PM2.5-Bound Organophosphate Flame Retardants in Hong Kong: Occurrence, Origins, and Source-Specific Health Risks

Aqueous secondary formation substantially contributes to hydrophilic organophosphate esters in aerosols

Chemicals of emerging concern (CECs), like organophosphate esters (OPEs), are toxic substances threatening human and wildlife health. Yet the atmospheric transformation of CECs remains poorly understood. Here we combine field measurements and partitioning models to reveal that OPEs could be enhanced by aqueous-phase processes in aerosols. We show that hydrophobic OPEs are absorbed favorably into the organic phase, whereas hydrophilic OPEs preferably partition into the aqueous phase. We provide field evidence that enhanced aqueous secondary formation of OPEs occurs in winter, and its magnitude is strongly dependent on aerosol water content. We suggest that dissolved inorganic salts and transition metals in aerosols positively impact the formation of particle-bound hydrophilic OPEs, by facilitating aqueous partitioning and/or oxidation. Our findings highlight the important role of aqueous oxidation chemistry for the fate of CECs in the atmosphere, urging better consideration of transformation products in future risk assessment and chemical management.

Melamine derivatives in indoor dust from China: Temporal trends and human exposure before and during COVID-19 pandemic

Melamine-based compounds (MELs) are emerging indoor contaminants with potential health risks, yet their temporal variations and exposure implications remain poorly characterized. In this study, we analyzed MELs in 66 paired indoor dust samples from residential households in Tianjin, China, comparing pre- and during-COVID-19 periods. Four traditional MELs, i.e., MEL, ammeline, ammelide, and cyanuric acid (CYA), were detected in all samples, with total MEL concentrations (∑MELs) ranging from 61.2 to 5.83 × 104 ng/g (median: 6.73 ×103 ng/g). During the pandemic, ∑MEL concentrations increased 1.73-fold (8.25 ×103 vs. 4.76 ×103 ng/g, p < 0.01), with CYA emerging as the predominant compound (median: 2.82 ×103 ng/g), likely due to its extensive use in disinfectants (up to 0.4 % and 20 % in liquid and tablet formulations, respectively). Human exposure assessment revealed that infants had the highest estimated daily intakes (EDIs, 40.1-69.6 ng/kg bw/day), about an order of magnitude higher than adults (3.31-5.74 ng/kg bw/day), primarily through dust ingestion. Non-carcinogenic risks (HQs<1) and lifetime cancer risks (maximum median from teenagers: 7.98 ×10-8) remained within negligible limits. Monte Carlo simulations identified indoor dust concentration and body weight as key risk determinants. These findings underscore the environmental consequences of pandemic-driven disinfection practices and the urgent need for regulatory oversight of MEL-containing materials.

Artificial Intelligence for the Discovery of Safe and Effective Flame Retardants

Organophosphorus flame retardants (OPFRs) are important chemical additives that are used in commercial products. However, owing to increasing health concerns, the discovery of new OPFRs has become imperative. Herein, we propose an explainable artificial intelligence-assisted product design (AIPD) methodological framework for screening novel, safe, and effective OPFRs. Using a deep neural network, we established a flame retardancy prediction model with an accuracy of 0.90. Employing the SHapley Additive exPlanations approach, we have identified the Morgan 507 (P═N connected to a benzene ring) and 114 (quaternary carbon) substructures as promoting units in flame retardancy. Subsequently, approximately 600 compounds were selected as OPFR candidates from the ZINC database. Further refinement was achieved through a comprehensive scoring system that incorporated absorption, toxicity, and persistence, thereby yielding six prospective candidates. We experimentally validated these candidates and identified compound Z2 as a promising candidate, which was not toxic to zebrafish embryos. Our methodological framework leverages AIPD to effectively guide the discovery of novel flame retardants, significantly reducing both developmental time and costs.

Identification and seasonal variation of PM2.5-bound organophosphate flame retardants from industrial parks and the associated human health risk

Organophosphate flame retardants (OPFRs) have become pervasive environmental pollutants. However, there is a lack of information available regarding PM2.5-bound OPFRs emitted from industrial parks dedicated to the manufacturing and processing of metal-related products. In this study, 15 OPFRs in PM2.5 were identified from two industrial parks specializing in aluminum products and the deep processing of metals, respectively. The seasonal variations and health risks of OPFRs were investigated. The PM2.5 and OPFR concentrations were 26.0-203 μg/m3 and 12.4-6.38 × 104 pg/m3, respectively. The OPFRs concentrations in the aluminum-processing industrial park exceeded those found in the metal-fabrication industrial park. Among the chloro-, aryl-, and alkyl-substituted OPFRs (i.e., Cl-OPFRs, aryl-OPFRs, and alkyl-OPFRs), Cl-OPFRs were the predominant homologues in the two parks (69.3% and 51.4%) and the control site. Tetraethyl diphosphate and tris(2-chloroethyl) phosphate were the most commonly occurring homologues in the aluminum and metal-fabrication industrial parks, respectively. Seasonal variations of the target OPFRs were observed, although there were slightly different concentrations between the sites. The correlation and principal component analyses with multiple linear regression identified metal waste disposal as the leading source of OPFRs in metal parks (68.0%), followed by traffic emissions (25.3%), adhesives and flame retardants in construction-related substances (3.82%), and mechanical emissions (2.85%). The health risk assessment showed that the hazard quotients for non-carcinogenic risk were <1, and the carcinogenic risks were <10-6, which indicated that PM2.5-bound OPFRs presented no obvious non-carcinogenic or carcinogenic risks. Comparatively, the notably elevated noncarcinogenic and carcinogenic risks associated with Cl-OPFRs highlighted the importance of enforcing strict emission regulations during the disposal of metal waste.

