A study of toxic metals in kerb-side soils

Abstract

In urban environments motor vehicles are by far the largest source oflead. In areas subjected to heavy and slow moving vehicular traffic, the amount of lead exhausted may be quite high. Since exhaust fumes settle on kerb-sides, soil samples from these areas may not only give a good measure of the accumulation of lead but also eliminate the need to risk expensive sampling equipment in collecting air samples. In order to determine the levels of lead and other toxic metals such as chromium, cadmium, nickel, copper and aluminium, soil samples were collected from kerb-sides and road islands around the City of Durban and along the national road N3 in the vicinity of Shongweni. City, peri-urban and rural roads were selected for sampling. In a preliminary study, kerb-side dust from one of the streets with very heavy vehicular traffic was collected. It is also a street where many vendors have food stalls. The horizontal distribution of metals as a function of distance from the kerb was determined by analyzing samples which were collected at various distances from the edge of a road. The determination of vertical distribution of metals in the soil was also performed. Samples for this work were collected by digging 0 to 2 cm, 10 to 15 cm and 20 to 25 cm deep at various points along the National Highway (N3). 111 Some sub-samples were leached at pHs found in soils using a Hazardous Waste Filtration System while other sub-samples from the same gross sample were aciddigested in a Microwave Digester. The analyses were done using ICP-ABS, AAS and GF-AAS. As expected the values for lead were the highest for urban sites and lowest for rural ones and values from leaching experiments were lower than those for digested samples from the same site. Taken over all sites, the values for lead ranged from 0.02 to 298 ppm for leached samples and from 25 to 1900 ppm for digested samples.