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Toxicity of Cadmium in the Freshwater Snail, Physa gyrina Say¹

ABSTRACT

Using both mature and immature snails and cadmium as the toxicant, 50% tolerance limits (TL₅₀) for various exposure durations were determined graphically. The immature snails 96-hour TL₅₀ of 0.43 ppm indicates they are three times as sensitive to Cd as mature snails whose 96-hour TL₅₀ was 1.37 ppm. Survivors of bioassays and their offspring were observed. The rate of Cd uptake by snails exposed to 1.30 ppm Cd solution over a 24-hour period was 0.550 ppm/hour. Following the 24-hour exposure, the rate of elimination during the next 24 hours was 0.229 ppm/hour. The rate of uptake was nearly twice the rate of elimination, allowing accumulation of Cd in the snail. The higher the Cd concentration to which snails were exposed, the fewer the survivors, the lower their reproductive potential, and the shorter the period the young survived.

Key Words: acute toxicity • bioassay • biomagnification • biological monitor • fecundity reduction • heavy metals • reproduction

¹ Based on a thesis partially satisfying requirements for the M.S. degree, Western Illinois Univ., Macomb, IL 61455.

² M. S., WIU and Associate Professor of Biology, respectively.

Received for publication May 19, 1975.