Event based analysis of Chlorothalonil concentrations following application to managed turf

Authors: King, Kevin; BALOGH, JAMES - Spectrum Research, Inc

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2012
Publication Date: 2/19/2013
Citation: King, K.W., Balogh, J.C. 2013. Event based analysis of Chlorothalonil concentrations following application to managed turf. Environmental Toxicology and Chemistry. 32(3):684-691.

Interpretive Summary: The pesticide chlorothalonil is commonly applied in the late fall in cold regions to control snow mold disease on managed turfgrass areas. Chlorothalonil can be transported from the applied areas into adjacent streams where elevated concentrations in water can be a concern for certain aquatic organisms. Measurements have shown concentration can occasionally exceed established toxicity levels, but the duration and timing of those occurrences has not previously been explored. We determined that the duration of those events approached but did not surpass the allowable exposure time associated with the fifty percent lethal concentrations. Additionally the timing of the events was highly correlated to widespread fall applications. The findings from this study may provide regulatory guidance for chemical companies trying to obtain registration of certain pesticides.

Technical Abstract: Chlorothalonil concentrations exceeding acute toxicity levels for certain organisms have been measured in surface water discharge events from managed turf watersheds. However, the duration of exceedence and the timing of those events with respect to precipitation/runoff and time since application have not been explored. Chlorothalonil concentrations were measured from discharge waters draining a managed turf watershed in Duluth, Minnesota, for a seven year period (2003-2009). The median chlorothalonil concentration was 0.58 'g/L (n=1400). Approximately 2% of all concentrations exceeded the 7.6 'g/L LC50 acute toxicity level for rainbow trout. The concentrations that exceeded the threshold were associated with nine rainfall/runoff events. However, no duration of exceedence surpassed the 96 hour exposure limit, for rainbow trout. Concentrations for two events approached the 96 hour exposure limit. Exceedence concentrations were significantly (p<0.05) predicted by time since application and were only measured in the fall following extensive application on the course. Avoiding application until after the major fall rainfall period but before the first snow coverage is recommended to reduce the occurrence of chlorothalonil concentrations that exceed any published toxicity levels.