Observations on persistent organic pollutants (POPs) in plants: implications for their use as passive air samplers and for global POPs cycling.

Pine needle (Pinus sylvestris) and lichen (Hypogymnia physodes) samples from various remote sites across Norway have been analyzed for a range of persistent organic pollutants (POPs). Results have shown differences in accumulation between species, with higher concentrations being noted in the H. physodes than the P. sylvestris. This indicates that to use vegetation as a biomonitor, intraspecies and not interspecies comparisons in vegetation pollutant loading between sites are necessary. α/γ-HCH ratios were highest at colder northern sites, indicating increased distance from source areas and long-range atmospheric transport. Concentrations of PCBs 101, 118, 138, and 153 in H. physodes were found to be higher at lower temperatures. Trends between burdens of the other POPs in H. physodes or P. sylvestris and site temperature or latitude were not apparent. Plant/air partition coefficients indicate favored accumulation of PCBs in vegetation at lower temperatures and for higher chlorinated congeners

Further developments in the use of semi-permeable membrane devices as passive air samplers : issues concerning their use for PCBs.

There are several incentives for developing passive air sampling techniques for persistent organic pollutants (POPs). This paper reports on studies to further calibrate and optimize semipermeable membrane devices (SPMDs) for use as “integrated” air samplers of gas-phase POPs. These samplers are deployed over weeks/months/years. Polychlorinated biphenyls (PCBs) were used as the test compounds in this study, with three specific objectives: (i) to determine whether ambient wind speed limits the rate of uptake during typical deployment conditions; (ii) to monitor uptake and SPMD−air equilibrium for a range of compounds; and (iii) to assess the application of performance reference compounds (PRCs) in air sampling, to “correct” for site-specific differences in uptake rates. When deployed in Stevensons screens under ambient conditions, wind speed did not significantly affect uptake rates. Rather, differences in summer/winter uptake rates reported previously, using the same deployment devices as here, are due to temperature affecting compound permeability through the membrane. Results from the use of PRCs indicate that SPMDs should be spiked prior to exposure with a range of compounds that are not present in the atmosphere, so that uptake rates can be estimated from depuration rates during a particular deployment. Short-term deployments (e.g. days; few weeks) would need to use compound(s) with a low octanol:air partition coefficient (KOA) (e.g. 13C12 labeled PCB-28); long-term deployments (of many months to years) would need to use intermediate KOA compounds (e.g. 13C12 PCB-101; 13C12 PCB-153)

Further developments in the use of semipermeable membrane devices (SPMDs) as passive air samplers for persistent organic pollutants: field application in a spatial survey of PCDD/Fs and PAHs.

Semipermeable membrane devices (SPMDs) were deployed at 19 sites in northwest England to test their efficacy as passive atmospheric samplers for polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs). SPMDs were found to be efficient samplers for vapor phase species in the atmosphere, with good reproducibility between samplers. Species which are partially or completely particle associated under ambient U.K. conditions were also sampled by the SPMDs but with poorer reproducibility. It is suggested that SPMDs could be used to indicate “hot-spots” of particulate associated species, however. Differences in absolute and relative concentrations of all PCDD/Fs and PAHs sequestered by the SPMDs were observed between sites. High amounts were sequestered in SPMDs at sites where previous active monitoring has indicated relatively high atmospheric concentrations, confirming the potential of SPMDs as a tool for semiquantitative spatial monitoring of atmospheric species. SPMDs also respond to differences in the mixture of compounds present in the atmosphere, thereby aiding source apportionment studies

The significance of PCBs in the atmosphere of the southern hemisphere.

Air monitoring stations were set up at 2 sites in the southern hemisphere — Moody Brook, Falkland Islands (51° 25′ S, 57° 56′W) and Halley, Research Station, Antarctica (75° 35′ S, 26° 30′ W). PCBs were monitored at the stations throughout 1999. Highest concentrations were observed when temperatures were greater. In general, concentrations were greater at Moody Brook than at Halley, although the difference in concentrations between sites was less for more chlorinated congeners. Air concentrations at both sites were compared with samples collected nearby over-water. Over water air concentrations were found to be greater than over land air concentrations. Concentrations were also compared with literature data for air concentrations at a remote site in the Canadian Arctic. Atmospheric concentrations of tri-chlorinated biphenyls were found to be approximately double those reported for Ellesmere Island in the Canadian Arctic, whilst concentrations in samples from Antarctica were very similar to those found in the high Arctic. Most other PCBs were a factor of 2–4 greater in the Canadian Arctic

Passive air sampling for PCBs : field calculation of atmospheric sampling rates by Triolein containing semi-permeable membrane devices.

