Chronic Toxicity of Atrazine to Sago 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 life-cycle atrazine subchronic toxicity tests with sago pondweed, Potamogeton pectinatus, at salinities of 1, 6, and 12 ppt. These data will be used for development of a chronic estuarine criterion for atrazine in Maryland waters of Chesapeake Bay and to determine possible ecological risk for a sensitive nontarget species. The three endpoints used for this submerged aquatic macrophyte were final wet weight, final dry weight, and final number of rhizome tips at the termination of the 28-d test. Dry weight was determined to be the most sensitive endpoint. Chronic values from a one-way ANOVA using dry weight were 21.2, 21.2, and 10.6 μg/L at salinities of 1, 6, and 12 ppt, respectively. Chronic values using wet weight were 21.2 μg/L at all three salinities. A chronic value of 94.9 μg/L was reported at all three salinities using rhizome tips as the endpoint. A two-way ANOVA was also used for analysis of data to increase the power of detecting differences among treatments and assess salinity interaction. The salinity effects were averaged in the two-way ANOVA. Both rhizome tips and dry weight were used in the two-way ANOVA; wet weight did not satisfy the equal variance assumption. The chronic value for rhizome tips was 94.9 μg/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 concentration. The chronic value determined from the two-way ANOVA using dry weight was 5.3 μg/L; there was a salinity effect but no significant salinity/atrazine concentration interaction. Salinity was not reported 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 compared with 1 and 6 ppt. Ecological risk to sago pondweed from atrazine exposure was judged to be low based on recent exposure data from the mainstem, tributaries, and streams in Chesapeake Bay. Received: 4 September 1996/Accepted: 9 March 1997