Response and recovery of acetylcholinesterase activity in freshwater shrimp, Paratya australiensis (Decapoda: Atyidae) exposed to selected anti-cholinesterase insecticides

Mixture Toxicity of Three Unconventional Gas Fracking Chemicals, Barium, O-Cresol, and Sodium Chloride, to the Freshwater Shrimp Paratya australiensis

The 96-h acute toxicity of barium (Ba²⁺ ), o-cresol, and sodium chloride (NaCl) to Paratya australiensis was assessed in single, binary, and ternary combinations in addition to three biochemical assays: glutathione S-transferase, acetylcholinesterase, and sodium-potassium adenosine triphosphatase. The 96-h lethal concentrations that expressed 50% mortality (LC50) in the single-toxicant exposures were Ba²⁺  = 23.4 mg/L, o-cresol = 12.2 mg/L, and NaCl = 4198 mg/L. Mortality from o-cresol exposure occurred between 11 and 22 mg/L, whereas Ba²⁺ was more gradual across 10-105 mg/L, and most of the NaCl mortality occurred between 2050 and 4100 mg/L. Toxic units were used to assess the binary and ternary interactions of the toxicants. A more than additive effect was observed for most combinations in the binary chemical exposures, with the ternary combinations yielding highly synergistic interactions. Greater synergism was observed with the 96-h LC50 of o-cresol in combination with the three concentrations of NaCl (1025, 2050, and 3075 mg/L) compared with Ba²⁺ , with toxic units of 0.38, 0.48, and 0.10 (o-cresol) and 0.71, 0.67, and 0.50 (Ba²⁺ ). No notable enzyme activity trends were observed in the enzyme biomarker responses from both individual and mixture exposures. Although acute single-species toxicity tests tend to underestimate the effects of Ba²⁺ , o-cresol, and NaCl on populations, communities, and ecosystems in seminatural (e.g., mesocosms) and natural systems, there are currently no published acute toxicity data available for P. australiensis and the three toxicants used in the present study. The present study shows that chemicals with different toxicity mechanisms can potentially lead to more synergistic responses. Environ Toxicol Chem 2023;42:481-494. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Cyanidin-3-O-glucoside mediated photodegradation of profenofos in water

Flavonoids can sensitize and quench the photolysis of pesticides such as profenofos in surface water. Profenofos has been frequently detected in surface and underground water. The present study investigated the photolysis of profenofos under various conditions, including natural and artificial light illumination, with and without cyanidin-3-O-glucoside (Cy3G) and in pure and surface water. The degradation half-lives of profenofos in distilled water with 10 equivalents Cy3G of profenofos were 21.7 min, 9.5 h, 12.5 h and 180 h under high-pressure mercury light, UV, Xenon lamp and solar irradiation, respectively, while those without Cy3G were 8.1 min, 6.1 h, 8.2 h and 89.9 h, respectively. The photolysis rate of profenofos under sunlight and artificial light was reduced by 1.5-2.7 times due to Cy3G, compared to the Cy3G-free control. Under sunlight irradiation, the effects of Cy3G on profenofos photolysis were larger than those under high-pressure mercury lamp irradiation. Cy3G also significantly reduced the photolysis rate of profenofos under different pH conditions and in natural water. In addition, Cy3G exhibited a significant capacity of scavenging hydroxyl radicals and quenching ¹O₂ in water. The effect of Cy3G on profenofos photolysis was demonstrated through their interrelations in the natural environment. These findings can help understanding of the effect of flavonoids on profenofos photolysis and are of significance for predicting the degradation kinetics of profenofos and accurately assessing its potential biological impacts.

Mixture toxicity assessment of selected insecticides to silver perch fingerling, Bidyanus bidyanus

The organophosphorus (OP) and carbamate (CB) insecticides are responsible for inhibition of the Acetylcholinesterase (AChE) enzyme. The AChE activity, therefore, has been demonstrated to be a potent biomarker for these insecticides in terrestrial and aquatic environments. The objective of this study was to investigate the response of AChE in the brain of four-week old fingerlings of silver perch, Bidyanus bidyanus exposed to OP and CB insecticides. The fish fingeling were exposed to three OPs and one CB insecticide as individual and their binary mixtures for 48 h. The OP insecticides with oxon (PO) as well as thion (PS) group gets oxidized to oxon analogs in biological systems. The 50% AChE inhibition (48 h EC₅₀) in fingerling exposed to chlorpyrifos (CPF) and triazophos (TRZ) was evident at 2.3 and 6.7 µg/L, respectively. The toxicological interaction of three OPs and one CB insecticide was evaluated using the toxic unit method. A strong synergism was observed for binary combination of CPF with profenofos (PRF), and CPF with TAZ. In contrast, the mixture of TAZ with PRF and carbofuran (CBF) with CPF and PRF showed antagonistic behavior. Although OP and CB insecticides can break down rapidly in the environment, this study suggests that non-target aquatic biota may be exposed to mixtures of ChE-inhibiting insecticides for a period of several months, in agricultural regions where insecticides are applied for extended periods of the year. And at environmentally relevant concentrations such mixtures may lead to deleterious effects in non-target organisms.

Combined toxicity of therapeutic pharmaceuticals to duckweed, Lemna minor

Pharmaceuticals, which are designed to be biologically active at low concentrations, are found in surface waters, meaning aquatic organisms can be exposed to complex mixtures of pharmaceuticals. In this study, the adverse effects of four pharmaceuticals, 17α-ethynylestradiol (synthetic estrogen), methotrexate (anticancer drug), diclofenac (nonsteroidal anti-inflammatory drug) and fluoxetine (antidepressant), and their binary mixtures at mg/L concentrations were assessed using the 7-day Lemna minor test, with both apical and biochemical markers evaluated. The studied biochemical markers included chlorophyll a, chlorophyll b, carotenoids and oxidative stress enzymes catalase, glutathione-S-transferase and glutathione reductase, with effects compared to solvent controls. The adverse effects on Lemna minor were dose-dependent for frond number, surface area, relative chlorophyll content and activity of glutathione S-transferase for both individual pharmaceuticals and binary mixtures. According to the individual toxicity values, all tested pharmaceuticals can be considered as toxic or harmful to aquatic organisms, with methotrexate considered highly toxic. The most sensitive endpoints for the binary mixtures were photosynthetic pigments and frond surface area, with effects observed in the low mg/L concentration range. The concentration addition model and toxic unit approach gave similar mixture toxicity predictions, with binary mixtures of methotrexate and fluoxetine or methotrexate and 17α-ethynylestradiol exhibiting synergistic effects. In contrast, mixtures of diclofenac with fluoxetine, 17α-ethynylestradiol or methotrexate mostly showed additive effects. While low concentrations of methotrexate are expected in surface water, chronic ecotoxicological data for invertebrates and fish are lacking, but this is required to better assess the environmental risk of methotrexate.

