Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses

Abstract

The exposure of animals to pollution in ecosystems is not always chronic. Toxicants can remain in aquatic ecosystems for a short-term. To improve the extrapolation of laboratory results to natural scenarios the inclusion of post-exposure periods is a relevant issue. The present study focuses on the assessment of cadmium toxicity on survival and behavior of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca) during exposure and post-exposure. Animals were exposed for 48 h to cadmium (0.05, 0.14, 0.44 and 1.34 mg Cd/L) and 168 h of post-exposure. During the post-exposure period an increase in mortality in all concentrations was observed. The effects observed during the post-exposure period on the LC50 and EC50 were significant. During the post-exposure, behavior showed a clear recovery in surviving animals exposed to 0.44 mg Cd/L. Animals exposed to 0.05 mg Cd/L did not show differences with control. Therefore, mortality after exposure should be included in the ecotoxicological bioassays for a more realistic estimation of the cadmium effects. To assess the degree of animal recovery after cadmium exposure, behaviour has been shown as an adequate parameter.

Keywords: Behavioral activity; Cadmium; Mortality; Recovery.

Fig. 1

Percentage of cumulative mortality (A) and mortality plus immobility (B) of Potamopyrgus antipodarum for control and cadmium treatments (0.05, 0.14, 0.44 and 1.34 mg Cd/L) for each exposure (24 and 48 h) and post-exposure periods (24, 48, 120 and 168 h)

Fig. 2

Lethal Concentrations 50 (LC50) and Effective Concentrations 50 (EC50) (mortality plus inactive animals) at 48 h of exposure and at 168 h of post-exposure for Potamopyrgus antipodarum. Squares represent the LC and EC, and the black lines represents the 95% confidence intervals. Asterisks show significant differences between the final exposure period (48 h) and the final of post-exposure period (168 h) for each endpoint (LC50 and EC50) (p < 0.05; overlap test)

Fig. 3

Time to start activity (in seconds) of Potamopyrgus antipodarum for control and each cadmium treatment (0.05, 0.14, 0.44 and 1.34 mg Cd/L) during the exposure and post-exposure periods. Standard deviations have been removed for clarity. Only active animals have been included

Fig. 4

Mean (n = 17–18) differences (and 95% confidence intervals) between the time to start activity of each animal and the mean activity of control for 48 h of exposure and for 168 h of post-exposure to cadmium (0.05 and 0.14 mg Cd/L). Asterisks indicate significant differences with respect to zero for each cadmium concentration and exposure and post-exposure periods (p < 0.05; t-test). ns: no significant. Cadmium treatments of 0.44 and 1.34 mg Cd/L were not analyzed as the number of active animals was less than 3