Screening Criteria for Long-Range Transport Potential of Organic

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Screening Criteria for Long-Range Transport Potential of Organic Substances in Water Christiane Zarfl,†,§ Martin Scheringer,‡ and Michael Matthies† † ‡

Institute of Environmental Systems Research, University of Osnabr€uck, Germany Institute for Chemical and Bioengineering, ETH Zurich, Switzerland

bS Supporting Information ABSTRACT: Screening of long-range transport potential (LRTP) of organic chemicals in water requires the development of criteria in analogy to the existing LRTP criteria for airborne chemicals. According to the Stockholm Convention, compounds mainly partitioning into air are assumed to be prone to LRTP if they have a half-life in air of more than two days. Using mean flow velocities of European rivers (0.7
1 m/s) and of ocean currents running into the Arctic Ocean (0.28
0.9 m/s), we derived corresponding half-life criteria for freshwater and seawater (10 days and 90 days, respectively). Next, we calculated the characteristic travel distance (CTD) of several thousand chemicals from the Canadian Domestic Substances List (DSL) and all current POPs using the multimedia model ELPOS. This shows that the CTD in water dominates the CTD in air only for chemicals that are characterized by a large half-life in water and a low air
water partition coefficient (about 38% of the nonionic organic substances selected from the DSL). In particular, there are substances that are not classified as persistent compounds in water but exhibit higher CTDs for transport in water than for transport in air. Finally, we evaluated whether the LRTP boundary derived from POP reference chemicals has to be revised if LRTP in water is included and found that this boundary can be applied to all organic chemicals regardless of their transport in air or water.

’ INTRODUCTION The Stockholm Convention on Persistent Organic Pollutants (POPs),1 in short Stockholm Convention, assesses chemicals based on criteria for specific substance properties. It declares a substance to be a POP if it is persistent, bioaccumulates, shows adverse effects on humans and ecosystems and is subject to longrange environmental transport. Persistence means that the investigated compound does not degrade or degrades very slowly in at least one of the environmental compartments water, sediment, and soil. According to the Stockholm Convention, persistence is defined by criteria based on half-lives in water, sediment, and soil. Long-range transport of pollutants poses a risk to Polar or mountain regions, which are often especially vulnerable. However, transport of pollutants may occur via air or ocean currents or by accumulation in and transport with migrating animals. In addition, compounds partitioning into air are assumed to undergo LRTP if their half-life in air is greater than two days. In this way, a half-life screening criterion is explicitly given for organic compounds transported via air. In order to account for environmental partitioning, degradation and transport behavior, several metrics for LRTP have been developed based on multimedia box models. Although these concepts result from different approaches, most metrics lead to similar rankings of chemicals, which are assessed according to their LRTP.2 Therefore, in the following investigations we r 2011 American Chemical Society

applied the characteristic travel distance (CTD) as a metric of LRTP.3,4 The advantage of this approach is that the CTD is independent of the emission rate of chemicals, which makes it possible to compare the LRTP of different substances according to the physicochemical properties of the substances and their mode-of-entry (emission to air, or water). Furthermore, the CTD results, because they are derived with a multimedia environmental fate model, reflect the interplay of chemical degradation and partitioning between different environmental media, including sorption to settling particles. The CTD concept has already been employed to relatively assess halogenated aromatic compounds5
7 and current-use pesticides (CUPs).8 Most of these compounds, even the CUPs, mainly undergo atmospheric transport.9 Nevertheless, many chemicals are directly emitted into surface waters or may be washed out if released to the atmosphere since many of them are hydrophilic. Thus, they may be transported with rivers and finally ocean currents into remote regions where they directly pose a risk to sensitive organisms and ecosystems via the water compartment, which represents the habitat of several marine organisms at the Received: April 13, 2011 Accepted: October 19, 2011 Revised: October 18, 2011 Published: October 19, 2011 10075

