Particulate-bound phthalates as blind spot pollutant in air quality monitoring

Particulate-bound phthalates (PBP) are often believed to be proportional to the concentration of particulate matter (PM_2.5). However, this belief may be misguided. Phthalates are well-known endocrine disruptors and they are regulated as water and foodborne contaminants. However, airborne phthalates, particularly PBP, have become monitoring and regulatory blind spots. We conducted a sampling campaign across five cities, Ulaanbaatar, Beijing, Seoul, Seosan, and Noto in the Northeast Asian region, and obtained counter-intuitive results. Our findings showed that elevated PM_2.5 levels do not necessarily correspond to elevated PBP levels. Beijing and Ulaanbaatar had similarly high PM_2.5 levels (18.67 and 18.69 μg/m³, respectively), whereas Ulaanbaatar had a much lower total PBP concentration (1.98 ± 0.65 ng/m³) compared to Beijing (101.94 ± 62.52 ng/m³). The correlation between PM_2.5 and total PBP concentration among the five cities was weak (R² = 0.223). Interestingly, elevated PBP levels appeared to be more closely correlated with the quantity of plastic waste generated in the country. China generates approximately five times more plastic waste than Mongolia. The correlation between plastic waste and the total PBP concentration was strong (R² = 0.945). This suggests that PBP are blind spot pollutants where their exposure could be misinterpreted by the overall PM_2.5 presence.