Effects of environmentally realistic daily temperature variation on pesticide toxicity to aquatic invertebrates

Thresholds and interactive effects of BPA-gradient and temperature on life history traits of Daphnia magna

Bisphenol A (BPA), a synthetic organic compound widely used in the production of plastics, is recognized as an emerging contaminant because of its toxicity and the potential risks associated with bioaccumulation in organisms. Despite potential environmental hazards, there is a lack of studies examining BPA toxicity mechanisms and its potential impact on various trophic levels, with even fewer exploring whether global stressors such as temperature can affect the toxicity of BPA in organisms. Our aim was to assess the combined impact of BPA and varying temperature regimes on life-history traits in Daphnia magna. Our results revealed a significant impact of BPA on the growth, reproduction, and accumulated moulting of D. magna, with adverse effects primarily associated with the assimilation of BPA in algae rather than the BPA present in the medium, pointing to a trophic transfer mechanism. The interactive effect between BPA and temperature demonstrated a slight stimulatory effect of low BPA level on D. magna growth rate under warming constant conditions, but an inhibitory under warming fluctuating temperatures. Additionally, a BPA threshold was identified, below which growth became temperature-dependent. This study emphasizes the crucial role of considering temperature in predicting how toxins may affect Daphnia within aquatic food webs.

Assessment of the impact of chemical pollution on endangered migratory fish in two major rivers of France, including spawning grounds

Water pollution is a one of the most contributors to aquatic biodiversity decline. Consequently, ecological risk assessment methods have been developed to investigate the effects of existing stresses on the environment, including the toxic effects of chemicals. One of the existing approaches to quantify toxic risks is called "Potentially Affected Fraction of species" (PAF), which estimates the potential loss of species within a group of species studied. In this study, the PAF method was applied to the Garonne catchment (southwest France) due to the limited information available on the involvement of water pollution in the decline of diadromous fish populations. This approach was used to quantify the potential toxic risk associated with chemical contamination of water for fish species. The objectives were to quantify this risk (1) in the Garonne and Dordogne rivers and (2) in the spawning grounds of two endangered anadromous fish species: the allis shad and the European sturgeon during the development period of their early life stages. Environmental pollution data was provided for 21 sites within the Garonne catchment between 2007 and 2022, and toxicity data was obtained specifically from freshwater toxicity tests on fish species. Then, for each site and each year, the potential toxic risk for a single substance (ssPAF) and for a mixture of substances (msPAF) was calculated and classified as high (>5 %), moderate (>1 % and < 5 %) or low (<1 %). Potential toxic risks were mostly moderate and mainly associated with: metals > other industrial pollutants and hygiene and care products > agrochemicals. In summary, this study highlights the probable involvement of water contamination on the decline, fate and restoration of diadromous fish populations in the Garonne catchment, focusing notably on the toxic effects on early life stages, a previously understudied topic.

Daily temperature fluctuation interacts with the mean temperature to increase the toxicity of a pyrethroid insecticide in a moth

Climate change complicates ecotoxicology studies because species responses to pesticides depend on temperature. Classically illustrated by the effect of constant laboratory temperatures, a recent review revealed that the toxicity of pesticides is also often increased by daily temperature fluctuations. Here, we investigated the combined effects of daily temperature fluctuation and mean temperature on the toxicity of two insecticides in the moth Spodoptera littoralis. Our study tested the toxicity of chlorpyrifos and deltamethrin on larvae of six experimental groups that crossed three treatments of daily temperature fluctuations (0, 5 or 10 °C) and two treatments of mean temperatures (25 or 33 °C). We showed that daily temperature fluctuation increased larval mortality induced by chlorpyrifos and deltamethrin. However, the response differed between the organophosphorus insecticide chlorpyrifos and the pyrethroid insecticide deltamethrin. The increase in chlorpyrifos toxicity by daily temperature fluctuation did not differ between mean temperatures of 25 and 33 °C. Remarkably, the increase in deltamethrin toxicity by daily temperature fluctuation was dependent on the crossed effects of the amplitude of daily fluctuation and mean temperature. This increase in deltamethrin toxicity occurred with a daily fluctuation of only 5 °C for larvae reared at 25 °C and a daily fluctuation of 10 °C in larvae reared at 33 °C. To confidently quantify the responses of insecticide toxicity to temperature, future ecotoxicology studies will have to evaluate the generality of the interaction between the effects of daily temperature fluctuation and mean temperature.

Assessment of the impacts of GABA and AChE targeting pesticides on freshwater invertebrate family richness in English Rivers

Globally, riverine system biodiversity is threatened by a range of stressors, spanning pollution, sedimentation, alterations to water flow, and climate change. Pesticides have been associated with population level impacts on freshwater invertebrates for acute high-level exposures, but far less is known about the chronic impact of episodic exposure to specific classes of pesticides or their mixtures. Here we employed the use of the UK Environment Agency's monitoring datasets over 40 years (covering years 1980 to 2019) to assess the impacts of AChE (acetylcholinesterase) and GABA (gamma-aminobutyric acid) receptor targeting pesticides on invertebrate family richness at English river sites. Concentrations of AChE and GABA pesticides toxic to freshwater invertebrates occurred (measured) across 18 of the 66 river sites assessed. For one of the three river sites (all found in the Midlands region of England) where data recorded over the past 40 years were sufficient for robust modelling studies, both AChE and GABA pesticides associated with invertebrate family richness. Here, where AChE total pesticide concentrations were classified as high, 46 of 64 invertebrate families were absent, and where GABA total pesticide concentration were classified as high, 16 of 64 invertebrate families were absent. Using a combination of field evidence and laboratory toxicity thresholds for population relevant endpoints we identify families of invertebrates most at risk in the selected English rivers to AChE and GABA pesticides. We, furthermore, provide strong evidence that the absence of the invertebrate family Polycentropodidae (caddisfly) from one field site is due to exposure effects to AChE pesticides.

