Abstract
doi: https://doi.org/10.15447/sfews.2016v14iss4art5 Many contaminants in the California Bay–Delta (Bay–Delta) exceed regulatory standards, affect aquatic species, and potentially affect human health. Recent studies provide multiple lines of evidence that contaminants affect species of concern in the Bay–Delta (e.g., the decline of several important fish species referred to as the “Pelagic Organism Decline” or POD). Contaminants occur as dynamic complex mixtures and exert effects at multiple levels of biological organization. Multiple chemicals impair processes at cellular and physiological levels (measured as growth, development, and behavior abnormalities), and when viability and reproductive output are affected, populations are affected. As an important example, the population decline of the endangered Delta Smelt (Hypomesus transpacificus) is significantly associated with multiple stressors, including insecticide use. New analyses presented in this paper show significant correlations between pyrethroid use and declining abundance of POD fish species. Water sampled from the Bay–Delta causes multiple deleterious effects in fish, and Delta Smelt collected from the Bay–Delta exhibit contaminant effects. Fish prey items are also affected by contaminants; this may have an indirect effect on their populations. Co-occurrence with thermal changes or disease can exacerbate contaminant effects. Contaminants also pose threats to human health via consumption of fish and shellfish, drinking water, and contact recreation, in particular, mercury, cyanobacteria toxins, disinfection byproducts, pathogens, pesticides, and pharmaceuticals and personal care products. The role of contaminants in the decline of Bay–Delta species is difficult to accurately assess in a complex, dynamic system. However, tools and approaches are available to evaluate contaminant effects on Bay–Delta species, and separate the effects of multiple stressors. Integrated monitoring and focused mechanistic studies are instrumental for addressing management needs. Effect and risk assessments should be conducted for different species across multiple life stages, with emphasis on early life stages of high-priority Bay–Delta species.
Highlights
The term contaminant refers broadly to a large number of substances from distributed and diverse sources that include urban and agricultural runoff, treated industrial and municipal wastewater, atmospheric deposition, and chemicals applied directly to surface waters for invasive plant and pest control.The San Francisco Bay and Sacramento–San Joaquin Delta (Bay–Delta) has been identified as impaired for aquatic life by several specific contaminants on the Environmental Protection Agency 2010 List of Impaired Water Bodies (SWRCB 2010)
Monitoring, special studies, and models are needed to link the processes that occur from contaminant sources to a resulting species decline
It must be noted that pyrethroids are only one class of a multitude of pesticides detected in Bay–Delta waters, and are presented here as an example
Summary
The term contaminant refers broadly to a large number of substances from distributed and diverse sources that include urban and agricultural runoff, treated industrial and municipal wastewater, atmospheric deposition, and chemicals applied directly to surface waters for invasive plant and pest control. Monitoring, special studies, and models are needed to link the processes that occur from contaminant sources to a resulting species decline (e.g., pesticide runoff, bioenergetic costs of exposure to contaminants, decreases in food availability, or reductions in fecundity or fish survival) It must be noted that pyrethroids are only one class of a multitude of pesticides detected in Bay–Delta waters, and are presented here as an example. Delta Smelt collected from the estuary were observed to have tissue-level effects, demonstrated through histopathology, which was associated with decreased growth (Hammock et al 2015) These lines of evidence support that contaminants are bioavailable in Bay–Delta waters at concentrations that are affecting Delta Smelt. Feist et al (2011) describe how urban runoff contaminants in the U.S Pacific Northwest caused up to 90% mortality of prespawning Coho Salmon (Oncorhynchus kisutch), severely affecting population numbers through reductions in recruitment
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