News website Matangi Tonga reports hair samples from women aged 18 to 44 from the Cook Islands, the Marshall Islands, Tuvalu and Kiribati were examined as part of a joint study by the secretariat of the Minamata Convention, Biodiversity Research Institute and the global network IPEN.
The Pacific women were found to contain average mercury concentrations up to three times higher than the recommended daily mercury intake.
Mercury exposure can damage the nervous system, kidneys and cardiovascular system.
Researchers think Pacific Islanders may have a higher mercury level than other people because of the consumption of fish species with high mercury concentrations.
One of the research co-ordinators, Jacob Duer, said mercury was recognised as a substance of global concern with impacts on vulnerable populations.
Biodiversity Research Institute chief scientist David Evers said the study highlighted the importance of biomonitoring mercury pollution.