Application of Tracer Techniques to Continuous-flow Toxicity Testing

-Frequent toxicant analyses are essential for good quality data in long-term continuous-flow tests. Due to the time consuming and costly chemical analyses, exposure levels are measured at best on a daily basis. These infrequent determinations may not detect variability in toxicant concentrations that could result in test failures. To minimize repetitive testing and improve data quality, a dye tracer method was evaluated. Rhodamine WT was selected as a toxicant tracer because of easy detectability, low toxicity to aquatic organisms, and negligible transformation in the aquatic environment. Results over a 24 h period showed that rhodamine reliably predicted the toxicant (diquat) concentrations with an r value of 0.99. Based upon these data, two replicate long-term tests with and without tracer were carried out exposing fathead minnows Pimephales promelas to diquat (I: l'-ethylene-2:2'-dipiridium dibromide). The test results indicated that the added rhodamine WT did not alter the diquat toxicity to fathead minnows using LC50 and ECs0 values for comparisons. From these findings it is concluded that dye tracers are suitable toxicant surrogates. Their use in flow-through tests allow more frequent analyses which result in better data and minimizes experimental failure. Key words--flow-through fish bioassays, dye tracer, toxicant analysis