Lethal and sub-lethal effects of environmentally relevant levels of imidacloprid pesticide to Eastern School Prawn, Metapenaeus macleayi

Pesticides are frequently employed to enhance agricultural production. Neonicotinoid pesticides (including imidacloprid) are often used to control sucking insects but have been shown to impact aquatic crustaceans. Imidacloprid is highly water soluble and has been detected in estuaries where it has been applied in adjacent catchments. We examined the impact of environmentally relevant concentrations of imidacloprid on Eastern School Prawn (Metapenaeus macleayi), an important exploited crustacean in Australia. Prawns were held for 8 days in estuarine water containing 0-4 μg L^-1 of imidacloprid to assess potential lethal and non-lethal impacts. There was a non-linear relationship between exposure concentration and tissue concentration, with tissue concentrations peaking at exposures of 1.4 μg L^-1 (1.16 to 1.64 μg L^-1, 90% C.I.). There was no evidence for direct mortality associated with imidacloprid exposure, but exposure did influence the organism metabolome which likely reflects alterations in metabolic homeostasis, such as changes in the fatty acid composition which indicate a shift in lipid homeostasis. There was a positive correlation between exposure concentration and moulting frequency. Shedding of the exoskeleton may represent a mechanism through which prawns can expel the contaminant from their bodies. These results indicate that prawns experience several different sub-lethal effects when exposed to these pesticides, which may have implications for the health of populations.

Influence of pesticides and abiotic conditions on biochemical biomarkers in Aegla aff. longirostri (crustacea, anomura): Implications for conservation

Freshwater ecosystems are constantly threatened by the advance of agricultural activities. Abiotic variables (such as temperature, ammonia, and nitrite) and contaminants (e.g. pesticides) can potentially interact, increasing metabolism and the absorption of toxic substances, which can alter the ability of organisms to establish adequate stress responses. This study aimed to verify which pesticides were most frequently found and in the greatest quantities in low-order streams, and whether the combination of these pesticides with the abiotic variables altered the biological metabolism of aeglids. These freshwater crustaceans are important shredders that inhabit low-order streams and are sensitive to disturbances and/or abrupt environmental variations. The animals were exposed in situ in four streams (reference site and sites 1, 2, and 3). The reference site is a preserved stream with no apparent anthropogenic interference where aeglids still occur, while the other sites no longer exhibit populations of these animals and are influenced by agricultural activities. The exposure was performed bimonthly from November 2017 to September 2018 and lasted 96 h. Measured abiotic data and water samples were collected through all days of exposure. The analyzed biochemical parameters were acetylcholinesterase activity in muscle; and glutathione S-transferase, lipid peroxidation, protein carbonylation, non-protein thiols, antioxidant capacity against peroxides, and reactive oxygen species (ROS) in muscle, gills, and hepatopancreas. We found 24 active principles of pesticides, the most frequently being clomazone, atrazine, and propoxur. Bentazone was present at the highest amounts. The parameters evaluated in this study, including biochemical biomarkers and abiotic factors measured from the water, provided a separation of the months as a function of environmental conditions. There was a difference in activity and biomarker levels throughout the year within the same site and in some months between sites. The greater concentration or variety of pesticides associated with extreme abiotic (very high temperatures) data generated increased oxidative stress, with high levels of protein damage and considerable lipid damage in all tissues, as well as elevation in ROS, even with high levels of antioxidant capacity and non-protein thiols. With these data, we intend to warn about the risks of exposure to these environmental conditions by trying to contribute to the preservation of limnic fauna, especially aeglid crabs, because most species are under some degree of threat.

Addressing challenges in providing a reliable ecotoxicology data for graphene-oxide (GO) using an algae (Raphidocelis subcapitata), and the trophic transfer consequence of GO-algae aggregates

The graphene oxide (GO) due to its exceptional structure, physicochemical and mechanical properties is a very attractive material for industry application. Even though, the unique properties of GO (e.g. structure, size, shape, etc.) make the risk assessment of this nanomaterial very challenging in comparison with conventional ecotoxicology studies required by regulators. Thus, there is a need for standardized characterization techniques and methodology to secure a high quality/reliable data on the ecotoxicology of GO, and to establish environmentally acceptable levels. Herein, authors address the crucial quality criteria when evaluating the ecotoxicology of GO using an algae (Raphidocelis subcapitata) and a shrimp (Paratya australiensis). This study provides a detail characterization and modification of the used GO, robust quantification and a suspension stability in different media for ecotoxicology studies. It was observed that under the same exposure conditions the behavior of GO and the estimated outcomes (IC₅₀ values) in modified algae media differed in comparison to the referent media. Further to that, the adverse effects of GO on the algae cell structure and the potential uptake of GO by the algae cells were examined using the TEM with different staining techniques to avoid artefacts. Shrimps which were exposed to GO-algae aggregates via the food intake did not indicate stress or accumulation of GO. Our work presents an important insight to necessity of establishing a benchmark ecotoxicology assays for GO (e.g. characterization techniques, choice of media, etc.) and providing a reliable data to be used by regulators in risk assessment of two-dimensional (2D) nanomaterials.

