RELATIONSHIP BETWEEN DAILY TRAFFIC VOLUME AND THE DISTRIBUTION OF LEAD IN ROADSIDE SOIL AND VEGETATION

Lead from automotive sources in roadside soil and vegetation is found to follow a double exponential function of the following form: Pb = A1 e-k + A2 e-k. The terms A1 and A2 are linear functions of average daily traffic volume. The two exponents are assumed to represent two families of particles of different sizes. The larger particles are deposited within about 5 m of the roadside and are relatively inert in the soil. The smaller particles settle more slowly and are deposited within about 100 m of the roadside. Based on the differences between the relative lead content of the soil and vegetation attributable to the two exponents, the lead contained in the smaller particles is assumed to be more soluble than that of the larger ones. An estimated 72-76% of the historical lead deposited on the soil has been lost from the surface 10 cm of soil. © 1979.