Non-biting Midge Chironomus Riparius Research Articles

Why insect swarms seem unduly complicated

Mating swarms of flying male insects are a form of collective behaviour, albeit one different from flocks and schools as they do not display ordered collective movements. In recent years, much progress has been made in uncovering the emergent mechanical-like and thermodynamic-like of such swarms. Nonetheless, two basic properties of this swarming behaviour remain unexplained. Namely, why do individual insects have erratic rather than regular flight patterns? And why are the swarms elliptical rather than circular? Here I account for this seemingly undue complexity. I show that regular flight patterns weaken an individual’s attraction to the swarm centre, making swarms less resilient to the presence of environmental disturbances. I then show that the elliptical shape of swarms of the non-biting midge Chironomus riparius optimizes the trade-off between maximizing swarm size (target size for females) and maximizing swarm stability. Finally, I show that the observed excess velocity kurtosis of swarming C. riparius maximizes swarm cohesiveness. Taken together the new results provide the first tentative evidence for fine-tuning in insect mating swarms driven by selection pressure for advantageous behaviours.Graphic abstract

A multigenerational study can detect the evolutionary response to BaP exposure in the non-biting freshwater midge Chironomus riparius

The release of polycyclic aromatic hydrocarbons (PAHs) into the environment is posing a threat to ecosystems and human health. Benzo(a)pyrene (BaP) is considered a biomarker of PAH exposure and is classified as a Group 1 carcinogen. However, it was not known whether BaP is mutagenic, i.e. induces inherited germline mutations. In this study, we used a recently established method, which combines short-term mutation accumulation lines (MAL) with whole genome sequencing (WGS) to assess mutagenicity in the non-biting midge Chironomus riparius. The mutagenicity analysis was supplemented by an evaluation of the development of population fitness in three successive generations in the case of chronic exposure to BaP at a high concentration (100 μg/L). In addition, the level of ROS-induced oxidative stress was examined in vivo. Exposure to the higher BaP concentration led to an increase in germline mutations relative to the control, while the lower concentration showed no mentionable effect. Against expectations, BaP exposure decreased ROS-level compared to the control and is thus probably not responsible for the increased mutation rate. Likewise, the higher BaP concentration decreased fitness measured as population growth rate per day (PGR) significantly over all generations, without signs of rapid evolutionary adaptations. Our results thus highlighted that high BaP exposure may influence the evolutionary trajectory of organisms.

Aquatic-Terrestrial Insecticide Fluxes: Midges as Neonicotinoid Vectors.

Exposure of freshwater ecosystems to insecticides can negatively impact the development of emerging aquatic insects. These insects serve as an important nutritional subsidy for terrestrial insectivores. Changes in insect emergence phenology (i.e., emergence success and temporal pattern) or fluxes of insecticides retained by the emerging adults have the potential to negatively impact terrestrial food webs. These processes are influenced by contaminant toxicity, lipohilicity, or metabolic processes. The interplay between emergence phenology, contaminant retention through metamorphosis, and associated contaminant flux is not yet understood for current-use insecticides. In a microcosm study, we evaluated the impacts of a 24-h pulse exposure of one of three current-use insecticides, namely pirimicarb, indoxacarb, and thiacloprid, at two environmentally realistic concentration levels on the larval development and emergence of the nonbiting midge Chironomus riparius. In addition, we measured insecticide concentrations in the larvae and adults using ultrahigh performance liquid chromatography coupled to tandem mass spectrometry by electrospray ionization. Exposure to pirimicarb delayed larval development and emergence, and exposure to indoxacarb reduced emergence success. The neonicotinoid thiacloprid had the greatest impact by reducing larval survival and emergence success. At the same time, thiacloprid was the only insecticide measured in the adults with average concentrations of 10.3 and 37.3 ng/g after exposure at 0.1 and 4 µg/L, respectively. In addition, an approximate 30% higher survival to emergence after exposure to 0.1 µg/L relative to a 4-µg/L exposure resulted in a relatively higher flux of thiacloprid, from the aquatic to the terrestrial environment, at the lower exposure. Our experimental results help to explain the impacts of current-use insecticides on aquatic-terrestrial subsidy coupling and indicate the potential for widespread dietary exposure of terrestrial insectivores preying on emerging aquatic insects to the neonicotinoid thiacloprid. Environ Toxicol Chem 2023;42:60-70. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessment of pollution variability across the central part of the Büyük Menderes River (Turkey) using water physicochemical parameters and biomarker responses in the non-biting midge Chironomus riparius (Diptera: Chironomidae)

