Ana Cabrerizo

Past, Present, and Future Controls on Levels of Persistent Organic Pollutants in the Global Environment

Understanding the legacy of persistent organic pollutants requires studying the transition from primary to secondary source control.

Ubiquitous Net Volatilization of Polycyclic Aromatic Hydrocarbons from Soils and Parameters Influencing Their Soil−Air Partitioning

Soils are a major reservoir of organic pollutants, and soil-air partitioning and exchange are key processes controlling the regional fate of pollutants. Here, we report and discuss the soil concentrations of polycyclic aromatic hydrocarbons (PAHs), their soil fugacities, the soil-air partition coefficients (K(SA)) and soil-air gradients for rural and semirural soils, in background areas of N-NE Spain and N-NW England. Different sampling campaigns were carried out to assess seasonal variability and differences between sampling sites. K(SA) values were dependent on soil temperature and soil organic quantity and type. Soil fugacities of phenanthrene and its alkyl homologues were 1-2 orders of magnitude higher than their ambient air fugacities for all sampling sites and periods. The soil to air fugacity ratio was correlated with soil temperature and soil redox potential. Similar trends for other PAHs were found but with lower fugacity ratios. The ubiquitous source of PAHs from background soils to the atmosphere found in all temperate regions in different seasons provides an indirect evidence of potential in situ generation of two to four ring PAHs and their alkyl homologues in the surface soil. We discuss this hypothetical biogenic source and other potential processes that could drive the high soil to air fugacity ratios of some PAHs.

Factors influencing the soil-air partitioning and the strength of soils as a secondary source of polychlorinated biphenyls to the atmosphere.

Soils are a major reservoir of persistent organic pollutants, and soil-air partitioning and exchange are key processes controlling the atmospheric concentrations and regional fate of pollutants. Here, we report and discuss the concentrations of polychlorinated biphenyls (PCBs) in soils, their measured fugacities in soil, the soil-air partition coefficients (K(SA)) and soil-air fugacity gradients in rural background areas of N-NE Spain and N-NW England. Four sampling campaigns were carried out to assess seasonal and daily variability and differences between sampling sites. K(SA) values were significantly dependent on soil temperature and soil organic matter quantity, and to a minor extent organic matter type. All the PCB congeners in the soil are close to equilibrium with the atmosphere at rural Ebro sites, but soil fugacities tend to be higher than ambient air fugacities in early and late summer, consistent with the influence of temperature on soil-air partitioning. Therefore, during warm periods, soils increment their strength as secondary sources to the atmosphere. The mixture of PCBs found in the atmosphere is clearly strongly influenced by the mixture of PCBs which escape from soil, with significant correlations between them (R(2) ranging between 0.35 and 0.74 and p-level <0.001 for the Ebro sampling sites). Conversely, the close-to-equilibrium to net sink status of rural UK sites, suggest a close coupling of air and soil concentrations, but it is not possible to elucidate the importance of these soils as secondary sources yet, and presumably there are still significant primary sources to the regional/global environment.

Climatic and biogeochemical controls on the remobilization and reservoirs of persistent organic pollutants in Antarctica.

After decades of primary emissions, reservoirs of persistent organic pollutants (POPs) have accumulated in soils and snow/ice in polar regions. These reservoirs can be remobilized due to decreasing primary emissions or due to climate change-driven warmer conditions. Results from a sampling campaign carried out at Livingston Island (Antarctica) focusing on field measurements of air-soil exchange of POPs show that there is a close coupling of the polychlorinated biphenyls (PCBs) in the atmosphere and snow/ice and soils with a status close to air-surface equilibrium to a net volatilization from Antarctic reservoirs. This remobilization of PCBs is driven by changes in temperature and soil organic matter (SOM) content, and it provides strong evidence that the current and future remobilization and sinks of POPs are a strong function of the close coupling of climate change and carbon cycling in the Antarctic region and this is not only due to warming. Whereas an increase of 1 °C in ambient temperature due to climate change would increase current Antarctic atmospheric inventories of PCBs by 21-45%, a concurrent increase of 0.5% SOM would counteract the influence of warming by reducing the POP fugacity in soil. A 1 °C increase in Antarctic temperatures will induce an increase of the soil-vegetation organic carbon and associated POPs pools by 25%, becoming a net sink of POPs, and trapping up to 70 times more POPs than the amount remobilized to the atmosphere. Therefore, changes in soil biogeochemistry driven by perturbations of climate may increase to a larger degree the soil fugacity capacity than the decrease in air and soil fugacity capacity due to higher temperatures. Future research should focus on quantifying these remobilization fluxes and sinks for the Antarctic region.

