LONG-TERM CHANGES IN THE POLYCHLORINATED BIPHENYL CONTENT OF UNITED-KINGDOM SOILS

Archived soils collected from five different long-term agricultural experiments in southern England have been analyzed retrospectively for a range of polychlorinated biphenyl (PCB) congeners. The change in soil PCB concentration over time has been similar in each field experiment, namely, that soil samples exhibited a sharp rise in soil PCB concentrations between about 1940 and the early 1960s, reaching a maximum (ca. 140-560 mug of SIGMAPCB/kg of soil) during the late 1960s/early 1970s. Since then there has been a dramatic reduction in SIGMAPCB concentrations, Such that contemporary concentrations (ca. 20-30 mug/kg) are now similar to those of the early 1940s soils. If these soil loadings were reflected nationwide, the SIGMAPCB burden of U.K. soils has fallen from ca. 26 600 t in 1970 to a contemporary burden of ca. 1500 t. This is equivalent to an annually averaged net loss of approximately 14 mug SIGMAPCB m-2 day-1, but a slower approximately 1 mug SIGMAPCB m-2 day-1 in recent years. Volatilization and subsequent long-range transport probably account for the bulk of this loss. A total of 67 000 t of PCBs was manufactured in the United Kingdom between 1954 and 1977, with an estimated 40 000 t used within the United Kingdom. There has been a gradual shift in the relative proportion of individual congeners since the peak, with a move toward greater proportions of the heavier homologue groups in the most recent samples.