Insect Chironomus Riparius Research Articles

Metal Exposure and Sex Shape the Fatty Acid Profile of Midges and Reduce the Aquatic Subsidy to Terrestrial Food Webs.

Aquatic micropollutants can be transported to terrestrial systems and their consumers by emergent aquatic insects. However, micropollutants, such as metals, may also affect the flux of physiologically important polyunsaturated fatty acids (PUFAs). As certain PUFAs have been linked to physiological fitness and breeding success of terrestrial consumers, reduced fluxes from aquatic systems could affect terrestrial populations and food webs. We chronically exposed larvae of the aquatic insect Chironomus riparius to a range of environmentally relevant sediment contents of cadmium (Cd) or copper (Cu) in a 28-day microcosm study. Since elevated water temperatures can enhance metals' toxic effects, we used two temperature regimes, control and periodically elevated temperatures (heat waves) reflecting an aspect of climate change. Cd and Cu significantly reduced adult emergence by up to 95% and 45%, respectively, while elevated temperatures had negligible effects. Both metal contents were strongly reduced (∼90%) during metamorphosis. Furthermore, the chironomid FA profile was significantly altered during metamorphosis with the factors sex and metal exposure being relevant predictors. Consequently, fluxes of physiologically important PUFAs by emergent adults were reduced by up to ∼80%. Our results suggest that considering fluxes of physiologically important compounds, such as PUFAs, by emergent aquatic insects is important to understand the implications of aquatic micropollutants on aquatic-terrestrial meta-ecosystems.

Altered gene expression in Chironomus riparius (insecta) in response to tire rubber and polystyrene microplastics

The extent until which plastics are present in our surrounding environment completely exceeds our expectations. Plastic materials in the form of microplastics have been found in terrestrial, freshwater and marine environments and are transported through the atmosphere even to remote locations. However, we are still far from understanding the effects that they may have caused and are causing to biota. In the present study, we investigated the alterations in the expression of twelve genes in the aquatic insect Chironomus riparius after 36 h exposures to polystyrene and tire rubber microplastics at nominal concentrations of 1 and 10 mg L−1. The results indicated that several genes encoding for heat shock proteins (hsp90, Glycoprotein 93 (Gp93), hsc70, hsp60, hsp40, and the small HSP hsp17) were overexpressed respect to the control. In addition, the genes coding for manganese superoxide dismutase (SOD Mn, related to alleviation of oxidative stress) and for the FK506-binding protein of 39 kDa. (FKBP39, related to development and pupation) showed altered expression. Most of the alterations on gene expression level occurred at a concentration of 10 mg L−1 of tire rubber microplastics, although specific modifications arose at other concentrations of both rubber and polystyrene. On the contrary, one hsp gene (hsp10) and genes related to biotransformation and detoxification (Cyp9f2, Cyp12a2, and ABCB6) did not alter their expression in any of the treatments. Overall, the results of the gene expression indicated that microplastics (especially tire rubber) or their additives caused cellular stress that led to some alterations in the normal gene expression but did not cause any mortality after 36 h. These results highlight the need for more studies that describe the alterations caused by microplastics at the molecular level. Additionally, it opens questions about the effects caused to aquatic fauna in environmental realistic situations, especially in hot spots of microplastic contamination (e.g., tire rubber released in storm water runoff discharge points).

Genotoxic effects and transcriptional deregulation of genetic biomarkers in Chironomus riparius larvae exposed to hydroxyl- and amine-terminated generation 3 (G3) polyamidoamine (PAMAM) dendrimers

