Review on heavy metal pollution in major lakes of India : Remediation through plants

The historical lakes of India are getting over burdened with the loads of pollution due to the rapid growth of small scale industries, nutrient enrichment and other anthropogenic activities. The high concentrations of metals in the water bodies, their entry into ecological food chain and the resulting health effects are of great concern to the researchers in the areas of ecology. Due to the problems associated with the conventional methods of pollutant removal, phytoremediation method is gaining more attention. The plants to be used in this technique, it must have high capacity of metal absorption, its accumulation and reduction in the time of decontamination in an ecosystem. It is an environment friendly and cost beneficial technique for the removal of toxicants from the environment. This article present over view on status of heavy metal pollution in lake and remediation through plants in Indian context may helpful to researcher not only in India but around the world also. This base line data can help governmental and non-governmental organization for the management of water pollution.


INTRODUCTION
A lake can be viewed as the most attractive and expressive characteristic of a landscape.In India there are some natural lakes that lies in the Himalayan region and in the flood plains of the Indus, Ganga and Brahmaputra.These lakes with various dimensions possess different names that are summarized in Table 1.However during the last 1000 years a large number of man-made water bodies were constructed in the western and peninsular India (Gopal et al., 2010).
Water qualities in such lakes have been studied by many researchers in different areas (states) of the country and are tabulated in Table 2 and the location of these lakes are shown in Figure 1.Accumulation of heavy metals in the freshwater ecosystem is a problem of global concern.On the recent time scale due to the continuous rise in the population, rapid industrialization, toxic chemicals used by agricultural industries and the technologies involved in waste disposals, there is increase in the rate of release of pollutants into the environment than the rates of their purification.Entry of these toxic metals to the ecosystem results in geoaccumulation, bio accumulation and bio magnifications *Corresponding author.E-mail: apu13@rediffmail.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License  (Lokeshwari and Chandrappa, 2006).The major sources of heavy metals are summarized in Table 3 and the most contaminated states of heavy metal in India are also depicted (Table 4 and Figure 2).Heavy metals can be described as any metallic elements which have a relatively high density and are poisonous even at very low concentration in every organism (Lenntech, 2004).These groups of metals and metalloid have atomic density greater than 4 gm/cm 3 which is 5 times higher than water (Nriagu, 1989;Garbarino et al., 1995).
In counties like ours, with developing economies, the sustainable development, efficient utilization and effective management of their water bodies should be the acceptable strategy for economic growth.But in the recent past improper management and the ineffective utilization of the natural resources for various purposes has resulted in various problems such as water logging and salinity in the field of agriculture and heavy metals contamination due to mining industries and municipal uses (Rai and Pal, 2001;Kumar et al., 2008).According to the Indian standards, the maximum permissible level of these heavy metals is shown in Table 5. Status of heavy metal pollution in lakes of different states of the country is summarized in Table 6.
Phytoremediation as an emerging clean up technology used for pollutes groundwater and wastewater treatment is described as the engineered use of green plants (including grasses, forbs, and woody species) to remove or eliminate environmental contaminants such as heavy metals, trace elements, organic compounds and radioactive compounds in many aquatic ecosystems.Macrophytes is one of the important component of the aquatic ecosystems, these can be used as an effective accumulator of heavy metals and is also a food source for many aquatic invertebrates (Preetha and Kaladevi, 2014).

