Possible Phytoremediation of Chlor-alkali Waste by Using Sesbania Aculeata. Pers

An attempt was made to decrease the toxic effect of waste soil from a Chlor-alkali factory by Sesbania aculeata pers. Sesbania is cultured in varying waste soil combinations accumulated an appreciable amount of mercury .The accumulat ion depends both on soil concentration and time. Alkaline pH of the waste soil combinations also decreased with time. After 35 days culture of Sesbania, a significant increase in the growth of rice Oryza sativa var IR 36 was reported over that of un-inoculated control set. It indicates that possible phytoremediation of chlor-alkali waste can be achieved with this plant.


Introduction
There is no gainsaying the fact that Industrialization is the key to economic g rowth and helps in raising the standard of liv ing of the people. It is also hard to disagree with the fact that industries provide the society with services necessary to conduct daily life and to engage in productive activities. But the wastes of Industries are of the majo r non-utilized substance in many countries and these wastes contaminate the whole Biosphere. These wastes could not fully exp loited due to non availability of v iable technology as the viable technology must be cost effective, eco friendly and socially acceptable. The conventional processes used for waste treatment are precipitation, hydro xides/sulphides, oxidation/reduction, and ion exchange which are expansive and not eco friendly [1,2]. That is why a biological mean of pollution control is most favored today and Phytoremediat ion can be suggested as an effective method [3,7] as the plant based technology is considered to be useful for cleaning up contaminated soils and waters because biological materials are cost effect ive, abundantly available, non toxic and biodegradable [5]. The heavy metal along with other pollutants can be accumulated biologically [6,7] and subsequently transferred with b io magnifications in different tropic levels in food chain [8,9].
Gan jam, situated at the ban k of the river Rushiku lya, about four kilo meters fro m the point where it meets the Bay of Bengal perceived the threat of mercury pollution by the establishment of the M/S Jayashree Chemicals -a ch loralkali factory, which releases effluent into the river,exhaust air into the atmosphere through ventilators and the waste soil is dumped by the side of the effluent channel. Because the factory is in the coastal region, the dump waste is subjected to aerial d ispersal during the summer. In monsoon, the dissolved salts, along with mercury, enter the nearby fields with runoff water and contaminate them. So me research has been conducted on mercury concentration in aquatic and terrestrial b iota around chlor-alkali factories [10][11][12]. However reports pertaining to the accumulation and effects of mercury in crop plants are very few [13,14] and Dash et al. [4] reported that the changes in the morphology of crop plants are induced by saturated solid factory extracts. Therefore, an attempt has been made in the present investigation to determine the possible phytoremediation by Sesbania aculeata pers. Sesbania aculeata pers is an erect, semi woody plant having 4-5ft height with nodulated root for fixation of nitrogen [15] and is known as a b iofert iliser in some of the regions of Orissa state of India.

Analysis of the Waste Soil
The waste soil of the chlor-alkali factory is periodically removed and dumped as heaps by the side of the effluent channel without any chemical processing for removal of its pollutants along with heavy metal before it is released. The waste soils were collected in gunny bags and kept under air in field condition for 48 hours to reduce its moisture content. The dried soil was then powdered manually and stored for use in the experiment. The powdered soil was subject to analysis for various important constituents.
The grey colored soil was alkaline in nature with a pH of 9.20 ± 0.05. It contained 0.95g o f mercury per kg of waste soil as analysed by cold atomic absorption technique using a Mercury Analyzer. Model No. MA 5800A, Sodiu m content of the waste soil analyzed by Flame Photometer, It was 6 g per kg of the waste soil and chloride content was 18g per Kg. Potassium and phosphate contents of the waste soil were almost equivalent to that of a nutrient solution being 55 and 60 mg per kg of the waste soil respectively.

Preparati on of Culture Pots
The dried and powdered waste soil was passed through a fine mesh and was used for the preparation of culture pots. Varying concentrations of the waste soil was prepared with normal garden soil (pH 6.44 ± 0.02) ranging fro m 10 per cent to 60 per cent at an interval of 10 per cent. Final weight of the soil co mbinations prepared was 4Kg. They were kept in earthen pots of equal size in triplicate to use as the mediu m to culture Sesbania seedlings. The pots were watered equally. The waste soil comb inations and water were mixed thoroughly and allo wed to settle. Seeds of Sesbania were sown in the pots containing varying contaminated waste soil combinations.

