Sub-organism (acetylcholinesterase activity), population (survival) and chemical concentration responses reinforce mechanisms of antagonism associated with malathion toxicity

Macroinvertebrate community and leaf litter breakdown measures lack concordance associated with singular or multiple stressors

Freshwater ecosystems are being degraded by a wide range of stressors resulting from human activities. Various structural and functional metrics or indices are used to assess the 'health' or condition of riverine ecosystems. It is uncertain if structural or functional metrics or indices respond to different stressors and whether some are more responsive to stressors in general. Here we conducted a multi-study synthesis, similar to a meta-analysis, across four independent outdoor mesocosm experiments involving the manipulation of various chemical stressors - two types of salinity (synthetic marine salts (SMS) and sodium bicarbonate), two insecticides (malathion and sulfoxaflor), increased nutrients (N and P), increased sedimentation and two combinations of stressors (1: malathion, nutrients and sedimentation, 2: sulfoxaflor, nutrients and sedimentation). We compare the effects of these singular or multiple stressors on stream macroinvertebrate community structure, and Eucalyptus camaldulensis leaf litter breakdown rates by microbes and total (microbes and invertebrates). Macroinvertebrate communities were adversely affected by the two sets of multiple stressors, SMS, and both insecticides yet, and in contrast to several published studies, both microbial and total leaf litter was unaffected. Nutrients and sodium bicarbonate, increased breakdown rates or had a unimodal 'Ո' shaped response, with maxima at intermediate levels. Sedimentation by fine sand, however, decreased total leaf litter breakdown, while not affecting microbial leaf litter breakdown. Divergent responses between the effects of stressors on leaf litter breakdown rates that we observed and those in the literature may be caused by multiple mechanisms, including differences between communities, functional redundancy and differences in stressor magnitude and interactions with other (unknown) variables.

Predicting the Combined Effects of Multiple Stressors and Stress Adaptation in Gammarus pulex

Global change confronts organisms with multiple stressors causing nonadditive effects. Persistent stress, however, leads to adaptation and related trade-offs. The question arises: How can the resulting effects of these contradictory processes be predicted? Here we show that Gammarus pulex from agricultural streams were more tolerant to clothianidin (mean EC50 148 μg/L) than populations from reference streams (mean EC50 67 μg/L). We assume that this increased tolerance results from a combination of physiological acclimation, epigenetic effects, and genetic evolution, termed as adaptation. Further, joint exposure to pesticide mixture and temperature stress led to synergistic interactions of all three stressors. However, these combined effects were significantly stronger in adapted populations as shown by the model deviation ratio (MDR) of 4, compared to reference populations (MDR = 2.7). The pesticide adaptation reduced the General-Stress capacity of adapted individuals, and the related trade-off process increased vulnerability to combined stress. Overall, synergistic interactions were stronger with increasing total stress and could be well predicted by the stress addition model (SAM). In contrast, traditional models such as concentration addition (CA) and effect addition (EA) substantially underestimated the combined effects. We conclude that several, even very disparate stress factors, including population adaptations to stress, can act synergistically. The strong synergistic potential underscores the critical importance of correctly predicting multiple stresses for risk assessment.

Combined metabolomics and proteomics to reveal the mechanism of S. oneidensis MR-1 degradation malathion enhanced by FeO/C

Iron oxide @ biochar (FeO/C) promotes bacterial growth and facilitates electron transfer, thereby effectively promoting malathion degradation by Shewanella oneidensis MR-1 (S. oneidensis MR-1). This study elucidated the underlying mechanism of FeO/C-enhanced malathion degradation by S. oneidensis MR-1 through a combination of metabolomics and proteomics analysis. The kinetic fitting results from the degradation experiment indicated that 0.1 g/L FeO/C exerted the most significant enhancement effect on malathion degradation by S. oneidensis MR-1. Observations from Scanning Electron Microscopy and Laser Scanning Confocal Microscopy, along with physiological and biochemical analysis, showed that FeO/C enhanced the growth and oxidative response of S. oneidensis MR-1 under malathion stress. In addition, metabolomics and proteomics analysis revealed an increase in certain electron transfer related metabolites, such as coenzymes, and the upregulation of proteins, including coenzyme A, sdhD, and petC. Overall, spectroscopic analysis suggested that Fe2+, which was reduced from Fe3+ by S. oneidensis MR-1 in FeO/C, promoted electron transfer in S. oneidensis MR-1 to enhance the degradation of malathion. This study offers enhanced strategies for efficient removal of malathion contaminants.