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Environmental Science & Technology base of the food chain. But, in contrast to the criteria given for atmospheric long-range transport potential, criteria for LRTP in fresh or marine water are not provided under the Stockholm Convention. The objectives of our investigations were to develop and discuss approaches for LRTP criteria for organic compounds partitioning into the water compartment in order to include these compounds in the assessment of long-range transport potential. We first derive half-life screening criteria for LRTP in fresh and marine water in analogy to the existing half-life criterion of two days in air. The purpose of this step is to establish a criterion that can be used in the regulatory context, for example by the POP Review Committee of the Stockholm Convention. Second, we identify from the Canadian Domestic Substances list a set of chemicals that exceed the half-life criterion for freshwater and have a high CTD in water, that is, are likely to undergo longrange transport in water. Third, we investigate whether LRTP in water changes the results for LRTP of established reference chemicals with POPs characteristics. These chemicals were used by Klasmeier et al.10 to establish a LRTP threshold of typical POPs and we evaluate whether LRTP in water makes it necessary to revise this threshold.

’ MATERIALS AND METHODS Half-Life Criteria. Half-life criteria for screening organic compounds on their LRTP in fresh and marine water were developed in analogy to the existing half-life criterion of two days for transport of chemicals with atmospheric currents. It should be noticed that the processes determining chemical half-life in air, that is, degradation or deposition to the ground, are not further specified. However, in the assessment procedure actually employed by the POP Review Committee, degradation half-lives are used for screening, whereas removal by exchange with or advection to adjacent compartments, for example, deposition to soil, are not considered loss processes. To derive the half-life criteria for freshwater and seawater, we assumed a mean continental wind velocity of 4 m/s at 10 m above the ground (regional scale) and a mean global wind velocity of 18 m/s in the upper troposphere higher than 1 km above the ground (global scale).3,11,12 On this basis, the distances (L) that are traveled by an airborne chemical within two days either at 4 m/s or at 18 m/s, were calculated on the regional and global scale, respectively. These distances were divided by flow velocities of large European rivers (freshwater on a regional scale) and main ocean currents (marine water on a global scale) running into the Arctic Ocean, which then yields the respective half-life criteria for fresh and marine water, respectively. Similar to air, the processes determining these half-lives (degradation, volatilisation, or sedimentation) are not further specified. The purpose of the half-life criteria is to be used in the regulatory context of the Stockholm Convention on POPs. They are not intended to reflect the natural variability of flow velocities in different types of aquatic systems, but to indicate the extent of long-range transport that would occur when a chemical is present in a relatively fast flowing river or ocean current. Characteristic Travel Distance. The characteristic travel distance (CTD) is a spatial metric similar to the temporal metric of the half-life criterion. It describes the distance, which a substance can travel until its concentration drops to 1/e (approximately 37%) of its initial value.13 In a multimedia model with a moving air compartment and under steady-state conditions, the

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CTD in air (CTDA) is proportional to the substance’s residence time in air τA and the wind speed uA, which is assumed to be constant3 mA CTDA ¼ uA 3 τA ¼ uA 3 ð1Þ Itot where mA is the substance mass in the air compartment (kg) and Itot is the total input (kg/day), which equals the total loss, because steady-state is assumed. In analogy, the CTD in water (CTDW) can be calculated based on the flow velocity uW and the residence time in water τW14 mW CTDW ¼ uW 3 τW ¼ uW 3 ð2Þ Itot where mW is the substance mass in the water compartment at steady-state. Model Application. In order to take partitioning and degradation of organic substances in all environmental compartments (air, freshwater, sediment, and soil) into account, the multimedia model ELPOS 2.2 was applied (http://www.usf.uos.de/usf/ arbeitsgruppen/ASW/ELPOS.de.html) providing the calculation of CTD. This model is a simplified version of the regional scale model of EUSES-SimpleBox which is legally accepted for chemical assessment in the European Union.15 The model includes the environmental compartments air, freshwater, sediment, and three different kinds of soil (natural, agricultural, and urban/rural). It represents a level-III fugacity model assuming steady state but accounting for the emission compartment and for transfer processes between the different compartments and advective outflow of chemical out of the model system. All environmental conditions are considered constant and all processes follow first-order kinetics. More details on the model formulation and parametrization are given by Matthies and Beyer,4 and Matthies et al.8 CTD strongly depends on the mode-of-entry, that is, the emission compartment. Thus, ELPOS separately calculates CTDA and CTDW for emission into air and water, respectively. CTDW/CTDA Ratio. Since the results obtained for the CTD are independent of emission rates, the CTD in air and water can be used to compare chemicals according to their LRTP properties. We applied the model ELPOS to simulate hypothetical compounds that were characterized by a range of partition coefficients and degradation half-lives in air and water. Logarithmic values of the partition coefficient between air and water (log KAW) ranged from
11 to +3, whereas the logarithmic range of the partition coefficient between n-octanol and water (log KOW) covered values from
1 to +12. Degradation half-lives in air and water varied between 4 hours and 10 years. No degradation, that is total persistence, was assumed in sediment and soil, which is certainly a conservative assumption. The ratio CTDW/CTDA was displayed in chemical space plots as a function of log KAW and log KOW to determine for which chemical properties transport in water dominates the transport in air.16,17 For each combination of half-lives in air and water, CTDW/CTDA was displayed in dependence of the partition coefficients. In a second step we selected nonionic organic compounds from the Canadian Domestic Substance List (DSL)18 and estimated their substance properties (molar mass, KOW, KAW) and environmental half-lives in air, water, soil, and sediment with the software package EPISuite v4.0.19 CTDW and CTDA were simulated with the multimedia model ELPOS to determine the fraction of DSLcompounds which are predominantly transported in the water compartment. The ratio of CTDW to CTDA indicates the 10076

