Spatial distribution and seasonal variations of atmospheric organophosphate esters (OPEs) in Tianjin, China based on gridded field observations

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.

Exploratory analysis of the association between organophosphate ester mixtures with high blood pressure of children and adolescents aged 8-17 years: cross-sectional findings from the National Health and Nutrition Examination Survey

Epidemiological studies on the effect of organophosphate esters (OPEs) on high blood pressure (BP) among children and adolescents are scant. Therefore, the main objective of the present study was to explore the effect of exposure to OPEs on high BP among children and adolescents. A total of 1340 participants were included in the current analyses. Multivariable logistic regression models were implemented to calculate odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to examine the association between OPE metabolites and high BP. We also assessed the modified effect of sex, age, and overweight/obesity on this association. Furthermore, quantile g-computation (Qgcomp) and Bayesian kernel machine regression (BKMR) were exhibited to analyze the association between multiple OPE metabolite mixtures and high BP. After adjusting for covariates, the highest (vs. lowest) tertiles of bis (1-choloro-2-propyl) phosphate (BCPP), bis-2-chloroethyl phosphate (BCEP), and di-n-butyl phosphate (DBUP) were associated with 1.23 (95% CI: 0.83, 1.83), 1.27 (95% CI: 0.85, 1.92), and 1.01 (95% CI: 0.67, 1.53) odds ratios for high BP, respectively. In the Qgcomp, a quartile increase in OPE metabolite mixtures was weakly associated with an elevated risk of high BP (adjusted OR: 1.06, 95CI%: 0.81, 1.37). The results from BKMR showed a positive trend of association between OPE metabolite mixture on the risk of high BP. In conclusion, our study demonstrated that higher levels of BCPP, BCEP, and DBUP were weakly associated with high BP among US children and adolescents. Moderate evidence suggested OPE metabolite mixtures had positive joint effects on high BP. Consequently, longitudinal studies with repeated measurements are warranted to examine the relationships between multiple OPE metabolites and high blood pressure among children and adolescents.

Distribution, sources, and ecological risk of organophosphate esters in the urbanized Jiaozhou Bay, East China

Organophosphate esters (OPEs), substitutes of polybrominated diphenyl ethers, have been found in a variety of marine environmental matrices, whereas little is known about the feature and sources of seawater OPEs from the environments simultaneously affected by multiple anthropogenic activities. Jiaozhou Bay is one typical bay heavily disturbed by human activities, which was semi-enclosed and surrounded by large amounts of discharged rivers and catchments, various types of ports, and aquaculture farms. This study found that concentrations of Σ₁₃OPEs ranged from 23.90 to 366.40 ng/L (median: 37.76 ng/L) in the seawater and from 90.15 to 1183.14 ng/L (median: 940.61 ng/L) in the inflowing river water. Tris (2-chloroisopropyl) phosphate, triethyl phosphate, and tris (2-chloroethyl) phosphate were the predominant congener, with the percentage of 43.76%, 22.80%, and 14.01%, respectively, in the bay water and 52.47%, 11.31%, and 23.66% in the river water. The overall spatial distribution was characterized by a higher concentration of Σ₁₃OPEs and halogenated-OPEs in the nearshore sites and in the inflowing rivers, which were surrounded by urbanized areas with dense anthropogenic activities, especially along the eastern coast. Effluent discharge and vehicular and marine traffic emissions were distinguished as two main plausible sources of OPEs to Jiaozhou Bay, based on the principal component analysis and Spearman correlations. Ecological risk analysis indicated that Σ₁₃OPEs posed a low risk to aquatic organisms in the bay and low-to-medium risks in the inflowing rivers.

