At a snail’s pace : suitability of cornu aspersum and theba pisana as bioindicators for heavy metals in Malta

Abstract

Heavy metals are a cause for great concern in the environment due to their toxic and bioaccumulative effects and therefore monitoring their prevalence is considered greatly important. One way of doing this is by using a bioindicator such as terrestrial snails. This study set out to determine the suitability of both the soft part and the shell of two snail species Cornu aspersum and Theba pisana, for monitoring the heavy metals arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), chromium (Cr), aluminium (Al), manganese (Mn), barium (Ba), and vanadium (V) in Malta. Snails were sampled from various environmental situations from around Malta, acid digested, and analysed using MP-AES to identify and quantify the selected heavy metals. It was determined through ordination plots that individual samples had enough variation to constitute calling them effective bioindicators and that there was significant variation between shell and soft part samples. PERMANOVA tests showed statistically significant differences between the soft parts of the two species, with T. pisana soft parts being found to be the better bioindicator for arsenic (p=0.046), cadmium (0.032), nickel (0.008), lead (0.012), chromium (0.007), and aluminium (0.014). The soft parts of C. aspersum were shown to be the most effective bioindicator for barium (0.004). In the case of vanadium, it was only detected in shell samples, meaning that shells (especially those of T. pisana) must be used as bioindicators for this metal, making it the only time analysing shells was preferential to soft parts. For zinc, copper, manganese, and vanadium there was no statistically significant difference between the two species. The most abundant metals found in T. pisana was Arsenic > Cadmium > Chromium, while in C. aspersum this was Arsenic > Cadmium > Barium.