Selenium and other trace elements in bluegills from agricultural return flows in the San Joaquin Valley, California

The effects of water quality and exposure to trace elements in irrigation return flows on bluegills (Lepomis macrochirus) were studied in the Merced River and Salt Slough, tributaries to the San Joaquin River, California, during 1988. Our study revealed that conductivity, turbidity, pH, total filterable residue, total hardness, and alkalinity were significantly greater in the Salt Slough, which receives tile drainage, then in the Merced River, which does not receive tile drainage. The concentrations of all trace elements, except aluminum and selenium, were below levels that are expected to have significant chronic toxic effects on bluegills. Selenium body burdens in bluegills from the Salt Slough have increased over fourfold since 1973. Age 1 bluegills from the Salt Slough were significantly shorter than age 1 bluegills from the Merced River. No other significant differences were noted in length by age. The mean length of age 1 bluegills from the Merced River has been increasing since 1983. In contrast, the length of age 1 bluegills from the Salt Slough has been decreasing. Fecundity of bluegills was lower in the Salt Slough than in the Merced River. The concurrent rise in selenium body burdens in bluegills from the Salt Slough and the decreasing total length of age 1 bluegills suggest a causal link between the two. In addition, the apparent depressed fecundity may also be related to the increased body burdens of selenium.