Behavioral, biochemical and histological responses of the clam Ruditapes decussatus to a triazole fungicide

Clams (Ruditapes decussatus) were exposed for 7 days to a triazole fungicide, Alto Super 330EC (AS330), widely used in agriculture in the Bizerte Lagoon watershed. Its two active substances (propiconazole and cyproconazole) were detected in wastewater discharges at Oued Guenniche. Considering the environmental levels of these compounds, clams were exposed in microcosms under controlled conditions to three concentrations: C1 (25 µg.L⁻¹), C2 (50 µg.L⁻¹) and C3 (100 µg.L⁻¹). Behavioral (filtration capacity), oxidative and neurotoxic stress and histological damage responses were assessed to evaluate clam health status. Four biomarkers; catalase (CAT), glutathione S-transferase (GST), malondialdehyde (MDA) and acetylcholinesterase (AChE) were measured in gills and digestive gland. After exposure, the filtration rate was significantly increased at the lowest pesticide concentration. Antioxidant enzyme activities (CAT, GST) and cellular damage (MDA) exhibited organ- and concentration-dependent responses. The AChE activity decreased in a highly significant, dose-dependent manner. Exposure induced significant histopathological alterations. In gills, malformations at the tips of lamellae and marked hemocyte infiltration were observed. In the digestive gland, extensive degeneration of digestive tubules occurred, characterized by accumulation of cellular debris and necrotic areas within the tubule lumen. These changes indicate a pronounced pathological response to contamination.