Combined application of up to ten pesticides decreases key soil processes.

Natural systems are under increasing pressure by a range of anthropogenic global change factors. Pesticides represent a nearly ubiquitously occurring global change factor and have the potential to affect soil functions. Currently the use of synthetic pesticides is at an all-time high with over 400 active ingredients being utilized in the EU alone, with dozens of these pesticides occurring concurrently in soil. However, we presently do not understand the impacts of the potential interaction of multiple pesticides when applied simultaneously. Using soil collected from a local grassland, we utilize soil microcosms to examine the role of both rate of change and number of a selection of ten currently used pesticides on soil processes, including litter decomposition, water stable aggregates, aggregate size, soil pH, and EC. Additionally, we used null models to enrich our analyses to examine potential patterns caused by interactions between pesticide treatments. We find that both gradual and abrupt pesticide application have negative consequences for soil processes. Notably, pesticide number plays a significant role in affecting soil health. Null models also reveal potential synergistic behavior between pesticides which can further their consequences on soil processes. Our research highlights the complex impacts of pesticides, and the need for environmental policy to address the threats posed by pesticides.

Pesticides in Agricultural Soils: Major Findings from Various Monitoring Campaigns in Switzerland.

Synthetic pesticides are widely applied in modern agriculture, where they are used against diseases, pests, and weeds to secure crop yield and quality. However, their intensive application has led to widespread contamination of the environment, including soils. Due to their inherent toxicity, they might pose a risk to soil health by causing harm to non-target organisms and disrupting ecosystem services in both agricultural and other exposed soils. Following the Swiss National Action Plan on the reduction of pesticide risks, Agroscope has conducted several soil monitoring studies that are briefly presented here. All of them resort to different multi-residue trace analytical approaches to simultaneously quantify up to about 150 modern pesticides by either accelerated solvent, or Quick, Easy, Cheap, Efficient, Rugged, Safe (QuEChERS) extraction, followed by separation and detection with liquid chromatography-triple quadrupole mass spectrometry. While partly still in progress, our investigations led to the following major findings this far: Multiple pesticides are commonly present in soils, with individual concentrations in agricultural soils often reaching up to a few tens of µg/kg. Pesticide occurrence and concentrations in agricultural soils primarily depend on land use, land use history and cultivated crops. Pesticides can prevail much longer than predicted by their half-lives, and were found in soils even decades after conversion from conventional to organic farming. Corresponding residual fractions can be in the order of a few percent of the originally applied amounts. We further found negative associations of pesticide residues with the abundance of beneficial soil life, underpinning their potential risk to the fertility of agricultural soils. Traces of pesticides are also detected in soils to which they were never applied, indicating contamination, e.g., via spray drift or atmospheric deposition. These results confirm the general notion of both scientists and legislators that prospective risk assessments (RA; as executed during registration and use authorization) should be confirmed and adjusted by retrospective RA (e.g., by environmental monitoring studies of currently used compounds) to jointly lead to an overall reduced environmental risk of pesticides.

Pesticide residues in agricultural soils in light of their on-farm application history.

The application of synthetic pesticides to agricultural fields for the protection of crops leads to the formation of residues in soils. While the short-term behavior of pesticide residues in soils after an application is generally known from laboratory and field studies required for authorization (prospective risk assessments), there is still a lack of in-situ observations that address their long-term fate. Long-term soil monitoring programs, with comprehensive site-specific records of pesticide application data, constitute an invaluable, complementary, retrospective exposure assessment tool to address this gap. Considering the pesticide applications over the past 10-15 years, this study assessed the occurrence of pesticides in agricultural soils of Switzerland and put their presence or absence, as well as their concentrations, in the context of their previous application. The results showed that pesticides could also be detected at sites without a connection to previous applications and that small residual mass fractions of pesticides, even of some non-persistent compounds, were found in soils, years or decades after their last application. This finding points to an environmental issue that may not be adequately captured in prospective risk assessment and calls attention to the need for comprehensive long-term recording and monitoring as a complementary retrospective exposure assessment.

Increasing the number of stressors reduces soil ecosystem services worldwide.

Increasing the number of environmental stressors could decrease ecosystem functioning in soils. Yet this relationship has never been globally assessed outside laboratory experiments. Here, using two independent global standardized field surveys, and a range of natural and human factors, we test the relationship between the number of environmental stressors exceeding different critical thresholds and the maintenance of multiple ecosystem services across biomes. Our analysis shows that, multiple stressors, from medium levels (>50%), negatively and significantly correlates with impacts on ecosystem services, and that multiple stressors crossing a high-level critical threshold (over 75% of maximum observed levels), reduces soil biodiversity and functioning globally. The number of environmental stressors >75% threshold was consistently seen as an important predictor of multiple ecosystem services, therefore improving prediction of ecosystem functioning. Our findings highlight the need to reduce the dimensionality of the human footprint on ecosystems to conserve biodiversity and function.

