Pyrethroid effects on freshwater invertebrates: a meta-analysis of pulse exposures

Fish predation affects invertebrate community structure of tropical temporary ponds, with downstream effects on phytoplankton that are obscured by pesticide pollution

Aquatic biota of tropical temporary ponds typically experience a wide range of stressors that can drive the structure and dynamics of natural communities. Particularly in regions with intense agricultural activity, aquatic biota may not only experience predation pressure but also stress from pesticides that inadvertently enter the ponds. We increasingly understand how these different sources of stress affect classic model taxa under controlled laboratory conditions, but how predators and pesticides may jointly affect pond invertebrate communities is still unclear, particularly for tropical systems. Here, we conducted an outdoor mesocosm experiment to study how fish predation combined with exposure to an environmentally relevant concentration of the commonly used insecticide cypermethrin (0.8 ng/L) affects the structure of invertebrate communities, and its potential effects on leaf litter decomposition and invertebrate grazing efficiency as measures of ecosystem functioning. A total of seven invertebrate taxa were recorded in the mesocosm communities. Fish predation effectively lowered the number of invertebrate taxa, with fish mesocosms being dominated by high densities of rotifers, associated with lower phytoplankton levels, but only when communities were not simultaneously exposed to cypermethrin. In contrast, cypermethrin exposure did not affect invertebrate community structure, and neither fish predation nor cypermethrin exposure affected our measures of ecosystem functioning. These findings suggest that predation by killifish can strongly affect invertebrate community structure of tropical temporary ponds, and that downstream effects on phytoplankton biomass can be mediated by exposure to cypermethrin. More broadly, we contend that a deeper understanding of (tropical) temporary pond ecology is necessary to effectively manage these increasingly polluted systems.

Multiple lines of evidence point to pesticides as stressors affecting invertebrate communities in small streams in five United States regions

Multistressor studies were performed in five regions of the United States to assess the role of pesticides as stressors affecting invertebrate communities in wadable streams. Pesticides and other chemical and physical stressors were measured in 75 to 99 streams per region for 4 weeks, after which invertebrate communities were surveyed (435 total sites). Pesticides were sampled weekly in filtered water, and once in bed sediment. The role of pesticides as a stressor to invertebrate communities was assessed by evaluating multiple lines of evidence: toxicity predictions based on measured pesticide concentrations, multivariate models and other statistical analyses, and previously published mesocosm experiments. Toxicity predictions using benchmarks and species sensitivity distributions and statistical correlations suggested that pesticides were present at high enough concentrations to adversely affect invertebrate communities at the regional scale. Two undirected techniques-boosted regression tree models and distance-based linear models-identified which pesticides were predictors of (respectively) invertebrate metrics and community composition. To put insecticides in context with known, influential covariates of invertebrate response, generalized additive models were used to identify which individual pesticide(s) were important predictors of invertebrate community condition in each region, after accounting for natural covariates. Four insecticides were identified as stressors to invertebrate communities at the regional scale: bifenthrin, chlordane, fipronil and its degradates, and imidacloprid. Fipronil was particularly important in the Southeast region, and imidacloprid, bifenthrin, and chlordane were important in multiple regions. For imidacloprid, bifenthrin, and fipronil, toxicity predictions were supported by mesocosm experiments that demonstrated adverse effects on naïve aquatic communities when dosed under controlled conditions. These multiple lines of evidence do not prove causality-which is challenging in the field under multistressor conditions-but they make a strong case for the role of insecticides as stressors adversely affecting invertebrate communities in streams within the five sampled regions.

Influences of continuous and pulse atrazine exposure on intestinal flora and metabolites of Pelophylax nigromaculatus tadpoles

Atrazine, a widely used herbicide, has adverse effects on the growth and metabolism of amphibians. Due to the cyclical application use of the pesticide atrazine in agricultural production, atrazine concentrations in water occur in the form of pulses. However, knowledge of the effects of atrazine pulse exposure on the gut microbiota and metabolism of amphibians is limited. In this study, Pelophylax nigromaculatus tadpoles (Gs 26) were exposed to continuous and pulse atrazine (100 μg/L) for 60 days. The results showed that continuous exposure and pulse exposure had different effects on the diversity of gut microbiota. At the phyla level, pulse exposure significantly increased the relative abundance of Actinobacteria, and decreased the relative abundance of Firmicutes compared to continuous exposure. At the genus level, continuous and pulse exposure to atrazine significantly altered the relative abundance of Acetobacterium, Microbacterium, Bacteroides, Eulopiscium and Leuconostoc. Compared to continuous exposure, pulse exposure significantly increased the relative abundance of Microbacterium, and significantly decreased the relative abundance of Acetobacterium and Eplopiscium. In terms of metabolism, pulse exposure significantly increased the relative abundance of creatine, guanine, and inosine and significantly decreased the relative abundance of 3-hydroxysebacic acid, ganoderic acid F, hypoxanthine, and withaperuvin H compared to continuous exposure. Continuous and pulse exposure to atrazine significantly altered the relative abundance of metabolites of the pymidine metabolism, purine metabolism, beta-alanine metabolism and other pathways in the gut of P. nigromaculatus tadpoles. In addition, changes in most metabolites had a significant correlation with changes in gut microorganisms. In conclusion, our study confirmed that pulse exposure to atrazine has a greater effect on the composition of the gut microflora and the metabolism of P. nigromaculatus tadpoles than continuous exposure.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Effects of ivermectin treatment of backyard chickens on mosquito dynamics and West Nile virus transmission

Background

Vector control strategies typically rely on pesticides to target mosquitoes involved in enzootic and zoonotic transmission of West Nile virus (WNV). Nevertheless, increasing insecticide resistance and a desire to reduce pesticide usage provide the impetus for developing alternative strategies. Ivermectin (IVM), an antiparasitic drug which is widely used in human and veterinary medicine, is a potential alternative for targeted control because Culex mosquitoes experience increased mortality following ingestion of IVM in bloodmeals.

Methodology/Principal findings

We conducted a randomized field trial to investigate the impact of treating backyard chicken flocks with IVM in urban neighborhoods across Davis, California on mosquito populations and WNV transmission dynamics. We observed a significant reduction in WNV seroconversions in treated vs. untreated chickens, suggesting a reduction in WNV transmission intensity around treated flocks. We also detected a reduction in parity rates of Cx. tarsalis near treated vs. untreated flocks and increased mortality in wild mosquitoes following a bloodmeal on treated chickens (IVM serum concentration > 5ng/mL) vs. chickens with IVM serum concentrations < 5 ng/mL. However, we did not find a significant difference in abundance or infection prevalence in mosquitoes between treatment groups associated with the reductions in seroconversions. Mosquito immigration from surrounding larval habitat, relatively low WNV activity in the study area, and variable IVM serum concentrations likely contributed to uncertainty about the impact.

Conclusions/Significance

Taken together, our results point to a reduction in WNV transmission due to the impact of IVM on Culex mosquito populations and support the ongoing investigation of oral administration of IVM to wild birds for local control of WNV transmission, although further work is needed to optimize dosing and understand effects on entomological endpoints.