Occurrence and temperature dependence of atmospheric gas-phase organophosphate esters in high-mountain areas (Pyrenees)

The air concentrations of organophosphate esters (OPEs) were studied in a network of six remote high-mountain areas of the Pyrenees located along an altitudinal profile between 1619 m and 2453 m above sea level on a restricted planar surface to assess their vertical distribution based on long-range atmospheric transport and temperature gradients. Polyurethane foam passive samplers were used in five periods spanning over three years (September 2017-October 2020). The sum of concentrations of five OPEs were between 5.3 and 100 pg m^-3, averaging 16-53 pg m^-3 across campaigns at the different locations. These concentrations were much lower than those observed in areas under anthropogenic influence but also than those found in low altitude remote continental sites. A significant progressive change in predominant compounds was observed along the altitudinal gradient, with prevalence of tris(1-chloro-2-propyl) phosphate (TCIPP) or tris(2-chloroethyl) phosphate (TCEP) below or above 2300 m above sea level, respectively. This trend was consistent with the higher volatility of TCEP, which was retained at greater extent at lower environmental temperatures (higher altitude). A significant temperature dependence of the gas phase concentrations was observed for TCEP, TCIPP and triphenyl phosphate (TPHP), which could be explained by retention in the cold periods, predominantly adsorbed in snow, and their release to the atmosphere during snowmelt. This mechanism was consistent with the good agreement found between the vaporization enthalpies measured under laboratory conditions and the experimental values obtained from the slopes of the significant linear regressions when representing the vertical gradients.

Formal waste treatment facilities as a source of halogenated flame retardants and organophosphate esters to the environment: A critical review with particular focus on outdoor air and soil

Extensive use of halogenated flame retardants (HFRs) and organophosphate esters (OPEs) has generated great concern about their adverse effects on environmental and ecological safety and human health. As well as emissions during use of products containing such chemicals, there are mounting concerns over emissions when such products reach the waste stream. Here, we review the available data on contamination with HFRs and OPEs arising from formal waste treatment facilities (including but not limited to e-waste recycling, landfill, and incinerators). Evidence of the transfer of HFRs and OPEs from products to the environment shows that it occurs via mechanisms such as: volatilisation, abrasion, and leaching. Higher contaminant vapour pressure, increased temperature, and elevated concentrations of HFRs and OPEs in products contribute greatly to their emissions to air, with highest emission rates usually observed in the early stages of test chamber experiments. Abrasion of particles and fibres from products is ubiquitous and likely to contribute to elevated FR concentrations in soil. Leaching to aqueous media of brominated FRs (BFRs) is likely to be a second-order process, with elevated dissolved humic matter and temperature of leaching fluids likely to facilitate such emissions. However, leaching characteristics of OPEs are less well-understood and require further investigation. Data on the occurrence of HFRs and OPEs in outdoor air and soil in the vicinity of formal e-waste treatment facilities suggests such facilities exert a considerable impact. Waste dumpsites and landfills constitute a potential source of HFRs and OPEs to soil, and improper management of waste disposal might also contribute to HFR contamination in ambient air. Current evidence suggests minimal impact of waste incineration plants on BFR contamination in outdoor air and soil, but further investigation is required to confirm this.

Organophosphate Esters in China: Fate, Occurrence, and Human Exposure

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers. OPEs have been released into various environments (e.g., water, sediments, dust and air, and soil). To investigate the occurrence and distribution of OPEs in various environments in China, this review collects and discusses the published scientific studies in this field. Chlorinated OPEs, as flame retardants, are the predominant OPEs found in the environment. The analysis of data revealed large concentration variations among microenvironments, including inflowing river water (range: 0.69-10.62 µgL^-1), sediments (range: 0.0197-0.234 µg/g), dust (range: 8.706-34.872 µg/g), and open recycling sites' soil (range: 0.122-2.1 µg/g). Moreover, OPEs can be detected in the air and biota. We highlight the overall view regarding environmental levels of OPEs in different matrices as a starting point to monitor trends for China. The levels of OPEs in the water, sediment, dust, and air of China are still low. However, dust samples from electronic waste workshop sites were more contaminated. Human activities, pesticides, electronics, furniture, paint, plastics and textiles, and wastewater plants are the dominant sources of OPEs. Human exposure routes to OPEs mainly include dermal contact, dust ingestion, inhalation, and dietary intake. The low level of ecological risk and risk to human health indicated a limited threat from OPEs. Furthermore, current challenges and perspectives for future studies are prospected. A criteria inventory of OPEs reflecting the levels of OPEs contamination association among different microenvironments, emerging OPEs, and potential impact of OPEs on human health, particularly for children are needed in China for better investigation.

