Evaluating bioavailability of elements in municipal wastewater sludge (Biosolids) from three rural wastewater treatment plants in East Texas (USA) by a sequential extraction procedure

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Biosolids (also known as sludge) are nutrient-rich materials used as soil amendments. A modified Tessier sequential extraction protocol was utilized for speciation and bioavailability of metals in samples from Nacogdoches and Lufkin wastewater sludges (NWWS, LWWS) and the Neches Compost sludge (NCS). Application of five steps (adsorbed, exchangeable, organically bound, carbonate and residual/sulfide) was performed to fractionate 26 elements (macroelements: Ca, Fe, K, Mg, Na, P, S, Li, Cs; microelements: As, B, Ba, Cd, Co, Cu, Hg, Mn, Mo, Pb, Se, V, Zn, Ni, Al, Cr, Sr) in samples via inductively coupled plasma optical emission spectrometry (ICPOES). The proximate amounts for most elements were predominant in the sulfide/residual fractions. Among macroelements 88.62–92.23% of K was found bioavailable vis-à-vis the organically-bound or sulfide fractions. About 100% of Li exists in the sulfide fractions vis-a-vis Group 2A elements. In contrast to microelements and transition metals, about 19–32 % Mo was found readily bioavailable. Additionally, Mo occurred in relatively lesser percent in sulfide/residual fractions vis-à-vis other elements. Cd, Pb, Co, V and Al were the least bioavailable. The percent relative bioavailabilities of microelements varied in the order:Mn > Zn > Cu > Ba > Sr > Pb > V > B > Ni > Co > Cr > V > Mo > Hg > Se > Li > Cd.Assessment of the bioavailability of micro- and macro- elements, is essential to predicting element uptake by plants grown in biosolid amended soils, and the possible environmental exposure levels.