Exchange Of Persistent Organic Pollutants Research Articles

Sediment-water column exchange of persistent organic pollutants (PAHs and PCBs) and their transport vector in El Bey watershed, Tunisia

El Bey river, which drains 60% of the pollutant load of several urban cities in the northeast of Tunisia, provides a good example of the transfer of organic and metallic pollutants that result from industrial and urban activity, and can be used to show how these charges are transported and discharged into the Gulf of Tunis. Persistent organic pollutants (PAH and PCB) in dissolved, particulate matter, bed sediments, and three wastewater effluents in El Bey watershed were analyzed. PAH (∑14PAHs) concentration ranged from 0.248 to 9.955 mg L−1 and from 0.836 to 28.539 mg L−1 in dissolved and particulate fraction respectively. The particulate/dissolved partition coefficient value (Kd) was less than one which confirmed the affinity of PAH to be adsorbed. In sediment, the high-molecular weight PAHs were found principally with percentage between 50 and 100% witch present 239.99 to 5362.19 μg kg−1, which is relatively higher in comparison with other estuaries river. Contrary to PAH patterns, PCB were bound to dissolve fraction. Kd (PCB) value (Kd > 1) reflected this affinity which is related to environment energy. The spatial distribution and profile of analyzed organic pollutants confirmed the direct impact of wastewater effluent on the organic pollution level in three compartment of El Bey watershed and his profiles suggested different transport patterns.

Determination of temperature dependent Henry's law constants of polychlorinated naphthalenes: Application to air-sea exchange in Izmir Bay, Turkey

The Henry's law constant (H) is a crucial variable to investigate the air-water exchange of persistent organic pollutants. H values for 32 polychlorinated naphthalene (PCN) congeners were measured using an inert gas-stripping technique at five temperatures ranging between 5 and 35 °C. H values in deionized water (at 25 °C) varied between 0.28 ± 0.08 Pa m3 mol−1 (PCN-73) and 18.01 ± 0.69 Pa m3 mol−1 (PCN-42). The agreement between the measured and estimated H values from the octanol-water and octanol-air partition coefficients was good (measured/estimated ratio = 1.00 ± 0.41, average ± SD). The calculated phase change enthalpies (ΔHH) were within the interval previously determined for other several semivolatile organic compounds (42.0–106.4 kJ mol−1). Measured H values, paired atmospheric and aqueous concentrations and meteorological variables were also used to reveal the level and direction of air-sea exchange fluxes of PCNs at the coast of Izmir Bay, Turkey. The net PCN air-sea exchange flux varied from −0.55 (volatilization, PCN-24/14) to 2.05 (deposition, PCN-23) ng m−2 day−1. PCN-19, PCN-24/14, PCN-42, and PCN-33/34/37 were mainly volatilized from seawater while the remaining congeners were mainly deposited. The overall number of the cases showing deposition was higher (67.9%) compared to volatilization (21.4%) and near equilibrium (10.7%).

Air–soil exchange of organochlorine pesticides in a sealed chamber

So far little is known about air–soil exchange under any sealed circumstances (e.g., in plastic and glass sheds), which however has huge implications for the soil–air–plant pathways of persistent organic pollutants including organochlorine pesticides (OCPs). A newly designed passive air sampler was tested in a sealed chamber for measuring the vertical concentration profiles of gaseous phase OCPs (hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs)). Air was sampled at 5, 15, and 30cm above ground level every 10th day during a 60-day period by deploying polyurethane foam cylinders housed in acrylonitrile butadiene styrene-covered cartridges. Concentrations and compositions of OCPs along the vertical sections indicated a clear relationship with proximity to the mixture of HCHs and DDTs which escapes from the soils. In addition, significant positive correlations were found between air temperatures and concentrations of HCHs and DDTs. These results indicated revolatilization and re-deposition being at or close to dynamic pseudo-equilibrium with the overlying air. The sampler used for addressing air–soil exchange of persistent organic pollutants in any sealed conditions is discussed.

Research progress in uptake of persistent organic pollutants by plants

Plants can absorb persistent organic pollutants(POPs) from air and soil. Roots sorption is one of uptake processes,while evidence showed that POPs absorbed by roots was hardly transferred to the aerial tissues of the plant. The POPs re-volatilized from soil may only influence the parts of plants near the surface of the ground. Compared to the absorption from soil,the absorption of atmospheric POPs by foliage raised more concern. The airborne POPs can be accumulated by plant leaves by wet and dry deposition,which is the main pathway of the atmospheric POPs entering the aerial parts of plants. Air-plant exchange equilibrium is an important state that determines the direction of gas exchange between air and plant. The airborne POPs partition onto plant and approach plant gas-phase equilibrium rather rapidly,within less than 6 days of exposure. Besides exposure time,other environmental factors(temperature,wind speed,humidity,etc.) and the shape,areas and life time of the leaves have impacts on the air-plant exchange equilibrium of POPs. Through the air-plant exchange the airborne POPs were fixed by the plants and finally transferred into soil by falling off the leaves. Therefore,the air-plant exchange of POPs will influence the long-range atmospheric transport and the regional,even global distribution of POPs. Plants such as lichens,mosses,grass and forest have been used as passive samplers to monitor the levels of atmospheric POPs on different time scales and reflect the spatial distribution of POPs. Lichens and mosses are extensively used in environmental pollution studies especially in the polar region,since their collection is relatively easy. For grass,different species have the same ability to absorb the airborne POPs,which was used as bio-monitor to compare the POPs in different regions over the world. Numerous studies indicated that plants act as a "sink" for global cycling of POPs. The POPs absorbed by plants will enter the terrestrial food chains through the consumption of plants by animals and will be transported from one trophic level to a higher one,which will result in bio-concentration and even pose potential threat to the health of humans. However,there are a few studies focusing on the bio-concentration of POPs in the terrestrial food chains currently and most of them utilize models to simulate the bio-concentration process. In this paper,the research progress on the accumulation of POPs by plants including the ways of POPs entering the plants and the air-plant exchange of the airborne POPs were reviewed; the advantage and disadvantage of vegetation passive samplers(lichens,mosses and grass) were discussed. We also pointed out the problems needed to be solved in further studies.

