Availability of pesticide-treated seeds on the soil surface in different crops and countries: A comprehensive data set reflecting modern agronomic practice.

For plant protection products applied as seed treatments, the risk to birds and mammals possibly feeding on such treated seeds needs to be addressed in the EU, in order to register these products for commercial use. For this purpose, the European Food Safety Food Authority (EFSA) has provided guidance on how to execute such a risk assessment. The risk assessment follows a tiered approach. In the Tier 1 risk assessment of the EFSA guidance (2023), it is assumed that birds or mammals have ad libitum access to treated seeds and exclusively feed on treated seeds. Due to this conservative assumption, the Tier I risk assessment typically indicates an unacceptable risk to birds and mammals and higher-tier refinements are required. One option for refinement is to use data on the availability of treated seeds on the soil surface directly after drilling. Published data on seed counts are, however, limited to a few countries and crops, and often these data are not contemporary, that is, do not reflect advances in sowing technology and current agronomic practice. To address this data gap, we provide recently generated data from industry field trials (the studies were conducted from 2000 to 2022, >70% between 2019 and 2022), covering 270 fields from seven countries (Austria, France, Germany, Hungary, Poland, Spain, UK) for spring and winter cereals, winter oilseed rape, and sunflower. This comprehensive data set realistically reflects modern agronomic practice and is thus suitable for consideration in a regulatory context for refining the risk assessment for birds and mammals. Integr Environ Assess Manag 2024;00:1-8. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Decline of pesticide residue on treated crop seeds: An analysis of comprehensive industry data and implications of the current risk assessment scheme for plant protection products.

For plant protection products applied as seed treatments, the risk to birds and mammals possibly feeding on treated seeds must be addressed in the EU to register products for commercial use. One assumption of the Tier 1 long-term risk assessment of the European Food Safety Authority (EFSA) is that residues of pesticides on treated seeds do not decline over time after seeding. Consequently, a time-weighted average factor (fTWA ) of 1 (i.e., no dissipation) is used to calculate residue concentrations on seeds. In contrast, for spray applications, a default dissipation half-life (DT50 ) of 10 days is considered corresponding to an fTWA of 0.53. The aim of this study was to establish a default fTWA for treated seeds based on 29 industry-conducted seed dissipation studies, providing 240 datasets covering different active substances, crops, and regions. For fTWA calculation, two approaches were used: (i) kinetic fitting and (ii) using measured data without kinetic fitting. From kinetic fitting, 145 reliable DT50 values were obtained. Because there were no significant differences in DT50 values between crops and between the central and southern EU, the DT50 data from all studies were pooled. The geometric mean DT50 was 3.8 days and the 90th percentile was 13.0 days, corresponding to 21-day fTWA values of 0.27 and 0.59, respectively. Twenty-one-day fTWA values could be calculated directly from measured residues for 204 datasets. The resulting 21-day fTWA values were comparable with those from kinetic fitting (geometric mean: 0.29, 90th percentile: 0.59). The results demonstrate that residue decline on seeds is comparable with foliar dissipation after spray applications. Therefore, the risk assessment scheme by EFSA should implement a default fTWA < 1.0 in the Tier 1 risk assessment for treated seeds (e.g., either 0.53 as for foliage or 0.59, the 90th percentile fTWA in seeds reported in this study). Integr Environ Assess Manag 2024;20:239-247. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Residue Levels of Pesticides on Fruits for Use in Wildlife Risk Assessments.

The guidance document on risk assessment for birds and mammals (GD) provides generic residue values of pesticides on potential diet items for use in wildlife risk assessments. For most diet items, these values are based on a large number of residue studies. However, the default residues per unit dose (RUD; standardized for application of 1 kg substance per hectare) values for fruits were taken from a few literature trials of unclear relevance for regulatory purposes. These trials were conducted according to neither current European Union (EU) agricultural practice nor to recommendations given in the GD about how to conduct wildlife-relevant residue studies. Therefore, field study data on fruit residue levels from applications of pesticides in fruiting crops were compiled and evaluated. Corresponding studies had been conducted during the last 26 y in the EU. In the final data set, 291 studies provided 1002 residue values in different fruits, including grapes, berries (currants, raspberries, gooseberries), fruits from orchards (apple, peach, pear, lemon, mandarin, orange, apricot, cherry, plum), gourds (pumpkins, cucumbers, squash, melons), and strawberries. This data set provides a basis for revising registration-relevant RUD values for fruits as potential diet items for birds and mammals in environmental wildlife risk assessments. The objective of this study was to estimate the resulting residue levels in different fruits determined under field conditions following the application of pesticides across their growing areas within the EU in diverse climatic areas that can be used directly in wildlife risk assessments. The large data set of usually about more than 100 residue values per "fruit group," all evaluated at EU member state level, revealed significantly lower RUDs compared to the current default RUDs presented in the GD. These new RUD values for fruits should be considered for use as default values in future bird and mammal risk assessments and in respective guidance documents. Integr Environ Assess Manag 2021;17:552-561. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology Chemistry (SETAC).

