Mycoremediation of heavy metal contaminated soil using mushrooms

Abstract

Remediation of soil contaminated with heavy metals has received considerable attention in recent years even though contamination of soil is not considered as pollution compared to air and water pollution. Low cost mitigation measures like phytoremediation and mycoremediation are commonly employed. Mycoremediation using macro fungi (mushroom) have proven to be efficient in removing heavy metals from soil through bioaccumulation. In the present study, Galerina vittiformis, a wild mushroom belonging to Strophariacea family was identified to effectively remove the heavy metals namely, Cu(II), Cd(II), Cr(VI), Pb(II) and Zn(II) at both 50 and 100 mg/kg from the soil under study (in-vitro). G. vittiformis was found to be effective in removing the metals from soil within 30 days. The bioaccumulation factor (BAF) for both mycelia and fruiting bodies with respect to these heavy metals at 50 mg/kg concentrations were found to be greater than one, which indicates hyper accumulating mechanism by this mushroom species. Bioaccumulation by both mycelial and fruiting body stage of the mushroom is found to follow the order; Pb(II) > Cd(II) > Zn(II) > Cu(II) > Cr(VI). The metal removal rates by the mushroom was analyzed using different kinetic rate constants and found to follow the second order kinetic rate equation for Pb(II), Cr(VI), Zn(II) and Cu(II) and first order rate kinetics for Cd(II). The metal uptake mechanism studies of G.vittiformis revealed the production of two types of Phytochelatins, namely PC1 and PC3 in response to heavy metal stress. These Phytochelatins are known to transfer the excess metal ions into the vacuoles of the cell and thereby reducing the metal toxicity in the cell. Both chemical and biological chelaters up to 10 mmol/ kg concentrations did not have any significant role in increasing the bioaccumulation potential of the G.vittiformis. Thus G.vittiformis exhibited high potential for mycoremediation of heavy metals without the help of chelaters. The maximum activity of G. vittiformis in terms of metal bioaccumulation from soil was found to occur at metal concentrations around 150 mg/kg for each of the metals under study in a multi-metal interaction system. G. vittiformis was found to be more effective in the removal of Pb(II), Cd(II), Cu(II) and Zn(II) from multi metal contaminated soil when compared to Cr(VI). The soil pH of around 6.5 was found toMycoremediation of heavy metal contaminated soil using mushrooms (2014) Department of Chemical Engineering, National Institute of Technology Karnataka Surathkal Page 4 be favorable for metal removal. Thus it may be suggested that G. vittiformis was identified as an effective bio-remediating agent in both single and multi-metal contaminated conditions in comparison to any other mushrooms reported in the literature.