Abstract

LOPEZ-DIAZ, Jazmin Alaide et al. Chemical fractionation of potentially toxic heavy metals and metalloids in residual mud obtained from the wastewater treatment plant at Taxco de Alarcón, Guerrero, Mexico. Bol. Soc. Geol. Mex [online]. 2022, vol.74, n.2, A121221.  Epub June 05, 2023. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2022v74n2a121221.

The goals of this work were: i) to identify and quantify the potentially toxic heavy metals and metalloids in sewage sludge generated by “Taxco de Alarcón” wastewater treatment plant; ii) to determine the potentially toxic heavy metals and metalloids speciation through sequential chemical extraction, and iii) to provide a detailed methodological procedure for total digestion and sequential chemical extraction to sewage sludge. The methodology was a total digestion and sequential chemical extraction using sewage sludge. Analysis of potentially toxic heavy metals and metalloids was performed by inductively coupled plasma atomic emission spectroscopy. From total digestion Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Sr, V, and Zn were identified and quantified. Seven potentially toxic heavy metals and metalloids analyzed and considered by NOM-004-SEMARNAT-2002 were found in sewage sludge at the following concentrations: 51, 50, 38, 752, 153, 190, and 3,134 mg/kg (dry basis), for As, Cd, Cr, Cu, Pb, Ni, and Zn, respectively. However, the concentration of As, Cd, and Zn exceeds the maximum allowable limit set by the standard to be classified as excellent quality sludge. On the other hand, the analysis of the different fractions obtained by sequential chemical extraction exhibited that the highest concentrations of As, Cd, and Zn are mainly associated with the most geo-available fractions (exchangeable fraction and bound to carbonates). The total concentrations in these fractions were 34, 34, and 1,723 sewage sludge mg/kg (dry basis) for As, Cd, and Zn, respectively. Finally, in function of the seven potentially toxic heavy metals and metalloids analyzed as well as their total concentrations determined in the sewage sludge from the Taxco de Alarcón wastewater treatment plant, the sewage sludge are classified as a good quality sludge. In other words, the sewage sludge have the potential to be used for urban handling without direct contact during its application in forest use or as agricultural soil improvers in the region.

Keywords : acid digestion; geodisponibility; potentially toxic heavy metals and metalloids; sequential chemical extraction; sewage sludge.