A multi-residue method for trace analysis of pesticides in soils with special emphasis on rigorous quality control.

A multi-residue trace analytical method is presented to accurately quantify 146 currently used pesticides in (agricultural) soils with varying soil properties. Pesticides were extracted using an optimized quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach and chemical analysis was carried out by liquid chromatography coupled to tandem mass spectrometry (triple quadrupole). Quantification was based on matrix-matched internal standards calibration, using 95 isotopically labeled analyte analogues. In contrast to the common approach of method validation using soils freshly spiked with analytes shortly before the extraction, our method is additionally validated via an in-house prepared partly aged soil, which contains all target pesticides and via agricultural field soils with native pesticide residues. The developed method is highly sensitive (median method limit of quantification: 0.2 ng/g), precise (e.g., median intra-day and inter-day method precision both ~ 4% based on field soils), and true ((i) quantified pesticide concentrations of the partly aged soil remained stable during 6 months, were close to the initially spiked nominal concentration of 10 ng/g, and thus can be used to review trueness in the future; (ii) median freshly spiked relative recovery: 103%; and (iii) participation in a ring trial: median z-scores close to one (good to satisfactory result)). Its application to selected Swiss (agricultural) soils revealed the presence of in total 77 different pesticides with sum concentrations up to 500 ng/g. The method is now in use for routine soil monitoring as part of the Swiss Action Plan for Risk Reduction and Sustainable Use of Plant Protection Products.

Geochemical Soil Atlas of Switzerland - Distribution of Toxic Elements.

Chemical elements such as copper and molybdenum are essential for animal and human health but may become toxic at elevated concentrations depending on the exposure and intake rate. Other elements such as mercury pose a threat to human health at already low concentrations. The soil acts as the main source of these elements for plant uptake and is thus driving accumulation along the food chain. However, in Switzerland, no nationwide information on elemental distributions in soils has existed up to now. The geochemical soil atlas of Switzerland will fill this gap by presenting the concentration ranges and the spatial distribution of 20 elements in the topsoil. In this summary, we present the methodological approaches and some main findings of the atlas with a focus on toxic elements as well as elements that can be or are toxic at higher concentrations.

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.

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.

Twenty-five years of observations of soil organic carbon in Swiss croplands showing stability overall but with some divergent trends.

The temporal evolution of soil organic carbon (SOC) is of major importance given its status as a key parameter in many soil functions. Furthermore, soils constitute an important reservoir of carbon in our environment. In light of climate change, consistent SOC data over extended periods in combination with information on agricultural management are much required, but still scarce. We report SOC changes in the topsoil (0-20 cm) of Swiss cropland measured at well-defined monitoring sites resampled every 5 years from 1990 to 2014 by the Swiss Soil Monitoring Network NABO using consistent sampling protocols and quality assurance. Data on agricultural management practices were retrieved from farmers. Overall, SOC remained stable for the ensemble of monitoring sites, although increasing and decreasing trends were observed for individual sites, ranging from - 11 to + 16% relative change per decade. Changes in the agricultural management of cropland triggered substantial changes in SOC contents for some sites. Moreover, sites with a low ratio of SOC/clay (< 0.1) generally showed more positive trends than sites with higher ratios. We presume that SOC was either at or near steady state, given the consistency of management practices over the last few decades. Finally, our study provides insights into the uncertainties related to (real-world) SOC monitoring and underlines the relevance of short-term SOC variations that could hamper the detection of long-term trends. The minimum detectable change (MDC) by the applied monitoring scheme is estimated at 0.35% per year, in relative terms.

Long-Term Persistence of Pesticides and TPs in Archived Agricultural Soil Samples and Comparison with Pesticide Application.

