**7. Discussion**

**Zone Plants**

564 Environmental Risk Assessment of Soil Contamination

**3**

IVI- Importance Value Index

**Table 9.** Phytosociological parameters of flora at test sites

**Relative frequency**

*C. procera* has been demonstrated as a potential phytoremediator species. The shrub showed good accumulation of metals and is a potential phytoextractor for As and Zn as well as a promising phytostabiliser for Pb, Cd, Cu and Mn [28, 29, 35]. *C. procera* was observed to have a high degree of sociability i.e. relative frequency, relative density, relative dominance and IVI. *P. hysterophorus* was also important in this context and was most dominant in zone 2. This species has been identified for As phytoextraction along with *A. spinosus*, *C. bonplandianum,* and *D. stramonium* [28]*.* The latter two have also been indicated for phytoextraction—*C. bonplandianum* for Mn and *D. stramonium* for Mn, Cr, and Cu—together with *R. dentatus* for Pb. Another species with high IVI, *C. murale* has been suggested for Zn, Cd, Pb and Cu phytoextraction [28, 29]. Among the less dominant species, *Tridex procumbens* and *Euphorbia*

*Parthenium hysterophorus* 7.14 9.65 0.17 16.97 *Abutilon indicum* 4.76 3.46 0.01 8.23 *Calotropis procera* 7.14 12.57 0.18 19.89 *Croton bonplandianum* 5.56 5.65 0.17 11.37 *Cynodon dactylon* 4.76 2.91 0.06 7.74 *Chenopodium murale* 6.35 12.39 0.14 18.88 *Poa annua* 4.76 3.28 0.01 8.05 *Rumex dentatus* 3.97 1.64 0.01 5.62 *Barleria diffusa* 4.76 4.55 0.00 9.32 *Achyranthes aspera* 5.56 4.19 0.01 9.76 *Sida longifolia* 4.76 3.64 0.00 8.41 *Withania somnifera* 4.76 3.83 0.09 8.68 *Boerahvia diffusa* 4.76 2.55 0.00 7.31 *Sida cordifolia* 4.76 3.28 0.00 8.04 *Amaranthus spinosus* 7.14 8.56 0.10 15.80 *Gnaphalium luteo-album* 4.76 3.83 0.03 8.62 *Euphorbia hirta* 3.17 3.46 0.00 6.64 *Ageratum conyzoides* 3.17 2.37 0.00 5.55 *Datura stramonium* 4.76 4.19 0.00 8.95 *Tridex procumbens* 3.17 4.01 0.00 7.18

**Relative density**

**Relative dominance**

**IVI**

The occurrence as well as concentrations of heavy metals like Pb, Zn, Cu, Co, Mn, Fe, Cr and Cd in streams and rivers all over the world is increasing. In the present case study, heavy metal contamination was consistently higher in city of Agra, which may be attributed to the heavy industrialization combined with agricultural and urban runoff. The situation is made worse by atmospheric deposition, again attributable to industrial and vehicular pollution. In general, freshwater ecosystems have low natural background metal levels and therefore tend to be sensitive to even small additions of most trace metals. The river water far exceeded the limits of metals prescribed by WHO and USEPA for drinking water standards and Pb, Cd, and Cr content at all sites and Ni at most sites exceeded the prescribed limits. In a heavily populated country like India where a sizeable portion of the population is illiterate and resides in slums/ poorly planned neighbourhoods without proper sanitation and drainage, day-to-day activities also contribute to the overall pollution load. Provision of suitable alternatives along with proper education and awareness is integral to the minimization of this problem at the source. Apart from taking measures like effluent treatment before it enters the river and subsequent treatment of river water at the most polluted sites, a steady flow of water is to be ensured throughout the year, by way of channelizing the river with canals at crucial points. Such measures can address this problem to a substantial extent. Expenditure of more than US\$ 500 million without much success appears to be an unjustified proposition.

Phytoremediation has been receiving attention lately as an innovative, cost-effective alterna‐ tive to the otherwise tedious and expensive methods in use, which are not only a burden on the exchequer but also, require efforts on a recurring basis. Lack of information on the agricultural management of hyperaccumulator species, together with their poor biomass and root proliferation, increases the difficulties in their practical application. It has been amply demonstrated that wild native plants may be better phytoremediating tools. These species can be an ecologically viable option for sustainable and cost-effective management especially in scenarios where expertise, technical expertise and/or funding is a limiting factor. Ecological surveys are necessary for adequate characterization of a plant community and subsequent identification of prospective candidates for phytoremedial strategies since metal toxicity issues generally do not arise in plants already established on contaminated soils. Allowing native species to remediate site is an attractive proposition since these species do not require frequent irrigation, fertilizers, and pesticide treatments, while simultaneously a plant community comparable to that existing in the vicinity can be established. The outcome is, thus site remediation, ecological restoration and addition in aesthetic value. This is also in concurrence with the ruling (2006) of the Hon'ble Supreme Court of India prohibiting cultivation of plants requiring fertilizers and pesticides along the river Yamuna. Using these perennial phytore‐ medial candidates without any special needs holds much promise in this context. In addition, versatility of the candidate plant to tolerate and at the same time accumulate multiple metal contaminants and/or metal-organic mixtures would be an asset for any phytoremediation strategy.
