Combined effects of three insecticides with different modes of action on biochemical responses of the solitary bee Osmia bicornis

Bees are simultaneously exposed to a variety of pesticides, which are often applied in mixtures and can cause lethal and sublethal effects. The combined effects of pesticides, however, are not measured in the current risk assessment schemes. Additionally, the sublethal effects of pesticides on a variety of physiological processes are poorly recognized in bees, especially in non-Apis solitary bees. In this study, we used a full-factorial design to examine the main and interactive effects of three insecticide formulations with different modes of action (Mospilan 20 SP, Sherpa 100 EC, and Dursban 480 EC) on bee biochemical processes. We measured acetylcholinesterase (AChE), glutathione S-transferase (GST) and esterase (EST) activities, as well as a nonenzymatic biomarker associated with energy metabolism, i.e., ATP level. All studied endpoints were affected by Sherpa 100 EC, and the activities of AChE and EST as well as ATP levels were affected by Dursban 480 EC. Moreover, complex interactions between all three insecticides affected ATP levels, showing outcomes that cannot be predicted when testing each insecticide separately. The results indicate that even if interactive effects are sometimes difficult to interpret, there is a need to study such interactions if laboratory-generated toxicity data are to be extrapolated to field conditions.

Mortality Pattern of Poecilus cupreus Beetles after Repeated Topical Exposure to Insecticide─Stochastic Death or Individual Tolerance?

The mortality of organisms exposed to toxicants has been attributed to either stochastic processes or individual tolerance (IT), leading to the stochastic death (SD) and IT models. While the IT model follows the principles of natural selection, the relevance of the SD model has been debated. To clarify why the idea of stochastic mortality has found its way into ecotoxicology, we investigated the mortality of Poecilus cupreus (Linnaeus, 1758) beetles from pesticide-treated oilseed rape (OSR) fields and unsprayed meadows, subjected to repeated insecticide treatments. We analyzed the mortality with the Kaplan-Meier estimator and general unified threshold model for survival (GUTS), which integrates SD and IT assumptions. The beetles were exposed three times, ca. monthly, to the same dose of Proteus 110 OD insecticide containing thiacloprid and deltamethrin, commonly used in the OSR fields. Kaplan-Meier analysis showed that the mortality of beetles from meadows was much higher after the first treatment than after the next two, indicating the IT model. Beetles from the OSR displayed approximately constant mortality after the first and second treatments, consistent with the SD model. GUTS analysis did not conclusively identify the better model, with the IT being marginally better for beetles from meadows and the SD better for beetles from OSR fields.

Effects of agricultural landscape structure and canola coverage on biochemical and physiological traits of the ground beetle Poecilus cupreus

The intensifications in the agricultural landscape and the application of pesticides can cause adverse effects on the fitness of organisms in that landscape. Here, we investigated whether habitats with different agricultural pressures influenced acetylcholinesterase (AChE) activity - a biomarker for exposure to pesticides, respiration rate, and resistance to starvation in the ground beetle Poecilus cupreus. Two differently structured landscapes were selected for the study, one dominated by small (S) and another by large (L) fields. Within each landscape three habitat types were selected: in the S landscape, these were habitats with medium (M), small (S) and no canola (meadow, 0) coverage (i.e., SM, SS, S0), and in the L landscape habitats with large (L), medium (M) and no canola (meadow, 0) coverage (i.e., LL, LM, L0), representing different levels of agricultural pressure. The activity of AChE was the highest in beetles from canola-free habitats (S0 and L0), being significantly higher than in beetles from the SM and SS habitats. The mean respiration rate corrected for body mass was also the highest in S0 and L0 beetles, with significant differences between populations from L0 vs. SS and from S0 vs. SS. Only beetles from S0, SS, L0, and LM were numerous enough to assess the resistance to starvation. Individuals from the LM habitat showed better survival compared to the canola-free habitat in the same landscape (L0), whereas in S landscape the SS beetles survived worse than those from S0, suggesting that characteristics of L landscape may lead to developing mechanisms of starvation resistance of P. cupreus in response to agricultural pressure.

Floral resources,energetic value and pesticide residues in provisions collected by Osmia bicornis along a gradient of oilseed rape coverage

Pollinators in agricultural landscapes are facing global decline and the main pressures include food scarcity and pesticide usage. Intensive agricultural landscapes may provide important food resources for wild pollinators via mass flowering crops. However, these are monofloral, short-term, and may contain pesticide residues. We explored how the landscape composition with a different proportion of oilseed rape (6-65%) around Osmia bicornis nests affects floral diversity, contamination with pesticides, and energetic value of provisions collected by this species of wild bees as food for their offspring. Altogether, the bees collected pollen from 28 plant taxa (6-15 per nest) and provisions were dominated by Brassica napus (6.0-54.2%, median 44.4%, 12 nests), Quercus sp. (1.2-19.4%, median 5.2%, 12 nests), Ranunculus sp. (0.4-42.7%, median 4.7%, 12 nests), Poaceae (1.2-59.9%, median 5.8%, 11 nests) and Acer sp. (0.6-42%, median 18.0%, 8 nests). Residues of 12 pesticides were found in provisions, with acetamiprid, azoxystrobin, boscalid, and dimethoate being the most frequently detected at concentrations up to 1.2, 198.4, 16.9 and 17.8 ng/g (median 0.3, 10.6, 11.3, 4.4 ng/g), respectively. Floral diversity and energetic value of provisions, but not the Pesticide Risk Index depended on landscape structure. Moreover, pollen diversity decreased, and energetic value increased with landscape diversity. Thus, even a structurally simple landscape may provide diverse food for O. bicornis if the nest is located close to a single but resource-diverse patch. Both B. napus and non-crop pollen were correlated with pesticide concentrations.

Homogeneity of agriculture landscape promotes insecticide resistance in the ground beetle Poecilus cupreus

The intensification of agriculture leads to increased pesticide use and significant transformation from small fields towards large-scale monocultures. This may significantly affect populations of non-target arthropods (NTA). We aimed to assess whether the multigenerational exposure to plant protection products has resulted in the evolution of resistance to insecticides in the ground beetle Poecilus cupreus originating from different agricultural landscapes. Two contrasting landscapes were selected for the study, one dominated by small and another by large fields. Within each landscape the beetles were collected at nine sites representing range of canola coverage and a variety of habitat types. Part of the collected beetles, after acclimation to laboratory conditions, were tested for sensitivity to Proteus 110 OD-the most commonly used insecticide in the studied landscapes. The rest were bred in the laboratory for two consecutive generations, and part of the beetles from each generation were also tested for sensitivity to selected insecticide. We showed that the beetles inhabiting areas with medium and large share of canola located in the landscape dominated by large fields were less sensitive to the studied insecticide. The persistence of reduced sensitivity to Proteus 110 OD for two consecutive generations indicates that either the beetles have developed resistance to the insecticide or the chronic exposure to pesticides has led to the selection of more resistant individuals naturally present in the studied populations. No increased resistance was found in the beetles from more heterogeneous landscape dominated by small fields, in which spatio-temporal diversity of crops and abundance of small, linear off-crop landscape elements may provide shelter that allows NTAs to survive without developing any, presumably costly, resistance mechanisms.