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Table 1. Half-Life Criteria (t1/2(W)) Derived from Selected European Rivers (Regional Scale: 700 m) and Ocean Currents Running into the Arctic (Global Scale: 3000 km) flow velocity [m s
1]

t 1/2(W) [d]

21

Weser

0.7

11.6

Rh^one22

1.0

Gulf Stream23

0.28

Kuroshio Current24

0.90

39

Bering Strait25

0.33

105

8.1 124

dominant transport pathway. In particular, we calculated the CTD for those compounds from the Canadian DSL that are not persistent in water but satisfy the suggested half-life in water designation (10 days). Of these, we determined the compounds, which are predominantly transported within the water compartment. LRTP Classification. ELPOS offers an approach to classifying substances as persistent or/and showing a potential of long-range transport. This concept is based on a plot of LRTP against overall persistence (POV).5 POV is the reciprocal value of the summarized degradation rate constants of each compartment weighted by the steady-state mass fraction in the respective compartment.20 In this way, the temporal and spatial scale of organic substances can be displayed simultaneously. ELPOS uses maximum POV and CTD values derived from the three emission scenarios into air, water, and soil.16 Klasmeier et al.10 established a set of reference chemicals with well-known substance properties and environmental behavior. POV and CTD values of these reference chemicals calculated with ELPOS were displayed in the “maximum POV”-“maximum CTD” plot. These reference chemicals are mainly prone to airborne transport and indicate a LRTP threshold for POP-like chemicals of 5200 km. However, some of the new POPs included in Annex A, B and C of the Stockholm Convention in May 2009 (“POPs 2009”) primarily partition into the water compartment. To investigate whether LRTP in water makes it necessary to revise the LRTP threshold of 5200 km, CTD in air and water were calculated with ELPOS for all current POPs including the “POPs 2009”.

’ RESULTS AND DISCUSSION Half-Life Criteria. According to the Stockholm Convention, substances show long-range transport potential that are characterized by half-lives in air larger than two days. Assuming a continental wind speed of 4 m s
1 at 10 m above the ground3,11 this half-life can be converted into a corresponding transport distance, Lregional, of 700 km. This assumption includes constant environmental conditions and a homogeneous substance distribution. On a global scale, however, transport of air and, thus, of persistent semivolatile organic compounds does not only occur within the lower ground-level layers of the atmosphere, but especially within the free troposphere more than 1 km above the ground. This atmospheric layer is not, in contrast to the groundlevel layers, influenced by friction resulting from the relief of the earth surface. Consequently, a significantly higher wind speed of about 8 m s
1 (1 km height) up to 24 m s
1 (11 km height) can be expected worldwide.12 Assuming a global average wind speed in the free troposphere of 18 m s
1 leads to a corresponding transport distance, Lglobal, of 3000 km. On the continental scale, local river properties such as water flow volume and coarseness of the riverbed are not crucial.

