Rainer Lohmann

Critical Review of Low-Density Polyethylene’s Partitioning and Diffusion Coefficients for Trace Organic Contaminants and Implications for Its Use As a Passive Sampler

Polyethylene (PE)-water equilibrium partitioning constants, K(PEw), were reviewed for trace hydrophobic organic contaminants (HOCs). Relative standard deviations were <30% for phenanthrene, anthracene, fluoranthene, and pyrene implying excellent reproducibility of K(PEw) across laboratories and PE sources. Averaged K(PEw) values of various HOCs were best correlated with aqueous solubility, logC(w)(sat)(L): logK(PEw) = -0.99(±0.029)logC(w)(sat)(L) + 2.39(±0.096) (r(2) = 0.92, SE = 0.35, n = 100). For 80% of analytes, this equation predicted logK(PEw) within a factor of 2. A first-order estimation of K(PEw) can be obtained assuming constant solubility of the compounds in the PE, such that the variation in C(w)(sat)(L) determines the differences in K(PEw). For PE samplers, K(PEw) values do not change with the thickness of the PE sampler. The influence of temperature on K(PEw) seems dominated by solubility-changes of the compound in water, not in PE. The effect of salt is rather well understood, using a Schetschenow-style approach. The air-PE partitioning constant, K(PEa), can be approximated as the ratio of K(PEw)/K(aw) (the air-water partitioning constant). A critical review of diffusivities in PE, D(PE), suggests that best results are obtained when using the film-stacking method. A good correlation is then found between D(PE) and molar volume, V(m) (Ǻ(3)/mol): logD(PE) (m(2)/s) = 0.0145(±0.001)V(m) + 10.1(±0.20) (r(2) = 0.76, SE = 0.24, n = 74).

A Thermodynamic Approach for Assessing the Environmental Exposure of Chemicals Absorbed to Microplastic

The environmental distribution and fate of microplastic in the marine environment represents a potential cause of concern. One aspect is the influence that microplastic may have on enhancing the transport and bioavailability of persistent, bioaccumulative, and toxic substances (PBT). In this study we assess these potential risks using a thermodynamic approach, aiming to prioritize the physicochemical properties of chemicals that are most likely absorbed by microplastic and therefore ingested by biota. Using a multimedia modeling approach, we define a chemical space aimed at improving our understanding of how chemicals partition in the marine environment with varying volume ratios of air/water/organic carbon/polyethylene, where polyethylene represents a main group of microplastic. Results suggest that chemicals with log KOW > 5 have the potential to partition >1% to polyethylene. Food-web model results suggest that reductions in body burden concentrations for nonpolar organic chemicals are likely to occur for chemicals with log KOW between 5.5 and 6.5. Thus the relative importance of microplastic as a vector of PBT substances to biological organisms is likely of limited importance, relative to other exposure pathways. Nevertheless, a number of data-gaps are identified, largely associated with improving our understanding of the physical fate of microplastic in the environment.

Use of passive sampling devices for monitoring and compliance checking of POP concentrations in water

BackgroundThe state of the art of passive water sampling of (nonpolar) organic contaminants is presented. Its suitability for regulatory monitoring is discussed, with an emphasis on the information yielded by passive sampling devices (PSDs), their relevance and associated uncertainties. Almost all persistent organic pollutants (POPs) targeted by the Stockholm Convention are nonpolar or weakly polar, hydrophobic substances, making them ideal targets for sampling in water using PSDs. Widely used nonpolar PSDs include semi-permeable membrane devices, low-density polyethylene and silicone rubber.Results and discussionThe inter-laboratory variation of equilibrium partition constants between PSD and water is mostly 0.2–0.5 log units, depending on the exact matrix used. The sampling rate of PSDs is best determined by using performance reference compounds during field deployment. The major advantage of PSDs over alternative matrices applicable in trend monitoring (e.g. sediments or biota) is that the various sources of variance including analytical variance and natural environmental variance can be much better controlled, which in turn results in a reduction of the number of analysed samples required to obtain results with comparable statistical power.ConclusionCompliance checking with regulatory limits and analysis of temporal and spatial contaminant trends are two possible fields of application. In contrast to the established use of nonpolar PSDs, polar samplers are insufficiently understood, but research is in progress to develop PSDs for the quantitative assessment of polar waterborne contaminants. In summary, PSD-based monitoring is a mature technique for the measurement of aqueous concentrations of apolar POPs, with a well-defined accuracy and precision.