The toxicity of non-aged and aged coated silver nanoparticles to the freshwater shrimp Paratya australiensis

Nanoparticles (NPs) transform in the environment which result in alterations to their physicochemical properties. However, the effects of aging on the toxicity of NPs to aquatic organisms remain to be determined. Further the reports that have been published present contradictory results. The aim of this study was to examine the stability of differently coated silver nanoparticles (AgNPs) in media and the influence of aging of these NP on potential toxicity to freshwater shrimp Paratya australiensis. Coating-dependent changes in the stability of AgNP were observed with aging. Curcumin (C) coated AgNPs were stable, while tyrosine (T) coated AgNPs and epigallocatechin gallate (E) coated AgNPs aggregated in the P. australiensis medium. Increased lipid peroxidation and catalase activity was noted in P. australiensis exposed to AgNPs, suggesting oxidative stress was associated with NP exposure. The enhanced oxidative stress initiated by aged C-AgNPs suggests that aging of these NPs produced different toxicological responses. In summary, data suggest that coating-dependent alterations in NPs, together with aging affect both persistence and subsequent toxicity of NPs to freshwater organisms. Thus, the coating-dependent fate and toxicity of AgNPs together with the effect of their aging need to be considered in assessing the environmental risk of AgNPs to aquatic organisms.

Effects of Sublethal Chlorpyrifos Exposure on Postlarval American Lobster (Homarus americanus)

The organophosphate pesticide chlorpyrifos has been introduced to the marine environment via adsorption to agricultural soil runoff or as spray drift. Chlorpyrifos affects the survival of some larval decapod crustaceans, but no data exist on the impacts to the American lobster, Homarus americanus. The purpose of the present study was to assess the levels at which chlorpyrifos affects the survival of postlarval H. americanus. Using acute saltwater exposures, the 24- and 48-h median lethal concentrations were established for stage IV H. americanus (1.56 and 1.33 µg/L, respectively). Movement, acetylcholinesterase activity, intermoult period, specific growth rate, and moult increment were measured during exposure to sublethal concentrations. Movement patterns were assessed to establish a 48-h median inhibition concentration for cessation of normal movement (0.66 µg/L). Acetylcholinesterase activity was found to be inhibited immediately post-exposure to 0.50, 0.57, and 0.82 µg/L chlorpyrifos but could be recovered within a period (9-15 d) in clean seawater. Sublethal growth effects of increased intermoult period, decreased specific growth rate, and decreased moult increment were observed during exposure to an environmentally relevant concentration (0.82 µg/L). The present study suggests that H. americanus stage IV larvae were marginally less sensitive to chlorpyrifos compared with other decapods and that acute lethality of H. americanus postlarvae is not likely to occur with chlorpyrifos concentrations previously reported from aquatic environments. Environ Toxicol Chem 2019;38:1294-1301. © 2019 SETAC.

Assessment of the oxidative and genotoxic effects of the glyphosate-based herbicide roundup on the freshwater shrimp, Macrobrachium nipponensis

In the present study, an acute toxic test was performed to assess the oxidative stress and genotoxic effects of the herbicide on the freshwater shrimp Macrobrachium nipponensis. The results showed that the 48-h and 96-h LC50 values of Roundup to M. nipponensis were 57.684 mg/L and 11.237 mg/L, respectively. For further investigation, the shrimps were exposed to sublethal concentrations of 0.35, 0.70, 1.40, 2.80 and 5.60 mg/L for 96 h. A significant decrease in total haemocytes count (THC) was observed at concentration of 5.60 mg/L throughout the experiment. The level of superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) in all the treatments decreased in a dose- and time-dependent manner except for the concentration group of 0.35 mg/L. The malondialdehyde (MDA), hydrogen peroxide (H2O2) and protein carbonyl in serum increased significantly at concentrations of 2.80 mg/L and 5.60 mg/L. A significant decrease in acetylcholinesterase (AChE) activity was observed at each concentration (P＜0.05). In addition, the micronucleus (MN) frequency of haemocytes significantly increased (P＜0.05) at concentrations of 1.40, 2.80 and 5.60 mg/L, whereas the comet ratio and %DNA in the tails exhibited a clear time- and dose-dependent response during the exposure. The analysis of the integrated biomarker response (IBR) showed the induction of oxidative stress biomarkers and the inhibition of antioxidants, and this dose-dependent relation suggests the sensitivity and availability of all the biomarkers. These results revealed that Roundup had a prominent toxic effect on M. nipponensis based on the antioxidative response inhibition and genotoxicity.

Assessing interactive mixture toxicity of carbamate and organophosphorus insecticides in the yabby (Cherax destructor)

Carbamate (CB) and organophosphorus (OP) pesticides are commonly detected in aquatic ecosystems and predominantly occur as mixtures of varying complexity. These pesticides inhibit the activity of total cholinesterase (ChE) and thus have the potential to interfere with behaviours that may be essential for the survival of aquatic species. Although the effects of individual ChE insecticides on aquatic species have been reported for decades, the neurotoxicity of mixtures is still poorly understood. This study examined the chronic toxicities of two OP insecticides (chlorpyrifos (CPF) and malathion (MAL)) and one carbamate insecticide (methomyl (METH)) in binary and ternary mixtures on the ChE activity of the yabby (C. destructor). Using the concentration addition approach to estimate mixture toxicity, the observed inhibition of ChE activity caused by all binary mixtures of CPF plus MAL, CPF plus METH and MAL plus METH was additive. In ternary mixtures, all combinations of CPF, MAL and METH were either additive or antagonistic depending on the relative ratios of these chemicals in the mixtures. The effect of mixtures of these three insecticides on C. destructor has not previously been assessed, and the data suggest that individual chemical risk assessments are likely to incorrectly estimate the effect of these insecticides on C. destructor in the aquatic environment where combinations of such chemicals occur.

