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Assessment of Soil Toxicity: a Nematode BioassayEPA Grant Number: U915723
Title: Assessment of Soil Toxicity: a Nematode Bioassay
Investigators: Boyd, Windy A.
Institution: University of Georgia
EPA Project Officer: Edwards, Jason
Project Period: December 1, 2000 through December 1, 2002
Project Amount: $102,000
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Toxicology , Academic Fellowships , Health Effects
The goal of this research is to compare the expression of toxic effects on several species of nematodes (Caenorhabditis elegans, Plectus acuminatus, Heterocephalobus pauciannulatus) using lethality, behavior, and reproduction as endpoints.
The methods below detail procedures already in use with the nematode C. elegans and are currently under review as a standard guide by the American Society for Testing and Materials (ASTM). Similar approaches will be used for concurrent testing with the other nematode species. Ideal species for comparison should be easily identifiable when observed in the field, easy to maintain in laboratory settings, and possess similar feeding and behavior activities as C. elegans. Other free-living bacterial feeders include P. acuminatus and H. pauciannulatus, both of which can be found in large numbers in topsoils and are easily identifiable. Although feeding habits are similar to C. elegans, the life cycle and reproductive periods of P. acuminatus and H. pauciannulatus are considerably longer, which affords more diversity to the standardized soil nematode test. Many soil properties affect the bioavailability and thus the toxicity of heavy metals. Therefore, several soils with varying soil properties will be tested. All species of nematodes will be exposed to a variety of metals in several natural and artificial soil matrices. After exposure, the soil is rinsed from the dishes with Ludox, a colloidal silica suspension that causes the nematodes to float to the top while the soil sinks to the bottom. For lethality and reproduction, dead and live worms or larvae are scored in the Ludox supernatant with the aid of a dissecting microscope. Rate of movement and change in direction of nematodes are monitored with a CCD camera interfaced with a computer to observe any behavioral changes at sub-lethal toxicant concentrations. Further emphasis will be placed on the length of exposure, reproductive effects, and additional behavioral endpoints, such as the response of nematodes to sensory stimuli after toxicant exposure.
This study will evaluate the effectiveness of the nematode toxicity test as an alternative and/or complement to chemical analyses of soil solutions, phytotoxicity tests, and earthworm toxicity tests.