Freshwaters are not only used locally in many developing countries but they are often over exploited for domestic purposes, agriculture and disposal of industrial wastes which result in an overload of excess nutrients, harmful chemicals and heavy metals. Plant species together with sediments and water samples collected from eleven aquatic water bodies in the vicinity of industrial units in Kolkata were studied for their potential to uptake Pb, Cd and Cr under field conditions. Cd and Cr concentrations in the sediments were higher than background values considered to be toxic. Alternanthera philoxeroides and Eichhornia crassipes were the two invasive species present, with the former being more widely distributed. Among native plants, Ipomoea aquatica was the most abundant. Metal uptake in the plants differed among species, tissues and sites. Pb and Cd accumulation in root tissues for all plants in most sites suggested an exclusion strategy for metal tolerance. Since I. aquatica is widely consumed in many parts of SE Asia, its metal content should be checked before use since it was found to efficiently translocate both Pb and Cd from roots to shoots. The potential of A. philoxeroides as a metal excluder needs to be explored further since it translocates less to its shoots as compared to E. crassipes and I. aquatica.
Rapid urbanization and industrialization are occurring in many parts of the world. Human activities such as mining, landfill leachates, industrial emissions, vehicular emissions, fossil fuels, fertilizer erosion from agricultural run-off, herbicides and pesticides, sewage and municipal wastes all contribute to the accumulation of pollutants in nearby aquatic systems [
Freshwater ecosystems, which have greater biodiversity per surface area, are subject to more anthropogenic impacts compared to terrestrial or marine ecosystem [
The use of aquatic plants for heavy metal removal has been extensively reviewed [
Contaminated sites along canals and ponds with direct discharge of raw industrial effluents, untreated sewage and wastewater from commercial, industrial and domestic establishments were extensively surveyed in and around the metropolitan city of Kolkata, India. Eleven accessible sites with presence of plant species were finally selected for the study. A global positioning system (GPS) was used for recording the coordinates of the sites chosen for sampling.
At each site, a quadrat of size 0.5 × 0.5 m2 was floated on stands of vegetation present at
Site number | Location | Latitude (N) | Longitude (E) | Waterbody type | Probable source of contamination | Number of plant species present | |
---|---|---|---|---|---|---|---|
Invasive | Native | ||||||
1 | Chowbaga | 22˚31'15.4" | 88˚25'15.0" | Pond | Tannery effluents | 2 | 2 |
2 | Sodepur | 22˚43'01.7" | 88˚23'36.8" | Canal | Domestic waste | 2 | 1 |
3 | Dunlop | 22˚38'58.3" | 88˚22'36.9" | Pond | Vehicular emission and construction | 1 | 1 |
4 | Kamalgachi | 22˚27'00.1" | 88˚23'29.7" | Pond | Servicing and repairing of motor vehicles | 1 | 2 |
5 | Old Delhi road | 22˚43'59.7" | 88˚18'51.2" | Canal | Iron industry | 1 | 3 |
6 | Bighati | 22˚48'25.7" | 88˚18'53.4" | Pond | Logs products industry | 1 | 1 |
7 | Satragachi | 22˚35'18.9" | 88˚15'56.6" | Pond | Domestic waste dumping ground | 2 | 1 |
8 | Chingrighata | 22˚33'30.8" | 88˚24'35.1" | Canal | Sewage canal | 2 | 0 |
9 | Khalpole | 22˚26'56.1" | 88˚17'21.7" | Canal | Sewage canal | 2 | 0 |
10 | Nilganj | 22˚44'53.9" | 88˚25'17.8" | Canal | Brick industry | 1 | 2 |
11 | Anandapur | 22˚30'26.8" | 88˚24'16.3" | Canal | Slum waste | 1 | 2 |
the junction of the littoral slope and the water body. Species with adequate growth to cover the quadrat area were sampled along with contiguous sediments. Sparsely present species were not considered for the study. Samples collected for each plant species were labeled, put in individual polythene bags and brought to the laboratory. The plant samples were separated into root and shoot portions and thoroughly washed with distilled water to remove all adhering soil and dirt particles. Fresh weight of root and shoot were recorded for all plants. Samples were then oven dried to constant weight at 70˚C for 72 hours and dry weights recorded. Each dried sample was ground to powder using a Cyclotec Mill (Model 1093 sample mill, Tecator) and stored for subsequent analysis. The labeled sediment samples were brought to the laboratory, air dried to constant weight, ground into a fine powder using a mortar and pestle and sieved through a 2 mm mesh. Water samples from each site were collected using a Van Dorn sampler and on-site measurements for pH and conductivity were done using hand held probes (pHTestr 30, Eutech Instruments; ECTestr11+, Eutech Instruments). A 250 ml bottle and three 1 litre bottles were filled separately, preserved with 2 mL concentrated HNO3 and brought to the laboratory under ice for other water quality and heavy metal analysis.
