Historical Data Review and Source Analysis of Polychlorinated Biphenyls (PCBs) in the Lower Leon Creek Watershed




Sokoly, Diana

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The health effects of PCBs became a growing concern in the early 1970's, at which time Monsanto voluntarily limited their PCB production (De Voogt and Brinkman, 1989). By 1976, the Toxic Substances Control Act (TSCA) was passed, which authorized the United States Environmental Protection Agency (US EPA) to control any substances determined to cause unreasonable risk to the health of the public or environment (EPA, 2014). The TSCA also called for a ban on production, sale, and new use of PCBs. The Lower Leon Creek Watershed is located in the San Antonio River Basin in Bexar County, Texas. In the early 1970's, the Texas Water Quality Board (TWQB), now the TCEQ, conducted an intensive surface water monitoring survey for Leon Creek which found there to be high levels of the pesticide DDT, as well as PCBs at several stations to the south of Kelly Air Force Base in sediments (TWQB, 1974). A monitoring program in Leon Creek was initiated voluntarily in 1989 at the former Kelly Air Force Base (KAFB) and later formalized by the Resource Conservation and Recovery Act (RCRA) Permit and Compliance Plan for the area. At one time, Kelly AFB was the largest military installation in the state; however, the installation was decommissioned in 2001 and renamed "KellyUSA" (DSHS, 2010). There has been consistent monitoring for PCBs in Leon Creek bed sediment and surface water for decades as well as some fish tissue sampling, but there has been no comprehensive analysis of that data. This study presents such an analysis and uses it to determine data gaps and a best path forward for characterizing and delineating the persistent PCB contamination in Leon Creek. This study also evaluates the most likely potential source of said contamination and calculates half-lives for the various congeners for which historic data exists. For sediment and fish tissue sampling results, historic data shows high concentrations of PCBs over the course of several decades. The historical data is characterized as being widely variable for detections in Arochlors and concentrations between years, with a dramatic drop in concentrations detected starting in 2009. Overall, the sampling locations adjacent to and downstream from the former Kelly Air Force Base have the highest concentrations of PCBs over the longest period. Half-lives were calculated for congeners identified in the watershed from 2007-2012. Statistical analyses indicated there were significant differences in the half-lives among the PCB congeners detected from 2007-2012. Shorter half-lives are indicative of sedimentation process (Hebert et al, 1999) that could account for changes over time by selective removal based on physicochemical properties such as the octanol-water partition coefficient (Log Kow). There was a positive relationship between half-life and environmental persistence as Log Kow. In general, it appears the half-lives increased with the chlorine content and number of chlorines in the congener. Changes driven by the physiochemical properties of individual congeners seem to have been important in creating a gradual transition from lower to higher chlorinated congeners in this period (Shipley et al, 2017). Filling data gaps identified to the north and south of former KAFB would lend itself to assessing the mobility of the PCBs and determine if the decreasing concentrations are due to natural attenuation. Conducting evaluations of this nature earlier in the life of a monitoring program could inform the sampling program design to reduce the necessary length or scope of the research.


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Arochlor, Environmental monitoring, PCB



Civil and Environmental Engineering