Current mosquito control strategies aimed to prevent pathogen transmission to humans have limited ability to target mosquitoes involved in amplification and spillover transmission of pathogens like West Nile virus (WNV). Additionally, growing prevalence of insecticide resistance in mosquito populations limit the efficacy of these insecticide-based control strategies. Ivermectin (IVM) provides an alternative avenue for control by increasing the mortality of mosquitoes that ingest this drug in bloodmeals. Therefore, IVM treatment of avian species that account for the majority of mosquito bloodmeals during the WNV transmission season could be an effective control strategy. Building on pilot studies indicating the efficacy and feasibility of IVM-deployment for WNV control, we performed a randomized field trial to investigate the impact of IVM-treatment of backyard chickens on local population dynamics of Culex mosquitoes and WNV transmission. We were able to link changes in mosquito populations to reduction in WNV transmission, as measured by chicken seroconversions, through IVM-induced mortality in mosquitoes. However, further work is needed to identify the impact of treatment on mosquito abundance and infection prevalence to fully attribute observed changes to IVM administration. Overall, our results support IVM treatment as a potentially effective alternative to insecticide-based vector control strategies and one that can be used to target WNV transmission on the local scale.

Using TKTD Models in Combination with In Vivo Enzyme Inhibition Assays to Investigate the Mechanisms behind Synergistic Interactions across Two Species

The aim of this study is to compare the azole synergy across an insect, Chironomus riparius, and a crustacean species, Daphnia magna. We use a combination of in vivo measurements of cytochrome P450 monooxygenase (CYP) biotransformation potential and toxicokinetic (TK) and toxicodynamic (TD) modeling to understand the mechanism behind the synergy of two azole fungicides: the imidazole prochloraz and the triazole propiconazole on the pyrethroid insecticide α-cypermethrin. For both species, the synergistic effect of prochloraz was well-described by its effect on in vivo CYP activity, which corresponded to the biotransformation rate of the TK model parameterized on the survival data of the mixture experiment. For propiconazole, however, there were 100-fold and 50-fold differences between the 50% effect concentration of in vivo CYP activity and the modeled biotransformation rate for C. riparius and D. magna, respectively. Propiconazole, therefore, seems to induce synergy through a mechanism that cannot be quantified solely by the CYP activity assay used in this study in either of the two species. We discuss the differences between prochloraz and propiconazole as synergists across the two species in the light of the type and time dynamics of affected biotransformation processes.

Assessment of the risk of death of Clarias gariepinus and Oreochromis niloticus pulse-exposed to selected agricultural pesticides

Aquatic organisms are often exposed briefly to high pesticide concentration. Survival time model was used to study risk of death in C. gariepinus and O. niloticus fingerlings exposed to 24 mg/L atrazine, 42 mg/l mancozeb, 1 mg/L chlorpyrifos and 0.75 µg/L lambda cyhalothrin for 15, 30, 45 and 60 minutes and continuously for 96 hours. Mortality, time-to-death, weight, length, and condition factor of the fingerlings were recorded. Results obtained showed tilapia was more susceptible than catfish to continuous exposure but not pulse exposure. The survival probability of both species was similar when exposed for 15, 30 and 45 minutes (p > 0.05) but differed after 60 minutes (p < 0.05). Risk of death of catfish exposed briefly to atrazine, mancozeb and chlorpyrifos for 60 minutes was similar to 96 hours continuous exposure, same for tilapia exposed to 1 mg/L chlorpyrifos (p > 0.05). Survival probability of tilapia exposed to chlorpyrifos for 15, 30, 45 and 60 minutes was similar (p > 0.05) and was not influenced by pulse length. Pesticide hazard and risk of death decreased as fish size (weight, length, and condition factor) increased. Pulse toxicity assessment using survival models could make pesticides exposure assessment more realistic by studying factors that can influence the toxicity of pesticides.

Repeated insecticide pulses increase harmful effects on stream macroinvertebrate biodiversity and function

We exposed twelve mesocosm stream channels and four instream channels to one, two, and four pulses of the insecticide lambda-cyhalothrin (0.1 μg L-1) applied at two day intervals, each pulse lasting 90 min. Unexposed controls were included. We monitored macroinvertebrate taxonomic composition in the channels and in deployed leaf packs one day before and 29 days after the first exposure. Further, we measured drift in and out of the channels and leaf litter decomposition. Lambda-cyhalothrin exposures induced significantly increased drift in both experiments especially for Gammarus pulex, Amphinemura standfussi, and Leuctra spp. Macroinvertebrate taxonomic composition increasingly changed with increasing number of lambda-cyhalothrin exposures being most pronounced in the mesocosm channels. Further, leaf decomposition significantly decreased with increasing number of exposures in the mesocosm channels. Our study showed that species with predicted highest sensitivity to lambda-cyhalothrin were primary drivers of significant changes in taxonomic composition lasting for at least one month despite continuous recolonization of exposed channels from upstream parts of the natural stream and from the water inlet in the mesocosm channels. The overall results highlight the importance of sequential exposures to insecticides for understanding the full impact of insecticides on macroinvertebrates at the community level in streams.

Sublethal effects on Simocephalus vetulus (Cladocera: Daphnidae) of pulse exposures of cypermethrin

Pyrethroids are among the most widely applied insecticides worldwide and cypermethrin is the pyrethroid most used in Argentina. Pesticides used in crops can reach adjacent watercourses through runoff and may lead to non-target fauna receiving toxic pulse exposures. The aim of this study was to determine the effects of cypermethrin pulse exposures on the widely distributed crustacean Simocephalus vetulus. The 48h-LC50 of cypermethrin for S. vetulus was determined at 0.18 ± 0.09 μg/L. To assess the effects of cypermethrin under environmentally realistic exposures, two experiments were performed. In the first one, specimens were exposed for 90 min to cypermethrin at 0.02 (T1), 0.2 (T2) and 1 μg/L (T3), transferred to clean water and monitored for 24 h as regards survival and feeding rates; specimens exposed to T2 and T3 concentrations showed significant lower feeding rates than those in the control group. In the second experiment, specimens were exposed for 90 min every 7 days and monitored over 25 days; S. vetulus showed lower cumulative fecundity and reproduction rates at all concentrations tested, and lower population growth at the highest concentration. All exposure concentrations lay within reported environmental concentrations and risk assessment indicated risk (RQ > 1), suggesting that sensitive species would be affected by such pulse exposures of cypermethrin. The present study thus suggests that ongoing agricultural practices affect the non-target invertebrates in streams adjacent to crops.

Linking Morphology, Toxicokinetic, and Toxicodynamic Traits of Aquatic Invertebrates to Pyrethroid Sensitivity

Pyrethroid insecticides are known to be highly toxic to most aquatic nontarget organisms, but little is known about the mechanisms causing some species to be highly sensitive while others are hardly affected by the pyrethroids. The aim of the present study was to measure the sensitivity (EC₅₀-values) of 10 aquatic invertebrates toward a 24 h pulse of the pyrethroid cypermethrin and subsequently test if the difference in sensitivity could be explained by measured morphological and physiological traits and modeled toxicokinetic (TK) and toxicodynamic (TD) parameters. Large differences were observed for the measured uptake and elimination kinetics, with bioconcentration factors (BCFs) ranging from 53 to 2337 at the end of the exposure. Similarly, large differences were observed for the TDs, and EC₅₀-values after 168 h varied 120-fold. Modeling the whole organism cypermethrin concentrations indicated compartmentation into a sorbed fraction and two internal fractions: a bioavailable and non-bioavailable internal fraction. Strong correlations between surface/volume area and the TK parameters (sorption and uptake rate constants and the resulting BCF) were found, but none of the TK parameters correlated with sensitivity. The only parameter consistently correlating with sensitivity across all species was the killing rate constant of the GUTS-RED-SD model (the reduced general unified threshold models of survival assuming stochastic death), indicating that sensitivity toward cypermethrin is more related to the TD parameters than to TK parameters.

