Atmospheric deposition, seasonal variation, and long-range transport of organophosphate esters on Yongxing Island, South China Sea

A data synthesis on air-water exchange flux of plasticizers of phthalates and organophosphates in surface water

Microplastic pollution has become an emerging environmental issue in the past decades. Plasticizers are organic compounds applied during the manufacturing process and are of particular interests to researchers. Phthalate esters (PAEs) and organophosphate esters (OPEs) are two common types of plasticizers that have been found to be prevalent in water and the atmosphere. Investigating their air-water exchange process is crucial for understanding their sources and fate as pollutants. This study employs a systematic review and data synthesis to evaluate the air-water exchange and dry deposition flux of PAEs and OPEs on a global scale, aiming to identify the factors influencing their exchange process. Results showed that the air-water exchange and dry deposition flux vary among different types of plasticizers, and climatic conditions may also have impact on the air-water exchange flux. Future research is needed to explore more mechanisms related to the influencing factors. PRACTITIONER POINTS: The study presents a data synthesis of air-water exchange and dry deposition flux of plasticizers. Results indicate the sources and sinks of plasticizers on surface water, which helps to understand the consequence of plastic pollution. The air-water exchange and dry deposition flux of PAEs and OPEs vary due to different chemical properties and climatic conditions. Further research is needed to better understand the influencing factors of this process.

A new empirical equation for the gas/particle partitioning of OPFRs in ambient atmosphere

Gas/particle (G/P) partitioning is a core process governing the atmospheric transport of organophosphate flame retardants (OPFRs). However, accurately predicting the G/P partition performance of OPFRs remains a challenge. In this study, four independent models were employed to estimate the characteristics of OPFR G/P partitioning within the octanol-air partition coefficient range of 4.7 (TMP) to 14.2 (TMPP). The results showed that in the maximum partition domain, the Li-Ma-Yang steady-state model fitted the best, with 85.2% of the predicted G/P partition quotient (log KP) values within an acceptable deviation range of ±1 log units for OPFRs. Accordingly, no significant deviations were observed between the predicted (0.56 ± 0.32) and monitored (0.52 ± 0.11) values of the average particle-bound fraction (φP) for the Li-Ma-Yang model in the maximum partition domain. Large deviations were observed between the monitored values and predicted log KP values by these four models in the equilibrium domain. Several factors responsible for the significant deviations observed in G/P partitioning values of OPFRs were discussed. These identified factors were used to develop a new empirical equation, which substantially improved log KP predictions for OPFRs to 75.8% in the equilibrium domain.

Target and Nontarget Analysis of Organophosphorus Flame Retardants and Plasticizers in a River Impacted by Industrial Activity in Eastern China

Industrial activities are a major source of organophosphorus flame retardants (OPFRs) and plasticizers in aquatic environments. This study investigated the distribution of 40 OPFRs in a river impacted by major industrial manufacturing plants in Eastern China by target analysis. Nontarget analysis using high-resolution mass spectrometry was further employed to identify novel organophosphorus compounds (NOPs). Thirty-four OPFRs were detected in river water samples, with total concentrations of 62.9-1.06 × 103 ng/L (median: 455 ng/L). Triphenylphosphine oxide and diphenyl phosphoric acid were ubiquitously detected up to 620 and 127 ng/L, respectively. Among 26 identified NOPs, 17 were reported for the first time in the environment, including 14 novel organophosphate esters (especially 4 heterocycles and 3 oligomers), 2 organophosphites, and an organophosphonate. Bis(2,4-di-tert-butylphenyl) hydrogen phosphate and 2,2-dimethylpropoxy(propyl)phosphinic acid with high predicted persistence or toxicity were widely detected, with semiquantified concentrations up to 990 and 1.0 × 103 ng/L, respectively. Structurally similar organophosphorus heterocycles exhibited consistent variation trends, suggesting a common emission source. Estimated annual river discharges to the sea were 20.6-37.0 kg/yr for OPFRs and 30.8-161 kg/yr for NOPs. These findings indicate that industrial activities contribute OPFRs and NOPs to the river catchment and its estuary, posing ecological risks to both terrestrial and marine environments.

