Degradation kinetics of anilofos in soil and residues in rice crop at harvest

Residue Kinetics of Ethofumesate in Texturally Diverse Soils of Sugar Beet Crop under Field Conditions

Indiscriminate use of pesticides and growing awareness of environmental and health problems had led to monitoring their residues in soil and crops. Ethofumesate is one of the widely used herbicides for controlling weeds in sugar beet. Dissipation kinetics and terminal residues of ethofumesate were investigated in two diverse soils under subtropical field conditions. Ethofumesate dissipated slowly after application and follows biphasic first-order kinetics in soils. The average half-life for initial and later phases in sandy loam soil, respectively, was 14.54 and 20.42 and 51.83 and 65.21 days, while for silty clay loam, it was 10.09 and 13.00 and 71.42 and 73.10 days, respectively. Recoveries in soil, leaves, and beetroot ranged from 78.15 to 88.05, 77.01 to 88.58, and 76.25 to 84.50%, respectively. The quantitation limit for soil, roots, and leaves was 0.002 μg g−1. At harvest, no residues were detected in soils, leaves, and sugar beetroots. Residues were below the maximum residue limits in sugar beetroots and leaves as set by EU (0.2 ppm). Ethofumesate is safe from weed control and environmental aspects as it does not persist for a long duration in soils and does not appear to pose any adverse effect on human/animal health under subtropical field conditions.

Kinetics of diuron under aerobic condition and residue analysis in sugarcane under subtropical field conditions

The phenylureas group includes persistent herbicides which are major pollutants to soil and water. Dissipation kinetics of diuron in different soils under sugarcane field conditions was investigated. Diuron was extracted with acetone and florisil solid phase extraction clean-up and characterized by high-performance liquid chromatography-UV. Diuron persisted for more than 100 days and dissipation followed monophasic first-order kinetics. Persistence was more in sandy loam compared to silty clay loam soil. Half-life of diuron in silty clay loam soil was 22.57 and 32.37 days and in sandy loam was 28.35 and 43.93 days at 2 and 4 kg ha-1applications, respectively. Average recovery in soil, bagasse, leaf-straw and juice ranged from 75.95% to 84.20%, 80.15% to 89.35%, 77.46% to 86.19% and 81.88% to 92.68%, respectively. The quantitation limits for soil, bagasse, leaf-straw and juice were 0.01, 0.03, 0.04 μg g^-1 and 0.008 μg mL^-1, respectively. Application of diuron inhibited growth of soil microbes initially but they recovered later. At harvest, diuron residues were below maximum residue limits in all samples. The study revealed that under subtropical conditions, diuron is safe for use in weed management and would not pose any residual/environmental problem and that sugarcane crop could be used safe for human/animal consumption.

Mobility and persistence of the herbicide fomesafen in soils cultivated with bean plants using SLE/LTP and HPLC/DAD

A method has been optimized and validated for the determination of fomesafen in soils using solid-liquid extraction with low-temperature partitioning (SLE/LTP) and analysis by liquid chromatography with a high-efficiency diode array detector (HPLC/DAD). The method was used to evaluate the persistence and mobility of this herbicide in different soils cultivated with bean plants. Recovery values were ≥98.9 %, with variations in the repeatability coefficients of ≤15 %, and a detection limit of 7.3 μg kg(-1). Half-life values of fomesafen were between 60 and 71 days in soil cultivated using a no-till system and 99 and 114 days in soil cultivated using a conventional tillage system. The mobility of fomesafen was moderate and mainly influenced by the organic matter content, pH, and soil type. In Red-Yellow Argisol, which has a higher content of organic matter, the leaching of fomesafen was less pronounced. In Red-Yellow Latosol, which has smaller amounts of organic matter and high pH, the leaching of fomesafen was more pronounced.