Effectiveness of three rapid digestion methods to estimate total lead in orchard soils

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Abstract
High concentrations of lead in contaminated soils comprise a potential public health hazard. Limits between safe and dangerous levels are often based on total soil lead content. Current chemical procedures to determine total lead are unsuitable for routine soil analysis because they are time‐consuming and require highly trained personnel. This paper describes the effectiveness of three rapid extraction procedures to estimate total lead in a large number of lead arsenate‐contaminated orchard soils. Dissolution of soil lead in Kjeldahl flasks using a nitric acid‐perchloric acid mixture was virtually complete (98%) when compared to values for total lead measured by treatment with a mixture of HF, HNO3 and KClO4. Shaking of 5‐g samples in 50 ml of lN HCl or lN HNO3 for 1½ hours extracted 95 and 93 percent of the total lead, respectively. Regression equations were derived to allow estimation of total lead from values obtained in the HNO3‐HClO4, HCl, or HNO3 extracts. The HNO3‐HClO4 digestion procedure is preferred with atomic absorption spectrophotometry, while HCl extraction is suitable for routine soil analysis with inductively coupled argon plasma spectrophotometers or similar instrumentation. Grinding of the soils to promote sample uniformity appeared unnecessary, at least in the silt loam soils tested.

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