Increases in the polychlorinated dibenzo-p-dioxin and -furan content of soils and vegetation since the 1840s

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