Uptake of Fungicide Fluopyram from Soil by Scallions during Greenhouse Cultivation

Unintentional pesticide contamination in rotational crops, often caused by soil contamination from pesticide use in the preceding crops, is a major concern in a positive list system. The residue and dissipation pattern of fluopyram in soil and scallions were investigated to evaluate the uptake of fluopyram from the soil by scallions. In addition, the management concentration in soil (MC_soil) was calculated based on bioconcentration factors (BCFs) and the maximum residue limit (0.2 mg/kg) in leaf-and-stem vegetables. In a field experiment, plots in two different trials, A and B, were treated with 0.06 g fluopyram/m² and maintained for 30 days according to OECD guidelines. Scallion seedlings were cultivated for 48 days. Soil samples were taken at three different time points: DAP (Days after planting) 0, 34, and 48. Scallion samples were collected at five different time points: DAP 20, 27, 34, 41, and 48. The initial amounts of fluopyram in soil at DAP 0 were 0.94 ± 0.03 and 0.96 ± 0.04 mg/kg in trials A and B, respectively. The half-life of fluopyram in the soil was 87-231 days. Fluopyram uptake by the roots increased over time, but fluopyram residue in the scallions decreased due to the dilution effect caused by an increase in plant weight. The residues in the scallions at DAP 48 were 0.22 ± 0.01 and 0.15 ± 0.01 mg/kg in trials A and B, respectively. The BCFs of scallions for fluopyram were 0.21-0.24 (trial A) and 0.14-0.18 (trial B). The MC_soil was proposed as 0.8 mg/kg, and may be utilized as a safe management guideline for precautionary practices to cultivate safe rotational crops.

Efficacy of rhizobacteria for degradation of profenofos and improvement in tomato growth

Pesticides are widely used for managing pathogens and pests for sustainable agricultural output to feed around seven billion people worldwide. After their targeted role, residues of these compounds may build up and persist in soils and in the food chain. This study evaluated the efficiency of bacterial strains capable of plant growth promotion and biodegradation of profenofos. To execute this, bacteria were isolated from an agricultural area with a history of repeated application of profenofos. The profenofos degrading bacterial strains with growth-promoting characteristics were identified based on biochemical and molecular approaches through partial 16S ribosomal rRNA gene sequencing. The results revealed that one strain, Enterobacter cloacae MUG75, degraded over 90% profenofos after 9 days of incubation. Similarly, plant growth was significantly increased in plants grown in profenofos (100 mg L^-1) contaminated soil inoculated with the same strain. The study demonstrated that inoculation of profenofos degrading bacterial strains increased plant growth and profenofos degradation. Novelty statementPesticides are extensively applied in the agriculture sector to overcome pest attacks and to increase food production to fulfill the needs of the growing world population. Residues of these pesticides can persist in the environment for long periods, may enter the groundwater reservoirs and cause harmful effects on living systems highlighting the need for bioremediation of pesticide-contaminated environments. Microbes can use pesticides as a source of carbon and energy and convert them into less toxic and non-toxic products. Application of profenofos degrading rhizobacteria in interaction with the plants in the rhizosphere can remediate the pesticide-contaminated soils and minimize their uptake into the food chain. Hence, this approach can improve soil health and food quality without compromising the environment.

In vivo removal of profenofos in agricultural soil and plant growth promoting activity on Vigna radiata by efficient bacterial formulation

This study evaluated the plant growth and profenofos (PF) removal efficiency of Acinetobacter sp.33F and Comamonas sp. 51 F bacteria as individual strains and in combination F1. Plant growth-promoting activities such as indole 3 acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, phosphate solubilization, ammonia production, and exopolysaccharide (EPS) production were observed in Acinetobacter sp. 33 F and Comamonas sp. 51 F. However, PGP properties observed were higher in Acinetobacter sp. 33 F as compared to the Comamonas sp. 51 F. In pot sand and pot soil studies, the physiological parameters such as sprout length, shoot length, root length, chlorophyll a, chlorophyll b, and carotenoids were higher for combination F1. PF degradation in pot sand and pot soil resulted in highest degradation by combination F1. In pot soil study, soil enzyme activities such as cellulase, dehydrogenase, urease, protease, and phosphate activities and root cross-section area, total stele area and xylem vessel area were recorded higher for the formulation F1. The study demonstrated that the together Acinetobacter sp. 33 F and Comamonas sp. 51 F as formulation has higher plant growth-promoting activities as compared to the individual bacteria.

Comparison of theoretical and experimental values for plant uptake of pesticide from soil

Pesticides that persist in soils may be taken up by the roots of plants. One way to assess plant uptake is to theoretically predict the extent of plant uptake using a mathematical model. In this study, a model was developed to predict plant uptake of pesticide residues in soils using various parameters, such as pesticide mobility within soil, plant transpiration stream, root-soil transfer rate, plant growth, and pesticide dissipation in either soils or plants. The accuracy of the model was evaluated by comparing the modeled concentrations with measured uptake concentrations of chlorpyrifos (CP) in lettuce, grown on treated soils with concentrations of approximately 10 and 20 mg kg-1 CP. Measured concentrations of CP in lettuce at 21, 30, and 40 d after planting were between the 5th and 95th percentiles of model variation. A high correlation coefficient of > 0.97 between modeled and measured concentrations was found. Coefficients of variation of mean factors to residual errors were between 25.3 and 48.2%. Overall, modeling results matched the experimental results well. Therefore, this plant uptake model could be used as an assessment tool to predict the extent of plant uptake of pesticide residues in soils.

Plant Uptake and Distribution of Endosulfan and Its Sulfate Metabolite Persisted in Soil

The distributions of endosulfan (ED) residues (α-, β-isomers, and sulfate-metabolite) in cucumbers grown in soils treated with ED at concentrations of 20 and 40 mg kg^-1 were assessed using indoor and outdoor experiments. In all treatments, degradation rates of the α-isomer in soils were higher than that of the β-isomer. In the indoor tests, uptake amounts of total ED by cucumbers, after 15 d of growth, were 7.8 and 14.5 mg kg^-1 in 20 and 40 mg kg^-1-treated pots, respectively. For growth time from 15 to 30 d, uptake amounts in 20 and 40 mg kg^-1-treated pots were 3.8 and 7.9 mg kg^-1, respectively. Outdoor tests resulted in smaller ED residues in cucumbers than those in indoor tests. In both indoor and outdoor tests, ED residues absorbed were highest in roots, and the α-isomer was the more frequently absorbed isomer. These results will be useful for determining management criteria for soil persistent pesticides.