Response of biomarkers in amphibian larvae to in situ exposures in a fruit-producing region in North Patagonia, Argentina

Abstract

We evaluated biomarker responses in caged larvae of the amphibian Rhinella arenarum in water channels during fruit production season, and compared them with those elicited by a transient exposure to azinphos methyl (AzM) (0.02-2 mg/L; 4 h), the main pesticide applied in the Alto Valle region, Patagonia Argentina, taking into account the maximum environmental concentration detected in superficial water (22.5 µg/L). The traditional biomarkers of organophosphate exposure, acetylcholinesterase (AChE) and carboxylesterase (CE), were inhibited in tadpoles after one week of exposure in channels potentially receiving pesticide drift, while the antioxidant glutathione (GSH) and the detoxifying activity of GSH-S-transferase (GST) were induced. In a two-week monitoring study, AChE activity was induced and CE activity showed a temporary inhibition in larvae exposed at the agricultural site, and CE showed an inhibition followed by the return to control values suggesting an exposure episode followed by a recovery process. GSH levels were first depleted and then surpassed control levels while GST activity was continuously induced. These responses were mimicked in the laboratory by 2 mg/L AzM-pulse exposure and recovery, which notably exceeds the expected environmental concentrations. The results draw attention to the complexity of the responses under pesticide exposure, strongly depending on exposure time-concentration and recovery periods among other possible factors, and support the necessity of the integrated use of biomarkers to assess exposure episodes in agricultural areas.