Effects of agricultural landscape structure, insecticide residues, and pollen diversity on the life-history traits of the red mason bee Osmia bicornis

Agricultural landscapes have changed substantially in recent decades, shifting from the dominance of small fields (S) with diverse cropping systems toward large-scale monoculture (L), where landscape heterogeneity disappears. In this study, artificial nests of the red mason bee, Osmia bicornis, were placed in S and L landscape types on the perimeter of oilseed rape fields representing different oilseed rape coverages (ORC, % land cover). The local landscape structure around each nest was characterised within a 100, 200, 500, and 1000 m radius using ORC and 14 landscape characteristics, which were then reduced by non-metric multidimensional scaling (nMDS) to two axes: nMDS1 characterised the dataset primarily according to land fragmentation and the main crop, whereas nMDS2 captured the prevalence of more natural areas in the landscape. Pollen diversity and insecticide risk levels in the pollen provisions collected by the bees were analysed, and their dependence on the landscape structure was tested. Thereafter, the effects of pollen diversity, insecticide risk, and landscape structure on the life-history traits of bees and their sensitivity to topically applied Dursban 480 EC were determined. Pollen taxa richness in a single nest ranged from 3 to 12, and 34 pesticides were detected in the pollen at concentrations of up to 320 ng/g for desmedipham. The O. bicornis foraging range was relatively large, indicating that the landscape structure within a radius of ~1000 m around the nest is important for this species. Pollen diversity in the studied areas was of minor importance for bee performance, but the ORC or landscape structure significantly affected the life-history traits of the bees. Contamination of pollen with insecticides affected the bees by decreasing the mass of newly emerged adults but their sensitivity to Dursban 480 EC was not related to environmental variables.

Toxicokinetics of three insecticides in the female adult solitary bee Osmia bicornis

The worldwide decline of pollinators is of growing concern and has been related to the use of insecticides. Solitary bees are potentially exposed to many insecticides through contaminated pollen and/or nectar. The kinetics of these compounds in solitary bees is, however, unknown, limiting the use of these important pollinators in pesticide regulations. Here, the toxicokinetics (TK) of chlorpyrifos (as Dursban 480 EC), cypermethrin (Sherpa 100 EC), and acetamiprid (Mospilan 20 SP) was studied for the first time in Osmia bicornis females at sublethal concentrations (near LC_20s). The TK of the insecticides was analysed in bees continuously exposed to insecticide-contaminated food in the uptake phase followed by feeding with clean food in the decontamination phase. The TK models differed substantially between the insecticides. Acetamiprid followed the classic one-compartment model with gradual accumulation during the uptake phase followed by depuration during the decontamination phase. Cypermethrin accumulated rapidly in the first two days and then its concentration decreased slowly. Chlorpyrifos accumulated similarly rapidly but no substantial depuration was found until the end of the experiment. Our study demonstrates that some insecticides can harm solitary bees when exposed continuously even at trace concentrations in food because of their constant accumulation leading to time-reinforced toxicity.

Physiological and biochemical response of the solitary bee Osmia bicornis exposed to three insecticide-based agrochemicals

The physiological and biochemical stress induced by pesticides need to be addressed in economically and ecologically important non-Apis solitary bees, particularly at lower than field-applied concentrations. Thus, the aim of the present study was to analyse the physiological and biochemical changes in female adult Osmia bicornis bees upon continuous oral exposure to three insecticide-based agrochemicals - i.e. Dursban 480 EC (active ingredient - a.i. chlorpyrifos), Sherpa 100 EC (a.i. cypermethrin), and Mospilan 20 SP (a.i. acetamiprid), in a toxicokinetic manner (feeding with either insecticide-contaminated food or uncontaminated food (controls) for 8 d in the contamination phase followed by 8 d of decontamination (i.e. feeding with uncontaminated food)). All three tested agrochemicals altered the energetic budget of bees by the deprivation of energy derived from lipids and carbohydrates (but not proteins) and/or a decrease in respiration based metabolic rate (energy consumption) compared to the controls. The activities of acetylcholinesterase and glutathione-S-transferase enzymes were not altered by insecticides at tested concentrations. These results show that chronic exposure to at least some pesticides even at relatively low concentrations may cause severe physiological disruptions that could potentially be damaging for the solitary bees.

The development of the solitary bee Osmia bicornis is affected by some insecticide agrochemicals at environmentally relevant concentrations

Solitary bees provide essential pollination services for many arable crops, but are prone to global decline. Agricultural intensification, which is connected with pesticide usage, is among major threats to bees and, thus, to the food security and ecosystem stability. As it may not be possible to cease pesticide usage currently because of the growing demand for food, it is crucial to understand the pesticide toxicities to bees for better protection of pollinator populations. The majority of studies have focused on social bees, and those on solitary bees studied effects of adult exposure, whereas these bees are also likely to be exposed as larvae via the consumption of contaminated pollen. Here, the effects of three commonly used insecticide-based plant protection products on the development of the solitary bee, Osmia bicornis (red mason bee), were studied by exposing larvae to insecticide-contaminated multifloral pollen. The tested insecticides were: Dursban480EC, containing the organophosphate chlorpyrifos (CHP), Sherpa100EC, containing the pyrethroid cypermethrin (CYP), and Mospilan20SP with the neonicotinoid acetamiprid (ACT). When compared to the control larvae fed with uncontaminated-pollen, both CHP and CYP significantly reduced the O. bicornis larval survival and their body mass at all tested concentrations. In contrast, ACT did not affect either larval survival or body mass, but the length of larval stage to cocoon formation was significantly shortened compared to controls. None of studied insecticides affected the mass of cocooned individuals. However, at least 80% of individuals exposed to any of the tested insecticides died before reaching the adult stage, whereas 43% of the controls emerged successfully after overwintering. Although no clear monotonic dose-response relationships were found, our study showed that at least some insecticide formulations affect the development of O. bicornis even at concentrations actually found in pollen in the field, indicating an urgent need for revising current pesticide usage recommendations.

