Suitability of environmental indices in assessment of soil remediation with conventional and next generation washing agents

Abstract

Remediation of soils contaminated with metal must ensure high efficiency of metals removal, reduce bioavailability of residual metals and decrease ecological risk. Thus, for comprehensive environmental soil quality assessment, different indices must be used. In this study, suitability of 8 indices was used for soil highly contaminated with Cu (7874.5 mg kg−1), moderately with Pb (1414.3 mg kg−1) and low with Zn (566.1 mg kg−1), washed in batch and dynamic conditions with both conventional and next-generation washing agents. The following indices were used: modified contamination factor (mCf), modified contamination factor degree (mCdeg), mobility factor (MF), reduced partition index (IR), potential ecological risk factor (Er,Z), modified potential ecological risk factor (Er,m), potential ecological risk index (RIZ) and modified ecological risk index (RIm). For mCf,mCdeg and IR own classification scale was proposed. It was proven that most useful indices for assessment of soil pollution with metals were mCf and mCdeg. The mCf together with the IR allow to simultaneous assessment of soil pollution and stability for individual metals. These indices were appropriate for soil contaminated with different concentrations of metals, washed under both hydrodynamic conditions using various washing agents and different effectiveness of metals removal. Thus, they may be considered as most useful for evaluation of remediation method, feasibility of washing agent and assessing soil quality after washing.

Short-Term Soil Flushing with Tannic Acid and Its Effect on Metal Mobilization and Selected Properties of Calcareous Soil

“…The advantage of using TA is that it decreases metal mobility (MF), defined as the ratio of the metal concentration in the F1 fraction to the sum of the metal concentrations in the F1, F2, F3, and F4 fractions [ 20 ]. Based on the MF, metal in soil can be considered immobile (<1%), weakly mobile (1–10%), moderately mobile (11–30%), highly mobile (31–50%), or very highly mobile (>50%) [ 7 ]. On the basis of this classification, metals in the unflushed soil were highly and very highly mobile.…”

“…The distribution of the metals in the soil was determined using a modified BCR (Commission of the European Communities Bureau of Reference) procedure [ 31 ] in which metals were fractionated into four fractions using specific reagents: exchangeable and acid-soluble (mobile F1) extracted with 0.11 mol/L CH 3 COOH; reducible (potentially mobile F2) extracted with 0.5 mol/L NH 2 OH·HCl; oxidizable (potentially mobile F3) extracted with 1 mol/L CH 3 COONH 4 ; residual (immobile F4) extracted with HCl and HNO 3 mixed at a volume ratio of 3:1. Based on metal fractionation, the mobility factor (MF) was calculated [ 7 ] to compare metal mobility in soil before and after soil flushing. All physico-chemical analyses were performed in triplicate.…”

“…This may be related to the fact that soil washing usually removes pollutants more efficiently than soil flushing. Both methods differ in hydrodynamic conditions [ 7 ]. In soil washing, the soil is thoroughly mixed with the washing solution, whereas in soil flushing, the solution is percolated through the soil.…”

Remediation of Smelter Contaminated Soil by Sequential Washing Using Biosurfactants

“…In recent studies on soil washing, the I r was a useful tool to evaluate metal-binding intensity in different matrices (soil, sludge), contaminated with different metals at different concentrations, washed under different conditions with various washing agents and with different effectiveness of metals removal [ 29 ]. Tang et al [ 51 ] demonstrated that after triple washing of sewage sludge with combined rhamnolipid and saponin, the stability of Cu increased from 0.23 to 0.47, and that of Pb from 0.25 to 0.55.…”

“…Metal stability in contaminated and washed soil, based on their chemical fractionation, was calculated according to Equation (2): where i is the index number of the BCR sequential extraction step, progressing from 1 (for F1 fraction) to 4 (for F4 fraction), k is the total number of fractions in the BCR procedure, F i is relative metal content in fraction i. The classification of metal stability based on the I r is as follows: lack of stability (I r ≤ 0.1), low stability (0.1 < I r ≤ 0.3), medium stability (0.3 < I r ≤ 0.5), elevated stability (0.5 < I r ≤ 0.7), high stability (0.7< I r ≤ 0.9) [ 29 ].…”