Rising temperatures caused by climate change could increase levels of mercury in fish by nearly seven times, say experts.

A new study by Swedish researchers has found that increased runoff into the oceans could result in a drastic rise in mercury levels in marine life. This would harm the food chains, also contaminating human food supplies.

Shifting rainfall patterns could send 10 – 50 percent more organic matter flowing into the seas. This organic matter leads to muddying of seawater and disrupts the balance of plankton at the base of the food web.

Mercury accumulates in aquatic life as methylmercury. This is a neurotoxin formed by the reaction of bacteria with mercury in water, soil or plants.

The researchers state that the input of mercury to ecosystems is estimated to have increased two to five- fold during the industrial era. They project that methylmercury in zooplankton could increase by a factor of 3 to 6 in coastal areas, with a 15-30 percent rise in terrestrial runoff.

As this mercury enters the food web, it reaches humans through the consumption of fish and is easily absorbed into the body.

According to the World Health Organisation, mercury is one of the top ten chemicals that are a cause of concern to public health.

High levels of mercury in the human body have been associated with damage to the central nervous system, kidney failure, birth defects and mental impairment in children.

Researchers replicated the conditions using miniature estuaries with microbes and increased levels of organic matter.

They noted that increased runoff would reduce the amount of sunlight reaching the water. This leads to a reduction in phytoplankton and triggers the growth of bacteria.

“When bacteria become abundant in the water there is also a growth of a new type of predators that feed on bacteria,” said lead author Erik Bjorn from Umea University, Sweden. “You basically get one extra step in the food chain and methylmercury is enriched by about a factor of ten in each such step in the food web.”

The findings show the importance of including climate-induced changes to the food web in methylmercury accumulation models and risk assessments.

The study has been published in the journal Science Advances.