Analysis for Mercury
After 7, 14, 21,28, 35 days of transplantation the Sesbania plants were removed, washed thoroughly, blotted and analyzed for mercury accu mulation. The values obtained were subjected to statistical analysis [16] and the levels of significance were determined.

Analysis for Possible Detoxification
To assess the degree of detoxificat ion seedlings of Oryza sativa var. IR 36 were transplanted in the waste soil combinations after the gro wth and decomposition of Sesbania (35 days). Two control sets containing varying waste soil co mbinations (freshly prepared) were also run for comparison along with the set containing varying waste soil combinations without Sesbania growth to study possible microbial activity due to native and contaminated microbes. Height and tiller nu mber of the seedlings were studied at the time of maximu m tillering stage.

Mercury Accumul ati on by Root
Mercury accumulation by root of Sesbania seedlings was found to be dependent on both waste soil percentage and time (Table 1). Mercury accu mulation was found to increase with increase in waste soil fro m 10 per cent to 60 per cent and also time period after transplantation from 7 days to 35 days. In the control set with only garden soil mercury accumulat ion was not reported. After 7 days transplantation of the Sesbania seedlings mercury uptake increased from 4.86 ± 0.06µg g -1 fresh weight in 10 percent to 13.85 ± 0.05 µg g -1 fresh weights in 60 per cent waste soil co mbination. A highly significant correlat ion was obtained between waste soil and mercury uptake by root (r = 0.992, p<0.01). 14 days after transplantation of Sesbania seedlings, mercury accumulat ion increased fro m 7.11 ± 0.11µg g -1 in 10 percent to 18.27 + 0.07 µg g -1 fresh weight in 60 per cent waste soil combination. The correlation (r = 0.991) between waste soil combinations and mercury uptake by root was h ighly significant (P < 0.01) ( Table 2). After 21 days transplantation of the Sesbania seedlings mercury uptake increased from 9.16 ± 0.06 µg g -1 fresh weight in 10 percent to 21.34 ± 0.04 µg g -1 fresh weights in 60 per cent waste soil co mbination. A highly significant correlat ion was obtained between waste soil and mercury uptake by root (r = 0.990, p<0.01). 28 days after transplantation of Sesbania seedlings, mercury accumulat ion increased fro m11.00 ± 0.05 µg g -1 in 10 percent to 24.00 + 0.05 µg g -1 fresh weight in 60 per cent waste soil co mbination. The correlation (r = 0.982) between waste soil co mb inations and mercury uptake by root was highly significant (P < 0.01) ( Table 2). After 35 days transplantation of the Sesbania seedlings mercury uptake increased fro m 12.85 ± 0.05 µg g -1 fresh weights in 10 percent to 25.61 ± 0.06 µg g -1 fresh weights in 60 per cent waste soil co mbination. A h ighly significant correlation was obtained between waste soil and mercury uptake by root (r = 0.971, p<0.01).  Table 3 depicts accumulat ion of mercury in shoot of Sesbania seedlings. The accumulat ion of mercury in shoot was dependent on amount of waste soil and time period. It increases with increased waste soil and time period. It increases with increasing waste soil form 10 per cent to 60 per cent and fro m 7 days after t ransplantation to 35 days after transplantation. Highly significant correlat ions were observed between mercury uptake by shoot and varying waste soil comb inations.

