Determination of the Levels of Lead and Cobalt from Soils of an Irrigated Farmland in Lafia Nasarawa State-Nigeria Using Two Different Methods of Digestion

Washing of vehicles (lorries, cars, buses and motor-bikes), clothes and kitchen utensils, bathing and the release of smoke from exhausts of motor-vehicles and other anthropogenic sources continuously increase the levels of heavy metals in water bodies, especially the Amba river of Lafia used for the irrigation of farmlands thereby resulting to contamination and elevation of heavy metals uptake by crops. This study was carried out to provide information on heavy metals concentration in soils of an irrigated vegetable farmland in Lafia. Soil samples were collected at surface levels of 0-30 cm depth. Samples were analyzed for pH, organic matter, electrical conductivity and soil particle sizes. The soil samples were digested using Aqua regia and Nitric acid methods of digestion. The concentrations of lead (Pb) and cobalt (Co) were determined by Atomic Absorption Spectrophotometric (AAS) technique. The values of soil pH ranged between 5.60 and 6.35, organic carbon between, 1.40-1.49 %, organic matter content between, 2.40 and 2.57 %, electrical conductivity between 100 and 240 ?S cm –1 and clay, sand and silt content between 10.4-11.4 %, 82-85 % and 4.6-6.6 % respectively. Total concentration of extractable Pb and Co (Aqua regia method) ranged between 0.083–0.105 and 1.473 – 1.573 mg kg-1 respectively. The concentrations of heavy metals for Nitric acid method were as follows: Pb: 1.363-1.512 and Co: 0.060-0.086. Concentrations of heavy metals in both methods were all below DPR-EGASPIN (2002) and US EPA. (2014) recommended limits. The results showed that aqua regia method was more efficient than the Nitric acid Method of digestion.