CHRONIC TOXICITY OF ATRAZINE TO SAGE PONDWEED AT A RANGE OF SALINITIES - IMPLICATIONS FOR CRITERIA DEVELOPMENT AND ECOLOGICAL RISK

The objective of this study was to conduct a series of 28-d partial li fe-cycle atrazine subchronic toxicity tests with sage pondweed, Potamo geton pectinatus, at salinities of 1, 6, and 12 ppt. These data will b e used for development of a chronic estuarine criterion for atrazine i n Maryland waters of Chesapeake Bay and to determine possible ecologic al risk for a sensitive nontarget species. The three endpoints used fo r this submerged aquatic macrophyte were final wet weight, final dry w eight, and final number of rhizome tips at the termination of the 28-d test. Dry weight was determined to be the most sensitive endpoint. Ch ronic values from a one-way ANOVA using dry weight were 21.2, 21.2, an d 10.6 mu g/L at salinities of 1, 6, and 12 ppt, respectively. Chronic values using wet weight were 21.2 mu g/L at all three salinities. A c hronic value of 94.9 mu g/L was reported at all three salinities using rhizome tips as the endpoint. A two-way ANOVA was also used for analy sis of data to increase the power of detecting differences among treat ments and assess salinity interaction. The salinity effects were avera ged in the two-way ANOVA. Both rhizome tips and dry weight were used i n the two-way ANOVA; wet weight did not satisfy the equal variance ass umption. The chronic value for rhizome tips was 94.9 mu g/L atrazine, which is the same value reported from the one-way ANOVA. There was no salinity effect and no interaction between salinity and atrazine conce ntration. The chronic value determined from the two-way ANOVA using dr y weight was 5.3 mu g/L; there was a salinity effect but no significan t salinity/atrazine concentration interaction. Salinity was not report ed to effect either dry weight or rhizome tips after 28-d exposures in the controls but wet weight was significantly lower at 12 ppt when co mpared with 1 and 6 ppt. Ecological risk to sage pondweed from atrazin e exposure was judged to be low based on recent exposure data from the mainstem, tributaries, and streams in Chesapeake Bay.