Integrated RNA sequencing and biochemical studies reveal endoplasmic reticulum stress and autophagy dysregulation contribute to Tri (2-Ethylhexyl) phosphate (TEHP)-induced cell injury in Sertoli cells

Tri (2-Ethylhexyl) phosphate (TEHP), widely used as a fire retardant and plasticizer, has been commonly found in the environment. Its potential health-related risks, especially reproductive toxicity, have aroused concern. However, the potential cellular mechanisms remain unexplored. In this study, we aimed to investigate the molecular mechanisms underlying TEHP-caused cell damage in Sertoli cells, which play a crucial role in supporting spermatogenesis. Our findings indicate that TEHP induces apoptosis in 15P-1 mouse Sertoli cells. Subsequently, we conducted RNA sequencing analyses, which suggested that ER stress, autophagy, and MAPK-related pathways may participate in TEHP-induced cytotoxicity. Furthermore, we demonstrated that TEHP triggers ER stress, activates p38 MAPK, and inhibits autophagy flux. Then, we showed that the inhibition of ER stress or p38 MAPK activation attenuates TEHP-induced apoptosis, while the inhibition of autophagy flux is responsible for TEHP-induced apoptosis. These results collectively reveal that TEHP induces ER stress, activates p38, and inhibits autophagy flux, ultimately leading to apoptosis in Sertoli cells. These shed light on the molecular mechanisms underlying TEHP-associated testicular toxicity.

Seasonal variations of organophosphate esters (OPEs) in atmospheric deposition, and their contribution to soil loading

Organophosphate esters (OPEs) are ubiquitous in surface soil, and atmospheric deposition is considered to be the major pollution source. However, the research on the environmental transport behaviors of OPEs between atmospheric deposition and soil is very limited. In this study, we investigated the contamination levels and seasonal variations of OPEs in atmospheric deposition samples (n = 33) collected from an area of South China every month between February 2021 and January 2022, and evaluated the contribution of OPEs in atmospheric deposition to soil. The concentrations of ∑21target-OPEs ranged from 3670 to 18,600 ng/g dry weight (dw), with a mean of 8200 ng/g dw (median: 7600 ng/g dw). ∑21target-OPEs concentrations in all atmospheric deposition samples exhibited significant seasonal differences (p < 0.05) with higher concentrations observed in winter and lower concentrations in summer. Tris(2,4-di-tert-butylphenyl) phosphate (TDTBPP) was the most dominant target OPE in atmospheric deposition (4870 ng/g dw), and its seasonal variation trend was consistent with ∑21OPEs (p < 0.05). Simultaneously, in order to further explore the effect of atmospheric deposition on the levels of OPEs in soil of the study region, input fluxes and accumulation increments were estimated. Ten OPEs (including seven target OPEs and three suspect OPEs) exhibited high input flux means and accumulation increments, indicating that these compounds are prone to accumulate in soil via atmospheric deposition. It is noteworthy that the non-target phosphonate analyte bis(2,4-di-tert-butylphenyl) dibutyl ethane-1,2-diylbis(phosphonate) (BDTBPDEDBP) was detected at highest median concentration (8960 ng/g dw) in atmospheric deposition. Correspondingly, the average input flux and accumulation increment of BDTBPDEDBP were higher than those of all target and suspect OPEs. Collectively, this study quantifies the environmental transport behavior of OPEs between atmospheric deposition and soil, and provides new evidences for the fact that atmospheric deposition is the important pollution source of OPEs in soil.

