The analysis of the coherent data on nonextractable (bound) residues (NER) from the literature and EU pesticide registration dossiers allows the identification of general trends, in spite of the large variability and heterogeneity of data. About 50% of the pesticides reviewed exhibit a low proportion of NER (less than 30% of the initial amount) while only 12% of pesticides have a proportion of NER exceeding 70%. The lowest proportion of NER was found for dinitroanilines (<20%), and the largest value was obtained for carbamates, and in particular dithiocarbamates. The presence of chemical reactive groups, such as aniline or phenol, tends to yield a larger proportion of NER. NER originating from N-heteroatomic ring were found to be lower than those from phenyl-ring structures. Among the environmental factors affecting the formation of NER, microbial activity has a direct and significant effect. Concerning the NER uptake or their bioavailability, consistent data suggest that only a small percentage of the total amounts of NER can be released. The analysis of NER formation kinetics showed that incubation experiments are often stopped too early to allow a correct evaluation of the NER maturation phase. Therefore, there is a need for longer term experiments to evaluate the tail of the NER formation kinetics. Still, the heterogeneity of the NER data between pesticides and for specific pesticides calls for great care in the interpretation of the data and their generalization.

Critical knowledge gaps about environmental fate and unintentional effects of currently used pesticides (CUPs) hamper the understanding and mitigation of their global impacts on ecological processes. We investigated the exposure of earthworms to 31 multiclass CUPs in an arable landscape in France. We highlighted the presence of at least one pesticide in all soils (n=180) and 92% of earthworms (n=155) both in treated crops and nontreated habitats (hedgerows, grasslands, and cereals under organic farming). Mixtures of at least one insecticide, one herbicide, and one fungicide (> limit of quantification) contaminated 90% of soils and 54% of earthworms at levels that could endanger these nontarget beneficial soil organisms. A high risk of chronic toxicity to earthworms was found (46% of samples) both in treated winter cereals and nontreated habitats considered as refuges. This may alter biodiversity, hinder recovery, and impair ecosystem functions. These results provide essential insights for sustainable agriculture and CUP regulation, and highlight the potential of pesticides as agents of global change.

-Reducing tillage intensity through the implementation of conservation practices is a way to reach a more sustainable agriculture. Reducing tillage is indeed an efficient way to control soil erosion and to decrease production costs. Nonetheless, the environmental impact of reduced tillage is not well known because conservation techniques may induce strong changes in soil physicochemical properties and biological activity. Knowledge on the fate of applied pesticides under conservation practices is particularly important from this point of view. We review here the advances in the understanding, quantification and prediction of the effects of tillage on pesticide fate in soils. We found the following major points: (1) for most dissipation processes such as retention, degradation and transfer, results of pesticide behaviour studies in soils are highly variable and sometimes contradictory. This variability is partially explained by the multiplicity of processes and contributive factors, by the variety of their interactions, and by their complex temporal and spatial dynamics. In addition, the lack of a thorough description of tillage systems and sampling strategy in most reports hampers any comprehensive interpretation of this variability. (2) Implementation of conservation tillage induces an increase in organic matter content at the soil surface and its gradual decrease with depth. This, in turn, leads to an increase in pesticide retention in the topsoil layer. (3) Increasing retention of pesticides in the topsoil layer under conservation tillage decreases the availability of the pesticides for biological degradation. This competition between retention and degradation leads to a higher persistence of pesticides in soils, though this persistence can be partially compensated for by a more intensive microbial activity under conservation tillage. (4) Despite strong changes in soil physical properties under conservation tillage, pesticide transfer is more influenced by initial soil conditions and climatic conditions than by tillage. Conservation tillage systems such as no-tillage improve macropore connectivity, which in turn increases pesticide leaching. We conclude that more knowledge is needed to fully understand the temporal and spatial dynamics of pesticide in soil, especially preferential flows, in order to improve the assessment of pesticide risks, and their relation to tillage management.

The fate of the herbicide isoproturon [3‐(4‐isopropylphenyl)‐l,1‐dimethylurea] was investigated in soil from a grassed buffer strip. Compared to a cropped soil originating from the same experimental site (Kd = 1.8 L kg−1), sorption of isoproturon was enhanced in the grassed soil and especially in the surface layer (0‐2 cm) containing high proportion of nondecomposed plant residues (Kd = 5.0 L kg−1). Nonhumified organic fractions isolated from the surface soil layer and corresponding to above and bdow‐ground plant residues derived from the grass exhibited high sorption coefficients Kd and Koc compared to the rest of the soil. Reversibility of sorption was lower in the grassed soil than in the cropped soil and decreased rapidly with time. A rapid degradation of isoproturon was observed at different depths of the grassed soil whereas most of the herbicide remained nondegraded in the cultivated soil: half‐lives were respectively 72 d in the cultivated soil, and only 8 d in the superficial layer (0–2 cm) of the grassed soil. The highest mineralization rate of the isoproturon ring (20% after 35 d) was observed in the top layer (0–2 cm) having the highest mineralization rates of organic matter. In relation with this fast degradation, a large proportion of isoproturon residues became nonavailable to water and methanol extractions (54% of the initial applied isoproturon found as nonextractable (bound) residues). Thus the grassed strip surface soil had a high potential to dissipate isoproturon trapped from run‐off.

