AN HISTORICAL RECORD OF POLYCHLORINATED DIBENZO-P-DIOXIN (PCDD) AND POLYCHLORINATED DIBENZOFURAN (PCDF) DEPOSITION TO A REMOTE LAKE SITE INNORTH-WEST SCOTLAND, UK

Present day and historical background levels of polychlorinated dibenz o-p-dioxin (PCDD) and dibenzofuran (PCDF) deposition to a remote UK si te have been investigated by looking at the temporal record of PCDDs a nd PCDFs held in lake sediments. Results showed that PCDD/F concentrat ions started to increase above pre-industrial background levels during the 1860s and 1870s, reaching a peak in the 1950s-1960s and then decr easing to the present day. Increases in PCDD/F concentrations since th e late 1800s have been attributed to increased combustion of fossil fu els, and to the growth of the chemical industry in the 1930s and 1940s . The more recent decrease in PCDD/F concentrations may be due to incr easing controls on the production and use of chlorinated chemicals, an d to a decrease in the consumption of fossil fuels and leaded petrol. The contribution of different homologue groups to total PCDD/F concent rations has remained broadly similar since the 1800s, with a dominance of OCDD being the main feature. Minor changes in the homologue profil e over time suggest that changing PCDD/F sources are having some impac t on deposition patterns, although atmospheric transport and depositio n processes are likely to have mixed the inputs from different sources , producing a more uniform PCDD/F homologue profile once incorporated into remote lake sediments. (C) 1997 Elsevier Science B.V.