Human activities such as fossil fuel burning may have tripled the amount of mercury at the ocean’s surface since preindustrial times.
Marine chemist Carl Lamborg of the Woods Hole Oceanographic Institution in Massachusetts and colleagues used seawater samples from around the world to estimate the amount of anthropogenic mercury that pollutes the oceans. Along with the tripling in shallow waters, the researchers found that waters between 100 and 1,000 meters deep had levels about 2.5 times as high as in preindustrial times. The researchers estimate that in total, humans have dumped about 42,000 to 74,000 metric tons of mercury into the ocean. The results appear in the Aug. 7 Nature.
It’s unclear what the mercury pollution means for human or wildlife health. Mercury pollution can convert to methylmercury, a toxic substance that can build up in fish and poison people. How that conversion happens is mostly a mystery, Lamborg says, although scientists know that microbes are involved.
“If you tripled the amount of mercury in the ocean, do you triple the amount of mercury in fish as well?” he asks. “We don’t know.”