Bioassays show promise for CEC screening in SMC study

SCCWRP and its partners have demonstrated in a proof-of-concept study that commercially available bioanalytical tools have the potential to cost-effectively screen Southern California waterways for the presence of bioactive contaminants of emerging concern (CECs).

The two-year study, completed in June in partnership with the Southern California Stormwater Monitoring Coalition (SMC), examined the relationship between the results of the high-throughput cell assays and the results of a whole-animal screening test. In all, 31 stream sites across Southern California were sampled over a two-year period.

The study found that one of the cell screening assays – the aryl hydrocarbon receptor assay – detected low to moderate levels of a group of bioactive contaminants known as dioxin-like chemicals across both urban and agricultural sites. A subsequent whole-animal screening test showed that these levels of bioactivity were not associated with cardiac malformations during early zebrafish embryo development.

These findings are significant because SCCWRP and other experts have proposed using bioanalytical tools as a cost-efficient first line of defense for screening California waterways for bioactive contaminants, an approach that has the potential to reduce the frequency of whole-animal testing, which is more expensive.

Thus, the study’s finding that cell assays are more sensitive than whole-animal tests is a seminal outcome, as it underscores the potential to use cell assays as an initial screening test, to be followed by whole-animal testing to ascertain whether the bioactive contaminants could be impacting organisms in the environment.

SCCWRP proposed this multi-tiered approach to CEC screening in 2015, as part of a draft CEC monitoring framework intended to help water-quality managers more effectively narrow down the classes of CECs that pose the greatest potential risks to aquatic ecosystems. Since that time, researchers have launched multiple studies to evaluate the utility of the proposed CEC management strategy for statewide application.

The outcomes of the SMC zebrafish embryo test are in agreement with previous studies on the toxicity associated with dioxin-like chemicals. When these bioactive contaminants are present at concentrations much higher than those found in the SMC samples, zebrafish embryos begin to experience developmental anomalies. Researchers are still working to link these biological impacts to relevant cell assay screening thresholds.

The SMC study also explored whether the bioactive contaminants detected during the initial bioanalytical screening step could be correlated in a meaningful way with the level of urbanization of the study sites, as well as with the observed condition of the stream biological communities living at the sites.

Researchers found that the biological condition of benthic invertebrate communities – as measured by the California Stream Condition Index co-developed by SCCWRP – correlated with the aryl hydrocarbon receptor assay responses. The poorer the biological condition at a given site, the more likely it was to have a relatively high bioassay response, although researchers cautioned that additional linkage studies are needed to confirm whether aryl hydrocarbon receptor-mediated pathways play an influential role in the observed biological degradation.

The full study has been published by the journal Environmental Science: Processes & Impacts. For more information, contact Dr. Alvina Mehinto.