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Comment on “Evidence for the Presence of PCDD/Fs in the Environment Prior to 1900 and Further Studies on Their Temporal Trends” SIR: The time-course of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the environment is an important clue about the sources of these compounds. Many studies have indicated that environmental concentrations of PCDD/F increased dramatically in about 1940 ( 5 (for a review see 1). The timing of this increase indicates that PCDD/F sources are largely anthropogenic. A recent paper of Alcock et al. (2), however, suggests that the concentrations of these compounds in stored soil samples from Broadbalk, England have been similar from the late 19th century until today. For example, in terms of total tetra- through octachlorinated PCDD/F, the concentrations in these soils were 50 ng/kg in 1881, 31 ng/kg in 1893, and 84 ng/kg in 1986 (2). These data suggest that the deposition of PCDD/F to these soils has increased by less than a factor of 2 over a 105-year interval. This observation contrasts with European sediment core studies (1, Figure 1B), which indicate that PCDD/F levels increased by at least a factor of 20 starting in about 1950. Thus, we would like to offer our comments on these Broadbalk soil data. The soil samples that were the subject of this study were apparently stored at Rothamsted, England since they were collected, but the details of the storage conditions are somewhat vague. For example, an early paper indicates that these samples were “stored in glass jars with cork lids” (3), but a later paper (4) indicates that these samples were “sealed until subsampled for this project”. It would be good to know how these samples were “sealed” (with wax for example). According to Alcock et al. (2), the 1881 sample had been “previously unopened”, but it is not clear how this was known. Was a record kept of access to these samples? Was an authentication seal unbroken since sample collection in 1881? Were the jars and the cork lids, in fact, airtight? In addition, this storage facility seems to have had a checkered history. We are told that “in the early 1950s, ... these old farm buildings, which were converted to army mess rooms during the war, were converted to house the archive” (2). One wonders where the archive was stored before the early 1950s. Clearly, the integrity of these soil samples (at least for trace levels of organic pollutants) cannot be evaluated unless the details of the storage and history of the samples are known. Knowledge of these sample storage and history details is particularly important given the very high levels of PCDD/F in the dust samples collected from the current storage facility. Two dust samples were collected. Dust sample A, from the facility used to store the pre-1960 samples, had a total PCDD/F concentration of 41 000 ng/kg; dust sample B, from
10.1021/es980695s CCC: $18.00 Published on Web 11/20/1998
1998 American Chemical Society
the facility used to store the more recent samples, had a concentration of 160 000 ng/kg. The older dust sample A showed a homologue profile typical of pentachlorophenol sources, but the newer dust sample B showed an odd homologue profile dominated by the heptachlorodibenzofurans. It is not clear why the authors compared only the homologue profile of the newer dust sample B in Figure 2 to the homologue profiles in the older soils. Had they used sample A for this comparison, they might have been less adamant about the impossibility of the dust contaminating the soil samples. In our opinion, soil sample contamination is a very real possibility given that the total PCDD/F concentration in the dust averages 100 000 ng/kg, which is more than 2000 times higher than the concentrations in the older soils (2). Under these conditions, it is very difficult to be sure that these samples had not been contaminated sometime since 1881. As the authors point out (2, Table 3), it would take only a few milligrams of dust to double the concentration of some PCDD/F in these soil samples. Finally, although it is not directly relevant to the issue of contamination of the Broadbalk soil samples, we should point out an error in the discussion of the paper bags contaminating the Woburn soil samples. From Table 7 (2), we find (by adding the columns) that the mass of total PCDD/F in the 1976 and 1956 paper bags were 19 000 and 620 ng, respectively. By the same approach, we find that the mass in the 1977 and 1957 soils were 44 000 and 27 000 ng, respectively. Table 6 tells us that the total PCDD/F concentrations in the 1976 and 1956 paper bags were 2400 and 78 ng/kg, respectively. Table 5 tells us that the concentrations in the 1977 and 1957 Woburn soils were 110 and 68 ng/kg, respectively. Dividing the masses in the bags or soils by the appropriate concentrations, we find that the bags must have weighed 8 kg and of the soil contained in them must have weighed 400 kg. These are unreasonably high values, and we conclude that one or more of the units in these tables must be in error. Perhaps the authors confused “nanograms” with “picograms”.
Literature Cited (1) Alcock, R. E.; Jones, K. C. Environ. Sci. Technol. 1996, 30, 31333143. (2) Alcock, R. E.; McLachlan, M. S.; Johnston, A. E.; Jones, K. C. Environ. Sci. Technol. 1998, 32, 1580-1587. (3) Kjeller, L. O.; Jones, K. C.; Johnston, A. E.; Rappe, C. Environ. Sci. Technol. 1991, 25, 1619-1627. (4) Alcock, R. E.; Johnston, A. E.; McGrath, S. P.; Berrow, M. L.; Jones, K. C. Environ. Sci. Technol. 1993, 27, 1918-1923.
John I. Baker and Ronald A. Hites* School of Public and Environment Affairs and Department of Chemistry, Indiana University Bloomington, Indiana 47405 ES980695S
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