Supporting non-target arthropods in agroecosystems: Modelling effects of insecticides and landscape structure on carabids in agricultural landscapes

Intensification of agricultural practices is one of the most important drivers of the dramatic decline of arthropod species. We do not know, however, the relative contribution to decline of different anthropogenic stressors that are part of this process. We used high-resolution dynamic landscape models and advanced spatially-explicit population modelling to estimate the relative importance of insecticide use and landscape structure for population dynamics of a widespread carabid beetle Bembidion lampros. The effects of in-crop mitigation measures through the application of insecticides with reduced lethality, and off-crop mitigation measures by increasing abundance of grassy field margins, were evaluated for the beetle along the gradient of landscape heterogeneity. Reducing the insecticide-driven lethality (from 90 to 10%) had larger positive impacts on beetle density and occupancy than increasing the abundance of field margins in a landscape. The effects of increasing field margins depended on their width and overall abundance in the landscape, but only field margins 4 m wide, applied to at least 40% of fields, resulted in an increase in beetle population density comparable to the scenario with the smallest reduction of insecticide-driven lethality we considered. Our findings suggest the importance of field margins rather as a supporting not stand-alone mitigation measure, as they generally improved effects of reduction of insecticide-driven lethality. Therefore, adding sufficiently broad off-field habitats should help to maintain viable beetle populations in agricultural landscapes even with moderate use of insecticides. In general, the less persistent the insecticides are in the environment, the larger positive impacts of applied mitigation measures on beetle populations were found. We also showed that the effectiveness of applied mitigation measures strongly depends on landscape and farmland heterogeneity. Thus, to achieve the same management or mitigation target in different landscapes might require different strategies.

Different effects of Zn nanoparticles and ions on growth and cellular respiration in the earthworm Eisenia andrei after long-term exposure

In this study, the effects of zinc nanoparticles (ZnO-NPs) and ions (ZnCl₂) on the mortality, growth, maturation, and cellular respiration of the earthworm Eisenia andrei were assessed. Earthworms were individually exposed for 98 days, starting from the juvenile stage, to soils contaminated with either ZnO-NPs or ZnCl₂ (125, 250, 500 and 1000 mg Zn kg^-1 dry weight (dw)). Exposure to the highest-concentration ionic treatments (500 and 1000 mg kg^-1) caused 100% mortality, while for other treatments, mortality did not exceed 15% at the end of exposure. Compared to the control treatment, both 125-1000 mg kg^-1 ZnO-NPs and 125 or 250 mg kg^-1 ZnCl₂ stimulated earthworm growth, which might be due to a hormetic effect. ZnO-NPs and ZnCl₂ caused different responses at medium Zn concentrations (250 and 500 mg kg^-1): earthworms exposed to ionic treatment at 250 mg kg^-1 were characterized by a significantly lower growth constant, lower cellular respiration rate, later inflection point, and higher final body weight than those exposed to ZnO-NPs treatments at the same (250 mg kg^-1) or twice as high (500 mg kg^-1) nominal Zn concentrations. However, differences were not observed in all examined parameters between the studied forms when the highest-concentration ZnO-NPs treatment was compared with the lowest-concentration ionic treatment, which was likely due to the same levels of available Zn concentrations in those treatments. Overall, different growth and maturation strategies accompanied by pronounced differences in cellular respiration were adopted by earthworms exposed to low and medium levels of either ZnO-NPs or ZnCl₂.

Unravelling the ZnO-NPs mechanistic pathway: Cellular changes and altered morphology in the gastrointestinal tract of the earthworm Eisenia andrei

A major uptake route of nanoparticles (NPs) occurs via the gastrointestinal (GI) tract. When GI tract cells are exposed, NPs cytotoxic effects are observed that subsequently adversely affect the GI tract morphology and have consequences for the whole organism. The aim of this study was to understand the mechanism of effects caused by ZnO-NPs compared to Zn ions on the earthworm Eisenia andrei. The following aspects of individually exposed earthworms were investigated: 1) qualitative structural alterations in the gut epithelium and chloragogen cells of the GI tract, 2) quantitative changes within chloragogen tissues after 48 h of exposure (using morphometric analysis), and 3) the ADP/ATP ratio in homogenized tissue of the whole organism after 21 days of exposure to contaminated soil (contamination phase) followed by 14 days of elimination in clean soil (decontamination phase) to identify possible recovery. Both ZnO-NPs and Zn ions adversely affect the gut epithelium and chloragogen tissue of earthworms after 48 h of exposure to contaminated soil. Morphometric measurements revealed that the proportions of debris vesicles in the chloragocytes were significantly lower in worms exposed to ZnO-NPs than in worms exposed to Zn ions. Moreover, numerous spherite granules were observed in the chloragocytes of ionic Zn-treated worms, but not the ZnO-NPs-treated worms, suggesting differential regulation of these Zn forms. The Zn cytotoxic effect was not reflected in ADP/ATP ratio measurements. Our study provides new insights into nano-specific effects that are distinctive from ion regulation inside the GI tract and furthers our understanding of the relationship between effects at the cellular and whole-body levels.

Effects of Cadmium Bioavailability in Food on Its Distribution in Different Tissues in the Ground Beetle Pterostichus oblongopunctatus

In most laboratory studies with oral exposure of terrestrial invertebrates to metals an artificial food, which is easy to handle, is used. The bioavailability of metals from this artificial food may, however, be much higher than from more field relevant food sources. Such differences may affect toxicokinetic processes in different tissues. To test the effect of bioavailability of Cd in food on Cd toxicokinetics and internal distribution in terrestrial invertebrates, we performed the experiment using the ground beetle Pterostichus oblongopunctatus exposed to Cd via food differing in their soluble Cd pool. We showed that in carabids Cd accumulation and elimination pattern in different tissues is not governed by the metal availability in food.

Energy reserves and respiration rate in the earthworm Eisenia andrei after exposure to zinc in nanoparticle or ionic form

The energy budget is an indicator of an organism's overall condition. Changes in energy reserves and/or energy consumption have been used as biomarkers of toxic stress. To understand the effects of different forms and concentrations of Zn and the costs of effective Zn regulation by the earthworm Eisenia andrei, we performed a toxicokinetic experiment in which individuals were sampled over time to determine the available energy reserves (total carbohydrate, protein, and lipid content), energy consumption (measured at the cellular level and as the whole-animal respiration rate), and internal Zn concentration. The earthworms were exposed to ZnCl2 or zinc nanoparticles (ZnO-NPs) in Lufa 2.2 soil for 21 days (contamination phase), followed by 14 days of elimination in clean soil (decontamination phase). Carbohydrates were the only energy reserves with significantly lower levels following ZnO-NP 1000 treatment than following other treatments (p ≤ 0.00001) in the contamination phase. The total available energy reserves and protein content did not differ among treatments, but a significant effect of exposure time was observed (p ≤ 0.0001). Exposure to Zn (both ions and NPs) increased energy consumption at the cellular level, reflecting the high energy demand of the stress response. The results indicated that E. andrei can regulate internal Zn concentrations efficiently, regardless of form or concentration, without considerable impact on energy reserves or respiration rate.

