Effects of an Endocrine Disruptor Triclosan on <i>Ruditapes decussatus</i>: Multimarker and Histological Approaches

The aim of this work was to study the ecotoxicological effects of an endocrine disruptor triclosan on the clam <i>Ruditapes decussatus</i>. The bivalves were exposed to three concentrations of this biocide (C1 = 100 ng/L, C2 = 200 ng/L and C3 = 500 ng/L) for three and seven days. The impact was assessed at the gills and digestive glands, through activities of an antioxidant defense biomarker (Gluthatione <i>S</i>-Transferase, GST), a damage biomarker (Malondialdehyde, MDA), and a neurotoxicity biomarker (Acetylcholinesterase, AChE). Furthermore, histological traits were approached in different organs to evaluate any possible alteration induced by triclosan. It appears from this study that both gills and digestive glands responded discernibly to triclosan and effects were concentration-dependent. The stressed clams showed a significant increase in their GST and MDA activities in gills and digestive glands compared to controls for both time slots considered. In turn, the AChE activity was clearly inhibited in both organs in a time dependent way. The histological study made it possible to observe several structural pathologies caused by triclosan in the gills and the digestive gland. These alterations consisted mainly of inflammatory reactions, malformations of the lamellae and fusion of the gill filaments, degeneration of the connective tissue, and the erosion of the gill cilia with the appearance of certain severe alterations (cell necrosis and apoptosis), which can thus cause a malfunction of the gills and eventually lead to a reduction in oxygen consumption and a disruption of the osmoregulation for bivalves. Alterations in the digestive gland have also been detected, mainly by epithelial alterations, thinning of the tubules, and alteration of the basal cell membrane which can impair the ability of clams to absorb food. At germinal cells, several damages were observed in the oocytes which probably disturbed the reproductive function and the fertility of the clams. The damages observed in female gonads were caused by the cytolysis of a large number of oocytes through autophagy and necrosis at 200 ng triclosan/L. Moreover, at 500 ng triclosan/L, hemocytic infiltration was observed in acini and apoptotic bodies reflected in the fragmentation of more than 90% of oocytes.