Efficacy of Pleurotus Species for Mycoremediation of Heavy Metals – A Case Study of Vinoba Bhave University, Hazaribag

INTRODUCTION

Soil may be defined as a product of interaction of several factors such as the influence of organisms, climate, minerals present etc. Soil acts as an emerging medium in different function it performs. Increased rate of anthropogenic activities have deteriorated the soil entity (Facchinelli et al., 2001, Jonathan et al., 2004). The presence of toxic metal in soil is becoming a matter of concern as these toxic metal reduces the fertility of the soil, enters food chain which eventually leads to severe health problems (Denti et al., 1998, Sandaa et al., 1999). Although various chemical and mechanical methods for removal of heavy metals are available but all of them are costly, energy consuming and complicated. Mycoremediation on the other hand is an eco-friendly and cost effective techniques where fungal hypae especially mushroom are utilised for biosorption of heavy metals from substratum. These trace metal can be removed by a promising technology ―Mycoremediation‖ which uses fungi as a remediation tool. Mycoremediation is listed amongst the best tool to remove heavy metals from soil and water. It comes under the category of very cost effective technique and gives quick results. Pleurotus species is commonly known as Oyster mushroom and it belongs to Basidiomycetes of fungi. Although approximately 70 species of this genus have been identified. 7 of them are commonly found. Typical of mushroom, they are Saprophytic and are mainly found in rainy season especially in forest ecosystem. They are highly adaptive to different climatic condition (Agrahar Murugkar & Subbuakshmi 2005) and they prefer different agricultural waste for their growth. Pleurotus species is an important edible mushroom but in recent past their capacity of Biosorption has attracted a large number of researchers (Tay et al., 2011; Das et al., 2007, Dulay et al., 2015; Arbanah et al., 2012; Prasad et al., 2013; Favero et al., 1990) etc. have indicated that different portions of oyster mushroom differently accumulate heavy metals. Keeping Hazaribag. Soil samples were collected to examine the presence of heavy metal. As we know everything in excess in harmful; increased rate of heavy metal in soil is harmful for the plants.

Vinoba Bhave University campus was selected as the sampling area. The University was established in the year 1992. Soil samples were collected from 3 different stations i.e. Samraat Ashok Bhawan garden, Vehicle stand and Botanical garden of the University campus. For sample collection, simple random sampling method was applied. Sterilized plastic spatula was used to collect the soil samples. After removing 3-4cm top layer of soil, sample was collected in a pp bag ensuring that the bag was air tight. Five replica of experiment was maintained and average was taken.

The soil samples were air dried to remove the moisture content. Oversized particles were removed and then crushed in a clean sterilized dry mortar and pestle to generate fine soil. The obtained fine soil was sieved through 2mm sieve. Thereafter, 3g soil sample was weighed and digested with a mixture of 10ml conc.HCl and 3.5ml conc.HNO3. The mixture was left overnight without any kind of heating process under switch on fume cupboard. On the next day, it was heated for 2hrs at 104°C. Distilled water was added to the digested sample and was filtered with whatman filter paper and then using distilled water, final volume was set to 100ml. The solution was further transferred into sampling bottles for analysis of concentration of Cu, Cd and Zn using AAS (Ogundele et al., 2015).

Standard protocol was followed to prepare oyster mushroom bags. The straw was dipped in water overnight (For 1kg straw, 10L water was required). Formaldehyde was added in water and mixed well (1ml formaldehyde/1L water). The next day, wet straw was decanted and allowed to dry leaving around 60 – 70% moisture in it. The same day mushroom bag was prepared. pp bags were taken samples. Then, again a layer of straw was added on top to cover the spawn completely. The bag was tightly packed and few holes were made in the layer of the spawn to let the fruiting body grow outward. The mushroom bags were kept in a dark room (23°C) as required for better cultivation oyster mushroom (Pleurotus ostreatus). Water was sprinkled at a time interval of 2 days, to maintain the moisture up to 80%. Spawn run was observed within 15 days and after few days mycelium was seen growing and the bag turned to seems whitish. After 2-3 day, fruiting bodies start growing. Fruiting bodies was harvested on 3rd day, 7th day and on 10th day to check the difference in concentration of absorbed heavy metals. Determination of the total Heavy metal in the Mushroom: 5g of oyster mushroom from each bag of sample was harvested on 3rd day, 7th day and on 10th day and dried in the oven at 105°C for 1 hour, 1g of the dried sample was weighed into a 50 mL beaker and then placed in a muffle furnace, set at 500°C. The mushroom was left to ash for 3hrs and then 10 mL of the ash mushroom sample was dissolved in 20% HNO3 and heated gently on a hot plate for about 5mins. The sample was then allowed to cool and then filtered into 5mL flask. The sample were then analysed in Atomic Absorption Spectrophotometer (Asiriuwa et al., 2013).

