New TBT biomarkers for the cultivated clam Tapes philippinarum

The search for new biomarkers to assess the effects of TBT contamination in marine coastal ecosystems is essential for both improving productivity in culture farms of the edible clam Tapes philippinarum and controlling risks to human health. We have set up short-time hemocyte cultures 860 min at 25 °C) in order to expose them to various TBT sublethal concentrations (0.05, 0.01, 0.1 µM), not causing cell mortality and numerical decrease. Three peculiar indexes were established as TBT pollution biomarkers since they supply different information related to different intracellular targets of TBT: 1) Amoebocytic index (A.I.): percentage of hemocytes with an amoeboid shape. 2) Phagocytic index (P.I.): percentage of hemocytes containing ingested yeast particles preincubated in blood plasma for 30 min. 3) Enzymatic index (E.I.): percentage of hemocytes showing histoenzymatic staining properties for beta-glucuronidase, a widespread hydrolase in T. philippinarum hemocytes. Following the index kinetics, after 30 min A.I., P.I. and E.I. were significantly inhibited by all the tested TBT concentrations, except for E.I. which was significantly inhibited only after 60 min at the lowest TBT concentration. The time course decrease of A.I. and P.I. up to 30 min was always higher than that between 30 and 60 min. On the contrary, in the same range the time course decrease of E.I. always rose, except fo the highest TBT concentration. Therefore, we propose all the three indexes could be used as valuable biomarkers to assess the risk of TBT even at low concentrations. In particular, P.I. appears the most reliable, sensitive and effective over a shorter time.