The Anhydrobiotic Potential of the Terrestrial Nematodes Plectus parietinus and Plectus velox.

Within the taxon Nematoda, many species possess an anhydrobiotic potential similar to other microscopic animals, such as tardigrades and rotifers. This interesting capability enables them to survive conditions even of extreme dehydration. We examined the anhydrobiotic abilities of the two widespread terrestrial nematode species, Plectus parietinus and P. velox, by subjecting adult and juvenile life stages of both species to two different desiccation regimes, one with a short time of adaption (2 hr) and the other with a long time of adaption (48 hr) prior to complete desiccation and recorded the nematodes' recovery after 24 hr of rehydration. We found adults of P. parietinus to be the superior anhydrobiotes compared to adults of P. velox at short times of adaption, whereas at a long time of adaption this pattern was reversed. Moreover, our results showed that a long time of adaption significantly increased the recovery rate, independent of species or life stage. Additionally, we found adults to have a remarkable higher anhydrobiotic potential than juveniles, presumably due to a larger amount of resources in adult nematodes or due to a different morphology (cuticle, surface area to volume ratio). Plectus parietinus as well as P. velox showed a distinct anhydrobiotic potential although there were obvious differences between those two species, probably ascribable to different species-specific anhydrobiotic mechanisms and rates of water loss.

A comparative approach using ecotoxicological methods from single-species bioassays to model ecosystems.

Soft sediments are often hotspots of chemical contamination, and a thorough ecotoxicological assessment of this habitat can help to identify the causes of stress and to improve the health of the respective ecosystems. As an important component of the ecologically relevant meiobenthic fauna, nematodes can be used for sediment assessments, with various assay tools ranging from single-species toxicity tests to field studies. In the present study, microcosms containing sediment were used to investigate direct and indirect effects of zinc on natural nematode assemblages, and acute community toxicity tests considering only direct toxicity were conducted. The responses of the various freshwater nematode species in both approaches were compared with those of Caenorhabditis elegans, determined in standardized tests (ISO 10872). At a median lethal concentration (LC50) of 20 mg Zn/L, C. elegans represented the median susceptibility of 15 examined nematode species examined in the acute community toxicity tests. In the microcosms, Zn affected the nematodes dose-dependently, with changes in species composition first detected at 13 mg Zn/kg to 19 mg Zn/kg sediment dry weight. The observed species sensitivities in the microcosms corresponded better to field observations than to the results of the acute community toxicity tests. Environ Toxicol Chem 2016;35:2987-2997. © 2016 SETAC.

Varying Patterns on Varying Scales: A Metacommunity Analysis of Nematodes in European Lakes.

Ecological community patterns are often extremely complex and the factors with the greatest influence on community structure have yet to be identified. In this study we used the elements of metacommunity structure (EMS) framework to characterize the metacommunities of freshwater nematodes in 16 European lakes at four geographical scales (radius ranging from 80 m to 360 km). The site characteristics associated with site scores indicative of the structuring gradient were identified using Spearman rank correlations. The metacommunities of the 174 nematode species included in this analysis mostly had a coherent pattern. The degree of turnover increased with increasing scale. Ordination scores correlated with geographical variables on the larger scales and with the trophic state index on a regional scale. The association of the structuring gradient with spatial variables and the scale-dependent increase in turnover showed that nematode dispersal was limited. The different metacommunity patterns identified at the increasing geographical scales suggested different, scale-related mechanisms of species distribution, with species sorting dominating on smaller and mass effects on larger geographical scales.

Toxicity in relation to mode of action for the nematode Caenorhabditis elegans: Acute-to-chronic ratios and quantitative structure-activity relationships.

Acute-to-chronic ratios (ACRs) and quantitative structure-activity relationships (QSARs) are of particular interest in chemical risk assessment. Previous studies focusing on the relationship between the size or variation of ACRs to substance classes and QSAR models were often based on data for standard test organisms, such as daphnids and fish. In the present study, acute and chronic toxicity tests were performed with the nematode Caenorhabditis elegans for a total of 11 chemicals covering 3 substance classes (nonpolar narcotics: 1-propanol, ethanol, methanol, 2-butoxyethanol; metals: copper, cadmium, zinc; and carbamates: methomyl, oxamyl, aldicarb, dioxacarb). The ACRs were variable, especially for the carbamates and metals, although there was a trend toward small and less variable ACRs for nonpolar narcotic substances. The octanol-water partition coefficient was a good predictor for explaining acute and chronic toxicity of nonpolar narcotic substances to C. elegans, but not for carbamates. Metal toxicity could be related to the covalent index χm2r. Overall, the results support earlier results from ACR and QSAR studies with standard freshwater test animals. As such C. elegans as a representative of small soil/sediment invertebrates would probably be protected by risk assessment strategies already in use. To increase the predictive power of ACRs and QSARs, further research should be expanded to other species and compounds and should also consider the target sites and toxicokinetics of chemicals.

