Cycling Of Persistent Organic Pollutants Research Articles

Critical roles of secondary sources in global cycling of persistent organic pollutants under climate change

The Stockholm Convention on persistent organic pollutants (SC-POPs) has been adopted for nearly 20 years, under which the fresh emissions of most POPs have been forbidden globally. Under this situation, the atmospheric levels of POPs have decreased, and thus the POPs that had accumulated in surface earth and/or water have tended to re-evaporate. Moreover, the climate change in recent years and the changes of surface matrices related to climatic factors (e.g., warming in soils, glacial retreat, permafrost thaw, and forest fires) have forced POPs to be released into air and/or water, which may have increased the contributions of “secondary sources”. These processes may speed up the global cycling of POPs and weaken the efforts of SC-POPs in protecting humans and ecosystems from POP pollution. We appeal to scientists and policymakers working on POPs and their elimination to focus on this issue.

Persistent organic pollutants (POPs) in coastal wetlands: A review of their occurrences, toxic effects, and biogeochemical cycling

Coastal wetlands, such as mangroves, seagrass beds, and salt marshes, are highly threatened by increasing anthropic pressures, including chemical pollution. Persistent organic pollutants (POPs) have attracted attention in these particularly vulnerable ecosystems, due to their bioaccumulative, pervasive, and ecotoxic behavior. This article reviews and summarizes available information regarding current levels, biogeochemical cycling, and effects of POPs on coastal wetlands. Sediment POP levels were compared with international quality guidelines, revealing many areas where compounds could cause damage to biota. Despite this, toxicological studies on some coastal wetland plants and microorganisms showed a high tolerance to those levels. These taxonomic groups are likely to play a key role in the cycling of the POPs, with an active role in their accumulation, immobilization, and degradation. Toxicity and biogeochemical processes varied markedly along three main axes; namely species, environmental conditions, and type of pollutant. While more focused research on newly and unintentionally produced POPs is needed, mainly in salt marshes and seagrass beds, with the information available so far, the environmental behavior, spatial distribution, and toxicity level of the studied POPs showed similar patterns across the three studied ecosystems.

Climate change and global cycling of persistent organic pollutants: A critical review

Abstract Climate warming, one of the main features of global change, has exerted indelible impacts on the environment, among which the impact on the transport and fate of pollutants has aroused widespread concern. Persistent organic pollutants (POPs) are a class of pollutants that are transported worldwide. Determining the impact of climate warming on the global cycling of POPs is important for understanding POP cycling processes and formulating relevant environmental policies. In this review, the main research findings in this field over the past ten years are summarized and the effects of climate warming on emissions, transport, storage, degradation and toxicity of POPs are reviewed. This review also summarizes the primary POP fate models and their application. Additionally, research gaps and future research directions are identified and suggested. Under the influence of climate change, global cycling of POPs mainly shows the following responses. (1) Global warming directly promotes the secondary emission of POPs; for example, temperature rise will cause POPs to be re-released from soils and oceans, and melting glaciers and permafrost can re-release POPs into freshwater ecosystems. (2) Global extreme weather events, such as droughts and floods, result in the redistribution of POPs through intense soil erosion. (3) The changes in atmospheric circulation and ocean currents have significantly influenced the global transport of POPs. (4) Climate warming has altered marine biological productivity, which has changed the POP storage capacity of the ocean. (5) Aquatic and terrestrial food-chain structures have undergone significant changes, which could lead to amplification of POP toxicity in ecosystems. (6) Overall, warming accelerates the POP volatilization process and increases the amount of POPs in the environment, although global warming facilitates their degradation at the same time. (7) Various models have predicted the future environmental behaviors of POPs. These models are used to assist governments in comprehensively considering the impact of global warming on the environmental fate of POPs and therefore controlling POPs effectively. Future studies should focus on the synergistic effects of global changes on the cycling of POPs. Additionally, the interactions among global carbon cycling, water cycling and POP cycling will be a new research direction for better understanding the adaptation of ecosystems to climate change.

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.

