Individual and joint toxicity of the herbicide S-metolachlor and a metabolite, deethylatrazine on aquatic crustaceans: Difference between ecological groups

Widely used herbicide metolachlor can promote harmful bloom formation by stimulating cyanobacterial growth and driving detrimental effects on their chytrid parasites

Metolachlor (MET) is a widely used herbicide that can adversely affect phytoplanktonic non-target organisms, such as cyanobacteria. Chytrids are zoosporic fungi ubiquitous in aquatic environments that parasitize cyanobacteria and can keep their proliferation in check. However, the influence of organic pollutants on the interaction between species, including parasitism, and the associated ecological processes remain poorly understood. Using the host-parasite system consisting of the toxigenic cyanobacterium Planktothrix agardhii and its chytrid parasite Rhizophydium megarrhizum, we investigated the effects of environmentally relevant concentrations of MET on host-parasite interactions under i) continuous exposure of chytrids and cyanobacteria, and ii) pre-exposure of chytrids. During a continuous exposure, the infection prevalence and intensity were not affected, but chytrid reproductive structures were smaller at the highest tested MET concentration. In the parasite's absence, MET promoted cyanobacteria growth possibly due to a hormesis effect. In the pre-exposure assay, MET caused multi- and transgenerational detrimental effects on parasite fitness. Chytrids pre-exposed to MET showed reduced infectivity, intensity, and prevalence of the infection, and their sporangia size was reduced. Thus, pre-exposure of the parasite to MET resulted in a delayed decline of the cyanobacterial cultures upon infection. After several parasite generations without MET exposure, the parasite recovered its initial fitness, indicating that detrimental effects are transient. This study demonstrates that widely used herbicides, such as MET, could favor cyanobacterial bloom formation both directly, by promoting cyanobacteria growth, and indirectly, by inhibiting their chytrid parasites, which are known to play a key role as top-down regulators of cyanobacteria. In addition, we evidence the relevance of addressing multi-organism systems, such as host-parasite interactions, in toxicity assays. This approach offers a more comprehensive understanding of the effects of pollutants on aquatic ecosystems.

Amide herbicides: Analysis of their environmental fate, combined plant-microorganism soil remediation scheme, and risk prevention and control strategies for sensitive populations

In this study, we predicted the environmental fate of amide herbicides (AHs) using the EQC (EQuilibrium Criterion) model. We found that the soil phase is the main reservoir of AHs in the environment. Second, a toxicokinetic prediction indicated that butachlor have a low human health risk, while the alachlor, acetochlor, metolachlor, napropamide, and propanil are all uncertain. To address the environmental and human-health-related threats posed by AHs, 27 new proteins/enzymes that easily absorb, degrade, and mineralize AHs were designed. Compared with the target protein/enzyme, the comprehensive evaluation value of the new proteins/enzymes increased significantly: the absorption protein increased by 20.29-113.49%; the degradation enzyme increased by 151.26-425.22%; and the mineralization enzyme increased by 23.70-52.16%. Further experiments revealed that the remediating effect of 13 new proteins/enzymes could be significantly enhanced to facilitate their applicability under real environmental conditions. The hydrophobic interactions, van der Waals forces, and polar solvation are the key factors influencing plant-microorganism remediation. Finally, the simulations revealed that appropriate consumption of kiwifruit or simultaneous consumption of ginseng, carrot, and spinach, and avoiding the simultaneous consumption of maize and carrot/spinach are the most effective means reduce the risk of exhibiting AH-linked toxicity.

Contribution of differential alteration in oxidative stress and anti-oxidation related molecular signals to toxicity difference between atrazine and its main metabolites in nematodes

As a widely used herbicide, atrazine and its two main metabolites of deethylatrazine (DEA) and deisopropylatrazine (DIA) pose an exposure risk for both human beings and animals in the environment. In this study, Caenorhabditis elegans was selected as an in vivo model to compare the toxicity between atrazine and its main metabolites. Upon exposure from the larval stage L1 to adult day 3, both DEA and DIA showed less toxicity on locomotion and reproduction compared with atrazine at concentration of 0.001, 0.01 0.1 and 1 mg/L for parental generation. In addition, exposure to DEA and DIA at concentration of 0.1 mg/L also induced less transgenerational toxicity on locomotion than exposure to atrazine for both parental generation and offspring of F1-F4. Accordingly, exposure to DEA and DIA caused less ROS production and alteration in the expression of some genes (mev-1, gas-1, and clk-1) governing oxidative stress compared to atrazine. Meanwhile, DEA and DIA lead to less increase in expression of superoxide dismutase genes (sod-2 and sod-3) and SOD-3::GFP than atrazine. Moreover, atrazine and its two main metabolites differentially activated the daf-16 encoding FOXO transcriptional factor in insulin signaling pathway during the control of downstream target of SOD-3. Overall, our results highlighted the important role of oxidative stress and anti-oxidation related molecular signals in mediating toxicity of atrazine, DEA and DIA, which provided a novel explanation for the different toxicity between atrazine and its main metabolites.

