The Uptake of Sporopollenin Exine Capsules and Associated Bioavailability of Adsorbed Oestradiol in Selected Aquatic Invertebrates.

Lycopodium clavatum sporopollenin exine capsules (SpECs) are known to both adsorb and absorb chemicals. The aim of the present work was to determine whether oestradiol (E2) is 'bioavailable' to bioindicator species, either pre-adsorbed to, or in the presence of, SpECs. SpEC uptake was confirmed for Daphnia magna and Dreissena bugensis. E2 levels varied among treatments for Caenorhabditis elegans though there was no relationship to SpEC load. E2 was not detected in D. bugensis tissues. Expression changes of general stress and E2-specific genes were measured. For C. elegans, NHR-14 expression suggested that SpECs modulate E2 impacts, but not general health responses. For D. magna, SpECs alone and with E2 changed Vtg1 and general stress responses. For D. bugensis, SpECS were taken up but no E2 or change in gene expression was detected after exposure to E2 and/or SpECs. The present study is the first to investigate SpECs and bound chemical dynamics.

Surface-Related Toxicity of Polystyrene Beads to Nematodes and the Role of Food Availability.

Microplastics released into freshwaters from anthropogenic sources settle in the sediments, where they may pose an environmental threat to benthic organisms. However, few studies have considered the ecotoxicological hazard of microplastic particles for nematodes, one of the most abundant taxa of the benthic meiofauna. This study investigated the toxic effects of polystyrene (PS) beads (0.1-10.0 µm) and the underlying mechanisms thereof on the reproduction of the nematode Caenorhabditis elegans. The observed effect of the PS beads on the nematodes correlated well with the total surface area of the beads per volume, with a 50% inhibition of reproduction at 55.4 ± 12.9 cm2/mL, independent of the bead size. The adverse effects were not explained by styrene monomers leaching from the beads because chemical activities of styrene in PS suspensions were well below the toxic levels. However, the observed effects could be related to the bead material because the same-sized silica (SiO2) beads had considerably less impact, probably due to their higher specific density. PS and SiO2 beads affected the food availability of C. elegans, with greater effects by the PS beads. Our results demonstrate the importance of including indirect food web effects in studies of the ecological risks posed by microplastics.

Comparing the effects of fludioxonil on non-target soil invertebrates using ecotoxicological methods from single-species bioassays to model ecosystems.

The lower tier toxicity tests used for risk assessment of plant protection products are conducted with single species, only regarding direct effects of the tested substances. However, it is not clear, if lower tier tests are able to protect in situ soil communities, as these tests are not able to account for direct and indirect effects of chemicals on multi-species systems in natural soil communities. This knowledge gap between single-species tests and field studies can be bridged using model ecosystems (microcosms), which allow for the assessment of direct and indirect effects of the compounds under evaluation. In the present study, single-species toxicity tests and soil-spiked microcosms were used to comparatively investigate the toxicity of the non-systemic fungicide fludioxonil (FDO) on non-target soil organisms, with nematodes being the test organisms of choice. The potential effects of FDO on nematodes were investigated in two different test systems: (i) standardized toxicity tests using Caenorhabditis elegans exposed to FDO-spiked soil (FDO concentrations 50-1207 mg/kg soil dry weight) and (ii) in situ nematode communities sampled from microcosms containing FDO-spiked soil (FDO concentrations 75-600 mg/kg soil dry weight). FDO dose-dependently inhibited the reproduction of C. elegans, with an effect concentration (EC50) of 209.9 mg FDO/kg soil dry weight and a no observed effect concentration (NOEC) of 63.0 mg FDO/kg soil dry weight. In the microcosms, FDO significantly affected trait-based indices, such as the Maturity Index (MI25) and the Enrichment Index (EI), which responded already at FDO concentrations of 14.3 and 62.4 mg/kg dry soil. Overall, this study provides new insights into the impact of the non-systemic fungicide FDO on non-target soil organisms and demonstrates the suitability of nematode-based tools, that allow for a quick and cost-effective lower and higher tier risk assessment of plant protection products.

Response of nematode communities to metals and PAHs in freshwater microcosms.

