Paper No. 9
Presentation Time: 4:35 PM
ECOLOGICAL STUDY OF BIOACCUMULATION OF MERCURY IN SUBSISTENCE FISHING COMMUNITIES--LAKE CHAPALA, MEXICO
Mercury (Hg) occurs naturally in elemental (Hg0
) form, is highly volatile and readily oxidized to inorganic (Hg2+
) form. Volcanic outgassing, coal burning power plants, and artisinal gold mining are significant sources of atmospheric deposition. Monomethylmercury (MeHg) is a recognized neurotoxin. In situ
formation in aquatic ecosystems and resulting bioaccumulation is the predominant source of MeHg toxicity to humans. Studies of subsistence fishing populations in the Faroe Islands, Seychelles, and New Zealand have raised concerns of MeHg toxicity to the developing fetus and small children. Our research focused on subsistence fishing communities on the shores of Lake Chapala, Mexico, where elevated concentrations of Hg in fish have been documented. Our goal was to shed light on sources and routes of Hg exposure.
Utilizing CV-AAS, total Hg concentrations were measured in sediment, suspended particles, fish flesh and human hair. Sections of two sediment cores were analyzed for both Hg and radionuclides (for dating purposes). Hg was measured on suspended particulate matter filtered from water samples collected along a transect from mid-lake to the mouth of the major tributary. Three types of fish were purchased from fishermen and markets along the shores of the lake and analyzed for Hg. Finally, hair samples were collected from 92 women of child-bearing age, and hair segments proximal to the scalp were analyzed for Hg content. Entire length of selected samples were further cut into 1cm segments and analyzed for Hg, with the goal of discovering possible temporal variations in Hg exposure. Surveys were administered to the hair-sample volunteers to investigate a possible relationship between fish consumption and hair Hg levels.
Highest concentrations of Hg in fish samples were found in carp (mean 0.87 ppm). Sediment data suggest a pattern of moderate ongoing contamination. Analyses of particles filtered from the water column showed highest concentrations of Hg near the mouth of the Lerma. Almost 30% of women had >1ppm hair Hg. Consumption of fish, especially carp, from Lake Chapala was associated with significantly higher mean hair Hg concentrations. Seasonal variability in Hg sequestered to hair was discovered.