Ground beetle communities in a mountain river subjected to restoration: The Raba River, Polish Carpathians

Effects of passive restoration of mountain rivers on the organisms inhabiting exposed riverine sediments are considerably less understood than those concerning aquatic biota. Thus, the effects of a recovery of the Raba River after abandonment of maintenance of its channelization scheme on ground beetle (Coleoptera: Carabidae) communities were investigated by comparing 6 unmanaged cross-sections and 6 cross-sections from adjacent channelized reaches. In each cross-section, ground beetles were collected from 12 sampling sites in spring, summer, and autumn, and 8 habitat parameters characterizing the cross-sections and sampling sites were determined. Within a few years after abandonment of the Raba River channelization scheme, the width of this gravel-bed river increased up to three times and its multi-thread pattern became re-established. Consequently, unmanaged river cross-sections had significantly larger channel width and more low-flow channels and eroding cutbanks than channelized cross-sections. Moreover, sampling sites in the unmanaged cross-sections were typified by significantly steeper average surface slope and larger average distance from low-flow channels than the sites in channelized cross-sections. In total, 3992 individuals from 78 taxa were collected during the study. The ground beetle assemblages were significantly more abundant and richer in species in the unmanaged than in the channelized cross-sections but no significant differences in carabid diversity indices between the two cross-section types were recorded. Redundancy Analysis indicated active river zone width as the only variable explaining differences in abundance and species richness among the cross-sections. Multiple regression analysis indicated species diversity to predominantly depend on the degree of plant cover and substrate grain size. The study showed that increased availability of exposed sediments in the widened river reaches allowed ground beetles to increase their abundance and species richness within a few years after the onset of river restoration, but more time may be needed for development of more diverse carabid communities.

Effect of cadmium bioavailability in food on its compartmentalisation in carabids

Metals assimilated by organisms are sequestered in various compartments and some forms are more stable than others. Sequestration mechanisms used by invertebrates to detoxify metals and prevent interaction with important biomolecules include metal binding to proteins and other ligands, and storage in inorganic granules. The rate and extent at which metal concentrations in different compartments respond to metal concentrations in food and food characteristics has not received much attention, despite being of great relevance. We performed an experiment on the carabid beetle Pterostichus oblongopunctatus exposed to Cd via food made of ground mealworm (Tenebrio molitor) larvae, either reared on Cd contaminated medium or artificially spiked after grinding with CdCl₂ solution. Thus, in both cases we used the same type of food, differing only in the soluble Cd pool available to the predators, represented by P. oblongopunctatus. Subcellular compartmentalisation of Cd into organelles, heat-sensitive and heat-stable proteins (the first supernatant, S1 fraction), cellular debris (the second supernatant, S2 fraction) and metal-rich granules (G fraction) was checked a few times during the contamination (90 d) and decontamination (24 d) phases in a toxicokinetic experiment by using different centrifugation steps. The results showed no effect of the type of food (naturally, Cd-N, vs. artificially contaminated with Cd, Cd-A) on Cd sequestration kinetics in P. oblongopunctatus, but the amount of Cd sequestered in the S1 and G fractions were in general higher in the Cd-A than the Cd-N treatment, indicating that Cd transfer in the food web depends on the speciation of the metal in the food. The proportional distribution of Cd over different fractions was, however, similar in beetles fed both food types. Most of the accumulated Cd in the beetles existed as fraction S1 (ca. 35%), which is important for the transfer of metals to higher trophic levels in a food web.

Toxicokinetics of zinc-oxide nanoparticles and zinc ions in the earthworm Eisenia andrei

The toxicokinetics of zinc in the earthworm Eisenia andrei was investigated following exposure for 21 days to ionic zinc (ZnCl₂) or zinc oxide nanoparticles (ZnO-NPs) in Lufa 2.2 soil, followed by 21 days elimination in clean soil. Two concentrations were tested for both ZnCl₂ (250 and 500μg Zn g^-1) and ZnO-NPs (500 and 1000μg Zn g^-1), corresponding to EC₂₅ and EC₅₀ for effects on reproduction. Based on the measured internal Zn concentrations in the earthworms over time of exposure, the kinetics parameters k_a - assimilation rate constant (g_soil g^-1_{body weight} day^-1) and k_e - elimination rate constant (day^-1) were estimated using a one-compartment model for either total Zn concentrations in the soil or porewater Zn concentrations. In the ZnCl₂ treatments, k_a was higher for total Zn concentrations in soil, whereas in the ZnO-NP treatments, k_a was higher for porewater Zn concentrations. The value of k_e did not differ between the two Zn forms (ZnCl₂ vs ZnO-NPs) for either EC₅₀ or EC₂₅ when related to total Zn concentrations in soil, but for EC₅₀, k_e related to porewater Zn concentrations was significantly higher for ZnCl₂ than for ZnO-NPs. It is concluded that differences in kinetic parameters between treatments were connected with exposure concentrations rather than with the form of Zn. Zinc was efficiently regulated by the earthworms in all treatments: a 2-fold increase in exposure concentration resulted in a less than 2-fold increase in internal concentration, and after transfer to uncontaminated soil the internal Zn concentrations in the earthworms returned to ca 111μgg^-1 dw in all treatments.