Freshwater microcosms were used to investigate the effects of various metals and polycyclic aromatic hydrocarbons (PAHs), applied as single substances and in mixtures, on sediment-inhabiting nematode assemblages. Several community measures, including nematode abundance, biomass, species richness, species composition and the NemaSPEAR[%]-index, were assessed and their changes in response to the chemical treatments were compared with the results of single-species toxicity testing using the nematode Caenorhabditis elegans. The diagnostic power of endpoints revealing toxic effects was then evaluated to assess the general suitability of nematodes as bioindicators of sediment contamination by a set of relevant chemicals. Overall, community measures based on species-level (detected with principle response curves) responded most sensitively to chemical stress in the microcosms, especially in terms of biomass, with the C. elegans toxicity test was for the most part as sensitive to the chemicals as the nematode species composition. Generally, this study justified the suitability of nematodes in assessments of the risk of chemicals frequently associated with freshwater sediments and underlined the value of C. elegans in the prospective risk assessment of chemicals, as this species was able to indicate the negative effects of comparatively low sediment concentrations of the contaminants.

Passive Dosing in Chronic Toxicity Tests with the Nematode Caenorhabditis elegans.

In chronic toxicity tests with Caenorhabditis elegans, it is necessary to feed the nematode with bacteria, which reduces the freely dissolved concentration (Cfree) of hydrophobic organic chemicals (HOCs), leading to poorly defined exposure with conventional dosing procedures. We examined the efficacy of passive dosing of polycyclic aromatic hydrocarbons (PAHs) using silicone O-rings to control exposure during C. elegans toxicity testing and compared the results to those obtained with solvent spiking. Solid-phase microextraction and liquid-liquid extraction were used to measure Cfree and the chemicals taken up via ingestion. During toxicity testing, Cfree decreased by up to 89% after solvent spiking but remained constant with passive dosing. This led to a higher apparent toxicity on C. elegans exposed by passive dosing than by solvent spiking. With increasing bacterial cell densities, Cfree of solvent-spiked PAHs decreased while being maintained constant with passive dosing. This resulted in lower apparent toxicity under solvent spiking but an increased apparent toxicity with passive dosing, probably as a result of the higher chemical uptake rate via food (CUfood). Our results demonstrate the utility of passive dosing to control Cfree in routine chronic toxicity testing of HOCs. Moreover, both chemical uptake from water or via food ingestion can be controlled, thus enabling the discrimination of different uptake routes in chronic toxicity studies.

Latent heparanase facilitates VLA-4-mediated melanoma cell binding and emerges as a relevant target of heparin in the interference with metastatic progression.

Heparanase is an endo-ß-glucuronidase that enzymatically cleaves heparan sulfates (HS) and heparan sulfate proteoglycan (HSPG) structures. Heparanase expression levels by tumors were correlated with cell invasion, angiogenic activity, and poor prognosis. Heparanase can also possess pro-tumorigenic effects independent of its enzymatic activity. Using human melanoma MV3 cells, we demonstrate that latent heparanase activates in a tightly temporary-regulated manner the binding function of the integrin very late antigen-4 (VLA-4), an important component in the metastatic spread of melanoma cells. shRNA-mediated knockdown of syndecan-4 (SDC-4) indicated that this proteoglycan is the key element to convey heparanase binding via focal adhesion complex formation, detected by vinculin staining, to an upregulated VLA-4 binding function. This inside-out signaling pathway of VLA-4 involved activated FAK and Akt, but apparently not PKCα/δ. VLA-4, however, appears representative of other integrins which together impact the heparanase/integrin activation axis in tumorigenicity. Biosensor measurements provided an insight as to how heparin can interfere with this activation process. While low-molecular-weight heparin (LMWH) cannot replace heparanase bound to SDC-4, LMWH can compete with SDC-4 binding of heparanase. Since blockade of heparanase by LMWH has functional consequences for reduced VLA-4 binding, latent heparanase appears as a novel, so far unnoticed target of heparin, underlying its antimetastatic activity.

Size- and composition-dependent toxicity of synthetic and soil-derived Fe oxide colloids for the nematode Caenorhabditis elegans.

Colloidal iron oxides (FeOx) are increasingly released to the environment due to their use in environmental remediation and biomedical applications, potentially harming living organisms. Size and composition could affect the bioavailability and toxicity of such colloids. Therefore, we investigated the toxicity of selected FeOx with variable aggregate size and variably composed FeOx-associated organic matter (OM) toward the nematode Caenorhabditis elegans. Ferrihydrite colloids containing citrate were taken up by C. elegans with the food and accumulated inside their body. The toxicity of ferrihydrite, goethite, and akaganeite was dependent on aggregate size and specific surface area, with EC50 values for reproduction ranging from 4 to 29 mg Fe L(-1). Experiments with mutant strains lacking mitochondrial superoxide dismutase (sod-2) showed oxidative stress for two FeOx and Fe(3+)-ions, however, revealed that it was not the predominant mechanism of toxicity. The OM composition determined the toxicity of mixed OM-FeOx phases on C. elegans. FeOx associated with humic acids or citrate were less toxic than OM-free FeOx. In contrast, soil-derived ferrihydrite, containing proteins and polysaccharides from mobile OM, was even more toxic than OM-free Fh of similar aggregate size. Consequently, the careful choice of the type of FeOx and the type of associated OM may help in reducing the ecological risks if actively applied to the subsurface.