A study of long-term toxicity of multiple mixtures with hormetic effects by the characteristic parameter σ2(k∙ECx) and stepwise method

A previous study found that the characteristic parameter σ2(k∙ECx) (the concentration ECx and slope k of the concentrationresponse curve (CRC) at the effect x %) can predict the acute combined toxicity of multiple mixtures with S-shaped CRCs. In this paper, the competence of σ2(k∙ECx) to predict the long-term toxicity of multiple mixtures with J-shaped CRCs was explored using the Aliivibrio fischeri as the test organism. The combined toxicity was evaluated by the independent action (IA) model and the effect ratio (ERx) model. The stepwise method was used to divide J-shaped CRC into ML and MR (SL and SR). The results showed that the σ2(k∙ECx) and ERx of each segment was in good agreement with the exponential function. A new type of mixture was added to the original type A and type B, whose rules of interaction were opposite to those of type B (named opposite B, OB). This paper improves the understanding and analysis of the J-shaped CRCs in environmental risk assessment.

Towards evidence-based conservation of subterranean ecosystems

Subterranean ecosystems are among the most widespread environments on Earth, yet we still have poor knowledge of their biodiversity. To raise awareness of subterranean ecosystems, the essential services they provide, and their unique conservation challenges, 2021 and 2022 were designated International Years of Caves and Karst. As these ecosystems have traditionally been overlooked in global conservation agendas and multilateral agreements, a quantitative assessment of solution-based approaches to safeguard subterranean biota and associated habitats is timely. This assessment allows researchers and practitioners to understand the progress made and research needs in subterranean ecology and management. We conducted a systematic review of peer-reviewed and grey literature focused on subterranean ecosystems globally (terrestrial, freshwater, and saltwater systems), to quantify the available evidence-base for the effectiveness of conservation interventions. We selected 708 publications from the years 1964 to 2021 that discussed, recommended, or implemented 1,954 conservation interventions in subterranean ecosystems. We noted a steep increase in the number of studies from the 2000s while, surprisingly, the proportion of studies quantifying the impact of conservation interventions has steadily and significantly decreased in recent years. The effectiveness of 31% of conservation interventions has been tested statistically. We further highlight that 64% of the reported research occurred in the Palearctic and Nearctic biogeographic regions. Assessments of the effectiveness of conservation interventions were heavily biased towards indirect measures (monitoring and risk assessment), a limited sample of organisms (mostly arthropods and bats), and more accessible systems (terrestrial caves). Our results indicate that most conservation science in the field of subterranean biology does not apply a rigorous quantitative approach, resulting in sparse evidence for the effectiveness of interventions. This raises the important question of how to make conservation efforts more feasible to implement, cost-effective, and long-lasting. Although there is no single remedy, we propose a suite of potential solutions to focus our efforts better towards increasing statistical testing and stress the importance of standardising study reporting to facilitate meta-analytical exercises. We also provide a database summarising the available literature, which will help to build quantitative knowledge about interventions likely to yield the greatest impacts depending upon the subterranean species and habitats of interest. We view this as a starting point to shift away from the widespread tendency of recommending conservation interventions based on anecdotal and expert-based information rather than scientific evidence, without quantitatively testing their effectiveness.

