Interactions between effects of environmental chemicals and natural stressors: a review

Combined effects of temperature and pyriproxyfen stress in a full life-cycle test with Chironomus riparius (Insecta)

Traditional risk assessment guidelines employ acute or chronic toxicity tests for a maximum of one generation of organisms. These tests are usually performed in the laboratory at a constant standard temperature, although in the field organisms may experience different temperatures, which may be a source of additional stress. Climate change-related temperature shifts may have serious impacts on ectotherm populations that are key components of the aquatic food chains, particularly in combination with the exposure of pollutants affecting their development. Here, a chronic full life-cycle test with Chironomus riparius from the first-instar larvae in the parental (P) generation until emergence in the subsequent F1 generation was conducted at different temperatures (16 and 24°C), testing the effect of the insect growth regulator pyriproxyfen at 1, 3, 10, 30, and 100 µg/L. The emergence ratios were significantly affected by the interaction of temperature, chemical treatment, and generation, showing that, at lower temperatures, the negative effects of pyriproxyfen exposure were significantly greater in the F1 generation than in the P generation. The development rate showed that the effects of the interactions were significant in the F1 generation, underscoring the importance of extended exposure as a useful amendment to the risk assessment of those agrochemicals potentially influencing developmental and reproductive parameters in intact organisms. Moreover, results demonstrated that any difference from the standard temperature of 20°C might result in additional stress, leading to disruption of biological functions in C. riparius, highlighting the interaction among different global climate change-related variables.

Assessing the quality of freshwaters in a protected area within the Tagus River basin district (central Portugal)

Water-sediment quality was assessed in an agricultural zone of a protected area within the Tagus River basin district (central Portugal) combining chemical analysis to 12 pesticide compounds and whole toxicity testing using the bacterium , the algae , the crustacean , and the midge . The herbicides alachlor, atrazine ethofumesate, metolachlor, terbuthylazine, the insecticides chlorfenvinphos and chlorpyrifos, and the metabolite 3,4-dichloroaniline were detected in surface water samples at four sites and in groundwater samples from six wells, during four sampling occasions. Measured concentrations were compared with parametric values for human consumption, groundwater quality standards, and environmental quality standards applicable to surface water established in European Union legislation. Most severe adverse effects were noted on the growth of and lethality of in nondiluted water samples. Taking into account the values calculated by the method of toxic unit summation for pesticide mixtures, it was not possible to link the pesticides found to the toxicity detected in the water samples. Conducting this study with chemical analyses and biotests provided a more comprehensive quality assessment and realistic picture of the environmental samples analyzed, although additional studies are needed to evaluate the performance of mixture models for predicting mixture toxicity. This study underlines the importance of chemical analysis and whole toxicity testing as tools for assessing the impact of human activity on the status of water, mainly in protected zones.

A review of multiple stressor studies that include ionising radiation

Studies were reviewed that investigated the combined effects of ionising radiation and other stressors on non-human biota. The aim was to determine the state of research in this area of science, and determine if a review of the literature might permit a gross generalization as to whether the combined effects of multi-stressors and radiation are fundamentally additive, synergistic or antagonistic. A multiple stressor database was established for different organism groups. Information was collected on species, stressors applied and effects evaluated. Studies were mostly laboratory based and investigated two-component mixtures. Interactions declared positive occurred in 58% of the studies, while 26% found negative interactions. Interactions were dependent on dose/concentration, on organism's life stage and exposure time and differed among endpoints. Except for one study, none of the studies predicted combined effects following Concentration Addition or Independent Action, and hence, no justified conclusions can be made about synergism or antagonism.