Evaluating the non-lethal effects of organophosphorous and carbamate insecticides on the yabby (Cherax destructor) using cholinesterase (AChE, BChE), Glutathione S-Transferase and ATPase as biomarkers

The toxicity of two organophosphorus insecticides, chlorpyrifos (CPF), malathion (MAL), and one carbamate insecticide, methomyl (METH), to the yabby (Cherax destructor) was assessed by measuring cholinesterase (AChE, BChE), Glutathione S-Transferase (GST) and Na⁺/K⁺ATPase activity after 96h of exposure. Yabbies exposed to all three insecticides at 2 and 5µgL^-1 exhibited significant AChE, BChE, GST and Na⁺/K⁺ATPase inhibition. Based on these enzyme inhibition tests, the toxicity of the three insecticides to C. destructor was CPF > MAL > METH. After 14 days of recovery the yabbies enzymatic activities of AChE, BChE, GST and Na⁺/K⁺ATPase was measured. Recovery of The enzyme activity recovery was faster after the exposure to METH than for the yabbies exposed to CPF and MAL. Slow recovery of enzyme activity could affect the physical activities of organisms and produce indirect effects on populations if such crayfish are less able to elude predators or search for food.

Allelopathic effects of volatile organic compounds from Eucalyptus grandis rhizosphere soil on Eisenia fetida assessed using avoidance bioassays, enzyme activity, and comet assays

Allelopathy has been identified as an underlying mechanism of detrimental environmental impacts within commercial plantations. Eucalyptus spp. are known to generate huge amounts of volatile organic compounds (VOCs) that can function as phytotoxins and thus inhibit other plants. In the present study, biochemical markers, including activities of acetylcholinesterase (AChE) and oxidative stress enzymes, such as superoxide dismutase (SOD) and glutathione S-transferase (GST), were assayed to assess changes in Eisenia fetida at the physiological level induced by different doses of VOCs as part of an acute toxicity test over 7 and 14-day exposures. In addition, the toxicities of VOCs were investigated using a soil avoidance test and comet assay. The results revealed that E. fetida exhibited significant avoidance behavior towards the highest concentrations of undecane, decane, 2,4-dimethyl heptane, and 2,2,4,6,6-pentametyl heptane. The tail DNA percentages were significantly increased for all experimental treatments relative to control. However, under the treatments of VOCs, Olive tail moment content and comet tail length also display an obvious increase compared to control, except for that of octane, undecane and decane treatments. As VOC concentrations and durations increased in the soil, activities of AChE, SOD, and GST were either stimulated or inhibited. Among the VOCs, decane, 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol exerted stronger effects on enzymatic activities. In summary, VOCs in rhizosphere soils of E. grandis might exert a toxic impact on E. fetida, among which 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol have the strongest effects.

Repeated sublethal exposures to the sea lice pesticide Salmosan® (azamethiphos) on adult male lobsters (Homarus americanus) causes neuromuscular dysfunction, hypoxia, metabolic disturbances and mortality

In Atlantic Canada and other salmon-growing regions, treatment of sea lice infestations in salmon aquaculture is necessary to protect fish health. The product Salmosan®, which contains the organophosphate azamethiphos as the active ingredient, is a pesticide presently used for treatment against sea lice. It is applied as a bath treatment and then released into the surrounding seawater. The potential for lethality to non-target species following acute and chronic exposures to Salmosan® has been studied over the past decade, however, the potential for sublethal effects on lobsters remains a concern. Adult male lobsters were exposed to 0.06, 0.5, and 5µgL^-1 azamethiphos for one hour, repeated five times, over 48h. Lobsters were assessed immediately after exposure and over six days of recovery. Inhibition of muscle cholinesterase activity was detected in lobsters exposed to 0.5 and 5µgL^-1 azamethiphos. The 5µgL^-1 dose was considered lethal (93% cumulative mortality). Significant changes in hemolymph plasma biochemistry were most apparent in the 5µgL^-1 exposure group in the immediate post-exposure samples. Citrate synthase activity was significantly lower in muscles of the 0.5µgL^-1 exposure group compared to control lobsters. Mean electron transport system and standard metabolic rates tended to be lower in muscle tissue of the 0.5µgL^-1 exposure group than control group lobsters. These results suggest that sublethal effects on lobster energetics may occur under laboratory exposure conditions (i.e., concentrations and duration) considered environmentally relevant, which could result in impairment under natural conditions.

De novo assembly and analysis of changes in the protein-coding transcriptome of the freshwater shrimp Paratya australiensis (Decapoda: Atyidae) in response to acid sulfate drainage water

Background

The atyid shrimp Paratya australiensis occurs in surface freshwater habitats throughout eastern Australia and has been used to study the ecotoxicology of contaminants such as pesticides and metals. The acidification of surface water that can occur after acid sulfate material in soils and sediments is oxidised and subsequently re-wetted is a serious environmental issue in coastal regions and inland riverine floodplains worldwide. Solubilisation of soil-associated minerals can result in high waterborne concentrations of mineral salts and dissolved metals, which together with low pH represent a potential threat to aquatic ecosystems in affected regions. The aims of the present study were to gain insight into stress responses induced by exposure to acid drainage water (ADW) in P. australiensis by determining changes in the abundance of protein-coding transcripts and to generate a comprehensive transcriptomic resource to facilitate further research into gene regulation or protein structure and function in this species. Adult P. australiensis were exposed for 24 h to undiluted ADW, 50 % ADW diluted in river water, or to river water as control, and high-throughput mRNA sequencing (RNA-Seq) conducted on whole-body tissues. A reference transcriptome was generated using de novo assembly and putative protein-coding regions were identified and annotated. Changes in transcript abundance in response to ADW exposure were determined by aligning reads to the reference transcriptome and quantifying coverage.

Results

A high proportion of arthropod benchmarking universal single-copy orthologues were present in the reference transcriptome. Functions associated with cuticle biosynthesis and oxidative stress were significantly enriched in the lists of transcripts exhibiting differential abundance in either direction after exposure to 50 % or 100 % ADW. Transcripts involved in osmoregulation exhibited decreased abundance following exposure to ADW. The transcriptome contained full-length coding sequences for numerous proteins known to be involved in environmental response pathways, including two putative metallothioneins, four glutathione peroxidases and 19 nuclear receptors.

