Mercury levels near the surface of many of the world’s oceans have more than tripled since the beginning of the industrial revolution, according to a study published Wednesday in the journal Nature.
The paper stated that pollutants generated as a result of indiscriminate mining and burning of fossil fuels coupled with mercury emissions from coal-fired power plants had resulted in an alarming build-up of the toxic metal in surface layers of the seas.
Researchers, led by Carl Lamborg -- a marine geochemist at Woods Hole Oceanographic Institution in Massachusetts -- analyzed thousands of samples collected from the north and south Atlantic, Arctic and Pacific oceans between 2006 and 2011.
To determine the change in mercury levels over time, they compared samples of seawater from depths below three miles with water closer to the surface that had been more recently exposed to mercury pollution. They found that mercury levels in the upper 100 meters had “increased by a factor of 3.4.”
“The total amount of anthropogenic mercury in the world's seas now stands at 290 million moles, with the highest levels in the Arctic and North Atlantic oceans,” the study said.
Circulation patterns in the oceans, which cause cold, salty and dense water carrying high levels of mercury to sink deep into the ocean from shallower regions where life abounds, had, to some extent, offset the harmful effects of the rise in marine mercury and provided a buffer to marine life, the researchers noted.
However, Lamborg warned that the “deep water’s ability to sequester mercury may soon be exhausted...(humans) are on track to emit as much mercury in the next 50 years as they did in the last 150 years.”
“You're starting to overwhelm the ability of deep water formation to hide some of that mercury from us, with the net result that more and more of our emissions will be found in progressively shallower water,” Lamborg said.
The toxic effects of mercury, due to a phenomenon known as bio-magnification, tend to amplify with every step in the food chain. This poses a direct threat to humans consuming fish like tuna and mackerel, as the levels of mercury in their bodies are much higher than in the surrounding seawater.
Pregnant women are considered to be at higher risk from mercury toxicity because it can accumulate in the growing fetus and cause serious developmental disorders.
The researchers said that further research was needed to assess the potential impact of the increase in marine mercury levels, adding that “this information may aid our understanding of the processes and the depths at which inorganic mercury is converted into toxic methyl mercury and subsequently bioaccumulated in marine food webs.”