Combating arsenic in the soil using zeolite – Nikos Lygeros
There are two main categories of arsenic: organic and inorganic. The latter is more toxic than the former. It is a compound of oxygen, chlorine or sulphur. Organic arsenic, on the other hand, is a compound of carbon or hydrogen. In this form, it is toxic in large doses but beneficial in small ones, as it is one of the super-trace elements essential for humans and other animals. It is therefore important to examine soil toxicity in relation to arsenic. Studies have already been carried out showing that, to address the ecotoxicity of an environment contaminated with arsenic, we can achieve a reduction by using iron oxides or zeolites mixed with organic matter in the soil.
Thus, compost enriched with iron oxide and/or zeolite has been applied to arsenic-contaminated soil. The bioavailability of arsenic was determined by the percentage of arsenic absorbed by ryegrass grown on this soil in a greenhouse. The uptake rate was reduced to 2 mg/kg (dry matter) with 15% compost containing either 5% iron oxide or 5% zeolite. Thus, in both cases, the plants absorbed less than 0.01 per cent of the soil’s arsenic content. Further details can be found in the study by Gadepalle, Ouki, Herwijnen and Hutchings entitled: ‘Effects of amended compost on mobility and uptake of arsenic by ryegrass in contaminated soil’ in the journal *Chemosphere* (Volume 72, Issue 7, July 2008, pages 1056–1061).