THE INFLUENCE OF SALINITY ON THE CHRONIC TOXICITY OF ATRAZINE TO AN ESTUARINE COPEPOD - IMPLICATIONS FOR DEVELOPMENT OF AN ESTUARINE CHRONIC CRITERION

The goal of this study was to determine the influence of a range of sa linities (5, 15, and 25 ppt) on the chronic toxicity of atrazine to th e copepod, Eurytemora affinis during 8-day life-cycle tests. Survival, development (proportion of immature organisms) and reproduction (perc ent of egg-carrying females) were the endpoints used to determine chro nic toxicity. Survival was the most sensitive endpoint and was therefo re used to determine chronic values. The No Observed Effect Concentrat ion (NOEC) and the Lowest Observed Effect Concentration (LOEC) at 5 pp t were 12.25 and 17.5 mg/L, respectively. The calculated chronic value was 14.6 mg/L. The NOEC and LOEC at 15 ppt were 17.5 and 25 mg/L, res pectively, and the calculated chronic value at 15 ppt was 20.9 mg/L. T he NOEC and LOEC at 25 ppt were 4.2 and 6.0 mg/L, respectively, while the calculated chronic value at 25 ppt was 5.01 mg/L. Results from a b ootstrapping statistical technique demonstrated that there was a signi ficant difference (p < 0.05) between chronic values at 5 ppt (14.6 mg/ L) and 25 ppt (5.01 mg/L), and between 15 ppt (20.9 mg/L) and 25 ppt ( 5.01 mg/L). There was no significant difference between chronic values at 5 ppt (14.6 mg/L) and 15 ppt (20.9 mg/L). These specific data for atrazine have important implications for development of estuarine wate r quality criteria, as toxicity test results at one salinity are not r epresentative of the salinity range found in many estuaries.