Groundwater fauna downtown - Drivers, impacts and implications for subsurface ecosystems in urban areas

Groundwater fauna (stygofauna) comprises organisms that have adapted to the dark subterranean environment over a course of thousands and millions of years, typically having slow metabolisms and long life cycles. They are crucial players in the groundwater of oxygenic aquifers, and contribute to various ecosystem services. Today's knowledge of their sensitivity to anthropogenic impacts is incomplete and a critical analysis of the general relevance of local findings is lacking. In this review, we focus on those areas with the highest interference between humans and stygofauna: cities. Here is where local pollution by various contaminants and heat strongly stresses the unique groundwater ecosystems. It is demonstrated that it is difficult to discern the influence of individual factors from the findings reported in field studies, and to extrapolate laboratory results to field conditions. The effects of temperature increase and chemical pollution vary strongly between tested species and test conditions. In general, previous findings indicate that heating, especially in the long-term, will increase mortality, and less adapted species are at risk of vanishing from their habitats. The same may be true for salinity caused by road de-icing in cold urban areas. Furthermore, high sensitivities were shown for ammonium, which will probably be even more pronounced with rising temperatures resulting in altered biodiversity patterns. Toxicity of heavy metals, for a variety of invertebrates, increases with time and chronic exposure. Our current knowledge reveals diverse potential impacts on groundwater fauna by urban pollution, but our insights gained so far can only be validated by standardized and long-term test concepts.

Screening of NaCl salinity sensitivity across eight species of subterranean amphipod genus Niphargus

Secondary salinization of freshwater is becoming a growing environmental problem. Currently, there is few data available on the effects of salinisation on subterranean crustaceans that are vital for the maintenance of groundwater ecosystem functioning. In this study, the sensitivity of subterranean Niphargus amphipods to NaCl was investigated. We expected that cave-dwelling species would be more sensitive as surface-subterranean boundary species. Eight ecologically different Niphargus species were tested: four live at the boundary between the surface and subterranean ecosystems (N. timavi, N. krameri, N. sphagnicolus, N. spinulifemur), three live in cave streams (N. stygius, N. scopicauda, N. podpecanus), and one species (N. hebereri) lives in anchialine caves and wells. The organisms were exposed to five concentrations of NaCl for 96 h and afterwards the immobility, mortality, and electron transfer system (ETS) activity (a measure for metabolic rate of animals) were evaluated. As expected, the most tolerant species was N. hebereri dwelling in naturally high-salinity habitat. However, contrary to our expectations, the species collected at the surface-subterranean boundary were more sensitive as cave stream species when their immobility and mortality were assessed. Interestingly, the majority of Niphargus tested were more NaCl tolerant as can be deduced from currently available data for subterranean and surface crustaceans. We could not observe a clear trend in ETS activity changes between groups of surface-subterranean boundary and cave streams species after exposure to NaCl stress, but it appears that osmotic stress-induced metabolic rate changes are species-specific. This study shows that amphipods Niphargus can be a valuable subterranean environmental research model and further ecotoxicity research is of interest.

Four scenarios of environmental risk of diclofenac in European groundwater ecosystems

Groundwater is the largest source of liquid freshwater on Earth. Groundwater ecosystems harbor a rich biodiversity, mainly consisting of microbes and invertebrates that provide substantial ecological services. Despite its importance, groundwater is affected by several anthropic pressures, including pollution from pharmaceutical compounds. Diclofenac is the non-steroidal drug most widely detected in freshwaters, both in surface waters (e.g., rivers, streams, lakes etc.) and groundwaters. Unlike surface waters, the environmental risk of diclofenac in European groundwaters has not yet been assessed by the competent Authorities. The environmental risk assessment refers to the analysis of the potential risk that a chemical compound poses to a given environment by comparing its measured environmental concentrations to its predicted no-effect concentration. In this study, we explored four environmental risk scenarios in European groundwaters using different methodologies. We obtained diverse risk expectations, some indicative of a moderately diffuse environmental risk for concentrations of diclofenac ≥42 ng/L and others indicative of a widespread environmental risk for concentrations ≥5 ng/L. The difference among the four scenarios mainly related to the methods of calculating the predicted no-effect concentration of diclofenac. We discussed the four scenarios in order to identify the most realistic risk expectations posed by diclofenac to European groundwater ecosystems.

