FUNGAL BIOACCUMULATION OF MERCURY IN THE AVERY BROOK WATERSHED, WEST WHATELY, MASSACHUSETTS

Increases in atmospheric deposition of Hg since the industrial revolution have led to high mercury concentrations in forest soil organic horizons. Fungi in this ecosystem can bioaccumulate mercury, and may, through facultative anaerobic processes, contribute to mercury methylation. As a result, fungi are important in soil mercury cycling and methylation. This study examines the role of fungi in the biogeochemical cycling of mercury within the Avery Brook Watershed located in West Whately, Massachusetts.

Fungi samples together with their substrates were collected from rotting wood, leaf litter, trees, and soil. Samples were dried at 105˚C prior to analysis of total mercury (THg) using a Teledyne Leeman Labs Hydra IIC Automated Direct Mercury Analyzer.

Fruiting bodies had higher THg concentrations than substrates, indicating, that THg was translocated from the substrate to the fruiting body through the mycelia. For example, samples of Ganoderma applanatum were found to have ~600% more THg in their fruiting bodies than their rotting wood substrates. On average, fungal fruiting bodies had THg concentrations of approximately 100 ng/g. This compares to an average THg content for the soil horizon (Oi, OE, OA) of 188 ng/g. Although the soil had higher THg levels than the fruiting bodies, it should be noted that the soil actually contained a large amount of fungal mycelia, which is visible to the human eye, but difficult to separate from the rest of the soil material. Mycelia translocate nutrients from the soil to tree roots. THg was transferred from the soil to the mycelium and then to the tree roots, and finally to the substrates. Fruiting bodies grew directly from the mycelium and therefore had more THg. Fungi with leaf litter substrates translocate THg directly from soil pools to their fruiting bodies. Fungi may be a viable means to temporarily remove THg from the soil but rapid decomposition of the fruiting bodies will release it back into the soil.

Those wishing to collect wild mushrooms for consumption should be aware that fruiting bodies contain elevated levels of THg and other heavy metals. In order to determine how THg is translocated into the fungal fruiting bodies from the soil, mycelia located in the B horizon, where heavy metals and nutrients are accumulated, should be analyzed for THg.