Combined effects of herbicides and insecticides reduce biomass of sensitive aquatic invertebrates.

The structure and biomass of aquatic invertebrate communities play a crucial role in the matter dynamics of streams. However, biomass is rarely quantified in ecological assessments of streams, and little is known about the environmental and anthropogenic factors that influence it. In this study, we aimed to identify environmental factors that are associated with invertebrate structure and biomass through a monitoring of 25 streams across Germany. We identified invertebrates, assigned them to taxonomic and trait-based groups, and quantified biomass using image-based analysis. We found that insecticide pressure generally reduced the abundance of insecticide-vulnerable populations (R2 = 0.43 applying SPEARpesticides indicator), but not invertebrate biomass. In contrast, herbicide pressure reduced the biomass of several biomass aggregations. Especially, insecticide-sensitive populations, that were directly (algae feeder, R2 = 0.39) or indirectly (predators, R2 = 0.29) dependent on algae, were affected. This indicated a combined effect of possible food shortage due to herbicides and direct insecticide pressure. Specifically, all streams with increased herbicide pressure showed a reduced overall biomass share of Trichoptera from 43 % to 3 % and those of Ephemeroptera from 20 % to 3 % compared to streams grouped by low herbicide pressure. In contrast, insecticide-insensitive Gastropoda increased from 10 % to 45 %, and non-vulnerable leaf-shredding Crustacea increased from 10 % to 22 %. In summary, our results indicate that at the community level, the direct effects of insecticides and the indirect, food-mediated effects of herbicides exert a combined effect on the biomass of sensitive insect groups, thus disrupting food chains at ecosystem level.

Elevated Fungicide and Nutrient Concentrations Change Structure but not Function of Aquatic Microbial Communities.

Leaf decomposition is a key process in stream ecosystems within forested catchments; it is driven by microbial communities, particularly fungi and bacteria. These microorganisms make nutrients and energy bound in leaves available for wider parts of the food web. Leaf-associated microorganisms are subjected to anthropogenic pressures, such as the increased exposure to nutrients and fungicides associated with land-use change. We assessed the sensitivity of leaf-associated microbial communities with differing exposure histories, namely, from pristine (P) streams, and streams impacted by wastewater (W) and agricultural run-off (vineyards; V). In the laboratory, microbial communities were exposed to elevated nutrient (NO3-N: 0.2-18.0 mg/L, PO4-P: 0.02-1.8 mg/L) and fungicide concentrations (sum concentration 0-300 µg/L) in a fully crossed 3 × 4 × 4-factorial design over 21 days. Leaf decomposition and exoenzyme activity were measured as functional endpoints, and fungal community composition and microbial abundance served as structural variables. Overall, leaf decomposition did not differ between fungicide treatments or exposure histories. Nonetheless, substantial changes in the fungal community composition were observed after exposure to environmentally relevant fungicide concentrations. Elevated nutrient concentrations assisted leaf decomposition, and the effect size depended on the exposure history. The observed changes in the fungal community composition support the principle of functional redundancy, with highly efficient decomposers maintaining leaf decomposition. Environ Toxicol Chem 2024;43:1300-1311. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Transcriptomic sequencing data illuminate insecticide-induced physiological stress mechanisms in aquatic non-target invertebrates.

Pesticides are major agricultural stressors for freshwater species. Exposure to pesticides can disrupt the biotic integrity of freshwater ecosystems and impair associated ecosystem functions. Unfortunately, physiological mechanisms through which pesticides affect aquatic organisms are largely unknown. For example, the widely-used insecticide chlorantraniliprole is supposed to be highly selective for target pest species, i.e. Lepidoptera (butterflies), but its effect in aquatic non-target taxa is poorly studied. Using RNA-sequencing data, we quantified the insecticide effect on three aquatic invertebrate species: the caddisfly Lepidostoma basale, the mayfly Ephemera danica and the amphipod Gammarus pulex. Further, we tested how the insecticide-induced transcriptional response is modulated by biotic interaction between the two leaf-shredding species L. basale and G. pulex. While G. pulex was only weakly affected by chlorantraniliprole exposure, we detected strong transcriptional responses in L. basale and E. danica, implying that the stressor receptors are conserved between the target taxon Lepidoptera and other insect groups. We found in both insect species evidence for alterations of the developmental program. If transcriptional changes in the developmental program induce alterations in emergence phenology, pronounced effects on food web dynamics in a cross-ecosystem context are expected.

