Level and Chemical Forms of Lead in Soil of Sewage Irrigation Area in Guangdong Province, South China

The research reveals the level and chemical forms of lead in soil of sewage irrigation area in Guangdong province, South China. Samples were collected from topsoil (0-10cm) and subsoil (30-40cm), and the total content and different fractions of lead were extracted by HNO₃-HF-HClO₄ and Tessier sequential extraction procedure, respectively. It is concluded that the soil of study area has been contaminated by lead. The total contents of lead in soil of the study area are in the range of 77.0 mg/kg to 241.4 mg/kg, and the mean total content is 112.7 mg/kg. The total lead contents in topsoil are higher than that in subsoil, whereas the mean content of carbonate fraction in subsoil is higher than that in topsoil, which may since the pH in subsoil is higher than that in topsoil. Lead in topsoil of study area is mainly of residual fraction which is more than 50% of the total content, and the lead content of different fractions in topsoil has an order: residual fraction > Fe-Mn oxide fraction > weak organic fraction > carbonate fraction > strong organic fraction > water soluble fraction > ion exchangeable fraction. Similar to topsoil, lead in subsoil of study area is also mainly of residual fraction, and the lead content of different fractions in subsoil has an order: residual fraction > Fe-Mn oxide fraction > carbonate fraction > weak organic fraction > strong organic fraction > water soluble fraction > ion exchangeable fraction.