Seasonal variation in diffusive exchange of polycyclic aromatic hydrocarbons across the air-seawater interface in coastal urban area

Air-sea exchange of PAHs in the Taiwan Strait: Seasonal dynamics and regulation mechanisms revealed by machine learning approach

In this study, to understand the seasonal dynamics of air-sea exchange and its regulation mechanisms, we investigated polycyclic aromatic hydrocarbons (PAHs) at the air-sea interface in the western Taiwan Strait in combination with measurements and machine learning (ML) predictions. For 3-ring PAHs and most of 4- to 6-ring, volatilization and deposition fluxes were observed, respectively. Seasonal variations in air-sea exchange flux suggest the influence of monsoon transitions. Results of interpretable ML approach (XGBoost) indicated that volatilization of 3-ring PAHs was significantly controlled by dissolved PAH concentrations (contributed 24.0 %), and the gaseous deposition of 4- to 6-ring PAHs was related to more contaminated air masses originating from North China during the northeast monsoon. Henry's law constant emerged as a secondary factor, influencing the intensity of air-sea exchange, particularly for low molecular weight PAHs. Among environmental parameters, notably high wind speed emerges as the primary factor and biological pump's depletion of PAHs in surface seawater amplifies the gaseous deposition process. The distinct dynamics of exchanges at the air-water interface for PAHs in the western TWS can be attributed to variations in primary emission intensities, biological activity, and the inconsistent pathways of long-range atmospheric transport, particularly within the context of the monsoon transition.

Investigating industrial PAH air pollution in relation to population exposure in major countries: A scoring approach

Polycyclic aromatic hydrocarbons (PAHs) are common air pollutants worldwide, associated with industrial processes. In the general population, both modeling and field studies revealed a positive correlation between air PAH concentrations and urinary PAH metabolite levels. Many countries lack population urinary data that correspond to local PAH air concentrations. Thus, we proposed a scoring-based approximate approach to investigating that correlation in selected countries, hypothesizing that PAH air concentrations in selected regions could represent the national air quality influenced by industrial emission and further correlate to PAH internal exposure in the general population. This research compiled 85 peer-reviewed journal articles and 9 official monitoring datasets/reports covering 34 countries, 16 of which with both atmospheric PAH data and human biomonitoring data. For the air pollution score (AirS), Egypt had the highest AirS at 0.94 and Pakistan was at the bottom of the score ranking at -1.95, as well as the median in the UK (AirS: 0.50). For the population exposure score (ExpS), China gained the top ExpS at 0.44 and Spain was with the lowest ExpS of -1.52, with the median value in Italy (ExpS: 0.43). Through the correlation analysis, atmospheric PAHs and their corresponding urinary metabolites provided a positive relationship to a diverse extent, indicating that the related urinary metabolites could reflect the population's exposure to specific atmospheric PAHs. The findings also revealed that in the 16 selected countries, AirS indexes were positively correlated with ExpS indexes, implying that higher PAH levels in the air may lead to elevated metabolite urinary levels in general populations. Furthermore, lowering PAH air concentrations could reduce population internal PAH exposure, implying that strict PAH air regulation or emission would reduce health risks for general populations. Notably, this study was an ideal theoretical research based on proposed assumptions to some extent. Further research should focus on understanding exposure pathways, protecting vulnerable populations, and improving the PAH database to optimize PAH pollution control.

Occurrence, spatial patterns, air-seawater exchange, and atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) from the Northwest Pacific to Arctic Ocean

Numerous studies have elucidated the characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Arctic; however, their behavior in different environments has not been studied at a large scale. To investigate the occurrence, spatial trends, air-seawater exchange and atmospheric deposition of 16 polycyclic aromatic hydrocarbons (PAHs), this study takes sample from the Northwest Pacific Ocean. to the Arctic Ocean.The concentrations of 16 PAHs in air and seawater ranged from 27 to 5658 pg/m³ and 34-338 ng/L, respectively. The air-seawater exchange flux of the region was calculated with a Whitman two-film model to be -82681-24613 ng/m²/day. Meanwhile, low-ring PAHs were transported from seawater to the air, while high-ring PAHs were transported from air to seawater. A correlation analysis between multiple environmental factors and particle phase ratio suggested that temperature might be the major driving factor for PAHs in the long-range atmospheric transport (LRAT) process. Moreover, the dry atmospheric deposition fluxes in the region were analyzed by considering environmental factors and the physicochemical properties of each PAHs monomer, these fluxes ranged from 0.001 to 696 ng/m²/day and were greater inshore than offshore and at higher latitudes. This study highlights that PAHs are affected by LRAT during their transport from Asia to Northwest Pacific and further to the Arctic Ocean, while emphasizing that air-seawater exchange plays an important role in air-sea interactions in the open ocean.

