Assessing Contaminant Effects in Multi-Stress Ecosystems: Lessons from and for the San Francisco Bay-Delta Estuary
Thomas Jabusch, San Francisco Estuary Institute, David Ostrach, Ostrach Consulting and Stephanie Fong, Central Valley Regional Water Quality Control Board
The session “Assessing Contaminant Effects in Multi-Stress Ecosystems: Lessons from and for the San Francisco Bay-Delta Estuary” was organized for the SETAC North America 33rd Annual Meeting by members of the Pelagic Organism Decline Contaminants Work Team (POD CWT). The POD CWT is a peer review committee and venue for coordination to address the possible role(s) of contaminants in pelagic organism decline. It is a component of the Interagency Ecological Program (IEP), a consortium of nine state and federal agencies that has been monitoring aquatic organisms and water quality in the San Francisco estuary for decades.
Since late 2004, scientific and public attention has focused on the unexpected decline of several pelagic (open-water) fishes (delta smelt, longfin smelt, striped bass and threadfin shad) in the San Francisco Estuary. In 2005, the IEP formed a multi-agency POD Management Team tasked with designing and managing a comprehensive study to evaluate the causes of the decline and to synthesize and report the results. The causes under investigation include water diversions resulting in inappropriate flows adversely altering the ecosystem habitat; contaminants, stock-recruitment effects, increased mortality rates; and reduced food availability due to invasive species and altered habitat.
The session highlighted the San Francisco Bay-Delta as a case study for addressing the possible role(s) of contaminants in a multi-stress environment. Several platform presentations focused on research advances in the diagnosis of toxic effects in multi-stress environments. Other presentations covered aspects of toxicity to fish (exposure), chemical analysis and predicting the effectiveness of management measures.
Effects of chemicals on aquatic organisms can be readily detected in the laboratory. However, the in situ effects of chemical exposure need to be distinguished from the effects caused by other stressors to optimize management response. In a diagnostic study, striped bass was the indicator organism for determining chemical exposure of early life stages of fishes in the San Francisco Estuary. The study evaluated contaminant effects in the field followed by laboratory verification. Ethoxyresorufin-O-deethylase (EROD) activity is one of the most sensitive indicators (biomarkers) of contaminant exposure in fish and was detected in juvenile striped bass from all sampled sites in the estuary along with expression of various other biomarkers of contaminant exposure. Another study showed that distinct subpopulations of striped bass in the San Francisco Estuary accumulate different amounts of methylmercury and other contaminants, emphasizing the importance of understanding habitat use patterns for analyzing and predicting contaminant effects.
DNA microarrays are capable of providing expression profiles for thousands of genes in organism and therefore a powerful tool for assessing molecular responses to chemical exposure. The molecular responses of delta smelt to several contaminants known to occur in the estuary demonstrated how functionally characterized molecular biomarkers may be used to assess the sublethal effects of contaminants.
The presence of endocrine-disrupting chemicals has raised concerns over the long-term reproductive success of fishes. Results were presented from a concentration-response study with environmentally relevant concentrations of bifenthrin, a commonly used urban pyrethroid insecticide, in juvenile steelhead (Oncorhynchus mykiss) in fresh and brackish water. The study showed an abnormal physical condition called atresia in the ovaries of fishes exposed as juveniles that was exacerbated by high salinity. The research may lead to the identification of additional biomarkers of reproductive dysfunction that can be used to assess the long-term reproductive health of spawning fish exposed to pesticides as juveniles.
Additional presentations addressed the occurrence of new generation pesticides and modeling. The occurrence of dozens of new pesticides and degradation products that have never been monitored was discussed. One presentation reviewed results from a comprehensive study of the occurrence of pyrethroids in the water and sediment of the American River, a tributary that traverses the urban Sacramento area. Another topic was the predicted reduction of pyrethroid exposure that can be expected from proposed mitigation strategies for outdoor nonagricultural uses, such as structural perimeter band and barrier treatments or switching liquid product formulations from suspension concentrate to emulsifiable concentrate. This research showed that even though these mitigation strategies would achieve reductions, the predicted concentration of some pyrethroids would continue to exceed chronic aquatic life criteria on a frequent basis. A last presentation discussed the effectiveness of label changes in reducing pyrethroid loads.
In the San Francisco Bay-Delta Estuary, investigations into the potential role of contaminants in the decline of the ecosystem have shifted from a search for “the smoking gun” to the diagnosis and characterization of biological impacts in a complex system affected by multiple, interactive stressors. New conceptual models have been proposed and the development of diagnostic and chemical-analytical tools, comprehensive assessments and predictive models is in process. Molecular biological endpoints and the monitoring of emerging contaminants are receiving more attention and the effectiveness of exposure reduction measures is being studied and discussed. However, guidance on how to perform integrated assessments of multiple stress responses at the community and ecosystem level is still needed. “Omics” genomics, transcriptomics, proteomics and metabolomics—are promising molecular tools that may help fill this need by allowing a better understanding between a chemical’s effects at the molecular level and how it alters biological processes at higher levels of biological organization.
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