Spatial variation, emissions, transport, and risk assessment of organophosphate esters in two large petrochemical complexes in southern China

Organophosphate esters (OPEs) serve as significant flame retardants and plasticizers in various petrochemical downstream products. The petrochemical industry could be a potential source of atmospheric OPEs, but their emissions from this industry are poorly understood. The present study revealed the spatial variation, emission, and atmospheric transport of traditional and novel OPEs (TOPEs and NOPEs, respectively) in atmospheric particulate matter (PM) across Hainan and Guangdong petrochemical complexes (HNPC and GDPC, respectively) in southern China. The total concentrations of TOPEs ranged from 232 to 46,002 pg/m3 and from 200 to 20,347 pg/m3 in the HNPC and GDPC, respectively, which were substantially higher than those of NOPEs (HNPC: 23.5-147 pg/m3, GDPC: 13.9-465 pg/m3). Enterprises involved in the production of downstream petrochemical products presented relatively high concentrations of OPEs, indicating evident emissions of these pollutants in the petrochemical industry. The correlations of PM-bound OPEs in the atmosphere are determined mainly by their coaddition to industrial products or their coexistence in technical mixtures. The annual emissions of TOPEs and NOPEs in the HNPC were 42.6 kg and 0.34 kg, respectively, and those in the GDPC were 116 kg and 1.85 kg, respectively. OPEs from the HNPC can reach Vietnam, Cambodia, and Guangxi Province, China, and those from the GDPC can reach Guangxi Province and Hunan Province via atmospheric transmission after 24 h of emission. The OPE concentrations reaching the receptor regions were generally less than 3.20 pg/m3. Risk assessment revealed that OPE inhalation exposure on two petrochemical complexes likely poses minor risks for people living in the study areas, but the risk resulting from two chlorinated OPEs should be noted since they are close to the threshold values. This study has implications for enhancing control measures for OPE emissions to reduce health risks related to the petrochemical industry.

Estimated daily intake and cumulative risk assessment of organophosphate esters and associations with DNA damage among e-waste workers in Hong Kong

Organophosphate esters (OPEs) are extensively used as additives in various products, including electronic equipment, which becomes e-waste when obsolete. Nevertheless, no study has evaluated OPEs exposure levels and the related health risks among e-waste workers in Hong Kong. Therefore, 201 first-spot morning urine samples were collected from 101 e-waste workers and 100 office workers to compare eight urinary OPE metabolites (mOPEs) levels in these groups. The concentrations of six mOPEs were similar in e-waste workers and office workers, except for significantly higher levels of diphenyl phosphate (DPHP) in e-waste workers and bis(1-chloro-2propyl) phosphate (BCIPP) in office workers. Spearman correlation analysis showed that most non-chlorinated mOPEs were correlated with each other in e-waste workers (i.e., nine out of ten pairs, including di-p-cresyl phosphate (DpCP) and di-o-cresyl phosphate (DoCP), DpCP and bis(2-butoxyethyl) phosphate (BBOEP), DpCP and DPHP, DpCP and dibutyl phosphate (DBP), DoCP and BBOEP, DoCP and DPHP, DoCP and DBP, BBOEP and DPHP, DPHP and DBP), indicating that handling e-waste could be the exposure source of specific OPEs. The median values of estimated daily intake (EDI) and hazard quotient (HQ) suggested that the health risks from OPEs exposures were under the recommended thresholds. However, linear regression models, Quantile g-computation, and Bayesian kernel machine regression found that urinary mOPEs elevated 8-hydroxy-2-deoxyguanosine (8-OhdG) levels individually or as a mixture, in which DPHP contributed prominently. In conclusion, although e-waste might not elevate the internal OPEs levels among the participating Hong Kong e-waste workers, attention should be paid to the potential DNA damage stimulated by OPEs under the currently recommended thresholds.

Characteristics and source apportionment of water-soluble organic nitrogen (WSON) in PM2.5 in Hong Kong: With focus on amines, urea, and nitroaromatic compounds

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO3, nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere.

TDCPP and TiO2 NPs aggregates synergistically induce SH-SY5Y cell neurotoxicity by excessive mitochondrial fission and mitophagy inhibition

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP), a halogen-containing phosphorus flame retardant, is widely used and has been shown to possess health risks to humans. The sustained release of artificial nanomaterials into the environment increases the toxicological risks of their coexisting pollutants. Nanomaterials may seriously change the environmental behavior and fate of pollutants. In this study, we investigated this combined toxicity and the potential mechanisms of toxicity of TDCPP and titanium dioxide nanoparticles (TiO2 NPs) aggregates on human neuroblastoma SH-SY5Y cells. TDCPP and TiO2 NPs aggregates were exposed in various concentration combinations, revealing that TDCPP (25 μg/mL) reduced cell viability, while synergistic exposure to TiO2 NPs aggregates exacerbated cytotoxicity. This combined exposure also disrupted mitochondrial function, leading to dysregulation in the expression of mitochondrial fission proteins (DRP1 and FIS1) and fusion proteins (OPA1 and MFN1). Consequently, excessive mitochondrial fission occurred, facilitating the translocation of cytochrome C from mitochondria to activate apoptotic signaling pathways. Furthermore, exposure of the combination of TDCPP and TiO2 NPs aggregates activated upstream mitochondrial autophagy but disrupted downstream Parkin recruitment to damaged mitochondria, preventing autophagosome-lysosome fusion and thereby disrupting mitochondrial autophagy. Altogether, our findings suggest that TDCPP and TiO2 NPs aggregates may stimulate apoptosis in neuronal SH-SY5Y cells by inducing mitochondrial hyperfission and inhibiting mitochondrial autophagy.