Organophosphate ester in surface water of the Pearl River and South China Sea, China: Spatial variations and ecological risks

This study focused on investigating the concentrations, compositional profiles, partitioning behaviors and spatial variations of organophosphate esters (OPEs) in the Pearl River (PR), South China Sea (SCS) region, to evaluate their environmental risks. ∑OPEs concentrations in the surface water of the PR ranged from 117.5 to 854.8 ng/L in the dissolved phase and from 0.5 to 13.3 ng/L in the suspended particulate matter. In the surface seawaters of the northern and western parts of the SCS, ∑OPEs concentrations were 1.3-17.6 ng/L (mean: 6.7 ± 5.2) and 2.3-24.4 ng/L (mean: 7.6 ± 5.5), respectively. The percentage of chlorinated OPEs in surface water samples from the PR to the SCS was 79 ± 15%. Tripentyl phosphate (TPeP) (average: 28.3%) and triphenylphosphate (TPhP) (average: 9.6%) exhibited significant particulate fraction. A significant negative correlation (p < 0.05) between salt concentration and OPE congeners in seawater suggested that river runoff predominantly introduced OPEs into the coastal waters of the SCS. The findings also showed higher levels of OPEs in the PR and estuary than in offshore waters. The OPE loading from the PR into the SCS was estimated to be ∼119 t y-1. The presence of TCEP (RQmax = 2.1), TnBP (RQmax = 0.48) and TPhP (RQmax = 0.3) in PR water samples pose a high risk to aquatic organisms, whereas OPEs (RQ < 0.1) in SCS water samples do not pose a threat to aquatic organisms. This research emphasizes the environmental fate and impact of OPEs on surface waters of the PR and SCS.

Spatiotemporal patterns and deposition of organophosphate esters (OPEs) in air, foliage and litter in a subtropical forest of South China

Recent studies revealed the un-negligible impact of airborne organophosphate esters (OPEs) on phosphorus (P)-limited ecosystems. Subtropical forests, the global prevalence P-limited ecosystems, contain canopy structures that can effectively sequester OPEs from the atmosphere. However, little is known about the behavior and fate of OPEs in subtropical forest ecosystem, and the impact on the P cycling in this ecosystem. OPE concentrations in the understory air (at two heights), foliage, and litterfall were investigated in a subtropical forest in southern China. The median ∑OPE concentrations were 3149 and 2489 pg/m3 in the upper and bottom air, respectively. Foliage exhibited higher ∑OPE concentrations (median = 386 ng/g dry weight (dw)) compared to litter (median = 267 ng/g dw). The air OPE concentrations were ordered by broadleaved forest > mixed forest > coniferous forest, which corresponds to the results of canopy coverage or leaf area index. The spatial variation of OPEs in foliage and litter was likely caused by the leaf surface functional traits. Higher OPE concentrations were found in the wet season for understory air while in the dry season for foliage and litter, which were attributed to the changes in emission sources and meteorological conditions, respectively. The inverse temporal variation suggests the un-equilibrium partitioning of OPEs between leaf and air. The OPE concentrations during the litter-incubation presented similar temporal trends with those in foliage and litter, indicating the strong interaction of OPEs between the litter layer and the near-soil air, and the efficient buffer of litter layer played in the OPEs partitioning between soil and air. The median OPEs-associated P deposition fluxes through litterfall were 270, 186, and 249 μg P/m2·yr in the broadleaved, mixed, and coniferous forests, respectively. Although the fluxes accounted for approximately 0.2% of the total atmospheric P deposition, their significance to this P-limited ecosystem may not be negligible.

Organophosphate esters in water and air: A minireview of their sources, occurrence, and air-water exchange

Organophosphate esters (OPEs) have received considerable attention in environmental research due to their extensive production, wide-ranging applications, prevalent presence, potential for bioaccumulation, and associated ecological and health concerns. Low efficiency of OPE removal results in the effluents of wastewater treatment plants emerging as a significant contributor to OPE contamination. Their notable solubility and mobility give OPEs the potential to be transported to coastal ecosystems via river discharge and atmospheric deposition. Previous research has indicated that OPEs have been widely detected in the atmosphere and water bodies. Atmospheric deposition across air-water exchange is the main input route for OPEs into the environment and ecosystems. The main processes that contribute to air-water exchange is air-water diffusion, dry deposition, wet deposition, and the air-water volatilization process. The present minireview links together the source, occurrence, and exchange of OPEs in water and air, integrates the occurrence and profile data, and summarizes their air-water exchange in the environment.