Higher temperature and daily fluctuations aggravate clothianidin toxicity towards Limnodrilus hoffmeisteri

In nature, aquatic organisms may suffer from chemical pollution, together with thermal stress resulted from global warming. However, limited information is available on the combined effects of pesticide with climate change on aquatic organisms. In this study, the acute toxicity of clothianidin to Limnodrilus hoffmeisteri as well as its effect on the induction of oxidative stress under both constant temperature and daily temperature fluctuation (DTF) regimes was investigated. Results showed that clothianidin exhibited the minimal toxicity to L. hoffmeisteri at 25 °C, which was magnified by both increased or decreased temperatures and 10 °C DTF. At different temperatures (15 °C, 25 °C and 35 °C), clothianidin exposure led to the elevated reactive oxygen species (ROS) levels and activated the antioxidant enzymes to resist against the oxidative stress. However, the antioxidant response induced by clothianidin was overwhelmed at high temperature as evidenced by decreased glutathione (GSH) content. Significant elevation of catalase (CAT) and peroxidase (POD) activities but depletion of GSH was also observed in worms treated with clothianidin under DTF after 24 h. The results indicated that high temperature and DTF could aggravate the clothianidin-induced oxidative stress. Moreover, the critical thermal maximum (CTmax) of the worms decreased with the increasing clothianidin concentrations, suggesting that exposure to clothianidin could reduce the heat tolerance of L. hoffmeisteri. Our work highlights the crucial importance to integrate temperature changes into risk assessment of pesticides under global warming.

Thermal Performance Curves in a Polluted World: Too Cold and Too Hot Temperatures Synergistically Increase Pesticide Toxicity

Ecotoxicological studies typically cover only a limited part of the natural thermal range of populations and ignore daily temperature fluctuations (DTFs). Therefore, we may miss important stressor interaction patterns and have poor knowledge on how pollutants affect thermal performance curves (TPCs), which is needed to improve insights into the fate of populations to warming in a polluted world. We tested the single and combined effects of pesticide exposure and DTFs on the TPCs of low- and high-latitude populations of Ischnura elegans damselfly larvae. While chlorpyrifos did not have any effect at the intermediate mean temperatures (20-24 °C), it became toxic (reflecting synergisms) at lower (≤16 °C, reduced growth) and especially at higher (≥28 °C, reduced survival and growth) mean temperatures, resulting in more concave-shaped TPCs. Remarkably, these toxicity patterns were largely consistent at both latitudes and hence across a natural thermal gradient. Moreover, DTFs magnified the pesticide-induced survival reductions at 34 °C. The TPC perspective allowed us to identify different toxicity patterns and interaction types (mainly additive vs synergistic) across the thermal gradient. This highlights the importance of using thermal gradients to make more realistic predictions about the impact of pesticides in a warming world and of warming in a polluted world.

Effects of temperature and salinity on bioconcentration and toxicokinetics of permethrin in pyrethroid-resistant Hyalella azteca

Recent studies demonstrated pyrethroid resistance associated with voltage-gated sodium channel mutations in populations of the epibenthic amphipod, Hyalella azteca. Resistant populations were able to tolerate and bioconcentrate pyrethroids at concentrations significantly higher than toxic levels for non-resistant populations. In conjunction with elevated bioconcentration potential, environmental alteration particularly as a result of global climate change is anticipated to significantly alter abiotic parameters including temperature and salinity. These changes are expected to influence uptake and biotransformation of contaminants. Thus, the aims of the current study were a) to examine the bioconcentration potential of permethrin in two pyrethroid-resistant clades of H. azteca and b) assess the influence of temperature and salinity changes on toxicokinetic parameters. Two pyrethroid-resistant clades of H. azteca were exposed to ¹⁴C-permethrin at three salinities (0.2, 1.0 and 6.0 practical salinity units (PSU)) and temperatures (18, 23 and 28 °C). Tests were conducted for up to 36 h and uptake, elimination and biotransformation rates were calculated. Both populations demonstrated bioconcentration factors (BCFs) between five and seven times greater than published data for non-resistant H. azteca, with significant differences between clades. Calculated BCF values were comparable to field populations of resistant H. azteca, emphasizing the potential for elevated pyrethroid bioconcentration in the natural environment and increased exposure for predators consuming pyrethroid-resistant aquatic invertebrates. Alterations to temperature and salinity had no statistically significant effect on uptake or parent compound half-life in either population, though biotransformation was elevated at higher temperatures in both populations. Salinity had a variable effect between the two populations, with lower BCF values at 1.0 PSU in clade D H. azteca and greater BCFs at 6.0 PSU in clade C H. azteca. This is the first study to demonstrate the potential for future climate scenarios to influence toxicokinetics in pyrethroid-resistant aquatic organisms.

Daily temperature fluctuations can magnify the toxicity of pesticides

We review the effect of daily temperature fluctuations (DTF), a key thermal factor predicted to increase under climate change, on pesticide toxicity. The effect of DTF on pesticide toxicity may be explained by: (i) a DTF-specific mechanism (caused by Jensen's inequality) and (ii) general mechanisms underlying an increased pesticide toxicity at both higher (increased energetic costs, pesticide uptake and metabolic conversion) and lower constant temperatures (lower organismal metabolic and associated elimination rates, increased sodium channel modulated nervous system vulnerability and energetic costs). Furthermore, DTF may enhance pesticide-induced reductions in heat tolerance due to stronger effects on oxygen demand (increase) and oxygen supply (decrease). Our literature review showed considerable support that DTF increase the negative impact of pesticides on insects, especially in terms of decreased survival. Therefore, we suggest that considering DTF in ecotoxicological studies may be of great importance to better protect biodiversity in our warming world.