Combined effects of chlorpyriphos, copper and temperature on acetylcholinesterase activity and toxicokinetics of the chemicals in the earthworm Eisenia fetida

In polluted environments organisms are commonly exposed to a combination of chemicals with different modes of action, and their effects can be additionally modified by natural abiotic conditions. One possible mechanism for interactions in mixtures is via toxicokinetics, as chemicals may alter the uptake, distribution, biotransformation and/or elimination of each other, and all these processes can be affected by temperature. In this study, the effect of temperature (T) on the toxicokinetics of copper (Cu) and chlorpyriphos (CHP), applied either singly or in binary mixtures, was studied in the earthworm Eisenia fetida. The experiments were conducted at 10 or 20 °C and the earthworms were exposed to environmentally realistic concentrations of Cu and/or CHP for 16 d, followed by a depuration period of 4 d in uncontaminated soil. The earthworms were sampled for body Cu and/or CHP concentrations and acetylcholinesterase (AChE) activity measurements. The CHP degradation rate in the soil was substantially higher at 20 °C and in soil treated with Cu. The significant (p < 0.05) inhibition of AChE activity in the earthworms exposed to CHP was found. The effect of Cu was significant only at p < 0.1. No synergistic effect of the parallel CHP and Cu exposure was found. Four days after transferring the earthworms to uncontaminated soil, the AChE activity recovered to the level observed in control animals. The temperature effect on the toxicokinetic parameters was more pronounced for CHP than for Cu. In the case of CHP, the assimilation rate constant (k_A) was significantly higher at 20 °C than at 10 °C, both in CHP-only and CHP + Cu treatments. A similar trend was found for the elimination rate constant (k_E), but the difference was statistically significant only for non-Cu treatments. In the case of Cu, the general trend of higher k_A and k_E at 20 °C and in the absence of CHP was observed.

Metal toxicokinetics and metal-driven damage to the gut of the ground beetle Pterostichus oblongopunctatus

Toxicokinetics makes up the background for predicting concentrations of chemicals in organisms and, thus, ecological risk assessment. However, physiological and toxicological mechanisms behind toxicokinetics of particular chemicals are purely understood. The commonly used one-compartment model has been challenged recently, showing that in the case of metals it does not describe the pattern observed in terrestrial invertebrates exposed to highly contaminated food. We hypothesised that the main mechanism shaping toxicokinetics of metals in invertebrates at high exposure concentrations in food is the cellular damage to the gut epithelial cells. Gut damage should result in decreased metal assimilation rate, while shedding the dead cells - in increased elimination rate. We performed a typical toxicokinetic experiment, feeding the ground beetles Pterostichus oblongopunctatus food contaminated with Cd, Ni or Zn at 40 mM kg^-1 for 28 days, followed by a depuration period of 14 days on uncontaminated food. The male beetles were sampled throughout the experiment for body metal concentrations and histopathological examinations of the midgut. All metals exhibited a complex pattern of internal concentrations over time, with an initial rapid increase followed by a decrease and fluctuating concentrations during further metal exposure. Histopathological studies showed massive damage to the midgut epithelium, with marked differences between the metals. Cd appeared the most toxic and caused immediate midgut cell degeneration. The effects of Ni were more gradual and pronounced after at least 1 week of exposure. Zn also caused extensive degeneration in the gut epithelium but its effects were the weakest among the studied metals.

Subcellular partitioning of cadmium and zinc in mealworm beetle (Tenebrio molitor) larvae exposed to metal-contaminated flour

By studying the internal compartmentalization of metals in different subcellular fractions we are able to better understand the mechanisms of metal accumulation in organisms and the transfer of metals through trophic chains. We investigated the internal compartmentalization of cadmium (Cd) and zinc (Zn) in mealworm beetle (Tenebrio molitor) larvae by breeding them in flour contaminated with either Cd at 100, 300 and 600mgkg(-1), or Zn at 1000 and 2000mgkg(-1). We separated the cellular components of the larvae into 3 fractions: the S1 or cytosolic fraction containing organelles, heat-sensitive and heat-stable proteins, the S2 or cellular debris fraction and the G or metal-rich granule fraction. The concentration of Cd and Zn in each fraction was measured at 0, 7, 14 and 21 days of being fed the flour. The concentration of Cd in the flour affected the concentration of Cd measured in each larval subcellular fraction (p≤0.0001), while the concentration of Zn in the flour only affected the Zn concentration in the S2 and G fractions (p≤0.02). Both Cd and Zn concentrations in mealworms remained relatively constant during the exposure (days 7, 14 and 21) in all three fractions, but the Cd concentrations were much higher than those found in larvae before the exposure (day 0). The concentration of Cd in the flour, however, did not affect the percentage of Cd in the S1 fraction. The contribution of Cd in the G fraction to the total Cd amount was similar (30-40%) in all Cd treatments. The percentage of Zn in all three fractions was not affected by the concentration of Zn in the flour and the relative contributions of each subcellular fraction to the total burden of Zn remained generally constant for both control and treated larvae. In general, larvae sequestered approximately 30% of Cd and Zn in the S1 fraction, which is important for the transport of metals to higher trophic levels in a food web.

Using toxicokinetic-toxicodynamic modeling as an acute risk assessment refinement approach in vertebrate ecological risk assessment

Recent guidance identified toxicokinetic-toxicodynamic (TK-TD) modeling as a relevant approach for risk assessment refinement. Yet, its added value compared to other refinement options is not detailed, and how to conduct the modeling appropriately is not explained. This case study addresses these issues through 2 examples of individual-level risk assessment for 2 hypothetical plant protection products: 1) evaluating the risk for small granivorous birds and small omnivorous mammals of a single application, as a seed treatment in winter cereals, and 2) evaluating the risk for fish after a pulsed treatment in the edge-of-field zone. Using acute test data, we conducted the first tier risk assessment as defined in the European Food Safety Authority (EFSA) guidance. When first tier risk assessment highlighted a concern, refinement options were discussed. Cases where the use of models should be preferred over other existing refinement approaches were highlighted. We then practically conducted the risk assessment refinement by using 2 different models as examples. In example 1, a TK model accounting for toxicokinetics and relevant feeding patterns in the skylark and in the wood mouse was used to predict internal doses of the hypothetical active ingredient in individuals, based on relevant feeding patterns in an in-crop situation, and identify the residue levels leading to mortality. In example 2, a TK-TD model accounting for toxicokinetics, toxicodynamics, and relevant exposure patterns in the fathead minnow was used to predict the time-course of fish survival for relevant FOCUS SW exposure scenarios and identify which scenarios might lead to mortality. Models were calibrated using available standard data and implemented to simulate the time-course of internal dose of active ingredient or survival for different exposure scenarios. Simulation results were discussed and used to derive the risk assessment refinement endpoints used for decision. Finally, we compared the "classical" risk assessment approach with the model-based approach. These comparisons showed that TK and TK-TD models can bring more realism to the risk assessment through the possibility to study realistic exposure scenarios and to simulate relevant mechanisms of effects (including delayed toxicity and recovery). Noticeably, using TK-TD models is currently the most relevant way to directly connect realistic exposure patterns to effects. We conclude with recommendations on how to properly use TK and TK-TD model in acute risk assessment for vertebrates.

