Global distribution and budget of PCBs and HCB in background surface soils: Implications for sources and environmental processes

This paper presents data from a survey of polychlorinated
biphenyls (PCBs) and hexachlorobenzene (HCB) concentrations
in 191 global background surface (0-5 cm) soils. Differences of up to 4 orders of magnitude were found
between sites for PCBs. The lowest and highest PCB
concentrations (26 and 97 000 pg/g dw) were found in
samples from Greenland and mainland Europe (France,
Germany, Poland), respectively. Background soil PCB
concentrations were strongly influenced by proximity to
source region and soil organic matter (SOM) content. Most
(>80%) of the estimated soil PCB burden remains in the
“global source region” of the Northern Hemisphere (NH)
temperate latitudes (30-60° N) or in the OM-rich soils just
north of that. %SOM correlated with PCB and HCB in the global data set, with the correlation coefficients being
greater for HCB and the lighter PCBs than for heavier
homologues. OM-rich soils in the NH consistently contained
the highest burdens; such soils are a key global compartment
for these compounds. Evidence for global fractionation
of PCBs was found in the subset of soils from latitudes north of the global source region but was not discerned with
the global data set. The full data set was used to estimate
the burden for individual congeners/homologues in
surface background soils and a global soil total PCB
burden of 21 000 t. The significance of the inventory is
briefly discussed in relation to the latest estimates of global production and atmospheric emission.