Prioritization of Pesticides for Assessment of Risk to Aquatic Ecosystems in Canada and Identification of Knowledge Gaps

Pesticides can enter aquatic environments via direct application, via overspray or drift during application, or by runoff or leaching from fields during rain events, where they can have unintended effects on non-target aquatic biota. As such, Fisheries and Oceans Canada identified a need to prioritize current-use pesticides based on potential risks towards fish, their prey species, and habitats in Canada. A literature review was conducted to: (1) Identify current-use pesticides of concern for Canadian marine and freshwater environments based on use and environmental presence in Canada, (2) Outline current knowledge on the biological effects of the pesticides of concern, and (3) Identify general data gaps specific to biological effects of pesticides on aquatic species. Prioritization was based upon recent sales data, measured concentrations in Canadian aquatic environments between 2000 and 2020, and inherent toxicity as represented by aquatic guideline values. Prioritization identified 55 pesticides for further research nationally. Based on rank, a sub-group of seven were chosen as the top-priority pesticides, including three herbicides (atrazine, diquat, and S-metolachlor), three insecticides (chlorpyrifos, clothianidin, and permethrin), and one fungicide (chlorothalonil). A number of knowledge gaps became apparent through this process, including gaps in our understanding of sub-lethal toxicity, environmental fate, species sensitivity distributions, and/or surface water concentrations for each of the active ingredients reviewed. More generally, we identified a need for more baseline fish and fish habitat data, ongoing environmental monitoring, development of marine and sediment-toxicity benchmarks, improved study design including sufficiently low method detection limits, and collaboration around accessible data reporting and management.

Reproductive cycle progression arrest and modification of cell morphology (shape and biovolume) in the alga Pseudokirchneriella subcapitata exposed to metolachlor

Metolachlor (MET) is an herbicide widely used and frequently found (at μg L^-1) in aquatic systems. This work aimed to study the modes of action of MET on the green microalga Pseudokirchneriella subcapitata. Algae exposed to 115 or 235 μg L^-1 MET, for 48 or 72 h, presented a reduction of metabolic activity, chlorophyll a and b content and photosynthetic efficiency. The exposure to 115 or 235 μg L^-1 MET also induced growth yield reduction, mean cell biovolume increase and alteration of the typical algae shape (cells lunate or helically twisted) to "French croissant"-type; at these MET concentrations, algal population was mainly composed by multinucleated cells (≥ 4 nuclei), which suggest that MET impairs the normal progression of the reproductive cycle but did not hinder nuclear division. The accumulation of multinucleated cells seems to be the consequence of the incapacity of the parent cell to release the autospores. In conclusion, MET disrupts the physiology of P. subcapitata cells; the disturbance of the progression of the reproductive cycle should be in the origin of growth slowdown (or even its arrest), increase of mean cell biovolume and modification of algal shape. This work contributed to elucidate, in a systematically and integrated way, the toxic mechanism of MET on the non-target organism, the alga P. subcapitata.

Ecotoxicological effects of anthropogenic stressors in subterranean organisms: A review

How anthropogenic stressors affect biodiversity is a central question in a changing world. Subterranean ecosystems and their biodiversity are particularly vulnerable to change, yet, these species are frequently neglected in analyses of global biodiversity and assessments of ecological status and risk. Are these hidden species affected by anthropogenic stressors? Do they survive outside of the current thermal limits of their ecosystems? These and other important questions can be addressed with ecotoxicological testing, relating contaminants and temperature resistance of species with measured environmental concentrations and climatic data. Ecotoxicological knowledge specific to subterranean ecosystems is crucial for establishing thresholds for their protection, but such data are both scarce and scattered. Here, we review the existing ecotoxicological studies of these impacts to subterranean-adapted species. An effort that includes 167 measured endpoints and presents a database containing experimentally derived species' tolerance data for 28 contaminants and temperature, for 46 terrestrial and groundwater species, including fungi and animals. The lack of standard data among the studies is currently the major impediment to evaluate how stressors affect subterranean-adapted species and how differently they respond from their relatives at surface. Improving understanding of ecotoxicological effects on subterranean-adapted species will require extensive analysis of physiological responses to a wide range of untested stressors, standardization of testing protocols and evaluation of exposures under realistic scenarios.

Environmental risk assessment of propranolol in the groundwater bodies of Europe

A growing concern for contamination due to pharmaceutical compounds in groundwater is expanding globally. The β-blocker propranolol is a β-adrenoceptors antagonist commonly detected in European groundwater bodies. The effect of propranolol on stygobiotic species (obligate groundwater dweller species) is compelling in the framework of environmental risk assessment (ERA) of groundwater ecosystems. In fact, in Europe, ERA procedures for pharmaceuticals in groundwater are based on data obtained with surrogate surface water species. The use of surrogates has aroused some concern in the scientific arena since the first ERA guideline for groundwater was issued. We performed an ecotoxicological and a behavioural experiment with the stygobiotic crustacean species Diacyclops belgicus (Copepopda) to estimate a realistic value of the Predicted No Effect Concentration (PNEC) of propranolol for groundwater ecosystems and we compared this value with the PNEC estimated based on EU ERA procedures. The results of this study showed that i) presently, propranolol does not pose a risk to groundwater bodies in Europe at the concentrations shown in this study and ii) the PNEC of propranolol estimated through the EU ERA procedures is very conservative and allows to adequately protect these delicate ecosystems and their dwelling fauna. The methodological approach and the results of this study represent a first contribution to the improvement of ERA of groundwater ecosystems.

