Effects of in vivo chronic exposure to pendimethalin/Prowl 400® on sanitary status and the immune system in rainbow trout (Oncorhynchus mykiss).

The in vivo effects of the herbicide active substance (AS) pendimethalin (alone and with Prowl 400® adjuvant) were evaluated on sanitary status i.e. the health status with regard to chemical pollution and on the physiological state via the immune system in rainbow trout, Oncorhynchus mykiss. Four nominal exposure conditions were tested: i) control (C), ii) AS at 500 ng L(-1) (P500), iii) AS at 800 ng L(-1) (P800) and iv) Prowl 400® at 500 ng L(-1) (Pw). After a 28 day exposure period (D28), 10 fish were sampled for each condition and 10 other after a 15 day recovery period in clean fresh water (D43). Pendimethalin concentrations in the exposure water and muscles were followed. White blood cell counts, differential leucocyte counts, cell mortality and phagocytosis activity were measured. Haemolytic alternative complement activity, lysozyme concentration and stress parameters were analyzed. The resulting concentration of pendimethalin in the exposure water was lower than the expected concentration. At D28, the concentration quantified in the contaminated fish was negligible in comparison with the Reference Dose for Oral Exposure estimated by US-EPA's Integrated Risk Information System. Leucopenia was noted in all contaminated fish. A decrease in phagocytosis activity and ACH(50) was also observed in contaminated fish by P800 and Pw. Disturbed lysozyme activity was noted only in fish exposed to Pw. Furthermore, during exposure to a similar concentration of pendimethalin, the commercial product seemed to be more immunotoxic than the AS alone. Finally, at D43, the effects proved reversible for sanitary status while immunity was still disturbed in contaminated fish by P800 and Pw.