Assessment of pesticide residues in surface and groundwater in tea growing areas in Mulanje, Malawi

Abstract

Malawi's tea industry, despite adopting an integrated pest management approach (IPM) emphasizing cultural and natural practices, struggles with the challenge of widespread illicit pesticide use by local farmers. This investigation aimed to assess the extent of pesticide residues in surface and groundwater within the tea-growing regions of Mulanje during both dry and rainy seasons. Levels of alpha-cypermethrin, cypermethrin, and deltamethrin were determined using Gas Chromatography-Mass Spectrometry (GC MS) and glyphosate, s-metolachlor, and terbuthylazine by Liquid chromatography-mass spectrometry-mass spectrometry (LC-MS/MS). Levels of pH, electrical conductivity (EC), total dissolved solids (TDS), temperature, and dissolved oxygen (DO) were measured in situ using the Multiparameter meter model HI98194. The human health risk assessment was evaluated using the hazard quotient. In the dry season, surface and groundwater exhibited varying levels: pH (6.66 – 7.71), EC (26 – 227 µS/cm), TDS (17 – 135 mg/L), TSS (0.47 – 26.9 mg/L), temperature (24.5 – 26.5°C), and DO (4.09 – 6.69 mg/L). In the rainy season, corresponding ranges were observed: pH (5.65 – 7.55), EC (8 – 243.67 µS/cm), TDS (5 – 148 mg/L), TSS (178 – 316 mg/L), temperature (23.0 – 25.0°C), and DO (3.43 – 4.86 mg/L). The levels of s-metolachlor ranged from below detection to 13.324 µg/L, while cypermethrin ranged from below detection to 1.137 µg/L for both seasons. Although these concentrations fell below the 300 µg/L guideline for Australia, they exceeded the European Union's 0.100 µg/L limits. Groundwater exhibited lower pesticide levels compared to surface water. The risk assessment of human health for chronic exposure for adults and children revealed some level of risk in surface and groundwater in the rainy season for cypermethrin and s – metolachlor. The study established the presence of s-metolachlor and cypermethrin residues in surface and groundwater, increasing the risk of adverse environmental and public health effects. Frequent monitoring of the contamination of the surface and groundwater in the tea estates to ensure that the limits are within the WHO regulations for drinking water is highly recommended.