ROLE OF AUTOCHTHONOUS FUNGI IN PHYTOEXTRACTION OF HEAVY METALS FROM TOXIC TANNERY SOLID WASTE

Abstract

The TSW generated by the Leather industry has been a hazardous entity for agricultural soils in the vicinity of KTWMA landfill site, Kasur, Pakistan. The presence of enormous amounts of toxic metals like Cr, Cd, Cu, Fe, Na, K in the TSW has been a major hindrance in converting its organic and combustible components into products like manure, compost and fertilizer, etc. Finding solution for the decontamination of heavy metals present in TSW has been one the primary concerns of environmental biotechnologists in Pakistan. The current study is focused at phytoextraction of heavy metals from TSW through phytoextraction bioreinforced with autochthanous saprobic fungi isolated from TSW. After repetitive analyses, the TSW was observed to have high pH (8.9), ECe (2.89 dS cm- 1 ), NaCl (421 %), bicarbonates and chlorides (359.9 and 3118 mgL-1 respectively), considerable amount (4.5 %) of organic matter and very low bulk density (0.66 g cm-3 ). The multi-metal contaminated TSW had high levels of both essential and trace metals. The total metal fraction of Category-I and II metals was much higher than the in the upper part of permissible limits of USEPA (1999) with concentrations of Ca, Mg and Na (6320, 4210 and 9440 mg kg-1 respectively) as well as Cd, Cr, Cu, Fe, Mg, Ni, Pb and Zn (10097, 25534, 10554, 2250, 3840, 590, BDL and 7590 mg kg-1 respectively). Screening of hyperaccumulator fungi isolated from TSW on different fungal nutrient media and selection of ornamental plants for phytoextraction on the basis of germination response (%) on TSW-Soil mixtures short listed the upper level of TSW (%) in TSW-Soil mixtures on the basis of toxicity contribution in soil. The total thirteen autochthonous fungal species were isolated from TSW and four of them viz. Alternaria alternata, Aspergillus niger, Fusarium sp. and Trichoderma pseudokoningii were shortlisted for in vitro mutual growth interaction studies. The four shortlisted fungi were also tested for their in situ mutual interaction studies in soil by applying their inoculations in different combinations to marigold (Tagetes patula). On the basis of plant vegetative biomass production incurred by the fungal inoculations, the isolates of Trichoderma pseudokoningii and Aspergillus niger were ultimately selected for actual phytoextraction trials on marigold (Tagetes patula) and sunflower (Helianthus annuus) in greenhouse and field conditions. The TSW-Soil mixtures for these trials were 0 (only soil), 5, 10 and 20 % (TSW-Soil w:w). The plants cultivated on 20% TSW-soil mixture showed less significant growth as compared to 5 and 10 % lower TSW-soil Mixtures, with lower values of all biochemical parameters in terms of chlorophyll content, total protein, SOD and CAT activity. The metal extraction efficiency was found to be the highest in F1 + F2 treatment. The metal extraction efficiency from higher to lower order was in the order: F1 + F2 > F2 > F1 > C. Both the tested plants were found to be effective accumulators of metals. The plants given inoculation of both fungi (F1 + F2) showed a significantly higher growth in all types of soil. Plants given only fungus (F1 or F2) also showed significant growth rate as compared with control treatment. The statistical analyses of the results showed increase in all growth parameters in lower TSW-soil mixtures at all exposures followed by a decrease at the highest TSW-soil ratio i.e. 20%. According to Tolerance Index (TI) and translocation Index, H. annuus and T. patula proved to be the suitable for phytoextraction of multimetal contaminated TSW and showed the ability to serve as phytostabilizing plants for metals in the phytoremediation process. Tolerance Index (TI) values more than 1.0 for Cr and Zn suggested the hyperaccumulative potential of both plants for these metals. Greater SEY (%) values also suggested the efficiency of both these plants to remove metals from TSW. Keeping in view the growth parameters and metal accumulation in the plant, it was observed that lower percentage (5 and 10%) of tannery solid waste was suitable for the phytoremediation of most of the studied metals. The better growth, elevated levels of antioxidants (SOD and CAT), high accumulation of metals and significant statistical data showed that there is synergistic effect of both fungal inocula (F1 + F2). Thus autochthonous fungi along with tolerant plants can be exploited for phytoremediation of tannery waste by products.