Distribution and mobility of Cr in tannery waste amended semi-arid soils under simulated rainfall

Abstract

This study was conducted to evaluate the distribution and mobility of Cr in tannery waste that has been added to semi-arid soils. In addition, the amount of total oxidizable soil Cr (III), Cr (VI), pH and soil microbial activities were determined. Tannery sludge alone or mixed with fleshing waste was added to two types of soils, which were then incubated at 25 °C for 6 months and subsequently subjected to simulated rainfall. The highest total amount of Cr loss occurred due to infiltration, regardless of the treatments. The Cr loss ranged from 0.452 to 0.825 μg g −1 soil for all soils from 1 to 3 months, with the exception of those that were located under the canopy and treated with tannery sludge and fleshing waste, which had the highest runoff (from 1.312 to 1.667 μg Cr g −1 soil). The pH of the soil increased from 1 to 3 months (from 7.35 to 8.46), while the total oxidizable soil Cr (III) (2.12–4.31 mg g −1 soil) peaked after 1 month of treatment. The majority of the fractionated chromium was bound to carbonates at initial time, 3 and 6 months prior to and after application of the simulated rainfall. The microbial activities decreased in each of the treated soils from initial time to 3 months; however, after 6 months bacterial activity increased, while pH decreased (from 8.03 to 7.63). Overall, these data suggest that pH is responsible for Cr loss in response to infiltration and runoff, Cr speciation and the equilibrium of Cr fractionation.