No abstract

The United Kingdom is used as a study area in which to examine (i) the relationship between primary and potential secondary emissions of PCDD/Fs; (ii) the balance between atmospheric emissions and deposition; and (iii) the contemporary environmental burden of PCDD/Fs and possible historical input profiles. This critical review exercise is seen as an important aid to identifying gaps in knowledge and research needs and directing a scientifically sound strategy for PCDD/F risk reduction. The paper focuses on two key compartments, air and soil, as these play an important role in the movement and storage of PCDD/Fs. The terrestrial agricultural food chain supplies the majority of human exposure to PCDD/Fs via the pathway air−deposition−crop/pasture/soil−grazing animals−meat/dairy products−human diet. Primary emissions of PCDD/Fs to the atmosphere are expected to decline in the future following the implementation of new legislative controls. This should be reflected by a further decline in ambient air concentrations, as our calculations indicate that primary emissions are currently the main PCDD/F sources to air. The soil burden will take much longer to decline, due to the extreme persistence of these compounds in this environmental matrix. The paper highlights uncertainties and future research needs concerning the environmental sources, fate, and behavior of this group of compounds.

Polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) are two groups of organic compounds that are ubiquitous in the environment at ultratrace levels, but that have attracted considerable scientific and political concern because of their environmental persistence, tendency to bioaccumulate through the foodchain, and toxicity. In recent years they have attracted particular interest because of their presence in sewage sludges, and they have been included on listings of the "priority organic contaminants". PCDD/Fs are not produced intentionally, but are released into the environment in ultratrace amounts from various combustion processes and as a result of their occurrence as unwanted byproducts in various chlorinated chemical formulations (e.g., pentachlorophenol, PCP). There is continuing uncertainty over the relative importance of different sources of PCDD/Fs to the environment. The lowest and highest TEQ values for sewage sludge reported in the literature are 0.5 and 4100 ng/kg (DW). U.K. data reported in three surveys range between 9 and 206 ng/kg, with typical or representative values internationally in the range of 20 to 100 ng/kg. Many sources have been suggested as potential contributors to the PCDD/F composition of sludges. Combustion-derived inputs will provide a "baseline" input to the environment and hence sludge, which may be supplemented by trace impurities released from the manufacture and use of various chloroaromatics. PCP use in textiles has attracted attention as an important contributor in Germany. More recently, impurities in a dyestuff chloroanil have attracted attention. Atmospheric deposition and sewage sludge would appear to supply roughly equal amounts of PCDD/F to U.K. soils each year, although deposition will supply a greater TEQ. Based on the average composition of individual 2,3,7,8-substituted PCDD/Fs measured in U.K. sludges, OCDD has the greatest potential to be enriched in sludge-amended soil, followed by a range of Hp-and Hx-CDD/Fs and OCDF. These PCDD/Fs all have relatively low TEF values. Enrichment of the lower-chlorinated tetra-and penta-CDD/Fs that have higher TEFs is less marked.A simple pathways assessment procedure is presented, focusing on the transfers into milk and meat from pastureland and based on TEQs. This is designed for dairy and beef cattle separately. The scheme could accommodate differences in dietary composition, with animals eating a mixture of herbage, fodder/grain, soil, and (potentially) sludge. Scenarios for unsludged rural and urban and typical and worst-case sludge amendment are considered. Increases in livestock PCDD/F intake due to most routine sludge additions in rural areas are shown to be minor compared with the differences 1064-3389/97/$.50 © 1997 by CRC Press LLC 1 Downloaded by [University of South Florida] at 10:51 09 October 2014projected between rural and urban grazing pasture. The only exceptions to this would result from unusually high rates of soil or sludge ingested. An assessment is made of the influence of unsludged rural and urban an...

Data are presented on PCDD/F persistence in a sludgeamended soil sampled from a long-term field experiment started in 1968. Over 50% of the PCDD/ Fs present in the soil in 1972 were still present in 1990. The concentrations of all congeners were observed to decrease gradually and in the same manner over this time, indicating that either physical loss of material from the experimental plot had occurred or all congeners had undergone a uniform reduction in extractability over time. Half-lives for the disappearance of PCDD/Fs from the sludge-amended plot post-1972 were of the order of 20 years; however, the degradation/alteration of PCDD/Fs in soil may take much longer since these half-lives are believed to be principally affected by physical removal.