Triolein-containing standard U.S. Geological Survey (USGS) designed semipermeable membrane devices (SPMDs) were deployed in the field alongside conventional active air sampling equipment for durations of up to 3 months. A high degree of reproducibility between duplicate samples and linear uptake of polychlorinated biphenyls (PCBs) by the USGS SPMDs were observed. USGS SPMD air sampling rates were calculated for a range of PCBs. Sampling rates were found to be higher in winter than in summer and in general increased with increasing chlorination and decreased with increasing ortho-substitution. The sampling rate for the sum of the ICES congeners (IUPAC congeners 28, 52, 101, 118, 138, 153, and 180) was found to be 1.9 m3 day-1 SPMD-1 in summer (mean temperature 18 °C) and 7.6 m3 day-1 SPMD-1 in winter (mean temperature 4 °C). In a separate study USGS SPMDs were deployed for 2 months, and sequestered concentrations and the aforementioned sampling rates were used to calculate atmospheric concentrations. Excellent agreement was found between air concentrations calculated from the SPMDs and active samplers. The immense potential of these lipid-containing USGS SPMDs for time-integrated passive atmospheric monitoring of gas-phase persistent organic pollutants (POPs), for example, in remote areas or for spatial mapping near potential sources, is confirmed

Air-pasture transfer of PCBs.

A field experiment was conducted to study the air to pasture transfer of PCBs at a rural site in northwest England. Strong positive linear correlations were obtained between the log plant−air partition coefficients (m3 of air g-1 of plant dry weightdefined here as the scavenging coefficient) and log octanol−air (Koa) partition coefficients. Pasture typically retained amounts of PCB per g dry weight equivalent to that in 7 m3 of air for congener 18 and ranging up to 64 m3 for congener 170, regardless of whether the pasture growth (exposure) time had been 2, 6, or 12 weeks. This indicates that airborne PCBs partition onto freshly grown pasture and approach plant surface−air gas-phase equilibrium rather rapidly at this site, i.e., within 2 weeks of exposure. In late April−June, when grassland production is at a maximum, sequestering rates could approach 1.2 ng of PCB-18, 0.17 ng of PCB-170, and 12 ng of ∑PCB m-2 day-1. With 7 million ha of managed and rough grassland in the U.K., fresh pasture production in the spring and summer is estimated to remove an average of 0.8 kg of ∑PCB day-1 from the air during these times (80 kg of ∑PCB per growing season). Some buffering influence may be exerted on surface air concentrations during the most active periods of plant biomass production, while the incorporation of PCBs into pasture following air−pasture transfer processes controls the supply of PCBs to grazing animals and the human food chain

Global distribution and budget of PCBs and HCB in background surface soils: implications for sources and environmental processes.

6 pages, 5 figures, 5 tables.-- PMID: 12636263 [PubMed].-- Printed version published Feb 15, 2003.-- Supporitng information available at: http://pubs.acs.org/doi/suppl/10.1021/es025809lThis paper presents data from a survey of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) concentrations in 191 global background surface (0−5 cm) soils. Differences of up to 4 orders of magnitude were found between sites for PCBs. The lowest and highest PCB concentrations (26 and 97 000 pg/g dw) were found in samples from Greenland and mainland Europe (France, Germany, Poland), respectively. Background soil PCB concentrations were strongly influenced by proximity to source region and soil organic matter (SOM) content. Most (>80%) of the estimated soil PCB burden remains in the “global source region” of the Northern Hemisphere (NH) temperate latitudes (30−60° N) or in the OM-rich soils just north of that. %SOM correlated with PCB and HCB in the global data set, with the correlation coefficients being greater for HCB and the lighter PCBs than for heavier homologues. OM-rich soils in the NH consistently contained the highest burdens; such soils are a key global compartment for these compounds. Evidence for global fractionation of PCBs was found in the subset of soils from latitudes north of the global source region but was not discerned with the global data set. The full data set was used to estimate the burden for individual congeners/homologues in surface background soils and a global soil total PCB burden of 21 000 t. The significance of the inventory is briefly discussed in relation to the latest estimates of global production and atmospheric emission.Is grateful to Eurochlor for funding at Lancaster University for work on HCB and to the Dow Chemical Company Foundation for financially supporting research on the global cycling of POPs. K.B. acknowledges financial support from the European Chemical Industry Council (CEFIC-LRI).Peer reviewe

The global re-cycling of persistent organic pollutants is strongly retarded by soils.

Persistent organic pollutants’ (POPs) are semi-volatile, mobile in the environment and bioaccumulate. Their toxicity and propensity for long-range atmospheric transport (LRAT) has led to international bans/restrictions on their use/release. LRAT of POPs may occur by a ‘single hop’ or repeated temperature-driven air–surface exchange. It has been hypothesised that this will result in global fractionation and distillation—with condensation and accumulation in polar regions. Polychlorinated biphenyls (PCBs)—industrial chemicals banned/restricted in the 1970s—provide a classic illustration of POP behaviour. A latitudinally-segmented global PCB inventory has been produced, which shows that 86% of the 1.3×106 tonnes produced was used in the temperate industrial zone of the northern hemisphere. A global survey of background surface soils gives evidence for ‘fractionation’ of PCBs. More significantly, however, very little of the total inventory has ‘made the journey’ via primary emission and/or air–surface exchange and LRAT out of the heavily populated source regions, in the 70 years since PCBs were first produced. Soils generally occlude PCBs, especially soils with dynamic turnover of C/bioturbation/burial mechanisms. This limits the fraction of PCBs available for repeated air–soil exchange. The forested soils of the northern hemisphere, and other C-rich soils, appear to be playing an important role in ‘protecting’ the Arctic from the advective supply of POPs. Whilst investigations on POPs in remote environments are important, it is imperative that researchers also seek to better understand their release from sources, persistence in source regions, and the significant loss mechanisms/global sinks of these compounds, if they wish to predict future trends