury pollution remains trapped in subsurface ocean layers, current global emission cuts have not yet lowered contamination levels in tropical tunas. Understanding this environmental delay helps international policymakers, such as those guiding the Minamata Convention, recognise that much stricter emission targets and sustained biomonitoring are needed to safeguard food supplies.
The abstract does not indicate an application pathway, as the findings represent fundamental environmental monitoring and modelling rather than a direct commercial technology or product.
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Humans are exposed to toxic methylmercury mainly by consuming marine fish. While reducing mercury emissions and releases aims to protect human health, it is unclear how this affects methylmercury concentrations in seawater and marine biota. We compiled existing and newly acquired mercury concentrations in tropical tunas from the global ocean to explore multidecadal mercury variability between 1971 and 2022. We show the strong inter-annual variability of tuna mercury concentrations at the global scale, after correcting for bioaccumulation effects. We found increasing mercury concentrations in skipjack in the late 1990s in the northwestern Pacific, likely resulting from concomitant increasing Asian mercury emissions. Elsewhere, stable long-term trends of tuna mercury concentrations contrast with an overall decline in global anthropogenic mercury emissions and deposition since the 1970s. Modeling suggests that this limited response observed in tunas likely reflects the inertia of surface ocean mercury with respect to declining emissions, as it is supplied by legacy mercury that accumulated in the subsurface ocean over centuries. To achieve measurable declines in mercury concentrations in highly consumed pelagic fish in the near future, aggressive emission reductions and long-term and continuous mercury monitoring in marine biota are needed.
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DOI: 10.1021/acs.estlett.3c00949
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