ECORISK2050: An Innovative Training Network for predicting the effects of global change on the emission, fate, effects, and risks of chemicals in aquatic ecosystems

By 2050, the global population is predicted to reach nine billion, with almost three quarters living in cities. The road to 2050 will be marked by changes in land use, climate, and the management of water and food across the world. These global changes (GCs) will likely affect the emissions, transport, and fate of chemicals, and thus the exposure of the natural environment to chemicals. ECORISK2050 is a Marie Skłodowska-Curie Innovative Training Network that brings together an interdisciplinary consortium of academic, industry and governmental partners to deliver a new generation of scientists, with the skills required to study and manage the effects of GCs on chemical risks to the aquatic environment. The research and training goals are to: (1) assess how inputs and behaviour of chemicals from agriculture and urban environments are affected by different environmental conditions, and how different GC scenarios will drive changes in chemical risks to human and ecosystem health; (2) identify short-to-medium term adaptation and mitigation strategies, to abate unacceptable increases to risks, and (3) develop tools for use by industry and policymakers for the assessment and management of the impacts of GC-related drivers on chemical risks. This project will deliver the next generation of scientists, consultants, and industry and governmental decision-makers who have the knowledge and skillsets required to address the changing pressures associated with chemicals emitted by agricultural and urban activities, on aquatic systems on the path to 2050 and beyond.

A transportable temperature and heatwave control device (TENTACLE) for laboratory and field simulations of different climate change scenarios in aquatic micro- and mesocosms

Future global climate change with higher mean temperatures and increased intensity and frequency of heatwaves as extreme weather events will affect aquatic ecosystems with, yet, unpredictable severity and consequences. Although models suggest increased risk of species extinction up to the year 2050 for series of different climate change scenarios, environmental complexity may result in unconsidered effects of future temperature alterations on ecosystems. Apart from these environmental changes, additional anthropogenic stressors, e.g. chemical release, may cause unprecedented interaction effects on ecosystems. Ongoing efforts to better understand such temperature-chemical interaction effects comprise almost exclusively experimental designs using constant temperature regimes instead of environmentally realistic daily temperature variations. In this paper we describe an Arduino-based temperature and heatwave control device (TENTACLE) that is transportable, inexpensive, multifunctional, and easily reproducible. TENTACLE offers water temperature monitoring and manipulation of up to 3 different climate change-related scenarios: i) natural (ambient) sinusoidal fluctuations (laboratory applications), ii) elevated fluctuations, and iii) heatwaves as extreme events. The use of replaceable heating elements and low-cost materials suitable for field studies creates a high flexibility for researchers who may conduct in- or out-door, small- or large-scale, fresh- or salt-water experiments at different geographical locations.

Thermal plasticity and sensitivity to insecticides in populations of an invasive beetle: Cyfluthrin increases vulnerability to extreme temperature

Climate change increases average temperatures and the occurrence of extreme weather events, in turn accentuating the risk of organism exposure to temperature stress. When thermal conditions become stressful, the sensitivity of insects toward insecticides can be exacerbated. Likewise, exposure of insects to insecticides can subsequently influence their ability to handle stressful temperatures. Here, we investigated the effects of constant temperature and daily heat spikes, in presence/absence of insecticide treatment (cyfluthrin), on the condition (impairment of mobility) and thermal tolerance to cold (-6 °C) and heat (42.5 °C) of the terrestrial beetle Alphitobius diaperinus. The responses of insects from four populations (three farm-collected populations, one laboratory population) to different durations of extreme temperature exposure were compared. The results showed that the laboratory population was generally more sensitive to extreme cold and heat temperatures, with less than 50% of adults recovering after an exposure at -6 or +42.5 °C for 3h. Significant differences in the level of thermal tolerance were also found among insects from poultry farms. Cyfluthrin exposure incurred detrimental effects to insects' condition in all but one population. For two out of the four populations, mobility impairment was increased when adults were exposed to daily heat spikes (6 h per day at 38 °C) and cyfluthrin simultaneously, compared to cyfluthrin exposure at constant temperatures; yet, no significant interaction between the two stressors was found. Finally, using one farm collected population, effects of pre-exposure to cyfluthrin on extreme temperature tolerance provided another example of the toxicant-induced climate sensitivity in insects.

Higher mean and fluctuating temperatures jointly determine the impact of the pesticide chlorpyrifos on the growth rate and leaf consumption of a freshwater isopod

There is growing evidence that both increases in mean temperature and the widespread daily temperature fluctuations (DTF) may increase pesticide toxicity. Nevertheless, the likely more stressful, realistic combination of the two warming-related stressors has rarely been considered in ecotoxicology. Moreover, we have little knowledge on whether these stressor combinations could impair ecosystem functioning. We examined the effect of the pesticide chlorpyrifos under an increased mean temperature (+4 °C, from 18 °C to 22 °C) and in the presence of DTF (constant and 8 °C) on two life-history traits (mortality and growth rate) and one ecologically important behavioural trait (feeding rate) in the freshwater isopod Asellus aquaticus. The chlorpyrifos concentration used, 0.2 μg/L, did not cause mortality in any thermal condition, nor did it cause sublethal effects at the mean temperature of 18 °C. A key finding was that growth rate was strongly reduced by the pesticide only under the combination of both a higher mean temperature and DTF, highlighting the importance of testing toxicity under this realistic thermal scenario. The leaf consumption of chlorpyrifos-exposed isopods increased at the higher mean temperature when this was kept constant, however, it lowered again towards control levels when DTF was induced, thereby contributing to the growth reduction at this most stressful condition. These alterations of growth and leaf degradation rates may impact nutrient recycling, a key ecosystem function. Our results highlight the importance of integrating both increases in mean temperature and in DTF to improve current and future ecological risk assessment of pesticides.

