The effect of atrazine on Atlantic salmon (Salmo salar) smolts in fresh water and after sea water transfer.

Groups of Atlantic salmon smolts were exposed to low levels of the pesticide atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine) (0-22.7microgl(-1)) in fresh water and the physiological effects of exposure were measured. Further experiments exposed salmon smolts to similar levels of atrazine in fresh water, and then exposed them to full strength sea water. Atrazine in fresh water resulted in a significant reduction in gill Na(+)K(+)ATPase activity at concentrations of 2.0, 5.0 and 10.0microgl(-1). There were few other physiological changes in the smolts except for slightly elevated plasma cortisol concentrations and monovalent ion concentrations at and above 5.0microgl(-1). However, a sea water challenge caused mortalities in smolts that had been pre-exposed to atrazine in fresh water at concentrations of 1.0, 2.0, 5.0, 10.0 and 22.7microgl(-1). Moreover, surviving fish showed signs of major physiological stress: elevated plasma cortisol, thyroxine, osmolality, and monovalent ion concentrations. However, atrazine exposure had no effect on muscle or plasma water contents. The data suggests that exposure of salmon smolts to atrazine in fresh water may compromise their physiological capabilities to survive in saline conditions.