1. Achi MM, Uzairu A, Gimba CE, Okunola OJ (2011) Chemical fractionation of heavy metals in soils around the vicinity of automobile mechanic workshops in Kaduna Metropolis, Nigeria. J Environ Chem Ecotoxicol 3(7):184–194
2. Ahmed AB, Bouhadjera K (2010) Assessment of metals accumulated in Durum wheat (Triticum durum Desf.), pepper (Capsicum annuum) and agricultural soils. Afr J Agric Res 5(20):2795–2800
3. Alloway WH (1968) Agronomic controls over the environmental cycling of trace elements. Adv Agron 20:235–275
4. Alonso E, Callejon M, Jimenez JC, Ternero M (2002) Heavy metal extraction forms in sludge from waste water treatment plants. Chemosphere 47:765–775
5. American Public Health Association [APHA] (2005) Standard methods for the examination of water and wastewater, 21st edn. American Water Works Association, Washington, DC