Tracing Xenobiotics Across a Full-Scale Composting System: Compartment-Specific Aqueous and Atmospheric Pathways

Composting transforms organic waste together with anthropogenic compounds that may be retained, degraded, or redistributed among solid, aqueous, and atmospheric compartments. However, chemical continuity of individual xenobiotics across these compartments remains poorly resolved. This study traced organic compounds through a full-scale composting system integrating solid compost, experimental aqueous leachability, pit water, compost-pore gas, air above pit water, compost-surface emissions, and ambient air. Compounds were classified according to probable origin, with cross-compartment evaluation focused on strict xenobiotics. Concentrations of all 20 monitored solid-phase xenobiotics decreased during 45 days of composting, with a median decrease of 65.6%. These results describe the leachable fraction rather than total contaminant removal from solid compost. Diisobutyl phthalate (DIBP) and bis(2-ethylhexyl) terephthalate (DEHT/DOTP) were reported in both compost leachates and pit water. The pit-water inventory and the pooled air-above-water inventory contained 15 and 16 strict xenobiotics, respectively, with no shared listed identity. These inventories differed in temporal coverage and did not constitute a fully paired detection dataset. Methyl methacrylate (MMA) was the only strict xenobiotic shared between the compost-surface chamber and pooled ambient-air datasets, with detections in different campaigns. No strict xenobiotic persisted throughout the complete sequence of investigated compartments. Xenobiotic fate in full-scale composting is therefore better represented by interconnected but selectively filtered aqueous and atmospheric pathways than by a single conserved chemical fingerprint.