Multi-matrix baseline monitoring of toxic metals and targeted pesticide residues in a highland vegetable agroecosystem, southern Lao PDR: Implications for adaptive surveillance design

<title>Abstract</title> <p> Vegetable production systems receive contaminants through interconnected environmental pathways, yet baseline evidence from data-scarce tropical highlands remains limited. This pilot study established an environmental baseline for toxic contaminants in a highland vegetable production system on the Bolaven Plateau, Pakxong District, Lao PDR. Fresh vegetables ( <italic>n</italic> = 45) were screened for 213 target-analyte entries using LC–MS/MS multi-residue methods, while toxic metals (Pb, Cd, As, and Cr) were quantified across sub-sampled vegetables ( <italic>n</italic> = 27), co-located cultivation soils ( <italic>n</italic> = 15), and stored irrigation water ( <italic>n</italic> = 15) using matrix-appropriate atomic spectrometric methods. Targeted pesticide screening yielded uniform non-detections (&lt; LOD) for all monitored compounds. These non-detections should be interpreted within the analytical target-list boundary rather than as evidence of a pesticide-free production system, and they suggest a potential mismatch between fixed laboratory panels and locally relevant agrochemicals, particularly pyrethroids not included in the target list. Toxic metals occurred at low, matrix-dependent concentrations. Acidic cultivation soils (pH 5.2–5.5) contained measurable Pb (2.251–3.091 mg kg⁻¹ DW), As (0.688–1.011 mg kg⁻¹ DW), and total Cr (10.019–12.021 mg kg⁻¹ DW), whereas stored irrigation water contained detectable Pb (0.031–0.045 mg L⁻¹) and total Cr (0.024–0.038 mg L⁻¹). In vegetables, multi-element detections were mainly observed in coriander (Pb: 0.066–0.074; Cd: 0.011–0.012; As: 0.011–0.012; Cr: 0.032–0.037 mg kg⁻¹ FW), while heading cabbages showed minimal or non-detectable metal occurrence. This pattern is consistent with morphology-related exposure differences, although internal uptake and surface-associated contributions could not be fully separated. Overall, the study demonstrates the value of co-located crop–soil–water monitoring for interpreting contaminant occurrence, and provides an empirical basis for adaptive, context-informed, and matrix-prioritized surveillance in southern Lao PDR and comparable transboundary highland agricultural zones. </p>