A freshwater symbiosis as sensitive bioindicator of cadmium

The vulnerability of aquatic ecosystems due to the entry of cadmium (Cd) is a concern of public and environmental health. This work explores the ability of tissues and symbiotic corpuscles of Pomacea canaliculata to concentrate and depurate Cd. From hatching to adulthood (4 months), snails were cultured in reconstituted water, which was a saline solution in ASTM Type I water. Then, adult snails were exposed for 8 weeks (exposure phase) to Cd (5 μg/L) and then returned to reconstituted water for other 8 weeks (depuration phase). Cadmium concentration in the digestive gland, kidney, head/foot and viscera (remaining of the snail body), symbiotic corpuscles, and particulate excreta was determined by electrothermal atomic absorption spectrometry. After exposure, the digestive gland showed the highest concentration of Cd (BCF = 5335). Symbiotic corpuscles bioaccumulated Cd at a concentration higher than that present in the water (BCF = 231 for C symbiotic corpuscles, BCF = 8 for K symbiotic corpuscles). No tissues or symbiotic corpuscles showed a significant change in the Cd levels at different time points of the depuration phase (weeks 8, 9, 10, 12, and 16). The symbiotic depuration through particulate excreta was faster between weeks 8 and 10, and then slower after on. Our findings show that epithelial cells of the digestive gland of P. canaliculata and their symbiotic C corpuscles are sensitive places for the bioindication of Cd in freshwater bodies.