Toxicity and accumulation of lead and cadmium in the land snail, Archachatina papyracea, in a tropical Alfisol from Southwestern Nigeria

Abstract

Snails are an important link in the transfer of contaminants, especially metals in the food chain. Yet, few studies have examined the toxicity and accumulation of metals in snails in the tropics. This study assessed the toxicity and accumulation of two non-essential metals (cadmium and lead) to the tropical snail Archachatina papyracea. Specimens of the snail A. papyracea were exposed in a loamy soil collected from Ile-Ife, Nigeria and spiked with varying concentrations of Cd and Pb over 28 days. Survival and weight change of snails were monitored weekly, while tissue accumulation was assessed at the end of the 28-day period. Survival was a more sensitive endpoint than the weight change of snails. The Cd median lethal concentration (LC50) value was 93 ± 4.4 mg/kg, while the median effect concentration (EC50) for snail weight change was 131 ± 41 mg/kg. For Pb, LC50 value was 1121 ± 457 mg/kg, while the EC50 value for weight change was higher at 4541 ± 1180 mg/kg. Therefore, Cd was a factor of about 10 to 30 × more toxic than Pb, consistent with findings on the relative toxicity of Cd and Pb to other soil organisms, including earthworms, springtails, and mites. Although not included initially as an endpoint, egg production in the snails decreased with increasing Cd and Pb concentrations in the substrate. Metal analysis of the foot and visceral mass of surviving snails showed progressive accumulation of Cd and Pb as concentration increased, showing the tendency to use body residue of A. papyracea as an indicator of metal pollution. It further suggests the role of this snail species in above-ground metal transfer in the food chain and highlights the potential danger for human consumption.

Keywords: Accumulation; Archachatina papyracea; Metals; Snail; Toxicity; Tropics.