Seas and oceans, the cradle of life par excellence, are dying slowly, suffocated by plastic and poisoned by the toxic substances we discharge into them. Among these is mercury, and in particular methylmercury, a highly toxic organic compound of mercury that moves up the entire food chain from the smallest organisms. Large predatory fish, such as tuna, marlin, sharks and mackerel, can accumulate extremely high concentrations of mercury over the course of their lives. This phenomenon, already known and documented, is being further exacerbated by climate change, which could raise mercury levels in fish by as much as seven times.

The study

This is what emerged from a study conducted by a team of Swedish and American scientists from the universities of Umeå and Rutgers, and published in the journal Science advances. According to the researchers, rising temperatures would exponentially increase the already high presence of mercury in marine ecosystems, with a further growth of 300–600 per cent. "With climate change we expect an increase in precipitation in many areas of the northern hemisphere, with a consequent increase in water runoff into the seas," explained Jeffra Schaefer, co-author of the study. "This means there will be a large release of mercury into coastal ecosystems, which are the primary sources of sustenance for the fish that people eat."

A threat to the environment and to our health

Mercury is therefore initially absorbed by microorganisms and, step by step, climbs every rung of the food chain until it reaches the humans who eat fish. According to Erik Bjorn, lead author of the study, "at each new step in the food chain, the accumulation of methylmercury increases tenfold." This is a process called bioaccumulation; this is why toxic substances build up in large predators — when one fish eats another, certain indigestible substances, such as mercury, cannot be processed. The World Health Organization considers mercury to be among the ten most serious threats to health.

The effects of mercury poisoning

The effects of mercury on animals are not yet fully understood, even though fish, just like us, are equipped with nerve endings designed to register pain. The terrible effects on humans, however, are well known. According to Rick Smith and Bruce Lourie, "mercury poisoning can cause permanent brain damage, central nervous system disorders, memory loss, heart disease, kidney failure, liver damage, cancer, loss of vision, loss of perception and tremors. It is also among the suspected 'endocrine disruptors' that cause damage to the reproductive and hormonal development of foetuses and children. Some studies also suggest that mercury may be linked to neurological diseases such as multiple sclerosis, attention deficit disorders and Parkinson's disease, although the evidence in this case does not yield certain results." Methylmercury is readily absorbed by the digestive system and tends to accumulate in the brain. According to experts, there is no safe level of mercury — even small doses can cause physical and mental harm.

How mercury reaches the seas

Mercury is released into lakes and rivers, from which it then reaches the sea, by industries — especially coal-fired power plants.

The most affected areas

According to the research findings, the exponential increase in mercury levels will affect above all the northern hemisphere, and in particular the Baltic Sea, the North Sea, the Arctic Ocean and part of the North Atlantic. It could, however, decrease in some areas such as the Mediterranean, southern Africa and North America.