Recommendations for ecotoxicity testing with stygobiotic species in the framework of groundwater environmental risk assessment

As a consequence of the growing global dependence on groundwater resources, environmental risk assessments (ERA) for groundwater are increasingly required and, with that, ecotoxicological studies with groundwater fauna (stygofauna). However, the literature on the ecotoxicological studies with stygobiotic species (i.e. species that complete their life cycle exclusively in groundwater) has not expanded significantly since the first paper published in this field. The limitations regarding the use of stygobiotic species for ecotoxicological testing are clear and consistent across the globe; stygobiotic species are often 1) naturally present in low numbers, 2) difficult to collect, and 3) difficult to culture under laboratory conditions. This paper reviews the methods used in ecotoxicological studies performed with stygobiotic species, and provides ten recommendations for Good Laboratory Practice (GLP) for such tests. The recommendations focused on the following 10 points: 1) the taxonomic identification, the life stage/size and gender of the test organisms; 2) collection methodology of the organisms, including collection location, conditions and methods; 3) holding and acclimation conditions in the laboratory; 4) exposure conditions such as test set up and exposure time, number of replicates and densities of organisms in tests and in test vessels; 5) range-finding test set up and schedule; 6) final test design, including details of controls and treatments, and replication options; 7) incubation conditions, specifying temperature, pH and oxygenation levels throughout the test; 8) test duration; 9) observations and endpoints; 10) test validity criteria and compliance. The recommendations were developed for the purpose of supporting future short-term ecotoxicological testing with stygofauna through providing consistency in the protocols. A discussion of the potential implications for groundwater managers and decision-makers committed to ERA for groundwater is included.

Whether warming magnifies the toxicity of a pesticide is strongly dependent on the concentration and the null model

How global warming changes the toxicity of contaminants is a research priority at the intersection of global change biology and ecotoxicology. While many pesticides are more toxic at higher temperatures this is not always detected. We studied whether deviations from this general pattern can be explained by concentration-dependent interaction effects and by testing the interaction against the inappropriate null model. We exposed larvae of the mosquito Culex pipiens to three concentrations of the pesticide chlorpyrifos (absence, low and high) in the absence and presence of 4 °C warming. Both the low and high chlorpyrifos concentration were lethal and generated negative sublethal effects: activity of acetylcholinesterase (AChE) and total fat content decreased, and oxidative damage to lipids increased, yet growth rate increased. Warming was slightly lethal, yet had positive sublethal effects: growth rate, total fat content and metabolic rate increased, and oxidative damage decreased. For four out of seven response variables the independent action model identified the expected synergistic interaction between chlorpyrifos and warming. Notably, for three variables (survival, AChE and fat content) this was strongly dependent on the chlorpyrifos concentration, and for two of these (AChE and fat content) not associated with a significant interaction in the general(ized) linear models. For survival and fat content, warming only potentiated chlorpyrifos (CPF) toxicity at the low CPF concentration, while the opposite was true for AChE. Our results highlight that taking into account concentration-dependence and appropriate null model testing is crucial to improve our understanding of the toxicity of contaminants in a warming world.

Effects of S-metolachlor and its degradation product metolachlor OA on marbled crayfish (Procambarus virginalis)