Compositional and seasonal differences of gas and particle phase polycyclic aromatic hydrocarbons (PAHs) over the southern Baltic Sea coast

In this study, 16 USEPA-prioritized PAHs in gas- and particle-phase (PAH_g+p), associated chemical and meteorological parameters, and backward trajectory simulations were explored in a coastal city in Poland, between April 2019 and May 2020. This study reports several important aspects of PAH_g+p, i.e. variation, composition, distribution profiles, impact of weather conditions, and correlation analysis between target PAH compounds and influencing inorganic gaseous pollutants. Specifically, higher and more variable concentrations of total PAH_g+p (mean ± SD, ng m^-3) were observed during winter (36.38 ± 24.19) compared to autumn (22.3 ± 17.44), summer (21.52 ± 13.30) and spring (19.90 ± 13.13). A distribution profile of parent PAH_g+p was as follows: 3-ring > 4-ring > 2-ring > 5-ring > 6-ring, although their relative contribution to the total PAHs showed statistically significant differences between seasons (p < 0.05). Precipitation-driven loss of ΣPAH_g+p was lower in the warm period than in the cold one, reflecting higher PAH concentrations in winter. A seasonal model-based analysis of incremental lifetime cancer risk showed a higher potential cancer risk for children than those for adult females and males. The adverse health impacts associated with PAH exposure via inhalation route indicate the need for implementation of pollution-control policies in this region.

Seasonal variations of polycyclic aromatic hydrocarbons in coastal sediments of a marine resource hot spot: the case of pars special economic energy zone, Iran

Polycyclic aromatic hydrocarbons (PAHs) are an important group of compounds of major environmental concern, which are in the class of persistent organic pollutants. Therefore, the key purpose of this research was to analyze seasonal fluctuations and to determine the probability of polycyclic aromatic hydrocarbons in coastal sediments of the Iranian Marine Resource Center based on the evaluation of 16 US-EPA important PAH compounds. These compounds have been collected from intertidal sediments located in the marine resources of southern Iran in different seasons. These samples of the surficial sediment were collected at the PSEEZ area using a stainless steel grab sampler in four seasons, from depths between 0.5 and 30 m. Surface sediment samples were removed by spoons and carefully placed in an aluminum foil; they were taken to the laboratory on ice and held at 20° C until their study. After extraction, by using a rotary evaporator apparatus, samples were condensed. The assay was added to roughly 2 g of activated copper flasks in the refrigerator for 36 h for desulfurization. Among different seasons, the highest concentration was observed in winter, with a mean of 281.3 ng g^-1. According to ecological risk assessment (concentrations of possible effects, low effect range, degree of threshold effects, and median effect range), PAH risks in surface sediments of PSEEZ were lower than the threshold results levels (TEL), possible effects levels (PEL), low range of effects (ERL), and median range of effects (ERM), indicating that a biological effect would rarely occur. The dry weight scale of the concentration of ∑PAHs ranges from 145.7 to 348.42 ng g^-1 with a mean quantity of 260.52 ng g^-1. Therefore, according to the amount of ∑PAH concentration, the sediments in the PSEEZ area indicated moderate to heavy pollutions. In this way, the sedimentary surface ecosystems of the Persian Gulf were considered as moderately polluted compared with other ecosystems worldwide. Our study highlighted some of the research gaps in PAH contamination studies and the level of PAH contamination. Therefore, this study will provide a scientific background, planning, and policies for PAH pollution control and environmental protection in Iran and similar regions around the world.