Physiochemical properties of soil samples collected from different sites of Vinoba Bhave University campus is presented in Table 1. Texture of soil in Samrat Ashok Bhawan garden, Vehicle stand and Botanical garden is sandy loam. As the distance of 3 stations is not much, hence, variation in texture is not observed. Percentage of sand in garden and botanical garden is 33% and 37% respectively. Percentage of sand in vehicle stand is much higher and was recorded 64%, clay was 6% and 7.3% in garden soil and botanical garden soil. Percentage of clay was comparatively high in vehicle stand and was recorded 16%. Silt was 32% and 37% in Samrat Ashok Bhawan garden soil and botanical garden soil respectively. Whereas, silt content in soil collected from vehicle stand was 47%, once again higher than the earlier 2 values. pH of Samrat Ashok Bhawan garden soil and Botanical garden soil was 6.6 and 6.3 which indicated acidic nature. pH of soil collected from vehicle stand was 7.4 i.e slightly alkaline. Carbon content was high in 2 garden sites i.e Botanical garden and Samrat

leaves nd high microbial activities which is not upto that mark in vehicle stand. This explanation is further substantiated by the value of organic matter recorded in Samrat Ashok Bhawan garden i.e 32% and Botanical garden i.e 38%. Nitrogen content was also higher in soil from Samrat Ashok Bhawan garden and botanical garden as compared to the soil present in vehicle stand. The overall difference in soil property is also reflected in electric conductivity which is much higher in soils of garden than soil collected from vehicle stand.

Range and mean of heavy metals in soil of Vehicle stand is recorded in Table 4.3. Here, Cu ranged from 54.34 – 58.13mg/kg. Mean value for Cu was 56.19 ± 1.8mg/kg. Concentration of Cd was much low and it varied from 0.91 – 1.24mg/kg. The mean of the value was 1.09 ± 0.16mg/kg. Concentration of Zn varied from 43.11 – 46.14mg/kg. The mean value was 44.52 ± 1.52 mg/kg. Range and mean of three heavy metals is depicted in Table no. 4. The sample in this case collected from Botany garden. Cu here ranged between 52.30 – 59.61mg/kg. Mean value was 55.04 ± 3.77mg/kg. Range of Cd was on lower side and it varied from 1.21 – 1.93mg/kg. Mean value was 1.5 ± 0.37mg/kg. Zn in this sample varied from 56.91 64.32 mg/kg. The mean value was 59.85 mg/kg. Table 4.5 describes range of heavy metals and mean concentration present in mixture of soil (equal proportion) collected from 3 selected stations i.e Samrat Ashok Bhawan garden, Vehicle stand and Botanical garden. The data presented is mean of 5 replicas. Range of Cu varied from 38.16 – 48.72 mg/kg. The mean value was 43.14 ± 5.2mg/kg. Cd ranged from 1.62 – 3.34mg/kg and the mean was 2.02 ± 1.06 mg/kg. Similarly, Zn was recorded 41.48 - 51.62 mg/kg. The mean of 5 replicas was 47.15 ± 5.17 mg/kg. The variation was analysed statistically and was found significant.

Similar observation was made with the soil sample recorded from Vehicle stand which is presented in Table 4.7. Total absorption for all three heavy metals was noted down after 3days and 7days. Cu was absorbed 4.06mg/kg which further increased to 14mg/kg after 7days. On 10th day Cu absorption increased by 0.95 mg/kg as compared to the value recorded on the 7th day. Cd uptake was 0.02 mg/kg and 0.24 mg/kg after 3days and 7days respectively. Increase in Cd content in experimental condition after 10th day was recorded 0.04 mg/kg. 5.32mg/kg and 16.63mg/kg was the total uptake of Zn recorded after 3 days and 7days respectively. Zn further reduced 15.53 mg/kg as compared to 16.63 mg/kg recorded after 7days.

Table 4.9 is depicted for mixture of soil from all the three stations selected during this study. Almost similar trend was observed in the mixture of sample taken into consideration. Cu absorption was 5.39 mg/kg after 3days and 15.33 mg/kg after 7days. Absorption of Cu increased from 15.33 mg/kg when absorption period was extended to 3days further. Our test material Oyster mushroom observed 8.34 and 18.36 mg/kg of Zn after 3days and 7days respectively. Zn content after 10days once again decreased by 2.25 mg/kg.

Note: Sample 1 – Soil sample collected from Samrat Ashok Bhawan garden Sample 2 – Soil sample collected from University Vehicle stand Sample 3 – Soil sample collected from University Botanical garden Sample 4 – Mixture of all 3 soil samples

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Department of Biotechnology, Vinoba Bhave University, Hazaribag, Jharkhand, India mani4nov@gmail.com