The physical-chemical properties of polyamidoamine (PAMAM) dendrimers give them attractive qualities for multiple applications, including biomedical purposes. Their use has significantly increased in recent years, and there is currently a lack of information on their potential adverse effects on biological systems, which raises particular concerns about the risks to human health and the environment from their use and disposal. Studies focusing on ecotoxicological effects are particularly scarce. In the present work, we have used the model insect Chironomus riparius to assess the toxicity of hydroxyl-terminated and amine-terminated generation 3 PAMAM dendrimers: PAMAM G3-OH and PAMAM G3-NH2. Fourth-instar larvae were exposed to 10 or 100 ppm G3-OH or G3-NH2 dendrimers for 24 h (acute toxicity) or 24 + 24 h (delayed toxicity). Using quantitative real-time PCR, we analyzed transcriptional alterations in genes related to relevant physiological pathways: EcR, GAPDH, GPx, GST, hsp10, hsp24, Gp93, and rpL4. We also used the comet assay to assess the possible genotoxic characteristics of the dendrimers and their ability to induce DNA breakage. Regarding the effects on transcriptional activity, our results showed that G3-NH2 dendrimers induced greater (and in many cases opposite) alterations than G3-OH dendrimers, especially in acute 24-hour exposures. Delayed toxicity studies showed that both dendrimers produced transcriptional alterations even 24 h after the withdrawal of the compound and frequently contrary to what was observed acutely. In both cases, the lowest concentration studied (10 ppm) was the most toxic. On the other hand, the comet assay allowed us to detect genotoxic effects for the two dendrimers, thus demonstrating their ability to interact with DNA. This work provides new information about the possible disruptive effects of PAMAM G3 dendrimers on the health of exposed organisms, alerting the need to carry out more studies to deepen their toxic characteristics and mode of action, especially in natural environments.

Chiral conazole fungicides – (Enantioselective) terrestrial bioaccumulation and aquatic toxicity

Five conazole fungicides (CFs) (epoxiconazole, tebuconazole, myclobutanil, uniconazole (P), rac-uniconazole, and diniconazole) were tested in order to provide additional information on i) the effects of CFs on the nematode Caenorhabditis elegans and on the aquatic insect Chironomus riparius under acute exposure scenarios and in multi-generation exposure studies, taking advantage of the short life cycle of nematodes and ii) on the bioaccumulation (earthworm Eisenia andrei) profiles of CFs including also the enantiomer-specific assessment of degradation in soils and uptake/elimination by earthworms. Acute toxicity was considered low following the exposure of up to 2.5 mg of CFs per liter of the test medium. In a multigeneration study on nematodes, all five generations exposed to epoxiconazole were significantly negatively affected in terms of reproductive efficiency, and the severity of effects increased from F0 to F1 generation and was sustained thereafter. Adverse effects were also observed in the case of uniconazole (P) and diniconazole, and similarly to epoxiconazole, the effects occurred within the active life of the pesticides and were assumed to be based on their half-lives in soil (e.g., 53.3 to 691 days for uniconazole and diniconazole in our study) and in sediment/water. Bioaccumulation of diniconazole and uniconazole by earthworms varied between soils (Lufa 2.1 ≥ Lufa 2.4 > sandy soil > Lufa 2.2) and compounds (diniconazole > uniconazole) and was enantioselective. Earthworms preferentially accumulated R-uniconazole as a result of faster elimination of the S-form, which was evidenced from the enantiomer-specific uptake/elimination rate constants derived from the bioaccumulation profiles. Our results suggest that multigeneration exposure studies can advantageously be used for assessing the long-term and trans-general effects of pesticides. Also, the enantioselectivity in bioaccumulation observed for both uniconazole and diniconazole suggests that enantioselectivity in the fate and effects should be considered when exploring ways for safer and sustainable use of chiral pesticides.