Increasing production of energy crops in Europe, mainly maize and rapeseed, has altered patterns of pesticide use in recent decades. The long-term effects of S-metolachlor (S-M) and of its metabolite metolachlor OA (M-OA) at the environmentally relevant concentration of 4.2 μg L^-1 and at 42 μg L^-1 (ten-fold concentration) on marbled crayfish (Procambarus virginalis) were evaluated in a 28-day exposure and after a subsequent 28-day recovery period. Indicators assessed were behaviour; biochemical haemolymph profile; oxidative and antioxidant parameters of gill, hepatopancreas, and muscle; and histology of hepatopancreas and gill. Results showed biochemical haemolymph profile (lactate, alanine aminotransferase, aspartate aminotransferase, inorganic phosphate), lipid peroxidation in hepatopancreas, and antioxidant parameters (catalase, reduced glutathione, glutathione S-transferase) of hepatopancreas and gill of crayfish exposed to S-M and M-OA to significantly differ from controls (P < 0.01). Antioxidant biomarker levels remained different from controls after a 28-day recovery period. Differences in behaviour including speed of movement and velocity, and histopathological damage to gill and hepatopancreas were associated with S-M and M-OA exposure and persisted after 28 days in S-M- and M-OA-free water. Results suggest harmful effects of low concentrations of S-M and its metabolite M-OA on non-target organisms and provide information for assessing their effects at environmentally relevant concentrations.

Impacts of S-metolachlor and terbuthylazine in fatty acid and carbohydrate composition of the benthic clam Scrobicularia plana

S-metolachlor (SMOC) and terbuthylazine (TBA) are herbicides that commonly appear as active ingredients (a.i.) in the composition of plant protection products. In a previous work, experimental bioassays were performed using those chemicals to find suitable molecular biomarkers to assess its toxicity to the non-target species Scrobicularia plana. The results obtained showed that the pollutants produce mortality and biochemical changes at the species, namely in protein contents and enzymatic activity levels. Thus, for a better understanding of the total biochemical impacts of those pollutants in S. plana, the composition of fatty acids (FA) and carbohydrates (CH) of the survival organisms are investigated here. In addition, since this species is edible its biochemical profile is directly related to its nutritious quality, which is analysed in this study. Furthermore, the analyses were performed in two types of tissue - the muscle and visceral mass of each survival organism. The greatest changes in FA composition are observable in small size class, being the most sensitive size class both at the toxicological and biochemical level. FA contents are higher in small organisms, both at the field and under laboratory conditions, being the disparity between size classes higher in visceral masses than in muscles. Indeed, muscles adequately represent the FA profile since those molecules appear in higher content in this tissue compared to visceral masses, becoming the better indicator tissue of biochemical changes. Besides, using muscles, less amount of biomass is needed, so it turns out to be the most cost-effective tissue to be used as endpoint in future studies. FA profiles observed at SMOC and TBA exposure are different, organisms from TBA exposure presenting a lower nutritious quality, in terms of FA abundance and diversity, than the organisms exposed to SMOC. Still, SMOC produces reductions of HUFA, essential fatty acids that cannot be synthesized by the species. Moreover, HUFA (mostly EPA and DHA) occupied the greatest part of the FA composition of organisms exposed to the control treatments and to TBA; however, the decreases of HUFA caused by the SMOC exposure change the profiles and make SFA the most dominant group. These findings represent a risk of low occurrence of essential fatty acids in entire aquatic environments exposed to the chemicals studied. Regarding CH, glucose is the only monosaccharide found in S. plana which was expected since glycogen is the main polysaccharide in animal tissues. In general, the glucose content increases with a concentration of pollutants, whereas the glycogen concentration decreases, suggesting that the glucose is being released as a response to chemical stress. Thus, this work presents tools to assess biochemical impacts of S-metolachlor and terbuthylazine in aquatic systems and to goes deeper in the knowledge of these pollutants' toxicity to non-target species to predict its propagation through aquatic trophic webs.

Chronic toxicity of metolachlor OA on growth, ontogenetic development, antioxidant biomarkers and histopathology of early life stages of marbled crayfish

The metolachlor OA is a metabolite of herbicide metolachlor and s-metolachlor. The objective of the present study was to assess the effect metolachlor OA on early life stages of marbled crayfish (Procambarus virginalis). The early life stages of marbled crayfish were exposed for 45 days to three concentrations of metolachlor OA: 4.2 μg/L (environmentally relevant concentration, E1), 42 μg/L (E2) and 420 μg/L (E3) under laboratory conditions. The effects were assessed on the basis of mortality, growth, ontogenetic development, behaviour, oxidative stress, antioxidant biomarkers and histopathology. Metolachlor OA caused significantly lower growth, superoxide dismutase, catalase and glutathione s-transferase activity in all tested concentrations. Metolachlor OA in higher concentrations (42 and 420 μg/L) resulted in significantly delayed ontogenetic development, lower reduced glutathione level and lipid peroxidation. Metolachlor OA has not significant effect on behaviour (activity, total distance moved and walking speed). Histological examination revealed alteration of hepatopancreas and gills in crayfish exposed to two higher tested concentrations. Hepatopancreas reflected histomorphological structural changes of individual cell types. Changes of gills included focal hemocytic infiltration together with enlargement of intralamellar space packed with granular substance. In conclusion, chronic metolachlor OA exposure affected growth, ontogenetic development, and the antioxidant system and caused pathological changes in hepatopancreas and gills of early life stages of marbled crayfish.