Development of a soil fugacity sampler for determination of air-soil partitioning of persistent organic pollutants under field controlled conditions.

Soils are the main reservoir of persistent organic pollutants (POPs) and thus air-soil exchange and partitioning are key processes controlling the fate and transport of POPs at regional and global scales. To date, soil fugacity has been estimated from models of the soil-air partition coefficients, with the associated unavoidable uncertainties; or by experimental procedures in the laboratory with uncertain application in field conditions. The development of an operational soil fugacity sampler is presented here; one which ensures optimal field data of the POP fugacity in soil and environmentally relevant surface (soil+grass, etc.) and therefore ensuring accurate soil-air partition coefficients and surface-air fugacity gradients. The sampler flow rate is optimized, sampler reproducibility is assessed, and equilibrium between the gas and soil concentrations of polychlorinated biphenyls and polycyclic aromatic hydrocarbons is demonstrated. The development and comprehensive validation of a soil fugacity sampler opens the door for the first time to field studies that accurately determine the variables driving the soil-air partitioning and fluxes of POPs.

Sources and fate of polycyclic aromatic hydrocarbons in the Antarctic and Southern Ocean atmosphere

Polycyclic aromatic hydrocarbons (PAHs) are a geochemically relevant family of semivolatile compounds originating from fossil fuels, biomass burning, and their incomplete combustion, as well as biogenic sources. Even though PAHs are ubiquitous in the environment, there are no previous studies of their occurrence in the Southern Ocean and Antarctic atmosphere. Here we show the gas and aerosol phase PAHs concentrations obtained from three sampling cruises in the Southern Ocean (Weddell, Bellingshausen, and South Scotia Seas), and two sampling campaigns at Livingston Island (Southern Shetlands). This study shows an important variability of the atmospheric concentrations with higher concentrations in the South Scotia and northern Weddell Seas than in the Bellingshausen Sea. The assessment of the gas-particle partitioning of PAHs suggests that aerosol elemental carbon contribution is modest due to its low concentrations. Over the ocean, the atmospheric concentrations do not show a temperature dependence, which is consistent with an important role of long-range atmospheric transport of PAHs. Conversely, over land at Livingston Island, the PAHs gas phase concentrations increase when the temperature increases, consistently with the presence of local diffusive sources. The use of fugacity samplers allowed the determination of the air-soil and air-snow fugacity ratios of PAHs showing that there is a significant volatilization of lighter molecular weight PAHs from soil and snow during the austral summer. The higher volatilization, observed in correspondence of sites where the organic matter content in soil is higher, suggests that there may be a biogenic source of some PAHs. The volatilization of PAHs from soil and snow is sufficient to support the atmospheric occurrence of PAHs over land but may have a modest regional influence on the atmospheric occurrence of PAHs over the Southern Ocean.

Anthropogenic and biogenic hydrocarbons in soils and vegetation from the South Shetland Islands (Antarctica)

Two Antarctic expeditions (in 2009 and 2011) were carried out to assess the local and remote anthropogenic sources of aliphatic and aromatic hydrocarbons, as well as potential biogenic hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs), n-alkanes, biomarkers such as phytane (Ph) and pristane (Pr), and the aliphatic unresolved complex mixture (UCM), were analysed in soil and vegetation samples collected at Deception, Livingston, Barrientos and Penguin Islands (South Shetland Islands, Antarctica). Overall, the patterns of n-alkanes in lichens, mosses and grass were dominated by odd-over-even carbon number alkanes. Mosses and vascular plants showed high abundances of n-C21 to n-C35, while lichens also showed high abundances of n-C17 and n-C19. The lipid content was an important factor controlling the concentrations of n-alkanes in Antarctic vegetation (r(2)=0.28-0.53, p-level<0.05). n-C12 to n-C35 n-alkanes were analysed in soils with a predominance of odd C number n-alkanes (n-C25, n-C27, n-C29, and n-C31), especially in the background soils not influenced by anthropogenic sources. The large values for the carbon predominance index (CPI) and the correlations between odd alkanes and some PAHs suggest the potential biogenic sources of these hydrocarbons in Antarctica. Unresolved complex mixture and CPI values ~1 detected at soils collected at intertidal areas and within the perimeter of Juan Carlos research station, further supported the evidence that even a small settlement (20 persons during the austral summer) can affect the loading of aliphatic and aromatic hydrocarbons in nearby soils. Nevertheless, the assessment of Pr/n-C17 and Ph/n-C18 ratios showed that hydrocarbon degradation is occurring in these soils.