Experimental studies with nematodes in ecotoxicology: an overview.

With respect to their high abundances, their role as intermediaries between microorganisms and higher trophic levels, and their ubiquitous occurrence in all habitats, nematodes are of strong potential interest as environmental indicators. Ecotoxicological methods to evaluate the risk of anthropogenic pollutants on ecosystems require both in vitro and in vivo toxicity tests to investigate either mechanisms or pathways of toxicity and to set accurate toxicity thresholds. For this, the interest in nematodes as model organisms in ecotoxicology increased over the past few decades and existing appropriate experimental methods are reviewed in this manuscript. An overview of the various existing ecotoxicological tools for nematodes, ranging from molecular laboratory methods to experimental model ecosystem approaches, and their role as indicator organisms is given. The reviewed studies, approaches that range from species-based to community-based methods, reveal exciting possibilities for the future use of nematodes in ecotoxicological studies. Suitable ecotoxicological tools and ecological indices for nematodes should be integrated in weight-of-evidence approaches for assessing the ecological risk of contamination.

Determining the toxicity of organic compounds to the nematode Caenorhabditis elegans based on aqueous concentrations.

Caenorhabditis elegans is used for assessing the toxicity of chemicals in aqueous medium. However, chemicals can absorb to the bacterial food, which reduces the freely dissolved concentrations of the tested compounds. Thus, based on total or nominal concentrations, toxicity is underestimated, resulting in misleading assumptions on toxicity mechanisms or comparisons to other test organisms. As the verification of freely dissolved exposure concentrations (Cfree) is challenging in small test systems, simple partitioning models might by a good option for estimating Cfree. Therefore, C. elegans was exposed to seven differently acting organic chemicals with varying hydrophobicities, thus also different affinities to bind to the food of C. elegans. Measured concentrations of the dissolved aqueous and the bacterial-bound fraction allowed the calculation of binding constants (Kb). Experimental Kb were comparable to literature data of hydrophobic chemicals and correlated well with their hydrophobicity, expressed as log KOW. The chronic toxicity of the various compounds on C. elegans' reproduction, based on their aqueous concentration, was weakly related to their log KOW. Toxicity expressed based on chemical activity and comparisons with a baseline toxicity model, nevertheless, suggested a narcotic mode of action for most hydrophobic compounds (except methylisothiazolinone and trichlorocarbanilide). Although revealing a similar toxicity ranking than Daphnia magna, C. elegans was less sensitive, probably due to its ability to reduce its internal concentrations by means of its very impermeable cuticle or by efficient detoxification mechanisms. It could be shown that measured aqueous concentrations in the nematode test system corresponded well with freely dissolved concentrations that were modeled using simple mass-balance models from nominal concentrations. This offers the possibility to estimate freely dissolved concentrations of chemicals from nominal concentrations, making routine testing of chemicals and their comparison to other species more accurate.

Organic carbon source in formulated sediments influences life traits and gene expression of Caenorhabditis elegans.

River water quality is strongly influenced by their sediments and their associated pollutants. To assess the toxic potential of sediments, sediment toxicity tests require reliable control sediments, potentially including formulated control sediments as one major option. Although some standardization has been carried out, one critical issue still remains the quality of sediment organic matter (SOM). Organic carbon not only binds hydrophobic contaminants, but may be a source of mild toxicity, even if the SOM is essentially uncontaminated. We tested two different sources of organic carbon and the mixture of both (Sphagnum peat (P) and one commercial humic substances preparation-HuminFeed(®), HF) in terms of life trait variables and expression profiles of selected life performance and stress genes of the nematode Caenorhabditis elegans. In synchronous cultures, gene expression profiling was done after 6 and 48 h, respectively. The uncontaminated Sphagnum P reduced growth, but increased numbers of offspring, whereas HF did not significantly alter life trait variables. The 6 h expression profile showed most of the studied stress genes repressed, except for slight to strong induction in cyp-35B1 (all exposures), gst-38 (only mixture), and small hsp-16 genes (all exposures). After 48 h, the expression of almost all studied genes increased, particularly genes coding for antioxidative defense, multiple xenobiotic resistance, vitellogenin-like proteins, and genes regulating lifespan. Overall, even essentially uncontaminated SOM may induce several modes of action on the molecular level in C. elegans which may lead to false results if testing synthetic xenobiotics. This contribution is a plea for a strict standardization of the SOM quality in formulated sediments and to check for corresponding effects in other model sediment organisms, especially if using molecular toxicity endpoints.

