Targeted pesticide screening and multi-matrix toxic-element monitoring in a highland vegetable production system of southern Lao PDR: implications for surveillance prioritization

Abstract

Vegetable-production systems connect edible crops with cultivation soil and irrigation water, yet multi-matrix evidence from tropical highland production areas remains limited. This pilot study characterized targeted pesticide residues and potentially toxic elements across co-located crop–soil–water matrices at three monitored sites in Pakxong District, Lao People’s Democratic Republic, during September–November 2024. Forty-five composite vegetable samples were screened using four predefined liquid chromatography–tandem mass spectrometry panels comprising 213 analyte–method combinations, with some analytes repeated across panels. Lead (Pb), cadmium (Cd), arsenic (As), and total chromium (Cr) were determined in selected vegetables (n = 27), cultivation soils (n = 15), and stored irrigation water (n = 15) using matrix-appropriate atomic spectrometric methods. No pesticide target was detected above the applicable limits of detection (0.004–0.005 mg kg⁻1 fresh weight), although several locally relevant pyrethroids were not included in the target lists. Acid-digestible cultivation soils contained Pb, As, and total Cr, whereas Cd remained below the applicable reporting limits. Stored irrigation water contained Pb at 0.031–0.045 mg L⁻1 and total Cr at 0.024–0.038 mg L⁻1. Coriander contained Pb, Cd, As, and total Cr at 0.066–0.074, 0.011–0.012, 0.011–0.012, and 0.032–0.037 mg kg⁻1 fresh weight, respectively; occurrence was limited or non-detectable in the two heading Brassica vegetables. These descriptive patterns identify priorities for confirmatory surveillance but do not establish contaminant sources, internal uptake, or cross-matrix transfer. Interpretation is limited by the three sites, one monitoring period, and the absence of field blanks and field duplicates.