Lethal and sublethal toxicity assessment of Bacillus thuringiensis var. israelensis and Beauveria bassiana based bioinsecticides to the aquatic insect Chironomus riparius

Despite being considered environmentally safe, a deeper environmental risk assessment is needed for microbial insecticides; special attention should be devoted to their sublethal toxicity to non-target species.This study evaluated effects of VectoBac® 12AS - VB (based on the bacterium Bacillus thurigiensis var. israelensis) and Naturalis®-L - NL (based on the fungus Beauveria bassiana) on the aquatic insect Chironomus riparius life-history and biochemical responses.Acute tests estimated a 48 h-LC50 (median lethal concentration) of 1.85 μg/L (VB) and 34.7 mg/L (NL). Under sublethal exposure, VB decreased adults' emergence (LOEC – lowest observed effect concentration of 80 ng/L) while NL impaired larval growth (LOEC of 0.32 mg/L) and delayed emergence (LOEC of 2 mg/L for males and 0.8 mg/L for females). Despite not being monotonic, phenoloxidase activity increased (LOEC of 20 ng/L (VB) and 2 mg/L (NL)), suggesting activation of the immune system. There were no indications of oxidative damage nor neurotoxicity. Catalase activity was stimulated with all VB treatments, possibly associated with detoxification of immune response products. Under NL exposure, glutathione-S-transferase activity increased but did not show a dose-dependent response and, total glutathione decreased in the highest concentration. Exposure to both formulations caused the increase in protein content, while carbohydrate and lipids were not altered.This study revealed the susceptibility of C. riparius to VB and NL at concentrations below the ones recommended for field application, with potential population-level effects. These results add important information for the risk assessment of these microbial insecticides in aquatic ecosystems, considering relevant sublethal endpoints and raising concern about the adverse effects on non-target aquatic organisms.

Two-generational effects of Benzophenone-3 on the aquatic midge Chironomus riparius

Organic UV-filters are emergent contaminants continuously released into the aquatic ecosystems. These compounds are persistent showing potential for bioaccumulation. Partial life-cycle tests may underestimate the toxicity of UV-filters especially since these compounds have shown to act as endocrine disruptors. In the present study, the benthic aquatic insect Chironomus riparius was exposed to a gradient of Benzophenone-3 (BP3) concentrations over two generations to assess effects over a full life cycle from the first-instar larvae in the parental (P) generation (emergence, fecundity and fertility) until emergence in the subsequent generation (filial – F1). Recovery from exposure was also assessed after one generational exposure. Our results showed that concentrations of up to 8mg BP3/kg, elicited no effects regarding emergence rate and development time of C. riparius in the P generation. Our results also showed that C. riparius fecundity was not affected by BP3 exposure, but a strong dose-response relationship was observed for fertility with none of the egg ropes hatching at 8mg BP3/kg. Regarding effects observed in the F1 generation, emergence and development time were impaired by continuous exposure to BP3. Moreover, reduced emergence and changes in development time were observed in the F1 generation maintained in control/clean conditions but whose parents were exposed to BP3. Results found in this two-generational study clearly show reproductive effects of BP3 on C. riparius that would not be detected using standard tests. Full life cycle and multigenerational assays are critical to properly evaluate the population level effects of endocrine disrupting compounds such as organic UV-filters.

Hydraulic fracturing fluid biocide, tributyl tetradecyl phosphonium chloride, causes mitochondrial dysfunction that is enhanced by sodium chloride in Chironomus riparius

Tributyl tetradecyl phosphonium chloride (TTPC) is a biocide used in hydraulic fracturing fluid to minimize bacterial contamination. This study used the larvae of the freshwater insect Chironomus riparius to investigate the toxicity of TTPC, NaCl, and TTPC+NaCl. LC50s (mg/L) at 24 hours for TTPC, NaCl, and TTPC+NaCl were 0.57, >10,000, and 0.32, respectively, indicating a synergistic effect for TTPC+NaCl. ATP production was significantly increased in response to TTPC alone as compared to controls, but decreased significantly when TTPC was combined with NaCl, indicating severe damage to mitochondria. Superoxide dismutase (SOD) activity and lipid hydroperoxides (LPO) levels both increased in response to TTPC treatment, however, only LPO activity increased when TTPC was combined with NaCl. Red laser stimulation failed to enhance ATP production in response to increasing concentrations of TTPC and TTPC+NaCl. Taken together, these results indicate that hydraulic fracturing fluids entering freshwater ecosystems may put macroinvertebrates at risk.