Sublethal propoxur toxicity to juvenile common carp (Cyprinus carpio L., 1758): biochemical, hematological, histopathological, and genotoxicity effects

The sublethal toxicological and genotoxic potential of propoxur, a widely used carbamate insecticide against household pests, in veterinary medicine, and in public health, was evaluated on carp as a model species (Cyprinus carpio L., 1758) using the erythrocyte micronucleus test. Based on the 96-h lethal concentration, 50% (LC50) data from the U.S. Environmental Protection Agency ECOTOX Database (10 mg/L), a sublethal exposure concentration of 5 mg/L was used under static bioassay laboratory conditions. Histopathological evaluation showed no significant changes in spleen, intestine, muscle, or skin tissues. However, the following conditions were recorded: hyperemia, branchitis in primary lamella, and telangiectasis, hyperplasia, fusion, epithelial lifting, and epithelial desquamation in secondary lamella of gill tissues; hemorrhage, destruction, prenephritis, and inflammation and desquamation in the tubules; edema in the kidney; passive hyperemia, albumin, and hydropic degeneration in the liver; and hyperemia, chromatolysis, and glial proliferation in brain tissues. No statistically significant increases in micronuclei frequencies were found. Hematological parameters showed decreased hematocrit values and mean corpuscular volume values, as well as increased erythrocyte and leukocyte counts compared with the control group (p < 0.01). Plasma glucose, cholesterol, triglycerides, phosphorus, sodium, total plasma protein, chloride, and aspartate aminotransferase levels were increased (p < 0.01). Only plasma calcium and potassium levels decreased in the experimental group. Propoxur has an ecotoxicological potential on fish, a nontarget organism.

Aquatic ecotoxicity of the fungicide pyrimethanil: effect profile under optimal and thermal stress conditions

The aquatic ecotoxic profile of the fungicide pyrimethanil and its acute and chronic thermal dependence in two aquatic invertebrates Chironomus riparius and Daphnia magna were investigated. The ecotoxicity of pyrimethanil at optimal thermal conditions did not depend on the trophic level, but was species-specific. The acute pyrimethanil-toxicity on C. riparius increased with higher temperature. The chronic response of Daphnia magna to the NOEC of the fungicide was examined in a multigenerational experiment under three near-natural temperature regimes. A pyrimethanil-induced increase of total mortality was buffered by the strongly related increase of the general reproductive capacity, while population growth was stronger influenced by temperature than by the fungicide. At a LOEC, however, a second generation could not be established with D. magna at all thermal regimes. This clearly shows that thermal and multigenerational effects should be considered when appraising the ecotoxicity of pesticides and assessing their future risk for the environment.

Behavioural and physiological responses of Gammarus pulex exposed to cadmium and arsenate at three temperatures: individual and combined effects

This study aimed at investigating both the individual and combined effects of cadmium (Cd) and arsenate (AsV) on the physiology and behaviour of the Crustacean Gammarus pulex at three temperatures (5, 10 and 15 °C). G. pulex was exposed during 96 h to (i) two [Cd] alone, (ii) two [AsV] alone, and (iii) four combinations of [Cd] and [AsV] to obtain a complete factorial plane. After exposure, survival, [AsV] or [Cd] in body tissues, behavioural (ventilatory and locomotor activities) and physiological responses (iono-regulation of [Na(+)] and [Cl(-)] in haemolymph) were examined. The interactive effects (antagonistic, additive or synergistic) of binary mixtures were evaluated for each tested temperature using a predictive model for the theoretically expected interactive effect of chemicals. In single metal exposure, both the internal metal concentration in body tissues and the mortality rate increased along metallic gradient concentration. Cd alone significantly impaired both [Na(+)] and [Cl(-)] while AsV alone had a weak impact only on [Cl(-)]. The behavioural responses of G. pulex declined with increasing metal concentration suggesting a reallocation of energy from behavioural responses to maintenance functions. The interaction between AsV and Cd was considered as 'additive' for all the tested binary mixtures and temperatures (except for the lowest combination at 10 °C considered as "antagonistic"). In binary mixtures, the decrease in both ventilatory and locomotor activities and the decline in haemolymphatic [Cl(-)] were amplified when respectively compared to those observed with the same concentrations of AsV or Cd alone. However, the presence of AsV decreased the haemolymphatic [Na(+)] loss when G. pulex was exposed to the lowest Cd concentration. Finally, the observed physiological and behavioural effects (except ventilation) in G. pulex exposed to AsV and/or Cd were exacerbated under the highest temperature. The discussion encompasses both the toxicity mechanisms of these metals and their interaction with rising temperature.