A Review of Biological Monitoring of Aquatic Ecosystems Approaches: with Special Reference to Macroinvertebrates and Pesticide Pollution

Biological monitoring is the evaluating changes in the environment using the biological responses with the intent of using such information in quality control of the ecosystem. Biomarkers and bioindicators are two main components of the hierarchy of biomonitoring process. Bioindicators can be used to monitor changes of ecosystems and to distinguish alteration of human impact from natural variability. There is a wide range of aquatic taxa such as macroinvertebrates, fish and periphyton, planktons which are successfully used in the biomonitoring process. Among them, macroinvertebrates are an important group of aquatic organisms that involves transferring energy and material through the trophic levels of the aquatic food chain and their sensitivity to environmental changes differs among the species. The main approaches of assessing freshwater ecosystems health using macroinvertebrates include measurement of diversity indices, biotic indices, multimetric approaches, multivariate approaches, Indices of Biological Integrity (IBI), and trait-based approaches. Among these, biotic indices and multimetric approaches are commonly used to evaluate the pesticide impacts on aquatic systems. Recently developed trait-based approaches such as SPEcies At Risk of pesticides (SPEAR) index was successfully applied in temperate regions to monitor the events of pesticide pollution of aquatic ecosystems but with limited use in tropics. This paper reviews the literature on different approaches of biomonitoring of the aquatic environment giving special reference to macroinvertebrates. It also reviews the literature on how biomonitoring could be used to monitor pesticide pollution of the aquatic environment. Thus the review aims to instil the importance of current approaches of biomonitoring for the conservation and management of aquatic ecosystems especially in the regions of the world where such knowledge has not been integrated in ecosystem conservation approaches.

Daily temperature variation lowers the lethal and sublethal impact of a pesticide pulse due to a higher degradation rate

Daily temperature variation (DTV) is an important warming-related stressor that may magnify pesticide toxicity. Yet, it is unknown whether the pesticide impact under DTV is partly ameliorated by a faster pesticide degradation caused by cyclically higher temperatures under DTV. As synergisms may be more likely under energy-limiting conditions, the impact of the pesticide chlorpyrifos was tested under DTV on the mosquito Culex pipiens in the absence and presence of interspecific competition with the water flea Daphnia magna. Chlorpyrifos exposure at a constant temperature without interspecific competition caused considerable mortality, decreased development time, and increased pupal mass of C. pipiens. Competition with D. magna had negative sublethal effects, but it did not affect the toxicity of chlorpyrifos. In contrast, the presence of C. pipiens decreased the impact of chlorpyrifos on D. magna probably due to corporal absorption of chlorpyrifos by C. pipiens. A key finding was that chlorpyrifos no longer caused lethal effects on C. pipiens under DTV, despite DTV on its own being mildly lethal. Additionally, chlorpyrifos exposure under DTV decreased development time less and had no effect anymore on pupal mass compared to chlorpyrifos exposure at a constant temperature. Similarly, the negative chlorpyrifos impact on adult survival of D. magna was less under DTV than at the constant temperature. This could be explained by a faster chlorpyrifos degradation under DTV. This antagonism between pesticide exposure and DTV is likely widespread because organisms experience DTV, many pesticides are applied in pulses, and pesticide degradation is faster at higher temperatures.

Acute and chronic toxicity of 2,4-D and fipronil formulations (individually and in mixture) to the Neotropical cladoceran Ceriodaphnia silvestrii

Brazil is the largest producer of sugarcane and the world's top pesticide market. Therefore, environmental consequences are of concern. The aim of the present study was to evaluate the acute and chronic toxicity of pesticide formulations largely used in sugarcane crops: the herbicide DMA® 806 BR (a.i. 2,4-D) and the insecticide Regent® 800 WG (a.i. fipronil), isolated and in mixture, to the Neotropical cladoceran Ceriodaphnia silvestrii. Toxicity tests with the individual formulated products indicated 48h-EC₅₀ values of 169 ± 18 mg a.i./L for 2,4-D and 3.9 ± 0.50 µg a.i./L for fipronil. In the chronic tests, the 8d-EC₅₀ values for reproduction were 55 mg a.i./L (NOEC/LOEC: 50/60 mg a.i./L) and 1.6 µg a.i./L (NOEC/LOEC: 0.40/0.80 µg a.i./L) for 2,4-D and fipronil, respectively. A significant decrease in reproduction of C. silvestrii in all concentrations tested of fipronil, except at the lowest, was observed. Regarding 2,4-D, the organisms had total inhibition of reproduction in the two highest concentrations. Probably your energy reallocation was focused (trade-off) only on its survival. The acute pesticide mixture toxicity (immobility) revealed a dose level dependent deviation with antagonism at low and synergism at high concentrations. For chronic mixture (reproduction) toxicity, antagonism occurred as a result of the interaction of the pesticides. Based on our results and concentrations measured in Brazilian water bodies, fipronil represents ecological risks for causing direct toxic effects on C. silvestrii. These results are worrisome given that agricultural production is likely to increase in the coming years.

Negative bioenergetic responses to pesticides in damselfly larvae are more likely when it is hotter and when temperatures fluctuate

To make more realistic predictions about the current and future effects of pesticides, we need to better understand physiological mechanisms associated with the widespread higher toxicity of many pesticides under increasing mean temperatures and daily temperature fluctuations (DTFs). One overlooked, yet insightful, mechanism are bioenergetic responses as these provide information about the balance between energy gains and costs. Therefore, we studied how the bioenergetic responses to the insecticide chlorpyrifos were affected by a higher mean temperature and a higher DTF in Ischnura elegans damselfly larvae. To quantify bioenergetic responses we measured energy availability (Ea), energy consumption (Ec) and total net energy budget (cellular energy allocation, CEA). Exposure to chlorpyrifos considerably reduced CEA values when a high mean temperature was combined with a high DTF (up to -18%). Notably, chlorpyrifos had little effect on CEA at a constant 20 °C, meaning that the bioenergetic impact of chlorpyrifos would have been underestimated if we had only tested under standard testing conditions. The chlorpyrifos-induced reductions in CEA under warming were driven by reductions in Ea (up to -16%, mainly through large reductions in sugar and fat contents) while Ec was unaffected by chlorpyrifos. Treatment groups with a lower CEA value showed a higher mortality and a lower growth rate, indicating bioenergetic responses are contributing to the higher toxicity of chlorpyrifos under warming. Our study highlights the importance of evaluating the effects of pesticides under an increase in both mean temperature and DTF to improve the ecological risk assessment of pesticides under global warming.