Thus, the average flow velocity describing the mean residence time of a substance over the whole course of a river is a parameter equivalent to the average continental wind speed. Mean flow velocities of large European rivers range from 0.7 to 1.0 m s
1 (Table 1), which in combination with Lregional = 700 km result in half-life criteria for LRTP in freshwater of 8
12 days. These values correspond to the mean residence time of the river Rhine in Germany (approximately 7 days) and from the source to the mouth (approximately 13 days), respectively. On a global scale, remote regions like the Arctic are especially endangered by long-range transport of pollutants emitted on the northern hemisphere, for example, in Europe or Northern America. Thus, main ocean currents running into the Arctic are additionally considered for the derivation of a half-life criterion for LRTP in marine water. Flow velocities of the Gulf Stream transporting Atlantic water beyond the Arctic Circle, of the Kuroshio Current, which is the Pacific analogue to the Gulf Stream, and of the Bering Strait range from 0.28 to 0.9 m s
1 (Table 1). In combination with Lglobal, these transport velocities result in a half-life criterion of 40 days to 130 days for LRTP in oceans. This is significantly higher than the criterion derived from river data on a regional scale (8
12 days). Consequently, a LRTP half-life criterion for the assessment of pollutant transport in water should be defined in accordance to the spatial scale: If the pollutant of concern is emitted into rivers, a half-life criterion of 10 days can be applied. On a global scale, however, a substance is prone to LRTP in water if it is characterized by a half-life in marine water larger than 90 days. Our screening criteria for LRTP in water are determined by our selection of water flow velocities in rivers and ocean currents. We selected relatively high, but still plausible and empirically observed flow velocities, because these lead to relatively short half-life values of 10 and 90 days. This is intended because in this way more chemicals exceeding the half-life criteria are identified than if we had used lower flow velocities. In other words, our selection of flow velocities makes the half-life criteria for LRTP in water relatively conservative. We think this is appropriate for screening level criteria. The persistence criterion in water is defined to be 60 days according to the Stockholm Convention. In the European chemicals legislation, REACH,26 40 days in fresh or estuarine water and 60 days in marine water and for very persistent chemicals are defined. This means that on a global scale compounds characterized by LRTP are already considered by the persistence criteria for water and do not need an additional assessment step. However, these results also indicate that on a regional scale the criterion for LRTP in freshwater of 10 days is below the persistence criterion in water. Thus, substances that are not considered persistent in water may still be prone to longrange transport in freshwater. This is of special concern since the Arctic Ocean is not only influenced by approximately 37.8  104 km3 of seawater per year27 but also by about 36.4  104 km3 of freshwater, especially draining from large Russian and Canadian arctic rivers.28 It has already been shown that these rivers are contaminated with persistent organic pollutants and pesticides29 and may thus also serve as point sources for organic compounds prone to long-range transport in freshwater. The hydrological regime of arctic rivers is characterized by high flows in early summer (May
June) and low flows in winter,30 which makes a determination of a typical flow velocity difficult. Arctic river systems are more complex with higher velocities upstream and low velocities in various areas of reservoirs or impoundments. 10077

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Environmental Science & Technology Thus, the range of flow velocities would be greater than for the considered large European rivers. However, low flow velocities shift the half-life criteria for LRTP in water to higher values, for instance 46 days for 0.2 m/s, which is less conservative. The same argument holds for transport in marine systems. We selected ocean currents leading to the arctic systems, which have higher

Figure 1. Mass fractions at steady state calculated with ELPOS after emission into air or water of reference chemicals (congeners of polychlorinated biphenyls (PCB-28, PCB-101, PCB-180), hexachlorobenzene (HCB), carbon tetrachloride (CCl4)) and of persistent organic pollutants included in the Stockholm Convention in May 2009 (POPs 2009: isomers of hexachlorocyclohexane (α-HCH, β-HCH, lindane), chlordecone, hexabromobiphenyl (HBB), pentabromodiphenylether (BDE-99), pentachlorobenzene (PeCB), perfluorooctanesulfonic acid (PFOS)). Missing bars indicate that fractions in air or water are virtually zero.