The pyrethroid esfenvalerate induces hypoactivity and decreases dopamine transporter expression in embryonic/larval zebrafish (Danio rerio)

Esfenvalerate is a pyrethroid insecticide used widely for agricultural and residential applications. This insecticide has been detected in aquatic environments at concentrations that can induce sub-lethal effects in organisms. In this study, zebrafish embryos were used to examine the effects of environmentally-relevant concentrations of esfenvalerate on development and behavior. It was hypothesized that esfenvalerate exposure would impair locomotion due to its effects on the central nervous system. We also measured mitochondrial bioenergetics and the expression of genes (dopamine system) as putative mechanisms of locomotor impairment. Concentrations of 0.02, 0.2 and 2 μg/L esfenvalerate did not induce significant mortality nor deformity in zebrafish, but there was an acceleration in hatching time for zebrafish exposed to 2 μg/L esfenvalerate. As an indicator of neurotoxicity, the Visual Motor Response (VMR) test was conducted with 5, 6, and 7 dpf zebrafish after continuous exposure, and higher concentrations were used (4 and 8 μg/L esfenvalerate) to better discern age-and dose dependent responses in behavior. Experiments revealed that, unlike the other stages, 6 dpf larvae showed evidence for hypo-activity with esfenvalerate, suggesting that different stages of larval development may show increased sensitivity to pyrethroid exposure. This may be related to age-dependent maturation of the central nervous system. We hypothesized that reduced larval activity may be associated with impaired production of ATP and the function of mitochondria at earlier life stages, however dramatic alterations in oxidative phosphorylation were not observed. Based on evidence that dopamine regulates behavior and studies showing that other pyrethroids affect dopamine system, we measured transcripts involved in dopaminergic signaling. We found that dopamine active transporter was down-regulated with 0.2 μg/L esfenvalerate. Lastly, we comprehensively summarize the current literature (>20 studies) regarding the toxicity of pyrethroids in zebrafish, which is a valuable resource to those studying these pesticides. This study demonstrates that esfenvalerate at environmentally-relevant levels induces hypoactivity that are dependent upon the age of the zebrafish, and these behavioral changes are hypothesized to be related to impaired dopamine signaling.

The pyrethroid (±)-lambda-cyhalothrin enantioselective biodegradation by a bacterial consortium

Chiral pesticides have been used in agriculture, including (±)-lambda-cyhalothrin ((±)-LC), which is a pyrethroid insecticide widely employed on crops for protection against different types of insects. However, enantioselectivity is poorly studied in biodegradation processes. Therefore, the (±)-LC enantioselective biodegradation by bacteria from Brazilian savannah was reported in this study with a validated analytical method. All bacterial strains biodegraded (±)-LC with different efficiencies. Residual concentrations of LC (3.7-43.1% of biodegradation) and its enantiomeric excesses (0-27% ee) were determined. Additionally, the formation of the main biodegradation metabolite 3-phenoxybenzoic acid was also quantified. A Bacillus consortium composed of the three most efficient strains biodegraded more LC than any isolated strain solely employed in this work, showing that the use of a consortium is an interesting approach. In addition, 13 metabolites were identified and a biodegradation pathway with biochemical reactions of hydrolysis, reduction, esterification, amidation, elimination and group transfer were proposed, confirming the bioremediation potential of these strains. The LC stereoisomer with the highest insecticidal activity (1R,3R,αS-enantiomer, also known as gamma-cyhalothrin) was preferentially biodegraded by the studied bacteria. Therefore, crops protection with gamma-cyhalothrin, which can be applied in lower concentrations than (±)-LC because it is a more effective product against insects, may also be biodegraded faster than the racemic mixture in the environment, decreasing the toxic effects on non-target organisms.

Evaluation of a novel West Nile virus transmission control strategy that targets Culex tarsalis with endectocide-containing blood meals

Control of arbovirus transmission remains focused on vector control through application of insecticides directly to the environment. However, these insecticide applications are often reactive interventions that can be poorly-targeted, inadequate for localized control during outbreaks, and opposed due to environmental and toxicity concerns. In this study, we developed endectocide-treated feed as a systemic endectocide for birds to target blood feeding Culex tarsalis, the primary West Nile virus (WNV) bridge vector in the western United States, and conducted preliminary tests on the effects of deploying this feed in the field. In lab tests, ivermectin (IVM) was the most effective endectocide tested against Cx. tarsalis and WNV-infection did not influence mosquito mortality from IVM. Chickens and wild Eurasian collared doves exhibited no signs of toxicity when fed solely on bird feed treated with concentrations up to 200 mg IVM/kg of diet, and significantly more Cx. tarsalis that blood fed on these birds died (greater than 80% mortality) compared to controls (less than 25% mortality). Mosquito mortality following blood feeding correlated with IVM serum concentrations at the time of blood feeding, which dropped rapidly after the withdrawal of treated feed. Preliminary field testing over one WNV season in Fort Collins, Colorado demonstrated that nearly all birds captured around treated bird feeders had detectable levels of IVM in their blood. However, entomological data showed that WNV transmission was non-significantly reduced around treated bird feeders. With further development, deployment of ivermectin-treated bird feed might be an effective, localized WNV transmission control tool.

West Nile virus (WNV) is a mosquito-borne virus that causes significant disease and death every year in humans, domesticated animals, and wildlife. Control of WNV transmission is focused on controlling the mosquito vector through applications of insecticides directly to the environment. In this study, we evaluate a novel control strategy for WNV transmission by targeting the main mosquito bridge vector in the Great Plains region, Culex tarsalis, through its blood feeding behavior. Because Culex tarsalis favor taking blood meals from particular bird species, our strategy aims to target these bird species with endectocide-treated bird feed that will result in lethal blood meals for Cx. tarsalis. In this study, we developed a safe and effective formulation of ivermectin-treated diet that resulted in increased mortality for Cx. tarsalis blood fed on birds consuming this treated diet as compared to mosquitoes feeding on control birds. We also conducted a pilot field trial in Fort Collins, Colorado to test this strategy in a natural transmission cycle, which demonstrated promising results.

Lambda-cyhalothrin affects swimming activity and physiological responses of Daphnia magna

λ-cyhalotrin is a pyrethroid pesticide used for protection of crops against various insect pests. Knowledge on behavioural and physiological responses of non-target organisms such as cladocerans is very limited. Daphnia is a sensitive organism commonly used in determination of ecotoxicological risk for various substances introduced to aquatic environment, however the main experimental endpoints used such as mortality or immobilisation may not be sufficient to evaluate subtle alterations in zooplankton. The aim of the present study was to evaluate swimming behaviour and physiological parameters of Daphnia magna exposed to λ-cyhalothrin (Karate Zeon 050 CS) at concentrations of 0.05, 0.5, 5 and 50 μg L^-1 for 2, 24 and 48 h. The results showed that λ-cyhalothrin affected D. magna swimming behaviour inducing a concentration-dependent inhibition of swimming track density, speed and turning ability. Depression of physiological parameters such as heart rate and thoracic limb activity was also noted. The results suggest that in natural conditions swimming behaviour and physiological endpoints of D. magna may be disturbed by environmental concentrations of λ-cyhalothrin leading to ecological consequences.