Clustering of Nonpolar Organic Compounds in Lipid Media: Evidence and Implications

Semivolatile and nonpolar organic compounds, such as persistent organic pollutants, have a tendency to accumulate in organic matter phases from air and water. Once they enter living systems, they partition into lipids/waxes and can exert adverse toxicological effects. The current paradigm assumes that such chemicals are uniformly distributed in organic phases such as soil organic matter, plant waxes, and animal lipids and that partitioning and adsorption processes occur independently of intermolecular contaminant interactions. With use of a recently developed technique, two-photon excitation microscopy coupled with autofluorescence allowed us to directly visualize novel organic chemical behavior in living vegetation and other matrixes. Here, we show for the first time that polycyclic aromatic hydrocarbons, which were uniformly distributed in pure oils and waxes at the beginning of a study, form clusters over time. The number and diameter (typically 0.2-5 microm) of these clusters are dependent on the physical-chemical properties of the compound-media systems and time. This behavior is not accounted for in current models of phase partitioning of chemicals and may have important implications for understanding their environmental fate and their potential toxicological effects.

Response to Comments on "unexpected Occurrence of Volatile Dimethylsiloxanes in Antarctic Soils, Vegetation, Phytoplankton and Krill"

Dimethylsiloxanes in Antarctic Soils, Vegetation, Phytoplankton and Krill” W appreciate the close scrutiny of our work by Mackay, Warner and coauthors (hereafter Mackay-2015 and Warner-2015). The consideration of blanks when analyzing persistent organic pollutants (POPs) in remote samples is always an important issue. We performed instrumental blanks, field blanks, and procedural blanks, with no significant different levels of volatile dimethylsiloxanes (VMS) among them. The quantification limits are based on these blanks (Table S4). The use of procedural blanks with real matrixes containing organic matter and lipids allowed controlling sample contamination during handling and analysis in the laboratory. Mackay-2015 and Warner-2015 raise concern on potential contamination from air to sample organic matter during sampling. Samples were transported and stored at −20 °C and were airtight sealed. The sealing of the soil and vegetation samples was performed in situ at the sampling sites. Krill samples were sealed on the ship deck (outdoors). Only phytoplankton samples were in contact with the ship wet lab air during the filtration process (few minutes), but the levels in these samples are among the lowest we determined. In order that our reported levels had originated from contamination from ambient air during sampling, the concentrations in the atmosphere would need to be very high, with extremely fast uptake kinetics, which are not feasible. The samples processed were duplicate samples from those used in earlier studies. Figure 3 shows the correlation of ∑VMS concentrations in phytoplankton against sea surface salinity (SSS), if the sample with the lowest salinity is removed, we obtain C∑VMS = −7.48 SSS + 259 (r = 0.51, p = 0.047). As noted by Mackay-2015, there was a mistake on the SSS values appearing in Table S2c. The correct salinities for samples P2−P11 appeared as assigned to samples P1−10. We have no SSS measure for sample P1. The correct SSS values can be corroborated by comparing the ancillary data of samples FA1, FA4, FA6, FA7, FA8, FA12, FA13, FA19, FA23, FA24, FA26 (duplicate samples of samples P1−P11) that appear in a companion work. Mackay-2015 defines the biomagnification factors (BMFs) as the ratio of dry weight concentrations in Krill and phytoplankton. However, the fugacity amplification by biomagnification is better described when concentrations are normalized by lipids or organic matter. We normalized the cVMS concentrations in Krill by the measured lipid content, and the phytoplankton concentrations by organic matter (≈dry weight). As stated in the methods section, all samples were collected during the ATOS-II campaign in 2009. There were only four pairs of Krill and phytoplankton samples that could be paired in terms of time and region of sampling, which were those used to derive eq 5 and Figure S7. The values of the octanol−water partition constant (KOW) were temperature corrected using