Temporal dynamics of total and bioavailable fungicide concentrations in soil and their effect upon nine soil microbial markers.

Pesticides constitute an integral part of today's agriculture. Their widespread use leads to ubiquitous contamination of the environment, including soils. Soils are a precious resource providing vital functions to society - thus, it is of utmost importance to thoroughly assess the risk posed by widespread pesticide contamination. The exposure of non-target organisms to pesticides in soils is challenging to quantify since only a fraction of the total pesticide concentration is bioavailable. Here we measured and compared the bioavailable and total concentrations of three fungicides - boscalid, azoxystrobin, and epoxiconazole - and evaluated which concentration best predicts effects on nine microbial markers. The experiments were performed in three different soils at five time points over two months employing nearly 900 microcosms with a model plant. The total and bioavailable concentrations of azoxystrobin and boscalid decreased steadily during the trial to levels of 25 % and 8 % of the original concentration, respectively, while the concentration of epoxiconazole in soil nearly remained unchanged. The bioavailable fraction generally showed a slightly faster and more pronounced decline. The microbial markers varied in their sensitivity to the three fungicides. Specific microbial markers, such as arbuscular mycorrhizal fungi, and bacterial and archaeal ammonia oxidizers, were most sensitive to each of the fungicide treatments, making them suitable indicators for pesticide effects. Even though the responses were predominantly negative, they were also transient, and the impact was no longer evident after two months. Finally, the bioavailable fraction did not better predict the relationships between exposure and effect than the total concentration. This study demonstrates that key microbial groups are temporarily susceptible to a single fungicide application, pointing to the risk that repeated use of pesticides may disrupt vital soil functions such as nutrient cycling in agroecosystems.

Soil contamination in nearby natural areas mirrors that in urban greenspaces worldwide.

Soil contamination is one of the main threats to ecosystem health and sustainability. Yet little is known about the extent to which soil contaminants differ between urban greenspaces and natural ecosystems. Here we show that urban greenspaces and adjacent natural areas (i.e., natural/semi-natural ecosystems) shared similar levels of multiple soil contaminants (metal(loid)s, pesticides, microplastics, and antibiotic resistance genes) across the globe. We reveal that human influence explained many forms of soil contamination worldwide. Socio-economic factors were integral to explaining the occurrence of soil contaminants worldwide. We further show that increased levels of multiple soil contaminants were linked with changes in microbial traits including genes associated with environmental stress resistance, nutrient cycling, and pathogenesis. Taken together, our work demonstrates that human-driven soil contamination in nearby natural areas mirrors that in urban greenspaces globally, and highlights that soil contaminants have the potential to cause dire consequences for ecosystem sustainability and human wellbeing.

Concerted Evaluation of Pesticides in Soils of Extensive Grassland Sites and Organic and Conventional Vegetable Fields Facilitates the Identification of Major Input Processes.

The intensive use of pesticides and their subsequent distribution to the environment and non-target organisms is of increasing concern. So far, little is known about the occurrence of pesticides in soils of untreated areas─such as ecological refuges─as well as the processes contributing to this unwanted pesticide contamination. In this study, we analyzed the presence and abundance of 46 different pesticides in soils from extensively managed grassland sites, as well as organically and conventionally managed vegetable fields (60 fields in total). Pesticides were found in all soils, including the extensive grassland sites, demonstrating a widespread background contamination of soils with pesticides. The results suggest that after conversion from conventional to organic farming, the organic fields reach pesticide levels as low as those of grassland sites not until 20 years later. Furthermore, the different pesticide composition patterns in grassland sites and organically managed fields facilitated differentiation between long-term persistence of residues and diffuse contamination processes, that is, short-scale redistribution (spray drift) and long-scale dispersion (atmospheric deposition), to offsite contamination.

Widespread Occurrence of Pesticides in Organically Managed Agricultural Soils-the Ghost of a Conventional Agricultural Past?

Pesticides are applied in large quantities to agroecosystems worldwide. To date, few studies assessed the occurrence of pesticides in organically managed agricultural soils, and it is unresolved whether these pesticide residues affect soil life. We screened 100 fields under organic and conventional management with an analytical method containing 46 pesticides (16 herbicides, 8 herbicide transformation products, 17 fungicides, seven insecticides). Pesticides were found in all sites, including 40 organic fields. The number of pesticide residues was two times and the concentration nine times higher in conventional compared to organic fields. Pesticide number and concentrations significantly decreased with the duration of organic management. Even after 20 years of organic agriculture, up to 16 different pesticide residues were present. Microbial biomass and specifically the abundance of arbuscular mycorrhizal fungi, a widespread group of beneficial plant symbionts, were significantly negatively linked to the amount of pesticide residues in soil. This indicates that pesticide residues, in addition to abiotic factors such as pH, are a key factor determining microbial soil life in agroecosystems. This comprehensive study demonstrates that pesticides are a hidden reality in agricultural soils, and our results suggest that they have harmful effects on beneficial soil life.