Warming Oceans and Low Oxygen Levels Drive Increased Mercury Risk in Seafood

Warming Oceans and Low Oxygen Levels Drive Increased Mercury Risk in Seafood
————————————
A new study led by Umeå University has discovered that climate change can increase mercury contamination in the marine food chain, not by adding more pollution, but by reducing oxygen levels in the ocean, according to Earth.com.

The research found that periods of deoxygenation (low oxygen) in marine environments—a condition expected to spread as oceans warm—supercharge the activity of specialized microbes. These microbes possess the hgcA gene, which allows them to convert common, inorganic mercury into methylmercury, a highly potent neurotoxin.

Methylmercury is dangerous because it biomagnifies: it moves up the marine food web from plankton to small fish to larger fish, with the concentration increasing at every step, ultimately making the consumption of seafood riskier for humans.

By analyzing ancient DNA preserved in Black Sea sediments spanning 13,500 years, researchers observed a sharp increase in the hgcA gene during a warm, humid interval between 9,000 and 5,500 years ago, which corresponded with a sharp drop in oxygen levels. This historical data confirms that climate-driven oxygen loss alone is sufficient to create conditions ideal for high methylmercury production.

The study serves as a crucial warning that even if human-related mercury emissions are cut, climate change alone can push ecosystems into a state where this dangerous toxin becomes easier to produce and harder to avoid.