Water monitoring for thiobencarb in California, related to its use on rice, has been in place for over 20 years. Water samples have been collected from agricultural drains that flow into the Sacramento River and from the Sacramento River. The primary focus for this effort was driven by concerns about water taste, as both the cities of Sacramento and West Sacramento abstract drinking water directly from the Sacramento River.<br/>Thiobencarb use on rice is restricted to counties near and above Sacramento, and a majority of the rice is grown in flooded fields. Thiobencarb is effective as an herbicide during the early development of the rice, and it requires warm temperatures during application. This use pattern narrows the window for sample collection to late spring/early summer. The connectivity of these waterways simplifies the monitoring, allowing for grab samples to be collected once or twice per week at 5 sample locations.<br/>The water monitoring program is part of a stewardship program for pesticide use on rice, which includes the California Rice Commission, growers, and applicators. The analytical results from this program are shared with the Sacramento River water utilities. The cities of Sacramento and West Sacramento also provide results for river water samples that they collect and analyze. The consistency between these results supports the design of this monitoring program.<br/>In 2012, the National Marine Fisheries Service used the water monitoring data and the management practices in an assessment for potential impact of thiobencarb on salmon. The determination that use of thiobencarb did not jeopardize salmon was due in part to the low level of exposure that was documented through the water monitoring program.

Trends observed from a long term collaborative surface water monitoring program for thiobencarb to manage water quality in the Sacramento River

252nd National Meeting (2016)

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