Thresholds for the effects of pesticides on invertebrate communities and leaf breakdown in stream ecosystems

We compiled data from eight field studies conducted between 1998 and 2010 in Europe, Siberia, and Australia to derive thresholds for the effects of pesticides on macroinvertebrate communities and the ecosystem function leaf breakdown. Dose-response models for the relationship of pesticide toxicity with the abundance of sensitive macroinvertebrate taxa showed significant differences to reference sites at 1/1000 to 1/10,000 of the median acute effect concentration (EC50) for Daphnia magna, depending on the model specification and whether forested upstream sections were present. Hence, the analysis revealed effects well below the threshold of 1/100 of the EC50 for D. magna incorporated in the European Union Uniform Principles (UP) for registration of single pesticides. Moreover, the abundances of sensitive macroinvertebrates in the communities were reduced by 27% to 61% at concentrations related to 1/100 of the EC50 for D. magna. The invertebrate leaf breakdown rate was positively linearly related to the abundance of pesticide-sensitive macroinvertebrate species in the communities, though only for two of the three countries examined. We argue that the low effect thresholds observed were not mainly because of an underestimation of field exposure or confounding factors. From the results gathered we derive that the UP threshold for single pesticides based on D. magna is not protective for field communities subject to multiple stressors, pesticide mixtures, and repeated exposures and that risk mitigation measures, such as forested landscape patches, can alleviate effects of pesticides.

How does growth temperature affect cadmium toxicity measured on different life history traits in the soil nematode Caenorhabditis elegans?

Environmental factors, in particular temperature, have been shown to affect the toxicity of chemicals. In the present study the authors exposed the nematode Caenorhabditis elegans to five concentrations of Cd (2, 4, 6, 8, and 10 mg Cd/L agar) at four constant temperatures (11, 15, 18, and 21°C) and monitored survival and reproduction on a daily basis. Data were incorporated in a population matrix model to determine the population growth rate (PGR). An additional experiment at 15 and 20°C and 0, 1, 5, and 10 mg Cd/L was performed to include growth measurements in order to relate changes in reproduction to resource allocations between investments in growth and reproduction. The impacts of Cd on PGR increased with increasing temperature, shifting the median effective concentration (EC50) for PGR from 11.6 ± 5.4 and 9.2 ± 1.3 at 11°C and 15°C, to 2.1 ± 0.1 and 1.7 ± 0.4 at 18°C and 21°C. Cadmium and temperature decreased growth rates, but Cd also increased maturation times and decreased final body size. It is hypothesized that Cd toxicity leads to a decrease in nutrient assimilation and that this "chemical anorexia" is more severe at high temperatures, where energy demands for growth and reproduction are the highest.

Parasite-insecticide interactions: a case study of Nosema ceranae and fipronil synergy on honeybee

In ecosystems, a variety of biological, chemical and physical stressors may act in combination to induce illness in populations of living organisms. While recent surveys reported that parasite-insecticide interactions can synergistically and negatively affect honeybee survival, the importance of sequence in exposure to stressors has hardly received any attention. In this work, Western honeybees (Apis mellifera) were sequentially or simultaneously infected by the microsporidian parasite Nosema ceranae and chronically exposed to a sublethal dose of the insecticide fipronil, respectively chosen as biological and chemical stressors. Interestingly, every combination tested led to a synergistic effect on honeybee survival, with the most significant impacts when stressors were applied at the emergence of honeybees. Our study presents significant outcomes on beekeeping management but also points out the potential risks incurred by any living organism frequently exposed to both pathogens and insecticides in their habitat.

Soil ecotoxicology: state of the art and future directions

Developments in soil ecotoxicology started with observations on pesticide effects on soil invertebrates in the 1960s. To support the risk assessment of chemicals, in the 1980s and 1990s development of toxicity tests was the main issue, including single species tests and also more realistic test systems like model ecosystems and field tests focusing on structural and functional endpoints. In the mean time, awareness grew about issues like bioavailability and routes of exposure, while biochemical endpoints (biomarkers) were proposed as sensitive and potential early-warning tools. In recent years, interactions between different chemicals (mixture toxicity) and between chemical and other stressors attracted scientific interest. With the development of molecular biology, omics tools are gaining increasing interest, while the ecological relevance of exposure and effects is translating into concepts like (chemical) stress ecology, ecological vulnerability and trait-based approaches. This contribution addresses historical developments and focuses on current issues in soil ecotoxicology. It is concluded that soil ecotoxicological risk assessment would benefit from extending the available battery of toxicity tests by including e.g. isopods, by paying more attention to exposure, bioavailability and toxicokinetics, and by developing more insight into the ecology of soil organisms to support better understanding of exposure and long-term consequences of chemical exposure at the individual, population and community level. Ecotoxicogenomics tools may also be helpful in this, but will require considerable further research before they can be applied in the practice of soil ecotoxicological risk assessment.