Trophic transfer of polyunsaturated fatty acids across the aquatic-terrestrial interface: An experimental tritrophic food chain approach.

Aquatic and their adjacent terrestrial ecosystems are linked via the flux of organic and inorganic matter. Emergent aquatic insects are recognized as high-quality food for terrestrial predators, because they provide more physiologically relevant long-chain polyunsaturated fatty acids (PUFA) than terrestrial insects. The effects of dietary PUFA on terrestrial predators have been explored mainly in feeding trials conducted under controlled laboratory conditions, hampering the assessment of the ecological relevance of dietary PUFA deficiencies under field conditions. We assessed the PUFA transfer across the aquatic-terrestrial interface and the consequences for terrestrial riparian predators in two outdoor microcosm experiments. We established simplified tritrophic food chains, consisting of one of four basic food sources, an intermediary collector gatherer (Chironomus riparius, Chironomidae), and a riparian web-building spider (Tetragnatha sp.). The four basic food sources (algae, conditioned leaves, oatmeal, and fish food) differed in PUFA profiles and were used to track the trophic transfer of single PUFA along the food chain and to assess their potential effects on spiders, that is, on fresh weight, body condition (size-controlled measurement of nutritional status), and immune response. The PUFA profiles of the basic food sources, C. riparius and spiders differed between treatments, except for spiders in the second experiment. The PUFA α-linolenic acid (ALA, 18:3n-3) and É£-linolenic acid (GLA, 18:3n-6) were major contributors to the differences between treatments. PUFA profiles of the basic food sources influenced the fresh weight and body condition of spiders in the first experiment, but not in the second experiment, and did not affect the immune response, growth rate, and dry weight in both experiments. Furthermore, our results indicate that the examined responses are dependent on temperature. Future studies including anthropogenic stressors would deepen our understanding of the transfer and role of PUFA in ecosystems.

Temporal scales of pesticide exposure and risks in German small streams.

Following agricultural application, pesticides can enter streams through runoff during rain events. However, little information is available on the temporal dynamics of pesticide toxicity during the main application period. We investigated pesticide application and large scale in-stream monitoring data from 101 agricultural catchments obtained from a Germany-wide monitoring from April to July in 2018 and 2019. We analysed temporal patterns of pesticide application, in-stream toxicity and exceedances of regulatory acceptable concentrations (RAC) for over 70 pesticides. On a monthly scale from April to July, toxicity to invertebrates and algae/aquatic plants (algae) obtained with event-driven samples (EDS) was highest in May/June. The peak of toxicity towards invertebrates and algae coincided with the peaks of insecticide and herbicide application. Future monitoring, i.e. related to the Water Framework Directive, could be limited to time periods of highest pesticide applications on a seasonal scale. On a daily scale, toxicity to invertebrates from EDS exceeded those of grab samples collected within one day after rainfall by a factor of 3.7. Within two to three days, toxicity in grab samples declined compared to EDS by a factor of ten for invertebrates, and a factor of 1.6 for algae. Thus, toxicity to invertebrates declined rapidly within 1 day after a rainfall event, whereas toxicity to algae remained elevated for up to 4 days. For six pesticides, RAC exceedances could only be detected in EDS. The exceedances of RACs coincided with the peaks in pesticide application. Based on EDS, we estimated that pesticide exposure would need a 37-fold reduction of all analysed pesticides, to meet the German environmental target to keep RAC exceedances below 1 % of EDS. Overall, our study shows a high temporal variability of exposure on a monthly but also daily scale to individual pesticides that can be linked to their period of application and related rain events.

