Comparison of Natural Humic Substances and Synthetic Ethylenediaminetetraacetic Acid and Nitrilotriacetic Acid as Washing Agents of a Heavy Metal–Polluted Soil

Abstract

Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and other synthetic polycarboxylic acids have been shown to possess substantial capacity as washing agents of heavy metal-polluted soils, but they are environmentally problematic. Therefore, a sample of natural soluble humic substances (HS) was tested as a possible substitute. The efficiency of HS to extract cadmium (Cd), copper (Cu), and lead (Pb) from a strongly polluted calcareous urban soil was compared with that of EDTA and NTA. The influence of extractant concentration (25-100 mmol L(-1) C), solution/soil ratio (5-100 L kg(-1)), and single-step vs. multistep extraction on heavy metal removal from the soil was investigated. The extracted pools were assessed by sequential extraction. Ethylenediaminetetraacetic acid and NTA extracted up to 86, 77, and 30% of total soil Cd, Cu, and Pb, respectively, whereas HS extracted 44, 53, and 4%. Extracted amounts of Cd, Cu, and Pb increased with increasing extractant concentration and solution/soil ratio in the range 5 to 100 L kg(-1). Single-step extraction removed about the same amounts of the three metals as multiple-step extraction. The metal-extracted pools of the soil depended on the metal and on the extractant. The overall conclusion is that soluble HS can replace synthetic EDTA and NTA as washing agents for Cd- and Cu-polluted soils, whereas HS is not a promising substitute of EDTA or NTA for cleaning Pb-polluted, calcareous soils.

Solubility of Heavy Metals/Metalloid on Multi-Metal Contaminated Soil Samples from a Gold Ore Processing Area: Effects of Humic Substances

“…However, although humic substances have been investigated as a washing agent for soils contaminated by polyaromatic hydrocarbons and other organic pollutants (Borggaard et al, 2009;Soleimani et al, 2010) and testing on heavy metal polluted soils is limited, in recent years some studies have been performed (Fonseca et al, 2013;Tang et al, 2014;An et al, 2015;Hwang et al, 2015).…”

Humic substances as a washing agent for Cd-contaminated soils

“…Thus, there is an ongoing search for cost-effective and eco-friendly washing chemicals. In this regard, humic substances have the potential of becoming the washing chemicals of choice (Soleimani et al, 2010;Kulikowska et al, 2015b). Besides being environmentally benign, humic substances can improve soil physical, chemical, and biological properties.…”

A laboratory test of NOM-assisted remediation of arsenic and copper contaminated soils

“…As and Cu can be 10 removed in-situ by phytoremediation on moderately contaminated 11 soils or ex-situ by soil washing of strongly contaminated soils. 12 Because As and Cu are often strongly bonded to soil solids, both 13 methods often use a strong complexant to increase contaminant 14 solubility, e.g. ethylenediaminetetraacetic acid (EDTA), nitrilotri- 15 acetic acid (NTA) or similar compounds [4][5][6][7][8].…”

“…ethylenediaminetetraacetic acid (EDTA), nitrilotri- 15 acetic acid (NTA) or similar compounds [4][5][6][7][8]. However, although 16 EDTA, NTA and other synthetic aminopolycarboxylates are effective 17 cleaning agents, they are environmentally problematic [9][10][11] 18 suggesting a need for their replacement with cheap natural organic 19 matter (NOM) compounds such as soluble humic substances (HS) 20 and citrate forming strong soluble complexes with Cu and other 21 heavy metals [2,4,5,8,9,12,13]. In fact, recent studies have shown 22 that NOM compounds such as HS-like materials formed by oxidative 23 hydrolytic degradation of cow slurry, leonardite HS and Sigma- 24 Aldrich HS as well as citrate can extract As, Cu and some other heavy 25 metals but they are clearly less effective than EDTA and NTA [2,8,13].…”

“…This is an 172 important finding in relation to the possibility of using HS in 173 remediation of As and Cu contaminated soils. 174 Copper, which is a cation (Cu 2+ ), is extracted because of 175 formation of stable soluble complexes with carboxylic acid groups 176 of the citrate, NTA and HS molecules [13,14]. In contrast, As occurs 177 in well-aerated soils as anions (arsenate HAsO 4 2À /H 2 AsO 4 À ), which 178 are strongly sorbed onto the surfaces of variable charge soil 179 components, in particular iron (Fe) oxides [1][2][3].…”