Effects of single exposure and binary mixtures of ultraviolet filters octocrylene and 2-ethylhexyl 4-(dimethylamino) benzoate on gene expression in the freshwater insect Chironomus riparius.

Ultraviolet filters are used extensively in the production of many personal care and industrial products. These products can inadvertently pollute the environment through recreational activities. They have been associated with endocrine disruption in vertebrates but their effects in invertebrates are poorly understood. Chironomus riparius is a species of the dipteran order, with aquatic larvae that are frequently used in toxicity tests. Previously, we showed that octocrylene (OC) and 2-ethylhexyl 4-(dimethylamino) benzoate (OD-PABA) differentially affected the mRNA levels of the ecdysone receptor and Hsp70 genes. For a better understanding of their mode of action, transcriptional activity by real-time PCR was analyzed in fourth instar larvae exposed to OC, OD-PABA, or a binary mixture of both. We studied 16 genes related to the endocrine system, stress, the immune system, and biotransformation mechanisms to elucidate the putative interactions between these compounds. No response was observed for the genes involved in biotransformation, suggesting that enzymes other than cytochromes P450 and glutathione-S-transferases (GSTs) could get involved in transformation of these compounds. Similarly, no response was observed for endocrine-related genes while the stress gene HYOU1 was inhibited by OD-PABA, suggesting an effect in response to hypoxia. In addition, no significant interactions were observed following exposure to a binary mixture of these compounds. Overall, the results suggest a weak, acute response in different metabolic pathways and a lack of interaction between the compounds. Finally, new genes are identified in this organism, opening the possibility to analyze new cellular pathways as targets of toxicants.

Can the inhibition of cytochrome P450 in aquatic invertebrates due to azole fungicides be estimated with in silico and in vitro models and extrapolated between species?

Azole fungicides, designed to halt fungal growth by specific inhibition of fungal cytochrome P450 (CYP51), inhibit cytochrome P450s involved in the metabolism of xenobiotics in several non-target organisms thus raising environmental concern. The present study investigates the degree by which inhibition strengths of azoles toward cytochrome P450 in rat liver, the insect Chironomus riparius larvae and the snail Lymnaea stagnalis can be extrapolated from estimated in silico affinities. Azoles’ affinities toward human cytochrome P450 isoforms involved in xenobiotic metabolism (CYP3A4, CYP2C9 and CYP2D6) as well as fungal CYP51 were estimated with a ligand-protein docking model based on the ChemScore scoring function. Estimated affinities toward the selected enzymatic structures correlated strongly with measured inhibition strengths in rat liver (ChemScore vs. logIC50 among cytochrome P450 isoforms: −0.662 < r < −0.891, n = 17 azoles), while weaker correlations were found for C. riparius larvae (−0.167 < r < −0.733, n = 9) and L. stagnalis (−0.084 < r < −0.648, n = 8). Inhibition strengths toward C. riparius and rat liver activities were found to be highly correlated to each other (r: 0.857) while no significant relationship was found between either of the species and L. stagnalis. The inhibition of cytochrome P450 due to azole fungicides could be estimated in vitro and to a lesser extent in silico for C. riparius but not for L. stagnalis, possibly due to different enzymatic susceptibility toward azole inhibition among the species.

The European water-based environmental quality standard for pentachlorophenol is NOT protective of benthic organisms