ABSTRACT This study aimed to examine the pollution level in the central part of the Büyük Menderes River (in both the main tributary and Çürüksu stream) in Denizli (Turkey) using water physicochemical parameters and biomarker responses in Chironomus riparius (Diptera: Chironomidae). In physicochemical parameter evaluations, Sığma, Korucuk, and Güzelköy stations were determined to have higher mean temperature, pH, salinity, conductivity, and total dissolved solids (TDS) values and lower dissolved oxygen (dO2) and saturated oxygen (sO2) values than Bekilli, Mahmutlu, and Sarayköy stations. In biomarker response evaluations, C. riparius larvae from Sarayköy, Sığma, Korucuk, and Güzelköy stations were found to exhibit inhibited acetylcholinesterase (AChE) activities (55%−68%) and elevated 7-ethoxyresorufin O-deethylase (EROD) activities (191%−281%), glutathione S-transferase (GST) activities (138%−187%), and metallothionein (MT) contents (155%−231%) when compared with the control values. This study proves that different stations are exposed to different pollution sources, the pollution level of a station varies depending on the season, and the stations on Çürüksu stream, among which Güzelköy appears to be the most contaminated, are exposed to more pollutants than those on the main tributary of the river.

Selective effects of a short transient environmental fluctuation on a natural population.

Natural populations experience continuous and often transient changes of environmental conditions. These in turn may result in fluctuating selection pressures leading to variable demographic and evolutionary population responses. Rapid adaptation as short-term response to a sudden environmental change has in several cases been attributed to polygenic traits, but the underlying genomic dynamics and architecture are poorly understood. In this study, we took advantage of a natural experiment in an insect population of the non-biting midge Chironomus riparius by monitoring genome-wide allele frequencies before and after a cold snap event. Whole genome pooled sequencing of time series samples revealed 10 selected haplotypes carrying ancient polymorphisms, partially with signatures of balancing selection. By constantly cold exposing genetically variable individuals in the laboratory, we could demonstrate with whole genome resequencing (i) that among the survivors, the same alleles rose in frequency as in the wild, and (ii) that the identified variants additively predicted fitness (survival time) of its bearers. Finally, by simultaneously sequencing the genome and the transcriptome of cold exposed individuals we could tentatively link some of the selected SNPs to the cis- and trans-regulation of genes and pathways known to be involved in cold response of insects, such as cytochrome P450 and fatty acid metabolism. Altogether, our results shed light on the strength and speed of selection in natural populations and the genomic architecture of its underlying polygenic trait. Population genomic time series data thus appear as promising tool for measuring the selective tracking of fluctuating selection in natural populations.

