Elimination of residual Hg from soils of Venezuela using gypsum and bacteria

Estela Adams¹, Antonio García¹, Fernando Santos², Encarna Velázquez⁴and M. Adams³

¹Instituto de Recursos Naturales y Agrobiología (IRNA). CSIC. Salamanca. SPAIN

²Facultad de Ciencias Agrarias y Ambientales. Universidad de Salamanca. SPAIN

³Facultad de Agronomía. Universidad Central de Venezuela. VENEZUELA

⁴Departamento de Microbiología y Genética. Universidad de Salamanca. SPAIN

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The Hg is one of most contaminant elements for the environmental due to its use in the gold mining and other antropogenic activities. In Venezuela, the mining of gold has been specially developed in the forestry reserve of Imataca, in the Orinoquia-Amazónica region, that should be preserved due to its high biodiversity. The analysis, stream and mining tailing in this area showed that the Hg contamination level reached up to 129,3 mgg^-1. Therefore, it is necessary develop remediation techniques able to immobilize Hg. The gypsum (as a residue of fertilizer industry) is composed basically by CaSO₄.2H₂O with lower amounts of P, F, Si, Fe and Al. Among the teasible Hg adsorbents previously tested, the gypsum showed a relatively high capacity to adsorb Hg, but its affinity grade by the Hg (K=0,810 l/mg) and correlation (R²=0,997) are high. To immobilize Hg in the soil is necessary to insolubilize it as HgS and this process might be made using gypsum and bacteria able to transform Hg²⁺ in this compound, such as Desulfovibrio desulfuricans. In this way, the bioremediation will be possible integrating several chemical and biological resources. D. desulfuricans is a Gram negative anaerobic rod included in the delta sub-class of Proteobacteria that is able to reduce sulphate and sulphite to sulphur that is easily detectable including ferrous citrate in the culture medium. In this work we have isolated anaerobic strains able to produce Fe₂S in Sulphite Iron Agar. These strains have been used in studies of immobilization of Hg in greenhouse and field conditions. The initial results showed variable results that are discussed in this work.