Risk management of toxic substances is often based on Environmental Quality Standards (EQS) set for the water compartment, assuming they will also protect benthic organisms. In the absence of experimental data, EQS for sediments can be estimated by the equilibrium partitioning approach. The present study investigates whether this approach is protective of benthic organisms against pentachlorophenol (PCP), a legacy contaminant and EU priority substance still used in some parts of the world. Three freshwater species of invertebrates with different life cycles and feeding behaviors (the oligochaetes Lumbriculus variegatus, Tubifex tubifex and the dipteran insect Chironomus riparius) were exposed to PCP spiked sediments (2.10–46.03mgPCP/kg d.w. plus controls) in laboratory standard tests. Exposure duration was 28days for T. tubifex and L. variegatus and 10 and 28days for C. riparius; according to the corresponding OECD guidelines. For each investigated end-point, dose-response data were normalized to the mean control and fitted to a four-parameter log-logistic model for calculating the corresponding EC50 and EC10. The ranges for EC50 and EC10 estimates were 4.39 (Chironomus riparius-emergence)–27.50 (Tubifex tubifex–cocoon) and 0.30 (T. tubifex–young worms) –16.70 (T. tubifex–cocoon) mg/kg d.w., respectively. The EC50 and the EC10 values of L. variegatus were within these ranges. Following the EU Technical Guidance for deriving EQS, the lowest EC10 value of 0.30mg/kg (T. tubifex–young worms) resulted in a PCP quality standard (QS) for sediments of 30ng/g, about one fourth of the tentative QS of 119ng/g estimated by the equilibrium partitioning (EqP) approach. The response of benthic biota to PCP varied across organisms and across end-points for the same organism, so that the use of sediment PCP-QS calculated using the EqP-approach may be under-protective of the most sensitive organisms. Information on the possible effects of PCP on resident organisms must therefore be collected for appropriately managing aquatic systems.

Assessment of thiamethoxam toxicity to Chironomus riparius

The insecticide thiamethoxam (TMX) is a systemic neonicotinoid widely used for pest control in several agricultural crops. TMX mimics the action of acetylcholine causing uncontrolled muscular contraction eventually leading to insect death. TMX is being found in freshwater ecosystems at concentrations of up to 225µg/L. Still, chronic toxicity data for freshwater invertebrates is limited. Therefore, the aim of this study was to evaluate the acute and chronic effects (at organismal and biochemical levels) of TMX on the freshwater insect Chironomus riparius. C. riparius life history responses were significantly affected by TMX exposure, namely with a decrease in growth and delay in emergence. Concerning the biochemical responses, after a short exposure (48h) to TMX, our results showed that low concentrations of TMX significantly reduced CAT activity and LPO levels of C. riparius. No effects were observed in AChE, GST and ETS activities. Effects in terms of survival, development rates and biochemical responses of C. riparius exposed to low concentrations of TMX observed in this study suggest potential deleterious effects of this neonicotinoid on aquatic insects inhabiting freshwaters environments near agricultural areas.

UV filters induce transcriptional changes of different hormonal receptors in Chironomus riparius embryos and larvae

Organic ultraviolet (UV) filters are emerging contaminants that are ubiquitous in fresh and marine aquatic systems due to their extensive use in cosmetics, plastics, paints, textiles, and many other industrial products. The estrogenic effects of organic UV filters have been long demonstrated in vertebrates, and other hormonal activities may be altered, according to more recent reports. The impact of UV filters on the endocrine system of invertebrates is largely unknown. We have previously reported that some UV filters may affect ecdysone-related genes in the aquatic insect Chironomus riparius, an ecotoxicologically important model organism. To further analyze other possible effects on endocrine pathways, we first characterized four pivotal genes related with hormonal pathways in insects; thereafter, these genes were assessed for alterations in transcriptional activity after exposure to 4-methylbenzylidene camphor (4MBC) or benzophenone-3 (BP-3), two extensively used sunscreens. We found that both chemicals disturbed the expression of all four genes analyzed: hormonal receptor 38 (HR38), methoprene-tolerant (Met), membrane-associate progesterone receptor (MAPR) and insulin-like receptor (INSR), measured by changes in mRNA levels by real-time PCR. An upregulatory effect at the genomic level was detected in different developmental stages. Interestingly, embryos appeared to be more sensitive to the action of the UV filters than larvae. Our results suggest that the risk of disruption through different endocrine routes is not negligible, considering the significant effects of UV filters on key hormonal receptor and regulatory genes. Further effort is needed to develop environmental risk assessment studies on these pollutants, particularly for aquatic invertebrate model organisms.