Organophosphate triesters and their diester degradation products in the atmosphere-A critical review

Organophosphate triesters (tri-OPEs) have found substantial use as plasticizers and flame retardants in commercial and industrial products. Despite upcoming potential restrictions on use of OPEs, widespread environmental contamination is likely for the foreseeable future. Organophosphate diesters (di-OPEs) are known biotic or abiotic degradation products of tri-OPEs. In addition, direct use of di-OPEs as commercial products also contributes to their presence in the atmosphere. We review the available data on contamination with tri-OPEs and di-OPEs in both indoor and outdoor air. Concentrations of tri-OPEs in indoor air exceed those in outdoor air. The widespread discovery of tri-OPE traces in polar regions and oceans is noteworthy and is evidence that they undergo long-range transport. There are only two studies on di-OPEs in outdoor air and no studies on di-OPEs in indoor air until now. Current research on di-OPEs in indoor and outdoor air is urgently needed, especially in countries with potentially high exposure to di-OPEs such as the UK and the US. Di-OPE concentrations are higher at e-waste dismantling areas than at surrounding area. We also summarise the methods employed for sampling and analysis of OPEs in the atmosphere and assess the relative contribution to atmospheric concentrations of di-OPEs made by environmental degradation of triesters, compared to the presence of diesters as by-products in commercial triester products. Finally, we identify shortcomings of current research and provide suggestions for future research.

Distribution and adsorption-desorption of organophosphate esters from land to sea in the sediments of the Beibu Gulf, South China Sea: Impact of seagoing river input

Organophosphate esters (OPEs) have been a class of emerging environmental contaminants. However, studies on their environmental behavior, specifically their adsorption-desorption behavior between sediment and seawater in estuarine and coastal areas, remain limited. To address this gap, our study focused on investigating the levels and behavior of 11 OPEs in sediment samples collected from the Beibu Gulf, South China Sea, encompassing estuaries and coastal regions. The total concentrations of 11 OPEs (Σ11OPEs) in the sediments exhibit a significant decrease in summer, both in seagoing rivers (4.67 ± 2.74 ng/g dw) and the coastal zone (5.11 ± 3.71 ng/g dw), compared to winter levels in seagoing rivers (8.26 ± 4.70 ng/g dw) and the coastal zone (7.71 ± 3.83 ng/g dw). Chlorinated OPEs dominated the sediments, constituting 63 %-76 % of the total. Particularly, port and mariculture areas showed the highest levels of OPEs. Through load estimation analysis, it was revealed that the sedimentary OPEs in Qinzhou Bay (221 ± 128 kg) had the highest load, with input from the Qin River identified as a significant source. Chlorinated OPEs showed a trend of desorption from sediments to the water column with increasing salinity, emphasizing the crucial role of land-based OPEs input through suspended particulate matter in rivers as a pathway to the ocean. The impact of strong flow in estuarine environments was highlighted, as it can scour sediments, generate suspended sediments, and release OPEs into the water bodies. Additionally, the results of the ecological risk assessment indicated that most of the OPEs posed low-risk levels. However, attention is warranted for the contamination levels of some chlorinated OPEs, emphasizing the need for ongoing monitoring and assessment.

Global environmental and toxicological impacts of polybrominated diphenyl ethers versus organophosphate esters: A comparative analysis and regrettable substitution dilemma

