Effect of soil washing with biodegradable chelators on the toxicity of residual metals and soil biological properties

Abstract

Soil washing with chelators is a promising and efficient method of remediating metals-contaminated soils. However, the toxicity of residual metals and the effects on soil microbial properties have remained largely unknown after washing. In this study, we employed four biodegradable chelators for removal of metals from contaminated soils: iminodisuccinic acid (ISA), glutamate-N,N-diacetic acid (GLDA), glucomonocarbonic acid (GCA), and polyaspartic acid (PASP). The maximum removal efficiencies for Cd, Pb, and Zn of 85, 55, and 64% and 45, 53, and 32% were achieved from farmland soil and mine soil using biodegradable chelators, respectively. It was found that the capacity of ISA and GLDA to reduce the labile fraction of Cd, Pb, and Zn was similar to that of the conventional non-biodegradable chelator ethylenediaminetetraacetic acid (EDTA). The leachability, mobility, and bioaccessibility of residual metals after washing decreased notably in comparison to the original soils, thus mitigating the estimated environmental and human health risks. Soil β-glucosidase activity, urease activity, acid phosphatase activity, microbial biomass nitrogen, and microbial biomass phosphorus decreased in the treated soils. However, compared with EDTA treatment, soil enzyme activities distinctly increased by 5-94% and overall microbial biomass slightly improved in the remediated soils, which would facilitate reuse of the washed soils. Based on soil toxicity tests that employed wheat seed germination as the endpoint of assessment, the washed soils exhibited only slight effects especially after ISA and GLDA treatments, following high-efficiency metal removal. Hence, ISA and GLDA appear to possess the greatest potential to rehabilitate polluted soils with limited toxicity remaining.

Lead Toxicity: Health Hazards, Influence on Food Chain, and Sustainable Remediation Approaches

“…Hu et al [200] achieved removal of 73% Pb using EDTA as a chelating agent. Wang et al [201] used iminodisuccinic acid, glutamate-N, N-diacetic acid, glucomonocarbonic acid, and polyaspartic acid to extract 53% and 55% Pb from Pb-Zn contaminated soil. However, these technologies have certain hurdles for their practical utility due to change in soil properties, loss of nutrients, adverse effect of washing chemicals, generation of wastewater, and cost of chemicals and their negative impact on the environment.…”

Feasibility of Chinese cabbage (Brassica bara) and lettuce (Lactuca sativa) cultivation in heavily metals−contaminated soil after washing with biodegradable chelators

“…It is frequently used for removing PTEs with soil washing (Golmaei et al, 2018;Sawai et al, 2017) but has been criticized because of its poor biodegradability and its persistence in soil (Mu'azu et al, 2018;Wang et al, 2016). [S,S]eethylenediaminedisuccinic acid (EDDS) has been proposed as an environmentallyefriendly substitute for EDTA (Beiyuan et al, 2017(Beiyuan et al, , 2018Yoo et al, 2018) because it is very biodegradable and gives comparable soil washing efficiencies to EDTA (Wang et al, 2018). However, more ecoefriendly and effective biodegradable chelators for soil washing are still desired (Mu'azu et al, 2018).…”

“…Biodegradable chelators such as polyaspartic acid (PASP) (Mu'azu et al, 2018;Fu et al, 2017), glutamateeN,Nediacetic acid (GLDA) (Tang et al, 2017;Suanon et al, 2016;Wang et al, 2016), iminodisuccinic acid (ISA) (Wu et al, 2015), and glucomonocarbonic acid (GCA) (Wang et al, 2018) have been described in many publications because they are biodegradable and have low toxicities (Pinto et al, 2014;Sawai et al, 2017). PASP and GCA are much more biodegradable than other common chelators such as EDTA (Wang et al, 2018;Mu'azu et al, 2018), and more that 60% of GLDA (Suanon et al, 2016) and ISA (Wu et al, 2015) in soils has been found to degrade within 28 d. Moreover, like other biodegradable chelators, and in contrast to strong acid or basic solutions, these chelators generally affect the soil composition, aggregate structure, and the fertility level little (Komínkov a et al, 2018;Wang et al, 2018). In addition, because they contain different types and amounts of groups (Fig.…”

“…Recent biodegradable chelator washing studies have predominantly been focused on identifying optimum operational conditions (Ferraro et al, 2016;Mu'azu et al, 2018;Wang et al, 2016) and determining metal removal efficiencies (Beiyuan et al, 2017;Suanon et al, 2016). We have previously investigated the fate and toxicity of residual metals (Wang et al, 2018) and changes in soil properties (Wang et al, 2016) in soil remediated by biodegradable chelator washing. However, the effects of washing with these biodegradable chelators on the overall health (Hu et al, 2014), ecological function, and reuse of remediated soil (Jelusic et al, 2013(Jelusic et al, , 2014a have not been studied sufficiently.…”

“…Decreasing pollutant concentrations is a crucial remediation objective, but attention should also be paid to reestablishing a healthy ecosystem capable of supporting fauna, flora, and microbes to ensure the treated soil is safe and can be sustainably reused (Guo et al, 2016;Jelusic and Lestan, 2015). Soil washing processes may adversely affect the activities of soil enzymes such as dehydrogenase (Im et al, 2015), acid phosphatase (Im et al, 2015;Wang et al, 2018), arylsulfatase (Yi and Sung, 2015), beglucosidase (Chae et al, 2017;Kaurin et al, 2018), and urease (Chae et al, 2017). These enzymes play critical roles in organic matter turnover and nutrient cycling in soil (Im et al, 2015;Kaurin et al, 2018).…”