Characterization of six small HSP genes from Chironomus riparius (Diptera, Chironomidae): Differential expression under conditions of normal growth and heat-induced stress

Small heat shock proteins (sHSPs) comprise the most numerous, structurally diverse, and functionally uncharacterized family of heat shock proteins. Several Hsp genes (Hsp 90, 70, 40, and 27) from the insect Chironomus riparius are widely used in aquatic toxicology as biomarkers for environmental toxins. Here, we conducted a comparative study and characterized secondary structure of the six newly identified sHsp genes Hsp17, Hsp21, Hsp22, Hsp23, Hsp24, and Hsp34. A characteristic α-crystallin domain is predicted in all the new proteins. Phylogenetic analysis suggests a strong relation to other sHSPs from insects and interesting evidence regarding evolutionary origin and duplication events. Comparative analysis of transcription profiles for Hsp27, Hsp70, and the six newly identified genes revealed that Hsp17, Hsp21, and Hsp22 are constitutively expressed under normal conditions, while under two different heat shock conditions these genes are either not activated or are even repressed (Hsp22). In contrast, Hsp23, Hsp24, and Hsp34 are significantly activated along with Hsp27 and Hsp70 during heat stress. These results strongly suggest functional differentiation within the small HSP subfamily and provide new data to help understand the coping mechanisms induced by stressful environmental stimuli.

Genotoxic effects of environmental endocrine disruptors on the aquatic insect Chironomus riparius evaluated using the comet assay

Genotoxicity is one of the most important toxic endpoints in chemical toxicity testing and environmental risk assessment. The aim of this study was to evaluate the genotoxic potential of various environmental pollutants frequently found in aquatic environments and characterized by their endocrine disrupting activity. Monitoring of DNA damage was undertaken after in vivo exposures of the aquatic larvae of the midge Chironomus riparius, a model organism that represents an abundant and ecologically relevant macroinvertebrate, widely used in freshwater toxicology. DNA-induced damage, resulting in DNA fragmentation, was quantified by the comet assay after short (24h) and long (96h) exposures to different concentrations of the selected toxicants: bisphenol A (BPA), nonylphenol (NP), pentachlorophenol (PCP), tributyltin (TBT) and triclosan (TCS). All five compounds were found to have genotoxic activity as demonstrated by significant increases in all the comet parameters (%DNA in tail, tail length, tail moment and Olive tail moment) at all tested concentrations. Persistent exposure did not increase the extent of DNA damage, except for TCS at the highest concentration, but generally there was a reduction in DNA damage thought to be associated with the induction of the detoxification processes and repairing mechanisms. Comparative analysis showed differences in the genotoxic potential between the chemicals, as well as significant time and concentration-dependent variations, which most likely reflect differences in the ability to repair DNA damage under the different treatments. The present report demonstrates the sensitivity of the benthic larvae of C. riparius to these environmental genotoxins suggesting its potential as biomonitor organism in freshwater ecosystems. The results obtained about the DNA-damaging potential of these environmental pollutants reinforce the need for additional studies on the genotoxicity of endocrine active substances that, by linking genotoxic activity to other biological responses, could provide further understanding of adverse effects in aquatic environments.

Effects of in vivo exposure to UV filters (4-MBC, OMC, BP-3, 4-HB, OC, OD-PABA) on endocrine signaling genes in the insect Chironomus riparius

