Archived soil samples (0-23 cm, plough layer depth) collected from the same semirural plot in southeast England between 1846 and 1986 have been analyzed for polychlorinated (tetra to octa) dibenzo-p-dioxins and -furans (PCDD/Fs). Atmospheric deposition will have been the major source of PCDD/Fs to the site over this time. PCDD/Fs were present in all the samples, and concentrations started to increase around the turn of the century, rising from 31 to 92 ng of £PCDD/Fs (kg of soil)"1 between 1893 and 1986. Unwashed bulked herbage samples from 1960-1970 and the 1980s contained 96 and 85 ng of £PCDD/F kg"1 respectively, compared to 12 ng of £PCDD/F kg'1 in a sample from 1880-1990. Average ^PCDD/F net rates of increase in the soil over the last century were calculated as ca. 190 ng m"2 year'1. It is suggested that the increases in soil and herbage PCDD/Fs observed this century at Rothamsted are representative of those likely for agricultural systems in many industrialized regions. The possible changing sources of PCDD/Fs to the environment are discussed in the context of the concentration trends and congener-specific observations.

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Contaminated fish such as those from the Baltic Sea are an important source of exposure to polychlorinated dibenzofurans and dibenzodioxins in persons who eat fish regularly. However, the clinical consequences of such exposure remain uncertain.

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