Overexpression of an Integument Esterase Gene LbEST-inte4 Infers the Malathion Detoxification in Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Liposcelis bostrychophila, commonly known as booklouse, is an important stored-product pest worldwide. Studies have demonstrated that booklices have developed resistance to several insecticides. In this study, an integument esterase gene, LbEST-inte4, with upregulated expression, was characterized in L. bostrychophila. Knockdown of LbEST-inte4 resulted in a substantial increase in the booklice susceptibility to malathion. Overexpression of LbEST-inte4 in Drosophila melanogaster significantly enhanced its malathion tolerance. Molecular modeling and docking analysis suggested potential interactions between LbEST-inte4 and malathion. When overexpressed LbEST-inte4 in Sf9 cells, a notable elevation in esterase activity and malathion tolerance was observed. HPLC analysis indicated that the LbEST-inte4 enzyme could effectively degrade malathion. Taken together, the upregulated LbEST-inte4 appears to contribute to malathion tolerance in L. bostrychophila by facilitating the depletion of malathion. This study elucidates the molecular mechanism underlying malathion detoxification and provides the foundations for the development of effective prevention and control measures against psocids.

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.

Short-term insecticide exposure amid co-occurring stressors reduces diversity and densities in north-east Indian experimental aquatic invertebrate communities

Globally, river pesticide concentrations are associated with regional and local stream invertebrate diversity declines. Pesticides often co-occur with elevated nutrients (e.g. nitrogen and phosphorus) and sediments related to agriculture, making their individual effects difficult to disentangle. These effects are also less well studied in Asia, than in other geographic regions. Within Asia, India is one of the largest producers and users of pesticides and has approximately 60% of total land mass used for agriculture. Here we examine the responses of Indian river invertebrate communities subjected to malathion, nutrients, and sediment additions in a semi-orthogonal design, in three sequential (through time) short-term (120 h) mesocosm experiments. Additionally, a series of single-species toxicity tests were run that used 24 h exposure and 72 h recovery to examine the sensitivity of 13 local invertebrate taxa to malathion, and 9 taxa to cypermethrin, comparing these results to those from other biogeographic regions. Mesocosm results indicate that malathion exposure had a major effect compared to other stressors on communities, with a lesser effect of nutrients and/or sediments. In mesocosms, taxa richness, total abundance and the abundance of sensitive species all declined associated with malathion concentrations. Comparisons of organism sensitivities from other geographic locations and those in the current paper suggest taxa in India are relatively tolerant to malathion and cypermethrin. Our results further reinforce that the high observed aquatic pesticide concentrations known to occur in Asian freshwater ecosystems are likely to be negatively affecting biodiversity, homogenising biota towards those most stress tolerant.

A global systematic review of the concentrations of Malathion in water matrices: Meta-analysis, and probabilistic risk assessment

Pesticide applications and the proximity of land use to water matrices have resulted in discharges of pollutants including Malathion -one of the most widely used organophosphorus pesticides- to water resources such as marine, freshwater, and under groundwater. Exposure to malathion through consumption of contaminated water may cause deleterious health effects on consumers. Determining the amount of pesticides used on farms can play an important role in preventing potential toxicity and pollution of nearby aquatic ecosystems. Therefore, this systematic review and meta-analysis is focused on evaluating the concentrations of Malathion in water resources while considering probabilistic health risk assessment. The international databases of Scopus, Embase, and PubMed were investigated to evaluate the related articles from January 01, 1968 to March 25, 2021. Thirty-four articles containing 206 samples from 15 countries were included. A meta-analysis of carcinogenic and non-carcinogenic risk assessments for Malathion was also performed. To determine uncertainty intervals, a Monte-Carlo simulation was conducted. The results of the meta-analysis showed that the rankings of Malathion pollution (from the most to the least) were: drinking water > surface waters > groundwaters. Moreover, the results of the risk assessments confirm that there is no non-carcinogenic risk for any of the study areas. The carcinogenic risk assessment was within the limit for the countries under this study, except for Ethiopia that was slightly over the limit as well as Iran, and Mexico had high carcinogenic risk.

