Effect of planting covers on herbicide persistence in landscape soils

Perspectives for Photocatalytic Decomposition of Environmental Pollutants on Photoactive Particles of Soil Minerals

The literature shows that both in laboratory and in industrial conditions, the photocatalytic oxidation method copes quite well with degradation of most environmental toxins and pathogenic microorganisms. However, the effective utilization of photocatalytic processes for environmental decontamination and disinfection requires significant technological advancement in both the area of semiconductor material synthesis and its application. Here, we focused on the presence and "photocatalytic capability" of photocatalysts among soil minerals and their potential contributions to the environmental decontamination in vitro and in vivo. Reactions caused by sunlight on the soil surface are involved in its normal redox activity, taking part also in the soil decontamination. However, their importance for decontamination in vivo cannot be overstated, due to the diversity of soils on the Earth, which is caused by the environmental conditions, such as climate, parent material, relief, vegetation, etc. The sunlight-induced reactions are just a part of complicated soil chemistry processes dependent on a plethora of environmental determinates. The multiplicity of affecting factors, which we tried to sketch from the perspective of chemists and environmental scientists, makes us rather skeptical about the effectiveness of the photocatalytic decontamination in vivo. On the other hand, there is a huge potential of the soils as the alternative and probably cheaper source of useful photocatalytic materials of unique properties. In our opinion, establishing collaboration between experts from different disciplines is the most crucial opportunity, as well as a challenge, for the advancement of photocatalysis.

Polymers Use as Mulch Films in Agriculture-A Review of History, Problems and Current Trends

The application of mulch films for preserving soil moisture and preventing weed growth has been a part of agricultural practice for decades. Different materials have been used as mulch films, but polyethylene plastic has been considered most effective due to its excellent mechanical strength, low cost and ability to act as a barrier for sunlight and water. However, its use carries a risk of plastic pollution and health hazards, hence new laws have been passed to replace it completely with other materials over the next few years. Research to find out about new biodegradable polymers for this purpose has gained impetus in the past few years, driven by regulations and the United Nations Organization's Sustainable Development Goals. The primary requisite for these polymers is biodegradability under natural climatic conditions without the production of any toxic residual compounds. Therefore, biodegradable polymers developed from fossil fuels, microorganisms, animals and plants are viable options for using as mulching material. However, the solution is not as simple since each polymer has different mechanical properties and a compromise has to be made in terms of strength, cost and biodegradability of the polymer for its use as mulch film. This review discusses the history of mulching materials, the gradual evolution in the choice of materials, the process of biodegradation of mulch films, the regulations passed regarding material to be used, types of polymers that can be explored as potential mulch films and the future prospects in the area.

A review of pesticides sorption in biochar from maize, rice, and wheat residues: Current status and challenges for soil application

The use of pesticides has been increasing in recent years for maintaining traditional agricultural practices. However, these chemicals are associated with several environmental impacts, demanding urgent remediation techniques. Biochar is a carbonaceous material produced by pyrolysis that has the potential for pesticide sorption and remediation. In this context, this interdisciplinary review systematically assessed the state of the knowledge of crop residues to produce biochar for pesticide sorption. We focused on maize, rice, and wheat residues since these are the three most-produced grains worldwide. Besides, we evaluated different biochar handling, storage, and soil dispersion techniques to ease its implementation in agriculture. In general, pyrolysis temperature influences biochar characteristics and its potential for pesticide sorption. Furthermore, biochar amended soils had greater pesticide sorption capacity, limiting potential leaching and runoff. Most studies showed that the feedstock and specific surface area influence the biochar sorption properties, among other factors. Also, biochar reduces pesticides' bioavailability, decreasing their toxicity to soil organisms and improving soil fertility and crop yields. Nonetheless, the retrieved papers assessed only 21 pesticides, mainly consisting of lab-scale batch experiments. Therefore, there is still a gap in studies evaluating biochar aging, its potential desorption, pesticide co-contaminations, the associated microbiological processes, and field applications. Determining flow properties for biochars of different sizes and pellets is vital for reliable handling equipment design, and performing techno-economic assessment under different farm contexts is encouraged. Ultimately, coupling biochar production with residue management could address this challenge on sustainable agricultural systems.

Pesticide fate modelling in conservation tillage: Simulating the effect of mulch and cover crop on S-metolachlor leaching

Conservation tillage practices mainly based on cover crops and no-tillage with accumulation of crop residues at the soil surface (mulch) modify the environmental fate of pesticides. However, only few pesticide fate models are able to consider mulch of crop residues as well as the effect of intermediate cover crops. Thus, the objective was to develop an approach to model the effects of crop residues left at the soil surface and cover crops on the fate of pesticides. This approach consisted in (1) considering the crop residues as a soil layer with specific physical, hydrodynamic and pesticide-reactivity properties close to that of a high organic content soil layer, and (2) introducing a correction factor of the potential evapotranspiration, estimated through a calibration step, to take into account the reduction of soil evaporation by the presence of a mulch. This approach was developed using MACRO as support pesticide model. To assess the model performances, we used the data from a field experiment designed in an irrigated maize monoculture under conservation tillage. Soil water content, water percolates, soil temperature and S-metolachlor herbicide concentrations in the leachate at 1m depth were measured during two years. The approach chosen to simulate the mulch effects allowed MACRO to make acceptable predictions of the observed water percolation, soil temperature and to a less extent herbicide leaching. However, it showed a poor performance to simulate the soil water content. Results are discussed in terms of further modelling options to better assess the environmental risks of pesticides under conservation tillage. This approach remains to be tested against various soils, crops, pesticides and types of mulch.