Global Aquatic Passive Sampling (AQUA-GAPS): Using Passive Samplers to Monitor POPs in the Waters of the World1

The Stockholm Convention (SC) on persistent organic pollutants (POPs) has highlighted the global risk(s) posed by organic contaminants that are persistent, bioaccumulate, are prone to long-range transport, and have the potential to cause adverse effects in humans and wildlife (1). As a result of the SC, monitoring programs are underway to record concentrations of POPs across the globe over time, with atmospheric sampling and human milk as the recommended media (2). The global atmospheric passive sampling (GAPS) program, which utilizes passive air sampling devices at monitoring sites on all continents, mostly in remote regions, has demonstrated the potential for global coverage (3, 4). While data from GAPS addresses the atmospheric compartment and potentially plants and soils exchanging with air, it does not readily address prevailing concentrations or trends in aquatic environments. A major concern with POPs is their biomagnification with top predators that rely on aquatic food webs, including humans, polar bears, seabirds, toothed whales, and seals (2, 5, 6). Often, the consumption of fish, and of marine mammals, is one of the main routes of exposure for humans (7). Hence, being able to sample the presence and longerterm trends of POPs in the water column would provide invaluable information related to long-term (human and aquatic wildlife) exposure. Additionally, monitoring POPs in water would provide vital information on whether reductions in primary emissions of POPs result in reduced concentrations of POPs in receiving waters, and ultimately in global ocean waters and aquatic foodchains. Conversely, as air concentrations of POPs are reduced due to bans and controls on use, oceans could become a major source of POPs to the air-this has been inferred from Arctic and Great Lakes air and water monitoring data (8–10). Deploying passive samplers at these sites coupled with matching air sampling (e.g., (11)) would enable a direct estimation of the direction of air-water exchange fluxes as a response to changing atmospheric concentrations. Concentrations of POPs in receiving surface waters reflect the balance between emissions delivered via rivers and those via atmospheric deposition, rerelease from POPs accumulated in sediments, and volatilization (12). Tracking POPs in water thus provides an important, unique perspective on the effectiveness of reducing emissions and lowering of exposure. Concentrations of POPs in surface water are directly linked to their bioaccumulation in the foodchain (13, 14); hence, knowing dissolved concentrations in the water enables a direct prediction of concentrations in aquatic species using bioaccumulation factors or lipid-water partitioning and food web (trophic) models (15, 16). In several parts of the world, bivalve molluscs are being used as sentinel organisms to reflect on water quality (e.g., “mussel watch”, refs 2, 17–19). Using bivalves for (bio)monitoring has the advantages of directly obtaining data on species consumed by humans, and information on bioaccumulation and bioavailability of POPs under field conditions. However, working with live organisms has several drawbacks that render their global use difficult at best. For example, there is no single species that could be used across the entire world. Purchasing, deploying, and analyzing bivalves is costly and requires trained personnel. Bivalves are generally deployed 1 Editor’s Note: This manuscript was submitted prior to ES&T changing its manuscript parameters for Viewpoints. For the new format, please read the details at http://pubs.acs.org/doi/abs/ 10.1021/es903081n. RA IN ER LO HM AN N /A CS DO I1 0.1 02 1/ ES 80 05 18 G Environ. Sci. Technol. 44, 860–864

Gas-particle partitioning of PCDD/Fs in daily air samples

Eight short-term (24–48 h) air samples were taken at Lancaster, UK, to study the gas–particle partitioning of PCDD/Fs. Sampling dates in autumn 1997 were selected with a view to minimising temperature fluctuation during the sampling events. ΣCl4-8DD/Fs (ΣTEQ) for the first 6 samples were 1.1–3.6 pg m−3 (15–44 fg TEQ m−3), typical of a rural site; two other samples had ΣCl4-8DD/Fs of 18 and 7.9 pg m−3, with 320 and 100 fg TEQ m−3. The observed gas–particle distributions varied from 0–34% particle-bound for Cl2/3DD/Fs to >70% for Cl6-8DD/Fs. Measured particle-bound fractions were compared to theoretical estimates of their distribution based on the Junge–Pankow model using three different reported sets of vapour pressures. The best correlation was obtained using vapour pressures derived from measured GC-retention time indices (Eitzer and Hites, 1988). Plotting log partition coefficient (Kp) versus log sub-cooled liquid vapour pressure (pL) gave excellent correlations with slopes of roughly −1 for all homologue groups. 2, 3, 7, 8-substituted congeners showed slopes of −1 for the first five sampling events. It is proposed that kinetic factors at the low ambient temperatures, coupled with additional emissions during the last sampling events resulted in non-equilibrium partitioning.

