Accumulation of lead and cadmium in the marine prosobranch Nerita saxtilis, chemical analysis, light and electron microscopy

Abstract

The potential value of the marine prosobranch Nerita saxtilis as an efficient biological monitor to heavy metal pollution in the Red Sea was investigated. Storage ability of lead and cadmium was compared in shell, headfoot and digestive gland of the marine snail N. saxtilis collected from Al-Hamrauin area at El-kuseir (lead, 300.35±28.53 μg/l, 1716±16.14, cadmium 20.01±1.8 μg/l, 161.72±21.4 mean±S.D. for water and sediment, respectively) relative to that of inhabiting marine water and sediment employing atomic absorption spectrometry to determine the organ with highest capability of heavy metal accumulation. The influence of metal storage on light microscopic structure of that organ was investigated. Also, the ultrastructure localization of storage sites in the same organ was determined employing transmission electron microscopy. The digestive gland was shown to accumulate both metals at concentrations that are several orders of magnitude higher than those in the surrounding marine water. The bioaccumulation capability of lead and cadmium was ranked in the following order; digestive gland>headfoot>shell for lead and digestive gland>shell>headfoot for cadmium. In spite of its evident highest metal storage capability, no histopathological changes were observed in the digestive gland of that marine prosobranch. Enlarged electron dense vesicles and many granules were observed in ultrathin sections in digestive cells of these snails and are suggested to be the sites of storage of detoxified metals. The results of that finding indicate the possibility of using the marine prosobranch N. saxtilis as biomonitor for heavy metal contaminants in the Red Sea.