Prediction of free metal ion activity in contaminated soils using WHAM VII, baker soil test and solubility model

• Published in: Chemosphere (Oxford) Vol. 243; p. 125408
• Main Authors: Golui, Debasis, Datta, S.P., Dwivedi, B.S., Meena, M.C., Trivedi, V.K.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.03.2020
• Subjects: Baker soil test; Biological Availability; Contaminated soil; Environmental Pollution - analysis; Free ion activity; India; Ions - chemistry; Metals; Metals - analysis; Metals - chemistry; Metals, Heavy - analysis; Metals, Heavy - chemistry; Rivers - chemistry; Sewage - chemistry; Soil - chemistry; Soil Pollutants - analysis; Solubility; Solubility model; WHAM VII; India; Baker soil test; Solubility model; Contaminated soil; Free ion activity; WHAM VII; Metals
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2019.125408

Bioavailability and ecotoxicity of metals in contaminated soils depend largely on their solubility. The present investigation was carried out to predict the free ion activity of Zn2+, Cu2+, Ni2+, Pb2+ and Cd2+ in contaminated soils as a function of pH, organic carbon content and extractable metal concentration. Twenty-five composite soil samples were collected from various locations which had a history of receiving sewage sludge (Keshopur and IARI, Delhi), municipal solid waste (Kolkata, West Bengal), polluted river water (Madanpur, Delhi) and industrial effluents (Debari, Rajasthan and Sonepat, Haryana). Four composite soil samples were also collected from adjacent fields which had not received contaminated amendments. Free ion activities (-log10 values), viz. pZn2+, pCu2+, pNi2+, pPb2+ and pCd2+ as measured by the Baker soil test, were 10.1 ± 1.12, 13.4 ± 1.23, 12.9 ± 0.85, 11.6 ± 0.74 and 12.6 ± 2.26, respectively. Free metal ion activities were also determined using the geochemical speciation model WHAM-VII following extraction of soil solution with porous Rhizon samplers from the rhizosphere of growing plants. pH dependent Freundlich model based on soil properties could explain the variation in pZn2+, pCu2+, pNi2+, pPb2+ and pCd2+ to the extent of 84, 52, 73, 60 and 70%, respectively, in the case of data from Rhizon samplers coupled with speciation modelling. Whereas, C-Q model could explain 84, 57, 82, 72 and 74% variability in pZn2+, pCu2+, pNi2+, pPb2+ and pCd2+, respectively, based on soil properties and free metal ion activity as determined with integrated use of Rhizon-WHAM-VII. Modelling approach was superior compared to that based on the Baker soil test solution. •Free ion activity of metal is the most potent index of availability and ecotoxicity.•This index decides the suitability of agricultural land for cultivation.•Assessing free ion activity of metal in soil solution is tedious and cumbersome.•Novel protocol was developed for routine assessment of free metal ion activity.•This protocol will go a long way in helping risk assessment of metal polluted soil.