Interpretation of Toxicity and Contaminant Monitoring Data: Case Studies from the Stream Pollution Trends Program (SPoT)
The California Surface Water Ambient Monitoring Program (SWAMP) conducts statewide and regional monitoring through the state’s Regional Water Quality Control Boards, as well as through three statewide monitoring programs. The University of California Davis Granite Canyon Laboratory administers the Stream Pollution Trends Program (SPoT), which is the only statewide program that directly studies toxicity associated with contaminants in sediments. Sediments are targeted as integrators of watershed contamination because many of the most toxic contaminants partition to sediments either at the source or during transport. The program benefits from a directed sampling design which allows yearly sampling of the same statewide stations over time. SPoT has been monitoring trends in 100 watersheds since 2008 and has a robust data set that describes significant trends in toxicity and contaminants at three scales: statewide, by land use, and at individual sites. One significant statewide trend related to toxicity is the ongoing increase in detections and concentrations of pyrethroid pesticides in watersheds dominated by urban land use. In addition, recent results have shown increasing detections and concentrations of fipronil and its degradates in urban watersheds between 2013 and 2014.
SPoT data are being used to monitor long-term trends in contaminants that are the target of regulatory actions. This includes the potential reduction of urban pyrethroid runoff due to Department of Pesticide Regulation (DPR) 2012 label modifications, and the eventual decline of copper concentrations related to the reduction of copper in automobile brake pads. SPoT data also support monitoring required by regional NPDES stormwater permits including those in the San Francisco Bay area and in southern California. Related data sets have been used to explain shifting pesticide detection patterns in receiving waters, as well as determine the effectiveness of stormwater bioswale treatment systems.
The purpose of this presentation is to summarize key findings of the SPoT program and demonstrate how toxicity data are interpreted relative to contaminant measurements in various components of the described monitoring programs. Audience members will receive a brief primer on aquatic toxicity testing and learn that determinations of toxicity can vary significantly depending on the tested organism and the contaminants in the receiving system. Appropriate organism choice for toxicity testing, coupled with quality chemical analyses, and proper application of toxicity thresholds is essential to determine potential impacts to water quality and beneficial uses.