Mercury Accumul ati on i n Shoot
After 7 days transplantation of the Sesbania seedlings mercury accu mulat ion in shoot increased fro m 2.46 ± 0.06 µg g -1 fresh weight in 10 per cent to 7.65 ± 0.15 µg g -1 fresh weight in 60 per cent waste soil co mb ination. The correlation between mercury uptake in shoot and waste soil combinations was highly significant (r = 0.996, P < 0.01) ( Table 2). 14 days after transplantation, mercury accumulat ion increased from 3.88 ± 0.07 µg in 10 per cent to 8.22 ± 0.20 µg in 60 per cent waste soil co mbination per g fresh weight of shoot. A highly significant (P < 0.01) correlation (r = 0.986) was obtained between mercury accumulat ion and waste soil co mbination. A fter 21 days transplantation of the Sesbania seedlings mercury accumulat ion in shoot increased from 5.10 ± 0.05 µg g -1 fresh weight in 10 per cent to 9.90 ± 0.10 µg g -1 fresh weight in 60 per cent waste soil co mbination. The correlation between mercury uptake in shoot and percent waste soil combinations was highly significant (r = 0.996, P < 0.01) ( Table 2). 28 days after transplantation, mercury accumulat ion increased from 6.20 ± 0.10 µg in 10 per cent to 10.45 ± 0.15 µg in 60 per cent waste soil co mbination per g fresh weight of shoot. A highly significant (P < 0.01) correlation (r = 0.818) was obtained between mercury accumulat ion and waste soil combination. 35 days after transplantation, mercury accumu lation increased fro m 7.00 ± 0.09 µg in 10 per cent to 11.15 ± 0.05 µg in 60 per cent waste soil comb ination per g fresh weight of shoot. A highly significant (P < 0.01) correlation (r = 0.984) was obtained between mercury accumu lation and waste soil co mbination.

Height and Tiller Number of Rice after Sesbania Gr owth
In the control set (35 days), at maximu m t illering stage height of the seedlings decreased from 48.00 ±1.67 cm in garden soil to 20.67 ±1.53 cm in 30% waste soil combinations (Table 4).In 40%, 50%, 60% waste soils rice seedlings failed to survive. Follo wing growth and decomposition of Sesbania after 35 days rice seedlings survived in 40%, 50%, and 60% waste soil but also there was growth of the seedlings. In the treated set however reduction in survivability of rice seedlings started from 40% waste soil combinations. In 40% waste soil co mbination 7 out of 12 transplanted survived, in 50% waste soil 5 survived and in 60% only one survived. However heights of the rice plants decreased from the garden soil. Similarly at maximu m tillering stage tiller number of the seedlings decreased from in garden soil to 30% waste soil comb inations (Table 5). In 40%, 50%, 60% waste soils rice seedlings failed to survive. Following growth and decomposition of Sesbania after 35 days rice seedlings survived in 40%, 50%, and 60% waste soil but also the tiller nu mbers increased.

Discussion
According to Chaney [17], the accumulation of metal depends on several factors like p lant variety, plant parts, plant age, amount of metal in soil, soil p H, organic matter content, characteristic of metal, presence and absence of competing ions, cations exchange capacity of soil and phosphate content of the soil. According to Nasu et al [18] the absorption of metal ions by plants is also influenced by the kind of co existing ions (metals and base cations) and it also differs fro m one metal to another. It was also found that the higher atomic weight ions like Hg were concentrated mo re effectively by plants than lower ato mic weight ions like Cd and Ni [19].
The accumulation and biological conversion (Methylation) of mercury by producer organisms in aquatic and terrestrial ecosystems [20] is a matter of great concern. Roger, [21] reported methylation of divalent mercury in agricultural soil, degree of methylation directly proportional to the concentration of mercury in the soil and the exposure time .The experiment discussed above shows that the accumulat ion of mercury by Sesbania is dependant on both on time and concentration of waste soil.
Thakur, [22] op ined that plants can be used to remediat ion environmental media in situ. These findings led to the conclusion that the heavy metal pollut ion can be min imized through cost effective approaches of environmental management through plants. Pytoremediation involves two aspects to clean up the environ ment like use of metal accumulat ing plants to remove toxic metals and use of plant roots to eliminate the bioavailability of to xic metals & Sesbania for these purposes fits best. It can also be used as a bio-monitoring agent for Hg pollution as well. Th is is probably due to the production of some phytosiderophores [23] or some biosurfacants [24] produced by the microorganisms present in the root nodules and rhizosphere of Sesbania. The rice plants (IR 36) grown in waste soil of M/S Jayashree chemicals show decrease in growth and also decrease in biochemical variab les like Protein, DNA and RNA. After the growth and decomposition of Sesbania suitable for the growth of rice plants (IR 36) indicates that possible phytoremediat ion of chlor-alkali waste can be achieved with this plant.