Gordon Sanders

Polychlorinated biphenyls (PCBs) in the British environment: Sinks, sources and temporal trends

This paper estimates the present UK environmental loading of polychlorinated biphenyls (PCBs). Of the estimated approximately 40,000 t SigmaPCB sold in the UK since 1954, only an estimated 1% (400 t) are now present in the UK environment. Comparisons of estimated production and current environmental loadings of congeners 28, 52, 101, 138, 153 and 180 suggest that PCB persistence broadly increases with increasing chlorination. Those PCBs that are not now present in the UK environment are considered to have been destroyed--by natural or anthropogenic mechanisms, to be still in use, to reside in landfills or to have undergone atmospheric and/or pelagic transport from the UK. The dramatic fall in PCB levels in archived UK soils and vegetation between the mid-1960s and the present is evidence that the latter mechanism is the most important and that a significant proportion of PCBs released into the UK environment in the 1960s have subsequently undergone environmental transport away from the UK. The bulk (93.1%) of the estimated contemporary UK environmental burden of SigmaPCBs is associated with soils, with the rest found in seawater (3.5%) and marine sediments (2.1%). Freshwater sediments, vegetation, humans and sewage sludge combined account for 1.4% of the present burden, whilst PCB loadings in air and freshwater are insignificant. Although consideration of individual congeners does not reveal any major deviations from the relative partitioning of Sigma PCBs, the importance of sinks other than soils is enhanced for individual congeners, particularly 138 and 180. In particular, around 2% of the total UK burden of congener 180 is present in humans, implying that biodata as a whole may constitute an important sink for the higher chlorinated congeners. The contemporary flux of SigmaPCBs to the UK surface is estimated at 19 t yr(-1), compared with an estimated annual flux to the atmosphere of 44-46 t. This implies that the major sources of PCBs to the UK atmosphere have been identified and that there is currently a net loss of these compounds from the UK. These sources are: volatilisation from soils (88.1%), leaks from large capacitors (8.5%), the production of refuse-derived fuel (RDF) (2.2%), leaks from transformers (0.6%), the recovery of contaminated scrap metal (0.5%) and volatilisation from sewage sludge-amended land (0.2%). Interestingly, whilst large excesses of estimated annual fluxes to the atmosphere over deposition fluxes for individual congeners exist for congeners 28, 52 and 101, estimates of fluxes in both directions across the soil-atmosphere interface agree closely for congeners 138, 153 and 180. This suggests that lower chlorinated congeners are more susceptible to both long-range environmental transport beyond the UK and to atmospheric degradation. Retrospective analysis of dated sediment cores, vegetation and soils indicates that environmental transport from North America and continental Europe introduced PCBs into the British environment well before the onset of their commercial production in the UK in 1954. Since that time, the input of PCBs to the UK environment has essentially reflected temporal trends in UK use. After peaking in the 1960s they declined rapidly through the 1970s following restrictions on PCB use. Recent evidence, however, is that the rate of decrease has diminished and that further significant reductions in fresh environmental input will take some time to occur. Such reductions will be especially slow for humans and other biota with long life-spans. This stems partly from cross-generational transfer from parents to offspring and also because the persistence of PCBs in biota means that present body burdens will reflect past as well as current exposure.

Accumulation, inventory, and diagenesis of chlorinated hydrocarbons in lake ontario sediments.

Five sediment cores were taken in 1990-1991 from the sedimentation basins of Lake Ontario and analyzed for the radionuclide 210 Pb and hydrophobic organic compounds (HOCs) in order to determine the accumulation, inventory, and diagenesis of these HOCs in the sediments. Two of these sites were sampled earlier in 1981, allowing the study of diagenetic processes affecting these HOCs over a decade-long interval. The shape and details of HOC sediment profiles agreed with the HOC production and usage history, despite evidence of bioturbation in the cores. The 210 Pb chronology showed a mixed depth of 2-5 cm, but mixing by deposit-feeding oligochaetes and benthic organisms was insufficient to homogenize the sediment over the time scale of HOC inputs. Recent HOC accumulation rates and inventories showed significant variability among cores, which was removed when corrected for 210 Pb-based sediment focusing. This suggests that particle-reactive compounds like HOCs are mixed and distributed evenly throughout the lake basins and that site-specific differences are due to differing amounts of sediment delivered via focusing of sediment to depositional basins. Comparison of 1981 and 1990 sediment cores showed expected downcore movement of HOC profiles due to 9 yr of accumulated sediment mass with effectively no loss or gain in mass.