Air−Boreal Forest Transfer and Processing of Polychlorinated Biphenyls

The exchange of persistent organic pollutants (POPs) between different compartments of a typical mature boreal forest was investigated. The study focused on fluxes of polychlorinated biphenyls (PCBs) between the atmosphere, vegetation and soil, and within the soil to assess whether this type of forest acts as a final sink or temporary repository for POPs. The study, at a Swedish site, suggested total PCB air-to-forest floor fluxes of 1.4 microg m(-2) year(-1). Much of this could be attributed to compounds bound to particles that may originate from needle surfaces. Degradation half-lives in soil between 6.4 and 30 years for tetra- to hepta-PCBs were obtained using a mass balance approach. This field data-based method derived degradation rates of POPs in background soils, although it may have underestimated the persistence of the heavy PCB congeners. Compounds reaching the forest soil appear to be stored efficiently and degraded slowly. As a first approximation, applying the findings from this study site to boreal forests on a global scale suggests that 2-21% (depending on the congener) of the estimated global atmospheric emission deposits to these ecosystems.

Soil Burdens of Persistent Organic Pollutants: Their Levels, Fate, and Risks. Part IV. Quantification of Volatilization Fluxes of Organochlorine Pesticides and Polychlorinated Biphenyls from Contaminated Soil Surfaces

A volatilization chamber, designed for direct measurements of the soil-air exchange of persistent organic pollutants (POPs) was applied for determination of the volatilization fluxes of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). The volatilization fluxes were determined for 13 model compounds at 3-5 concentration levels, for two soil organic carbon contents, and two wind velocities. The flux values were strongly correlated with physicochemical properties of the compounds. The higher fluxes were measured for soils with lower organic carbon contents, for higher contamination, and higher wind velocities. Experimentally derived values were compared to those predicted by the fugacity model. In general, the fugacity model underestimated the volatilization fluxes, especially for the compounds with higher molecular weights, and soils with higher organic carbon contents. It has been demonstrated that variability of the wind velocities as an important parameter for quantification of the soil-air exchange should be better considered in current models. Presented results draw the attention to often overlooked secondary sources of the atmospheric pollution and point out that their impact can be much greater than indicated by the fugacity models.

The impact of an urban-industrial region on the magnitude and variability of persistent organic pollutant deposition to Lake Michigan.

A predictive model for gas-phase PCBs and trans-nonachlor over Lake Michigan has been constructed and the resulting data examined for trends. In this paper, we describe the model results to show how the magnitude and variability of a plume of contaminants from the Chicago area contributes to a highly variable region of net contaminant deposition over the entire lake. For the whole lake, gross annual deposition of PCBs is approximately 3200 kg, although the net annual gas exchange is not significantly different from zero. The data-driven model illustrates that on a daily basis, the net exchange of persistent organic pollutants (POPs) can change from net deposition to net volatilization depending on the area of plume impact. These findings suggest that i) control of urban areas can accelerate the rate of volatilization from lakes; and ii) release of POPs from urban areas is largely a result of volatilization processes.

Reevaluation of air-water exchange fluxes of PCBs in Green Bay and southern Lake Michigan.

Air-water exchange of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is an import process for the delivery of contaminants to water bodies, as well as for their removal, and is thus a pivotal parameter in the construction of mass balances in aquatic systems. Simultaneous measurements of PCB concentrations in the gas and dissolved phases conducted in Green Bay in 1989 and in southern Lake Michigan in 1994-1995 were used to estimate air-water exchange fluxes. In this work, improved Henry's law constants for PCBs and new mass-transfer rates across the air-water interface were used to update the previous calculations. The new model calculations suggest that the net volatilization flux of PCBs out of Green Bay ranges from +170 to +5300 ng m(-2) day(-1), which is 2-20 times larger than previous estimates. The flux of PCBs in southern Lake Michigan exhibits net volatilization of +0.5 to +230 ng m(-2) day(-1) throughout the study period (May and July 1994, January 1995), whereas previous estimates reported that the net flux was seasonally absorptive. Thus, water-to-air fluxes are more important for the removal of PCBs from both Green Bay and Lake Michigan than previously recognized.

A review of processes involved in the exchange of persistent organic pollutants across the air–sea interface

Atmospheric deposition across the air–sea interface is the main input route for persistent organic pollutants (POPs) to the marine environment and its ecosystems. The main processes contributing to air–sea exchange of POPs are diffusive vapour exchange, precipitation scavenging of vapours and particle-sorbed chemicals, and dry deposition with particles. Additional processes within the atmosphere and surface water affecting this exchange are aerosol–vapour partitioning, and partitioning and sedimentation in the water-column. These processes are discussed and recent findings are summarised. Commonly employed expressions used for describing these processes in models are presented, with a special focus on the influence of temperature and other seasonal parameters. Research gaps are identified which have to be addressed to gain a solid understanding of the environmental transport and distribution of POPs. This is needed to implement and evaluate the effectiveness of recent international agreements to protect the marine environment from the deleterious effects of POPs.