Land–Ocean Exchange Mechanism of Chlorinated Paraffins and Polycyclic Aromatic Hydrocarbons with Diverse Sources in a Coastal Zone Boundary Area, North China: The Role of Regional Atmospheric Transmission

Abstract

The marine environment is regarded as a crucial "sink" of numerous land-origin pollutants. As typical boundary regions, the coastal and offshore areas are used to evaluate the dominating transfer process and land−ocean exchange mechanism of semivolatile organic compounds. In air samples collected from a coastal area in North China over a whole year, chlorinated paraffins (CPs), including short-chain CPs and medium-chain CPs, and prior control 16 polycyclic aromatic hydrocarbons (PAHs) were determined, with mean concentrations of 25.8 and 94.7 ng/m 3 , respectively. Results of different gas−particle partitioning models indicated that the steady-state hypothesis provides a better description of the possible land−ocean exchange molecular mechanism. The source−sink influences for CPs and PAHs were affected by the predominant atmospheric motion, which alternated between gaseous diffusion and particulate sedimentation in different seasons. Source apportionment results indicated that different transfer characteristics contributed to the source divergence of ambient CPs and PAHs within 12 nautical miles in the same area. Coal/biomass combustion and diesel/natural gas combustion were the main PAH sources in the coast site (43.1%) and sea site (35.3%), respectively. Similar industrial sources CP-52 and CP-42 were the main CP sources in the coast site (41.4%) and sea site (40.8%), respectively.

Chlorinated Paraffin Pollution in the Marine Environment

“…Most of the evidence has supported the LRAT potentials of SCCPs and MCCPs. For example, model estimations showed that SCCPs have LRAT potential, , consistent with field observations of SCCPs in the atmosphere globally. ,, Also, monitoring studies of SCCPs and MCCPs in the air from remote areas and polar environments have implied that both are subject to LRAT. ,− Compared to LCCPs, the existing observations indicated a tremendous LRAT potential for SCCPs and MCCPs. ,,− This is because SCCPs and MCCPs have lower vapor pressure and higher volatility than LCCPs and thus are more likely to attach to particulate matter in the atmosphere. , In addition, longer-chain CPs generally have larger particle fractions. Therefore, part of MCCPs and virtually all LCCPs are limited to LRAT potential by micro- and nanoplastics, considered potential vectors for the LRAT of POPs. , This finding highlights that the atmospheric transport of CPs varies between congeners due to a wide range of physical and chemical properties (Table S1).…”

“…By contrast, the lower concentrations of ∑CPs appeared in the particle samples (1.72–44.9 ng/m 3 ), with C14 and Cl9–10 congeners as the predominant compounds. Given the season, higher concentrations of ∑gCPs (gaseous CPs) and ∑pCPs (particle CPs) were found in summer and winter than in other seasons in Chinese coastal areas, which may be because a lower ambient temperature made less evaporation of CPs to the gas phase, leading to the condensation of CPs onto the particle phase in winter . Seasonal variations were also observed in Liaodong Bay, China, where higher concentrations of ∑CPs occurred in the summer (range of 8.3–39 ng/m 3 , mean of 24 ng/m 3 ) than in spring (range of 3.8–13 ng/m 3 , mean of 6.9 ng/m 3 ) in the gas phase of air samples.…”

“…CPs are generally transported from land to the marine environment − through riverine input and volatilization of CPs-containing products. ,,, Various sources can be integrated by riverine pathways and then enter into the ocean, such as atmospheric deposition, industrial leakage, , sewage treatment effluent, , runoff of plastic and electronic wastes. , These terrestrial sources cause CPs to reach coastal and offshore regions due to ocean current transport, atmospheric transport, and deposition. ,, Various CP congeners’ different physical and chemical properties have led to variations in transport pathways in marine environments (Table S1).…”

“…As described in section 2.3, the results of air-seawater exchange flux generally showed net deposition of CPs from air to ocean. Therefore, atmospheric deposition may lead to their burdens on marine ecosystems and accumulation in marine food webs, thus determining the environmental fate of CPs in the marine environment. ,, Atmospheric deposition mainly includes dry deposition by particles and wet deposition by rain and snow. ,, Dry deposition contributes substantially to the flux of CPs to the ocean, mainly depending on the physicochemical properties of CPs and weather conditions. In the BS, dry deposition fluxes of SCCPs have reached up to 26100 ng/m 2 /day and decreased with increasing distance from the nearshore to offshore areas .…”

Removal Efficiency and Fate of Chlorinated Paraffins (CPs) in a Municipal Sewage Treatment Plant near a Typical Petrochemical Park

“…Besides, the higher temperatures in the summer season might maximize the volatilization of CPs compared to the winter season. This was consistent with a previous study that the mean values of log K p were −2.12 and −2.52 in cold and warm seasons for CPs . In addition, other environmental conditions, such as moisture content and/or light intensity, could also influence the behavior of CPs in the STP.…”