Chemical and Toxicological Impacts to Cache Slough Following Storm-Driven Contaminant Inputs

Abstract

Chemical and toxicological testing in the Cache Slough complex (the slough) of the North Delta indicated the aquatic biota are exposed to a variety of wastewater-derived food additives, pharmaceuticals, and personal care products in highest concentration during dry periods, and many insecticides, herbicides and fungicides with peak concentrations after winter rains. The insecticide groups currently known to be of greatest toxicological concern are the pyrethroids and the fiproles (i.e., fipronil and its degradation products). After stormwater runoff enters the system via Ulatis Creek, both pesticide groups attained concentrations that posed a threat to aquatic life. When the commonly used testing species, Hyalella azteca, was placed in Cache Slough, toxicity-and, at times, near total mortality-was seen over at least an 8-km reach of Cache Slough that extended from the uppermost end almost to the junction with the Deep Water Ship Channel. Previous work over many years has shown similar results after other winter storms. However, when H. azteca that carried a mutation providing resistance to pyrethroid pesticides were also deployed in the slough, no ill effects were observed, which provided strong evidence that pyrethroids were responsible for toxicity to the non-resistant strain. Abundant resident H. azteca in Cache Slough carry any of four mutations that provide resistance to pyrethroids. They also carry a mutation that provides resistance to organophosphate pesticides, and likely carbamate pesticides as well. After many years of exposure, sensitive genotypes have been nearly eliminated from the system, and replaced by a population unaffected by many insecticides now in common use. We offer a variety of reasons why this shift to a population with mutant genotypes RESEARCH

Salinity Changes the Dynamics of Pyrethroid Toxicity in Terms of Behavioral Effects on Newly Hatched Delta Smelt Larvae

“…Pyrethroid insecticides are heavily used in agricultural and urban areas, and are commonly detected in waterbodies worldwide. In the San Francisco Bay Delta (SFBD) estuary, their concentrations increase during the rainy season (November to April) due to runoff, coinciding with the spawning season of Delta Smelt (December to May) [ 12 ]. Among these insecticides, the frequent detection of two pyrethroids, permethrin and bifenthrin, which are highly toxicity to aquatic life, is of great concern for the Delta Smelt habitat and overall fitness for species living in this system [ 12 , 13 , 14 ].…”

“…In the San Francisco Bay Delta (SFBD) estuary, their concentrations increase during the rainy season (November to April) due to runoff, coinciding with the spawning season of Delta Smelt (December to May) [ 12 ]. Among these insecticides, the frequent detection of two pyrethroids, permethrin and bifenthrin, which are highly toxicity to aquatic life, is of great concern for the Delta Smelt habitat and overall fitness for species living in this system [ 12 , 13 , 14 ]. Permethrin and bifenthrin are frequently detected in the low ng/L to µg/L range in sediment and surface waters [ 15 , 16 ].…”

The health and condition responses of Delta Smelt to fasting: A time series experiment

“…Thus, although the starved fish had unhealthy livers, like wild fish collected from Cache Slough, the specific lesions were quite distinct. Moreover, other lines of evidence support the hypothesis that the livers of Delta Smelt collected from Cache Slough were damaged by contaminants rather than nutritional stress, including: 1) both zooplankton abundance and stomach fullness are relatively high in freshwater in summer [44,45], 2) Delta Smelt collected from Cache Slough exhibited robust condition relative to fish collected from other regions [44], 3) contaminants have occurred in relatively high concentrations in the region [47], and 4) acute toxicity has been repeatedly detected in the region [46,48,77]. In addition, parasites and bacterial infections are unlikely causes of lesions because they are rare in the wild Delta Smelt population ( [90], S. Teh personal observation), as well as the hatchery Delta Smelt.…”

“…Another contributing factor to pro-oxidant effects of starvation may have been the loss of food-derived antioxidants such as vitamins C and E [ 94 ]. Given the evidence for both food limitation [ 41 – 43 , 45 ]) and contaminants [ 46 – 48 , 76 , 77 ] in its habitat, Delta Smelt in the wild may be vulnerable to oxidative damage caused by contaminants, especially xenobiotic electrophiles detoxified by glutathione (e.g., organophosphates, such as chlorpyrifos or polycyclic aromatic hydrocarbons). Future work could explore the potential interaction between starvation and xenobiotics that are detoxified by glutathione-dependent mechanisms.…”

“…There is a history of biomarker and stomach fullness work on Delta Smelt collected from the field, which provides evidence of contaminant and food limitation stress in the species [ 44 , 45 ]. However, the nutritional biomarkers have not been empirically validated in Delta Smelt, causing difficulties both in understanding the sensitivities of biomarkers to nutritional stress, and distinguishing between liver abnormalities caused by poor nutrition or contaminants, another known stressor in the SFE [ 46 – 48 ]. This study will therefore improve interpretation of health and condition data collected from wild Delta Smelt, informing conservation and restoration efforts.…”