Turbidity was measured in the laboratory using a turbidimeter (Model 2100P, HACH Company, USA) while total dissolved and suspended solids in the water samples were measured using standard methods [
In order to estimate a plant’s potential for phytoremediation purpose, bioaccumulation factor for shoot (BAFs) and root (BAFr) together with translocation factor (TF) were determined from the metal content in the sediments and plant parts as follows:
Bio-accumulation Factor (BAFs) = metal concentration in shoot/metal concentration in sediment.
Bio-accumulation Factor (BAFr) = metal concentration in root/metal concentration in sediment.
Translocation factor (TF) = metal concentration in shoot/metal concentration in root.
Bio-accumulation Factor (BAF) is used to quantify the toxic element accumulation efficiency in plants by comparing the concentration in the plant part and an external medium [
The plants which satisfied the “adequate growth” criterion, within each quadrat, at their sites of occurrence were Alternanthera philoxeroides, Commelina benghalensis, Eichhornia crassipes, Enhydra fluctuans, Ipomoea aquatica, Ludwigia adscendens, Sagittaria sagittifolia and the sedges. Among these, A. philoxeroides (alligator weed) and E. crassipes (water hyacinth) were the only two invasive species while the rest were native plants. While A. philoxeroides was present in all sites, E. crassipes occurred in 5 sites. Ipomoea aquatica (water spinach), the most commonly occurring native species, was present in 6 sites. It is interesting to note the complete absence of native species from Sites 8 and 9 (both sewage canal sites,
The overall shoot dry matter content in the plants studied ranged from 7.07% - 12.28% in A. philoxeroides (n = 11), 4.98% - 6.85% in E. crassipes (n = 5), 7.40% - 8.25% in I. aquatica (n = 6), 14.20% - 16.41% in the sedges (n = 3), 8.30% - 8.52% in C. benghalensis (n = 2), 5.55% - 6.12% in S. sagittifolia (n = 2), 4.42% in E. flutuans (n = 1) and 12.91% in L. adscendens (n = 1). In case of roots, dry matter values ranged from 6.33% - 11.22% in A. philoxeroides, 5.40% - 6.64% in E. crassipes, 7.25% - 9.80% in I. aquatica, 14.04% - 14.75% in the sedges, 8.00% - 8.33% in C. benghalensis, 7.25% - 8.37% in S. sagittifolia, 4.67% in E. flutuans and 6.67% in L. adscendens. E. fluctuans had lowest dry matter content for both shoot and root while the sedges showed highest dry matter content for both shoot (16.41% in site 11) and root (14.75% in site 5) among all the plants. Among sites, minimum variation in dry matter content of both shoot and root was observed in C. benghalensis while maximum variation was observed in A. philoxeroides.