Possibilities of poly(methyl methacrylate) as a passive sampler for determination of bioavailable concentrations in seawater

Solvent-treated poly(methyl methacrylate) (PMMA) was recently introduced as a passive sampler for determining bioavailable concentrations, i.e., freely dissolved concentrations. However, the much knowledge required to obtain accurate bioavailable concentrations using the thus treated PMMA, applied in a marine environment, is still lacking. In this study, uptake experiments with PMMA after solvent treatment were conducted to investigate its uptake capacity and the effects of water temperature and salinity on the PMMA-water partition coefficient (K_PMMA-W) for polycyclic aromatic hydrocarbons (PAHs). Thus, PMMA passive samplers preloaded with performance reference compounds were exposed to seawater to first estimate the deployment time and then to confirm if the PMMA could give the residual concentrations of PAH in mussel. The less hydrophobic PAHs (log octanol-water partition coefficient < 5.5) had higher uptake capacity of PMMA-uptake was increased by a factor of up to 10. Whereas for these PAHs the K_PMMA-W values and seawater temperature showed a parabolic relationship, the effect of salinity on K_PMMA-W was not observed. The less hydrophobic PAH concentrations in seawater can be measured using the PMMA passive sampler over a period of about three weeks. For the PAHs detected in both PMMA and mussel, the PAH concentrations in mussel predicted from PMMA were found to be within one order of magnitude of the measured concentrations. This, therefore, suggests that solvent-treated PMMA could be used as a passive sampler to provide information on bioavailable concentrations for less hydrophobic PAHs.

Polycyclic aromatic hydrocarbons in the Baltic Sea - Pre-industrial and industrial developments as well as current status

We report on Baltic Sea polycyclic aromatic hydrocarbon (PAH) pressure based on the U.S. EPA PAHs in view of millennial and decadal developments utilizing data from sediment deposits and seawater. Pre-industrial PAH contents ranged from 500 to 4500 ng/g TOC. Maximum PAH contents were up to 100,000 ng/g TOC and date back to the 1960s to 1970s with maximum pollutant inputs. Contemporary sediment PAH contents with 10,000 to 35,000 ng/g TOC and seawater concentrations with about 1 to 16 ng/l show spatial variability due to different local inputs and sediment characteristics. Pre-industrial compositional change from low molecular weight to high molecular weight (HMW) PAH indicates changing sources from mostly petroleum to combustion. Application of diagnostic ratios reveals petroleum and combustion as contemporary PAH sources and that traffic emissions continuously contribute to the Baltic PAH profile. Medium to high toxicological risk to the marine community might arise from current HMW PAH contents.

Tidal variability of polycyclic aromatic hydrocarbons and organophosphate esters in the coastal seawater of Dalian, China

We investigated the tidal variability of polycyclic aromatic hydrocarbons (PAHs) and organophosphate esters (OPEs) in water dissolved phase from a coastal area of Dalian, China, as well as their air-water exchange trends. The concentrations of PAHs and OPEs in water were in the range of 50.5-74.7 ng/L and 21.6-61.5 ng/L, respectively. Phenanthrene (PHE) was the dominant congener followed by fluorene (FLU) for PAHs, while tris(2-chloroisopropyl) phosphate (TCIPP) and tris(2-chloroethyl) phosphate (TCEP) dominated for OPEs. PAHs in coastal water showed a tidal variability, but not for OPEs, which may due to the influence of occasional wastewater discharges of OPEs. The source apportionments using principle component analysis and positive matrix factorization suggested that PAHs in the coastal water mainly came from oil spill from ships, coal combustion, and petroleum combustion, while OPEs were derived from diverse sources. The fugacity fractions (ff) suggested that ACY, ACE, FLU, PHE, TCEP, and TPHP volatilized from water into air, while TNBP, TCIPP, and TDCIPP deposited from air into water, and FLA, PYR, BaA, CHR, and EHDPP reached equilibrium. The ff values varied slightly with tidal circle, but the variations were not enough to alter the air-water exchange directions of those compounds. Although the influences of tide on the air-water exchange of PAHs and OPEs were limited, tide still played an important role on the transports and diffusions of those chemicals in the coastal water, which requires further studies.

