Data evaluation
The data were grouped into urban and semi-urban domains. The urban domain (n = 42) was defined by land-use, i.e. developed land and the semi-urban domain (n = 34), i.e. undeveloped land were assigned using information presented in 1953-present Ordnance Survey maps. Differences in PAH and PCB concentrations between the two domains were tested using Levene’s and Bartlett’s test for homogeneity of variance followed by a Student’s t-test to decide which domains should be used to derive NBC and compare with GAC.