Modelling the cycling of persistent organic pollutants (POPs) in the North Sea system: Fluxes, loading, seasonality, trends

The fate and cycling of two selected POPs is investigated for the North Sea system with an improved version of a fate and transport ocean model (FANTOM). The model uses atmospheric data from the EMEP MSC East POP model (Gusev et al., 2009), giving reasonable concentrations and seasonal distributions for the entire region, as opposed to the three observation stations that Ilyina et al. (2006) were limited to. Other model improvements include changes in the calculation of POP exchange between the water column and sediment.We chose to simulate the fate of two POPs with very different properties, γ-HCH and PCB 153. Since the fate and cycling of POPs are strongly affected by hydrodynamic processes, a high resolution version of the Hamburg Shelf Ocean Model (HAMSOM) was developed and utilised. Simulations were made for the period 1996–2005. Both models were validated by comparing results with available data, which showed that the simulations were of very satisfactory quality.Model results show that the North Sea is a net sink for γ-HCH and a net source to the atmosphere of PCB 153. Total masses of γ-HCH and PCB 153 in 2005 are reduced to 30% and 50%, respectively, of 1996 values.Storms resuspending bottom sediments into the water column mobilise POPs into the atmosphere and have the potential to deliver substantial loads of these POPs into Europe.

Levels and spatial distribution of gaseous polychlorinated biphenyls and polychlorinated naphthalenes in the air over the northern South China Sea

Monitoring marine persistent organic pollutants (POPs) is important because oceans play a significant role in the cycling of POPs. The South China Sea (SCS) is surrounded by developing countries in Southeast Asia which are centers of e-waste recycling and the ship dismantling industry. In this study, shipboard air samples collected over the SCS between September 6 and 22, 2005 were analyzed for polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs). The levels of ∑12PCBs ranged from 32.3 to 167pgm−3, with a mean value of 98.4±36.0pgm−3. Tetra-CBs were the predominant congeners. The concentrations of ∑18PCNs ranged from N.D. to 26.0pgm−3, with a mean value of 10.5±7.16pgm−3, and tri-CNs were predominant. The gaseous concentrations of PCBs and PCNs over the SCS were consistent with those over other seas and oceans. Compared with previous studies, it was found that the concentrations of PCBs exhibited an obviously declining trend. The measured PCB and PCN concentrations in the atmosphere over the SCS were influenced by their proximity to source regions and air mass origins. The highest gaseous PCB and PCN concentrations were found at sampling sites adjacent to the continental South China. E-waste recycling, ship dismantling and combustion in South China and some Southeast Asian countries might contribute PCBs and PCNs to the atmosphere of the SCS.

Plant uptake of organic chemicals: Current developments and recommendations for future research

Plant uptake of organic chemicals: Current developments and recommendations for future research

Microcosm studies on the air–soil exchange of hexachlorobenzene and polychlorinated biphenyls

Soils have an important role to play in supplying and receiving contaminants from the atmosphere, and in the global cycling of certain persistent organic pollutants (POPs). A microcosm study was conducted, in which some aspects of air-soil exchange likely to be important for the global cycling of POPs were simulated. HCB and PCBs were introduced into a sealed chamber, which contained soils of varying organic matter content, and in which soil mixing was a variable. Uptake of these compounds on to the soils was monitored over time. Subsequently, the primary chemical source was removed and further changes in the residues retained on the soils were monitored. The rates of uptake onto the different soil treatments are compared and the influence of the soil organic matter content and mixing evaluated. The implications for the global cycling of POPs are discussed.

Plant Uptake of Non-Ionic Organic Chemicals

Plant uptake of organic chemicals is an important process when considering the risks associated with land contamination, the role of vegetation in the global cycling of persistent organic pollutants, and the potential for industrial discharges to contaminate the food chain. There have been some significant advances in our understanding of the processes of plant uptake of organic chemicals in recent years; most notably there is now a better understanding of the air to plant transfer pathway, which may be significant for a number of industrial chemicals. This review identifies the key processes involved in the plant uptake of organic chemicals including those for which there is currently little information, e.g., plant lipid content and plant metabolism. One of the principal findings is that although a number of predictive models exist using established relationships, these require further validation if they are to be considered sufficiently robust for the purposes of contaminated land risk assessment or for prediction of the global cycling of persistent organic pollutants. Finally, a number of processes are identified which should be the focus of future research.

