Evidence for the presence of PCDD/Fs in the environment prior to 1900 and further studies on their temporal trends

This paper presents evidence for the existence of PCDD/Fs in the environment prior to the widespread development of the chloroaromatics and chlorine industry, by the analysis of a previously unopened bottle of soil collected in 1881 from a controlled long-term agricultural experiment at Rothamsted Experimental Station. Great care was taken to avoid contamination of the sample from dust or by exposure to modern air; an experiment was conducted to investigate the potential for contamination of the sample by such exposure, The 1881 soil sample (from the plowed 0-23 cm depth layer) contained 0.7 ng of Sigma TEQ/kg soil, and there were no detectable changes in its Sigma PCDD/F composition when aliquots of it were exposed over 32 days in a laboratory at Lancaster University. Modern soil sampled from the same field plot (which has never received any fertilizers or amendments) now contains 1.4 ng of Sigma TEQ/kg, an increase resulting from cumulative atmospheric deposition of PCDD/Fs retained in the surface layers of the soil. Post-collection contamination issues were also addressed by PCDD/F analysis of dust and paper bags used to store more recent samples. The Sigma TEQ concentration of archived herbage samples collected year-on-year from Rothamsted between 1980 and 1995 have trended downward by a factor of 3-4, implying a recent decline in the atmospheric deposition of PCDD/Fs and supporting a previously reported (Kjeller et al. Environ. Sci. Techol. 1996, 31, 458-463) longer term decline. The significance of these results is discussed.