Seasonal sensitivity of Gammarus pulex towards the pyrethroid cypermethrin

The aquatic toxicity of insecticides like the pyrethroids have been discussed intensively over the recent years especially in relation to risk assessment and how seasonality may or may not affect the sensitivity of non-target organisms. To address this issue, the crustacean Gammarus pulex was collected once a month for 16 months and acclimated to 10 °C for four days before being exposed to a 90 min pulse of cypermethrin. In vitro cytochrome P450 activity, total lipid content, total protein content, and dry weight were measured in male and female gammarids from each sampling date and used along with the water temperature as variables for sensitivity prediction by Partial Least Squares (PLS) regression models. The 24 h EC₅₀-values varied more than 30 fold across the sampling period from 0.21 ± 0.05 μg L^-1 (April 2015) to 6.60 ± 3.46 μg L^-1 (October 2015), indicating seasonal variances in the acute sensitivity of G. pulex towards cypermethrin. After 168 h of recovery this difference in EC₅₀-values was reduced to seven-fold. In both male and female gammarids seasonal patterns were observed in the total lipid content and in vitro CYP P450 activity, which peaked in spring and fall, respectively. The current study shows the importance of reporting time of organism collection and experimental execution for risk assessment of pyrethroids as season is important for the acute sensitivity of G. pulex. We suggest prolonged acclimation times of sampled macroinvertebrates to constant laboratory conditions in order to even out possible seasonal differences in sensitivity.

Structural and functional effects of a short-term pyrethroid pulse exposure on invertebrates in outdoor stream mesocosms

Agricultural land-use frequently results in short pulse exposures of insecticides such as pyrethroids in river systems, adversely affecting local invertebrate communities. In order to assess insecticide-induced effects, stream mesocosms are used within higher tier aquatic risk assessment. Regulatory acceptable concentrations (RACs) derived from those studies are often higher compared with tier 1 RACs. Hence, the present mesocosm study evaluates this aspect using a pulse exposure scenario typical for streams and the pyrethroid insecticide etofenprox. A 6-h pulse exposure with measured concentrations of 0.04, 0.3 and 5.3μgL^-1 etofenprox was used. We considered abundance, drift and emergence of invertebrates as structural endpoints and the in situ-measured feeding rates of the isopod Asellus aquaticus as functional endpoint. Most prominent effects were visible at 5.3μgL^-1 etofenprox which caused adverse effects of up to 100% at the individual and population level, as well as community structure alterations. Transient effects were observed for invertebrate drift (effect duration ≤24h) and for the invertebrate community (9 days after exposure) at 0.3μgL^-1 etofenprox. Furthermore, 0.04μgL^-1 etofenprox affected the abundance of the mayfly Cloeon simile (decrease by 66%) and the feeding rate of A. aquaticus (decrease by 44%). Thus, implications for the functional endpoint leaf litter breakdown in heterotrophic ecosystems may be expected. A hypothetical RAC derived from the present mesocosm study (0.004μgL^-1) is in line with the official tier 1 RAC (0.0044μgL^-1) and thus shows that the present mesocosm study did not result in a higher RAC.

Can Toxicokinetic and Toxicodynamic Modeling Be Used to Understand and Predict Synergistic Interactions between Chemicals?

Some chemicals are known to enhance the effect of other chemicals beyond what can be predicted with standard mixture models, such as concentration addition and independent action. These chemicals are called synergists. Up until now, no models exist that can predict the joint effect of mixtures including synergists. The aim of the present study is to develop a mechanistic toxicokinetic (TK) and toxicodynamic (TD) model for the synergistic mixture of the azole fungicide, propiconazole (the synergist), and the insecticide, α-cypermethrin, on the mortality of the crustacean Daphnia magna. The study tests the hypothesis that the mechanism of synergy is the azole decreasing the biotransformation rate of α-cypermethrin and validates the predictive ability of the model on another azole with a different potency: prochloraz. The study showed that the synergistic potential of azoles could be explained by their effect on the biotransformation rate but that this effect could only partly be explained by the effect of the two azoles on cytochrome P450 activity, measured on D. magna in vivo. TKTD models of interacting mixtures seem to be a promising tool to test mechanisms of interactions between chemicals. Their predictive ability is, however, still uncertain.

Energetic costs and biochemical biomarkers associated with esfenvalerate exposure in Sericostoma vittatum

Pyrethroid insecticides have been used for decades and their worldwide market continues to increase, despite their high toxicity to non-target insects. Recent studies reveal that it is essential to investigate the secondary mechanisms of action of type II pyrethroids to understand their cellular effects on invertebrates. The aim of this study was to evaluate the lethality, behaviour and physiological alterations and energetic costs in caddisfly larvae exposed to environmentally relevant concentrations of esfenvalerate (ESF). ESF caused both mortality and feeding inhibition of exposed caddisfly larvae: nominal ESF 96 h LC₅₀ was 2.29 μg/L; feeding activity was impaired at concentrations equal or above 0.25 μg/L. At the cellular level, glutathione-S-transferase (GST) activity was increased on caddisfly larvae exposed to 0.25 and 0.5 μg/L ESF, which might contribute to prevent oxidative damage since levels of lipid peroxidation (LPO) were not altered. The energy budget of exposed caddisfly larvae was impaired by exposure to 0.25 μg/L ESF since sugar and protein contents decreased, while a decline of energy consumption was observed. The analysis of feeding, energy reserves and consumption data through structural equation modelling (SEM) allowed to quantify the direct and indirect effects of ESF exposure on bioenergetics of caddisfly larvae. SEM analysis showed a strong negative direct influence of ESF onto feeding activity, sugars content and energy consumption, highlighting a significant positive relationship between sugars and protein contents. These results show that energy expenditure is related to oxidative defense mechanisms induced by ESF stress that may lead to deleterious effects on growth and development.

Treated wastewater effluent as a source of pyrethroids and fipronil at todos santos bay, Mexico: Its impact on sediments and organisms

Pyrethroids are insecticides widely used to control pests and disease vectors in residential areas and agricultural lands. Pyrethroids are emerging pollutants, and their use is a growing concern because of their toxicity potential to aquatic organisms. Todos Santos Bay and the Punta Banda estuary, 2 coastal bodies located to the south of the Southern California Bight, were studied to establish a baseline of the current conditions of pollution by pyrethroids and fipronil. Eight pyrethroids, along with fipronil and its 2 metabolites, were determined in effluents from wastewater-treatment plants (n = 3), surface sediments (n = 32), and 3 locations with mussels (Mytilus californianus, n = 9). Bifenthrin, permethrin, and cypermethrin were the most common pyrethroids found in the study areas and were widespread in sediments, mussels, and wastewater-treated effluents. Fipronil and its metabolites were detected in mussels and wastewater-treated effluents only. Total pyrethroid concentrations in sediments ranged from 0.04 to 1.95 ng/g dry weight in the Punta Banda estuary (n = 13) and from 0.07 to 6.62 ng/g dry weight in Todos Santos Bay (n = 19). Moreover, total pyrethroids in mussels ranged from 1.19 to 6.15 ng/g wet weight. Based on the toxic unit data calculated for pyrethroids and fipronil for Eohaustorius estuarius and Hyalella azteca, little to no impact is expected to the benthic population structure. Environ Toxicol Chem 2017;36:3057-3064. © 2017 SETAC.