Nematode Community of a Natural Grassland Responds Sensitively to the Broad-Spectrum Fungicide Mancozeb in Soil Microcosms.

Fungicides make up the largest part of total pesticide use, with the dithiocarbamate mancozeb being widely applied as a nonsystemic contact pesticide to protect a wide range of field crops against fungal diseases. Although nematodes are key drivers of soil functioning, data on effects of fungicides, and especially mancozeb, on these nontarget organisms are scarce. Therefore, the effects of mancozeb on a soil nematode community from a natural grassland were assessed in small-scale soil microcosms. Nematodes were exposed to mancozeb-spiked soil in six nominal concentrations (7-133 mg/kg dry soil) and analyzed after 14, 56, and 84 days in terms of densities, genus composition, and functional traits. Because this fungicide is known to quickly degrade in soils (50% degradation time <1 day), mancozeb concentrations were analyzed for all sampling occasions. Chemical analysis revealed considerably lower measured concentrations compared with the aimed nominal soil concentrations at the beginning of the exposure (1-18 mg/kg dry soil), suggesting fast degradation during the spiking process. Nevertheless, the native nematode community responded sensitively to the fungicide mancozeb, revealing lower no-observed-effect concentration and 10% effect concentration (EC10) values than reported for other soil invertebrates such as springtails and earthworms. Using the EC10 for the most sensitive nematode community endpoint (percentage of predators and omnivores: 1.2 mg/kg dry soil), the risk assessment exhibited a toxicity exposure ratio of 0.66 and, thus, a high risk of mancozeb for soil nematodes. Keeping in mind their abundance and their central roles in soil food-web functioning, the demonstrated sensitivity to a widely applied fungicide underscores the relevance of the inclusion of nematodes into routine risk-assessment programs for pesticides. Environ Toxicol Chem 2022;41:2420-2430. © 2022 SETAC.

Food availability is crucial for effects of 1-µm polystyrene beads on the nematode Caenorhabditis elegans in freshwater sediments.

Freshwater sediments represent a sink for microplastic (<5 mm) through various processes. Thus, benthic organisms can be exposed to relatively high concentrations of microplastics. Surprisingly, studies on benthic organisms are still underrepresented in the field of ecotoxicological effect assessment of microplastics. Therefore, we studied the effects of 1-µm polystyrene (PS) beads on the reproduction of the nematode Caenorhabditis elegans using a standardized protocol for toxicity testing in freshwater sediments (96 h; ISO 10872:2020), combined with ingestion experiments using fluorescent PS beads. To investigate the role of sediment properties (e.g., textures, organic contents) for ingestion and effects of PS beads, five different artificial and field-collected sediments were used. Body burdens of 1-µm PS beads in the intestinal tract of the nematodes after 96 h differed between the sediments, however, differences were not significant over the whole course of the experiment. EC10 and EC50-values of 1-µm PS beads for C. elegans' reproduction in the various sediments ranged from 0.9 to 2.0 and 4.8 to 11.3 mg PS/g dry sediment, respectively. The ECx-values showed to be considerably higher than values reported for water exposure (EC10/50: 0.2 and 0.6 mg PS/ml, respectively), which was probably due to higher food densities in sediment compared to water exposure. Based on the PS beads/bacteria ratio, ECx-values were comparable between sediment and water exposure, suggesting that also in sediments microplastic reduces the food availability for C. elegans causing lower reproduction. This indirect effect mechanism was confirmed by experiments with varying food densities. Thus, the nutritious conditions might play a crucial role for the overall ecological risk of microplastics in benthic ecosystems.

Long-term exposure of a free-living freshwater micro- and meiobenthos community to microplastic mixtures in microcosms.

