Pesticides in Soils

The hazardous effects of pesticides on the ecosystem are indisputable. Many studies have been devoted to the monitoring of pesticides and their occurrence in various systems and the adverse effects that they impose on different parts of the environment. However, most of the efforts have been dedicated to very persistent chlorinated compounds. Other compounds such as currently used pesticides (CUPs) have not been given appropriate attention. To clarify the situation regarding recent investigations in the field of monitoring CUPs in the soil, we performed a review of the studies which have been carried out in the last 5 years worldwide. This review makes clear an acute need for bringing the status of CUPs in the soil to greater consideration and shows the current shortcomings of actions towards monitoring CUPs in soil all around the world.

Pesticides reach the soil after direct application to the soil surface or after deposition from the treated crops. The environmental behaviour of pesticides in soil has been usually related to organic carbon and clay contents of soils. However, interest is growing in knowing how pesticide fate may be modified by dissolved organic matter (DOM) coming from a variety of sources, such as irrigation with solutions rich in DOM, leachates from organic amendments or plant litter. In this chapter the current extent of DOM impact on pesticide adsorption/desorption, transport or dissipation in soil is reviewed first and the findings contrasted with DOM origin or properties. The consequences of DOM on pesticide crop uptake are also discussed. Main gaps in knowledge stem from the complex composition of DOM originating from a wide variety of sources and its specific interactions with pesticides and soils that deploy an ample range of properties. A final summary of findings and implications for future research is also included.

Upon their application pesticides end up in soil where they interact with the soil microbial community. Considering the pivotal role of soil microorganisms in ecosystem homeostasis and the growing evidence about their potential toxicity response to pesticide exposure, there is an urgent need to revisit the relevant regulatory framework. This is necessary in light of the enormous methodological and standardization advances in soil microbial ecology in the last 20 years and the outdated assessment scheme currently in place. In this chapter we highlight the key elements of a new risk assessment scheme including (a) the definition of microbial indicator groups like ammonia-oxidizing microorganisms and arbuscular mycorrhizal fungi (b) the parallel determination of the level and the duration of the exposure including transformation products (c) the need for implementation in environmental risk analysis of advanced and standardized tools. Based on all these a new tiered-risk assessment scheme is proposed. Emerging issues in soil microbial ecotoxicology are discussed including (a) the assessment of pesticide soil microbial toxicity at ecosystem level and (b) the assessment of the soil microbial toxicity of biopesticides, pesticide mixtures and pesticide transformation products on soil microorganisms. We conclude by highlighting emerging scientific questions that are expected to puzzle the soil microbial ecotoxicologists working with pesticides in the next decade.

Chirality has received progressive attention in the field of pesticides. Enantiomers of chiral pesticides have identical physicochemical properties but, commonly, they exhibit stereoselective response with chiral host systems and, therefore, enantioselectivity against the target pest. Despite this, approximately 30% of the pesticides in current use are formulated as mixtures of enantiomers or racemic mixtures. This has engendered new environmental problems, which demand exhaustive knowledge regarding the enantioselectivity of the processes that chiral pesticides may undergo in the soil environment. Changes in the enantiomer composition of chiral pesticides are caused mainly by biological interactions and, consequently, factors affecting the biodegradation of pesticides can also alter the enantioselectivity of the biotransformation of chiral pesticides in soils. Accordingly, soil parameters such as pH, redox conditions, texture, or agronomic practices have been reported to indirectly influence the final enantioselective behavior of these pesticides in soils, although there is limited knowledge in this regard. Hence, predicting the environmental behavior of chiral pesticides in soil turns challenging. This chapter summarizes the most recent enantioselective studies on chiral pesticide transfer and transformation processes in soils. Future research needs scientific foundations to establish under which agricultural and environmental conditions it is appropriate to replace racemic chiral pesticide mixtures with the biologically active purified enantiomers, the underlying mechanisms of enantioselective interactions, and the relationships between the soil microbial diversity and the biotransformation of chiral pesticides, which remain largely unknown.

Pesticides are chemical compounds designed to be used as plant protection products (PPPs). They are applied in the field for the protection of plants against pests, weeds, and several diseases that affect and decrease the quantity and quality of agricultural crop products. After their environmental release, these synthetic substances undergo a variety of abiotic and biotic processes which determine their distribution in the environmental compartments, and consequently their fate and persistence. Sorption, desorption, and leaching are some of the processes that are included among the most important transportation pathways. Due to their extensive application and their potential ecotoxicological effects, the global scientific interest focusing on the research of the environmental fate and behavior of pesticides after their entrance in the environmental matrices is undiminished. The present chapter is a review of the recent scientific literature regarding the recent research on the fate of pesticides in soil regarding the processes of sorption/desorption and leaching. Based on the gathered information derived from the reviewed articles on the subject published in the last 5.5 years (from 01/01/2016 to 30/06/2021), useful conclusions and observations are reported about research trends. Furthermore, knowledge gaps in the current research are highlighted and suggestions for future research on this topic are also discussed.

During recent decades, agriculture production has intensified by using a large number of chemical substances as pesticides to protect crops from unwanted fungi, weeds, and insects. It has been reported that long-time exposure of pesticides to different environmental conditions results in persistence of many derivatives of them in the environment. Intense global environmental issues have been raised due to the uptake of those pesticide residues present in agricultural soils by non-target organisms and planted crops. Indeed, the movement of such pesticide residue chemicals through the food chain may still cause potential health risks to humans. However, uptake of pesticide residues is more complicated and many factors have promoted the process. The uptake process and bioavailable concentrations of pesticide residues can highly differ depending on environmental conditions, characters of the planted crops, and physicochemical properties of the pesticides. Meanwhile, this chapter summarizes the pesticide residue types and their fate in the agricultural soils, highlighting the mechanisms as well as influencing factors for the plant uptake. Field-based investigations under natural conditions are required for future researches to make reasonable risk predictions for human health.

