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

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.