First evidence of cryptic species diversity and significant population structure in a widespread freshwater nematode morphospecies (Tobrilus gracilis).

Free-living nematodes are ubiquitous and highly abundant in terrestrial and aquatic environments, where they sustain ecosystem functioning by mineralization processes and nutrient cycling. Nevertheless, very little is known about their true diversity and intraspecific population structure. Recent molecular studies on marine nematodes indicated cryptic diversity and strong genetic differentiation of distinct populations, but for freshwater nematode species, analogous studies are lacking. Here, we present the first extensive molecular study exploring cryptic species diversity and genetic population structure of a widespread freshwater nematode morphospecies, Tobrilus gracilis, from nine postglacially formed European lakes. Taxonomic species status of individuals, analysed for fragments of the mitochondrial COI gene and for the large (LSU) and small (SSU) ribosomal subunits, were determined by morphological characteristics. Mitochondrial and nuclear markers strongly supported the existence of three distinct genetic lineages (Tg I-III) within Tobrilus gracilis, suggesting that this morphospecies indeed represents a complex of highly differentiated biological species. High genetic diversity was also observed at the population level. Across the nine lakes, 19 mitochondrial, and seven (LSU) and four (SSU) nuclear haplotypes were determined. A phylogeographical analysis revealed remarkable genetic differentiation even among neighbouring lake populations for one cryptic lineage. Priority and persistent founder effects are possible explanations for the observed population structure in the postglacially colonized lakes, but ask for future studies providing direct estimates of freshwater nematode dispersal rates. Our study suggests therefore that overall diversity of limnetic nematodes has been so far drastically underestimated and challenges the assumed ubiquitous distribution of other, single freshwater nematode morphospecies.

The functional response of a freshwater benthic community to cadmium pollution.

Theory predicts that in freshwater communities under chemical stress secondary production will decrease while the rate of biomass turnover (P/B) will increase. However, this concept has never been tested on organisms of smaller size (bacteria, protozoans, small metazoans), although they form the basis of the heterotrophic food web. The present work describes the results of a 7-month microcosm study, in which the effects of low and high toxic stress on an entire sediment community were examined, with cadmium (Cd) as the model pollutant (50 and 400mg Cd kg(-1) dry sediment). While metazoans and protozoans generally followed the expected trend, in bacteria both production and P/B decreased under Cd stress. These observations provide new insights into the functioning of freshwater ecosystems and demonstrate the functional consequences of toxicants on biological systems.

Biomass estimation across the benthic community in polluted freshwater sediment--a promising endpoint in microcosm studies?

With respect to the ecological relevance of endpoints, biomass as an endpoint might be promising regarding ecotoxicological assessments of benthic communities. In a freshwater microcosm study the effect of two cadmium (Cd) concentrations (50 and 400 mg Cd kg(-1) dw) on biomass and abundance of a benthic community were investigated over a period of seven months. Specifically, the sensitivity of both endpoints in distinguishing differential effects was compared. While bacteria were found to be unaffected by Cd, abundance and biomass of protozoans and metazoans decreased. In a short-term comparison, differences between control and Cd treatments were, overall, more pronounced for flagellate biomass and for metazoan abundance with strong differences between the taxonomic groups; furthermore, over the long-term, the differences among organisms and endpoints changed. Based on toxicant sensitivity, the reasonably low variance of the data and the workload involved, biomass can provide a useful additional endpoint in microcosm studies.

Using meiofauna to assess pollutants in freshwater sediments: a microcosm study with cadmium.

The direct and indirect effects of Cd on benthic communities were assessed in a freshwater microcosm study over a period of seven months (218 d). Cadmium was regarded as a model substance to evaluate the usefulness of small-scale laboratory microcosm with microscopic fauna. In particular, effects on the meiofauna community, an ecologically important but rather neglected benthic component, were investigated. In addition, some microfaunal parameters (protozoan abundance and microbial activity) were determined. The sediment was spiked with nominal Cd concentrations of 10, 100, and 1,000 mg/kg dry weight. Because of the strong binding of Cd to sediment particles, measured Cd pore-water concentrations never exceeded 129.5 ± 40.7 µg/L. At 1,000 mg/kg dry weight, the abundances of the two dominant meiofauna taxa, nematodes and oligochaetes, were significantly reduced throughout the present study. Regarding nematodes, species of bacterivorous taxa (Daptonema, Eumonhystera) decreased, whereas species of predacious and omnivorous taxa (Mononchus, Dorylaimus, and Ironus) increased in dominance in microcosms of the highest Cd concentration. Transient effects on microfauna were observed, especially in the first half of the present study, with a reduction in microbial activity and protozoan abundance. However, in microcosms receiving the highest Cd concentration, the abundance of the flagellate Euglena mutabilis increased significantly toward the end of the present study. The results of the present study support the use of small-scale microcosms with natural meiofauna communities as a suitable tool to assess the impact of pollutants in freshwater sediments.