Conclusions

The results of the present study provide insight into stress response pathways induced in crustaceans by short-term exposure to multiple stressors present in ADW such as low pH, high salinity and dissolved metals, and represent a resource for future toxicogenomics and protein functional studies in P. australiensis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3208-y) contains supplementary material, which is available to authorized users.

In vitro test systems supporting the development of improved pest control methods: a case study with chemical mixtures and bivalve biofoulers

Using the bivalve macrofouler Corbicula fluminea, the suitability of in vitro testing as a stepping stone towards the improvement of control methods based on chemical mixtures was addressed in this study. In vitro cholinesterase (ChE) activity inhibition following single exposure of C. fluminea tissue to four model chemicals (the organophosphates dimethoate and dichlorvos, copper and sodium dodecyl phosphate [SDS]) was first assessed. Consequently, mixtures of dimethoate with copper and dichlorvos with SDS were tested and modelled; mixtures with ChE revealed synergistic interactions for both chemical pairs. These synergic combinations were subsequently validated in vivo and the increased control potential of these selected combinations was verified, with gains of up to 50% in C. fluminea mortality relative to corresponding single chemical treatments. Such consistency supports the suitability of using time- and cost-effective surrogate testing platforms to assist the development of biofouling control strategies incorporating mixtures.

Sensitive biomarker responses of the shrimp Palaemonetes argentinus exposed to chlorpyrifos at environmental concentrations: Roles of alpha-tocopherol and metallothioneins

The aim of this study was to evaluate the toxic effects of chlorpyrifos (CPF) at environmental concentrations on the shrimp Palaemonetes argentinus, a South American native species. Organisms were exposed to environmentally relevant concentrations of CPF (from 3.5 to 94.5ngCPFL(-1)) at laboratory conditions for 96h. A wide battery of biochemical responses including bioaccumulation, damage and defense biomarkers were measured in cephalothorax and abdomen of shrimp. The concentration of CPF was below the detection limit of the method in both body sectors (8ngCPFg(-1)ww), probably indicating fast biotransformation of the parental compound. Our results showed that CPF exposure inhibits acetylcholinesterase activity from 3.5ngCPFL(-1), a concentration below the suggested Argentinean guidelines for the protection of aquatic biota. Moreover, oxidative stress was evidenced by increased H2O2 content and increased levels of TBARs and carbonyl groups in proteins. The induction of antioxidant enzymes like catalase, glutathione S-transferase and glutathione peroxidase seems not be sufficient to prevent oxidative damages. In addition, the mobilization of α-tocopherol from abdomen to cephalothorax was observed and reported for the first time in non-reproductive condition. Likewise, a strong diminution of metallothioneins occurred in cephalothorax from the lowest CPF concentration while induction occurred from the same treatment in abdomen as an oxidative stress response. Finally, significant correlation between Integrated Biomarker Response values and exposure concentrations suggest the usefulness of P. argentinus as bioindicator of CPF exposure at concentrations as low as environmental ones.

Internal Concentration and Time Are Important Modifiers of Toxicity: The Case of Chlorpyrifos on Caenorhabditis elegans

The internal concentration of chemicals in exposed organisms changes over time due to absorption, distribution, metabolism, and excretion processes since chemicals are taken up from the environment. Internal concentration and time are very important modifiers of toxicity when biomarkers are used to evaluate the potential hazards and risks of environmental pollutants. In this study, the responses of molecular biomarkers, and the fate of chemicals in the body, were comprehensively investigated to determine cause-and-effect relationships over time. Chlorpyrifos (CP) was selected as a model chemical, and Caenorhabditis elegans was exposed to CP for 4 h using the passive dosing method. Worms were then monitored in fresh medium during a 48-h recovery regime. The mRNA expression of genes related to CYP metabolism (cyp35a2 and cyp35a3) increased during the constant exposure phase. The body residue of CP decreased once it reached a peak level during the early stage of exposure, indicating that the initial uptake of CP rapidly induced biotransformation with the synthesis of new CYP metabolic proteins. The residual chlorpyrifos-oxon concentration, an acetylcholinesterase (AChE) inhibitor, continuously increased even after the recovery regime started. These delayed toxicokinetics seem to be important for the extension of AChE inhibition for up to 9 h after the start of the recovery regime. Comprehensive investigation into the molecular initiation events and changes in the internal concentrations of chemical species provide insight into response causality within the framework of an adverse outcome pathway.

Sublethal exposure to azamethiphos causes neurotoxicity, altered energy allocation and high mortality during simulated live transport in American lobster

In the Bay of Fundy, New Brunswick, sea lice outbreaks in caged salmon are treated with pesticides including Salmosan(®), applied as bath treatments and then released into the surrounding seawater. The effect of chronic exposure to low concentrations of this pesticide on neighboring lobster populations is a concern. Adult male lobsters were exposed to 61 ngL(-1) of azamethiphos (a.i. in Salmosan(®) formulation) continuously for 10 days. In addition to the direct effects of pesticide exposure, effects on the ability to cope with shipping conditions and the persistence of the effects after a 24h depuration period in clean seawater were assessed. Indicators of stress and hypoxia (serum total proteins, hemocyanin and lactate), oxidative damage (protein carbonyls in gills and serum) and altered energy allocation (hepatosomatic and gonadosomatic indices, hepatopancreas lipids) were assessed in addition to neurotoxicity (chlolinesterase activity in muscle). Directly after exposure, azamethiphos-treated lobsters had inhibition of muscle cholinesterase, reduced gonadosomatic index and enhanced hepatosomatic index and hepatopancreas lipid content. All these responses persisted after 24-h depuration, increasing the risk of cumulative impacts with further exposure to chemical or non-chemical stressors. In both control and treated lobsters exposed to simulated shipment conditions, concentrations of protein and lactate in serum, and protein carbonyls in gills increased. However, mortality rate was higher in azamethiphos-treated lobsters (33 ± 14%) than in controls (2.6 ± 4%). Shipment and azamethiphos had cumulative impacts on serum proteins. Both direct effects on neurological function and energy allocation and indirect effect on ability to cope with shipping stress could have significant impacts on lobster population and/or fisheries.