Standard Versus Natural: Assessing the Impact of Environmental Variables on Organic Matter Decomposition in Streams Using Three Substrates.

The decomposition of allochthonous organic matter, such as leaves, is a crucial ecosystem process in low-order streams. Microbial communities, including fungi and bacteria, colonize allochthonous organic material, break up large molecules, and increase the nutritional value for macroinvertebrates. Environmental variables are known to affect microbial as well as macroinvertebrate communities and alter their ability to decompose organic matter. Studying the relationship between environmental variables and decomposition has mainly been realized using leaves, with the drawbacks of differing substrate composition and consequently between-study variability. To overcome these drawbacks, artificial substrates have been developed, serving as standardizable surrogates. In the present study, we compared microbial and total decomposition of leaves with the standardized substrates of decotabs and, only for microbial decomposition, of cotton strips, across 70 stream sites in a Germany-wide study. Furthermore, we identified the most influential environmental variables for the decomposition of each substrate from a range of 26 variables, including pesticide toxicity, concentrations of nutrients, and trace elements, using stability selection. The microbial as well as total decomposition of the standardized substrates (i.e., cotton strips and decotabs) were weak or not associated with that of the natural substrate (i.e., leaves, r² < 0.01 to r² = 0.04). The decomposition of the two standardized substrates, however, showed a moderate association (r² = 0.21), which is probably driven by their similar composition, with both being made of cellulose. Different environmental variables were identified as the most influential for each of the substrates and the directions of these relationships contrasted between the substrates. Our results imply that these standardized substrates are unsuitable surrogates when investigating the decomposition of allochthonous organic matter in streams. Environ Toxicol Chem 2023;42:2007-2018. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Land use changes biomass and temporal patterns of insect cross-ecosystem flows.

Emergent aquatic insects constitute an important food source for higher trophic levels, linking aquatic to terrestrial ecosystems. Little is known about how land use affects the biomass or composition of insect emergence. Previous studies are limited to individual time points or seasons, hampering understanding of annual biomass export patterns and detection of phenological changes. Over 1 year's primary emergence period, we continuously determined the biomass, abundance, and identity of >45,000 aquatic insects and recorded land-use-related environmental variables in 20 stream sites using a paired design with upstream forested sites and downstream agricultural sites. Total insect biomass and abundance were 2-7 mg day-1  m-2 and 7-36 ind day-1  m-2 higher in agricultural than forested sites. However, we found turnover of families between forested and agricultural sites, with more insects with shorter generation time in agriculture, indicating lower sensitivity to land-use-related stress because of higher recovery potential. Except for stoneflies, biomass and abundance of major orders were higher in agriculture, but their phenology differed. For different orders, emergence peaked 30 days earlier to 51 days later in agriculture than forest, whereas total abundance and biomass both peaked earlier in agriculture: 3-5 and 3-19 days, respectively. The most important land-use-related drivers were pesticide toxicity and electrical conductivity, which were differentially associated with different aquatic insect order abundances and biomass. Overall, we found that land use was related to changes in composition and phenology of aquatic insect emergence, which is likely to affect food-web dynamics in a cross-ecosystem context.

Three perspectives on the prediction of chemical effects in ecosystems.

The increasing production, use and emission of synthetic chemicals into the environment represents a major driver of global change. The large number of synthetic chemicals, limited knowledge on exposure patterns and effects in organisms and their interaction with other global change drivers hamper the prediction of effects in ecosystems. However, recent advances in biomolecular and computational methods are promising to improve our capacity for prediction. We delineate three idealised perspectives for the prediction of chemical effects: the suborganismal, organismal and ecological perspective, which are currently largely separated. Each of the outlined perspectives includes essential and complementary theories and tools for prediction but captures only part of the phenomenon of chemical effects. Links between the perspectives may foster predictive modelling of chemical effects in ecosystems and extrapolation between species. A major challenge for the linkage is the lack of data sets simultaneously covering different levels of biological organisation (here referred to as biological levels) as well as varying temporal and spatial scales. Synthesising the three perspectives, some central aspects and associated types of data seem particularly necessary to improve prediction. First, suborganism- and organism-level responses to chemicals need to be recorded and tested for relationships with chemical groups and organism traits. Second, metrics that are measurable at many biological levels, such as energy, need to be scrutinised for their potential to integrate across levels. Third, experimental data on the simultaneous response over multiple biological levels and spatiotemporal scales are required. These could be collected in nested and interconnected micro- and mesocosm experiments. Lastly, prioritisation of processes involved in the prediction framework needs to find a balance between simplification and capturing the essential complexity of a system. For example, in some cases, eco-evolutionary dynamics and interactions may need stronger consideration. Prediction needs to move from a static to a real-world eco-evolutionary view.