Contribution of sediment contamination to multi-stress in lowland waters

Water bodies in densely populated lowland areas are often impacted by multiple stressors. At these multi-stressed sites, it remains challenging to quantify the contribution of contaminated sediments. This study, therefore, aimed to elucidate the contribution of sediment contamination in 16 multi-stressed drainage ditches throughout the Netherlands. To this end an adjusted TRIAD framework was applied, where 1) contaminants and other variables in the sediment and the overlying water were measured, 2) whole-sediment laboratory bioassays were performed using larvae of the non-biting midge Chironomus riparius, and 3) the in situ benthic macroinvertebrate community composition was determined. It was hypothesized that the benthic macroinvertebrate community composition would respond to all jointly present stressors in both water and sediment, whereas the whole-sediment bioassays would only respond to the stressors present in the sediment. The benthic macroinvertebrate community composition was indeed related to multiple stressors in both water and sediment. Taxa richness was positively correlated with the presence of PO4-P in the water, macrophyte cover and some pesticides. Evenness, the number of Trichoptera families and the SPEARpesticides were positively correlated to the C:P ratios in the sediment, whilst negative correlations were observed with various contaminants in both the water and sediment. The whole-sediment bioassays with C. riparius positively related to the nutrient content of the sediment, whereas no negative relations to the sediment-associated contaminants were observed, even though the lowered SPEARpesticides index indicated contaminant effects in the field. Therefore, it was concluded that sediment contamination was identified as one of the various stressors that potentially drove the benthic macroinvertebrate community composition in the multi-stressed drainage ditches, but that nutrients may have masked the adverse effects caused by low and diverse sediment contaminants on C. riparius in the bioassays.

Organic matter degradation and redistribution of sediment associated contaminants by benthic invertebrate activities

The fate of sediment associated compounds is the combined result of chemical properties and biological activities. Yet, studies simultaneously addressing the effects of biota on the redistribution and bioaccumulation of contaminants are scarce. Our aim was therefore to assess the effect of benthic invertebrate activities on organic matter degradation and the redistribution of metals and Polycyclic Aromatic Hydrocarbons (PAHs) in contaminated sediment. To this end, we introduced egg ropes of the non-biting midge Chironomus riparius into wastewater treatment plant sludge and allowed these to either develop until fourth instar larvae or to fully complete their life cycle into terrestrial flying adults. Chironomid larvae enhanced sludge degradation, resulting in increased metal concentrations in the sludge and in a flux of metals into the overlying water. Moreover, they hampered PAH degradation in the sludge. Contaminant transport from aquatic to terrestrial ecosystems with emerging invertebrates as a vector is widely acknowledged, but here we showed that biomanipulation prevailed over bioaccumulation, since due to chironomid activity, the flux of metals from the sludge into the overlying water was larger than into chironomid biomass. It is therefore concluded that contaminant-macroinvertebrate interactions are bilateral relationships driven by the interplay between macroinvertebrate traits and contaminant properties.

Polyamide microplastic exposure elicits rapid, strong and genome-wide evolutionary response in the freshwater non-biting midge Chironomus riparius

Susceptibility to hazardous materials and contamination is largely determined by genetic make-up and evolutionary history of affected organisms. Yet evolutionary adaptation and microevolutionary processes triggered by contaminants are rarely considered in ecotoxicology. Using an evolve and resequencing approach, we investigated genome-wide responses of the midge C. riparius exposed to virgin polyamide microplastics (0–180 μm size range, at concentration 1 g kg−1) during seven consecutive generations. The results were integrated to a parallel life-cycle experiment ran under the same exposure conditions. Emergence, life-cycle trait, showed first a substantial reduction in larval survival, followed by a rapid recovery within three generations. On the genomic level, we observed substantial selectively driven allele frequency changes (mean 0.566 ± 0.0879) within seven generations, associated with a mean selection coefficient of 0.322, indicating very strong selection pressure. Putative selection targets were mainly connected to oxidative stress in the microplastics exposed C. riparius population. This is the first multigenerational study on chironomids to provide evidence that upon exposure to polyamide microplastic there are changes on the genomic level, providing basis to rapid adaptation of aquatic organisms to microplastics.

Formation and dissolution of midge swarms.

Using external illumination cues, we induce the formation and dissolution of laboratory swarms of the nonbiting midge Chironomus riparius and study their behavior during these transient processes. In general, swarm formation is slower than swarm dissolution. We find that the swarm property that appears most rapidly during formation and disappears most rapidly during dissolution is an emergent mean radial acceleration pointing toward the center of the swarm. Our results strengthen the conjecture that this central effective force may be used as an indicator to distinguish when the midges are swarming from when they are not.

