a1 Pedology Department, Rothamsted Experimental Station, Harpenden, Herts
To measure the accumulation of Pb in an area 42 km from London and within 2 km of the A5, A6 and M1 trunk roads, the Pb contents of topsoils collected from sites at Rothamsted Experimental Station since 1881 have been determined. From 1883 to 1972 the increases ranged from 17 to 46% but because of the variable Pb contents within fields, the absolute rate of accumulation is difficult to determine. The Pb content of herbage harvested twice yearly since 1920 has not increased noticeably.
(Received August 16 1973)