Repeated pulse exposures to lambda-cyhalothrin affect the behavior, physiology, and survival of the damselfly larvae Ischnura graellsii (Insecta; Odonata)

Damselflies form an essential part of the aquatic and terrestrial food web. Pesticides may, however, negatively affect their behavior, physiology, and survival. To assess this, a 42-day-lasting bioassay was conducted, during which damselfly larvae (Ischnura graellsii; n = 20) were repeatedly exposed to lambda-cyhalothrin (3 days at; 0, 10, 50, 250, 1250, and 6250ng LCH L^-1), followed by recovery phases (4 days) in pesticide-free medium for six weeks. This exposure design was used to simulate frequent runoff events in the field. Variables related to the behavior (strikes against prey and capture success), growth, physiology (lipid content and fatty acid composition), as well as mortality were assessed throughout the experiment. The two highest LCH concentrations induced 100% mortality within the first 48h, whereas 85% of the test organisms survived 28 days under control conditions. The number of strikes against prey was not affected by LCH. In contrast, prey capture success decreased significantly (up to ~50% at 250ng LCH L^-1, for instance, after the third pulse exposure) following LCH-exposures compared to the control. This difference was not observed after recovery phases, however, which did not counteract the enhanced energy demand for detoxification and defense mechanisms indicated by a lower growth rate (up to ~20%) and lipid content (up to ~30%) of damselflies at 50 and 250ng LCH L^-1. In addition, two essential fatty acids (eicosapentaenoic acid and arachidonic acid) and two precursors (linolenic acid and α-linolenic acid) decreased in their concentrations upon exposure towards 250ng LCH L^-1. Thus the results of this study indicate that long-term exposure towards LCH pulses can affect damselfly behavior, physiology and survival. Given the essential role of damselflies in food web dynamics, these effects may potentially translate into local population impairments with subsequent bottom-up directed effects within and across ecosystem boundaries.

Acute effects of binary mixtures of Type II pyrethroids and organophosphate insecticides on Oreochromis niloticus

Pyrethroid and organophosphate insecticides have been used for more than 20 years worldwide to control a variety of insect pest in different settings. These pesticides have been detected in a variety of environmental samples, including surface waters and sediments and therefore there is significant concern about their potential toxic effects on non-target organisms. Mixtures of compounds from these groups of pesticides have been found to frequently show enhanced toxicity but it has been a challenge to predict whether or not enhanced toxicity will occur for a given combination of compounds. This study therefore studied the effects of binary pyrethroid-organophosphate mixtures using cypermethrin, deltamethrin and dimethoate in an acute toxicity test system with Oreochromis niloticus. The 96 h LC50s for individual insecticides were 9.13 µg/l, 9.42 µg/l and 45.52 mg/l for cypermethrin, deltamethrin and dimethoate respectively. These showed that the pyrethroid insecticides were highly toxic to Oreochromis niloticus and were far more toxic than dimethoate. All mixtures were also more toxic than single insecticides throughout the concentration-response curve with mixtures resulting in mortality at concentrations which the individual pesticides in the mixture were below their respective NOECs. In addition, observed mixture toxicities deviated from the predicted mixture effects based either on the Concentration Addition (CA) or Independent Action (IA) models independent of mixture ratio. However, the extent of observed mixture mortality deviation was dependent on the effect level. Significant deviations (MDR > 2.0) were observed at lower concentrations indicating synergistic effects at lower and possibly environmentally relevant concentrations. This is not unexpected since organophosphate insecticides are known to inhibit acetylcholinesterase as well as inactivate esterase, resulting in reduced detoxification of pyrethroid insecticides and consequently greater toxicity than would be expected. This has important implications for risk assessment of mixtures since the risk of pyrethroid-organophosphate mixtures may be underestimated if either the CA or IA model is employed.

Climate-change influences on the response of macroinvertebrate communities to pesticide contamination in the Sacramento River, California watershed

Limited studies have addressed how future climate-change scenarios may alter the effects of pesticides on biotic assemblages or the effects of exposures to repeated pulses of pesticide mixtures. We used reported pesticide-use data as input to a hydrological fate and transport model (Soil and Water Assessment Tool) under multiple climate-change scenarios to simulate spatiotemporal dynamics of pesticides mixtures in streams on a daily time-step in the Sacramento River watershed of California. We predicted that there will be increased pesticide application with warming across the watershed, especially in upstream areas. Using a statistical model describing the relationship between macroinvertebrate communities and pesticide dynamics, we found that compared to the baseline period of 1970-1999: (1) most climate-change scenarios predicted increased rainfall and warming across the watershed during 2070-2099; and (2) increasing pesticide contamination and increased impact on macroinvertebrates will likely occur in most areas of the watershed by 2070-2099; and (3) lower increases in effects of pesticides on macroinvertebrates were predicted for the downstream areas with intensive agriculture compared to some upstream areas with less-intensive agriculture. Future efforts on practical adaptation and mitigation strategies can be improved by awareness of altered threats of pesticide mixtures under future climate-change conditions.

Global occurrence of pyrethroid insecticides in sediment and the associated toxicological effects on benthic invertebrates: An overview

Pyrethroids are the third most applied group of insecticides worldwide and are extensively used in agricultural and non-agricultural applications. Pyrethroids exhibit low toxicity to mammals, but have extremely high toxicity to fish and non-target invertebrates. Their high hydrophobicity, along with pseudo-persistence due to continuous input, indicates that pyrethroids will accumulate in sediment, pose long-term exposure concerns to benthic invertebrates and ultimately cause significant risk to benthic communities and aquatic ecosystems. The current review synthesizes the reported sediment concentrations of pyrethroids and associated toxicity to benthic invertebrates on a global scale. Geographically, the most studied area was North America, followed by Asia, Europe, Australia and Africa. Pyrethroids were frequently detected in both agricultural and urban sediments, and bifenthrin and cypermethrin were identified as the main contributors to toxicity in benthic invertebrates. Simulated hazard quotients (HQ) for sediment-associated pyrethroids to benthic organisms ranged from 10.5±31.1 (bifenthrin) to 41.7±204 (cypermethrin), suggesting significant risk. The current study has provided evidence that pyrethroids are not only commonly detected in the aquatic environment, but also can cause toxic effects to benthic invertebrates, and calls for better development of accurate sediment quality criteria and effective ecological risk assessment methods for this emerging class of insecticides.