Spatiotemporal distribution, source apportionment and ecological risk assessment of PBDEs and PAHs in the Guanlan River from rapidly urbanizing areas of Shenzhen, China

In this study, nine congeners of polybrominated diphenyl ethers (PBDEs) and sixteen congeners of polycyclic aromatic hydrocarbons (PAHs) were measured in water samples to elucidate their spatial distribution, congener profiles, sources and ecological risks in the Guanlan River during both the dry season (DS) and the wet season (WS). The concentration of Σ₉PBDE ranged from 58.40 to 186.35 ng/L with an average of 115.72 ng/L in the DS, and from 8.20 to 37.80 ng/L with an average of 22.15 ng/L in the WS. Meanwhile, the concentration of Σ₁₆PAHs was ranged from 121.80 to 8371.70 ng/L with an average of 3271.18 ng/L in the DS and from 1.85 to 7124.25 ng/L with an average of 908.11 ng/L in the WS. The concentrations of PBDEs and PAHs in the DS were significantly higher than those in the WS, probably due to the dilution of the river during the rainy season. Moreover, the spatial distribution of pollutants revealed decreasing trend in the concentration from upstream to downstream and almost identical pattern was observed during both seasons. The source apportionment suggested that penta-BDE and to some extent octa-BDE commercial products were major sources of PBDEs in the study area. However, the sources of PAHs were mainly comprised of fossil fuels and biomass burning, followed by the petroleum products and their mixtures. The results of the ecological risk assessment indicated PBDEs contamination posed high ecological risks, while PAHs exhibited low or no ecological risks in the study area. Consistent with the environmental levels, the ecological risks of pollutants were relatively lower in the WS, compared to that in the DS. The results from this study would provide valuable baseline data and technical support for policy makers to protect the ecological environment of the Guanlan River.

Seasonal variation, air-water exchange, and multivariate source apportionment of polycyclic aromatic hydrocarbons in the coastal area of Dalian, China

The concentrations and seasonal variations of polycyclic aromatic hydrocarbons (PAHs) in air and seawater dissolved samples from the coastal area of Dalian were investigated, as well as their air-water exchanges. The average concentrations of PAHs were 27.5 ± 14.6 ng/m³ and 49.5 ± 20.5 ng/L in the air and water, respectively. Phenanthrene was the dominant congener in both air and water dissolved phase. Seasonality was discovered in the air with the concentrations higher in winter than in summer, but not in the water dissolved phase. Air-water exchange trends also displayed apparent seasonality with 3-4 ring PAHs generally being volatilization or equilibrium in summer but deposition in winter, which highlighted the important influence of temperature on the air-water exchange direction of PAHs. The air-water exchange fluxes of individual PAH congeners ranged from -24331 to 6541 ng/m²/d, and the highest deposition and volatilization fluxes both appeared at the industrial areas, which emphasized the influence of point source emission to the magnitude of air-water diffusion flux of PAHs. Multivariate source apportionment approaches, including principle component analysis, diagnostic ratios, and positive matrix factorization, were conducted, which suggested that PAHs in water originated from multiple sources. Frequent port transport correlated vehicle/ship emission rather than coal combustion may be the primary contributor of PAHs to the coastal air and water.

Distributions, sources and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in subsurface water of urban old industrial relocation areas: A case study in Shenyang, China

During a 12-month study period, the levels, distributions, sources and ecological risk of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in subsurface water of Shenyang (the largest urban industrial relocation base in China). The results showed that ΣPAH concentration ranged from 0.21 to 1.07 µg/L, in descending order as follows, summer, autumn, spring and winter. Comparing with the situations before relocation, there was a significant decrease in Fluorene, Phenanthrene and Anthracene levels. The content of Banzo[a]pyrene was in high level. Relatively high 16 EPA-PAHs concentrations were observed at downstream sites suggesting that after the industrial relocation, residual 16 EPA-PAHs in soil and sediments could be desorbed and resuspended in water. From a global perspective, contamination of subsurface water PAHs can be categorized as moderate level. Source analysis suggested that without industrial waste input, pyrogenic soureces were the major contributors for PAHs pollution in winter. Petrogenic and pyrogenic inputs were equally important sources for PAHs pollution in other seasons. Due to incomplete combustion of wood and coal, ecological risk of Banzo[a]pyrene was high in the winter, indicating that to alleviate 16 EPA-PAH contamination, segmented remediation and energy structure adjustment would be equally important in urban industrial relocation areas.