Binary combinations of organophosphorus pesticides exhibit differential toxicity under oxidised and un-oxidised conditions

Acetylcholinesterase (AChE) inhibition has been demonstrated to be useful as a biomarker for exposure to organophosphorus (OP) insecticides in many environments. The objective of this study was to investigate the response of housefly (Musca domestica) head AChE (HF-AChE) exposed to five OPs as individual compounds and their binary mixtures under in vitro conditions. To examine the effects of oxidation on OP potency in the HF-AChE system, bromine water was used as an oxidisng agent. With oxidation, the sensitivity of HF-AChE to chlorpyrifos (CPF), malathion (MLT) and triazophos (TRZ) increased significantly. Monocrotophos (MCP) and profenofos (PRF) did not exhibit any significant differences in toxicity under oxidised and un-oxidised conditions. The toxicological interaction of five organophosphorus pesticides was evaluated using the concentration addition model, the combination index-isobologram equation and the toxic unit approach. All three models provided similar predictions for the 10 binary combinations of OPs under oxidised and un-oxidised conditions. In the present study, the antagonistic effects of the binary combination of OPs (CPF+PRF, CPF+MLT, MCP+MLT, PRF+MLT, MLT+TRZ and PRF+TRZ) were observed under oxidised conditions. This may be due to dispositional and/or receptor antagonism. Most of the binary combinations assayed under un-oxidised conditions exhibited synergistic responses. Triazophos showed very strong synergism in binary combinations with CPF, MCP and PRF un-oxidised conditions. In contrast, under oxidised conditions, only CPF+TRZ exhibited synergism. The results obtained indicate differential toxicity of binary combinations of OPs under oxidised and un-oxidised conditions. This information could be a valuable tool in understanding the mechanisms of OPs interactions and the interpretation of future in vivo studies with mixtures of OP insecticides.

Antioxidant and neurotoxicity markers in the model organism Enchytraeus albidus (Oligochaeta): mechanisms of response to atrazine, dimethoate and carbendazim

The present study aimed to investigate the effects of dimethoate, atrazine and carbendazim on the antioxidant defences and neuronal function of the soil organism Enchytraeus albidus. Effects were studied at concentrations known to affect their reproduction (EC20, EC50 and EC90) and along time (2, 4, 8, 14 and 21 days). In general, responses were more pronounced at periods of exposure longer than 8 days and at the highest concentrations. Multivariate statistics (RDA-PRC) clearly displayed that exposure duration had an effect itself, biomarkers' responses showed interaction for all pesticides and catalase scored consistently high, indicating its relevancy in the group of measured markers. Univariate analysis indicated oxidative stress for all pesticides and atrazine induced oxidative damage in lipids. Atrazine seems to be effectively metabolized by GST of the biotransformation system, as its activity significantly increased after exposure to this pesticide. Dimethoate caused ChE inhibition, indicating an impairment of the neuronal function. Carbendazim impaired the antioxidant system, but no oxidative damage was observed, along with any effects on the ChE activity. The integrated biomarker response analysis was performed but we suggest modifications due to limiting artefacts.

Sublethal toxicity of untreated and treated stormwater Zn concentrations on the foraging behaviour of Paratya australiensis (Decapoda: Atyidae)

Aquatic organisms use chemical cues to perform key ecological behaviours such as locating food. Anthropogenic pollutants have the potential to disrupt these behaviours by down-regulating chemoreception. Urban stormwater runoff is a major source of metal pollution, particularly Zn, and is a leading contributor to the degradation of receiving waters. Consequently, significant remedial efforts have focused on using constructed stormwater wetlands to reduce pollutant loads. However, no studies have examined the efficacy of water quality improvements on ecologically relevant behaviours in aquatic biota. We conducted controlled laboratory experiments to test whether untreated (100 and 400 µg L(-1)) and treated (40 µg L(-1)) stormwater Zn concentrations observed in constructed wetlands interfere with the foraging behaviour of the glass shrimp (Paratya australiensis). The ability of shrimp to perceive, approach and search for a chemoattractant source was used to assess foraging behaviour. Abnormal foraging behaviour was observed in shrimp exposed to Zn at untreated stormwater concentrations. The strongest change relative to the control was observed for perception, which decreased by more than 80 and 60 % in the 400 µg Zn L(-1) and 100 µg Zn L(-1) groups, respectively. The behaviour of shrimp exposed to Zn concentrations measured in treated stormwater did not differ from the controls. The results suggest that the reduction of stormwater Zn concentrations via wetland treatment can prevent abnormal contamination-induced behaviours in shrimp, leading to improved aquatic ecosystem health. This study also highlights the subtle, but biologically significant impacts arising from sublethal exposures of Zn, and emphasise the utility of behavioural toxicology. The behavioural test used here is a simple and effective approach that could be incorporated into studies assessing the efficacy of stormwater treatment.