an enthalpy of phase change of −30 kJ mol−1. Warner-2015 raises concern on the high relative abundance of D4 in phytoplankton samples, but the atmospheric pattern of VMS in the remote atmosphere is dominated by D3 and D4, with field concentrations under-predicted by models. The only available measurement of atmospheric concentrations for the Southern Ocean is of 0.45 and 1.2 ng m−3 for D3 and D4, respectively. Mackay-2015 estimates the snow scavenging ratios (WS) from the sorption coefficients for snow−air partitioning (KSA, m m−2), and the Snow Area Index (SAI m m−2). Naphthalene has a similar vapor pressure than cVMS and a KSA of 1.05 × 10−3 m m−2. Applying Mackay-2015’s estimation method a value of WS of 1.05 is obtained for Naphthalene, 5 orders of magnitude lower than field measurements (4.6 × 105). If instead of SAI we use a reported snow surface area of 0.37 m g−1, and assume a snow density of 0.3 kg L−1, we obtain WS values of 89, 62 000, and 120 for L3, D6, and naphthalene, respectively. This Ws for Naphthalene is still 3 orders of magnitude lower than the field measures, suggesting thatWs for VMS could be significantly higher than these estimates. Mackay-2015 assumes that the organic carbon−water partition coefficients (KOC) derived from temperate soils and river sediments have applicability to Antarctic soils. Soils at Livingston Island are poorly developed, consisting of fragmented rocks, pyroclastic and volcanic ashes, lichen and animal residues, agglomerates, and penguin feces. The highest soil VMS concentrations were measured at penguin colonies, consistent with the known role of birds, and penguins in particular, amplifying POP concentrations in polar coastal environments. The VMS fugacity (expressed as concentrations) from soil penguin feces, estimated from the lipid− water partition constant and the dimensionless Henry’s Law constant (H′), result in concentrations in the range 40− 170 μg m−3, 3 orders of magnitude lower than Mackay-2015’s estimates. This discrepancy is due to the low organic carbon-air partition constant used by Mackay-2015, 3 orders of magnitude lower than the octanol−air partition constant, and their apparent assumption of 298 K. VMS fugacity amplification is common in high latitude and polar regions. For example, D5 concentrations in Arctic sculpin have been reported to be as high as 2150 ng gL −1, which imply a fugacity of 88 μg m−3, nearly 10 times higher than in Arctic air. We agree with Warner-2015 that wastewater is a source of VMS to the Arctic fjords, but despite the VMS dilution from wastewater to marine waters, this fugacity is more than 10 times higher than the atmospheric D5 concentrations in a wastewater treatment plant. The concentration of D5 in zooplankton from Lake Mjosa (Norway) is of 320−1660 ng gL −1, with an associated fugacity of 30−150 μg m−3. From work done with other POPs, it is known that there is an equilibrium partitioning between the dissolved phase and zooplankton lipids. Even though VMS in Lake Mjosa waters

Climatic Influence on Temporal Trends of Polychlorinated Biphenyls and Organochlorine Pesticides in Landlocked Char from Lakes in the Canadian High Arctic

Temporal trends and climate related parameters affecting the fate of legacy persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were examined in landlocked Arctic char from four lakes in the Canadian Arctic. Among biological parameters, lipid content was a key factor explaining the concentration of most POPs in Arctic char. Legacy PCBs and OCPs generally showed declining trends of concentrations in Arctic char, consistent with past restriction on uses and emissions of POPs. However, increases in lake primary productivity (measured as chlorophyll a) exerted a dilution effect on POPs concentrations in Arctic char. Concentrations of POPs in char from the last two decades were positively correlated with interannual variations of the North Atlantic Oscillation (NAO). Higher concentrations of POPs in Arctic char were observed in 3 of the 4 lakes during positive NAO phases. This, together with increasing local Arctic temperatures, could lead to increases on POPs concentrations in char from remote Arctic Lakes in future decades. Also, if there are nearby secondary sources as may be the case for Resolute Lake, located near an airport where increasing levels were found for hexachlorobenzene and toxaphene, probably due to the mobilization from secondary sources in soils.