Realistic pesticide exposure through water and food amplifies long-term effects in a Limnephilid caddisfly

Pesticides are increasingly recognized as relevant stressors in stream ecosystems. Stream biota is exposed to pesticides with low water solubility, e.g. pyrethroid insecticides, via water, habitat, and food. However, long-term effects of simultaneous exposure pathways are unknown. In this context, we conducted a microcosm experiment with the caddisfly Anabolia nervosa exposing the larvae to the pyrethroid insecticide esfenvalerate (EFV) at 0.1 and 1.0μgL^-1 via (i) water, (ii) food or a (iii) combination of water and food. Combined exposure through water and food significantly reduced emergence by 60% and significantly postponed emergence timing at the highest EFV level, whereas none of the single-phase exposures showed significant effects. Moreover, our study revealed that successfully emerged females from the highest biphasic treatment level were characterised by altered composition of storage lipids indicative of reduced energy reserves. Consequently, a realistic test scenario that represents simultaneous exposure of organisms and their food may reveal substantially increased long term effects of pyrethroids when compared with current ecological risk assessment applying only single phase exposure. We recommend that relevant concurrent exposure routes of pesticides should be considered in order to derive realistic regulatory acceptable concentrations of pesticides.

Determining lower threshold concentrations for synergistic effects

Though only occurring rarely, synergistic interactions between chemicals in mixtures have long been a point of focus. Most studies analyzing synergistic interactions used unrealistically high chemical concentrations. The aim of the present study is to determine the threshold concentration below which proven synergists cease to act as synergists towards the aquatic crustacean Daphnia magna. To do this, we compared several approaches and test-setups to evaluate which approach gives the most conservative estimate for the lower threshold for synergy for three known azole synergists. We focus on synergistic interactions between the pyrethroid insecticide, alpha-cypermethrin, and one of the three azole fungicides prochloraz, propiconazole or epoxiconazole measured on Daphnia magna immobilization. Three different experimental setups were applied: A standard 48h acute toxicity test, an adapted 48h test using passive dosing for constant chemical exposure concentrations, and a 14-day test. Synergy was defined as occuring in mixtures where either EC₅₀ values decreased more than two-fold below what was predicted by concentration addition (horizontal assessment) or as mixtures where the fraction of immobile organisms increased more than two-fold above what was predicted by independent action (vertical assessment). All three tests confirmed the hypothesis of the existence of a lower azole threshold concentration below which no synergistic interaction was observed. The lower threshold concentration, however, decreased with increasing test duration from 0.026±0.013μM (9.794±4.897μgL^-1), 0.425±0.089μM (145.435±30.46μgL^-1) and 0.757±0.253μM (249.659±83.44μgL^-1) for prochloraz, propiconazole and epoxiconazole in standard 48h toxicity tests to 0.015±0.004μM (5.651±1.507μgL^-1), 0.145±0.025μM (49.619±8.555μgL^-1) and 0.122±0.0417μM (40.236±13.75μgL^-1), respectively, in the 14-days tests. Testing synergy in relation to concentration addition provided the most conservative values. The threshold values for the vertical assessments in tests where the two could be compared were in general 1.2 to 4.7 fold higher than the horizontal assessments. Using passive dosing rather than dilution series or spiking did not lower the threshold significantly. Below the threshold for synergy, slight antagony could often be observed. This is most likely due to induction of enzymes active in metabolization of alpha-cypermethrin. The results emphasize the importance of test duration when assessing synergy, but also show that azole concentrations within the typically monitored range of up to 0.5μgL^-1 are not likely to cause severe synergy concerning Daphnia magna immobilization.

Response of macroinvertebrate communities to temporal dynamics of pesticide mixtures: A case study from the Sacramento River watershed, California

Pesticide pollution from agricultural field run-off or spray drift has been documented to impact river ecosystems worldwide. However, there is limited data on short- and long-term effects of repeated pulses of pesticide mixtures on biotic assemblages in natural systems. We used reported pesticide application data as input to a hydrological fate and transport model (Soil and Water Assessment Tool) to simulate spatiotemporal dynamics of pesticides mixtures in streams on a daily time-step. We then applied regression models to explore the relationship between macroinvertebrate communities and pesticide dynamics in the Sacramento River watershed of California during 2002-2013. We found that both maximum and average pesticide toxic units were important in determining impacts on macroinvertebrates, and that the compositions of macroinvertebrates trended toward taxa having higher resilience and resistance to pesticide exposure, based on the Species at Risk pesticide (SPEAR_pesticides) index. Results indicate that risk-assessment efforts can be improved by considering both short- and long-term effects of pesticide mixtures on macroinvertebrate community composition.

Comparisons of discrete and integrative sampling accuracy in estimating pulsed aquatic exposures

Most current-use pesticides have short half-lives in the water column and thus the most relevant exposure scenarios for many aquatic organisms are pulsed exposures. Quantifying exposure using discrete water samples may not be accurate as few studies are able to sample frequently enough to accurately determine time-weighted average (TWA) concentrations of short aquatic exposures. Integrative sampling methods that continuously sample freely dissolved contaminants over time intervals (such as integrative passive samplers) have been demonstrated to be a promising measurement technique. We conducted several modeling scenarios to test the assumption that integrative methods may require many less samples for accurate estimation of peak 96-h TWA concentrations. We compared the accuracies of discrete point samples and integrative samples while varying sampling frequencies and a range of contaminant water half-lives (t₅₀ = 0.5, 2, and 8 d). Differences the predictive accuracy of discrete point samples and integrative samples were greatest at low sampling frequencies. For example, when the half-life was 0.5 d, discrete point samples required 7 sampling events to ensure median values > 50% and no sampling events reporting highly inaccurate results (defined as < 10% of the true 96-h TWA). Across all water half-lives investigated, integrative sampling only required two samples to prevent highly inaccurate results and measurements resulting in median values > 50% of the true concentration. Regardless, the need for integrative sampling diminished as water half-life increased. For an 8-d water half-life, two discrete samples produced accurate estimates and median values greater than those obtained for two integrative samples. Overall, integrative methods are the more accurate method for monitoring contaminants with short water half-lives due to reduced frequency of extreme values, especially with uncertainties around the timing of pulsed events. However, the acceptability of discrete sampling methods for providing accurate concentration measurements increases with increasing aquatic half-lives.

A meta-analysis synthesizing the effects of pesticides on swim speed and activity of aquatic vertebrates

Pesticide contaminants are ubiquitous in aquatic environments and pose a threat to biodiversity. Pesticides also have diverse mechanisms of action that make it difficult to identify impacts on exposed wildlife. Behavioral measures represent an important link between physiological and ecological processes, and are often used to generalize sub-lethal effects of pesticide exposure. In order to bridge the toxicological and behavioral literature, and identify chemical classes that denote the largest threat, we conducted a meta-analysis summarizing the effects of pesticides on swim speed and activity of aquatic vertebrates. We found that exposure to environmentally relevant concentrations of pesticides reduced the swim speed of exposed amphibians and fish by 35%, and reduced overall activity by 72%. There were also differences in the magnitude of this effect across chemical classes, which likely reflect underlying physiological processes. Pyrethroids, carbamates, and organophosphates all produced a large decrease in swim speed, where as phosphonoglycines and triazines showed no overall effect. Pyrethroids, carbamates, organophosphates, organochlorines, and organotins also produced a large decrease in activity, while phosphonoglycines had no overall effect, and triazines had the opposite effect of increasing activity. Our results indicate that even sub-lethal concentrations of pesticides have a strong effect on critical behaviors of aquatic vertebrates, which can affect fitness and alter species interactions. We expect our synthesis can be used to identify chemical classes producing the largest sub-lethal effects for further research and management.