The prevalence of organophosphate esters (OPEs) in the global environment is increasing, which aligns with the decline in the usage of polybrominated diphenyl ethers (PBDEs). PBDEs, a category of flame retardants, were banned and classified as persistent organic pollutants (POPs) through the Stockholm Convention due to their toxic and persistent properties. Despite a lack of comprehensive understanding of their ecological and health consequences, OPEs were adopted as replacements for PBDEs. This research aims to offer a comparative assessment of PBDEs and OPEs in various domains, specifically focusing on their persistence, bioaccumulation, and toxicity (PBT) properties. This study explored physicochemical properties (such as molecular weight, octanol-water partition coefficient, octanol-air partition coefficient, Henry's law constant, and vapor pressures), environmental behaviors, global concentrations in environmental matrices (air, water, and soil), toxicities, bioaccumulation, and trophic transfer mechanisms of both groups of compounds. Based on the comparison and analysis of environmental and toxicological data, we evaluate whether OPEs represent another instance of regrettable substitution and global contamination as much as PBDEs. Our findings indicate that the physical and chemical characteristics, environmental behaviors, and global concentrations of PBDEs and OPEs, are similar and overlap in many instances. Notably, OPE concentrations have even surged by orders of several magnitude compared to PBDEs in certain pristine regions like the Arctic and Antarctic, implying long-range transport. In many instances, air and water concentrations of OPEs have been increased than PBDEs. While the bioaccumulation factors (BAFs) of PBDEs (ranging from 4.8 to 7.5) are slightly elevated compared to OPEs (-0.5 to 5.36) in aquatic environments, both groups of compounds exhibit BAF values beyond the threshold of 5000 L/kg (log10 BAF > 3.7). Similarly, the trophic magnification factors (TMFs) for PBDEs (ranging from 0.39 to 4.44) slightly surpass those for OPEs (ranging from 1.06 to 3.5) in all cases. Metabolic biotransformation rates (LogKM) and hydrophobicity are potentially major factors deciding their trophic magnification potential. However, many compounds of PBDEs and OPEs show TMF values higher than 1, indicating biomagnification potential. Collectively, all data suggest that PBDEs and OPEs have the potential to bioaccumulate and transfer through the food chain. OPEs and PBDEs present a myriad of toxicity endpoints, with notable overlaps encompassing reproductive issues, oxidative stress, developmental defects, liver dysfunction, DNA damage, neurological toxicity, reproductive anomalies, carcinogenic effects, and behavior changes. Based on our investigation and comparative analysis, we conclude that substituting PBDEs with OPEs is regrettable based on PBT properties, underscoring the urgency for policy reforms and effective management strategies. Addressing this predicament before an exacerbation of global contamination is imperative.

Organophosphate Esters in Air and Seawater of the South China Sea: Spatial Distribution, Transport, and Air-Sea Exchange

Organophosphate esters (OPEs) have become one group of chemicals with emerging concern in the marine environment. In this work, we investigated OPEs in the air and seawater of the South China Sea in summer 2019. The concentrations of ∑10OPEs in the atmosphere ranged from 66 to 550 pg/m3, with TCIPP, TNBP, TPhP, and TEP predominating in the air. The total dissolved OPE concentrations (∑10OPEs without TEP) measured in high-volume water samples ranged from 300 to 3600 pg/L, with a mean concentration of 1180 ± 910 pg/L. TEP was measured with liquid-liquid extraction (LLE), and it showed the highest concentration (average 2000 ± 1450 pg/L) among the selected OPEs. Total suspended matter associated OPEs accounted for less than 4.7% of the sum of OPE concentrations in seawater. Fugacity fractions and air-sea exchange fluxes showed that TCEP, TCIPP, TIBP, TEHP, TPhP, and EHDPP were favored to volatilize, TEP dominated the deposition, while TPrP and TNBP varied between volatilization and deposition. Atmospheric particle deposition fluxes ranged from 5 to 71 ng/m2/day with an average of 17 ± 15 ng/m2/day. The input of ∑OPEs to the entire South China Sea via atmospheric particle deposition was estimated to be 22 ± 19 tons/year, while the net air-sea exchange fluxes of OPEs were volatilization from seawater to air with an average of 44 ± 33 tons/year. This work suggests that air-sea exchange and atmospheric particle deposition are significant processes interfering with the transport of OPEs in the marine environment.