Perfluoroalkyl Acids in the Atlantic and Canadian Arctic Oceans

We report here on the spatial distribution of C(4), C(6), and C(8) perfluoroalkyl sulfonates, C(6)-C(14) perfluoroalkyl carboxylates, and perfluorooctanesulfonamide in the Atlantic and Arctic Oceans, including previously unstudied coastal waters of North and South America, and the Canadian Arctic Archipelago. Perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) were typically the dominant perfluoroalkyl acids (PFAAs) in Atlantic water. In the midnorthwest Atlantic/Gulf Stream, sum PFAA concentrations (∑PFAAs) were low (77-190 pg/L) but increased rapidly upon crossing into U.S. coastal water (up to 5800 pg/L near Rhode Island). ∑PFAAs in the northeast Atlantic were highest north of the Canary Islands (280-980 pg/L) and decreased with latitude. In the South Atlantic, concentrations increased near Rio de la Plata (Argentina/Uruguay; 350-540 pg/L ∑PFAAs), possibly attributable to insecticides containing N-ethyl perfluorooctanesulfonamide, or proximity to Montevideo and Buenos Aires. In all other southern hemisphere locations, ∑PFAAs were <210 pg/L. PFOA/PFOS ratios were typically ≥1 in the northern hemisphere, ∼1 near the equator, and ≤1 in the southern hemisphere. In the Canadian Arctic, ∑PFAAs ranged from 40 to 250 pg/L, with perfluoroheptanoate, PFOA, and PFOS among the PFAAs detected at the highest concentrations. PFOA/PFOS ratios (typically ≫1) decreased from Baffin Bay to the Amundsen Gulf, possibly attributable to increased atmospheric inputs. These data help validate global emissions models and contribute to understanding of long-range transport pathways and sources of PFAAs to remote regions.

Polychlorinated biphenyls in air and water of the North Atlantic and Arctic Ocean

Air and seawater samples were collected on board the R/V Polarstern during a scientific expedition from Germany to the Arctic Ocean during June–August 2004. The air data show a strong decline with latitude with the highest polychlorinated biphenyl (PCB) concentrations in Europe and the lowest in the Arctic. ΣICES PCBs in air range from 100 pg m−3 near Norway to 0.8 pg m−3 in the Arctic. A comparison with other data from previous and ongoing land-based air measurements in the Arctic region suggests no clear temporal decline of PCBs in the European Arctic since the mid-1990s. Dissolved concentrations of Σ6PCBs (28/31, 52, 101, 118, 138, 153) in surface seawater were <1 pg L−1. Dominant PCBs in seawater were 28/31 and 52 (0.1–0.44 pg L−1), with PCBs 101, 118, and 138 < 0.1 pg L−1. In seawater, PCB 52 displayed the highest concentrations in the northernmost samples, while PCBs 101, 118, and 138 showed slightly decreasing trends with increasing latitude. Fractionation was observed for PCBs in seawater with the relative abundance of PCBs 28 and 52 increasing and that of the heavier congeners decreasing with latitude. However, in air only 15–20% of the variability of atmospheric PCBs can be explained by temperature. Owing to large uncertainties in the Henrys Law constant (HLC) values, fugacity quotients for PCBs were estimated using different HLCs reported in the literature. These indicate that on average, deposition dominates over volatilization for PCBs in the Arctic region with a strong increase in the middle of the transect near the marginal ice zone (78–79°N). The increase in fugacity ratio is mainly caused by an increase in air concentration in this region (possibly indirectly caused by ice melting being a source of PCBs to the atmosphere).

