Salivary Lactoferrin and sIgA Levels in Relation to Polycyclic Aromatic Hydrocarbon Exposure Among Children from an E-Waste Recycling Area

Elevated polycyclic aromatic hydrocarbon (PAH) exposure and dental caries have been reported in informal e-waste recycling areas. Oral mucosal immunity is linked to caries, but its association with PAH exposure remains unclear. This cross-sectional study included 202 children from Guiyu and Haojiang. Urinary PAH metabolites, salivary lactoferrin and secretory immunoglobulin A (sIgA), and circulating IL-6 and IL-17A were measured. Associations were assessed using multivariable regression and Bayesian kernel machine regression (BKMR). Network toxicology combined PAH- and caries-related targets from CTD and GeneCards to explore immune-related pathways. The exposed group had higher urinary PAH metabolites and inflammatory cytokines and lower salivary lactoferrin and sIgA. After adjustment, 1-OHNap showed nominal inverse associations with both salivary markers; 2-OHNap and 9-OHPhe showed nominal inverse associations with sIgA. None remained statistically significant after false discovery rate correction. BKMR indicated an inverse overall mixture association with sIgA, with credible intervals below zero at higher exposure quantiles, whereas evidence for lactoferrin was less conclusive. Network toxicology highlighted candidate pathways related to bacterial defense, immunoglobulin production, and immune regulation. These findings suggest that higher PAH exposure is associated with altered salivary immune marker concentrations, warranting longitudinal and mechanistic investigation.