Concentration dependent toxicokinetics of copper in the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae)

To predict internal metal concentrations in animals under specific environmental exposures, the relationship between the exposure concentrations and values of toxicokinetic parameters must be known. At high exposure levels, the availability of carriers transporting metal ions through cellular membranes may become limited, thereby decreasing the assimilation rates (k A ). Furthermore, increased metal concentrations in food may result in greater damage to the gut and reduce the assimilation efficiency and/or increase the elimination rate (k E ). Therefore, k A should decrease and k E should increase with increasing metal concentrations. In fact, our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg(-1) of dry flour showed that with increasing Cu concentrations, k A decreased from 0.0042 day(-1) at 500 mg kg(-1) to 0.0026 day(-1) at 4000 mg kg(-1) in females and from 0.0029 to 0.001 day(-1) in males and k E increased from 0.027 to 0.064 day(-1) and from 0.018 to 0.04 day(-1) in females and males, respectively. Significant differences in k A between the sexes were observed at 2000 and 4000 mg kg(-1), whereas significant differences between treatments were found for k A in males. Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration. No Cu effect on the respiratory metabolism of T. castaneum was found.

Regulation of body metal concentrations: Toxicokinetics of cadmium and zinc in crickets

Previous studies indicated that essential and xenobiotic metals differ substantially in terms of their toxicokinetics. Whether these differences are due to different assimilation rates, different elimination rates, or both, and whether all metals are regulated in a similar manner but with different efficiency remains unclear. To compare the mechanisms responsible for the regulation of different metals, parameters for toxicokinetic models have to be tested under exposures to the identical molar concentration of those metals. In this study, the cricket Gryllus assimilis was exposed to Zn or Cd at 2.5, 10, and 40mMkg(-1) dry food. The body concentrations of the metals were not perfectly regulated by the crickets. For Zn, a clear increase in the body concentration was found only at the highest treatment; whereas at the lowest treatment, the internal concentration remained unchanged throughout the experiment. At the lowest Zn concentration, the assimilation (kA) [day(-1)] and elimination (kE) [day(-1)] rate constants were balanced (kA=0.024, kE=0.024). When increasing the Zn exposure, kA decreased to 0.018 at 10mMkg(-1) and 0.01 at 40mMkg(-1), and kE increased to 0.05 and 0.07, respectively. Therefore, the body concentration of Zn was regulated by simultaneously changing the assimilation and elimination rate. By contrast, even at the lowest treatment, a significant increase in Cd concentration was observed in the crickets. The equilibrium Cd concentration resulted almost exclusively from increasing kE from 0.17, through 0.28 to 0.61 at 2.5, 10 and 40mMkg(-1). The kA for Cd did not reveal any clear trend. Zn was more efficiently regulated by crickets than was Cd: a 16-fold increase in exposure concentration (from 2.5 to 40mM Znkg(-1)) resulted only in a twofold increase of internal concentration, whereas the identical increase in Cd exposure concentration resulted in almost a sevenfold increase in internal concentration of this metal.

Combined effect of nickel and chlorpyrifos on the ground beetle Pterostichus oblongopunctatus

Although terrestrial invertebrates are often exposed to mixtures of chemicals in the field, little is known about their combined effects on metabolism. We studied the effects of nickel (Ni), chlorpyrifos (CPF) and their mixtures on the respiration rate of the ground beetle Pterostichus oblongopunctatus in a toxicokinetics experiment. The respiration rate was measured six times in the uptake phase (64 days) and four times in the decontamination phase (32 days), and internal Ni concentrations were measured in parallel. The beetles׳ respiration rate in the uptake phase was especially affected by CPF. Moreover, the significant interaction of Ni with the time of exposure indicated that at certain dates Ni also affected respiration rates. Respiration rates changed significantly with time, and the most pronounced increase was observed after 2 days of exposure to a high concentration of CPF. Increased respiration rates in CPF-exposed beetles compared with controls were still observed after switching the beetles to uncontaminated food, whereas the effect of Ni disappeared in the decontamination phase altogether. In the beetles exposed to both Ni alone and Ni mixed with CPF at a low concentration, Ni reached high internal concentrations by the second day of exposure. Two days later, the internal concentrations dropped significantly, indicating efficient decontamination, even if the beetles were still exposed to Ni-contaminated food. High-concentration CPF decreased the accumulation of Ni. No effect of CPF was found in the decontamination phase. The importance of accounting for time in the mixture toxicity testing and ecological risk assessment is discussed.

Toxicokinetics of metals in terrestrial invertebrates: making things straight with the one-compartment principle

In this analysis, we first performed a critical review of one-compartment models used to describe metal toxicokinetics in invertebrates and found mathematical or conceptual errors in almost all published studies. In some publications, the models used do not represent the exact solution of the underlying one-compartment differential equations; others use unrealistic assumptions about constant background metal concentration and/or zero metal concentration in uncontaminated medium. Herein we present exact solutions of two differential-equation models, one describing simple two-stage toxicokinetics (metal toxicokinetic follows the experimental phases: the uptake phase and the decontamination phase) and another that can be applied for more complex three-stage patterns (toxicokinetic pattern does not follow two phases determined by an experimenter). Using two case studies for carabids exposed via food, based on previously published data, we discuss and compare our models to those originally used to analyze the data. Our conclusion is that when metal toxicokinetic follows a one-compartment model, the exact solution of a set of differential equations should be used. The proposed models allow assimilation and elimination rates to change between toxicokinetic stages, and the three-stage model is flexible enough to fit patterns that are more complex than the classic two-stage model can handle.

More ecological ERA: incorporating natural environmental factors and animal behavior

We discuss the importance of selected natural abiotic and biotic factors in ecological risk assessment based on simplistic laboratory bioassays. Although it is impossible to include all possible natural factors in standard lower-tier ecotoxicological testing, neglecting them is not an option. Therefore, we try to identify the most important factors and advocate redesigning standard testing procedures to include theoretically most potent interactions. We also point out a few potentially important factors that have not been studied enough so far. The available data allowed us to identify temperature and O2 depletion as the most critical factors that should be included in ecotoxicity testing as soon as possible. Temporal limitations and fluctuations in food availability also appear important, but at this point more fundamental research in this area is necessary before making decisions on their inclusion in risk assessment procedures. We propose using specific experimental designs, such as Box-Behnken or Central Composite, which allow for simultaneous testing of 3 or more factors for their individual and interactive effects with greater precision and without increasing the effort and costs of tests dramatically. Factorial design can lead to more powerful tests and help to extend the validity of conclusions. Finally, ecological risk assessment procedures should include information on animal behavior, especially feeding patterns. This requires more basic studies, but already at this point adequate mechanistic effect models can be developed for some species.

