Pesticide Residues in a Protected Tropical Water Catchment: Baseline Evidence and Implications for Long-Term Drinking Water Safety in Malaysia

Abstract

This study investigated pesticide residues in raw water from the Sarawak Kiri River catchment, a critical drinking water source supplying the Batu Kitang Water Treatment Plant in Sarawak, Malaysia. Despite the presence of surrounding agricultural activities, comprehensive multi-residue analysis covering acid herbicides, organochlorine, organophosphate pesticides, and other herbicides revealed concentrations below method detection limits in samples collected in January 2025. While these findings suggest an absence of detectable contamination at the point of abstraction, interpretation requires caution. Non-detection does not necessarily equate to absence of risk, particularly given temporal variability, episodic runoff events, and limitations inherent in analytical detection thresholds. The apparent absence of pesticide residues may reflect a combination of low-intensity agricultural practices, effective riparian buffering, hydrological dilution due to high rainfall, and regulatory protection of the catchment.