Assessing the Relative Toxicity of Different Road Salts and Effect of Temperature on Salinity Toxicity: LCx Values versus No-Effect Concentration (NEC) Values

Freshwater biota are at risk globally from increasing salinity, including increases from deicing salts in cold regions. A variety of metrics of toxicity are used when estimating the toxicity of substances and comparing the toxicity between substances. However, the implications of using different metrics are not widely appreciated. Using the mayfly Colobruscoides giganteus (Ephemeroptera: Colobruscoidea), we compare the toxicity of seven different salts where toxicity was estimated using two metrics: (1) the no-effect concentrations (NEC) and (2) the lethal concentrations for 10, 25 and 50% of the test populations (LC_x). The LC_x values were estimated using two different models, the classic log-logistic model and the newer toxicokinetic-toxicodynamic (TKTD) model. The NEC and both types of LC_x values were estimated using Bayesian statistics. We also compared the toxicity of two salts (NaCl and CaCl₂) for C. giganteus at water temperatures of 4 °C, 7 °C and 15 °C using the same metrics of toxicity. Our motivation for using a mayfly to assess salinity toxicity was because mayflies are generally salt sensitive, are ecologically important and are common in Australian (sub-)alpine streams. The temperature ranges were chosen to mimic winter, spring and summer water temperatures for Australian (sub-)alpine streams. Considering 144-h classical LC_x values, we found toxicity differed between various salts, i.e., the lowest 144-h LC₅₀ (8 mS/cm) for a salt used by a ski resort was half that of the highest 144-h LC₅₀ from artificial marine salts and CaCl₂ applied to roads (16 mS/cm). The analytical grade NaCl (as shown by 144-h LC₅₀ value at 7 °C) was substantially more toxic (7.3 mS/cm) compared to analytical grade CaCl₂ (12.5 mS/cm). Yet for NEC values, there were comparably fewer differences in toxicity between salts and none between the same salts at different temperatures. We conclude that LC_x values are better suited to compare the difference in toxicity between substances or between the same substance at different test temperatures, while NEC values are better suited to estimating concentrations of substances that have no effect to the test species and endpoint measured under laboratory conditions.

Assessing the Relative Toxicity of Different Road Salts and Effect of Temperature on Salinity Toxicity: LCx Values versus No-Effect Concentration (NEC) Values

Freshwater biota are at risk globally from increasing salinity, including increases from deicing salts in cold regions. A variety of metrics of toxicity are used when estimating the toxicity of substances and comparing the toxicity between substances. However, the implications of using different metrics are not widely appreciated. Using the mayfly Colobruscoides giganteus (Ephemeroptera: Colobruscoidea), we compare the toxicity of seven different salts where toxicity was estimated using two metrics: (1) the no-effect concentrations (NEC) and (2) the lethal concentrations for 10, 25 and 50% of the test populations (LC_x). The LC_x values were estimated using two different models, the classic log-logistic model and the newer toxicokinetic-toxicodynamic (TKTD) model. The NEC and both types of LC_x values were estimated using Bayesian statistics. We also compared the toxicity of two salts (NaCl and CaCl₂) for C. giganteus at water temperatures of 4 °C, 7 °C and 15 °C using the same metrics of toxicity. Our motivation for using a mayfly to assess salinity toxicity was because mayflies are generally salt sensitive, are ecologically important and are common in Australian (sub-)alpine streams. The temperature ranges were chosen to mimic winter, spring and summer water temperatures for Australian (sub-)alpine streams. Considering 144-h classical LC_x values, we found toxicity differed between various salts, i.e., the lowest 144-h LC₅₀ (8 mS/cm) for a salt used by a ski resort was half that of the highest 144-h LC₅₀ from artificial marine salts and CaCl₂ applied to roads (16 mS/cm). The analytical grade NaCl (as shown by 144-h LC₅₀ value at 7 °C) was substantially more toxic (7.3 mS/cm) compared to analytical grade CaCl₂ (12.5 mS/cm). Yet for NEC values, there were comparably fewer differences in toxicity between salts and none between the same salts at different temperatures. We conclude that LC_x values are better suited to compare the difference in toxicity between substances or between the same substance at different test temperatures, while NEC values are better suited to estimating concentrations of substances that have no effect to the test species and endpoint measured under laboratory conditions.