Removing heavy metal toxins the eco-friendly way

Japanese researchers have highlighted the best biodegradable chemicals for removing heavy metals such as lead from contaminated soils.

Heavy metals from agricultural and industrial sources are found in soils and water courses worldwide. One way of decontaminating soils is by washing with chemicals such as aminopolycarboxylate chelants (APCs), which bind to the metal ions forming soluble molecules that can be removed with water. However, most current APCs are non-biodegradable, meaning they cause long-term pollution themselves, particularly in aquatic environments.

Hiroshi Hasegawa and Zinnat Begum at Kanazawa University led a study to determine the best biodegradable and environmentally friendly alternatives to APCs. The researchers measured the performance of five biodegradable APCs against the widely used chelant ethylenediaminetetraacetic acid (EDTA), to determine which was most effective in soils with a high organic content. Organic matter has a high affinity for metals and can form water-insoluble molecules, thereby affecting the chemical washing process.

The stability and effectiveness of a chelant-metal solution is determined by a number of factors, including the types and concentrations of chelant and metal ions present in the soils, and the pH level of the solution. Other non-toxic metal ions in the soils, such as aluminum, are known as ‘interfering cations’ because they also attach themselves to the chelant, leaving fewer bonding sites available to the heavy metals.

The researchers found that DL-2-(2-carboxymethyl) nitrilotiacetic acid, or GLDA, performed best out of the five APCs tested at neutral pH, and was just as effective as EDTA for some metals. Such non-toxic, biodegrable APCs could be used at higher concentrations without damaging the environment, in order to limit the influence of interfering cations.

Publication and Affiliation
Zinnat A. Begum1*, Ismail M.M. Rahman1,2, Yousuke Tate1, Hikaru Sawai1, Teruya Maki3, Hiroshi Hasegawa3*. Remediation of toxic metal contaminated soil by washing with biodegradable aminopolycarboxylate chelants. Elsevier: Chemosphere 87, 1161-1170 (2012). Link

1. Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan
2. Department of Chemistry, Faculty of Science, University of Chittagong, Chittagong 4331, Bangladesh
3. Institute of Science and Engineering, Kanazawa University, Kanazawa 920-1192, Japan

*corresponding author, e-mail addresses: zinnat.ara@gmail.com; hhiroshi@t.kanazawa-u.ac.jp

ID: 201212A008