Dissipation Behaviour And Safety Risk Assessment Of A Ready-Mix Formulation Of Clomazone And 2,4-D In Rice Field Under Tropical Agro-Climatic Conditions Of India

This study portrays the dissipation behaviour of the herbicide mixture of clomazone and 2,4-D (clomazone 20% + 2,4-D ethyl ester 30% EC) in a rice field system. The combined formulation is widely used in India as it controls a broad spectrum of weeds, but its fate in tropical environment and the risks involved to the consumer as well as to the environment are still unexplored. Therefore, a supervised field trial was conducted following the post-emergence application of clomazone 20% + 2,4-D ethyl ester 30% EC at recommended (625 g a.i./ha) and double the recommended dose (1250 g a.i./ha) in rice in two consecutive seasons (Kharif and Rabi). The analytical methods for both clomazone and 2,4-D validated as per the SANTE guideline. The residues of clomazone were extracted by the modified QuEChERS method and analysed by GC-MS/MS, whereas the residues 2,4-D were extracted by classical partitioning method and analysed by LC-MS/MS. The recovery percentage of both the compounds ranged between 86-95% with LOQ 0.01 mg/kg for all matrices (rice grain, straw, husk, and field soil). The dissipation of both the compounds followed first-order kinetics. The half-life of clomazone and 2,4-D in soil ranged between 1.06-1.27 days and 4.74-6.24 days, respectively. The residues of clomazone and 2,4-D were below quantification level (BLOQ) in the harvested rice co-products (rice grain, husk and straw) and soil samples. Therefore, it can be summarised that the application of this herbicide mixture in rice cultivation will not pose any residual toxicity and the rice grains are safe for human consumption. Besides, the soil ecological risk assessment indicated that both the compounds possess low risk towards earthworm and soil arthropods. However, there was a concern about soil algal toxicity, which needs to be reconfirmed by further studies to establish a conclusive inference.