Page 141 - Plant-Based Remediation Processes

7 Use of Wetland Plants in Bioaccumulation of Heavy Metals 131

7.11 Phytoremediation at East Calcutta Wetland: A Case Study

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The East Calcutta Wetlands (ECW; latitude 22 33 –22 40 N; longitude
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88 25 –88 35 E), a Ramsar site (no. 1208) and wetland international site (reference
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no. 2IN013), is a globally recognized conserved wetland area. The site receives
untreated municipal and industrial wastewater of the city of Kolkata (previously
known as Calcutta) for nearly the last 100 years through a web of wastewater
carrying canals passing through this area (Chatterjee et al. 2010). The ECW is the
biggest urban wetland ecosystem in India covering 125 square kilometers of area
with salt marshes, sewage farms, and settling ponds. Sewage from the city of
Kolkata is treated by this wetland, and the nutrients contained in the wastewater
also sustain fish farms and agriculture. In ECW areas, solid municipal garbage and
sludge-filled soils are used for agriculture. Between 2,000 and 3,000 metric tonnes
of solid wastes, in different forms, are being deposited daily in the wetland areas.
Garbage farming yields nearly 370,650 kg ha 1 per year, which amounts to
150 metric tonnes of vegetables daily. Huge composite industrial effluent mixed
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with city sewage (around 50,000 m per day) from Kolkata city is discharged,
without any pretreatment, to a number of canals. Most threatening was Cr contami-
nation of the area by untreated effluents from different industries including 538
tanneries located at the eastern fringe of Kolkata city. Therefore, biota in the ECW
ecosystem is thought to be under potential threat of hazardous metal contamination
to human. The wetland plants of this region have taken a key role in ameliorating
heavy metal contaminated soil and water. Metals namely, Cr, Cu, Pb, Zn, Mn, and
Fe were studied for phytoextraction properties in ten different plants of the region
(Chatterjee et al. 2011). It was found that plants like Bermuda grass (Cynodon
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dactylon) had the highest total Cr concentration (6,601 33 mg kg dw). In this
study (Chatterjee et al. 2011), it was also found that the extent of accumulation of
various elements in the plants of the study sites was Pb (4.4–57 mg kg 1 dw), Cu
(6.2–39 mg kg 1 dw), Zn (59–364 mg kg 1 dw), Mn (87–76 mg kg 1 dw), Fe
(188–8,625 mg kg 1 dw), Ca (969–3,756 mg kg 1 dw), and Cr (27–660 mg kg 1
dw) indicating an uptake gradient of elements by plants as Ca > Fe > Mn > Cr
> Zn > Cu > Pb (Chatterjee et al. 2011). Again, metal accumulation and locali-
zation in the root are of interest for the physiology and ecology of plant survival
under elevated metal levels. X-ray microanalysis study revealed the patterns of
distribution of elements along the length of roots of plants, water hyacinth
(Eichhornia crassipes (Mart.) Solms), and common arum (Colocasia antiquorum)
confirming their ability to amass heavy metals in higher concentration (Chatterjee
et al. 2007). Further, plant species like sunflower (Helianthus annuus), marigold
(Tagetes patula), and cock’s comb (Celocia cristata) grew on soil contaminated by
industrial sludge and irrigated regularly with wastewater in the ECW were also
examined for their potential role in the phytoremediation process. It was found that
general accumulation patterns of metals concerned in different plant parts were root
> leaf > stem > flower. Cultivation of economically important, nonedible, orna-
mental plant species is an alternative cost-effective practice to remediate heavily