Risks to aquatic organisms from use of chlorpyrifos in the United States

The risk of chlorpyrifos (CPY) to aquatic organisms in surface water of North America was assessed using measured concentrations in surface waters and modeling of exposures to provide daily concentrations that better characterize peak exposures.Ecological effects were compared with results of standard laboratory toxicity tests with single species as well as microcosm and mesocosm studies comprised of complex aquatic communities. The upper 90th centile 96-h concentrations(annual maxima) of chlorpyrifos in small streams in agricultural watersheds in Michigan and Georgia were estimated to be :-:;0.02 llg L-1; in a reasonable worstcase California watershed, the 90th centile 96-h annual maximum concentrations ranged from 1.32 to 1.54 llg L - 1• Measured concentrations of chlorpyrifos are less than estimates from simulation models. The 95th centile for more than I 0,000 records compiled by the US Geological Survey was 0.008 llg L -1• Acute toxicity endpoints for 23 species of crustaceans ranged from 0.035 to 457 llg L -I; for 18 species of aquatic insects, from 0.05 to 27 llg L -I; and for 25 species of fish, from 0.53to >806 llg L -I. The No Observed Adverse Effect Concentration (NOAECeco) in more than a dozen microcosm and mesocosm studies conducted in a variety of climatic zones, was consistently 0.1 llg L -1• These results indicated that concentrations of CPY in surface waters are rarely great enough to cause acute toxicity to even the most sensitive aquatic species. This conclusion is consistent with the lack of fish kills reported for CPY's normal use in agriculture in the U.S.Analysis of measured exposures showed that concentrations in surface waters declined after labeled use-patterns changed in 2001, and resulted in decreased risks for crustaceans, aquatic stages of insects, and fish. Probabilistic analysis of 96-h time-weighted mean concentrations, predicted by use of model simulation for three focus-scenarios selected for regions of more intense use of CPY and vulnerability to runoff, showed that risks from individual and repeated exposures to CPY in the Georgia and Michigan watersheds were de minimis. Risks from individual exposures in the intense-use scenario from California were de minimis for fish and insects and low for crustaceans. Risks from repeated exposures in the Californiain tense-use scenario were judged not to be ecologically relevant for insects and fish,but there were some risks to crustaceans. Limited data show that chlorpyrifos oxon(CPYO), the active metabolite of CPY is of similar toxicity to the parent compound.Concentrations of CPYO in surface waters are smaller than those of CPY and less frequently detected. Risks for CPYO in aquatic organisms were judged to be deminimis.Several uncertainties common to all AChE inhibitors were identified. Insufficient data were available to allow interpretation of the relevance of effects of CPY (and other pesticides that also target AChE) on behavior to assessment endpoints such as survival, growth, development, and reproduction. Data on the recovery of AChE from inhibition by CPY in fish are limited. Such data are relevant to the characterization of risks from repeated exposures, and represent an uncertainty in the assessment of risks for CPY and other pesticides that share the same target and toxico dynamics. More intensive monitoring of areas of greater use and more comprehensive models of cumulative effects that include rates of accumulation, metabolism and recovery of AChE in the more sensitive species would be useful in reducing this uncertainty.

Characterization of acetylcholinesterase inhibition and energy allocation in Daphnia magna exposed to carbaryl

The inhibition of acetylcholinesterase (AChE) activity and energy allocation in the freshwater organism Daphnia magna exposed to carbaryl and potential recovery from the effects was examined. The binding of carbaryl-AChE was characterized through in vitro assays. To evaluate the recovery from inhibition and the alteration in energy budget, in vivo exposure and recovery regime tests were conducted. In comparison to diazoxon, the active metabolite of the insecticide diazinon, the stability of enzyme-carbaryl complex was fifteen times lower and the reactivity toward the active site was two times lower, resulting in approximately 30 times lower overall inhibition rate than for diazoxon. The in vitro reactivation rate constant of the inhibited enzyme and the in vivo recovery rate constant of AChE activity were 1.9 h⁻¹ and 0.12 h⁻¹ for carbaryl, respectively, which are much higher than the corresponding rate constants for diazoxon. The lower AChE inhibition and greater reactivation/recovery rates are in accordance with the lower toxicity of carbaryl compared to diazinon. Carbaryl exposure also altered the profile of the energy reserve: the decrease in lipid and glycogen and the increase in protein content resulted in the reduction of the total energy budget by about 45 mJ/g(ww). This corresponds to 26 percent of the available energy, which might allocate for external stressors. The mechanistic model of AChE inhibition is helpful to get an insight into (eco-)toxicological effects of AChE inhibitors on freshwater crustaceans under environmentally realistic conditions.

The stepwise behavioral responses: behavioral adjustment of the Chinese rare minnow (Gobiocypris rarus) in the exposure of carbamate pesticides

In order to illustrate the behavioral regulation in environmental stress, the behavioral responses of the Chinese rare minnow (Gobiocypris rarus) to arprocarb, carbofuran, and oxamyl were analyzed with an online monitoring system. The Self-Organizing Map (SOM) was used to define the patterns of the behavioral data obtained from treatments at concentrations of 0.1 toxic unit (TU), 1 TU, 2 TU, 5 TU, 10 TU, and 20 TU and a control. In certain cases, differences among the carbamate pesticides (CPs) tested were observed. The profiles of behavioral strength (BS) in SOM varied according to the concentration used. The time of the first significant decrease of the BS varied inversely with the CP concentrations. The results suggested that the behavioral regulation in the stepwise behavioral responses (SBR) was evident. The primary movement behaviors shown by the SBR model included no effect, stimulation, acclimation, adjustment (readjustment), and toxic effect, especially at the lower concentrations. However, higher stress (10 TU and 20 TU) might limit the function of the behavioral adjustment produced by the intrinsic response mechanisms. It was concluded that SBR, which were affected by both the concentration and the exposure time, could be used as a suitable indicator in the ecotoxicological risk assessment of CPs.

Different effects of subchronic exposure to low concentrations of the organophosphate insecticide chlorpyrifos in a freshwater gastropod

Chlorpyrifos is an organophosphate insecticide used for pest control on a number of food crops in many parts of the world. In recent years, there has been an important decrease in the number of organisms of Planorbarius corneus. Since the presence of pesticides in the water can be one of the reasons for this decrease, it is very important to study the effect of subchronic exposure to environmental concentrations of pesticides on these organisms. The aim of the present work was to investigate different effects of the subchronic exposure to low concentrations of the organophosphate chlorpyrifos in P. corneus and the possibility to use these as biomarkers. To this end, we have exposed the organisms to 0.4 and 5 μg L(-1) of chlorpyrifos for 14 days and recorded the number of egg masses, the number of eggs per mass, the number of eggs without embryo, the time for hatching, and the % of hatching and survival. We have also determined the activities of cholinesterases, carboxylesterases and glutathione S-transferase in whole organism soft tissue and in the gonads. A 14 days exposure to 0.4 μg L(-1) caused an increase in the number of egg masses without eggs and a decrease in carboxylesterases measured with p-nitrophenyl butyrate. However the exposure to 5 μg L(-1) also caused an increase in the time for hatching, a decrease in the % of hatching and survival and also inhibition of cholinesterases and carboxylesterases with p-nitrophenyl acetate and butyrate. In contrast, the glutathione S-transferase has not been modified with the tested concentrations. We concluded that when P. corneus exposed to chlorpyrifos for 14 days, the CES determined with p-nitrophenyl butyrate proved to be the most sensitive biomarker. However, exposure to environmental concentrations showed a decrease in the reproduction ability which could cause a decrease in the number of organisms of this species.

