An historical record of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) deposition to a remote lake site in north-west Scotland, UK

Present day and historical background levels of polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) deposition to a remote UK site have been investigated by looking at the temporal record of PCDDs and PCDFs held in lake sediments. Results showed that PCDD/F concentrations started to increase above pre-industrial background levels during the 1860s and 1870s, reaching a peak in the 1950s-1960s and then decreasing to the present day. Increases in PCDD/F concentrations since the late 1800s have been attributed to increased combustion of fossil fuels, 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 increasing controls on the production and use of chlorinated chemicals, and to a decrease in the consumption of fossil fuels and leaded petrol. The contribution of different homologue groups to total PCDD/F concentrations has remained broadly similar since the 1800s, with a dominance of OCDD being the main feature. Minor changes in the homologue profile over time suggest that changing PCDD/F sources are having some impact on deposition patterns, although atmospheric transport and deposition 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.