ROLE OF PLANTS IN REMEDIATION
Plants can be used to cleanup or remediate contaminated sites by several ways in order to remove contaminants from the soil, sediment, or water.Such plants can breakdown or decompose organic pollutants or may stabilize metal pollutants by acting as filters or traps.Plants usually take contaminants through their root system in which the main mechanism for controlling the contaminant's toxicity lies.The root system of plants provides wide surface area to absorb and accumulate the nutrients and water that is required for growth and other non-essential pollutants.Research is still going on finding the use of trees rather than smaller plants for affective treatment in deeper contamination because tree roots can penetrate more deeply into the soil.Further polluted ground water can undergo treatment by pumping out the water from the ground and using plants to treat the contamination.Plants roots releases organic and inorganic compounds (root exudates) in the rhizosphere that causes changes at the soil root interface.This is an effective alternative technology which can replace mechanical conventional clean-up technologies that often needs high capital inputs, labour and energy.Phytoremediation is an in-situ remediation technique that uses the inherent capacities of living plants.It is also an ecofriendly, solar energy driven clean-up technology based on the principle of using nature itself to clean nature.Some hyperaccumulator species and their accumulation level are summarized in Table 7.
Most of the phytoremediation processes are targeted on inorganic pollutants through different attempts which is termed as phytoextraction (the utilization of metal accumulating species to transport and accumulate metals from the soil to roots and above ground biomass), rhizofiltration (the utilization of plant roots to absorb, precipitate and concentrate toxic contaminants from polluted effluents, phytovolatilization (some metal pollutants such as As, Hg and Se occur in gaseous forms in the environment; scientists have recently discovered genetically-modified plants that are capable of absorbing metals in their elemental forms from the soil, thus converting them biologically to gaseous species within the plants and release them into the atmosphere) and phytostabilization (the utilization of plants in lowering down the mobility of metals) (Mandal, 2014).

APPLICATIONS OF PHYTOREMEDIATION IN INDIA
One of the most promising applications of phytoremediation techniques is the possibility of deriving additional benefit from the plant system during or after the prevention or clean-up technology.Ali et al. (1999) studied the physico-chemical parameters of Nainital lake and the functions of macrophytes in phytoremediation and biomonitoring of metallic ions that are toxic in nature.Reports showed that the concentrations of metals such as Cr, Cu, Fe, Mn, Ni, and Pb are much higher than their recommended maximum permissible limits.Metal extracting capacity of existing plants is highly significant for biomonitoring studies.Sharma et al. (2014) prove to be an effective phytoremediation technique to restore the quality of water by harvesting both the submerged and the floating species from the littoral zone of the lake.Recently large numbers of submerged, free floating and emergent plant species have been recognized that can  (Rai et al., 1995;Nirmal Kumar et al., 2006;Prasad, 2007;Shah and Nongkynrih, 2007;Shrivastava, 2008;Dixit and Dhote, 2009;Mishra and Tripathi, 2009;Narendra et al., 2012;Swain et al., 2014;Phukan, 2015;Shafi et al., 2015;Kumar and Chopra, 2016;Shekhar and Prashik, 2016).Researches on phytoremediation in different states of India are shown in Table 8.

CONCLUSION
Phytoremediation for pollution control has many drawbacks as well and it requires further intensive research on plants and site-specific conditions.It is comparatively a slow process than other treatment processes viz chemical, physical process.Plants with low production yields and reduced root systems do not carry out effective phytoremediation and do not prevent the leaching of contaminants into the aquatic system.Environmental conditions play an important role in phytoremediation as the growth and the survival of plants are negatively affected to extreme environmental conditions.In this technology multiple metal polluted bodies are desire more metal accumulator species and thus it requires a broad range research studies before its applications.There are also several limitations like metals must be in their bio-available form to plants.The metals will pass down the root systems without accumulation if it is water soluble.Despite these drawbacks, phytoremediation technology has many applications

Figure 1 .
Figure 1.Location of studies lakes.

Figure 2 .
Figure 2. Heavy metals contaminated states of India.

Table 1 .
Various water bodies' dimensions have different names in India.
Source: Conservation and management of lakes-an Indian perspective (2010).

Table 2 .
Status of water quality of different lakes of India.

Table 5 .
Permissible level of heavy metal.

Table 6 .
Status of heavy metals pollution in different lakes of India.

Table 7 .
Some hyperaccumulator species and their accumulation level.

Table 8 .
Worked carried out heavy metal remediation through plants in different states of India.