Temperature variation magnifies chlorpyrifos toxicity differently between larval and adult mosquitoes

To improve risk assessment there is increasing attention for the effect of climate change on the sensitivity to contaminants and vice versa. Two important and connected topics have been largely ignored in this context: (i) the increase of daily temperature variation (DTV) as a key component of climate change, and (ii) differences in sensitivity to climate change and contaminants between developmental stages. We therefore investigated whether DTV magnified the negative effects of the organophosphate insecticide chlorpyrifos on mortality and heat tolerance and whether this effect was stronger in aquatic larvae than in terrestrial adults of the mosquito Culex pipiens. Exposure to chlorpyrifos at a constant temperature imposed mortality and reduced the heat tolerance in both larvae and adult males, but not in adult females. This provides the first evidence that the TICS ("toxicant-induced climate change sensitivity") concept can be sex-specific. DTV had no direct negative effects. Yet, consistent with the CITS ("climate-induced toxicant sensitivity") concept, DTV magnified the toxicity of the pesticide in terms of larval mortality. This was not the case in the adult stage indicating the CITS concept to be dependent on the developmental stage. Notably, chlorpyrifos reduced the heat tolerance of adult females only in the presence of DTV, thereby providing support for the reciprocal effects between DTV and contaminants, hence the coupling of the TICS and CITS concepts. Taken together, our results highlight the importance of integrating DTV and the developmental stage to improve risk assessment of contaminants under climate change.

Effects of insecticides, fipronil and imidacloprid, on the growth, survival, and behavior of brown shrimp Farfantepenaeus aztecus

Increased use of pesticide is causing detrimental effects on non-target species worldwide. In this study, we examined the lethal and sub-lethal effects of fipronil and imidacloprid, two commonly used insecticides, on juvenile brown shrimp (Farfantepenaeus aztecus), one of the most commercially and ecologically important species in the United States. The effects of six concentrations of fipronil (0.0, 0.005, 0.01, 0.1, 1.0, and 3.0 μg/L) and six concentrations of imidacloprid (0.0, 0.5, 1.0, 15.0, 34.5, 320.0 μg/L) were tested in a laboratory. We examined five different endpoints: growth, moulting interval, survivorship, behavioral change, and body color change. Growth of shrimp was reduced significantly under higher concentrations of both insecticides. Under fipronil exposure, shrimp in control showed the shortest inter-moult interval (7.57 ± 2.17 day) compared with other treatments; similarly, in the imidacloprid experiment, moulting increased from 8.43 ± 2.52 day in control to 11.95 ± 4.9 day in 0.5 μg/L treatment. Higher concentrations of fipronil (1.0 and 3.0 μg/L) showed a 0.0% survival rate compared with 100% survival in the control and 0.005 μg/L treatment. Under imidacloprid, survivorship decreased from 100% in the control to 33.33% in the 320.0 μg/L treatment. The 96-h LC50 of fipronil was 0.12 μg/L, which makes brown shrimp one of the most sensitive invertebrates to the pesticide. Changes in behavior and body color were observed under both insecticides after different durations of exposures depending on concentrations. We conclude that, at the corresponding EPA benchmark concentrations, fipronil had more lethal effects than imidacloprid, and imidacloprid had more sub-lethal effects than fipronil. Both effects are of serious concern, and we suggest monitoring is necessary in estuaries.

Shrinking Body Size and Physiology Contribute to Geographic Variation and the Higher Toxicity of Pesticides in a Warming World

To improve current and future risk assessment of pesticides under global warming, mechanistic insights and consideration of daily temperature fluctuations (DTFs) are needed. One overlooked mechanism how both higher mean temperatures and DTFs may increase toxicity is by reducing body size (temperature-size-rule). We studied whether a higher mean temperature and DTF magnified chlorpyrifos toxicity in Ischnura elegans damselfly larvae, and whether this was mediated by temperature-induced reductions in body size and/or physiological changes. The lethal effects of chlorpyrifos were magnified at the high mean temperature (up to ∼15%) and under DTF (up to ∼33%), and especially at their combination (up to ∼46%) indicating synergisms. This highlights that not only considering DTFs, but also their interaction with higher mean temperatures is pivotal for realistic predictions of pesticide toxicity. Both higher temperatures and DTFs resulted in smaller larvae, which were more sensitive to chlorpyrifos. Notably, the DTF-induced smaller body sizes, as well as the higher oxidative damage to lipids, contributed to the higher chlorpyrifos toxicity under DTF. By integrating the temperature-size rule and size-pesticide sensitivity pattern we provide proof-of-principle for a novel, likely general mechanism contributing to geographic variation and the higher toxicity of pesticides in a warming world.

Current and future daily temperature fluctuations make a pesticide more toxic: Contrasting effects on life history and physiology

There is increasing concern that climate change may make organisms more sensitive to chemical pollution. Many pesticides are indeed more toxic at higher mean temperatures. Yet, we know next to nothing about the effect of another key component of climate change, the increase of daily temperature fluctuations (DTFs), on pesticide toxicity. Therefore, we tested the effect of the pesticide chlorpyrifos under different levels of DTF (constant = 0 °C, low = 5 °C (current maximum level) and high = 10 °C (predicted maximum level under global warming)) around the same mean temperature on key life history and physiological traits of Ischnura elegans damselfly larvae in a common-garden experiment. At all levels of DTF, chlorpyrifos exposure was stressful: it reduced energy storage (fat content) and the activity of its target enzyme acetylcholinesterase, while it increased the activity of the detoxification enzyme cytochrome P450 monooxygenase. Notably, chlorpyrifos did not cause mortality or reduced growth rate at the constant temperature (0 °C DTF), yet increased mortality 6x and reduced growth rate with ca. 115% in the presence of DTF. This indicates that daily short-term exposures to higher temperatures can increase pesticide toxicity. Our data suggest that when 5 °C DTF will become more common in the studied high-latitude populations, this will increase the toxicity of CPF, and that a further increase from 5° DTF to 10 °C DTF may not result in a further increase of pesticide toxicity. Our results highlight the biological importance of including daily temperature fluctuations in ecological risk assessment of pesticides and as an extra dimension in the climate-induced toxicant sensitivity concept.