Commercial personal care product mixtures exhibit hormetic concentration-responses to Vibrio qinghaiensis sp.-Q67

The biological effects related to personal care products (PCPs) are almost induced by some active ingredients in the PCPs rather than the PCP itself. In this study, 23 common and widely used toner, skin water, and make-up water (TSM) commodities were directly taken as mixture samples, and Vibrio qinghaiensis sp.-Q67 (Q67) was used as the test organism. The toxicities of the TSMs to Q67 were determined via microplate toxicity analysis at 0.25 h and 12 h. Each TSM commodity can be regarded as a complicated mixture (relative concentration is 1). It was shown that the concentration-response curves (CRCs) of 23 TSMs are monotonic sigmoid-shaped (S-shaped) at 0.25 h, the CRCs of six TSMs are also S-shaped but the other 17 TSMs are non-monotonic hormetic or J-shaped at 12 h. In addition, to effectively characterize the nature of the stimulation and inhibition phases, it is suggested that five parameters such as the EC_L (the median stimulation effective concentration (left)), E_min (the maximum stimulation effect), EC_min (the maximum stimulation effective concentration), ZEP (zero effect point where the effect is 0 and the concentration is ZEP), and EC₅₀ can depict the non-monotonic CRC. To the best of our knowledge, this is the first study about the hormetic CRCs of commercial PCP mixtures.

Toxicological interaction of multi-component mixtures to Vibrio qinghaiensis sp.-Q67 induced by at least three components

It has been stated by researchers that the antibiotic polymyxin B sulfate (POL) is a key component inducing time-dependent antagonism in freshwater luminescent bacteria, Vibrio qinghaiensis sp.-Q67, exposed in the ternary mixture system of the ionic liquids, pesticide and antibiotics. However, the previous statement is limited to ternary and quaternary mixtures without considering situations such as the binary system. In order to prove the direct inducing of antagonism by POL in a more complete and systematic way, two categories of experiments (adding POL in non-antagonistic ternary system and decomposing antagonistic ternary system with POL into the binary system) have been conducted in this paper. The results showed that quaternary mixture systems (adding POL to non-antagonism ternary mixture, up verification) exhibit antagonistic action in a majority of rays, at some point in the experiment. However, by decomposing the antagonistic ternary mixtures with POL into binary mixtures (down verification), the combined toxicities of binary mixtures at all time points in the experiment are additive. Obviously, the POL has a significant contribution to antagonism only in the ternary and quaternary mixtures, but not in the binary mixtures. We can draw a new conclusion that the antagonism of the multi-component mixtures is induced by at least three components (including POL), with complex chemical interactions. Therefore, considering POL's influence of antagonism as an example, future environmental protection practitioners and academic researchers should construct more scenarios of mixtures when assessing the influences and reactions of certain chemicals causing pollutions.

Assessing the Effects of Alloxydim Phototransformation Products by QSAR Models and a Phytotoxicity Study

Once applied, an herbicide first makes contact with leaves and soil. It is known that photolysis can be one of the most important processes of dissipation of herbicides in the field. However, degradation does not guarantee detoxification and can give rise to byproducts that could be more toxic and/or persistent than the active substance. In this work, the photodegradation of alloxydim herbicide in soil and leaf cuticle surrogates was studied and a detailed study on the phytotoxicity of the main byproduct on sugar beet, tomato, and rotational crops was performed. Quantitative structure⁻activity relationship (QSAR) models were used to obtain a first approximation of the possible ecotoxicological and environmental implications of the alloxydim and its degradation product. The results show that alloxydim is rapidly degraded on carnauba and sandy loam soil surfaces, two difficult matrices to analyze and not previously studied with alloxydim. Two transformation products that formed in both matrices were identified: alloxydim Z-isomer and imine derivative (mixture of two tautomers). The phytotoxicity of alloxydim and the major byproduct shows that tomato possesses high sensitivity to the imine byproduct, while wheat crops are inhibited by the parent compound. This paper demonstrates the need to further investigate the behavior of herbicide degradation products on target and nontarget species to determine the adequate use of herbicidal products to maximize productivity in the context of sustainable agriculture.