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flow velocities than general circulation velocities in the Atlantic or Pacific Ocean. We here provide two screening criteria whose application depends on the respective spatial scale (regional vs global). As far as exposure of remote regions is concerned, the global scale might seem to be of major importance. Nevertheless, rivers, on a regional scale, serve as main exposure pathways of substances prone to transport into the oceans. Thus, for chemical assessment it is required to at least consider the environmental distribution and degradation behavior. This is taken into account in the CTD approach with CTDs calculated by means of the ELPOS model, which includes a moving freshwater compartment representing a river. CTD. The CTD describes the transport distance that a substance can be transported before its concentration drops to 37% of its initial concentration. The essential aspect of calculating the CTD with a multimedia model is the consideration of the substance’s distribution behavior and degradation processes in combination. The model ELPOS yields CTD values as a relative measure for LRTP. Based on a set of reference chemicals of legacy POPs, a LRTP threshold was defined in order to identify further compounds with high and POP-typical LRTP.10 This model-based approach is also implemented in the assessment tool of the OECD11 and is employed by the POP Review Committee of the Stockholm Convention to evaluate potential POPs that might be included in the Stockholm Convention. The set of reference chemicals consists of semivolatile POPs that are mainly transported in the air. Substance transport is dominated by advection in air, because the average wind speed is 1
2 orders of magnitude higher than the velocity of ocean currents. Some of the POPs, however, that were included in the Stockholm Convention in 2009 (“POPs 2009”) are predominantly distributed into the water compartment. Figure 1 shows

Figure 2. Chemical Space Plots (log KAW vs log KOW) of log (CTDW/CTDA) calculated for 4064 hypothetical compounds with the multimedia fate model ELPOS and displayed for four combinations of half-lives in air and water/soil/sediment). Blue indicates chemicals with predominant transport in water. 10078

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Environmental Science & Technology the maximum fractions in air and water at steady-state for the reference chemicals as well as for the “POPs 2009” derived with ELPOS for emissions into air or water. Only lindane (γ-hexachlorocyclohexane, γ-HCH), chlordecone, and perfluorooctanesulfonic acid (PFOS) are more likely to distribute into water than into the much faster transport compartment air. Therefore, it is of interest to identify those substance properties that lead to a dominating substance transport in water compared to transport in air. A set of 4064 hypothetical compounds covering the environmentally relevant range of partition coefficients (KAW and KOW) and different half-lives in air and water were evaluated for their CTD in water in relation to their CTD in air. Figure 2 displays the ratio CTD W/CTDA for different half-life combinations in chemical space plots, that is, as function of log KOW and log KAW. This shows that under the environmental conditions assumed in ELPOS the CTD in water exceeds the CTD in air by more than an order of magnitude if log KOW < 4 and log KAW <
4 (Figure 2a and b). With increasing

Figure 3. Fractions of the relation between CTD in water (CTDW) and CTD in air (CTDA) of nonionic organic substances contained in the Canadian Domestic Substance List. About 38% of the investigated compounds show dominant transport in water (log (CTDW/ CTDA) > 0).

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persistence in air, the log KAW boundary for dominant water transport decreases, because a stronger shift of steady-state concentrations toward the water compartment compensates for the more effective transport and thus higher CTD values in air. Thus, if in air the substance is degraded very slowly (four weeks) instead of within a few hours (Figure 2a), substance transport in water may only dominate transport in air if the substance is characterized by a log KAW even smaller than
6 (Figure 2b). This correlation is also reflected in the change of the CTDW/ CTDA ratio that is observed when the substance half-life in water, t1/2(W), is varied. Model results are even more sensitive to t1/2(W) than to half-life in air (t1/2(A)). With decreasing half-life in water, log KOW
log KAW combinations that result in a dominant substance transport in the water compartment finally disappear (Figure 2c and 2d). Therefore, simulations with continuously decreasing t1/2(W) revealed that only if half-life in water is above 10 days there are log KOW
log KAW combinations showing a CTDW larger than CTDA. Thus, the evaluation of LRTP in air and water based on the CTD approach has shown that also substances that are not classified as persistent compounds (t1/2(W) below 40 days) may be prone to a more efficient transport in water than in air. The deduced boundaries for KAW and t1/2(W) may be different in other models than ELPOS due to a different geometry of the environmental compartments and parametrization of phase exchange processes. Nevertheless, transport in water is only dominant for those compounds that are characterized by a large half-life in water and a low partition coefficient between air and water (KAW). Simulations of nonionic organic substances selected from the Canadian Domestic Substance List with ELPOS reveal that about 38% of the compounds show a higher CTDW than CTDA (Figure 3). Most of them have a CTD in water not greater than 1 order of magnitude than that in air. In addition, the DSL contains 4069 nonionic organic compounds which are not persistent in water (t1/2(W) < 40 d) but exceed the half-life criterion of 10 days in freshwater as derived above. Among these, 1238 compounds are primarily transported in water (CTDW/CTDA > 1), 76 of them exceed a CTDW to CTDA ratio of 10 (Table S1 of the Supporting Information),

