Phytoremediation of heavy metals from paper mill effluent soil using Croton sparsiflorus

Effluents from industries contain appreciable amount of metallic cations like zinc, copper, iron, manganese, lead and cadmium. Release of heavy metal without proper treatment poses a significant threat to public health because of its persistence biomagnifications and accumulation in food chain. To reduce metal pollution problems many processes have been developed for the treatment and disposal of metal containing wastes. Certain plants have the ability to accumulate heavy metals such as Pb, Cr, Cd and Zn. At present, phytoremediation of metals may be approaching commercialization. Hence, possibility can be explored to remove heavy metal load, present even in low concentration, in waste water of paper mill effluent soil by using Croton sparsiflorus .


INTRODUCTION
Industrial or domestic effluent is mostly used for the fertigation of agricultural crops, mainly in urban and per urban regions, due to its easy availability, disposal problems and scarcity of fresh water [1,2]. Irrigation with effluents is known to contribute significantly to the heavy metals content of soil as well as crop plants [3][4][5]. Heavy metals are very harmful because of their non-biodegrable nature, long biological half-lives and their potential to accumulate in different body parts [6][7][8]. Most of the heavy metals are extremely toxic because of their solubility in water [3,9,10]. The major short comings of the conventional treatments are low efficiency at low concentration of heavy metals, expensive handling and safe disposal of toxic sludge [11].
India has 666 pulp and paper mills, out of which 632 mills are agro-residue based mills [12,13]. They generate a huge amount of wastewater having high biological oxygen demand (BOD) and chemical oxygen demand (COD) values [14,15]. The various elements introduced through pulp mill wastewater irrigation not only affect the crop growth and soil properties but also their relative mobility in the soil profile [16,17]. Pulp and paper mill is a major industrial sector utilizing a huge amount of lignocellulogic materials and water during the manufacturing process, and release chlorinated lignosulphonic acids, chlorinated resin acids, chlorinated phenols and chlorinated hydrocarbon in the effluent [18].
In this regard, phytoremediation or plant -based cleanup, have generated much interest as effective low-cost and environmentally-friendly technologies for the clean-up of a broad spectrum of hazardous organic and inorganic pollutants [19]. The success of phytoremediation depends on the availability of plant species -ideally those native to the region of interestable to tolerate and accumulate high concentrations of heavy metals [20]. Phytoremediation technologies is an emerging technology for the remediation of metal contaminated soils. It can be defined as "use of green plants and their associated microbiota, soil amendments and agronomic techniques to remove, contain or render harmless the environmental contaminants [21]. The heavy metal accumulation efficiency of the Croton sparsiflorus plant and also effect of addition of biosolids like vermicompost on the bioaccumulation efficiency of the plant have been investigated and the concentration of heavy metals from effluent soil was also evaluated ( Figure 1).

1. Collection of materials
The garden soils are gathered from nearest places. The effluent is collected from paper mill located at Solagampatti, Thanjavur, Tamilnadu. Croton sparsiflorus seeds are collected from this plant Edavakkudi, Poondi, Thanjavur, Tamil nadu. Vermicompost was prepared with cow dung using earthworm species Eurdius euginae. Seeds were germinated in experimental pots and watered. On fifteenth, thirtieth, forty fifth and sixtieth days the plants were harvested from pots and the concentration of heavy metals Chromium (Cr), Lead (Pb), Cadmium (Cd) and Zinc (Zn) of the samples were noted.

Experimental setup
The seedlings were exposed to different concentrations of heavy metal chromium to find the toxicity. Chromium at high concentrations of 200 and 300 mg/kg showed high toxicity that the plants died. (Revathi et al., 2011). The various experimental setup used for the present study are listed below:

3. Heavy metal analysis of soil samples
Soil samples of each pot were air dried, crushed and pass through 0.2mm sieve and stored in Zip lock covers for analysis. Heavy metals present in all the samples were analyzed by AAS (Atomic Absorption Spectroscopy).

RESULTS AND DISCUSSION
The concentration of heavy metals are varies in paper mill effluent (Pb > Zn > Cr > Cd). Heavy metals concentration are decreases largely in B, D and F type (15 -60 days) pots, because it consists of vermicompost which is used to growing plant and accumulation of heavy metals. So, the well growing plants which accumulate heavy metals easily than other pots (A, C and E type). Finally, excess amount of heavy metals in soil are remediated by combination of vermicompost with garden soil.
Physico -chemical characteristics of the effluent collected from the paper industry is given below: Table 2. Physico -chemical characteristics of the effluent collected from the paper industry.

S. No Name of the parameter Sample details
Physical parameter

CONCLUSION
The results indicated that the concentration of heavy metals are gradually decreases in vermicompost with garden soil combination. So, it is suitable for well growing plant and heavy metals accumulation (15-60 days). Other pots (A, C and E type) are not suitable for the removal of heavy metals in contaminated soil, because it decreases heavy metals slowly than above type of combination. This study shows that Croton sparsiflorus has a good potential to uptake and accumulate the toxic heavy metals from paper mill polluted soil. It also pares away for the development of an economically cheap technology and suitable for a good phytoremediation method.