A review of environmental occurrence, analysis, bioaccumulation, and toxicity of organophosphate esters

The ban and restriction of polychlorinated biphenyls (PCBs) and major brominated flame retardants (BFRs), including hexabromocyclododecane (HBCD) and polybrominated diphenyl ethers (PBDEs), due to their confirmed detrimental effects on wildlife and humans have paved the way for the wide application of organophosphate esters (OPEs). OPEs have been extensively used as alternative flame retardants, plasticizer, and antifoaming agents in various industrial and consumer products, which leads to an increase in production, usage, and discharge in the environment. We compile recent information on the production/usage and physicochemical properties of OPEs and discussed and compared the available sample treatment and analysis techniques of OPEs, including extraction, clean-up, and instrumental analysis. The occurrence of OPEs in sediment, aquatic biota, surface, and drinking water is documented. Toxicity, human exposure, and ecological risks of OPEs were summarized; toxicological data of several OPEs shows different adverse health effects on aquatic organisms and humans. Much attention was given to document evidence regarding the bioaccumulation and biomagnification potential of OPEs in aquatic organisms. Finally, identified research gaps and avenues for future studies are forwarded.

Comprehensive evaluation of organophosphate ester contamination in surface water and sediment of the Bohai Sea, China

This study investigated the occurrence and profile of 14 organophosphate esters (OPEs) in surface water and sediment of the whole Bohai Sea. A total of 53 pairs of surface water and sediment samples were collected and the contained OPEs were quantified using a gas chromatography-mass spectrometry (GC-MS). The average concentrations of OPEs in surface water and sediment were in the range of 0-92.9 ng/L and 0.001-8.58 ng/g dry weight (dw), respectively, with tri (2-chloroethyl) phosphate (TCEP) as the predominant congener in both compartments. The total concentrations of 14 OPEs (∑₁₄OPEs) in surface water and sediment were in the range of 10.9-516.4 ng/L and 1.42-52.9 ng/g dw, respectively. The inventories of ∑₁₄OPEs were calculated to be 179.3 tons in the water and 101.5 tons in the sediment. Based on the risk quotients (RQs), the ecological risks of OPEs to the aquatic organisms in the Bohai Sea were considered to be negligible.

Passive air sampling for semi-volatile organic chemicals

During passive air sampling, the amount of a chemical taken up in a sorbent from the air without the help of a pump is quantified and converted into an air concentration. In an equilibrium sampler, this conversion requires a thermodynamic parameter, the equilibrium sorption coefficient between gas-phase and sorbent. In a kinetic sampler, a time-averaged air concentration is obtained using a sampling rate, which is a kinetic parameter. Design requirements for kinetic and equilibrium sampling conflict with each other. The volatility of semi-volatile organic compounds (SVOCs) varies over five orders of magnitude, which implies that passive air samplers are inevitably kinetic samplers for less volatile SVOCs and equilibrium samplers for more volatile SVOCs. Therefore, most currently used passive sampler designs for SVOCs are a compromise that requires the consideration of both a thermodynamic and a kinetic parameter. Their quantitative interpretation depends on assumptions that are rarely fulfilled, and on input parameters, that are often only known with high uncertainty. Kinetic passive air sampling for SVOCs is also challenging because their typically very low atmospheric concentrations necessitate relatively high sampling rates that can only be achieved without the use of diffusive barriers. This in turn renders sampling rates dependent on wind conditions and therefore highly variable. Despite the overall high uncertainty arising from these challenges, passive air samplers for SVOCs have valuable roles to play in recording (i) spatial concentration variability at scales ranging from a few centimeters to tens of thousands of kilometers, (ii) long-term trends, (iii) air contamination in remote and inaccessible locations and (iv) indoor inhalation exposure. Going forward, thermal desorption of sorbents may lower the detection limits for some SVOCs to an extent that the use of diffusive barriers in the kinetic sampling of SVOCs becomes feasible, which is a prerequisite to decreasing the uncertainty of sampling rates. If the thermally stable sorbent additionally has a high sorptive capacity, it may be possible to design true kinetic samplers for most SVOCs. In the meantime, the passive air sampling community would benefit from being more transparent by rigorously quantifying and explicitly reporting uncertainty.