Food rationing affects dietary selenium bioaccumulation and life cycle performance in the mayfly Centroptilum triangulifer

Selenium effects in nature are mediated by the relatively large bioconcentration of aqueous Se by primary producers and smaller, yet critical, dietary transfers to primary consumers. These basal processes are then propagated through food webs to higher trophic levels. Here we quantified the movement of dissolved Se (as selenite) to periphyton, and used the resultant periphyton as a food source for conducting full life-cycle dietary Se exposures to the mayfly Centroptilum triangulifer. Periphyton bioconcentrated Se ~2,200-fold from solution in a log-linear fashion over dissolved Se concentrations ranging from 1.1 to 23.1 μg L(-1). We examined the influence of two feeding ration levels (1x and 2x) on trophic transfer, tissue Se concentrations, maternal transfer, and functional endpoints of mayfly performance. Mayflies fed a lesser ration (1x) displayed greater trophic transfer factors (mean TTF, 2.8 ± 0.4) than mayflies fed 2x rations (mean TTF, 1.1 ± 0.3). In 1x exposures, mayflies exhibited significant (p < 0.05) reductions in survivorship and total body mass at dietary [Se] ≥ 11.9 μg g(-1), reduced total fecundity at ≥ 4.2 μg g(-1), and delayed development at ≥ 27.2 μg g(-1). Mayflies fed a greater ration (2x) displayed reduced tissue Se concentrations (apparently via growth dilution) relative to 1x mayflies, with no significant effects on performance. These results suggest that the influence of Se on mayfly performance in nature may be tied to food resource availability and quality. Furthermore, nutritional status is an important consideration when applying laboratory derived estimates of toxicity to risk assessments for wild populations.

Gene expression modifications by temperature-toxicants interactions in Caenorhabditis elegans

Although organophosphorus pesticides (OP) share a common mode of action, there is increased awareness that they elicit a diverse range of gene expression responses. As yet however, there is no clear understanding of these responses and how they interact with ambient environmental conditions. In the present study, we investigated genome-wide gene expression profiles in the nematode Caenorhabditis elegans exposed to two OP, chlorpyrifos and diazinon, in single and combined treatments at different temperatures. Our results show that chlorpyrifos and diazinon induced expression of different genes and that temperature affected the response of detoxification genes to the pesticides. The analysis of transcriptional responses to a combination of chlorpyrifos and diazinon shows interactions between toxicants that affect gene expression. Furthermore, our combined analysis of the transcriptional responses to OP at different temperatures suggests that the combination of OP and high temperatures affect detoxification genes and modified the toxic levels of the pesticides.

Conceptual modeling for identification of worst case conditions in environmental risk assessment of nanomaterials using nZVI and C60 as case studies

Conducting environmental risk assessment of engineered nanomaterials has been an extremely challenging endeavor thus far. Moreover, recent findings from the nano-risk scientific community indicate that it is unlikely that many of these challenges will be easily resolved in the near future, especially given the vast variety and complexity of nanomaterials and their applications. As an approach to help optimize environmental risk assessments of nanomaterials, we apply the Worst-Case Definition (WCD) model to identify best estimates for worst-case conditions of environmental risks of two case studies which use engineered nanoparticles, namely nZVI in soil and groundwater remediation and C(60) in an engine oil lubricant. Results generated from this analysis may ultimately help prioritize research areas for environmental risk assessments of nZVI and C(60) in these applications as well as demonstrate the use of worst-case conditions to optimize future research efforts for other nanomaterials. Through the application of the WCD model, we find that the most probable worst-case conditions for both case studies include i) active uptake mechanisms, ii) accumulation in organisms, iii) ecotoxicological response mechanisms such as reactive oxygen species (ROS) production and cell membrane damage or disruption, iv) surface properties of nZVI and C(60), and v) acute exposure tolerance of organisms. Additional estimates of worst-case conditions for C(60) also include the physical location of C(60) in the environment from surface run-off, cellular exposure routes for heterotrophic organisms, and the presence of light to amplify adverse effects. Based on results of this analysis, we recommend the prioritization of research for the selected applications within the following areas: organism active uptake ability of nZVI and C(60) and ecotoxicological response end-points and response mechanisms including ROS production and cell membrane damage, full nanomaterial characterization taking into account detailed information on nanomaterial surface properties, and investigations of dose-response relationships for a variety of organisms.

