Prioritizing stream types according to their potential risk to receive crop plant material--A GIS-based procedure to assist in the risk assessment of genetically modified crops and systemic insecticide residues.

Crop plant residues may enter aquatic ecosystems via wind deposition or surface runoff. In the case of genetically modified crops or crops treated with systemic pesticides, these materials may contain insecticidal Bt toxins or pesticides that potentially affect aquatic life. However, the particular exposure pattern of aquatic ecosystems (i.e., via plant material) is not properly reflected in current risk assessment schemes, which primarily focus on waterborne toxicity and not on plant material as the route of uptake. To assist in risk assessment, the present study proposes a prioritization procedure of stream types based on the freshwater network and crop-specific cultivation data using maize in Germany as a model system. To identify stream types with a high probability of receiving crop materials, we developed a formalized, criteria-based and thus transparent procedure that considers the exposure-related parameters, ecological status--an estimate of the diversity and potential vulnerability of local communities towards anthropogenic stress--and availability of uncontaminated reference sections. By applying the procedure to maize, ten stream types out of 38 are expected to be the most relevant if the ecological effects from plant-incorporated pesticides need to be evaluated. This information is an important first step to identifying habitats within these stream types with a high probability of receiving crop plant material at a more local scale, including accumulation areas. Moreover, the prioritization procedure developed in the present study may support the selection of aquatic species for ecotoxicological testing based on their probability of occurrence in stream types having a higher chance of exposure. Finally, this procedure can be adapted to any geographical region or crop of interest and is, therefore, a valuable tool for a site-specific risk assessment of crop plants carrying systemic pesticides or novel proteins, such as insecticidal Bt toxins, expressed in genetically modified crops.

Narrow pH Range of Surface Water Bodies Receiving Pesticide Input in Europe.

Fate and toxicity of the active ingredients (AI's) of plant protection products in surface waters is often influenced by pH. Although a general range of pH values is reported in literature, an evaluation targeting aquatic ecosystems with documented AI inputs is lacking at the larger scale. Results show 95% of European surface waters (n = 3075) with a documented history of AI exposure fall within a rather narrow pH range, between 7.0 and 8.5. Spatial and temporal variability in the data may at least be partly explained by the calcareous characteristics of parental rock material, the affiliation of the sampling site to a freshwater ecoregion, and the photosynthetic activity of macrophytes (i.e., higher pH values with photosynthesis). Nonetheless, the documented pH range fits well with the standard pH of most ecotoxicological test guidelines, confirming the fate and ecotoxicity of AIs are usually adequately addressed.

Effects of peak exposure scenarios on Gammarus fossarum using field relevant pesticide mixtures.

The present study investigated sublethal effects of a field relevant pesticide mixture (one herbicide, three fungicides, five insecticides) on Gammarus fossarum by considering different peak exposure scenarios, which may be generated by the inherent properties of vegetated ditches. Additional experiments aimed at the identification of germane exposure pathways (food and water). Therefore, G. fossarum were exposed in independent experiments to three scenarios, which differed besides in the peak concentration of the pesticide mixture also in the mixture's composition and exposure duration (n=20 per treatment). The exposure duration of 12 or 120 min was followed by a seven-day post-exposure observation period. At a constant concentration-time product, a lower exposure duration in concert with a proportionally higher peak concentration caused a substantially elevated ecotoxicity compared to a treatment with a longer exposure duration at a lower peak concentration. Given the importance of the insecticide lambda-cyhalothrin for the mixture's ecotoxicity it may be concluded that the fast mode of action of pyrethroids mainly explains this observation. Moreover, field relevant concentrations of the pesticide mixture applied at an exposure duration of 120 min resulted in reduced gammarids' feeding rate, which may be indicative for shifts in the ecosystem function of leaf litter breakdown and hence the provision of energy for local and downstream communities. Finally, the present study indicated that both pathways of exposure, namely via food or water, reduce gammarids' feeding rate synergistically. This suggests that both exposure pathways should be considered for compounds exhibiting a high Kow (e.g. pyrethroids) during the risk assessment of single substances and mixtures.

The Landau Stream Mesocosm Facility: pesticide mitigation in vegetated flow-through streams.

Vegetated treatment systems have the ability to reduce the risk of adverse effects of nonpoint source pesticide pollution in agricultural surface waters, however, flow-through systems have rarely been evaluated. Peak concentrations of a mixture of two insecticides and two fungicides (Indoxacarb, Tebuconazole, Thiacloprid and Trifloxystrobin) were reduced by more than 90% in 45 m experimental stream mesocosms. Plant density and solubility had the highest explanatory power for the response variable reduction of peak concentration (R² = 0.70, p < 0.001). Optimized vegetated streams can be highly effective in reduction of runoff related pesticide peak concentrations.