Figure 4. Double logarithmic plot of maximal characteristic travel distance (CTD) vs maximal overall persistence (POV). Results calculated with ELPOS for POPs included in Annexes A, B, and C in May 2009 (POPs 2009). Variable input data taken from the Risk Profiles of the Stockholm Convention31,32 (Table S1 of the Supporting Information). LRTP and Pov boundaries from Klasmeier et al.10 10079

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Environmental Science & Technology which underlines that even substances that are not classified as persistent compounds in water may be prone to more efficient transport within the water compartment than in air. LRTP Classification. Three of the eight “POPs 2009”, namely PFOS, chlordecone and lindane, show a significantly higher mass fraction in water at steady-state than in air (Figure 1). Parameter values according to the Stockholm Convention Risk Profiles31,32 of all ”POPs 2009” are summarized in the Supporting Information (Table S2). However, this condition (partitioning into water) is not yet sufficient to yield a dominant substance transport in the water compartment. Model simulations reveal that only the highly soluble PFOS has a higher CTD in water than in air. The transport of chlordecone occurs in both compartments to a similar extent, because chlordecone has a high persistence in all compartments (Supporting Information Table S1). Lindane, in contrast, still has a considerable substance fraction in air at steady-state (Figure 1) and is characterized by a half-life in water that is only 1 order of magnitude greater than the half-life in air. Figure 4 shows the maximum values of CTD and POV resulting from emission scenarios into air, water, and soil. Plotted are the mean values with maximum and minimum ranges arising from uncertain and variable input values as given in the Risk Profiles.31,32 PFOS is the only compound characterized by a CTD in water that exceeds the CTD in air and also the LRTP boundary of 5200 km. Mean CTD values of the mainly airborne compounds α-HCH, β-HCH, lindane, hexabromobiphenyl (HBB), and pentachlorobenzene (PeCB) are as well above the LRTP boundary of 5200 km. Only chlordecone and pentabromodiphenylether (BDE-99) reveal CTD values below the LRTP boundary derived by Klasmeier et al.10 from the POP reference chemicals PCB-28 and PCB-180 in ELPOS. Due to variable and uncertain substance property data, CTD values for PCB-28 and PCB-180 also cover a range of 1 order of magnitude. Under consideration of this uncertainty, which affects the LRTP values, our model results for BDE-99 and for chlordecone are close to the lower bound of the CTD range of PCB-28 and, thus, of the LRTP boundary. In addition, the CTD values of the eight “POPs 2009” are all higher than CTD values of the established nonPOP-references. We conclude that the LRTP boundary derived from the POP reference chemicals can be applied without modification to all organic chemicals currently listed as POPs regardless of their main transport pathway (air or water).

’ ASSOCIATED CONTENT

bS

Supporting Information. Summary of physical-chemical parameter values needed for simulation with ELPOS as given in the Risk Profiles of the Stockholm Convention; Table of organic, nonionic compounds from the DSL that are not persistent in water but are primarily transported within the water compartment. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

Phone: +49 (0)541 969-2576; e-mail: [email protected]. Present Addresses §

Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.