Effects of predator cues on pesticide toxicity: toward an understanding of the mechanism of the interaction

Pesticide toxicity may be modified by a number of co-occurring environmental and ecological stressors. Coexposure to predator cues has been shown to potentiate and/or synergize toxicity of pesticides. However, the mechanisms behind these interactions are not well understood. Here we examine the effects of fish predator (bluegill, Lepomis macrochirus) cues on toxicity of five different pesticides to the freshwater cladoceran, Ceriodaphnia dubia. The purpose for examining patterns among pesticides was to test the idea that the mechanism of the interaction could be explained by a general stress response; that is, the interaction patterns would be similar regardless of the pesticide's mechanism of action [MOA]). Acute 96-h concentration-response experiments were conducted for pesticides with and without fish cues. Predator cues influenced the toxicity of pesticides and the interaction patterns varied among pesticides. Fipronil exhibited a synergistic interaction, while predator cues interacted antagonistically for bifenthrin and thiacloprid. Other compounds previously reported to potentiate toxicity (malathion) were found to act additively. The results demonstrate that factors such as pesticide bioavailability, K(OC) , and exposure concentration may be important for predicting the occurrence of these interactions and that patterns were not consistent among pesticides varying in MOA. Predator stress is an important component for structuring communities and ecosystem processes. Fully understanding how this process may interact with organic contaminants may best be achieved by examination at toxicokinetic and toxicodynamic scales.

Exposure to sublethal doses of fipronil and thiacloprid highly increases mortality of honeybees previously infected by Nosema ceranae

Background

The honeybee, Apis mellifera, is undergoing a worldwide decline whose origin is still in debate. Studies performed for twenty years suggest that this decline may involve both infectious diseases and exposure to pesticides. Joint action of pathogens and chemicals are known to threaten several organisms but the combined effects of these stressors were poorly investigated in honeybees. Our study was designed to explore the effect of Nosema ceranae infection on honeybee sensitivity to sublethal doses of the insecticides fipronil and thiacloprid.

Methodology/Finding

Five days after their emergence, honeybees were divided in 6 experimental groups: (i) uninfected controls, (ii) infected with N. ceranae, (iii) uninfected and exposed to fipronil, (iv) uninfected and exposed to thiacloprid, (v) infected with N. ceranae and exposed 10 days post-infection (p.i.) to fipronil, and (vi) infected with N. ceranae and exposed 10 days p.i. to thiacloprid. Honeybee mortality and insecticide consumption were analyzed daily and the intestinal spore content was evaluated 20 days after infection. A significant increase in honeybee mortality was observed when N. ceranae-infected honeybees were exposed to sublethal doses of insecticides. Surprisingly, exposures to fipronil and thiacloprid had opposite effects on microsporidian spore production. Analysis of the honeybee detoxification system 10 days p.i. showed that N. ceranae infection induced an increase in glutathione-S-transferase activity in midgut and fat body but not in 7-ethoxycoumarin-O-deethylase activity.

Conclusions/Significance

After exposure to sublethal doses of fipronil or thiacloprid a higher mortality was observed in N. ceranae-infected honeybees than in uninfected ones. The synergistic effect of N. ceranae and insecticide on honeybee mortality, however, did not appear strongly linked to a decrease of the insect detoxification system. These data support the hypothesis that the combination of the increasing prevalence of N. ceranae with high pesticide content in beehives may contribute to colony depopulation.