Allied Biological Inc. applied Renovate OTF to about 224 acres of the lake between June 13 and June 15, 2012. The swimming restriction was lifted as of Saturday, June 16. We have begun the post-treatment monitoring for residual triclopyr levels in Cazenovia Lake and downstream in Chittenango Creek.
Results of the water testing are posted on the town web site. The lake should not be used as a source of drinking water until the residual concentrations drop below 0.050 ppm, which will likely require several weeks. Treated water should not be used for irrigation until the residual concentrations drop below 0.001 ppm.
The algal blooms that are visible in and on the water, especially at the lake’s southwestern end, occur early each summer and typically subside in a few weeks. The warm spring and relatively late chemical application in 2012 may have contributed to the large blooms that we are experiencing.
Why is the restriction on use of the lake for drinking water supply longer than the restriction on swimming? This is a classic dose and response calculation used in toxicology for estimating the risk of harm.
Triclopyr is not readily absorbed through the skin, so the potential exposure considers a worst-case scenario — children swimming and accidentally ingesting some water. In contrast, the drinking water risk calculations assume that an individual drinks two liters of lake water per day, for 70 years. However, Cazenovia Lake is not classified, monitored or regulated as a source of drinking water. There are many reasons for not drinking Cazenovia Lake water — bacteria, parasites, viruses, algal toxins, etc.
The herbicide treatment addresses the symptoms of over-enrichment of Cazenovia Lake. To be effective, we need to also address the root cause. The town board is continuing to focus on reducing the inflow of sediment and phosphorus to the lake. Phosphorus — both in the water and on soil particles — governs the abundance of aquatic plants and algae.