Patrick Bayou Sediment
Toxicity Identification

PBS&J uses specialized chemical adsorbents and exchange resins incorporated into whole sediments to identify classes of toxicants responsible for sediment toxicity.

Patrick Bayou, a shallow, tidal tributary of the Houston Ship Channel in Harris County, Texas, receives treated industrial and municipal wastewater, and non-point source stormwater runoff from the surrounding area. Based on results of sediment toxicity tests, the Texas Commission on Environmental Quality (TCEQ) placed the bayou on the 303(d) list of impaired waters. The Patrick Bayou Lead Organization, comprising permitted dischargers to the bayou, selected PBS&J to lead a team of consultants, and experts from Texas universities, to assess sediment quality and develop a total maximum daily load (TMDL), if required.

A chemical analysis identified many chemical contaminants; however, no constituent was uniquely correlated with sediment toxicity. Whole sediment bioassays conducted with crustaceans and worms confirmed that sediments from most locations in the bayou were toxic to sediment-dwelling organisms, yet sediment pore waters showed no toxicity. Therefore, standard toxicity identification evaluation (TIE) methods developed for effluents were not applicable and whole sediment TIE methods were needed.

Sediment TIE is an emerging science and standardized protocols are not established. To meet this challenge, PBS&J developed innovative techniques based on a variety of synthetic resins, ion-exchange media, and activated charcoals, which when mixed into the sediments, could classify groups of toxicants and effectively reduce the toxicity to sediment-dwelling organisms. Complete isolation of toxic fractions and identification of specific causative toxicants were not possible, however organic compounds were implicated as the potential toxic agents, with heavy metals being essentially ruled out.