For polar and more degradable pesticides, not many data on long-term persistence in soil under field conditions and real application practices exist. To assess the persistence of pesticides in soil, a multiple-compound screening method (log Kow 1.7-5.5) was developed based on pressurized liquid extraction, QuEChERS and LC-HRMS. The method was applied to study 80 polar pesticides and >90 transformation products (TPs) in archived topsoil samples from the Swiss Soil Monitoring Network (NABO) from 1995 to 2008 with known pesticide application patterns. The results reveal large variations between crop type and field sites. For the majority of the sites 10-15 pesticides were identified with a detection rate of 45% at concentrations between 1 and 330 µg/kgdw in soil. Furthermore, TPs were detected in 47% of the cases where the "parent-compound" was applied. Overall, residues of about 80% of all applied pesticides could be detected with half of these found as TPs with a persistence of more than a decade.

Characterization of a new heat dissipation matric potential sensor.

Soil moisture sensors can help to reduce the amount of water needed for irrigation. In this paper we describe the PlantCare soil moisture sensor as a new type of heat dissipation sensor, its calibration and the correction for temperature changes. With the PlantCare sensor it is possible to measure the matric potential indirectly to monitor or control irrigation. This sensor is based on thermal properties of a synthetic felt. After a defined heating phase the cooling time to a threshold temperature is a function of the water content in the synthetic felt. The water content in this porous matrix is controlled by the matric potential in the surrounding soil. Calibration measurements have shown that the sensor is most sensitive to -400 hPa and allows lower sensitivity measurements to -800 hPa. The disturbing effect of the temperature change during the measurement on the cooling time can be corrected by a linear function and the differences among sensors are minimized by a two point calibration.

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.

Environmental and Anthropogenic Factors Shape Major Bacterial Community Types Across the Complex Mountain Landscape of Switzerland.

Mountain areas harbor large climatic and geographic gradients and form numerous habitats that promote high overall biodiversity. Compared to macroorganisms, knowledge about drivers of biodiversity and distribution of soil bacteria in mountain regions is still scarce but a prerequisite for conservation of bacterial functions in soils. An important question is, whether soil bacterial communities with similar structures share environmental preferences. Using metabarcoding of the 16S rRNA gene marker, we assessed soil bacterial communities at 255 sites of a regular grid covering the mountainous landscape of Switzerland, which is characterized by close location of biogeographic regions that harbor different land-use types. Distribution of bacterial communities was mainly shaped by environmental selection, as revealed by 47.9% variance explained by environmental factors, with pH (29%) being most important. Little additional variance was explained by biogeographic regions (2.8%) and land-use types (3.3%). Cluster analysis of bacterial community structures revealed six bacterial community types (BCTs), which were associated to several biogeographic regions and land-use types but overall differed mainly in their preference for soil pH. BCT I and II occurred at neutral pH, showed distinct preferences for biogeographic regions mainly differing in elevation and nutrient availability. BCT III and IV differed only in their preferred soil pH. BCT VI occurred in most acidic soils (pH 3.6) and almost exclusively at forest sites. BCT V occurred in soils with a mean pH of 4 and differed from BCT VI in preference for lower values of organic C, total nitrogen and their ratio. Indicator species and bipartite network analyses revealed 3,998 OTUs associating to different levels of environmental factors and BCTs. Taxonomic classification revealed opposing associations of taxa deriving from the same phyla. The results revealed that pH, land-use type, biogeographic region, and nutrient availability were the main factors shaping bacterial communities across Switzerland. Indicator species and bipartite network analyses revealed environmental preferences of bacterial taxa. Combining information of environmental factors and BCTs yielded increased resolution of the factors shaping soil bacterial communities and provided an improved biodiversity framework. OTUs exclusively associated to BCTs provide a novel resource to identify unassessed environmental drivers.

Target and suspect screening analysis reveals persistent emerging organic contaminants in soils and sediments.