Understanding the thermodynamic properties of insect swarms

Sinhuber et al. (Sci Rep 11:3773, 2021) formulated an equation of state for laboratory swarms of the non-biting midge Chironomus riparius that holds true when the swarms are driven through thermodynamic cycles by the application external perturbations. The findings are significant because they demonstrate the surprising efficacy of classical equilibrium thermodynamics for quantitatively characterizing and predicting collective behaviour in biology. Nonetheless, the equation of state obtained by Sinhuber et al. (2021) is anomalous, lacking a physical analogue, making its’ interpretation problematic. Moreover, the dynamical processes underlying the thermodynamic cycling were not identified. Here I show that insect swarms are equally well represented as van der Waals gases and I attribute the possibility of thermodynamic cycling to insect swarms consisting of several overlapping sublayers. This brings about a profound change in the understanding of laboratory swarms which until now have been regarded as consisting of non-interacting individuals and lacking any internal structure. I show how the effective interactions can be attributed to the swarms’ internal structure, the external perturbations and to the presence of intrinsic noise. I thereby show that intrinsic noise which is known to be crucial for the emergence of the macroscopic mechanical properties of insect swarms is also crucial for the emergence of their thermodynamic properties as encapsulated by their equation of state.

Evaluation of the potential toxicity of UV-weathered virgin polyamide microplastics to non-biting midge Chironomus riparius

The relevance of the environmental hazard evaluation of virgin plastics particles is problematic, as plastics almost never occur in a virgin state after being discarded into the environment. However, the producers or importers must evaluate the environmental effect of their products as they are produced. Many plastic types e.g., polyamide, polyethylene are already under pre-registration, according to the database of the European Chemicals Agency (ECHA), in order to restrict the placing on the market of polymers (as defined by Article 3(5) of EU's REACH regulation (Registration, Evaluation, Authorization & Restriction of Chemicals), as a substance or in a mixture (ECHA, 2019). However, the hazard of microplastics could not be evaluated without relevant data on its (eco)toxic effects. In this work, the long-term toxicity of virgin polyamide microplastic (PA-MP) (size from 0 to 180 μm) and UV-weathered virgin PA-MP was investigated in the controlled life cycle experiments conducted in accordance with the OECD guidelines for testing of chemicals using Chironomus riparius (OECD test 218). In addition, a three-generation test was conducted to understand the trans-generational toxicity potential of virgin PA-MP. After UV irradiation (26 d) the buoyancy and color of the particles was changed and the share of smaller particles (of a few micrometer size range) increased. The exposure of C. riparius larvae to UV-weathered PA-MP (1000 mg kg−1) during their life cycle (28 d), negatively affected their development and subsequent emergence as adults. However, the exposure to virgin PA-MP throughout the life cycle and also over three consecutive generations did not significantly reduced the number of emerged adults. From the point of view of environmental hazard, the virgin polyamide plastics have probably no long-term hazard to chironomids. While it may not be relevant as environmental pollutant in the strict sense, UV-weathering may turn it hazardous.

Revealing the effects of cerium dioxide nanoparticles through the analysis of morphological changes in Chironomus riparius

Due to their many practical applications, engineered cerium dioxide (CeO2) nanoparticles (NPs) are commonly used today, although there are justified concerns about the environmental risks of their usage. Studies to date have shown that CeO2 NPs do not pose a lethal hazard to hydrobiocenoses at environmentally relevant concentrations, but that they induce significant negative sublethal effects. Therefore, intensive work is being done on the adaptation of standard ecotoxicological tests with the development of new, sublethal biomarkers. The present study aims to examine the sublethal effects of prolonged exposure to CeO2 NPs (2.5; 25; 250 and 2500 mg of CeO2 NPs per 1 kg of sediment) on the morphological features of the non-biting aquatic midge Chironomus riparius. Morphological variation was examined by means of two approaches: (1) Deformity rate analysis (analysis of visible morphological malformations) and (2) Geometric morphometric analysis (analysis of differences in the size and shape of the larval mandibles and mentums, as well as adult male and female wings). Changes in all the morphological structures examined were observed using a geometric morphometric approach at low and very high concentrations of CeO2 NPs (2.5 and 2500 mg of CeO2 NPs per 1 kg of sediment). The potential reduction of sexual dimorphism resulting from downsizing of the wings in females was observed. These results indicate that the sublethal changes observed in chironomids exposed to CeO2 NPs are significant and may potentially lead to further changes in metabolism, diet and behavior, which may lead to repercussions of as yet unexamined proportions. Considering our findings, and the advantages of geometric morphometrics (precision, uniformity, accurate qualification, quantification, and visualization of fine morphological changes), this approach is proven to be an exceptional assessment tool, with great applicative potential in the ecotoxicological testing of nanoparticles.