Increased Daily Temperature Fluctuations Overrule the Ability of Gradual Thermal Evolution to Offset the Increased Pesticide Toxicity under Global Warming

The widespread evidence that global warming can increase species sensitivities to chemical toxicants, and vice versa, and the recent insight that thermal evolution may mitigate these effects is crucial to predict the future impact of toxicants in a warming world. Nevertheless, a major component of global warming, the predicted increase in daily temperature fluctuations (DTFs), has been ignored at the interface of evolutionary ecotoxicology and global change biology. We studied whether 4 °C warming and a 5 °C DTF increase (to 10 °C DTF) magnified the negative impact of the insecticide chlorpyrifos (CPF) in larvae of low- and high-latitude populations of the damselfly Ischnura elegans. While 4 °C warming only increased CPF-induced mortality in high-latitude larvae, the high (10 °C) DTF increased CPF-induced larval mortality at both latitudes. CPF reduced the heat tolerance; however, this was buffered by latitude-specific thermal adaptation to both mean temperature and DTF. Integrating our results in a space-for-time substitution indicated that gradual thermal evolution in high-latitude larvae may offset the negative effects of CPF on heat tolerance under warming, unless the expected DTF increase is taken into account. Our results highlight the crucial importance of jointly integrating DTFs and thermal evolution to improve risk assessment of toxicants under global warming.

Daily temperature variation magnifies the toxicity of a mixture consisting of a chemical pesticide and a biopesticide in a vector mosquito

While many studies on the toxicity of pesticides looked at the effects of a higher mean temperature, effects of the realistic scenario of daily temperature variation are understudied. Moreover, despite the increasing interest for the toxicity of pesticide mixtures how this is influenced by temperature has been largely ignored. We tested whether daily temperature variation (DTV) magnifies the toxicity of two pesticides with a different mode of action, the organophosphate pesticide chlorpyrifos (CPF) and the biopesticide Bacillus thuringiensis var. israelensis (Bti), and of their mixture in the vector mosquito Culex pipiens. Single exposure to CPF and Bti increased mortality and reduced female development time, and exposure to CPF also increased female wing length. DTV was not lethal and did not change the toxicity of the individual pesticides. Yet, a key novel finding was that high DTV increased the mortality of the mixture by changing the interaction between both pesticides from additive to synergistic. Given that in nature daily temperature variation is omnipresent, this is important both for vector control and for ecological risk assessment. The higher toxicity of the mixture at high DTV compared to the typically used constant test temperatures in the laboratory urges caution when evaluating the environmental impact of pesticide mixtures.

Day/night temperature differences (DNTD) trigger changes in nutrient removal and functional bacteria in membrane bioreactors

Temperature is a well-known environmental stress that influences both microbial metabolism and community structure in the biological wastewater treatment systems. In this study, responses of biological performance and sludge microbiota to the long-term day/night temperature differences (DNTD) were investigated in membrane bioreactors (MBRs). The results showed that the functional bacteria could sustained their ecological functions at low DNTD (20/30 °C), resulting in relatively stable performance with respect to nutrient removal. However, when the activated sludge was subjected to a high DNTD (17/33 °C), the effluent concentrations of COD, TN and TP were significantly higher in MBR-B than that in MBR-A. In addition, more severe membrane fouling occurred under the perturbation of high DNTD as revealed by the transmembrane pressure (TMP) profile, which was mainly attributed to the accumulation of extracellular polymeric substances (EPS). The results of 16S rRNA gene sequencing showed that DNTD showed negligible effect on the bacterial community structures. Nonetheless, the functional bacteria responded differently to DNTD, which were in accordance with the bioreactor performances. Specifically, Nitrospina (NOB) and Tetrasphaera (PAOs) appeared to be sensitive to both low and high DNTD. In contrast, a low DNTD showed marginal effects on the denitrifiers, while a high DNTD significantly decreased their abundances. More strikingly, filamentous bulking bacteria were found to be well-adapted to DNTD, indicating their tolerance to the daily temperature fluctuation. This study will advance our knowledge regarding the response of microbial ecology of activated sludge to daily temperature variations in full-scale MBRs.

Contaminant exposure effects in a changing climate: how multiple stressors can multiply exposure effects in the amphipod Hyalella azteca

Global climate change (GCC) is likely to intensify the synergistic effects between altered physicochemical parameters [of changing habitats] and other anthropogenic threats, such as water pollution, posing increased risks to aquatic biodiversity. As such, it is critical to understand how organisms will respond to changes in water temperature and salinity in the presence of contaminants. We exposed the epibenthic amphipod Hyalella azteca to a 3 × 3 factorial treatment design of three temperatures and three salinities ranging from 12 to 18 °C and 0 to 8 parts per thousand (ppt), respectively, in combination with a low-level environmentally relevant concentration of the pyrethroid insecticide bifenthrin (1 ng/L). Effects on survival and swimming behavior were evaluated after 96 h exposure. Transcription of a select suite of genes was monitored at 24, 48, and 96 h using quantitative polymerase chain reaction (qPCR). Our results not only demonstrate that the changes in salinity and temperature result in negative effects to invertebrate survival, behavior, and gene response, but that the effects were significantly more pronounced in the presence of bifenthrin. This is particularly important since greater thermal fluctuations, changes in timing and extent of glacial melt, and changes in precipitation, could result in H. azteca experiencing lower temperatures at times that coincide with increased spraying of pyrethroids. These environmentally relevant exposures using the standard test species H. azteca provide essential information for understanding effects caused by GCC in conjunction with increasing pesticide use, further highlighting the need to incorporate GCC impacts into risk assessments of contaminants of concern.