Air-Sea Exchange and Atmospheric Deposition of Phthalate Esters in the South China Sea

Phthalate esters (PAEs) have been investigated in paired air and seawater samples collected onboard the research vessel SONNE in the South China Sea in the summer of 2019. The concentrations of ∑₇PAEs ranged from 2.84 to 24.3 ng/m³ with a mean of 9.67 ± 5.86 ng/m³ in air and from 0.96 to 8.35 ng/L with a mean of 3.05 ng/L in seawater. Net air-to-seawater deposition dominated air-sea exchange fluxes of DiBP, DnBP, DMP, and DEP, while strong water-to-air volatilization was estimated for bis(2-ethylhexyl) phthalate (DEHP). The estimated net atmospheric depositions were 3740 t/y for the sum of DMP, DEP, DiBP, and DnBP, but DEHP volatilized from seawater to air with an average of 900 t/y. The seasonally changing monsoon circulation, currents, and cyclones occurring in the Pacific can significantly influence the concentration of PAEs, and alter the direction and magnitude of air-sea exchange and particle deposition fluxes. Consequently, the dynamic air-sea exchange process may drive the transport of PAEs from marginal seas and estuaries toward remote marine environments, which can play an important role in the environmental transport and cycling of PAEs in the global ocean.

The aomogeneous and heterogeneous oxidation of organophosphate esters (OPEs) in the atmosphere: Take diphenyl phosphate (DPhP) as an example

Organophosphate esters (OPEs) are widely detected in the atmosphere. However, the atmospheric oxidative degradation mechanism of OPEs has not been closely examined. This work took density functional theory (DFT) to investigate the tropospheric ozonolysis of organophosphates, represented by diphenyl phosphate (DPhP), including adsorption mechanisms on the surface of titanium dioxide (TiO₂) mineral aerosols and oxidation reaction of hydroxyl groups (·OH) after photolysis. Besides, the reaction mechanism, reaction kinetics, adsorption mechanism, and ecotoxicity evaluation of the transformation products were also studied. At 298 K, the total reaction rate constants k_O3, k_OH, k_TiO2-O3, and k_TiO2-OH are 5.72 × 10^-15 cm³ molecule^-1 s^-1, 1.68 × 10^-13 cm³ molecule^-1 s^-1, 1.91 × 10^-23 cm³ molecule^-1 s^-1, and 2.30 × 10^-10 cm³ molecule^-1 s^-1. The atmospheric lifetime of DPhP ozonolysis in the near-surface troposphere is 4 min, much lower than that of hydroxyl radicals (·OH). Besides, the lower the altitude is, the stronger the oxidation is. The TiO₂ clusters carry DPhP promoting ·OH oxidation but inhibiting ozonolysis of DPhP. Finally, the main transformation products of this process are glyoxal, malealdehyde, aromatic aldehydes, etc., which are still ecotoxic. The findings shed new light on the atmospheric governance of OPEs.

The gas phase retention volume behavior of organophosphate esters on polyurethane foam

In this study, the gas-phase retention volume behavior of four highly volatile organophosphate esters (OPEs) on polyurethane foam (PUF) was studied using a frontal chromatogram. The breakthrough volumes (V_B) of trimethyl phosphate (TMP), triethyl phosphate (TEP), tripropyl phosphate (TPrP), and tri-n-butyl phosphate (TnBP) were 0.33, 0.59, 10.5, and 32.4 m³, respectively. A significant negative correlation was found between the logarithm value of V_B and the subcooled liquid vapor pressure (P_L) with an r² of 0.905, indicating that the vapor penetration depends on both the volatility and total air volume. The enthalpy of desorption and vaporization (ΔH_S-ΔH_V) showed a significant difference between the tested OPEs and polycyclic aromatic hydrocarbons (PAHs), revealing that the strength of the sorption interaction of the tested OPEs vapor on PUF should be different from that of PAHs. The PUF-air partition coefficients (K_PUF-air) of the tested OPEs ranged from 4.3 to 8.1, which were lower than those of three-to four-ring PAHs (7.02-10.2) and organochlorines (8.01-9.72), revealing that the partition of highly volatile OPEs on PUF is lower than that of low-volatile compounds. The PUF/XAD cartridge improved the absorption efficiency of the tested OPEs; however, its sorptive capacity was still limited.