Potential propagation of agricultural pesticide exposure and effects to upstream sections in a biosphere reserve.

In the last decades, several studies have shown that pesticides frequently occur above water quality thresholds in small streams draining arable land and are associated with changes in invertebrate communities. However, we know little about the potential propagation of pesticide effects from agricultural stream sections to least impacted stream sections that can serve as refuge areas. We sampled invertebrates and pesticides along six small streams in south-west Germany. In each stream, the sampling was conducted at an agricultural site, at an upstream forest site (later considered as "refuge"), and at a transition zone between forest and agriculture (later considered as "edge"). Pesticide exposure was higher and the proportion of pesticide-sensitive species (SPEARpesticides) was lower in agricultural sites compared to edge and refuge sites. Notwithstanding, at some edge and refuge sites, which were considered as being least impacted, we estimated unexpected pesticide toxicity (sum toxic units) exceeding thresholds at which field studies suggested adverse effects on freshwater invertebrates. We conclude that organisms in forest sections within a few kilometres upstream of agricultural areas can be exposed to ecologically relevant pesticide levels. In addition, although not statistically significant, the abundance of pesticide-sensitive taxa was slightly lower in edge compared to refuge sites, indicating a potential influence of adjacent agriculture. Future studies should further investigate the influence of spatial relationships, such as the distance between refuge and agriculture, for the propagation of pesticide effects and focus on the underlying mechanisms.

Pesticide effects on macroinvertebrates and leaf litter decomposition in areas with traditional agriculture.

Traditional forms of agriculture have created and preserved heterogeneous landscapes characterized by semi-natural meadows and pastures, which have high conversation value for biodiversity. Landscapes in Central and Eastern European countries with traditional agriculture are a stronghold for pollinators, butterflies and amphibians, which have declined in other parts of Europe. Despite different landscape structures, agriculture-associated pesticide exposure in streams can be similarly high as in Western Europe. This raises the question whether the heterogeneous landscape can buffer a temporary water quality decline by agriculture. We investigated the influence of landscape heterogeneity and water quality, in particular pesticide exposure, on macroinvertebrate communities in 19 small streams in Central Romania. We sampled the macroinvertebrate community, assessed the ecosystem function of leaf litter decomposition and analyzed the parasite prevalence in Baetis sp. and Gammarus balcanicus. No association between pesticide toxicity towards macroinvertebrates and several macroinvertebrate metrics was found. However, the level of pesticide toxicity was generally high, constituting a rather short gradient, and the pesticide indicator SPEARpesticides implied pesticide-driven community change in all sites. Landscape heterogeneity and forested upstream sections were among the most important drivers for the macroinvertebrate metrics, indicating increased dispersal and recolonization success. Agricultural land use in the catchment was negatively associated with vulnerable macroinvertebrate taxa such as Ephemeroptera, Plecoptera and Trichoptera. G. balcanicus dominated the shredder taxa and its abundance was positively associated with the pesticide indicator SPEARpesticides. Parasite prevalence in G. balcanicus increased with extensive land use (pastures and forests), whereas it decreased with arable land. Our results suggest that heterogeneous landscapes with structures of low-intensive land use may buffer the effects of agricultural land use and facilitate dispersal and recolonization processes of pesticide-affected macroinvertebrate communities.