Strong differences between two congeneric species in sensitivity to pesticides in a warming world

To predict the impact of pesticides in a warming world we need to know how species differ in the interaction pathways between pesticides and warming. Trait-based approaches have been successful in identifying the 'pace of life' and body size as predictors of sensitivity to pesticides among distantly related species. However, it remains to be tested whether these traits allow predicting differences in sensitivity to pesticides between closely related species, and in the strength of the interaction pathways between pesticides and warming. We tested the effects of multiple pulses of chlorpyrifos (allowing accumulation) under warming on key life history traits, heat tolerance (CTmax) and physiology of two congeneric damselfly species: the fast-paced (fast growth and development, high metabolic rate), small Ischnura pumilio and the slow-paced, large I. elegans. Chlorpyrifos reduced survival and growth, but contrary to current trait-based predictions I. pumilio was 8× less sensitive than I. elegans. The lower sensitivity of I. pumilio could be explained by a higher fat content, and higher activities of acetylcholinesterase and of detoxifying and anti-oxidant enzymes. While for I. pumilio the effect of chlorpyrifos was small and did not depend on temperature, for I. elegans the impact was higher at 20°C compared to 24°C. This matches the higher pesticide accumulation in the water after multiple pulses at 20°C than at 24°C. The expected reduction in heat tolerance after pesticide exposure was present in I. elegans but not in I. pumilio. Our results demonstrate that closely related species can have very different sensitivities to a pesticide resulting in species-specific support for the "toxicant-induced climate change sensitivity" and the "climate-induced toxicant sensitivity" interaction pathways. Our results highlight that trait-based approaches can be strengthened by integrating physiological traits.

Sequential exposure to low levels of pesticides and temperature stress increase toxicological sensitivity of crustaceans

Frequent pesticide-related impacts on ecosystems at concentrations considered environmentally safe indicate that the current risk assessment framework for registration of pesticides is not protective enough. Causes may include difficulties in assessing the effects of sequential pesticide pulses and their interaction with environmental stressors. By contrast to such realistic scenarios, risk assessment for registration of pesticides is typically based on tests of a single exposure period under benign laboratory conditions. Here, we investigated the toxicological sensitivity of Gammarus pulex, an ecologically relevant crustacean, from uncontaminated control streams and pesticide-contaminated agricultural streams by exposing them to pesticide contamination in the laboratory. Individuals from contaminated streams were 2.7-fold more sensitive to pesticide exposure than individuals from the reference streams. We revealed that this increase in sensitivity was the result of a synergistic interaction of sequential pesticide exposure and temperature stress. Such multiple stressor scenarios are typical for agricultural streams. We conclude that the interactive effects of sequential toxicant exposure and additional environmental stressors need to be considered in a realistic risk assessment framework.

Integrated Modeling of Survival Data from Multiple Stressor Ecotoxicology Experiments

Ecotoxicological assessments often focus on the response of an organism to an individual contaminant under standardized laboratory conditions. Under more ecologically realistic conditions, however, individuals are likely to be exposed to a range of environmental conditions that have the potential to act as additional stressors. Multiple-stressor experiments improve our understanding of an organism's response to a toxicant under ecologically relevant conditions and provide realistic risk assessment data. To date, there is no standardized method for analyzing multiple-stressor data using dose-response regression. We present a reliable technique to assess for the effects of additional stressors on an LCx estimate in a consistent framework, providing interpretable results that meaningfully deal with environmental changes and their possible impacts on sensitivity estimates to a toxicant. The method is applicable to any data set where toxicity tests are conducted at varying levels of one or more additional stressors. We illustrate the method with data from an experiment that investigates the effects of salinity and temperature on the sensitivity of the subantarctic isopod Limnoria stephenseni to copper, where it is shown that the major change in the LC50 can be primarily attributed to a specific temperature increase. This method has been incorporated into an R package available at github.com/ahproctor/LC50.

Effects of two fungicide formulations on microbial and macroinvertebrate leaf decomposition under laboratory conditions

Aquatic fungi contribute significantly to the decomposition of leaves in streams, a key ecosystem service. Little is known, however, about the effects of fungicides on aquatic fungi and macroinvertebrates involved with leaf decomposition. Red maple (Acer rubrum) leaves were conditioned in a stream to acquire microbes (bacteria and fungi) or leached in tap water (unconditioned) to simulate potential reduction of microbial biomass by fungicides. Conditioned leaves were exposed to fungicide formulations QUILT (azoxystrobin + propiconazole) or PRISTINE (boscalid + pyraclostrobin) in the presence and absence of the leaf shredder, Hyalella azteca (amphipods; 7-d old at start of exposures) for 14 d at 23 °C. The QUILT formulations (∼0.3 μg/L, 1.8 μg/L, and 8 μg/L) tended to increase leaf decomposition by amphipods (not significant) without a concomitant increase in amphipod biomass, indicating potential increased consumption of leaves with reduced nutritional value. The PRISTINE formulation (∼33 μg/L) significantly reduced amphipod growth and biomass (p < 0.05), effects similar to those observed with unconditioned controls. The significant suppressive effects of PRISTINE on amphipod growth and the trend toward increased leaf decomposition with increasing QUILT concentration indicate the potential for altered leaf decay in streams exposed to fungicides. Further work is needed to evaluate fungicide effects on leaf decomposition under conditions relevant to stream ecosystems, including temperature shifts and pulsed exposures to pesticide mixtures. Environ Toxicol Chem 2016;35:2834-2844. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Direct and indirect toxicity of the fungicide pyraclostrobin to Hyalella azteca and effects on leaf processing under realistic daily temperature regimes