An approach to identifying persistent organic contaminants in the environment was developed and executed for Switzerland as an example of an industrialized country. First, samples were screened with an in-house list using liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS) and gas chromatography tandem mass spectrometry (GC-MS/MS) in 13 samples from the Swiss National Soil Monitoring Network and three sediment cores of an urban and agricultural contaminated lake. To capture a broader range of organic contaminants, the analysis was extended with a suspect screening analysis by LC-HRMS/MS of >500 halogenated compounds obtained from a Swiss database that includes industrial and household chemicals identified, by means of fugacity modeling, as persistent substances in the selected matrices. In total, the confirmation of 96 compounds with an overlap of 34 in soil and sediment was achieved. The identified compounds consist generally of esters, tertiary amines, trifluoromethyls, organophosphates, azoles and aromatic azines, with azoles and triazines being the most common groups. Newly identified compounds include transformation products, pharmaceuticals such as the flukicide niclofolan, the antimicrobial cloflucarban, and the fungicide mandipropamid. The results indicate that agricultural and urban soils as well as sediments impacted by agriculture and wastewater treatment plants (WWTPs) are the most contaminated sites. The plausibility of this outcome confirms the combination of chemical inventory, modeling of partitioning and persistence, and HRMS-based screening as a successful approach to shed light on less frequently or not yet investigated environmental contaminants and emphasizes the need for more soil and sediment monitoring in the future.

Temporal trends of chlorinated paraffins and polychlorinated biphenyls in Swiss soils.

Persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), are ubiquitous environmental contaminants that have been targeted by national regulations since the 1970-1980s, followed in 2004 by the worldwide regulation under the Stockholm Convention on POPs. However, concerns are growing regarding the emergence of additional POP-like substances, such as chlorinated paraffins (CPs), which have particularly large production volumes. Whereas short-chain CPs (SCCPs) have recently been restricted in Europe and are currently under evaluation for inclusion into the Stockholm Convention, medium-chain CPs (MCCPs) have received little attention. On the one hand, temporal trends of CPs in the environment have hardly been investigated. On the other hand, the effectiveness of the Stockholm Convention on environmental levels of PCBs is still a matter of debate. Here, we reconstructed temporal trends of SCCPs, MCCPs, and PCBs in archived soil samples from six sampling sites in Switzerland, covering the period 1989-2014 (respectively 1988-2013 for one site). Concentrations of SCCPs have decreased in soil since 1994, which indicates positive effects of the reduction of production of SCCPs in Europe and the increasingly stringent regulation. However, the decline in soil is slow with a halving time of 18 years. Concentrations of MCCPs have continuously increased in soil over the entire period 1989-2014, with a doubling between 2009 and 2014. The concentrations of MCCPs have surpassed those of SCCPs, showing their relevance today, partly as replacements for SCCPs. Soil concentrations of PCBs peaked in 1999, i.e. three decades later than worldwide production and use of PCBs, but earlier than the entry into force of the Stockholm Convention. PCBs follow a decline in soil with a halving time of approx. 8 years. This study shows the usefulness of sample archives for the reconstruction and interpretation of time trends of persistent environmental contaminants.

Remarkably constant PAH concentrations in Swiss soils over the last 30 years.

Although polycyclic aromatic hydrocarbons (PAH) are of concern due to their carcinogenic, mutagenic, and teratogenic properties and their ubiquitous occurrence in environmental compartments, only few studies assessed the temporal evolutions of PAH contents of soils over extended time periods. The Swiss Soil Monitoring Network NABO runs long-term monitoring sites resampled every five years since the 1980s. In the present study, soil (0-20 cm) samples collected from 1985 through 2013 at 25 selected monitoring sites were analysed for the 16 priority PAH according to the U.S. EPA and five PAH marker substances. We observed divergent trends for light PAH, such as naphthalene and phenanthrene, compared with heavy PAH, such as benzo[a]pyrene and benzo[ghi]perylene. Whereas the former showed decreasing concentrations since the late 1980s, no significant trends were found for the latter. Furthermore, the analyses showed that naphthalene contents decreased most strongly at rural sites featuring low population densities, while phenanthrene contents generally decreased most strongly at semi-rural sites. The deviating evolutions of light and heavy PAH were mainly attributed to their differing physico-chemical properties. Temporal evolutions in soils contradict emission inventory data suggesting PAH emissions to decline since the 1980s.