PCB dry and wet weather concentration and load comparisons in Houston-area urban channels

All 209 PCB congeners are quantified in water in both dry and wet weather urban flows in Houston, Texas, USA. Total water PCBs ranged from 0.82 to 9.4 ng/L in wet weather and 0.46 to 9.0 ng/L in dry. Wet weather loads were 8.2 times higher (by median) than dry weather with some increases of over 100-fold. The majority of the PCB load was in the dissolved fraction in dry weather while it was in the suspended fraction in wet weather. Dissolved PCB loads were correlated with rain intensity and highly developed land area, and a multiple linear regression (MLR) equation was developed to quantify these correlations. PCA generated five PCB components with nearly all positive loadings. They were interpreted as DOC-associated A1248, wet weather primarily suspended fraction A1254/A1260 likely from building sealants, truly dissolved-associated wastewater dechlorination, watershed-sourced PCB 11, and monochlorinated PCBs (likely connected to a different state or source of dechlorination). The PCB 11 component was statistically higher in wet versus dry weather when no other component showed such clear distinctions. Hierarchical cluster analysis (HCA) did not always group dry and wet weather samples from the same location together illustrating the different congener composition that often exists between dry and wet conditions. Four wet weather samples from high percentage developed land (> 90%) watersheds had nearly the same fingerprint suggesting a generic “urban” signature in runoff, which in this case was caused by residual A1254/A1260 PCB stocks and currently produced PCB 11 in consumer goods.

Graphical AbstractWet weather in-stream loads of total PCBs (∑209) were often much higher than what was observed during dry weather flows. Though one location showed wet weather loading approximately the same as dry weather (due mostly to a poor time of sampling), all other locations were at least three times higher in wet weather, and two locations in highly developed land use areas (11139, Brays Bayou and 11387, White Oak Bayou) were 150 times greater in wet weather over dry. The photo at the bottom was taken by University of Houston research staff during a dry weather sampling event at Buffalo Bayou in the downtown Houston area. The area is at the confluence of White Oak and Buffalo Bayou just across the bayou from the University of Houston's downtown location (photo looking northward).Figure optionsDownload as PowerPoint slideResearch Highlights
► PCB loadings were 8.2 times by median higher in wet weather than in dry weather.
► Wet loadings heavily in suspended sediments fraction while dry in dissolved.
► Dissolved loadings correlated to highly developed land use and rainfall intensity.
► Wet concentrations influenced by PCB 11 and Aroclors from building sealants.
► Dry and wet weather PCB patterns showed influence from dechlorinated PCBs.