Toxicological responses in Laeonereis acuta (Annelida, Polychaeta) after arsenic exposure

Abstract

Several environmental pollutants, including metals, can induce oxidative stress. So, the objective of this study was to evaluate the effects of arsenic (AsIII, as As2O3) on the antioxidant responses in the polychaete Laeonereis acuta. Worms were exposed to two environmentally relevant concentrations of As, including the highest previously allowed by Brazilian legislation (50 μg As/l). A control group was kept in saline water(10‰) without added metal. It was observed that: (1) a peak concentration of lipid peroxide was registered after 2 days of exposure to 50 μg As/l (61±3.2 nmol CHP/g wet weight)compared to the control group (43±4.5 nmol CHP/g wet weight), together with a lowering of the activity of the antioxidant enzyme catalase (−47 and −48%, at 50 or 500 μg As/l respectively) and a higher superoxide dismutase activity (+305% at 50 μg As/l with respect to the control group); (2) a lower conjugation capacity through glutathione-S-transferase activity was observed after 7 days of exposure to 50 μg As/l (−48% compared to the control group); (3) a significant increase in As concentration was verified after 1 week of exposure to both As concentrations 50 and 500 μg/l); (4) worms exposed to As showed a limited accumulation of related methylated As species and the levels of non-toxic As species like arsenobetaine (AsB) and arsenocholine (AsC) remained unchanged during the exposure period when compared with the controls. Overall, it can be concluded that As interfered in the antioxidant defense system of L. acuta, even at low concentrations (50 μg/l)that Brazilian legislation previously considered safe. The fact that worms exposed to As showed high levels of methylated As species indicates the methylation capability of L. acuta, although the high levels of inorganic As suggest that not all the administered AsIII (as As2O3) is completely removed or biotransformed after 7 days of exposure.