Intrinsic stochasticity and the emergence of collective behaviours in insect swarms.

Intrinsic stochasticity associated with finite population size is fundamental to the emergence of collective behaviours in insect swarms. It has been assumed that this intrinsic stochasticity is purely additive (position independent) in quiescent (unperturbed) swarms. Here, I identify the hallmarks of intrinsic multiplicative (position dependent) stochasticity and show that they are evident in quiescent laboratory swarms of the non-biting midge Chironomus riparius. In accordance with theoretical expectations, the smallest well-documented laboratory swarms (containing between 14 and 46 individuals) are found to have q-Gaussian density profiles with [Formula: see text] 1, whereas larger laboratory swarms have Gaussian ([Formula: see text]1) density profiles. I show that these newly identified states are analogous to interstellar clouds and thereby extend a long-standing analogy between insect swarms and self-gravitating systems. Smaller laboratory swarms have been observed and are predicted to be gas-like, filling the available space rather than occupying just a small proportion of it. The new results unify laboratory swarms with wild swarms. Unlike laboratory swarms, wild swarms must contend with environmental (extrinsic) noise and have density profiles that are accurately represented by q-Gaussians with [Formula: see text] 1. Finally, it is shown how intrinsic multiplicative noise allows for the nucleation of swarms away from prominent visual features (basins of attraction) known as swarm markers.

Chironomus riparius Proteome Responses to Spinosad Exposure.

The potential of proteome responses as early-warning indicators of insecticide exposure was evaluated using the non-biting midge Chironomus riparius (Meigen) as the model organism. Chironomus riparius larvae were exposed to environmentally relevant concentrations of the neurotoxic pesticide spinosad to uncover molecular events that may provide insights on the long-term individual and population level consequences. The iTRAQ labeling method was performed to quantify protein abundance changes between exposed and non-exposed organisms. Data analysis revealed a general dose-dependent decrease in the abundance of globin proteins as a result of spinosad exposure. Additionally, the downregulation of actin and a larval cuticle protein was also observed after spinosad exposure, which may be related to previously determined C. riparius life-history traits impairment and biochemical responses. Present results suggest that protein profile changes can be used as early warning biomarkers of pesticide exposure and may provide a better mechanistic interpretation of the toxic response of organisms, aiding in the assessment of the ecological effects of environmental contamination. This work also contributes to the understanding of the sublethal effects of insecticides in invertebrates and their molecular targets.

Resilin Distribution and Sexual Dimorphism in the Midge Antenna and Their Influence on Frequency Sensitivity.