The release of micropollutants into surface water bodies may be due to different pathways, including wastewater treatment plant effluent, combined sewer overflows and surface runoff. Many studies have dealt with the chemical characteristics of the first two types, whereas less attention has been paid to those of surface runoff in agricultural areas. Pesticides are the main micropollutants occurring in this stream and their impact on the receiving water body may be of great concern. In this context, the current chapter aims to provide a snapshot of the occurrence of common pesticides in the runoff of arable land and it discusses the main factors affecting their fate and behaviour once in the soil. Collected measured concentrations are compared with the corresponding predicted-no-effect concentrations in order to evaluate the potential risk due to surface runoff release into the receiving water body. It also presents some best practices that aim to mitigate their migration towards surface water. The chapter concludes with a focus on the main pesticides found in surface and groundwater in Italy, in particular in the Po Valley, and on the environmental risk posed by residues of a selection of pesticides in the surface water in two Spanish regions.

Agricultural development and the sustainability of agrosystems are two topics of great current interest. The typical model of intensive or conventional agriculture provides highly productive agrosystems, but at an important environmental cost. Therefore, new cropping systems, soil management and/or agricultural practices are being put in place to ensure sustainable agricultural production and reduce the environmental impact, as a challenge facing agriculture both now and in the future. However, the use of pesticides remains necessary even in this new approach to agricultural management, as well as tracking their fate in these systems because it has generally been studied under conventional practices. Some laboratory-scale studies have reported the effects of these practices, but few studies have been conducted under field conditions. Accordingly, this chapter conducts a review of current studies including pesticide persistence, dissipation and mobility in soils according to conservation agricultural practices, such as the soil application of organic amendments, conservation tillage systems or crop rotation. The chapter also includes a review of existing models to simulate pesticide behaviour under these management practices. Finally, a summary with research gaps and recommendations is proposed for the future development of modelling under conservation practices as tools for predicting possible long-term soil and/or water pollution.

The mishandling of agrochemical residues in agriculture exerts an important risk for the environment due to point source contamination. To minimize environmental exposure to pesticides, biopurification systems (BPS) have been developed as a biotechnological tool for the on-farm treatment of pesticide-containing wastewater of agricultural origin. Although efficient in the removal of diverse pesticides, highly recalcitrant compounds have shown poor elimination in BPS; moreover, the performance of BPS still needs to be evaluated for many agrochemicals and their sustainability should be assessed in real pesticide application cycles for specific crops. Recent studies describe the use of BPS for the removal of antibiotics of agricultural use; this approach required a previous assessment on the impact of antibiotics on BPS performance, which in most cases has revealed the absence of significant adverse effects on pesticide removal. Similarly, novel applications propose the potential use of BPS for the removal of pharmaceuticals from polluted matrices such as water or sludge. The degradation processes taking place within BPS and their link with the resident microbial communities have been scarcely studied to date; they are critical to achieve proper design and optimization of these systems. This chapter covers general aspects of BPS and their application scope to pesticides; special attention is given to novel topics such as the treatment and effect of antibiotics from agricultural wastewater and pharmaceutical-containing matrices, as well as the description of microbial communities within BPS.

Phenylurea herbicides (PUHs) are reported to be amongst the most extensively used herbicides in agriculture for pre- and post-emergence control of weeds and mosses in a wide variety of crops. Most of the PUHs have been forbidden in some European countries due to their presence in water and soil, which leads to serious environmental and public health problems in a wide variety of organisms, including humans. This review gives an overview of abiotic and biological technologies used for the remediation of soils contaminated by PUHs, including their limitations and advantages. PUHs present from low to moderate adsorption to soils, the organic matter content being the main influencing factor. For this reason, the majority of the remediation studies in soils are based on the most hydrophobic PUHs, diuron and linuron. The degradation of PUHs in the environment is primarily considered to be due to microbial transformation, and most of the techniques developed for soils are based on bioremediation, which can be enhanced through biostimulation and bioaugmentation processes, and also by the addition of solubilizing agents to increase PUHs bioavailability. But also, abiotic processes have to be considered, remarkable are those that are based on advanced oxidation processes (AOPs), widely used in the decontamination of PUHs in water, but which can be considered as emerging technologies for soils tested only at lab scale.

Microorganisms play an important role in maintaining ecosystem environmental quality, including pesticide removal from soil and water. Triazine herbicides are among the most commonly used pesticide worldwide. Moreover, they are ubiquitous soil and water contaminants. Atrazine, simazine, and terbuthylazine removal from environment depends on abiotic (photolysis and hydrolysis) and above all biotic degradation; only the latter is able to mineralize these herbicides. The presence of an abundant and varied microbial community is a necessary prerequisite for a prompt and effective triazine elimination from contaminated soil and water. Degradation rates can be highly variable, depending on the history of the herbicide treatment and on site-specific characteristics (e.g., soil depth, texture, mineralogy, organic carbon (OC) content, and pH). Several microorganisms able to remove atrazine from soil and water have been identified and can be used for bioremediation (bioaugmentation and biostimulation) purposes. They comprise prokaryotic cells and fungi which can use triazines for growth (catabolic degradation) or transform these herbicides by cometabolism. Some plants can partially degrade and detoxify triazines, however the effectiveness of phytoremediation in removal of triazines is hampered by their intrinsic toxic effects (they act on photosynthesis and glycogenesis, inhibiting the photosystem II) and depends on a plant capability to resist to its biocide effect and to form synergic interactions with microorganisms.