Three reasons why the Water Framework Directive (WFD) fails to identify pesticide risks.

The Water Framework Directive (WFD) demands that good status is to be achieved for all European water bodies. While governmental monitoring under the WFD mostly concludes a good status with regard to pesticide pollution, numerous scientific studies have demonstrated widespread negative ecological impacts of pesticide exposure in surface waters. To identify reasons for this discrepancy, we analysed pesticide concentrations measured in a monitoring campaign of 91 agricultural streams in 2018 and 2019 using methodologies that exceed the requirements of the WFD. This included a sampling strategy that takes into account the periodic occurrence of pesticides and a different analyte spectrum designed to reflect current pesticide use. We found that regulatory acceptable concentrations (RACs) were exceeded for 39 different pesticides at 81% of monitoring sites. In comparison, WFD-compliant monitoring of the same sites would have detected only eleven pesticides as exceeding the WFD-based environmental quality standards (EQS) at 35% of monitoring sites. We suggest three reasons for this underestimation of pesticide risk under the WFD-compliant monitoring: (1) The sampling approach - the timing and site selection are unable to adequately capture the periodic occurrence of pesticides and investigate surface waters particularly susceptible to pesticide risks; (2) the measuring method - a too narrow analyte spectrum (6% of pesticides currently approved in Germany) and insufficient analytical capacities result in risk drivers being overlooked; (3) the assessment method for measured concentrations - the protectivity and availability of regulatory thresholds are not sufficient to ensure a good ecological status. We therefore propose practical and legal refinements to improve the WFD's monitoring and assessment strategy in order to gain a more realistic picture of pesticide surface water pollution. This will enable more rapid identification of risk drivers and suitable risk management measures to ultimately improve the status of European surface waters.

Small streams-large concentrations? Pesticide monitoring in small agricultural streams in Germany during dry weather and rainfall.

Few studies have examined the exposure of small streams (< 30 km2 catchment size) to agriculturally used pesticides, compared to large rivers. A total of 105 sites in 103 small agricultural streams were investigated for 76 pesticides (insecticides, herbicides, fungicides) and 32 pesticide metabolites in spring and summer over two years (2018 and 2019) during dry weather and rainfall using event-driven sampling. The median total concentration of the 76 pesticides was 0.18 µg/L, with 9 pesticides per sample on average (n = 815). This is significantly higher than monitoring data for larger streams, reflecting the close proximity to agricultural fields and the limited dilution by non-agricultural waters. The frequency of detection of all pesticides correlated with sales quantity and half-lives in water. Terbuthylazine, MCPA, boscalid, and tebuconazole showed the highest median concentrations. The median of the total concentration of the 32 metabolites exceeded the pesticide concentration by more than an order of magnitude. During dry weather, the median total concentration of the 76 pesticides was 0.07 µg/L, with 5 pesticides per sample on average. Rainfall events increased the median total pesticide concentration by a factor of 10 (to 0.7 µg/L), and the average number of pesticides per sample to 14 (with up to 41 in single samples). The concentration increase was particularly strong for 2,4-D, MCPA, terbuthylazine, and nicosulfuron (75 percentile). Metabolite concentrations were generally less responsive to rainfall, except for those of terbuthylazine, flufenacet, metamitron, and prothioconazole. The frequent and widespread exceedance of the regulatory acceptable concentrations (RAC) of the 76 pesticides during both, dry weather and rainfall, suggests that current plant protection product authorization and risk mitigation methods are not sufficient to protect small streams.

Pesticides are the dominant stressors for vulnerable insects in lowland streams.