Multiple exposure routes of a pesticide exacerbate effects on a grazing mayfly

Hydrophobic pesticides such as pyrethroid insecticides tend to occur in their soluble form mainly as transient pulses in streams. In addition, they are regularly detected in significant quantities adsorbed to stream sediments and other organic in-stream structures. Consequently, stream biota is likely subjected to pesticide exposure via multiple routes. In this study we aimed at investigating the influence of exposure routes for the pyrethroid insecticide lambda-cyhalothrin on the grazing mayfly Heptagenia sulphurea. Therefore, H. sulphurea was exposed to lambda-cyhalothrin via single- (water or biofilm) or biphasic exposure (water and biofilm) at environmentally realistic concentrations (0, 0.1, 1μgL(-1)) and exposure duration (2h) in a full factorial design (n=5). Mortality, moulting frequency, and biofilm accrual (proxy for feeding rate) were recorded subsequent to a 7 d post exposure period. Mortality significantly increased and moulting frequency significantly decreased with increasing concentrations of lambda-cyhalothrin in the water phase whereas exposure via biofilm prompted no significant effects on these endpoints (α=0.05). Effect predictions systematically underestimated and overestimated effects for mortality and moulting frequency, respectively. Similarly, mayfly feeding rate was significantly reduced by water phase exposure whereas pre-exposed biofilm did not significantly affect this variable. However, we found a significant but non-systematic interaction between water phase and biofilm exposure on mayfly feeding rate. Our results show that exposure to the same pesticide via multiple exposure routes may increase the magnitude of effects beyond the level predicted from single phase exposures which has clear implications for the aquatic risk assessment of hydrophobic pesticides. However, our results additionally reveal that interactions between pesticide exposure routes may vary between selected dependent variables. We emphasize that unravelling the underlying mechanisms causing these discrepancies in interactive effects between exposure routes is a major aspect that should receive further attention in future research.

Year-Round Monitoring of Contaminants in Neal and Rogers Creeks, Hood River Basin, Oregon, 2011-12, and Assessment of Risks to Salmonids

Pesticide presence in streams is a potential threat to Endangered Species Act listed salmonids in the Hood River basin, Oregon, a primarily forested and agricultural basin. Two types of passive samplers, polar organic chemical integrative samplers (POCIS) and semipermeable membrane devices (SPMDs), were simultaneously deployed at four sites in the basin during Mar. 2011-Mar. 2012 to measure the presence of pesticides, polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs). The year-round use of passive samplers is a novel approach and offers several new insights. Currently used pesticides and legacy contaminants, including many chlorinated pesticides and PBDEs, were present throughout the year in the basin's streams. PCBs were not detected. Time-weighted average water concentrations for the 2-month deployment periods were estimated from concentrations of chemicals measured in the passive samplers. Currently used pesticide concentrations peaked during spring and were detected beyond their seasons of expected use. Summed concentrations of legacy contaminants in Neal Creek were highest during July-Sept., the period with the lowest streamflows. Endosulfan was the only pesticide detected in passive samplers at concentrations exceeding Oregon or U.S. Environmental Protection Agency water-quality thresholds. A Sensitive Pesticide Toxicity Index (SPTI) was used to estimate the relative acute potential toxicity among sample mixtures. The acute potential toxicity of the detected mixtures was likely greater for invertebrates than for fish and for all samples in Neal Creek compared to Rogers Creek, but the indices appear to be low overall (<0.1). Endosulfans and pyrethroid insecticides were the largest contributors to the SPTIs for both sites. SPTIs of some discrete (grab) samples from the basin that were used for comparison exceeded 0.1 when some insecticides (azinphos methyl, chlorpyrifos, malathion) were detected at concentrations near or exceeding acute water-quality thresholds. Early life stages and adults of several sensitive fish species, including salmonids, are present in surface waters of the basin throughout the year, including during periods of peak estimated potential toxicity. Based on these data, direct toxicity to salmonids from in-stream pesticide exposure is unlikely, but indirect impacts (reduced fitness due to cumulative exposures or negative impacts to invertebrate prey populations) are unknown.

Suspended particles only marginally reduce pyrethroid toxicity to the freshwater invertebrate Gammarus pulex (L.) during pulse exposure

Current ecotoxicological research on particle-associated pyrethroids in freshwater systems focuses almost exclusively on sediment-exposure scenarios and sediment-dwelling macroinvertebrates. We studied how suspended particles influence acute effects of lambda-cyhalothrin and bifenthrin on the epibenthic freshwater amphipod Gammarus pulex (L.) using brief pulse exposures followed by a 144 h post exposure recovery phase. Humic acid (HA) and the clay mineral montmorillonite (MM) were used as model sorbents in environmentally realistic concentrations (5, 25 and 125 mg L(-1)). Mortality of G. pulex was recorded during the post exposure recovery phase and locomotor behavior was measured during exposure to lambda-cyhalothrin. We found that HA in concentrations ≥25 mg L(-1) adsorbed the majority of pyrethroids but only reduced mortality of G. pulex up to a factor of four compared to pyrethroid-only treatments. MM suspensions adsorbed a variable fraction of pyrethroids (10% for bifenthrin and 70% for lambda-cyhalothrin) but did not significantly change the concentration-response relationship compared to pure pyrethroid treatments. Behavioral responses and immobilisation rate of G. pulex were reduced in the presence of HA, whereas behavioral responses and immobilisation rate were increased in the presence of MM. This indicates that G. pulex was capable of sensing the bioavailable fraction of lambda-cyhalothrin. Our results imply that suspended particles reduce to only a limited extent the toxicity of pyrethroids to G. pulex and that passive uptake of pyrethroids can be significant even when pyrethroids are adsorbed to suspended particles.

Effects of the Pyrethroid Esfenvalerate on the Oligochaete, Lumbriculus variegatus

Esfenvalerate is a neurotoxic pyrethroid insecticide widely used for agricultural and residential purposes and is considered toxic to nontarget organisms such as fish and aquatic invertebrates. In this study, we evaluated the toxicity of esfenvalerate on the aquatic oligochaete Lumbriculus variegatus. In the acute test, organisms showed visible signs of stress but no LC50 value could be determined. In the 28-day chronic test, a significant decrease in reproduction was observed with a NOEC value of 0.25 µg/kg and a LOEC value of 2.34 µg/kg. As for biomass per worm, a significant decrease was also observed with a NOEC value of 2.34 µg/kg and a LOEC value of 36.36 µg/kg. Reproductive impairment and reductions in biomass of L. variegatus exposed to environmentally realistic concentrations of esfenvalerate observed in laboratory tests suggests potential deleterious effects of this pyrethroid on oligochaete natural populations.

