Urban and agricultural pesticide inputs to a critical habitat for the threatened delta smelt (Hypomesus transpacificus)

Abstract

The Cache Slough complex is an area of tidal sloughs in the Sacramento-San Joaquin River Delta of California (USA), and is surrounding by irrigated agricultural lands. Among the species of concern in the area is the delta smelt (Hypomesus transpacificus), a federally listed threatened species. Releases of the organophosphate insecticide chlorpyrifos and pyrethroid insecticides were examined to determine whether they represented a threat to the copepods on which delta smelt feed (Eurytemora affinis and Pseudodiaptomus forbesi) and to aquatic life in general, represented by the standard testing organism, Hyalella azteca. There was a single incident of toxicity to H. azteca as a result of discharge of agricultural irrigation water containing chlorpyrifos. Pyrethroids were not found in samples collected during the dry season. Following rain events, however, the waters of western Cache Slough repeatedly became toxic to H. azteca because of the pyrethroids bifenthrin and cyhalothrin. The 96-h median lethal concentrations (LC50s) for E. affinis and P. forbesi for the pyrethroids bifenthrin and cyhalothrin were 16.7 ng/L to 19.4 ng/L when tested at 20 °C. However, their LC50s may be 5 mg/L to 10 ng/L at in situ temperatures of the Cache Slough, comparable to the peak bifenthrin concentration observed. The dominant pyrethroid source appeared to be urban runoff entering a creek 21 km upstream of Cache Slough. Pyrethroids of urban origin were supplemented by agricultural inputs of pyrethroids and chlorpyrifos as the creek flowed toward Cache Slough.

Contaminant and food limitation stress in an endangered estuarine fish

“…The SRDWSC moves urban runoff from West Sacramento to the eastern portion of Cache Slough, and Ulatis Creek, a major freshwater input, carries urban and agricultural runoff and secondary wastewater into western Cache Slough, just upstream of the Cache Slough sampling location in our study (Fig. 1; Weston et al 2014). Weston et al (2014) repeatedly detected acute toxicity to Hyalella azteca following storms in both western Cache Slough and Ulatis Creek, and attributed the toxicity largely to pyrethroids in urban runoff.…”

“…1; Weston et al 2014). Weston et al (2014) repeatedly detected acute toxicity to Hyalella azteca following storms in both western Cache Slough and Ulatis Creek, and attributed the toxicity largely to pyrethroids in urban runoff. In a two-year study, Werner et al (2000) found that of the 24 sites sampled throughout the Delta, Ulatis Creek most frequently showed acute toxicity to Ceriodaphnia dubia (6 of 21 monthly samples were acutely toxic).…”

“…We therefore compared the condition of juvenile Delta Smelt (JDS) among five regions encompassing much of their range. Given the substantial evidence for food limitation in Suisun Bay (Alpine and Cloern 1992, Sobczak et al 2002, Greene et al 2011) and contaminants in Cache Slough (Werner et al 2000, Kuivila and Moon 2004, Weston et al 2014), our hypothesis was that fish from these regions would exhibit respective signs of these stressors. Three strategies were used to increase the likelihood of detecting regional differences, which could be homogenized by movement of fish among regions or be influenced by the chosen endpoints.…”

Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…Likewise, toxicity was found to be higher in agricultural areas (Weston et al 2008). Weston et al (2014) studied pesticides in Cache Slough and found no pyrethroids during the dry season, but pyrethroids were toxic to a test organism after storms. Urban and some agricultural runoff into Ulatis Creek, a tributary of Cache Slough, was responsible.…”

A comparison of the sublethal and lethal toxicity of four pesticides in Hyalella azteca and Chironomus dilutus

“…dilutus larvae and H. azteca are often used in toxicity testing because of their high sensitivity to pyrethroids and organophosphates (Ankley et al 1994b;Deanovic et al 2013;Rakotondravelo et al 2006b;Weston et al 2014). Both species are highly relevant for environmental risk assessments as they are found in water bodies throughout the Americas and are important food sources for fish, amphibians, aquatic insects, and other organisms.…”