Simple SummaryThe antennae of insects are multipurpose sensory organs that can detect chemicals, gravity, vibrations, and sound, among others. While such sensors are very specialized and adapted to their specific needs, the way the antenna itself is built has often been considered either uninteresting or unimportant. We used a laser to scan the antenna of the midge Chironomus riparius. Insect cuticle, if illuminated with laser light, reflects autofluorescent light, an emission that has long been known to indicate the material properties of the scanned cuticle sample. Rather than a simple beam-like structure of constant material stiffness, we saw bands of hard and soft material, distributed along the length of the antenna. We were able to computer-simulate the effect of this banded structure on the antenna’s resonant frequency and showed that it allows the beam to vibrate at different frequencies than would be expected only by its shape. This discovery will help us to better understand these animals’ biology and can inspire future biomimetic sensors for detecting sound or vibration.Small-scale bioacoustic sensors, such as antennae in insects, are often considered, biomechanically, to be not much more than the sum of their basic geometric features. Therefore, little is known about the fine structure and material properties of these sensors—even less so about the degree to which the well-known sexual dimorphism of the insect antenna structure affects those properties. By using confocal laser scanning microscopy (CLSM), we determined material composition patterns and estimated distribution of stiffer and softer materials in the antennae of males and females of the non-biting midge Chironomus riparius. Using finite element modelling (FEM), we also have evidence that the differences in composition of these antennae can influence their mechanical responses. This study points to the possibility that modulating the elastic and viscoelastic properties along the length of the antennae can affect resonant characteristics beyond those expected of simple mass-on-a-spring systems—in this case, a simple banded structure can change the antennal frequency sensitivity. This constitutes a simple principle that, now demonstrated in another Dipteran group, could be widespread in insects to improve various passive and active sensory performances.

Environmental perturbations induce correlations in midge swarms.

Although collectively behaving animal groups often show large-scale order (such as in bird flocks), they need not always (such as in insect swarms). It has been suggested that the signature of collective behaviour in disordered groups is a residual long-range correlation. However, results in the literature have reported contradictory results as to the presence of long-range correlation in insect swarms, with swarms in the wild displaying correlation but those in a controlled laboratory environment not. We resolve these apparently incompatible results by showing that the external perturbations generically induce the emergence of correlations. We apply a range of different external stimuli to laboratory swarms of the non-biting midge Chironomus riparius, and show that in all cases correlations appear when perturbations are introduced. We confirm the generic nature of these results by showing that they can be reproduced in a stochastic model of swarms. Given that swarms in the wild will always have to contend with environmental stimuli, our results thus harmonize previous findings. These findings emphasize that collective behaviour cannot be understood in isolation without considering its environmental context, and that new research is needed to disentangle the distinct roles of intrinsic dynamics and external stimuli.

Is developmental instability in chironomids a sensitive endpoint for testing uranium mine-affected sediments?

There is increasing interest in effects of radionuclides on non-human species, but methods for studying such effects are not well developed. The aims of the current study were to investigate the effects of uranium mine-affected sediments on non-biting midge Chironomus riparius and to compare sensitivity of different endpoints. The midge larvae were exposed in controlled laboratory conditions to sediments from two ponds downstream from an abandoned uranium mine and a reference pond not receiving water from the mining site. Quartz sand was used as an additional control. Developmental effects were assessed by evaluating emergence of adult midges, body mass, and fluctuating asymmetry (FA) in the length of wing upper vein. FA has been suggested to be a sensitive indicator of developmental instability, but the results of previous studies are inconsistent. In the present study, no difference in FA was observed between the treatment groups, but time to emergence was significantly delayed in the contaminated sediments. The approach used in this study (laboratory experiments with sediments from a contaminated site) avoids confounding due to uncontrolled environmental variables and adaptation to long-term contamination, which may mask effects on natural populations. Using this approach, we found no effects on FA of wing length. Time to emergence, in contrast, was found to be a more sensitive endpoint.

Exposure to a microplastic mixture is altering the life traits and is causing deformities in the non-biting midge Chironomus riparius Meigen (1804)

