Occurrence and Spatial Distribution of Pesticide Residues in Tropical Agricultural Soils of Northwestern Mexico.

Pesticide contamination in tropical agricultural soils represents a growing concern due to its impacts on environmental integrity and human health, particularly in transition zones where intensive agricultural converges with coastal wetlands. This study aimed to identify and quantify pesticide residues in soils from northwestern Mexico. Forty-eight composite soil samples were collected within a ≈ 30,000 ha polygon surrounding the study area in the municipality of Santiago Ixcuintla, one of the most agriculturally productive regions of the country. Sampling sites were preselected using remote sensing and geographic information systems. Pesticide extraction was performed using a modified QuEChERS method, and compounds were analyzed by UPLC-MS/MS and GC-TQ-MS/IT-MS. Of the 73 validated pesticides, 26 active ingredients (31.5%) were detected, including 19 insecticides, six fungicides, and one herbicide. Organochlorine compounds were the most frequently detected, with p,p'-DDE present in 97.9% of samples and chlorpyrifos in 87.0%. Total pesticide concentrations (ΣPesticides) ranged from 10.3 to 1491 ng/g. The highest concentrations were observed at sites 27, 36, and 43, exceeding the European Union's soil limit (0.1 mg/kg). Spatial analysis revealed a heterogeneous distribution, with elevated concentrations associated with active agricultural areas and runoff pathways toward coastal wetlands. The predominance of chlorinated and aromatic pesticides indicates environmental persistence and bioaccumulation potential. These findings highlight the vulnerability of habitats adjacent to intensive agriculture and suggest that soils may function as contaminant reservoirs and secondary sources through dust resuspension or water transport. Improved understanding of pesticide degradation is essential for soil management strategies globally.