Grazer gastropods as alternative species for monitoring butyltins contamination in harbors

Abstract

Butyltin contamination was monitored in seven Tunisian harbors using soft tissue of three grazer gastropods (the Mediterranean limpet Patella caerulea, the turbinate monodont Phorcus turbinatus and the false-limpet Siphonaria pectinata), as well as sediments from the rocky substratum. The results revealed that butyltins (BuTs) were still present in the study sites three years after the Tunisian authorities banned their use. Tributyltin (TBT) concentrations in the substratum ranged from 1.5 to 5.7 ngSn/g dw (dry weight), dibutyltin (DBT) from 2.5 to 8.3, and monobutyltin (MBT) from 6.0 to 15.7. Higher concentrations were found in gastropods, ranging from 1.2 to 6.75 ngSn/g dw for TBT, 2.6 to 42.7 ngSn/g for DBT and 2.4 to 78.5 ngSn/g dw for MBT. The species P. caerulea and P. turbinatus accumulated TBT within the same range and at a higher level than S. pectinata, making them more appropriate for monitoring organotin contamination. Furthermore, DBT and MBT accumulated markedly in P. caerulea, up to 5–8 times the concentration recorded in the other two gastropods, suggesting further utility of this species as a good bioaccumulator of BuTs. Among the seven harbors studied, Zarzouna was the most contaminated whereas Zarat was the least polluted. The contamination is directly related to vessel traffic and shipyard activity at the studied harbors. The temporal comparison with previous studies shows that BuTs contamination is decreasing and that Tunisia's prohibition of TBT is effective in terms of environmental recovery.