Mode of action of high concentrations of terbuthylazine and nicosulfuron in human erythrocytes in vitro

Terbuthylazine (T) and nicosulfuron (N) are herbicides widely used in maize fields. They differ significantly in chemical structure and partition coefficient, with terbuthylazine being more liposoluble. We investigated the effects of high concentrations of the herbicides terbuthylazine (T: 0.85 and 8.5 mg/L) and nicosulfuron (N: 250 and 400 mg/L), on lipid peroxidation (malondialdehyde, MDA concentration), and antioxidative parameters (superoxide dismutase, SOD1; catalase, CAT) of human erythrocytes in vitro.

Human erythrocytes were treated with T and N for 1 h in vitro. The percentage of T and N entry into erythrocytes was determined by HPLC. Concentrations of haemoglobin (Hb), MDA and membrane proteins were determined spectrophotometrically. The isoforms of SOD1 and CAT were separated by native electrophoresis and their activities were determined densitometrically.

Given the initial herbicide concentrations used for treatment, the percentage of T entry into erythrocytes were 48% and 43%, respectively, while for N were 19 and 21%, respectively. Increase in haemoglobin (Hb) concentration was detected only after treatment with 8.5 mg L⁻¹ T. Both herbicides increase concentrations of MDA, protein concentration in erythrocyte membranes and SOD1 activity. On the other hand, CAT activity was increased only after erythrocyte treatment with 8.5 mg L⁻¹ T.

Results indicate that N, although administered in higher concentrations, has a less toxic effect on human erythrocytes compared to terbuthylazine. Also, the results obtained lead to the conclusion that log K_OW may be important in the selection of herbicides for field applications to reduce toxicity to non-target organisms.