Grantee Research Project Results
Final Report: Potential for Increased Bioavailability of Mercury in Selenium Contaminated Sites: Risk Assessment and Ecological Effects
EPA Grant Number: R830841Title: Potential for Increased Bioavailability of Mercury in Selenium Contaminated Sites: Risk Assessment and Ecological Effects
Investigators: Trumble, John T.
Institution: University of California - Riverside
EPA Project Officer: Hahn, Intaek
Project Period: March 1, 2003 through February 28, 2005 (Extended to February 28, 2006)
Project Amount: $199,802
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Safer Chemicals , Land and Waste Management
Objective:
The overall objective of this research project was to test the hypothesis that selenium (Se) buffers the effects of mercury, thus allowing insects to attain higher levels of mercury in their bodies before toxic effects manifest. The objectives for the project included elucidation of developmental effects of the pollutants and joint analyses of the toxicity and developmental/survivorship effects of mercury and selenium on common insects and their associated insect predators found in aquatic and terrestrial ecosystems.
Summary/Accomplishments (Outputs/Outcomes):
We had several primary goals for this proposal. These included studies in both an aquatic system (mosquito larvae in water polluted with mercury and selenium compounds) and a terrestrial system (using an important insect detritivore feeding on food sources contaminated by mercury and selenium compounds). A no-cost extension through March 2006 was needed to allow populations to recover from flood waters caused by heavy rains. Nonetheless, the progress has met or exceeded our expectations, resulting in three peer-reviewed publications already published, a fourth peer-reviewed journal article accepted, a fifth peer-reviewed paper submitted, and five presentations that have been given since our last report. At least one more peer-reviewed paper is in preparation.
The studies of the independent and joint actions of selenate and methylmercury on a ubiquitous insect detritivore, Megaselia scalaris (Loew), were completed. Ovipositing females did not distinguish between untreated food sources and diets contaminated with toxic concentrations of selenate, methylmercury, or a combination of both. Larval survival, however, was decreased significantly and development was prolonged significantly by selenate and methylmercury individually at low or intermediate treatment levels that are ecologically relevant. Potentiation was strongly evident, as mixtures containing concentrations as low as only 1 percent of the respective individual median lethal concentration (LC50) values caused significantly more mortality and delayed larval development than would be expected from the responses that selenate and methylmercury elicit individually. The relative toxicity to M. scalaris of each of the individual and joint treatments was selenate (LC50 = 260 μg/g) less than methylmercury (LC50 = 22 μg/g) less than the mixture at approximately 5 percent of the LC50 concentration of each of the components (12 μg/g of selenate plus 1.0 μg/g of methylmercury). The increased mortality and delayed larval development within sites contaminated by selenate, methylmercury, or the combination have substantial implications for the ecology, population dynamics, and sustainability of M. scalaris populations. If these results can be extrapolated to other arthropod detritivores, ecosystem food-web function may be affected substantially.
Similarly, experiments on the southern house mosquito (Culex quinquefasciatis: Diptera) for the individual and joint effects of dissolved sodium selenite (Se) and methylmercury chloride (MeHg) have been completed. No evidence was found for female ovipositional preference in field trials using artificial ponds. Larvae were more sensitive to MeHg than Se, with LC50 values of 30 μg/L and 11 mg/L respectively. In addition, larval survival was reduced significantly at concentrations as low as 25 μg/L of MeHg and 8 mg/L of Se. A greater than additive interaction was observed in the toxicity of the Se-MeHg mixtures to C. quinquefasciatis larvae. Larval survival was reduced significantly at 7.5 μg/L MeHg + 2.75 mg/L Se, and an LC50 value of 9 μg/L MeHg + 3.4 mg/L Se was determined for a fixed-ratio mixture. Sodium selenate caused a significant decrease in growth between larvae in treatment versus control solutions at concentrations as low as 2 mg/L after only 4 days. Similarly, MeHg caused significant growth reductions at concentrations as low as 25 μg/L MeHg after only 2 days and at concentrations greater than or equal to 30 μg MeHg/L plus 1.1 mg Se/L after 3 days. These are the first reported survival and developmental data for MeHg and Se-MeHg mixtures for an aquatic insect.
Conclusions:
We will complete studies designed to evaluate the form (species) of Se and MeHg found in insects and their associated insect predators. In cooperation with Ingrid Pickering, we have completed studies at the Stanford Synchrotron to evaluate the species of selenium and mercury occurring in herbivore-parasite, detritivore-predator, and aquatic insect-predator systems. These data currently are being analyzed, and analyses will be completed by March 2006.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
| Other project views: | All 15 publications | 5 publications in selected types | All 4 journal articles |
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Jensen PD, Arias M, Trumble JT. Developmental responses of a terrestrial insect detritivore, Megaselia scalaris (Loew) to four selenium species. Ecotoxicology 2005;14(3):313-322. |
R830841 (2003) R830841 (2004) R830841 (Final) |
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Jensen PD, Johnson LR, Trumble JT. Individual and joint actions of selenate and methylmercury on the development and survival of an insect detritivore Megaselia scalaris (Diptera: Phoridae). Archives of Environmental Contamination and Toxicology 2006;50(4):523-530. |
R830841 (2004) R830841 (Final) |
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Jensen PD, Sorensen MA, Walton WE, Trumble JT. Lethal and sublethal responses of an aquatic insect Culex quinquefasciatus (Diptera: Culicidae) challenged with individual and joint exposure to dissolved sodium selenate and methyl mercury chloride. Environmental Toxicology 2007;22(3):287-294. |
R830841 (Final) |
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Sorensen MA, Jensen PD, Walton WE, Trumble JT. Acute and chronic activity of perchlorate and hexavalent chromium contamination on the survival and development of Culex quinquefasciatus Say (Diptera: Culicidae). Environmental Pollution 2006;144(3):759-764. |
R830841 (Final) |
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Supplemental Keywords:
selenium, sodium selenate, sodium selenite, selenocysteine, selenomethionine, methylmercury, toxics, pollutants, entomology, ecotoxicology,, Health, RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, PHYSICAL ASPECTS, INTERNATIONAL COOPERATION, Waste, ENVIRONMENTAL MANAGEMENT, Water, POLLUTANTS/TOXICS, HUMAN HEALTH, Ecological Risk Assessment, Health Risk Assessment, Physical Processes, Mercury, Risk Assessments, chemical mixtures, Exposure, Bioavailability, Chemicals, Ecology and Ecosystems, Environmental Monitoring, Risk Assessment, health effects, heavy metals, dietary exposure, animal bioassays, Selenium, aquatic ecosystem, groundwater contamination, human exposure, animal model, chemical exposure, bioaccumulation, contaminated sites, fate and transport, hazardous waste, environmental toxicant, human health riskRelevant Websites:
http://faculty.ucr.edu/~john/TrumbleHome/Trumblelab.htm Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.