Despite elaborate regulation of agricultural pesticides, their occurrence in non-target areas has been linked to adverse ecological effects on insects in several field investigations. Their quantitative role in contributing to the biodiversity crisis is, however, still not known. In a large-scale study across 101 sites of small lowland streams in Central Europe, Germany we revealed that 83% of agricultural streams did not meet the pesticide-related ecological targets. For the first time we identified that agricultural nonpoint-source pesticide pollution was the major driver in reducing vulnerable insect populations in aquatic invertebrate communities, exceeding the relevance of other anthropogenic stressors such as poor hydro-morphological structure and nutrients. We identified that the current authorisation of pesticides, which aims to prevent unacceptable adverse effects, underestimates the actual ecological risk as (i) measured pesticide concentrations exceeded current regulatory acceptable concentrations in 81% of the agricultural streams investigated, (ii) for several pesticides the inertia of the authorisation process impedes the incorporation of new scientific knowledge and (iii) existing thresholds of invertebrate toxicity drivers are not protective by a factor of 5.3 to 40. To provide adequate environmental quality objectives, the authorisation process needs to include monitoring-derived information on pesticide effects at the ecosystem level. Here, we derive such thresholds that ensure a protection of the invertebrate stream community.

Environmentally relevant fungicide levels modify fungal community composition and interactions but not functioning.

Aquatic hyphomycetes (AHs), a group of saprotrophic fungi adapted to submerged leaf litter, play key functional roles in stream ecosystems as decomposers and food source for higher trophic levels. Fungicides, controlling fungal pathogens, target evolutionary conserved molecular processes in fungi and contaminate streams via their use in agricultural and urban landscapes. Thus fungicides pose a risk to AHs and the functions they provide. To investigate the impacts of fungicide exposure on the composition and functioning of AH communities, we exposed four AH species in monocultures and mixed cultures to increasing fungicide concentrations (0, 5, 50, 500, and 2500 µg/L). We assessed the biomass of each species via quantitative real-time PCR. Moreover, leaf decomposition was investigated. In monocultures, none of the species was affected at environmentally relevant fungicide levels (5 and 50 µg/L). The two most tolerant species were able to colonize and decompose leaves even at very high fungicide levels (≥500 µg/L), although less efficiently. In mixed cultures, changes in leaf decomposition reflected the response pattern of the species most tolerant in monocultures. Accordingly, the decomposition process may be safeguarded by tolerant species in combination with functional redundancy. In all fungicide treatments, however, sensitive species were displaced and interactions between fungi changed from complementarity to competition. As AH community composition determines leaves' nutritional quality for consumers, the data suggest that fungicide exposures rather induce bottom-up effects in food webs than impairments in leaf decomposition.

Invertebrate turnover along gradients of anthropogenic salinisation in rivers of two German regions.

Rising salinity in freshwater ecosystems can affect community composition. Previous studies mainly focused on changes in freshwater communities along gradients of absolute levels of electrical conductivity (EC). However, both geogenic and anthropogenic drivers contribute to the EC level and taxa may regionally be adapted to geogenic EC levels. Therefore, we examined the turnover in freshwater invertebrates along gradients of anthropogenic EC change in two regions of Germany. The anthropogenic change of EC was estimated as the difference between the measured EC and the modeled background EC driven by geochemical and climate variables. Turnover in freshwater invertebrates (ß-diversity) was estimated using the Jaccard index (JI). We found that invertebrate turnover between EC gradient categories is generally greater than 47%, with a maximum of approximately 70% in sites with a more than 0.4 mS cm-1 change compared to the baseline (i.e. no difference between predicted and measured EC). The invertebrates Amphinemura sp., Anomalopterygella chauviniana and Leuctra sp. were reliable indicators of low EC change, whereas Potamopyrgus antipodarum indicated sites with the highest EC change. Variability within categories of EC change was slightly lower than within categories of absolute EC. Elevated nutrient concentrations that are often linked to land use may have contributed to the observed change of the invertebrate richness and can exacerbate effects of EC on communities in water. Overall, our study suggests that the change in EC, quantified as the difference between measured EC and modeled background EC, can be used to examine the response of invertebrate communities to increasing anthropogenic salinity concentrations in rivers. However, due to the strong correlation between EC change and observed EC in our study regions, the response to these two variables was very similar. Further studies in areas where EC change and observed EC are less correlated are required. In addition, such studies should consider the change in specific ions.

Paradise lost? Pesticide pollution in a European region with considerable amount of traditional agriculture.

