The Biodiversity Research Institute and the UN Environment Programme were involved in the research on women of child-bearing age in four Pacific countries over the past year.
Mercury exposure can cause damage to the nervous system and kidneys and it’s particularly harmful to foetuses.
The Institute’s chief scientist David Evers said the elevated mercury levels were likely due to a diet high in certain fish.
“Some of the healthier choices can be younger, smaller fish, groper, for example, as long as they’re the younger smaller species or individuals of grouper.
“Conversely the larger, long-lived species like swordfish are much more riskier choices.”
David Evers said yellowfin and albacore tuna are healthier options than very large Pacific bluefin tuna which have higher concentrations of mercury.
The researchers sampled the hair of women aged 18 to 44 in the Cook Islands, Marshall Islands, Kiribati and Tuvalu.
Dr Evers said further studies were needed to find out if people in the Pacific were being harmed by high levels of mercury.
He said exposure could lead to neurological problems and lower the intelligence quotient (IQ) of children.
“There’s indications that people with elevated mercury concentrations can adapt to a certain degree of mercury in their bodies. Now how much they can adapt is unknown and it would be something that would need further study,” said Dr Evers.