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’ ACKNOWLEDGMENT We thank Mark Bonnell (Environment Canada) for providing the Canadian Domestic Substance List and Christian Ehling (Institute of Environmental Systems Research) for establishing a routine to produce the chemical space plots. Funding by the German Federal Environmental Agency is gratefully acknowledged (FKZ 370965409). ’ REFERENCES (1) UNEP. Stockholm Convention on Persistent Organic Pollutants; United Nations Environment Programme: Geneva, Switzerland, 2001; www.pops.int. (2) Fenner, K.; Scheringer, M.; MacLeod, M.; Matthies, M.; McKone, T.; Stroebe, M.; Beyer, A.; Bonnell, M.; Le Gall, A. C. Comparing estimates of persistence and long-range transport potential among multimedia models. Environ. Sci. Technol. 2005, 39, 1932–1942. (3) Beyer, A.; Mackay, D.; Matthies, M.; Wania, F.; Webster, E. Assessing long-range transport potential of persistent organic pollutants. Environ. Sci. Technol. 2000, 34, 699–703. (4) Beyer, A.; Matthies, M. Criteria for Atmospheric Long-range Transport Potential and Persistence of Pesticides and Industrial Chemicals, Report No. 7/02; German Federal Environmental Agency, E. SchmidtVerlag: Berlin, 2002; ISBN 3-503-06685-3. (5) Scheringer, M. Persistence and spatial range as endpoints of an exposure-based assessment of organic chemicals. Environ. Sci. Technol. 1996, 30, 1652–1659. (6) Wania, F. Assessing the potential of persistent organic chemicals for long-range transport and accumulation in polar regions. Environ. Sci. Technol. 2003, 37, 1344–1351. (7) Shen, L.; Wania, F.; Lei, Y. D.; Teixeira, C.; Muir, D. C. G.; Bidleman, T. F. Atmospheric distribution and long-range transport behavior of organochlorine pesticides in North America. Environ. Sci. Technol. 2005, 39, 409–420. (8) Matthies, M.; Klasmeier, J.; Beyer, A.; Ehling, C. Assessing persistence and long-range transport potential of current-use pesticides. Environ. Sci. Technol. 2009, 43, 9223–9229. (9) Muir, D. C. G.; Teixera, C.; Wania, F. Empirical and modeling evidence of regional atmospheric transport of current-use pesticides. Environ. Toxicol. Chem. 2004, 23, 2421–2432. (10) Klasmeier, J.; Matthies, M.; Fenner, K.; Scheringer, M.; Stroebe, M.; Le Gall, A.-C.; MacLeod, M.; McKone, T. E.; van de Meent, D.; Wania, F. Application of multimedia models for screening assessment of long-range transport potential and overall persistence. Environ. Sci. Technol. 2006, 40, 53–60. (11) Wegmann, F.; Cavin, L.; MacLeod, M.; Scheringer, M.; Hungerb€uhler, K. The OECD software tool for screening chemicals for persistence and long-range transport potential. Environ. Modell. Softw. 2009, 24, 228–237. (12) Archer, C. L.; Jacobson, M. Z. Evaluation of global wind power. J. Geophys. Res. 2005, 110, 1–20. (13) Bennett, D. H.; McKone, T. E.; Matthies, M.; Kastenberg, W. E. General formulation of characteristic travel distance for semivolatile organic chemicals in a multi-media environment. Environ. Sci. Technol. 1998, 32, 4023–4030. (14) Beyer, A.; Matthies, M. Long-range transport potential of semivolatile organic chemicals in coupled air-water systems. Environ. Sci. Pollut. Res. 2001, 8, 173–179. (15) European Commission. EUSES—The European Union System for the Evaluation of Substances. http://ecb.jrc.ec.europa.eu/euses/ (accessed March 2011). (16) Stroebe, M.; Scheringer, M.; Hungerb€uhler, K. Measures of overall persistence and the temporal remote state. Environ. Sci. Technol. 2004, 38, 5665–5673. (17) Meyer, T.; Wania, F.; Breivik, K. Illustrating sensitivity and uncertainty in environmental fate models using partitioning maps. Environ. Sci. Technol. 2005, 39, 3186–3196. 10080

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Environmental Science & Technology

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