The role of soil organic carbon in the global cycling of persistent organic pollutants (POPs): interpreting and modelling field data

Soil is an important global reservoir for persistent organic pollutants (POPs). The interaction between air (which often receives the majority of emissions) and soil plays a key role in the long term environmental cycling and fate of these chemicals. Soil surveys have been carried out to try and estimate regional and global distribution/inventory of POPs. A correlation between soil POPs concentration and soil organic carbon (SOC) has been observed in background soils [Meijer et al., 2003. Global distribution and budget of PCBs and HCB in baqckground surface soils: implications for sources and environmental processes. Environ. Sci. Technol., 37, 667], provoking discussion about whether POPs will approach steady-state (or equilibrium) between air and SOC, on a global scale. This manuscript investigates this relationship and in particular how soil concentrations can be influenced by factors such as temperature, SOC content and physicochemical properties. A simple two box model designed to investigate parameters that are likely to affect air–soil exchange revealed that more volatile chemicals such as HCB are likely to achieve steady-state conditions between air and soil relatively quickly whilst relatively involatile chemicals, such as heavy PCBs, may take considerably longer and other compounds (e.g. OCDD) may never achieve it. These model calculations provide an insight into which fate processes (e.g. volatilisation or degradation) may control a chemicals fate in the terrestrial environment. A different modelling exercise was used to explore the complex interaction of environmental parameters, representative of ‘real world’ conditions to study their potential influence on POPs cycling at the European scale. Results from the model suggested that compound degradation rates in soil (linked to SOC content), temperature, vegetation cover and ecosystem C turnover are all likely to significantly influence POP air–soil exchange and fate.

Evidence for dynamic air-water coupling and cycling of persistent organic pollutants over the open Atlantic Ocean.

Ship-board air samples collected between The Netherlands and South Africa in January-February 2001 were analyzed for PCBs and selected organochlorine compounds. Broad latitudinal trends in compound concentrations were influenced by proximity to source areas, land, and air mass origin. Lowest concentrations were observed in the remote south Atlantic (1-32 degrees S), where sigma7PCB concentrations were approximately 10 pg m(-3). Here, a diurnal cycle was noted for some PCB congeners, with the daytime concentrations higher than the nighttime concentrations, typically by a factor of 1.5-2.5. The data are consistent with a close coupling of air-open ocean concentrations, which has important implications for future rates of POP removal from the global "recyclable pool". The observations are discussed in the context of the potential controlling variables. Interactions between the phytoplankton and the dissolved phase are implicated in controlling the observations made here and a hypothesis to explain the cycling trends is presented. However, the precise mechanisms remain unclear; further studies are urgently required to elucidate them.

Use of α-, β- and γ-hexachlorocyclohexane in Europe, 1970–1996

Data on current and historical usage of α-, β- and γ-hexachlorocyclohexane (HCH ) in Europe are presented. The data were collected and estimated as a part of a project studying the regional cycling of persistent organic pollutants (POPs) in the Baltic environment (Popcycling-Baltic). Better data on sources, environmental discharges and atmospheric emissions of HCH and other POPs are needed to study, and hopefully reduce, the impact of these pollutants on the environment. Substantial uncertainties are assigned to the estimated data for individual countries and years, but it seems likely that the general trend of usage in Europe is captured. The quality of the estimates is thought to improve in general throughout the period, thus, reflecting the availability of reliable data. The results suggest that 382 000 t of technical HCH and 81 000 t of lindane were used in Europe from 1970 to 1996. This is equivalent to an estimated cumulative usage of 259 000 t α-HCH, 135 000 t γ-HCH and 20 000 t β-HCH. The usage of technical HCH was the major source of γ-HCH until the late 1970s, and thereafter lindane became the dominating source of this isomer. The use of γ-HCH in 1996 was estimated to still be nearly one-third of the European usage in 1970. The pattern of decreasing concentrations in biota follows the pattern of reductions in usage for the studied period within the Baltic area.