Biomarkers’ responses of the benthic clam Scrobicularia plana to the main active ingredients (S-metolachlor and Terbuthylazine) of a common herbicide

Abstract

The overexploitation of the farmlands in the Mediterranean region contributes to an overuse of herbicides that have the potential to pollute surrounding aquatic systems, like the Mondego estuary, located near the city of Figueira da Foz (Portugal). Primextra® Gold TZ is the most-used herbicide in this area and it is constituted by two main active ingredients, S-metolachlor (SMOC) and terbuthylazine (TBA) that have exhibited toxicity to aquatic animal species in previous studies. The benthic bivalve species Scrobicularia plana was selected to carry out bioassays because of its capacity to filter pollutants and its important position in the structure and functioning of estuarine communities. Organisms of two size classes (big and small) were exposed individually to a range of concentrations of the mentioned compounds to assess their responses in terms of mortality. S. plana showed a clear higher sensitivity to SMOC (big – LC50 = 40.702 mg/L; small – LC50 = 41.517 mg/L) than to TBA (big – LC50 = 118.590 mg/L; small – LC50 = 108.418 mg/L), and big size class organisms, generally, showed to be more tolerant than the ones of small size class. In order to evaluate contaminated aquatic systems, it is necessary to develop laboratory strategies to rapidly assess the potential impacts of pollutants in the environment and in human health. Thus, a battery of biomarkers was selected, including the activity of antioxidant enzymes (glutathione peroxidase (tGPx), glutathione reductase (GRed) and glutathione-S-transferase (GST)) and the lipid peroxidation occurrence (by quantification of TBARS levels). This work reports that GRed and GST activate under the chemicals’ exposure at concentrations that surpass the levels for environment protection. Moreover, GRed shows specificity to detect TBA presence and GST results more accurate to assess SMOC contamination.