A toxicokinetic model for thiamethoxam in rats: implications for higher-tier risk assessment

Risk assessment for mammals is currently based on external exposure measurements, but effects of toxicants are better correlated with the systemically available dose than with the external administered dose. So for risk assessment of pesticides, toxicokinetics should be interpreted in the context of potential exposure in the field taking account of the timescale of exposure and individual patterns of feeding. Internal concentration is the net result of absorption, distribution, metabolism and excretion (ADME). We present a case study for thiamethoxam to show how data from ADME study on rats can be used to parameterize a body burden model which predicts body residue levels after exposures to LD50 dose either as a bolus or eaten at different feeding rates. Kinetic parameters were determined in male and female rats after an intravenous and oral administration of (14)C labelled by fitting one-compartment models to measured pesticide concentrations in blood for each individual separately. The concentration of thiamethoxam in blood over time correlated closely with concentrations in other tissues and so was considered representative of pesticide concentration in the whole body. Body burden model simulations showed that maximum body weight-normalized doses of thiamethoxam were lower if the same external dose was ingested normally than if it was force fed in a single bolus dose. This indicates lower risk to rats through dietary exposure than would be estimated from the bolus LD50. The importance of key questions that should be answered before using the body burden approach in risk assessment, data requirements and assumptions made in this study are discussed in detail.

Costs of living in metal polluted areas: respiration rate of the ground beetle Pterostichus oblongopunctatus from two gradients of metal pollution

To address the question about costs of living in polluted areas, biomarkers linked to metabolism were measured in Pterostichus oblongopunctatus (Coleoptera: Carabidae) collected along two metal-pollution gradients in the vicinity of the two largest Polish zinc smelters: 'Bolesław' and 'Miasteczko Śląskie' in southern Poland. Both gradients covered a broad range of Zn and Cd concentrations in the humus layer (109-6151 and 1.48-71.4 mg kg(-1), respectively) and body metal concentrations increased with increasing soil metal concentrations. The whole-organism respiration rate was measured as oxygen consumption with Micro-Oxymax respirometer, and cellular energy consumption-as the activity of electron transport system, which is linked to cellular respiration rate. The significant increase in the whole-organism respiration rate with the body metal concentration was found when taking into account other factors such as body mass, gradient (or year of sampling as the beetles were collected on the gradients in different years) and the interactions: body metal concentrations × collection date, body metal concentrations × body mass, and body mass × gradient/sampling year. However, no relationships between metal concentrations in soil or body metal concentrations and the whole-organism or cellular respiration rate could be detected when using mean values per site, underlining the crucial importance of incorporating individual variability in such analyses. The observed increase of the whole-organism respiration rate with increasing body contamination with metals suggests that P. oblongopunctatus incurs energetic expenditures resulting from the necessity to facilitate metal elimination or repair of toxicant-induced damage.

Energy reserves and accumulation of metals in the ground beetle Pterostichus oblongopunctatus from two metal-polluted gradients

Living in an area chronically polluted with metals is usually associated with changes in the energy distribution in organisms due to increased energy expenses associated with detoxification and excretion processes. These expenses may be reflected in the available energy resources, such as lipids, carbohydrates, and proteins. In this context, the energy status of Pterostichus oblongopunctatus (Coleoptera: Carabidae) was studied in two metal pollution gradients near Olkusz and Miateczko Śląskie in southern Poland. Both regions are rich in metal ores, and the two largest Polish zinc smelters have been operating there since the 1970s. Beetles were collected from five sites at each gradient. Zinc and cadmium concentrations were measured in both the soil and the beetles. The possible reduction in energy reserves as a cost of detoxifying assimilated metals was evaluated biochemically by determining the total lipid, carbohydrates, and protein contents. At the most polluted sites, the Zn concentration in the soil organic layer reached 2,906 mg/kg, and the Cd concentration reached 55 mg/kg. Body Zn and Cd concentrations increased with increasing soil Zn and Cd concentrations (p = 0.003 and p = 0.0001, respectively). However, no relationship between pollution level and energetic reserves was found. The results suggest that populations of P. oblongopunctatus inhabiting highly metal-polluted sites are able to survive without any serious impact on their energy reserves, though they obviously have to cope with elevated body metal concentrations.

Two-phase uptake of nickel in the ground beetle Pterostichus oblongopunctatus (Coleoptera: Carabidae): implications for invertebrate metal kinetics

We studied nickel (Ni) kinetics in the ground beetle Pterostichus oblongopunctatus exposed to different, potentially stressful, temperatures. We found unexpected Ni kinetics in metal-exposed adult and larval beetles. Instead of the pattern observed commonly for other metals, i.e., an increase in metal concentration followed by stabilisation in the uptake phase and a decrease after transfer to uncontaminated food, the Ni-fed beetles apparently switched to decontamination soon after the start of Ni exposure while they were still being fed Ni-spiked food. In addition, internal body Ni concentrations showed high variance. The traditional first-order, one-compartment model with the switch to decontamination set to the last day of the uptake phase appeared inadequate and in most cases was nonsignificant. Instead, the model with a regression-estimated point of switching to decontamination fit the data better, explaining 57.2-91.5% of the temporal variability of mean Ni body concentrations (weighted regression) in adult beetles and 44.1-62.3% in larvae. Temperature did not affect Ni toxicokinetics in adults, but in larvae there were some temperature-dependent differences in kinetic parameters.

Interactions between toxic chemicals and natural environmental factors--a meta-analysis and case studies

The paper addresses problems arising from effects of natural environmental factors on toxicity of pollutants to organisms. Most studies on interactions between toxicants and natural factors, including those completed in the EU project NoMiracle (Novel Methods for Integrated Risk Assessment of Cumulative Stressors in Europe) described herein, showed that effects of toxic chemicals on organisms can differ vastly depending purely on external conditions. We compiled data from 61 studies on effects of temperature, moisture and dissolved oxygen on toxicity of a range of chemicals representing pesticides, polycyclic aromatic hydrocarbons, plant protection products of bacterial origin and trace metals. In 62.3% cases significant interactions (p< or =0.05 or less) between natural factors and chemicals were found, reaching 100% for the effect of dissolved oxygen on toxicity of waterborne chemicals. The meta-analysis of the 61 studies showed that the null hypothesis assuming no interactions between toxic chemicals and natural environmental factors should be rejected at p=2.7 x 10(-82) (truncated product method probability). In a few cases of more complex experimental designs, also second-order interactions were found, indicating that natural factors can modify interactions among chemicals. Such data emphasize the necessity of including information on natural factors and their variation in time and across geographic regions in ecological risk assessment. This can be done only if appropriate ecotoxicological test designs are used, in which test organisms are exposed to toxicants at a range of environmental conditions. We advocate designing such tests for the second-tier ecological risk assessment procedures.