Pesticide contamination of agricultural streams has widely been analysed in regions of high intensity agriculture such as in Western Europe or North America. The situation of streams subject to low intensity agriculture relying on human and animal labour, as in parts of Romania, remains unknown. To close this gap, we determined concentrations of 244 pesticides and metabolites at 19 low-order streams, covering sites from low to high intensity agriculture in a region of Romania. Pesticides were sampled with two passive sampling methods (styrene-divinylbenzene (SDB) disks and polydimethylsiloxane (PDMS) sheets) during three rainfall events and at base flow. Using the toxic unit approach, we assessed the toxicity towards algae and invertebrates. Up to 50 pesticides were detected simultaneously, resulting in sum concentrations between 0.02 and 37 µg L-1. Both, the sum concentration as well as the toxicities were in a similar range as in high intensity agricultural streams of Western Europe. Different proxies of agricultural intensity did not relate to in-stream pesticide toxicity, contradicting the assumption of previous studies. The toxicity towards invertebrates was positively related to large scale variables such as the catchment size and the agricultural land use in the upstream catchment and small scale variables including riparian plant height, whereas the toxicity to algae showed no relationship to any of the variables. Our results suggest that streams in low intensity agriculture, despite a minor reported use of agrochemicals, exhibit similar levels of pesticide pollution as in regions of high intensity agriculture.

Sampling rates for passive samplers exposed to a field-relevant peak of 42 organic pesticides.

Pesticide concentrations in agricultural streams are often characterised by a low level of baseline exposure and episodic peak concentrations associated with heavy rainfall events. Traditional sampling methods such as grab sampling, which are still largely used in governmental monitoring, typically miss peak concentrations. Passive sampling represents a cost-efficient alternative but requires the additional determination of sampling rates to calculate time-weighted average (TWA) water concentrations from the accumulated pesticide mass in the sampler. To date, sampling rates have largely been determined in experiments with constant exposure, which does not necessarily reflect field situations. Using Empore styrene-divinylbenzene (SDB) passive sampler disks mounted in metal holders, we determined sampling rates for 42 organic pesticides, of which 27 sampling rates were lacking before. The SDB disks were in an artificial channel system exposed to a field-relevant pesticide peak. We used an open-source algorithm to estimate coefficients of equations for the accumulated pesticide mass in disks and to determine exposure time-dependent sampling rates. These sampling rates ranged from 0.02 to 0.98 L d-1 and corresponded to those from previous studies determined with constant exposure. The prediction of sampling rates using compound properties was unreliable. Hence, experiments are required to determine reliable sampling rates. We discuss the use of passive sampling to estimate peak concentrations. Overall, our study provides sampling rates and computer code to determine these under peak exposure designs and suggests that passive sampling is suitable to estimate peak pesticide concentrations in field studies.

Assessing the Mixture Effects in In Vitro Bioassays of Chemicals Occurring in Small Agricultural Streams during Rain Events.

Rain events may impact the chemical pollution burden in rivers. Forty-four small streams in Germany were profiled during several rain events for the presence of 395 chemicals and five types of mixture effects in in vitro bioassays (cytotoxicity; activation of the estrogen, aryl hydrocarbon, and peroxisome proliferator-activated receptors; and oxidative stress response). While these streams were selected to cover a wide range of agricultural impacts, in addition to the expected pesticides, wastewater-derived chemicals and chemicals typical for street runoff were detected. The unexpectedly high estrogenic effects in many samples indicated the impact by wastewater or overflow of combined sewer systems. The 128 water samples exhibited a high diversity of chemical and effect patterns, even for different rain events at the same site. The detected 290 chemicals explained only a small fraction (<8%) of the measured effects. The experimental effects of the designed mixtures of detected chemicals that were expected to dominate the mixture effects of detected chemicals were consistent with predictions for concentration addition within a factor of two for 94% of the mixtures. Overall, the burden of chemicals and effects was much higher than that previously detected in surface water during dry weather, with the effects often exceeding proposed effect-based trigger values.