The effect of microplastics (MP) exposure on the chironomid species Chironomus riparius Meigen, 1804 was investigated using the OECD sediment and water toxicity test. Chironomid larvae were exposed to an environmentally relevant low microplastics concentration (LC), a high microplastics concentration (HC) and a control (C). The LC was 0.007 g m−2 on the water surface + 2 g m−3 in the water column + 8 g m−2 in the sediment, and the HC was 10 X higher than this for each exposure. The size of the majority of the manufactured microplastic pellets varied between 20 and 100 μm. The MP mixture consisted of: polyethylene-terephtalate (PET), polystyrene (PS), polyvinyl-chloride (PVC) and polyamide (PA) in a ratio of 45%: 15%: 20%: 20%, respectively, for the sediment exposure; 100% polyethylene for the water column exposure; and 50% polyethylene: 50% polypropylene for the water surface exposure. Different endpoints were monitored, including morphological changes in the mandibles and mentums of 4th instar larvae, morphological changes in the wings, mortality, emergence ratio, and developmental time. A geometric morphometric analysis showed a tendency toward widening of the wings, elongation of the mentums and changing the shape of the mandibles in specimens exposed to both concentrations of microplastics. The development time of C. riparius was significantly prolonged by the MP treatment: 13.8 ± 0.5; 14.4 ± 0.6; and 15.3 ± 0.4 days (mean ± SD) in the C, LC, and HC, respectively. This study indicates that even environmentally relevant concentrations of MP mixture have a negative influence on C. riparius, especially at the larval stage.

Evaluation of the hazard of irregularly-shaped co-polyamide microplastics on the freshwater non-biting midge Chironomus riparius through its life cycle.

Plastics pollution is increasingly attracting societal and political attention. However, despite extensive research effort recently dedicated to the hazard of plastics in the environment, the data obtained are often redundant and essential knowledge gaps exist: available freshwater ecotoxicity data mostly concern Daphnia magna and are derived from acute exposure to spherical particles. In this paper, we address this gap by exploring the biological effects of irregularly-shaped co-polyamide (PA, 10-180μm) on Chironomus riparius - a very versatile organism that during its life-stages inhabits both sediment and water column - relevant compartments for microplastics (MP) pollution. C.riparius represents an important part of the freshwater food chain and is also a standard OECD test organism. Different toxicity endpoints along the life cycle of C.riparius (28 days) were used as described in OECD 218: emergence, time to emergence, sex ratio of imagoes and the number of egg clutches per female. Chironomid larvae were exposed to 100mgPA kg-1 (i.e., 10,100 particles kg-1) sediment throughout. Soluble Zn-salt (1mg Zn L-1) was used as a positive control and as a co-pollutant in combination with PA. We demonstrated that the tested concentrations of PA and Zn alone as well in combination showed no adverse effects for C.riparius in chronic exposures. 100mgPA kg-1 also did not affect the life cycle traits of the offspring of PA-exposed parent Chironomids. The data obtained will be useful for environmental risk assessment of PA when actual environmental concentrations of PA will be available.

Laboratory-to-field extrapolation: Increase in carbamazepine toxicity in a higher tier, multiple-stress experiment

The toxicity and environmental risk of chemicals, such as the antiepileptic drug carbamazepine (CBZ), is commonly assessed using standardized laboratory tests and laboratory-to-field extrapolation. To investigate the toxicity of CBZ to aquatic key organisms in a more complex and environmentally relevant scenario, we conducted a 32-day multiple-stress experiment in artificial indoor streams. We exposed the non-biting midge Chironomus riparius, the blackworm Lumbriculus variegatus, and the New Zealand mud snail Potamopyrgus antipodarum to 80 and 400 μg CBZ/L in six artificial indoor streams. In addition to hydraulic stress, species’ interaction, and low organic content in the sediment, organisms were co-exposed to the herbicide terbutryn (TBY) as a second chemical stressor at a concentration of 6 μg/L. The exposure to CBZ under multiple stress conditions resulted in a 10- to more than 25-fold higher toxicity in C. riparius and P. antipodarum when compared to a previous, standardized laboratory experiment. The co-exposure to TBY enhanced the adverse effects of CBZ on snails (reduced production of embryos). This effect was additive as the single exposure to TBY also reduced the reproduction of snails, most likely through the reduction of biofilm biomass. The emergence of C. riparius declined at a CBZ concentration of 400 μg/L (without the co-exposure to TBY) and at 80 μg/L in combination with TBY. The difference in sensitivity between laboratory and indoor stream experiments is indicative of a potential underestimation of risk when toxicity data are extrapolated to field conditions. The present results suggest the inclusion of non-chemical and chemical stressors in environmental hazard and risk assessments.