Cycling of PCBs and HCB in the Surface Ocean-Lower Atmosphere of the Open Pacific

Surface ocean and lower atmosphere samples were collected on the R/V Revelle during a scientific cruise from San Diego, CA to New Zealand via Samoa and the South Pacific Gyre (SPG) from 12/2006 to 1/2007. Samples were analyzed for polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB). summation operator(ICES)PCBs gaseous concentrations (ICES: International Council for the Exploration of the Sea) ranged from 28-103 pg m(-3) in the northern hemisphere (NH) and 1.5-36 pg m(-3) in the southern hemisphere (SH), whereas dissolved seawater concentrations were between 0.2-15 pg L(-1) in the NH and 0.3-7.8 pg L(-1) in the SH. Both gas ([PCBs](gas)) and dissolved phase concentrations ([PCBs](sw_dis)) displayed highest concentrations near North America and lowest in the SPG. In the NH, [HCB](gas) ranged from 42-89 pg m(-3), higher than the average in the SH (31 pg m(-3)), while [HCB](sw_dis) were comparable in both hemispheres (NH: 0.4-1.6 pg L(-1), SH: 0.4-0.8 pg L(-1)). Fugacity ratio calculations suggest PCBs were volatilizing from surface waters to the overlying atmosphere, and air-water exchange fluxes were approximately 0.5 to approximately 30.4 ng m(-2) d(-1). This is the first study reporting the degassing of PCBs from the open ocean into the air. Previous studies deduced net deposition of PCBs into the Atlantic and Arctic Oceans. As has been observed for other oceans, HCB was at/near air-water equilibrium. A mass balance model was used to interpret the short-term variations in [PCBs](gas) in the SPG, which was not observed for HCB. It is suggested that hydroxyl radical depletion reaction and air-water gas exchange together controlled the variation in [PCBs](gas).

Dependency of polychlorinated biphenyl and polycyclic aromatic hydrocarbon bioaccumulation in Mya arenaria on both water column and sediment bed chemical activities.

The bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) by the filter-feeding soft-shell clam Mya arenaria was evaluated at three sites near Boston (MA, USA) by assessing the chemical activities of those hydrophobic organic compounds (HOCs) in the sediment bed, water column, and organisms. Polyethylene samplers were deployed to measure the activities of HOCs in the water column. Sediment activities were assessed by normalizing concentrations with sediment-water sorption coefficient values, including adsorption to black carbon in addition to absorption by organic carbon. Likewise, both lipids and proteins were considered in biota-water partition coefficients used to estimate chemical activities in the animals. Chemical activities of PAHs in M. arenaria were substantially less than those of the corresponding bed sediments in which they lived. In contrast, chemical activities of PCBs in M. arenaria often were greater than or equal to activities in the corresponding bed sediments. Activities of PAHs, such those of pyrene, in the water column were undersaturated relative to the sediment. However, some PCBs, such as congener 52, had higher activities in the water column than in the sediment. Tissue activities of pyrene generally were in between the sediment and water column activities, whereas activity of PCB congener 52 was nearest to water column activities. These results suggest that attempts to estimate bioaccumulation by benthic organisms should include interactions with both the bed sediment and the water column.

Atlantic ocean surface waters buffer declining atmospheric concentrations of persistent organic pollutants.

Decreasing environmental concentrations of some persistent organic pollutants (POPs) have been observed at local or regional scales in continental areas after the implementation of international measures to curb primary emissions. A decline in primary atmospheric emissions can result in re-emissions of pollutants from the environmental capacitors (or secondary sources) such as soils and oceans. This may be part of the reason why concentrations of some POPs such as polychlorinated biphenyls (PCBs) have not declined significantly in the open oceanic areas, although re-emission of POPs from open ocean water has barely been documented. In contrast, results from this study show that several polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) have undergone a marked decline (2-3 orders of magnitude for some homologues) over a major portion of the remote oligotrophic Atlantic Ocean. The decline appears to be faster than that observed over continental areas, implicating an important role of oceanic geochemical controls on levels and cycling of some POPs. For several lower chlorinated PCDD/Fs, we observed re-emission from surface water back to the atmosphere. An assessment of the effectiveness of the main sink processes highlights the role of degradation in surface waters as potentially key to explaining the different behavior between PCDD/Fs and PCBs and controlling their overall residence time in the ocean/atmosphere system. This study provides experimental evidence that the ocean has a buffering capacity - dependent on individual chemicals - which moderates the rate at which the system will respond to an underlying change in continental emissions.