![]() (3) However, recent screenings of agricultural sites revealed widespread contamination of soils with various modern pesticides. ![]() While earlier generations of pesticides, in particular organochlorine pesticides, were notorious for their high persistence, (26) currently used pesticides are supposedly designed to be more easily (bio-) degradable and therefore should be found less in the environment. (6,7,25) Concerning the soil characteristics, it is mainly the soil mineralogy (solid inorganic phases) and soil texture (especially clay content), the amount of soil organic matter, pH, the moisture levels, and the soil temperature that influence the behavior of pesticides over time. (15,24) These properties are responsible for volatilization, sorption, leaching to groundwater, uptake by plants or organisms, and abiotic and microbial transformation, with sorption and biodegradation being the most relevant for the fate of the substances. (18,23) To what extent substances are further dispersed or mostly remain as residues in the soil depends on both the physicochemical properties of the pesticides and soil characteristics. (21,22) However, recent studies showed that this is not only the case for older and more persistent pesticides but also for currently used ones including alachlor, chlorpyrifos, chlorothalonil, and S-metolachlor. (16) For atrazine, for instance, it has been shown that it can be volatilized, transported, and detected in rain water years after application. (16−20) Whether and to which degree volatilization takes place is dependent on meteorological and environmental conditions, such as humidity and nature of the surface as well as temperature, wind, and the chemical’s vapor pressure. ![]() (9) Volatilization is the origin of long-range transport via air and subsequent wet or dry deposition, causing pesticide contamination in places where they most likely were never applied, such as the Arctic or pristine mountain regions. (5,14) In contrast, volatilization of the substances is a continuous process, (15) which occurs mainly after application. (12) This off-target displacement can occur through aerosols or dust during application (13) and is largely influenced by wind speed and direction as well as the application methods, the formulation of the product, and the environmental conditions. (11) In this way, pesticides can be transported several meters away from their application source depending on the application technique. (9) Spray drift is the process that is responsible for pesticides to be carried away during application (10) and tends to result in short-range transport. (4−8) Drift and volatilization are the main contributors to environmental contamination, leading to dispersion of up to 9% of the applied substances on small or large scales, respectively. (1) However, a large proportion of pesticides miss their target organisms, (2,3) leading to an unintentional but widespread contamination of pesticides in other areas through spray drift, infiltration, runoff, volatilization, and long-range atmospheric deposition. ![]() Pesticides are indispensable in today’s agriculture, where they are used against diseases, pests, and weeds to secure crop yield and quality. 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. ![]() 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. Pesticides were found in all soils, including the extensive grassland sites, demonstrating a widespread background contamination of soils with pesticides. 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). 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. The intensive use of pesticides and their subsequent distribution to the environment and non-target organisms is of increasing concern. ![]()
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