Three-phase metal kinetics in terrestrial invertebrates exposed to high metal concentrations

Models of metal toxicokinetics are critically evaluated using both newly generated data in the NoMiracle project as well as those originating from older studies. The analysis showed that the most frequently used one-compartment two-phase toxicokinetic model, with one assimilation and one elimination rate constant, does not describe correctly certain data sets pertaining particularly to the pattern of assimilation of trace elements. Using nickel toxicokinetics in carabid beetles and earthworms as examples, we showed that Ni in fact exhibits a three-phase kinetics with a short phase of fast metal accumulation immediately after exposure, followed by partial elimination to an equilibrium concentration at a later stage of a metal exposure phase, and by final elimination upon transfer to an uncontaminated food/soil. A similar phenomenon was also found for data on cadmium kinetics in ground beetles and copper kinetics in earthworms in data already published in the literature that was not accounted for in the earlier analysis of the data. The three-phase model suggests that the physiology of controlling body metal concentrations can change shortly after exposure, at least in some cases, by increasing the elimination rate and/or decreasing metal assimilation. Hence, the three-phase model, that allows for different assimilation and/or elimination rates in different phases of exposure to a toxicant, may provide insight into temporal changes in the physiology of metal handling. Consequently, this alternative model should always be tested when describing metal toxicokinetics when temporal patterns of internal metal concentration exhibit an initial "overshoot" in body metal concentrations.

Locomotor activity and respiration rate of the ground beetle, Pterostichus oblongopunctatus (Coleoptera: Carabidae), exposed to elevated nickel concentration at different temperatures: novel application of Multispecies Freshwater Biomonitor

The aim of the work was to study effects of suboptimal temperature on nickel toxicity under chronic exposure and to apply the Multispecies Freshwater Biomonitor (MFB) for the first time to soil organisms in order to link behavioral to physiological endpoints. Ground beetles Pterostichus oblongopunctatus were reared at 10 or 20 degrees C on control or Ni-contaminated (2500 mg Ni kg(-1)) food. After 64 days half of the Ni-exposed beetles were transferred to uncontaminated food (elimination phase). The remaining Ni-exposed beetles were left on the contaminated food to the end of the experiment (96 days). After completing the experiment, respiration rate and locomotor activity were measured in Ni-contaminated beetles (Ni), Ni-contaminated ones after elimination (E), and controls (C). Then, the beetles were analyzed for Ni body loads. The respiration rate, which was always measured at 20 degrees C for all experimental groups, was highest in Ni beetles reared at 10 degrees C and did not differ between groups C and E. Similarly, locomotor activity was highest in Ni beetles, and marginally significant temperature effect was found. The study indicated thus that exposure to elevated Ni concentrations increased the maintenance costs in P. oblongopunctatus and that rearing the beetles at suboptimal temperature increased the respiration rate even further. However, the effects observed in both respiration rate and locomotor activity were reversible after decontamination. The study demonstrated also the potential of MFB for assessing the behavior of soil-dwelling organism in environmental toxicology.

Environmental conditions enhance toxicant effects in larvae of the ground beetle Pterostichus oblongopunctatus (Coleoptera: Carabidae)

The wide geographical distribution of ground beetles Pterostichus oblongopunctatus makes them very likely to be exposed to several environmental stressors at the same time. These could include both climatic stress and exposure to chemicals. Our previous studies demonstrated that the combined effect of nickel (Ni) and chlorpyrifos (CHP) was temperature (T)-dependent in adult P. oblongopunctatus. Frequently the different developmental stages of an organism are differently sensitive to single stressors, and for a number of reasons, such as differences in exposure routes, their interactions may also take different forms. Because of this, we studied the effects of the same factors on the beetle larvae. The results showed that all factors, as well as their interactions, influenced larvae survival. The synergistic effect of Ni and CPF was temperature-dependent and the effect of Ni x T interaction on the proportion of emerged imagines indicated stronger toxicity of Ni at 25 degrees C than at 10 degrees C.

Combined effect of environmental pollutants (nickel, chlorpyrifos) and temperature on the ground beetle, Pterostichus oblongopunctatus (Coleoptera: Carabidae)

Terrestrial organisms in the field often are exposed to a combination of stress factors of various origins, but little is known about interactions between different types of stressors. In the present study, we demonstrate the results of a study on interactions between Ni, chlorpyrifos (CPF), and temperature in the ground beetle, Pterostichus oblongopunctatus. The results revealed that all factors, and their interactions, influenced life-cycle parameters of the beetles (survival and reproduction). Significant three-factor interactions were found for effects on beetle survival, indicating that the combined negative effect of Ni and CPF was temperature dependent. In addition, significant effects of body mass were found: The survival of beetles treated with CPF and the reproduction of beetles exposed to Ni were positively correlated with body mass. All studied endpoints were affected by temperature. The results indicate that understanding interactions between temperature and toxicants, as well as among chemicals themselves, is essential for proper ecological risk assessment.

Effects of nickel and temperature on the ground beetle Pterostichus oblongopunctatus (Coleoptera: Carabidae)

In natural ecosystems it is not unusual for an organism to be exposed both to chemical and physical stressful factors at the same time. Herein we present results of the study on nickel toxicity to the carabid beetle, Pterostichus oblongopunctatus, and effect of Ni and temperature on the beetles respiration rates. In the first part of the study (Experiment I) we measured the survival, respiration rates and internal Ni concentrations in animals exposed for 245 d at constant temperature (20 degrees C) to food contaminated with Ni at nominal concentrations 0; 600; 1,200; 2,400; 4,800; and 9,600 mg kg(-1) dry weigh (dw). The LC(50) was estimated at 8,351 mg Ni kg(-1), with no effect on fertility. We found a significant positive correlation between Ni concentration in food and internal body concentration of Ni, and a negative correlation between Ni exposure and the respiration rate. Based on these results, the concentration of 2,400 mg kg(-1) (LOEC for the respiration rate) was selected for the second part of the study (Experiment II) in which field-collected males of P. oblongopunctatus were exposed to Ni-contaminated food for 64 d and then to uncontaminated food for the next 64 d at three temperatures: 10, 15 and 20 degrees C. In this part of the study we found that the temperature under which the beetles were kept affected their respiration rates, and that effect of Ni on the respiration was significant only in animals originating from 20 degrees C. The results from both experiments indicate that negative effects of nickel appear only after relatively long exposure.