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

Abstract

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases with increasing salinity, potentially increasing the risk of exposure for aquatic organisms at higher salinities. In the San Francisco Bay Delta (SFBD) estuary, pyrethroid concentrations increase during the rainy season, coinciding with the spawning season of Delta Smelt (Hypomesus transpacificus), an endangered, endemic fish. Furthermore, salinity intrusion in the SFBD is exacerbated by global climate change, which may change the dynamics of pyrethroid toxicity on aquatic animals. Therefore, examining the effect of salinity on the sublethal toxicity of pyrethroids is essential for risk assessments, especially during the early life stages of estuarine fishes. To address this, we investigated behavioral effects of permethrin and bifenthrin at three environmentally relevant concentrations across a salinity gradient (0.5, 2 and 6 PSU) on Delta Smelt yolk-sac larvae. Our results suggest that environmentally relevant concentrations of pyrethroids can perturb Delta Smelt larvae behavior even at the lowest concentrations (<1 ng/L) and that salinity can change the dynamic of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with anti-thigmotaxis at each concentration.

Salinity Alters Toxicity of Commonly Used Pesticides in a Model Euryhaline Fish Species (Menidia beryllina)

“…Rainbow Trout (Oncorhynchus mykiss) acclimated to 0 and 1.7 PSU, which resulted in changes in metabolic enzyme kinetics and distinctly different biotransformation pathways for fenoxon [48]. Others have found potential differences among mechanisms of toxicity when Delta smelt (Hypomesus transpacificus) exposed to bifenthrin and permethrin (log K OW = 6.4 and 6.9, respectfully) showed greater alteration in swimming behavior when exposed to bifenthrin, which is known to have a different mechanism of action than permethrin, which suggested the difference in toxicity maybe due to the compound's different mechanisms of action and not their physiochemical properties [10,25]. Organism-specific differences may also play a role in whether or not toxicity is seen; in a study comparing two strains of trout, Rainbow and Steelhead Trout (Oncorhynchus mykiss) were exposed to 0.1 µg/L and 1.5 µg/L bifenthrin at 0, 8, and 17 PSU, after which Rainbow Trout had significant increases in mortality at 0 PSU in the highest concentration and no significant impacts to mortality for either species at the higher salinities [49].…”

“…For example, the Delta Smelt (Hypomesus transpacificus) is listed as critically endangered and spawns in waters close to 0.5 PSU where the larvae stay before migrating to slightly higher salinities (1-6 PSU) [9]. Changes in rainfall patterns and increased salinity can alter salinity regimes and place stress on the developing larvae, especially when exposed to pesticide pollution [10]. As organisms experience additional stress from their environment due to climate change, their ability to tolerate pollution can be compromised [11,12].…”

“…Altered gill morphology at the different salinities was correlated with differences in bioaccumulation, since the gills are the route of exposure for many contaminants [23]. Overall, the interaction of salinity and contaminants on toxicity is likely complicated [10,23,24].…”

Interactions of Environmental Chemicals and Natural Products With ABC and SLC Transporters in the Digestive System of Aquatic Organisms

“…As a result of climate change and associated alterations in salinity, pH, and temperature of aquatic environments, the bioavailability and toxicity of environmental chemicals can increase ( Noyes et al, 2009 ; Hasenbein et al, 2018 ; Ross and Behringer, 2019 ; Paul et al, 2020 ; Derby et al, 2021 ; Fulton et al, 2021 ). Recent studies have shown that these environmental stressor can also affect gene regulation, expression, and overall fitness of fish populations both within and between species ( Jeffries et al, 2018 , 2019 ; DeCourten et al, 2019 ; Romney et al, 2019 ; Mundy et al, 2020 ; Komoroske et al, 2021 ; Segarra et al, 2021 ). Most of these investigations have been conducted in fish and focused on SLC-type transporters and the effect of pH and temperature on substrate affinity and transport rate.…”

Influence of preparative form on the target efficiency and toxicity of the solid insecticide based on pyrethroid and neonicatinoid

“…The results of a study [12] show that ecologically significant concentrations of pyrethroids can disrupt the behavior of delta smelt larvae even at the lowest concentrations (<1 ng/L) and that salinity can alter the dynamics of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with antithigmotaxis at each concentration.…”