Sorption of 14C-carbofuran in Austrian soils: evaluation of fate and transport of carbofuran in temperate regions

The adsorption effects of biochar on carbofuran in water and the mixture toxicity of biochar-carbofuran in rats

Carbofuran, a widely used carbamate insecticide, is frequently detected in water. In this study, a high-performance adsorbent (WAB4) for carbofuran was obtained from laboratory-synthesized biochars. The maximum adsorption of carbofuran by WAB4 reaches 113.7 mg/g approximately. The adsorption of carbofuran by biochar was a multi-molecular layer and the adsorption process conforms to the pseudo-second-order kinetic model (R2 = 0.9984) and Freundlich isotherm model (R2 = 0.99). Importantly, an in vivo rat model was used to assess the combined toxicological effects of biochar-carbofuran complexes. The toxicity of the complexes (LD50 > 12 mg/kg) is lower than that of carbofuran (LD50 = 7.9 mg/kg) alone. The damage of biochar-carbofuran complex on rat liver and lung is significantly less than that of carbofuran. The Cmax and bioavailability of carbofuran were found to be reduced by 64% and 68%, respectively, when biochar was present, by UPLC-MS/MS analysis of carbofuran in rat plasma. Furthermore, it was confirmed that the biochar-carbofuran complex is relatively stable in the gastrointestinal tract, by performing a carbofuran release assay in artificial gastrointestinal fluids in vitro. Collectively, biochar is a bio-friendly material for the removal of carbofuran from water.

Enhanced bioremediation of pesticides contaminated soil using organic (compost) and inorganic (NPK) fertilizers

This research examined the bioremediation of pesticides (Carbofuran and Paraquat) contaminated farmyard soil using compost and Nitrogen, Phosphorus, and Potassium (NPK) fertilizer. Microcosms representing each treatment were set-up in triplicates. Biostimulation was done using two concentrations (0.5 % and 1.0 % w/w) of NPK fertilizer and compost, following pesticides application at recommended rates [Carbofuran (1 g/kg) and Paraquat (5 ml/kg)] and four times the recommended rates. Two control soils were set-up; Abiotic control (sterile farmyard soil + pesticide) and Control (farmyard soil without treatment). Monitoring of the dynamics in microbial community abundance, and pesticide residues during the biostimulation period was done weekly for 28 days, using standard enumeration method, and High Performance Liquid Chromatography (HPLC), respectively. At the end of the monitoring period, considerable reduction in pesticide residues across the treatment set-ups was recorded. In Carbofuran-treated soils, there were no complete, but considerable losses in residual pesticide, however, in most of the Paraquat-treated soils, there were complete losses within 21 days. Lower pesticide residues were recorded in set-ups amended with compost than NPK, across both Carbofuran and Paraquat-treated soils. After pesticides application, decreases in microbial counts were recorded at Day 7 across all the treatments, followed by increases from Day 14-21, then decreases at Day 28. Microbial counts were lower in Carbofuran than in Paraquat-treated soils irrespective of nutrient (compost and NPK) amendments. Bacterial and fungal counts were in the magnitude of 106 and 105 CFU/g soil, respectively. Also, increased counts were recorded for Actinomycetes, Nitrifiers, Phosphate solubilizers across all treatments, and were in magnitude of 103-104 CFU/g soil. Soil microorganisms could breakdown and eliminate large concentrations of Carbofuran and Paraquat in compost-amended soils than in NPK-amended soils. This study suggests that bioremediation of pesticides contaminated soils can be achieved and enhanced by stimulating the indigenous microbial community with requisite nutrients (compost).

Conserved Metabolic and Evolutionary Themes in Microbial Degradation of Carbamate Pesticides

Carbamate pesticides are widely used as insecticides, nematicides, acaricides, herbicides and fungicides in the agriculture, food and public health sector. However, only a minor fraction of the applied quantity reaches the target organisms. The majority of it persists in the environment, impacting the non-target biota, leading to ecological disturbance. The toxicity of these compounds to biota is mediated through cholinergic and non-cholinergic routes, thereby making their clean-up cardinal. Microbes, specifically bacteria, have adapted to the presence of these compounds by evolving degradation pathways and thus play a major role in their removal from the biosphere. Over the past few decades, various genetic, metabolic and biochemical analyses exploring carbamate degradation in bacteria have revealed certain conserved themes in metabolic pathways like the enzymatic hydrolysis of the carbamate ester or amide linkage, funnelling of aryl carbamates into respective dihydroxy aromatic intermediates, C1 metabolism and nitrogen assimilation. Further, genomic and functional analyses have provided insights on mechanisms like horizontal gene transfer and enzyme promiscuity, which drive the evolution of degradation phenotype. Compartmentalisation of metabolic pathway enzymes serves as an additional strategy that further aids in optimising the degradation efficiency. This review highlights and discusses the conclusions drawn from various analyses over the past few decades; and provides a comprehensive view of the environmental fate, toxicity, metabolic routes, related genes and enzymes as well as evolutionary mechanisms associated with the degradation of widely employed carbamate pesticides. Additionally, various strategies like application of consortia for efficient degradation, metabolic engineering and adaptive laboratory evolution, which aid in improvising remediation efficiency and overcoming the challenges associated with in situ bioremediation are discussed.