Separation and determination of 2,4-D, dicamba and 2,4,5-T in tobacco by nonaqueous capillary electrophoresis

A practical method for residue analysis of 2,4-D, dicamba and 2,4,5-T in baked tobacco leaves has been developed using nonaqueous CE (NACE). The herbicide residues of 2,4-D, dicamba and 2,4,5-T in tobaccos were extracted by ultrasonication with ethyl acetate, followed by a cleanup procedure with gel permeation chromatography. The separation of 2,4-D, dicamba and 2,4,5-T by NACE was optimized based on orthogonal experiment design with four factors at three levels. The optimal NACE condition was established with the running buffer of 40.0 mmol/L ammonium acetate in 90% CH3CN (apparent pH 10.2), and the applied voltage of -25 kV over a capillary of 50 microm id x 46 cm (37.5 cm to the detector window), which gave a baseline separation of 2,4-D, dicamba and 2,4,5-T within 15 min. The LOD were ca. 0.4-0.6 microg/mL for the three herbicides, whereas the overall recovery ranged from 80.8 to 84.1%. The proposed method has been successfully applied to measure 300 real tobacco samples, and the residue profiles of the three herbicides in tobacco samples were obtained and evaluated.

Leaching of glyphosate and AMPA under two soil management practices in Burgundy vineyards (Vosne-Romanée, 21-France)

Some drinking water reservoirs under the vineyards of Burgundy are contaminated with herbicides. Thus the effectiveness of alternative soil management practices, such as grass cover, for reducing the leaching of glyphosate and its metabolite, AMPA, through soils was studied. The leaching of both molecules was studied in structured soil columns under outdoor conditions for 1 year. The soil was managed under two vineyard soil practices: a chemically treated bare calcosol, and a vegetated calcosol. After 680 mm of rainfall, the vegetated calcosol leachates contained lower amounts of glyphosate and AMPA (0.02% and 0.03%, respectively) than the bare calcosol leachates (0.06% and 0.15%, respectively). No glyphosate and only low amounts of AMPA (<0.01%) were extracted from the soil. Glyphosate, and to a greater extent, AMPA, leach through the soils; thus, both molecules may be potential contaminants of groundwater. However, the alternative soil management practice of grass cover could reduce groundwater contamination by the pesticide.

Diuron mobility through vineyard soils contaminated with copper

The herbicide diuron is frequently applied to vineyard soils in Burgundy, along with repeated treatments with Bordeaux mixture (a blend of copper sulfate and calcium hydroxide) that result in elevated copper concentrations. Cu could in principle affect the fate and transport of diuron or its metabolites in the soil either directly by complexation or indirectly by altering the populations or activity of microbes involved in their degradation. To assess the effect of high Cu concentrations on diuron transport, an experiment was designed with ten undisturbed columns of calcareous and acidic soils contaminated with 17--509 mg kg(-1) total Cu (field-applied). Grass was planted on three columns. Diuron was applied to the soils in early May and in-ground lysimeters were exposed to outdoor conditions until November. Less than 1.2% of the diuron applied was found in the leachates as diuron or its metabolites. Higher concentrations were found in the effluents from the grass-covered columns (0.1--0.45%) than from the bare-soil columns (0.02--0.14%), and they were correlated with increases in dissolved organic carbon. The highest amounts of herbicide were measured in acidic-soil column leachates (0.98--1.14%) due to the low clay and organic matter contents of these soils. Cu also leached more readily through the acidic soils (32.8--1042 microg) than in the calcareous soils (9.5--63.4 microg). Unlike in the leachates, the amount of diuron remaining in the soils at the end of the experiment was weakly related to the Cu concentrations in the soils.

Degradation of N-nitrosodimethylamine (NDMA) in landscape soils

N-nitrosodimethylamine (NDMA), a potential carcinogen, was commonly found in treated wastewater as a by-product of chlorination. As treated water is increasingly used for landscape irrigation, there is an imperative need to understand the leaching risk for NDMA in landscape soils. In this study, adsorption and incubation experiments were conducted using landscape soils planted with turfgrass, ground cover, and trees. Adsorption of NDMA was negligibly weak (K(d) < 1) in all soils, indicating that NDMA has a high potential for moving with percolating water in these soils. Degradation of NDMA occurred at different rates among these soils. At 21 degrees C, the half-life (t(1/2)) of NDMA was 4.1 d for the ground cover soil, 5.6 d for the turfgrass soil, and 22.5 d for the tree soil. The persistence was substantially prolonged after autoclaving or when incubated at 10 degrees C. The rate of degradation was not significantly affected by the initial NDMA concentration or addition of organic and inorganic nutrient sources. The relative persistence was inversely correlated with soil organic matter content, soil microbial biomass, and soil dehydrogenase activity, suggesting the importance of microorganisms in NDMA degradation in these soils. These results suggest that the behavior of NDMA depends closely on the vegetation cover in a landscape system, and prolonged persistence and increased leaching may be expected in soils with sparse vegetation due to low organic matter content and limited microbial activity.