PCB and PAH fluxes to a dated UK peat core

Concentrations of PCBs and PAHs have been determined from the individual sections of peat cores obtained from an ombrotrophic bog in rural north-west England. Chronological intervals throughout the core were determined from both radiometric (210Pb, 137Cs, 241Am) and independent, non-chemical characteristics (pollen, magnetics) information. Net fluxes of 25 individual PCB congeners and 14 PAH compounds to the bog were then derived. PCB inputs were apparent from the late-1930s/ early-1940s, with maximum sub-surface fluxes ( 1300 pg cm−2 year−1) observed at a depth corresponding to 1964. Loadings decreased by 65% over the following 15 year period before showing a surface enrichment. Initial increases in PAH loadings appear to coincide with the beginning of the Industrial Revolution, with fluxes peaking in the early-1930s (305 ng cm−2 year−1). Introduction of emission controls and the decline of heavy industry has led to an 80 % reduction in the net flux of PAHs to the bog over the last three to four decades. Potential effects of postdepositional diagenesis are considered, with particular reference to alteration of contaminant chronologies.

Contamination of Environmental Samples Prepared for PCB Analysis

Archived air-dried soil that had been collected, stored, and sealed in 1914, before the commercial manufacture of PCBs, together with wet freshly sampled ancient peat, which contained little or no PCBs, were exposed to contemporary air in a laboratory. Measurable increases in the concentration of PCBs, particularly the low molecular weight congeners, were detectable after exposure for as little as a few hours. Concentrations after a few days exposure to laboratory air were similar to those measured in contemporary field surface soils (-20-30 pg of CPCB kgl). Laboratory air concentrations ranged between 4.7 and 8.2 ng of CPCB m-3 during the period of exposure, markedly higher than routinely detected in outdoor U.K. urban air. The calculated average net dry deposition flux from air-soil in the laboratory over 25 days was 5 pg of CPCB m-2 day1. Indoor air concentrations might be expected to be higher than those routinely measured outside, exacerbating the potential problems of sample contamination. Extreme caution is needed in the preparation and handling of samples which contain inherently low concentrations of PCBs and before ascribing the presence of these compounds in certain samples to ‘natural production’ mechanisms.

A simple method to assess the susceptibility of polynuclear aromatic hydrocarbons to photolytic decomposition

Polynuclear aromatic hydrocarbons (PAHs) are a ubiquitous and persistent group of toxicologically important compounds in the environment, thought to be susceptible to photodecomposition. A simple method has been developed for assessing the relative susceptibilities of compounds in solution to photodecomposition under simulated natural light. The method was applied to 11 PAHs, having a range of physicochemical properties. Measured half-lives varied by a factor,of 25, from < 2 h for anthracene to 50 h for fluoranthene. The results are discussed in the light of the factors and conditions existing in the natural aquatic environment. The procedure outlined in this paper produces results comparable to those obtained by more complicated methodologies.

The rise and fall of PCBs: Time-trend data from temperateindustrialised countries.

Evidence for a decline in the fluxes of PCBs to terrestrial and aquatic ecosystems in the UK and US is reviewed. Peak inputs appear to have occurred in the 1960s. The relative merits of lake and peat cores, and the analysis of archived samples are briefly discussed.

A microcosm experiment to assess the outgassing potential of PCBs from sediment-water systems.

A laboratory microcosm study was performed to assess the outgassing potential of PCBs from sediment-water systems. PCBs collected in the headspace of the sampler units were adsorbed onto polyurethane foam plugs, which were intermittently sampled over a total period of 56 days. The sediment composition, the level of PCB contamination in the sediment, and incubation temperature were all found to influence the rate of outgassing. Total outgassing losses over the 56 days ranged between 0.04 and 2.5% of the initial sediment PCB burdens.

Accurate prediction of acute fish toxicity of fragrance chemicals with the RTgill‐W1 cell assay

Testing for acute fish toxicity is an integral part of the environmental safety assessment of chemicals. A true replacement of primary fish tissue was recently proposed using cell viability in a fish gill cell line (RTgill-W1) as a means of predicting acute toxicity, showing good predictivity on 35 chemicals. To promote regulatory acceptance, the predictivity and applicability domain of novel tests need to be carefully evaluated on chemicals with existing high-quality in vivo data. We applied the RTgill-W1 cell assay to 38 fragrance chemicals with a wide range of both physicochemical properties and median lethal concentration (LC50) values and representing a diverse range of chemistries. A strong correlation (R2  = 0.90-0.94) between the logarithmic in vivo LC50 values, based on fish mortality, and the logarithmic in vitro median effect concentration (EC50) values based on cell viability was observed. A leave-one-out analysis illustrates a median under-/overprediction from in vitro EC50 values to in vivo LC50 values by a factor of 1.5. This assay offers a simple, accurate, and reliable alternative to in vivo acute fish toxicity testing for chemicals, presumably acting mainly by a narcotic mode of action. Furthermore, the present study provides validation of the predictivity of the RTgill-W1 assay on a completely independent set of chemicals that had not been previously tested and indicates that fragrance chemicals are clearly within the applicability domain. Environ Toxicol Chem 2018;37:931-941.