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Final Progress Reports: Dartmouth College: Variation in Bioaccumulation and Biomagnification of Metals in Lakes throughout the Northeastern Region of the U.S.A.

Superfund Research Program

Variation in Bioaccumulation and Biomagnification of Metals in Lakes throughout the Northeastern Region of the U.S.A.

Project Leader: Carol L. Folt
Grant Number: P42ES007373
Funding Period: 1995 - 2000
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Final Progress Reports

Year:   1999 

The overall aim of this research is to determine mechanisms underlying the movement of five potentially toxic metals (arsenic, mercury, zinc, cadmium and lead) through aquatic food webs into fish, which are primary conduits for human exposure to metals. One of the objectives of the year's work was to quantify the accumulation of organic and inorganic mercury at the base of the aquatic food web in intact plankton communities at ecologically relevant metal concentrations. Two pilot mesocosm (500 L tanks) studies were conducted to examine the extent to which transfer of metals via freshwater organisms is dependent on taxonomic group and nutrient status of the lake. Large cladocerans were found to have significantly higher Me-Hg burdens than copepods, and inorganic Hg made up a significantly larger portion of total zooplankton Hg with high phytoplankton density. Moreover, zooplankton metal burdens were lower in higher nutrient treatments containing higher algal densities which suggests metal biodilution. In an ongoing collaboration with the MIT Superfund program, Project 7 investigated the seasonal accumulation and transfer of arsenic and other metals in Upper Mystic Lake which is located in the same watershed as the Woburn Superfund site. Samples were collected during the spring, summer, and fall of 1997 for particulate, micro- and macrozooplankton, individual zooplankton taxa and planktivorous fish (in fall only). Findings for As and Pb trophic transfer show diminution with increasing trophic level for both metals and elevated levels of As in water, particulates, and zooplankton. Arsenic concentrations in fish were not different from levels found in uncontaminated lakes although planktivorous species had significantly higher As burdens, most likely due to elevated metal burdens in the zooplankton. Finally, in collaboration with Project 2, this project is continuing to develop biomarkers that can be used to examine environmental exposures to toxic metals and assess their potential ecological and human health impacts. Differential display RT-PCR has been used to identify Cd-responsive genes in the freshwater invertebrate, Daphnia pulex, using concentrations at which biological effects are observed. A total of 18 differentially expressed Cd-altered cDNAs fragments were isolated, cloned, and sequenced. The longer term goal is to be able to use RT-PCR analysis of individuals and populations from field studies to determine Cd exposure.

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