RELATIVE TOXICITY OF FOUR PESTICIDES IN TAP WATER AND WATER FROM FLOODED RICE PADDIES

The toxic effects of four pesticides used in flooded rice production on channel catfish (Ictalurus punctatus) were determined in tap water and floodwater from two different rice fields. The pesticides, propanil, molinate, carbofuran and carbaryl, were all tested by static bioassay. In addition, the toxicity of carbofuran was evaluated in an intermittent flow system. The 96 hour median toxic limitations (TLM) in tap water were 7.94, 33.2, 1.52, and 1.30 ppm for propanil, molinate, carbofuran and carbaryl, respectively. The corresponding values for water from one field were 1.9, 29.4, 37 and 1.56 ppm. They were all lower in the water from the second field in which residual levels of field applied pesticides were suspected. The pesticides were more toxic in field water than in tap water. Differences between 96 hour TLM concentrations of carbofuran determined by static flow and intermittent flow were found in tap water but not in field water. Field measurements of the concentrations of the four pesticides indicated that maximum concentrations in the runoff of all but molinate were similar to or greater than the 96 hour values. © 1979, Taylor & Francis Group, LLC. All rights reserved.