Mitigation of biocide and fungicide concentrations in flow-through vegetated stream mesocosms.

Organic chemicals entering surface waters may interact with aquatic macrophytes, which in turn may reduce potential negative effects on aquatic organisms. The overall objective of the present study was to determine the significance of aquatic macrophytes to the retention of organic chemicals in slow-flowing streams and thus their contribution to the mitigation of the risks that these compounds may pose to aquatic ecosystems. Hence, we conducted a study on the mitigation of the biocides triclosan and triclocarban and the fungicides imazalil, propiconazole and thiabendazole, which were experimentally spiked to five flow-through stream mesocosms (45 m length, 0.4 m width, 0.26 m water depth, discharge 1 L/s), four of which were planted with the submerged macrophyte (Planch.). Chemical analyses were performed using liquid chromatography-tandem mass spectrometry following solid-phase extraction for water samples and accelerated solvent extraction for macrophyte and sediment samples. The peak reductions of biocide and fungicide concentrations from the inlet to the outlet sampling sites were ≥48% in all stream mesocosms, and the peak reductions in the vegetated stream mesocosms were 20 to 25% greater than in the unvegetated mesocosm. On average, 7 ± 3 to 10 ± 3% and 28 ± 8 to 34 ± 14% of the initially applied amount of fungicides and biocides, respectively, were retained by macrophytes. There was a significant correlation between retention by macrophytes and the lipophility of the compounds.

Pesticide risk mitigation by vegetated treatment systems: a meta-analysis.

Pesticides entering agricultural surface waters threaten water quality and aquatic communities. Recently, vegetated treatment systems (VTSs) (e.g., constructed wetlands and vegetated ditches) have been proposed as pesticide risk mitigation measures. However, little is known about the effectiveness of VTSs in controlling nonpoint source pesticide pollution and factors relevant for pesticide retention within these systems. Here, we conducted a meta-analysis on pesticide mitigation by VTSs using data from the scientific literature and the European LIFE ArtWET project. Overall, VTSs effectively reduced pesticide exposure levels (i.e., the majority of pesticide retention performances was >70%). A multiple linear regression analysis of 188 retention performance cases identified the two pesticide properties, organic carbon sorption coefficient value and water-phase 50% dissipation time, as well as the VTS characteristics overall plant coverage and hydraulic retention time for targeting high efficacy of pesticide retention. The application of a Tier I risk assessment (EU Uniform Principle) revealed a higher toxicity reduction for hydrophobic and nonpersistent insecticides compared with less sorptive and not readily degradable herbicides and fungicides. Overall, nearly half (48.5%) of all pesticide field concentrations ( = 130) failed Tier I standard risk assessment at the inlet of VTSs, and 29.2% of all outlet concentrations exceeded conservative acute threshold levels. We conclude that VTSs are a suitable and effective risk mitigation strategy for agricultural nonpoint source pesticide pollution of surface waters. Further research is needed to improve their overall efficacy in retaining pesticides.

Geodata-based probabilistic risk assessment and management of pesticides in Germany: a conceptual framework.

The procedure for the risk assessment of pesticides in Germany is currently further developed from a deterministic to a geodata-based probabilistic risk assessment (GeoPRA) approach. As the initial step, the exposure assessment for spray drift in permanent crops, such as vineyards, fruit orchards, and hops, is considered. In our concept, geoinformation tools are used to predict distribution functions for exposure concentrations based mainly on spatial information regarding the neighbourhood of crops and surface waters. A total number of 23 factors affecting the drift into surface waters were assessed and suggestions for their inclusion into the approach developed. The main objectives are to base the exposure estimation on a realistic representation of local landscape characteristics and on empirical results for the impact of each feature on the drift deposition. A framework for the identification of high-risk sites (active management areas [AMAs]) based on protection goals and ecological considerations was developed in order to implement suitable risk mitigation measures. The inclusion of active mitigation measures at sites with identified and verified risk is considered a central and important part of the overall assessment strategy. The suggested GeoPRA procedure itself is comprised of the following 4 steps, including elements of the extensive preliminary work conducted so far: 1) nationwide risk assessment, preferably based only on geodata-based factors; 2) identification of AMAs, including the spatial extension of contamination, the level of contamination, and the tolerable effect levels; 3) refined exposure assessment, using aerial photographs and field surveys; and 4) mitigation measures, with a focus on landscape-level active mitigation measures leading to effective risk reductions. The suggested GeoPRA procedure offers the possibility to actively involve the farming community in the process of pesticide management. Overall, the new procedure will aim at increased flexibility of pesticide application regulations and a high level of protection of surface waters.