Ecology-based evaluation of groundwater ecosystems under intensive agriculture: A combination of community analysis and sentinel exposure

Ecological criteria are needed for a comprehensive evaluation of groundwater ecosystem health by including biological components with the physical and chemical properties that are already required by European directives. Two methodological approaches to assess the ecological status of groundwater ecosystems were combined in two alluvial plains (the Ariège and Hers Rivers, southwestern France) varying in agriculture intensity (from grassland to crop rotation including maize and sunflower, and to maize monoculture). In the first approach, the composition of invertebrate assemblages (only obligate-groundwater crustaceans, i.e. stygobionts) sampled in 28 wells differing in their land use contexts was analysed. Abundance, species richness, and assemblage composition significantly changed with agricultural land use or urbanization around the wells. In the second approach, we tested an in situ exposure of sentinel organisms to quantify their response to the environmental pressures. The epigean and native amphipod species Gammarus cf. orinos was used as the sentinel species. Amphipods (30 individuals in each of 10 wells) were exposed for one week to the in situ conditions at two seasons with contrasted concentrations of pollutants. The Ecophysiological Index (EPI) synthetizing the survival rates and energetic storage decreased in wells with low oxygen and high nitrate concentrations, but only during the highest contamination period. Atrazine-related compounds negatively impacted sentinel health whatever the season. The combination of these two approaches may have major applications for orientating groundwater ecosystem management.

Time-dependent and Pb-dependent antagonism and synergism towards Vibrio qinghaiensis sp.-Q67 within heavy metal mixtures

Toxicity interaction has aroused many researchers' interest in the combined toxicity of pollutants. Recently, some published studies have shown that the toxicity of some mixture pollutants is time dependent and well correlated with certain components in the mixture. Therefore, to investigate whether toxicity interaction is affected by the exposure time or certain components, synergism and antagonism within typical environmental contaminants of heavy metal mixtures were analyzed in different exposure times. Herein, three binary and one ternary mixture systems were designed by using three heavy metals: cadmium chloride, lead chloride (Pb) and manganese(ii) chloride tetrahydrate (Mn). For each mixture system, five mixture rays with different concentration ratios were arranged by direct equipartition ray design and uniform design ray methods. The toxicities of the three heavy metals and 20 mixture rays towards photobacteria Vibrio qinghaiensis sp.-Q67 (Q67) were determined by the established time-dependent microplate toxicity analysis (t-MTA) in different exposure durations of 0.25, 2, 4, 8 and 12 h. It was shown that the toxicities of three heavy metals (Cd, Pb and Mn) as well as their binary and ternary mixture rays to Q67 were also time dependent, but different metals or mixture rays showed different time characteristics. Surprisingly, some mixture rays exhibited antagonism or synergism with time dependency and the time characteristics varied in different mixture systems. Furthermore, the binary or ternary mixture systems with Pb displayed antagonism, while the Cd–Mn mixture system without Pb exhibited additive action or synergism, which indicated that Pb was probably the causative agent of antagonism produced by mixtures.

Toxicity interaction has gained much interest in the research of toxicity of mixture pollutants.

The time-dependent synergism of the six-component mixtures of substituted phenols, pesticides and ionic liquids to Caenorhabditis elegans

Traditional environmental risk assessment rarely focused on exposures to multi-component mixtures which may cause toxicological interactions and usually ignored that toxicity is a process in time, which may underestimate the environment risk of mixtures. In this paper, six chemicals belonging to three categories, two substituted phenols, two pesticides and two Ionic liquids, were picked to construct a six-component mixture system. To systematically examine the effects of various concentration compositions, the uniform design ray method was employed to design nine mixture rays with nine mixture ratios and for every mixture ray 12 concentration levels were specified by the fixed ratio ray design. The improved combination index was used to evaluate the combined toxicities of the mixtures to Caenorhabditis elegans (C. elegans) in the exposure times of 6, 12 and 24h. It was shown that the mixture rays display time-dependent synergism, i.e. the range of synergistic effect narrows and the strength of synergism runs down with exposure time, which illustrates that the mixture toxicity of some chemicals is not a sum of individual toxicities at some exposure times and it is necessary to consider the toxicological interaction in mixtures.