Microplastics in a wide range of shapes and polymer types (MPs; <5 mm) accumulate in freshwater sediments, where they may pose an environmental threat to sediment-dwelling micro- and meiobenthos. To date, the effects of MPs on those organisms have mostly been studied in single-species experiments exposed to high particle concentrations. By contrast, there have been few investigations of the effects resulting from the long-term exposure of natural communities to environmental relevant MPs. This research gap was addressed in the present study. A microcosm experiment was conducted to examine the impact of a mixture of MPs of varying polymer composition, shape, and size (50% polystyrene (PS) beads: 1-µm diameter; 37% polyethylene terephthalate (PET) fragments: 32 × 21 µm in size, and 13% polyamide (PA) fibers 104 × 15 µm in size; % based on the total particle number) provided at two concentrations (low: 4.11 × 105 MPs/kg sediment dw and high: 4.11 × 107 MPs/kg sediment dw) and two exposure durations (4 and 12 weeks) on a micro- and meiobenthic community collected from a freshwater sediment. MPs exposure did not alter the abundance of protozoa (ciliates and flagellates) as well as the abundance and biomass of meiobenthic organisms (nematodes, rotifers, oligochaetes, gastrotrichs, nauplii), whereas the abundance and biomass of harpacticoid copepods was affected. Neither nematode species diversity (species richness, Shannon-Wiener index, and evenness) nor the NemaSPEAR[%]-index (pollution-sensitive index based on freshwater nematodes) changed in response to the MPs. However, changes in the structure of the meiobenthic and nematode community in the presence of environmentally relevant MPs mixtures cannot be excluded, such that microcosms experiments may be of value in detecting subtle, indirect effects of MPs.

On the balance between practical relevance and standardization - Testing the effects of zinc and pyrene on native nematode communities in soil microcosms.

Soils are among the most densely inhabited and biodiverse habitats on our planet, and many important soil ecosystem services depend on the health condition of the native soil fauna. Anthropogenic stress such as chemical pollution acting on the native soil fauna might jeopardize these functions. Laboratory microcosm tests are an appropriate tool for assessing the risk of chemicals on the native soil fauna and can be regarded as intermediate tier tests, bridging the gap between single species toxicity tests and field testing. Nematodes are one of the most abundant and divers soil invertebrates, and as such native nematode communities might be suitable for ecotoxicological assessments in laboratory microcosm set ups. In order to test such a small-scale (30 g soil) microcosm system, two different chemicals (zinc and pyrene) were assessed in various soil types for their effects on the respective native nematode communities. Various community parameters such as total nematode density, genus richness and genus composition, as well as trait-related indices (e.g. maturity index) were monitored over a period of 8-10 weeks. The response of the nematode communities strongly varied between soil types, and these differences were more pronounced for Zn than for pyrene. Interestingly, the structure of the respective native nematode communities was shown to play a larger role for explaining the varying toxic effects than soil properties governing the bioavailability of the spiked chemicals. We demonstrated that exposure of natural nematode communities in their original soil matrix to the metal zinc and to pyrene under climatically highly controlled conditions resulted in quantitatively and qualitatively distinct responses. Upon comparison of various community indices, the maturity index was shown to be the most sensitive toxicity endpoint for all tested soils and chemicals.

Food bacteria and synthetic microparticles of similar size influence pharyngeal pumping of Caenorhabditis elegans.

Toxicity tests using the model organism Caenorhabditis elegans have shown that exposure to small microplastics such as polystyrene (PS) beads lead to high body burdens and dietary restrictions that in turn inhibit reproduction. Pharyngeal pumping is the key mechanism of C. elegans for governing the uptake of food and other particles and can be easily monitored by determining the pumping rates. In this study, pharyngeal pumping of C. elegans was examined in response to increasing quantities of food bacteria (E. coli: 106-1010 cells ml-1) and synthetic particles (107-109 beads ml-1) of similar size (1 µm). While the average pumping rate of C. elegans exposed to E. coli depended on the density of the bacterial cells, this was not the case for the synthetic beads. At 107 items ml-1, bacterial cells and synthetic beads triggered a basic stimulation of the pumping rate, independent of the nutritional value of the particle. At quantities >107 items ml-1, however, the nutritional value was essential to maximize the pumping rate, as it was upregulated only by E. coli cells, which can be chemosensorially recognized by C. elegans. Given the unselective uptake of all particles in the size range of bacteria, restricting the pumping rates for particles with low nutritional value to a basic rate, prevents the nematodes from wasting energy by high-frequency pumping, but still allows a food-quality screening at low food levels.

Bacterial consumption by nematodes is disturbed by the presence of polystyrene beads: The roles of food dilution and pharyngeal pumping.