There is increasing evidence indicating that several UV filters might have endocrine disruptive effects. Numerous studies have evaluated hormonal effects in vertebrates, mainly reporting estrogenic and androgenic activities in mammals and fishes. There is only limited knowledge about potential endocrine activity in invertebrate hormonal systems. In this work, the effects on endocrine signaling genes of six frequently used UV filters were investigated in Chironomus riparius, a reference organism in aquatic toxicology. The UV filters studied were: octyl-p-methoxycinnamate (OMC) also called 2-ethylhexyl-4-methoxycinnamate (EHMC); 4-methylbenzylidene camphor (4-MBC); benzophenone-3 (BP-3); 4-hidroxybenzophenone (4-HB); octocrylene (OC); and octyldimethyl-p-aminobenzoate (OD-PABA). After in vivo exposure at different dosages, expression levels of the genes coding for the ecdysone receptor (EcR), the ultraspiracle (usp, ortholog of the RXR) and the estrogen-related receptor (ERR) were quantified by Real Time PCR. The EcR gene was significantly upregulated by 4-MBC, OMC/EHMC and OD-PABA, with a dose-related response following 24h exposure. In contrast, the benzophenones, BP-3 and 4-HB, as well as OC did not alter this gene at the same exposure conditions. The transcription profiles of the usp and ERR genes were not significantly affected, except for BP-3 that inhibited the usp gene at the highest concentration. To our knowledge, this is the first experimental evidence in invertebrates of a direct effect of UV filters on endocrine-related genes, and is consistent with the known effects on vertebrate hormonal receptor genes. The capability of 4-MBC, OMC/EHMC and OD-PABA to stimulate the expression of the ecdysone receptor, a key transcription factor for the ecdysone-genomic response in arthropods, suggests the possibility of a broad and long-term effect on this hormonal pathway. These findings strengthen the need for further research about the ecotoxicological implications of chronic exposure to these compounds in aquatic invertebrates.

Assessing Toxicity of the Insecticide Thiacloprid on Chironomus riparius (Insecta: Diptera) Using Multiple End Points

Since data documentation on neonicotinic toxicity to nontarget organisms should be enhanced, we investigate the effects of thiacloprid, a novel neonicotinoid insecticide, on the sediment-dwelling nontarget insect Chironomus riparius. Further, we wanted to validate the sensitivity of end points on different biological levels and obtain the greatest amount of information regarding the effects of this compound by using a battery of several end points such as larval mortality, behavior, body weight gain, emergence rate, time of development, gender ratio, Hsp70 stress protein level, and larval mouthpart deformities after exposure at a concentration range of 0.1 to 1000 microg/L thiacloprid. C. riparius was impacted starting at concentrations of 0.5 microg/L, a concentration that can be considered environmentally relevant. Larval mortality, behavior, emergence, and Hsp70 protein level were sensitive indicators for the toxic effect of thiacloprid, whereas gender ratio and mouthpart morphology were not affected. In our case life-cycle end points like survival rate (LC(50): 1.57 microg/L) and emergence rate (EC(50): 0.54 microg/L) proved to be more sensitive than tested physiological end points for the neurotoxic insecticide.

Selenium assimilation and loss by an insect predator and its relationship to Se subcellular partitioning in two prey types

Subcellular selenium (Se) distributions in the oligochaete Tubifex tubifex and in the insect Chironomus riparius did not vary with Se exposure duration, which was consistent with the observations that the duration of prey Se exposure had little influence on either Se assimilation or loss by a predatory insect (the alderfly Sialis velata). However, these two prey types differed in how Se was distributed in their cells. Overall, the predator assimilated a mean of 66% of the Se present in its prey, which was similar to the mean percentage of Se in prey cells (62%) that was theoretically available for uptake (that is, Se in the protein and organelle fractions). Likewise, data for cadmium, nickel and thallium suggest that predictions of trace element transfer between prey and predator are facilitated by considering the subcellular partitioning of these contaminants in prey cells.

Environmental chemicals with known endocrine potential affect yolk protein content in the aquatic insect Chironomus riparius

The use of vitellogenesis as a marker for possible effects of endocrine disrupting agents on insects was tested in the aquatic midge Chironomus riparius. As test substances the synthetic ecdysoid tebufenozide, and the endocrine disruptors bisphenol a and 4-n-nonylphenol were applied in a semi-static manner. The yolk protein contents of freshly emerged (24 h) male and female midges were determined by an ELISA procedure. In males, where always low amounts of immunoreactivity were apparent, yolk concentrations were lowered by 10% after a 80 μg/l tebufenozide treatment, and by 20–25% after exposition to bisphenol a at concentrations of 1, 100, and 3,000 μg/l. 4-n-nonylphenol contamination caused an inverted dose-response curve. At low test concentrations (1.9–30 μg/l) reduced yolk immunoreactivity occurred, while at medium concentrations (120 and 500 μg/l) no significant effects were observable. In the most highly contaminated group (2,000 μg/l) yolk protein immunoreactivity was elevated to 107% of the control. Female yolk protein contents were affected only in the 3,000 μg bisphenol a/l contaminated group, where yolk immunoreactivity was reduced by ca. 10% compared to the control.

