Effects of Herbicides (Glyphosate) Application on Heavy Metal Accumulation in Topsoil and Tea Leaves

Abstract

Weeds compete with tea mostly for light, water, and nutrients, which have a variable impact on the yield of tea. Herbicide use is the most famous method in tea plantations to control weeds. Glyphosate is a widely used herbicide in tea plantations to control weeds. However, its excessive use may increase human exposure to heavy metals. Thus, the prime aim of this study was to determine the levels of Copper (Cu), Zinc (Zn), Nickel (Ni), Chromium (Cr), Iron (Fe), Manganese (Mn), Lead (Pb), and Cadmium (Cd) in tea soils, fresh tea leaves, and black tea leaves (processed) of both herbicidesapplied tea plantation plots and herbicide-free tea plantation plots in Sri Lanka. Metal contamination levels were determined using Atomic Absorption Spectrometer (AAS) after sample preparation was carried out using the Microwave Digestion System. The data were statistically analyzed using the student’s t-test (95% confidence interval) to compare the difference in metal concentrations between herbicide-applied and herbicidefree tea plots. According to the obtained results, available Fe, Ni, and Pb levels of soils of herbicide-applied tea plantation plots are significantly higher (p<0.05) than the soils of herbicide-free tea plantation plots. Further, the Fe level in the soils of herbicideapplied plots exceeds the maximum permissible limit (50000 mg/kg) according to the World Health Organization (WHO). Furthermore, Zn and Pb levels of fresh tea leaves in herbicide-applied plots are significantly higher (p<0.05) than those in herbicide-free plots. In addition, Cr and Pb levels of black tea leaves were significantly higher (p<0.05) in herbicide-applied plots. Overall, it can be concluded that the long-term application of glyphosate in tea plantations has an impact on heavy metal accumulation in soil and tea leaves. Therefore, it is important to practice integrated weed management techniques to reduce herbicide use in tea plantations.