Fungicides in aquatic environments can impact non-target bacterial and fungal communities and the invertebrate detritivores responsible for the decomposition of allochthonous organic matter. Additionally, in some aquatic systems daily water temperature fluctuations may influence these processes and alter contaminant toxicity, but such temperature fluctuations are rarely examined in conjunction with contaminants. In this study, the shredding amphipod Hyalella azteca was exposed to the fungicide pyraclostrobin in three experiments. Endpoints included mortality, organism growth, and leaf processing. One experiment was conducted at a constant temperature (23 °C), a fluctuating temperature regime (18-25 °C) based on field-collected data from the S. Llano River, Texas, or an adjusted fluctuating temperature regime (20-26 °C) based on possible climate change predictions. Pyraclostrobin significantly reduced leaf shredding and increased H. azteca mortality at concentrations of 40 μg/L or greater at a constant 23 °C and decreased leaf shredding at concentrations of 15 μg/L or greater in the fluctuating temperatures. There was a significant interaction between temperature treatment and pyraclostrobin concentration on H. azteca mortality, body length, and dry mass under direct aqueous exposure conditions. In an indirect exposure scenario in which only leaf material was exposed to pyraclostrobin, H. azteca did not preferentially feed on or avoid treated leaf disks compared to controls. This study describes the influence of realistic temperature variation on fungicide toxicity to shredding invertebrates, which is important for understanding how future alterations in daily temperature regimes due to climate change may influence the assessment of ecological risk of contaminants in aquatic ecosystems.

Feeding response in marine copepods as a measure of acute toxicity of four anti-sea lice pesticides

Anti-sea lice pesticides used in salmon aquaculture are released directly into the environment where non-target organisms, including zooplankton, may be exposed. The toxicity of four pesticides to field-collected copepods was examined in 1-h exposures with lethality and feeding endpoints determined 5-h post-exposure using staining techniques. Copepods were immobilized within 1 h, at aquaculture treatment concentrations of deltamethrin (AlphaMax), cypermethrin (Excis), and hydrogen peroxide (InteroxParamove50). All organisms showed vital staining, indicating immobilized organisms were still alive, thus LC50s were not determined. Feeding on carmine particles was inhibited and EC50s ranged from 0.017 to 0.067 μg deltamethrin/L, 0.098-0.36 μg cypermethrin/L, and 2.6-10 mg hydrogen peroxide/L, representing 30- to 117-fold, 13- to 51-fold, and 120- to 460-fold dilutions of the respective aquaculture treatments. No effects were observed in copepods exposed to azamethiphos (Salmosan) at 5-times the aquaculture treatment. Acute exposure to three of the four pesticides affected feeding and mobility of copepods at environmentally-realistic concentrations.

Identification of the first neuropeptides from the Amphipoda (Arthropoda, Crustacea)

Despite being used as models in the field of ecotoxicology, including use in studies of endocrine disruption, little is known about the hormonal systems of amphipods, particularly their peptidergic signaling systems. Here, transcriptome shotgun assembly (TSA) sequences were used to predict the structures of the first neuropeptides from members of this crustacean order. Using a well-established workflow, BLAST searches of the extant amphipod TSA data were conducted for putative peptide-encoding transcripts. The pre/preprohormones deduced from the identified TSA sequences were then used to predict the mature structures of amphipod neuropeptides. In total, 43 putative peptide-encoding transcripts were identified from three amphipods, Echinogammarus veneris, Hyalella azteca and Melita plumulosa. Collectively, 139 distinct mature peptides (110 from E. veneris alone) were predicted from these TSA sequences. The identified peptides included members of the adipokinetic hormone/red pigment concentrating hormone, allatostatin A, allatostatin B, allatostatin C, bursicon α, bursicon β, crustacean hyperglycemic hormone, diuretic hormone 31, FLRFamide, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone (PDH), proctolin, RYamide, SIFamide, sulfakinin and tachykinin-related peptide families. Of particular note were the identifications of orcokinins possessing SFDEIDR- rather than the typical NFDEIDR- amino-termini, e.g. SFDEINRSNFGFN, a carboxyl-terminally amidated orcokinin, i.e. SFDEINRSNFGFSamide, PDHs longer than the stereotypical 18 amino acids, e.g. NSELLNTLLGSKSLAALRAAamide, and a 13 rather than 12 amino acid long SIFamide, i.e. GPYRKPPFNGSIFamide. These data not only provide the first descriptions of native amphipod neuropeptides, but also represent a new resource for initiating investigations of peptidergic signaling in the Amphipoda.

Nocturnal river water temperatures: Spatial and temporal variations

Nocturnal water temperature (Tw) affects the behaviour of aquatic biota and metabolism of whole rivers. However, night-time water temperature (nTw) is poorly understood because spot samples are typically taken during daylight hours, or Tw series are aggregated in ways that mask sub-daily properties. This paper examines 15-minute measurements of Tw and air temperature (Ta) collected at 36 sites in the Rivers Dove and Manifold, English Peak District. Data were stratified by day and night then analysed using hysteresis, auto-correlation and logistic regression techniques. Daily hysteresis loops show lagged responses between nTw and previous daylight air temperatures (dTa), plus the influence of groundwater and discharge variations. Logistic regression models were modified using a seasonal factor and explained between 80 and 94% of the variance in daily maximum nTw; minimum nTw were predicted with less skill, particularly for headwater sites in summer. Downstream variations in model parameters also reflect the influence of groundwater and/or riparian shade, and prevailing weather conditions. A case is presented where an intense summer storm resulted in the propagation of a thermal wave that produced maximum Tw at some sites during hours of darkness. Hence, our findings show that Tw management by riparian shade has to be seen in a catchment wide context, with anticipated benefits normalised for weather variability, extreme rainfall events, local influence of groundwater, and channel structures.