Comparison of the Toxicological Effects of Nitrate versus Chloride Metallic Salts on Caenorhabditis elegans in Soil

摘要

There is growing interest in the use of bioindicators to assess metal toxicity in soil. The current ASTM Standard Guide for Conducting Laboratory Soil Toxicity Test with the lumbricid earthworm Eisenia fetida (E 1676-97) uses a common earthworm. The nematode Caenorhabditis elegans is a natural soil inhabitant with many characteristics that make it an ideal alternate test organism. It has been used to assess metal toxicity in aquatic media, agar plates and in soil. Work is currently underway on the design of a C. elegans procedure for metals in soil. The objective of this study was to determine differences in LC_(50s) between the chloride salt and the nitrate salt forms of cadmium, copper, lead, nickel, and zinc in three types of soil: Cecil, Tifton, and ASTM artificial soil. Results indicated that the toxicological effect of the metallic salt varies and is dependent on the particular metal. For Cd and Pb the nitrate form is more toxic while Cu and Ni are more toxic in the chloride form. The composition of the soil also effected toxicity, with the metals being the least toxic in ASTM soil and the most toxic in Tifton soil. This is strongly correlated with organic matter and clay content of the soil. It is important to determine the effects of carrier salt form and soil composition on metal toxicity, not only in order to standardize the protocol for C. elegans soil toxocity testing, but also in establishing acceptable exposure concentrations in the soil.