Microplastics (MPs; <5 mm) released into freshwaters from anthropogenic sources accumulate in sediments, where they may pose an environmental threat to benthic organisms, such as nematodes. Several studies have examined the effects of nano- and microplastics on the nematode Caenorhabditis elegans, whereas reduced food availability was suggested as a possible explanation for the observed inhibitory effects. Therefore, this study should clarify whether micro-beads of different sizes (1.0 and 6.0 µm in diameter) and materials (polystyrene PS, silica) are able to interfere with the feeding of C. elegans on its bacterial diet (Escherichia coli), and, by this, lowering its consumption rate within 7 h of exposure. Moreover, it was examined whether an inhibited bacterial consumption was caused by a reduction of the nematode's pumping rate, as a primary indicator of food ingestion. Bacterial consumption by C. elegans was significantly decreased in the presence of 1.0- and 6.0-µm PS beads (49-67% lower bacterial consumption compared to control), whereas in the presence of 1.0-µm silica beads feeding was not impeded. Interestingly, the pumping rate was significantly lower in the presence of non-ingestible 6.0-µm PS beads with 161 ± 16 pumps min-1, while it was largely unchanged for nematodes exposed to ingestible 1.0-µm PS beads with 205 ± 12 pumps min-1, compared to control conditions with 210 ± 18 pumps min-1, respectively. As reduced bacterial consumption leads to generally lower energy reserves in C. elegans, these results allow to link observed inhibitory effects of MPs on the nematodes to a lower food availability. Such indirect, food-web related, effects of MPs should raise concern of ecological consequences in natural habitats, where temporal food deficiencies can occur. Consequently, disturbances in food availability and feeding efficiency should be regarded as important parameters in environmental risk assessments focusing on MPs.

Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden.

Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (ΣTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the ΣTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEARpesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEARpesticides was not correlated to ΣTUDaphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEARpesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study).

Dataset supporting the use of nematodes as bioindicators of polluted sediments.

We provide the dataset supporting the research article "Nematodes as bioindicators of polluted sediments using metabarcoding and microscopic taxonomy" [1]. Nematodes are frequently used as bioindicators and the NemaSPEAR[%] is an validated index that is originally based on morphological data. The index was compared to molecular sequence data for the 28S rDNA, 18S rDNA and COI gene for 7 locations. This dataset includes chemical analyses of the sediments for 33 different substances. The sequence data for OTU-based analyses for the 28S rDNA, 18S rDNA and COI gene is given, together with the read distribution during bioinformatics processing. We furthermore include alternative ASV data, based on a cluster-independent approach. The morphological data is presented, including the biomass for each species, as well as an overview about whether the species is represented in the NCBI database. Furthermore, rarefaction analysis is given for the morphological data, and furthermore NMDS plots for the species and genus level based on morphological and molecular data. The correlation between the mean PEC-Q and the NemaSPEAR[%] values is given in order to compare the efficiency of the index, based on morphological and molecular data.

Nematodes as bioindicators of polluted sediments using metabarcoding and microscopic taxonomy.

The use of bioindicator species is a widely applied approach to evaluate ecological conditions, and several indices have been designed for this purpose. To assess the impact of pollution, especially in sediments, a pollution-sensitive index based on nematodes, one of the most abundant and species-rich groups of metazoa, was developed. The NemaSPEAR[%] index in its original form relies on the morphological inspection of nematode species. The application of a morphologically based NemaSPEAR[%] at the genus-level was previously validated. The present study evaluated a NemaSPEAR[%] index based on metabarcoding of nematode communities and tested the potential of fragments from the 28S rDNA, 18S rDNA and cytochrome c oxidase subunit I (COI) genes. In general, molecular-based results tended to show a poorer condition than morphology-based results for the investigated sites. At the genus level, NemaSPEAR[%] values based on morphological data strongly correlated with those based on molecular data for both the 28S rDNA and the 18S rDNA gene fragments (R2 = 0.86 and R2 = 0.74, respectively). Within the dominant genera (>3%) identified by morphology, 68% were detected by at least one of the two ribosomal markers. At the species level, however, concordance was less pronounced, as there were several deviations of the molecular from the morphological data. These differences could mostly be attributed to shortcomings in the reference database used in the molecular-based assignments. Our pilot study shows that a molecularly based, genus-level NemaSPEAR[%] can be successfully applied to evaluate polluted sediment. Future studies need to validate this approach further, e.g. with bulk extractions of whole meiofaunal communities in order to circumvent time-consuming nematode isolation. Further database curation with abundant NemaSPEAR[%] species will also increase the applicability of this approach.