Rapid evolution of increased vulnerability to an insecticide at the expansion front in a poleward-moving damselfly

Many species are too slow to track their poleward-moving climate niche under global warming. Pesticide exposure may contribute to this by reducing population growth and impairing flight ability. Moreover, edge populations at the moving range front may be more vulnerable to pesticides because of the rapid evolution of traits to enhance their rate of spread that shunt energy away from detoxification and repair. We exposed replicated edge and core populations of the poleward-moving damselfly Coenagrion scitulum to the pesticide esfenvalerate at low and high densities. Exposure to esfenvalerate had strong negative effects on survival, growth rate, and development time in the larval stage and negatively affected flight-related adult traits (mass at emergence, flight muscle mass, and fat content) across metamorphosis. Pesticide effects did not differ between edge and core populations, except that at the high concentration the pesticide-induced mortality was 17% stronger in edge populations. Pesticide exposure may therefore slow down the range expansion by lowering population growth rates, especially because edge populations suffered a higher mortality, and by negatively affecting dispersal ability by impairing flight-related traits. These results emphasize the need for direct conservation efforts toward leading-edge populations for facilitating future range shifts under global warming.

Sub-lethal toxicity of environmentally relevant concentrations of esfenvalerate to Chironomus riparius

Integrative studies focused on sub-organismal responses to pyrethroid exposure are important to understand life history responses. In this study, the ecotoxicological effects of esfenvalerate (ESF) on Chironomus riparius were assessed using five biochemical biomarkers related to neurophysiological function (acetylcholinesterase) and oxidative stress (catalase; glutathione-S-transferase; total glutathione and lipid peroxidation). In addition, effects on cellular energy allocation were assessed and all results were compared with organismal level responses (larval growth, emergence and sex ratio). Exposure to sub-lethal concentrations of ESF caused the failure of C. riparius antioxidant defenses (inhibition of catalase activity and decreased levels of total glutathione), which was reflected as oxidative damage. C. riparius energy budget was decreased by exposure to ESF due to an increased energy consumption. Life cycle tests showed that exposure to ESF impaired C. riparius developmental rates and increased male:female ratios, thereby confirming its toxicity and potential population level effects at environmentally relevant concentrations.

The use of growth and behavioral endpoints to assess the effects of pesticide mixtures upon aquatic organisms

Aquatic communities are often subject to complex contaminant mixtures, usually at sublethal concentrations, that can cause long-term detrimental effects. Chemicals within mixtures can effectively interact, resulting in synergism, antagonism or additivity. We investigated the tertiary mixture effects of two pyrethroids, lambda-cyhalothrin and permethrin, and the organophosphate chlorpyrifos, evaluating sublethal endpoints; immobility and growth, on Chironomus dilutus in 10-day exposures. We utilized a toxic units (TU) approach, based on median lethal concentrations (LC50) for each compound. The concepts of independent action and concentration addition were used to compare predicted mixture toxicity to observed mixture toxicity. Increased immobility resulted from mixture concentrations ≥1 TU (7.45 ng/L lambda-cyhalothrin × 24.90 ng/L permethrin × 129.70 ng/L chlorpyrifos), and single pesticides concentrations ≥0.25 TU (5.50 ng/L lambda-cyhalothrin, 24.23 ng/L permethrin, 90.92 ng/L chlorpyrifos, respectively). Growth was inhibited by pesticide mixtures ≥0.125 TU (1.04 ng/L lambda-cyhalothrin × 3.15 ng/L permethrin × 15.47 ng/L chlorpyrifos), and singly by lambda-cyhalothrin ≥0.25 TU (5.50 ng/L), and permethrin ≥0.167 TU (18.21 ng/L). The no observed effect concentrations (NOEC) for immobility and growth, for both mixture and single-pyrethroid exposure, were up to 8.0 and 12.0 times respectively lower than the corresponding NOEC for survival. The median effective concentrations (EC50) for growth (mixture and single-pyrethroid exposure) were up to 7.0 times lower than the respective LC50. This study reinforces that the integration of sublethal endpoints in monitoring efforts is powerful in discerning toxic effects that would otherwise be missed by solely utilizing traditional toxicity assessments.

The synergistic potential of the azole fungicides prochloraz and propiconazole toward a short α-cypermethrin pulse increases over time in Daphnia magna

Pyrethroid insecticides are highly toxic to non-target aquatic invertebrates. Their high toxicity is synergized when co-occurring with azole fungicides in the aquatic environment. Little is known about the importance of synergy, when pyrethroids only occur during a short pulse of a few hours, as it is likely to happen in the environment, nor about the persistence of synergy over time. This study analyzed the synergistic potential of the fungicides propiconazole and prochloraz toward Daphnia magna, when exposed to a pulse (7.2 h) of α-cypermethrin at different concentrations (average pulse concentrations 0.07-11 nM). Immobilization was monitored during exposure and a subsequent recovery period (87.5h) with and without continuous co-exposure to the azoles (1.4 and 1.7 μM, respectively). EC50 values for immobilization decreased exponentially over time with a higher rate in the presence of the azoles. EC50 values for α-cypermethrin determined at the end of the experiment were 3.3±0.5 nM in the absence of azoles and 0.26±0.04, and 0.08±0.01 nM in the presence of propiconazole and prochloraz, respectively. The synergistic potential of the azoles was strongly dependent on time: no synergism could be detected during the pulse, but with azole co-exposure EC50 values decreased during the recovery period by a factor of up to 13 (propiconazole) and 61 (prochloraz) compared to values without azole exposure. Such high synergistic ratios have not been reported for pesticide mixtures in literature before. Our findings highlight that a pulse of the pyrethroid α-cypermethrin is synergized far beyond the actual pulse and beyond standardized test durations. Long post-exposure times are therefore mandatory in order to capture full synergism.

Spermiotoxicity and embryotoxicity of permethrin in the sea urchin Paracentrotus lividus

The toxicity of permethrin on the fertilization and early development of sea urchin Paracentrotus lividus embryos were studied. Spermiotoxicity was evaluated on the basis of fertilization rate. Embryotoxicity was determined by comparing the frequency of normal development and malformations in embryos exposed to permethrin throughout their development. Permethrin inhibited fertilization success, and yielded IC25 and IC50 values of 0.58 (CL = 0.44-0.77) and 0.94 (CL = 0.92-0.95) µg/L, respectively. The embryotoxicity of permethrin was concentration dependent indicating a decreased percentage of normally developed plutei with increasing permethrin concentrations: IC25 = 0.195 µg/L (CL = 0.15-0.26) and IC50 = 0.346 µg/L (CF = 0.29-0.41). Associated with the decrease in normal pluteus frequency was an increase in larval malformations as skeleton deformities. The results suggest that permethrin is more highly toxic to embryos than to sperm, and that this insecticide may present a potential risk for the sea urchin in contaminated marine environments.

Ecological responses to contamination: a meta-analysis of experimental marine studies

Identifying general response patterns to contamination in the environment is critical for reliable assessments of ecosystem health. However, it is not often clear if there are biases in the information used to understand general effects of contamination. To investigate this we conducted a review of 314 studies that experimentally manipulated contaminants and measured the effects on marine invertebrate taxa. The majority of studies investigated the effects of metals (54%) on individual taxa (mainly bivalves, amphipods, copepods). Ecologically relevant responses to contamination were measured in only 22% of the studies. A meta-analysis using studies that measured ecological responses to copper illustrated a general negative effect of copper and highlighted the bias towards field or laboratory experiments that measure community or individual-level responses. There is a need for diversification of studies that investigate the ecological effects of contamination as an important advancement in ecotoxicology and ecological research and environmentally relevant risk assessments.