Bioavailability of lambda-cyhalothrin to Chironomus riparius in sediment–water and water-only systems

The bioavailability of 14C-lambda-cyhalothrin and its bioconcentration by larvae of the aquatic insect Chironomus riparius was studied in laboratory sediment–water systems. Ten different sediments with a range of physico-chemical characteristics were investigated. The chemical was applied to sediment slurries and fourth instar C. riparius were exposed in the test system for 48 h. The distribution of the chemical between the sediment, water and organism phases was determined. In addition, the bioconcentration of 14C-lambda-cyhalothrin by C. riparius in a water-only test system was determined. In all the sediment–water test systems, the vast majority of the 14C-lambda-cyhalothrin (>99%) was adsorbed to the sediment. Aqueous phase concentrations varied between the test systems, as did concentrations of the chemical in the organisms. However, bioconcentration factors based on the aqueous phase concentrations showed little difference between systems, ranging from 1300 to 3400 (mean 2300, coefficient of variation 25%). These values were very similar to the bioconcentration factor determined in water alone after 48 h (2000). Bioconcentration factors based on measured concentrations of extractable 14C-lambda-cyhalothrin in the sediment phase were much more variable, although they were always <1, ranging from 0.11 to 0.84 (mean 0.39, coefficient of variation 61%). Sediment bioconcentration factors were inversely proportional to the measured sediment K ds, which ranged from 3290 to 22 100. That is, the higher the proportion of the chemical that was adsorbed, the lower the sediment bioconcentration factor. The results of the study supported equilibrium partitioning theory. In sediment–water systems, the lambda-cyhalothrin that was bioavailable was equivalent to the amount which was measured in the water phase.

Bioavailability of lambda-cyhalothrin to Chironomus riparius in sediment–water and water-only systems

Abstract The bioavailability of 14C-lambda-cyhalothrin and its bioconcentration by larvae of the aquatic insect Chironomus riparius was studied in laboratory sediment–water systems. Ten different sediments with a range of physico-chemical characteristics were investigated. The chemical was applied to sediment slurries and fourth instar C. riparius were exposed in the test system for 48 h. The distribution of the chemical between the sediment, water and organism phases was determined. In addition, the bioconcentration of 14C-lambda-cyhalothrin by C. riparius in a water-only test system was determined. In all the sediment–water test systems, the vast majority of the 14C-lambda-cyhalothrin (&amp;gt;99%) was adsorbed to the sediment. Aqueous phase concentrations varied between the test systems, as did concentrations of the chemical in the organisms. However, bioconcentration factors based on the aqueous phase concentrations showed little difference between systems, ranging from 1300 to 3400 (mean 2300, coefficient of variation 25%). These values were very similar to the bioconcentration factor determined in water alone after 48 h (2000). Bioconcentration factors based on measured concentrations of extractable 14C-lambda-cyhalothrin in the sediment phase were much more variable, although they were always &amp;lt;1, ranging from 0.11 to 0.84 (mean 0.39, coefficient of variation 61%). Sediment bioconcentration factors were inversely proportional to the measured sediment Kds, which ranged from 3290 to 22 100. That is, the higher the proportion of the chemical that was adsorbed, the lower the sediment bioconcentration factor. The results of the study supported equilibrium partitioning theory. In sediment–water systems, the lambda-cyhalothrin that was bioavailable was equivalent to the amount which was measured in the water phase.