Bioremediation Through The Use of Indigenous Natural Resources vis-a-vis Its Impact on Morphology, Metabolism, Yield, Soil Health and Soil Biodiversity of Paddy Field Under Fluoride Toxicity
Abstract
An assessment was undertaken to study the combating capacity of bacterial consortia isolated from different sources viz. oil spillage sludge and water spillage of petrol pump and rhizosphere of rice plant against the fluoride toxicity under field condition. Oryza sativa was selected as a test species. The recommended doses of chemical fertilizers (70:35:35) and different concentration of sodium fluoride (25 , 50 , 100 , 200 , 300 , 400 and 500 mg Kg-1 F) were used for first set of experiment and the second set were treated with vermicompost, compost, bacterial consortia and different concentration of sodium fluoride(25 ; 50 , 100 , 200 , 300 , 400 and 500 mg Kg-1 F). Among all of the species Penicillium, Aspergillus and Fusarium were resistant and survived under fluoride polluted condition. One unique thing was observed from these experiment that paddy which were grown under indigenous organic inputs treated plots gave maximum yield under T 1 treatment (25 mg Kg-1 F) which was above the control set. Moreover, stress enduring metabolites viz. proline content of flag leaves were lowest recorded under indigenous organic inputs treated plots as compared to chemical fertilizer treated plots. Data were significantly different at 5% level using Duncan’s Multiple Range Test. From the Air Pollution Tolerance Index (APTI) value of paddy clearly depicted that the crop of those plots were treated with indigenous organic inputs were more resistant for enduring stress condition. In these experiment combination of vermicompost, compost and bacterial consortia were capable of reducing the amount of fluoride within plant parts especially in grains (< 0 .3 mg Kg-1 as recommended by EPA, FAO and WHO), where fluoride was within permissible range as well as they reduced the fluoride content within the soil (2.57 -16.44 mg Kg-1. as recommended by FAO, EPA, and WHO) as was noted by measuring the fluoride in the plant parts and soil after the experiment. Therefore, bacterial consortia could be an alternative for bioremediation of fluoride.
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Introduction
Fluorine is a chemical element with symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. As the most electronegative element, it is extremely reactive, almost all other elements including some noble gases form compounds with fluorine. Among the elements, fluorine ranks 24th universal abundance and 13th in terrestrial abundance. Now a day’s, fluoride (F) is a most concerned environmental pollutant which is a toxic substance, present in air, water and soil. The toxic effects of F on plants and animals have been known for more than a hundred years. With recent industrial expansion they have been increasingly recognized for causing serious toxicity to vegetation (Dey et al., 2012). There are numerous papers regarding the impact of fluoride on ground water, soil and biochemical changes of different plants under laboratory condition. But, very few limited number of works have been reported about the amelioration of fluoride under the field condition.
F is a naturally occurring pollutant, which is often released into the soil-environment through the use of phosphatic fertilizers and other pesticidal sprays as well as through the disposal of industrial sludges (Singh et al., 1990).
Fluorine content in different soil is determined by its concentration in a parent material, while its distribution in soil profile depends on the rate of mineral decomposition, pH and content of the clay fraction (Omueti and Jones, 1980). Damage caused by fluorine in soil is connected mainly with the destabilization of natural soil structure due to changes of the soil humus-silt complex, and also mineral composition. The presence of alkaline metal fluorides decreases the content of organic matter soluble in water, also the mobility of mineral-organic complexes. As result of such changes the biological activity of soil can be decreased. Due to such detrimental effects growth and activity of microorganisms are present in soil become decreased. In case of plant/ crop species they can uptake fluoride from the soil as a free ion or it can enter into the plant body through the stomata from the air (Stevens et al., 1997; Mezghani et al., 2005). Sodium fluoride inhibit germination, cause ultra structure malformations, reduce photosynthetic capacities, alter membrane permeability, reduce productivity, decrease biomass and inflict other physiological and biochemical disorders in plants(Gautam et al., 2010). Moreover, F toxicity may have important consequences such as reduction in growth or yield (Singh et al., 2013).
To find out the impact of fluoride on growth, metabolism and yield of crops viz. paddy as well as ameliorating capability of indigenous organic inputs under field condition, one field experiment was carried out in the year 2013. From the experiments one unique thing was revealed i.e., the bioremediation measure of fluoride under field condition may be possible. Such bioremediation measures were mixture of vermicompost, compost (cow dung) and bacterial consortia isolated from different sources such as rhizospheric soil, oil spillage sludge and wastewater of petrol pump vicinity. Such type of indigenous organic resources are chosen as a bioremediation measure because there are some limitation or drawback in traditional agriculture practice viz. decline soil productivity, loss of organic matter, water holding capacity and biological activity. Traditional agriculture practice involved use of various kind of chemical fertilizers, pesticides etc. Use of chemical fertilizers contaminates soil and water bodies, such as lakes and rivers. Pesticides may kill the insects that destroy crops, but they also kill the good insects as well. To overcome such type of problems in recent year’s scientists and engineers started to generate cost effective technologies which includes use of microorganisms/biomass or live plants for cleaning of polluted areas (Qiu et al., 2006). It was well documented that above mentioned organic indigenous inputs having potentiality to combat against stress condition as well as reduce the uptake and transportation of toxic metals through the plant system (Jadia and Fulekar, 2008). Application of compost and vermicompost in contaminated soil improves soil fertility and physical properties as well as helps in successful approach to phytoremediation (Zheljazkov and Warman, 2004). It also enhances the quality of growing plants and increased biomass which could suggest that more metal taken up from the contaminated growth media and the tolerance to the metal toxicity is improved(Tang et al., 2003). It has been found to influence all growth and yield parameters such as improved seed germination, enhanced rate of seedling growth, flowering and fruiting of major crops like wheat, paddy, spinach, corn, tomato etc. Earthworms consume large quantities of organic mater and excrete it as cast and this cast contains several enzymes and is rich in plant nutrients which are beneficial for bacteria and mycorrhizae (Reddy and Reddi, 2002). They also noted that vermicompost is an excellent base for the establishment of beneficial non-symbiotic and symbiotic microbes. Application of vermicompost increases total microbial population of nitrogen-fixing bacteria and actinomycetes (Garai et al., 2013).
Bacterial consortium are assemblages of different species of microbes in physical (and sometimes intricate biochemical) contact with one another. These bacteria are capable of fixing atmospheric nitrogen, solubilize phosphorous and iron and enhance production of plant hormones. Additionally they improve the plant tolerance to stresses (Bashan et al., 2008; Chan, 2003).
Conclusion
From the field experiments, it is clear that fluoride reduce the growth, metabolism and yield of crops but inoculation of vermicompost, compost and bacterial consortia can make the plant more resistant as well as such organic resources also capable to maintain the soil health and biodiversity. In India, we have several indigenous natural inputs which can be use judiciously under field condition and they can be a potent tool for reduction in the level of contaminants. It was observed from such studies that the use of treatment combinations (vermicompost +compost+ bacterial consortium) was able to re duce the fluoride content in soil and plants growing upon there. Therefore, such treatment combination if used, have a positive role in combating fluoride level under such agroclimatic field conditions, Such low cost agro-technology needs further experimentations with diverse crops under diverse agro-climatic condition for supplying the knowledge to the farmer’s level. After studies on several agroecological conditions, in a vast country like India this technology could be released to farming community for the benefit of mankind as a whole.
