Fate and transport of glyphosate and degradation byproducts: implications for remediation at ckdu endemic areas in sri lanka

Abstract

Glyphosate, which is commercially available as Roundup®, was the widely used herbicide in Sri Lanka until 2015 and is suspected to be one of the causal factors for Chronic Kidney Disease of unknown etiology (CKDu). This research, therefore, focuses on investigation of glyphosate and Aminomethylphosphonic acid (AMPA), the major degradation product of glyphosate, immobilization in top soil and subsequent mobilization to water and their effective and efficient removal. A field study and a series of mesocosm studies were performed to investigate the immobilization of glyphosate in the top soil and the mobilization of glyphosate and AMPA to water. Further, a long term batch experimental study was carried out to study the degradation of glyphosate in water in the absence and presence of hardness, for 240 days. Finally, the applicability of Ozonation process for glyphosate removal from water was studied using batch experiments. Glyphosate and AMPA were analyzed using LC/MS and GC/MS. It was evident that glyphosate persistence in the environment was high, especially due to the sorption of glyphosate to soil. Mobilization of glyphosate to water was minimal and it was catalyzed by the event of first precipitation after the application of glyphosate and application of Triple Super Phosphate (TSP) to the soil. Furthermore, glyphosate degradation was hindered and its persistence was increased due to the presence of hardness in water and surfactants in commercial grade glyphosate. Ozonation process rapidly degraded the glyphosate present in water both in the absence and presence of hardness to levels less than 700 µg/L which is the USEPA Maximum Contaminant Level for drinking water. In conclusion, this study provides the insight that the dominant mechanism of glyphosate in the environment is adsorption of glyphosate to the topsoil and mobilization to water is minimal. Further, Ozonation is an effective and efficient method to remove glyphosate in water in CKDu prevalent areas despite the presence of hardness and surfactants.