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A comprehensive review of quantitative structure-activity relationships (QSAR) allowing the prediction of the fate of organic compounds in the environment from their molecular properties was done. The considered processes were water dissolution, dissociation, volatilization, retention on soils and sediments (mainly adsorption and desorption), degradation (biotic and abiotic), and absorption by plants. A total of 790 equations involving 686 structural molecular descriptors are reported to estimate 90 environmental parameters related to these processes. A significant number of equations was found for dissociation process (pKa), water dissolution or hydrophobic behavior (especially through the KOW parameter), adsorption to soils and biodegradation. A lack of QSAR was observed to estimate desorption or potential of transfer to water. Among the 686 molecular descriptors, five were found to be dominant in the 790 collected equations and the most generic ones: four quantum-chemical descriptors, the energy of the highest occupied molecular orbital (EHOMO) and the energy of the lowest unoccupied molecular orbital (ELUMO), polarizability (α) and dipole moment (μ), and one constitutional descriptor, the molecular weight. Keeping in mind that the combination of descriptors belonging to different categories (constitutional, topological, quantum-chemical) led to improve QSAR performances, these descriptors should be considered for the development of new QSAR, for further predictions of environmental parameters. This review also allows finding of the relevant QSAR equations to predict the fate of a wide diversity of compounds in the environment.

The sorption-desorption properties of three organic pollutants, 4-chlorophenol(4-CP), 2,4-dichlorophenol (2,4-DCP) and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on soil organic matter (SOM) were studied using kinetic and equilibrium measurements in aqueous suspensions. Chestnut wood, wheat straw, &aft lignin, composted straw and a soil humic acid were chosen as sorbents to model different states of humification. Physico-chemical characterization using chemical fractionation, potentiometric titration and IR spectroscopy was done on all sorbents. The microbial biomass, sizes of total bacterial and fungal microflora and phenoloxidases activities were determined for the plant materials. The irreversibility of sorption was revealed by the desorption isotherms. Only a small proportion of 2,4-D, which has little affinity for the fresh organic materials, was desorbed. Sorption of 2.4-DCP was strong on straw but was reversible to a large extent, indicating weaker interactions. By comparison, the sorption of 4-CP was significantly less reversible. Thus, the nature of SOM and the properties of the chemicals strongly influenced the extent of sorption and the type of interactions, and it controlled subsequent desorption and possible transformation of the sorbed species.Influence de la nature de la matibe organique du sol sur la sorption et la desorption du 4-chlorophenol, 2,4-dichlorophenol et de l'herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) RCsumCLes propriCtts de sorption et de dCsorption de la matibre organique du sol (MOS) vis h vis de trois polluants organiques, 4-chlorophCnol(4-CP), 2,4-dichlorophCnol (2,4-DCP), et acide 2,4-dichlorophCnoxyacCtique (2,4-D) ont Ct C CtudiCes en suspensions aqueuses lors d'expCrimentations cinttiques et a I'Cquilibre. Plusieurs matitres organiques ont Ct C choisies comme adsorbants pour modCliser diffkrents Ctats d'humification: bois de chgtaignier, paille de blb, lignine, paille de blC compostCe et acide humique extrait d'un sol. Les propriCtCs physicochimiques des diffkrents adsorbants ont Ct C caract6risCes en utilisant des techniques de fractionnement chimique, titration potentiomCtrique et spectroscopie IR. Une caractCrisation biologique des rCsidus vCgCtaux a Ct C menCe en effectuant des mesures de biomasse microbienne, de la taille des populations bacttrienne et fongique ainsi que d'activitks exoenzymatiques (phenoloxydases). Pour la plupart des associations polluant-matitre organique adsorbante, les cinCtiques d'adsorption ont une allure identique, montrant un Cquilibre d'adsorption atteint aprts les premikres heures de contact. Cependant, les cinCtiques d'adsorption des chlorophCnols sur la paille compostke suggtrent que des transformations microbiennes ou exoenzymatiques peuvent modifier la retention lorsque une activitd microbienne importante est associCe aux matibres organiques en cours de d6composition. Certains constituants vCgCtaux comme les lignines ou les composes phknoliques solubles influencent les proprittks de sorption et de dksorption. Les plus grande...

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