Abstract
Abstract. Coastal areas are vulnerable to the accumulation of semivolatile organic compounds, such as PAHs, OCPs and PCBs from atmospheric inputs. Dry particulate and wet depositions, and air-water diffusive exchange in the Singapore's south coastal area, where most of chemical and oil refinery industries are situated in, were estimated. Based on a yearly dataset, the mean annual dry particulate deposition fluxes of ∑16-PAHs, ∑7 OCPs and ∑21 PCBs were 1328.8±961.1 μg m−2 y−1, 5421.4±3426.7 ng m−2 y−1 and 811.8±578.3 ng m−2 y−1, and the wet deposition of ∑16-PAHs and ∑7 OCPs were 6667.1±1745.2 and 115.4±98.3 μg m−2 y−1, respectively. Seasonal variation of atmospheric depositions was influenced by meteorological conditions. Air-water gas exchange fluxes were shown to be negative values for PAHs, HCHs and DDXs, indicating Singapore's south coast as a sink for the above-mentioned SVOCs. The relative contribution of each depositional process to the total atmospheric input was assessed by annual fluxes. The profile of dry particulate deposition, wet deposition and gas exchange fluxes seemed to be correlated with individual pollutant's properties such as molecular weight and Henry's law constant, etc. For the water column partitioning, the organic carbon-normalized partition coefficients between particulate and dissolved phases (KOC) for both PAHs and OCPs were obtained. The relationships between KOC of PAHs and OCPs and their respective octanol-water partition coefficient (KOW) were examined. In addition, both adsorption onto combustion-derived soot carbon and absorption into natural organic matter for PAHs in marine water column were investigated. Enrichment factors in the sea-surface microlayer (SML) of the particulate phase were 1.2–7.1 and 3.0–4.9 for PAHs and OCPs, and those of dissolved phase were 1.1–4.9 and 1.6–4.2 for PAHs and OCPs, respectively. These enrichment factors are relatively higher than those reported for nearby coastal areas, which are most likely due to more organic surfactants floating in the south coastal surface of Singapore.
Highlights
Semi-volatile organic compounds (SVOCs) such as polycyclic aromatic hydrocarbons (PAHs), organo-chlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) can be transported widely from their original sources
In Singapore’s coastal area, the monthly dry deposition fluxes for PAHs, OCPs and PCBs were in the range of 46.0–275.6 μg m−2 month−1, 60.7–906.1 ng m−2 month−1 and 3.1–93.1 ng m−2 month−1, respectively
High wet deposition fluxes were observed from December 2007 to Mar 2008 for both PAHs and OCPs (Fig. 1a in sharp contrast to the low dry deposition fluxes during the same period (Fig. 1b)
Summary
Semi-volatile organic compounds (SVOCs) such as polycyclic aromatic hydrocarbons (PAHs), organo-chlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) can be transported widely from their original sources These three groups of pollutants, PAHs, OCPs and PCBs, have been studied for decades due to their inherent toxicity, persistence and ability to disperse in the environment (Iwata et al, 1993; Jones and De Voogt, 1999; Oskam et al, 2004). Other than the abovementioned processes, air-sea exchange can make SVOCs diffuse across the air-sea interface; the sea surface microlayer (SML), a unique compartment at the airsea boundary defined operationally as the upper millimeter (1–1000 μm) of the sea surface, has large storage capacity to delay the transport of SVOCs across the interface This interfacial effect has been reported as the enrichment of contaminants with different physicochemical properties (Hardy, 1982; Chernyak et al, 1996; Wurl et al, 2006a). The water-column partitioning was assessed by a shortterm measurement on different aquatic particulate matrices in the ocean
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