Dimethoate affects cholinesterases in Folsomia candida and their locomotion--false negative results of an avoidance behaviour test

The main mode of action of organophosphate insecticides is to inhibit acetylcholinesterase (AChE), which causes neuromuscular paralysis leading ultimately to death. The collembolan Folsomia candida is an important and standard test species in ecotoxicology, where effects on avoidance behaviour are assessed. Being related to insects they represent potential targets of insecticides such as the organophosphate dimethoate. In the present study we exposed F. candida to dimethoate having 2 main aims: 1) to assess the ability of F. candida to avoid it, and 2) to assess its effect on the cholinergic synapses to explore the link. For the latter, several sub-steps were needed: a) to characterise the existing ChE types and b) assess ChE activity (via exposure in vitro and in vivo). No avoidance was observed within the tested concentration range (0-0.32-1-3.2-10-32 mg/kg), in fact an apparent "attraction" (more animals on the spiked side) was observed. As expected, there was a significant decrease of AChE activities (AChE being the main ChE type) with an increase of dimethoate dose (IC(50)=1.4 mg/kg). Further, post-exposure video records showed that organisms were still alive in the spiked soil but lacked the locomotion ability (immobilised). The AChE inhibition correlated positively with immobilisation. Hence, this observation also showed that the apparent "attraction" behaviour observed in the avoidance test is rather a direct effect of not being able to escape due to paralysis hence a false-negative avoidance. This can constitute a confounding factor in an avoidance behaviour test and consequent interpretation, which is not accounted for at present.

The relationship between total cholinesterase activity and mortality in four butterfly species

The relationship between total cholinesterase activity (TChE) and mortality in four butterfly species (great southern white [Ascia monuste], common buckeye [Junonia coenia], painted lady [Vanessa cardui], and julia butterflies [Dryas julia]) was investigated. Acute contact toxicity studies were conducted to evaluate the response (median lethal dose [LD50] and TChE) of the four species following exposure to the organophosphate insecticide naled. The LD50 for these butterflies ranged from 2.3 to 7.6 µg/g. The average level of TChE inhibition associated with significant mortality ranged from 26 to 67%, depending on the species. The lower bounds of normal TChE activity (2 standard deviations less than the average TChE for reference butterflies) ranged from 8.4 to 12.3 µM/min/g. As a percentage of the average reference TChE activity for the respective species, the lower bounds were similar to the inhibition levels associated with significant mortality, indicating there was little difference between the dose resulting in significant TChE inhibition and that resulting in mortality.

Gene expression responses linked to reproduction effect concentrations (EC 10,20,50,90) of dimethoate, atrazine and carbendazim, in Enchytraeus albidus

Background

Molecular mechanisms of response to pesticides are scarce and information on such responses from soil invertebrates is almost inexistent. Enchytraeus albidus (Oligochaeta) is a standard soil ecotoxicology model species for which effects of many pesticides are known on survival, reproduction and avoidance behaviour. With the recent microarray development additional information can be retrieved on the molecular effects.

Methodology/Principal Findings

Experiments were performed to investigate the transcription responses of E. albidus when exposed to three pesticides – dimethoate (insecticide), atrazine (herbicide) and carbendazim (fungicide) – in a range of concentrations that inhibited reproduction by 10%, 20%, 50% and 90% (EC₁₀, EC₂₀, EC₅₀ and EC₉₀, respectively). The goal of this study was to further identify key biological processes affected by each compound and if dose-related. All three pesticides significantly affected biological processes like translation, regulation of the cell cycle or general response to stress. Intracellular signalling and microtubule-based movement were affected by dimethoate and carbendazim whereas atrazine affected lipid and steroid metabolism (also by dimethoate) or carbohydrate metabolism (also by carbendazim). Response to DNA damage/DNA repair was exclusively affected by carbendazim.

Conclusions

Changes in gene expression were significantly altered after 2 days of exposure in a dose-related manner. The mechanisms of response were comparable with the ones for mammals, suggesting across species conserved modes of action. The present results indicate the potential of using gene expression in risk assessment and the advantage as early markers.

Species-specific responsiveness of four enzymes to endosulfan and predation risk questions their usefulness as general biomarkers

General biochemical biomarkers are widely used in current ecotoxicology and may function as early warning signals. We have, however, poor knowledge on how ecologically similar species differ in their biomarker responsiveness and how predation risk may affect these biomarkers, potentially in an interactive way with pesticides. We evaluated this by exposing four corixid water bug species to combinations of endosulfan and predation risk and quantifying the activity of four general enzymatic biomarkers: acetylcholinesterase (AChE), phenoloxidase (PO), catalase (CAT) and superoxidedismutase (SOD). AChE activity was inhibited at an endosulfan concentration of 2 μg l(-1) and this did not differ significantly among species. Predation risk inhibited AChE activity with the same magnitude as endosulfan in one species, S. striata. Reduction in the investment of immune function following pesticide exposure, as measured by the activity of PO, was only observed in C. coleoptrata at 8 μg l(-1) while we observed an increase of PO levels in S. striata. Overall, PO was suppressed under predation risk at 8 μg l(-1) endosulfan. For SOD we observed a pesticide-induced increase across all species under predation risk, while for CAT the pesticide-induced increase was only present without predation risk. These results indicate that even within this group of ecologically similar and closely related species opposing biomarker responses may exist, as observed for PO. Effects of predation risk on all four enzymes, at a similar magnitude as the pesticide effects, further question their usefulness as general biomarkers.