Nicholas J. L. Green

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.

Survey of PCDD/Fs and non-ortho PCBs in UK sewage sludges

A survey of PCDD/F and non-ortho PCB concentrations in the mesophilic, anaerobically digested sludge of 14 UK wastewater treatment works was carried out. The range of total Cl1-Cl8DD/F concentrations in the sludges was 8880-428000 pg/g dw with a median of 23300 pg/g dw. The concentrations of the three non-ortho PCBs were in the range 272-63000 pg/g dw with a median of 695 pg/g dw. The PCDD/F I-TEQs of the sludges studied were comparable to those published in the literature with a range of 20-225 pg I-TEQ/g dw and a median of 40.4 pg/g dw. The non-ortho PCBs usually added 2-7 pg/g to the total TEQ with one notable exception which increased the TEQ value 20-fold. With three exceptions, the PCDD/F content of the sludges fell well below the draft EU limit values proposed on 27 April 2000. The homologue group pattern of the PCDD/Fs is dominated by the HpCDDs and OCDD and is consistent with that found in most sewage sludges. There appears to be no correlation between the degree of industrial input and the PCDD/F concentration. This suggests that trade effluent is not always the most significant source of PCDD/Fs to wastewater in the UK.

Fate of 1,2,3,4,6,7,8-heptachlorodibenzofuran and pentachlorophenol during laboratory-scale anaerobic mesophilic sewage sludge digestion.

The possibility of the formation of PCDDs and dechlorination of PCDFs during the anaerobic digestion of sewage sludge in laboratory scale digesters was investigated. Digesters were spiked with 1,2,3,4,6,7,8-HpCDF-13C(6) (240 ng/g organic matter (OM)) and pentachlorophenol (PeCP)-13C(6) (24 microg/g OM) and the output sludge monitored for 60 days. No dechlorination or formation of the labelled or native PCDD/Fs was observed. The detectable 1,2,3,4,6,7,8-HpCDF-13C(6) dechlorination yield was 0.0008-1% depending on homologue group and the detectable formation of OCDD yield was 0.00042% PeCP-13C(6). Preferential respiration of other, more bioavailable, substrates is suggested as the most plausible explanation for the lack of dechlorination. Formation of PCDDs from PeCP has been observed in aerobic environments but this study provides further evidence that it is not a precursor for formation during anaerobic digestion.

Interlaboratory comparison exercise for the analysis of PCDD/Fs in samples of digested sewage sludge.

Five UK laboratories participated in a study designed to explore the principal sources of interlaboratory variation in the analysis of PCDD/Fs in sewage sludge. Samples of wet sludge, dry sludge, toluene extract of sludge and cleaned extract of sludge were prepared by an organising laboratory. The samples were analysed in duplicate by each laboratory along with a solution of PCDD/F standards and reference sediment. Mean coefficients of variation between laboratories were 45% for the wet sludge, 33% for the dry sludge, 32% for the extract of sludge, 36% for the cleaned extract of sludge, 32% for the reference sediment and 28% for the standard solution. The results were subjected to statistical analysis, which showed that there was no specific part of the analysis that introduced a dominant part of the variation. The spread of data generated from the analysis of wet sludge samples was not appreciably greater than the spread for the analysis of cleaned extracts. Thus the drying, extraction and clean up processes in the PCDD/F analysis of wet sludge did not have a dramatic effect on the interlaboratory variation.

Contribution of coplanar and non-coplanar polychlorinated biphenyls to the toxic equivalence of grey seal (Halichoerus grypus) milk

We measured the concentration of coplanar polychlorinated biphenyl (PCB) congeners #77, #126 and #169 in the milk of 21 individual grey seals (Halichoerus grypus) from the same Scottish colony. Using the toxic equivalency factors (TEFs) of Ahlborg et al. (1994) we found TEQs ranged between 8.4 and 45.7 pg/g, with a mean of 22.3 +/- 9.3 pg/g on a lipid weight basis (n = 32). For some samples we also had concentrations of mono-ortho and di-orthochlorinated PCBs. Inclusion of these congeners approximately doubled the TEQ. There was a good correlation between the concentration of non-ortho PCBs and that of other congeners in the same sample.