The results of water quality analysis pertaining to the 11 sites are given in
Site number | Mean ± standard error | ||||
---|---|---|---|---|---|
pH | Electrical conductivity (µs/cm) | Turbidity (NTU) | Total dissolved solid (mg∙L−1) | Suspended solid (mg∙L−1) | |
1 | 7.23 ± 0.17 | 972.10 ± 10.43 | 33.33 ± 2.34 | 371.00 ± 34.25 | 20.77 ± 3.78 |
2 | 7.70 ± 0.06 | 1317.67 ± 34.14 | 70.27 ± 32.87 | 610.87 ± 92.69 | 98.86 ± 55.22 |
3 | 7.53 ± 0.14 | 910.33 ± 28.37 | 11.16 ± 3.14 | 384.47 ± 54.86 | 11.44 ± 6.39 |
4 | 7.73 ± 0.09 | 1719.67 ± 21.46 | 190.00 ± 29.67 | 876.97 ± 47.05 | 27.54 ± 2.68 |
5 | 7.82 ± 0.06 | 1343.67 ± 13.32 | 94.03 ± 44.75 | 724.31 ± 84.37 | 158.31 ± 69.93 |
6 | 8.30 ± 0.25 | 1036.67 ± 49.78 | 60.70 ± 29.08 | 656.99 ± 34.39 | 83.88 ± 66.84 |
7 | 7.86 ± 0.10 | 1968.67 ± 216.35 | 435.00 ± 143.15 | 999.76 ± 147.03 | 325.90 ± 59.52 |
8 | 8.42 ± 0.14 | 719.67 ± 22.84 | 37.93 ± 4.71 | 98.69 ± 0.32 | 63.49 ± 6.72 |
9 | 7.37 ± 0.09 | 1200.00 ± 5.77 | 47.67 ± 7.36 | 590.00 ± 0.00 | 29.78 ± 2.24 |
10 | 8.09 ± 0.16 | 832.67 ± 78.86 | 307.67 ± 129.62 | 343.37 ± 43.37 | 151.12 ± 54.14 |
11 | 7.33 ± 0.24 | 1620.00 ± 40.00 | 15.43 ± 0.32 | 810.00 ± 20.00 | 24.07 ± 3.66 |
The Pb, Cd and Cr content in the water collected from all 11 sites have been reported in
The low concentrations of all the three metals were probably because the sites were not located at the pollution source and were subject to dilution effects. However, Pb (0.022 mg∙L−1) and Cd (0.032 mg∙L−1) concentration in water was similar to those reported for an East Kolkata wetland site [
Due to variation in water levels and a low resting time, analysis of water for estimation of heavy metals may not be conclusive [
Site number | Mean ± standard error (mg∙L−1) | |||
---|---|---|---|---|
Lead | Cadmium | Chromium | ||
1 | 0.012 ± 0.000 | 0.002 ± 0.000 | 0.029 ± 0.008 | |
2 | 0.015 ± 0.002 | 0.002 ± 0.000 | 0.022 ± 0.005 | |
3 | 0.018 ± 0.003 | 0.002 ± 0.000 | 0.019 ± 0.004 | |
4 | 0.021 ± 0.001 | 0.003 ± 0.000 | 0.036 ± 0.004 | |
5 | 0.016 ± 0.001 | 0.003 ± 0.000 | 0.028 ± 0.004 | |
6 | 0.016 ± 0.001 | 0.003 ± 0.000 | 0.034 ± 0.001 | |
7 | 0.020 ± 0.003 | 0.004 ± 0.000 | 0.048 ± 0.004 | |
8 | 0.013 ± 0.003 | 0.003 ± 0.000 | 0.018 ± 0.003 | |
9 | 0.014 ± 0.001 | 0.002 ± 0.000 | 0.010 ± 0.001 | |
10 | 0.013 ± 0.002 | 0.002 ± 0.000 | 0.024 ± 0.007 | |
11 | 0.021 ± 0.001 | 0.003 ± 0.000 | 0.024 ± 0.006 | |
Safe limit (mg∙L−1) | ||||
CPCB* | 0.1 | 2.0 | 2.0 | |
FAO** | 5.0 | 0.01 | 0.1 | |
US EPA*** | 0.065 | 0.0018 | Cr(III) | Cr(VI) |
0.570 | 0.016 |
*Values provided by Central Pollution Control Board, India for discharge of environmental pollutants into the inland surface water. (Website: http://www.scpcb.nic.in/GeneralStandards.Pdf) **FAO water quality criteria for irrigational water (website: http://www.fao.org/docrep/t0551e/t0551e04.htm#2.4 water quality guidelines for maximum crop production). ***EPA National recommended aquatic life criteria table (website: https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table).
The heavy metal content of the sediments collected from the different sites are shown in Figures 1(a)-(c). The sediments were not polluted in terms of Pb (
Cd concentration in the sediments for all sites (
used for tanning leather products [
The overall Pb, Cd and Cr contents in the above and below ground portions of the plants studied have been provided in
Maximum Pb concentrations (>80 mg∙kg−1) could be detected in roots of both invasive (A. philoxeroides and E. crassipes) and native plants (C. benghalensis and sedges). The highest median Pb concentration was evident in the roots of C. benghalensis (76.4 mg∙kg−1) while the lowest was present in I. aquatica (42.18 mg∙kg−1). The median Cd concentration in roots varied from 7.89 mg∙kg−1 in I. aquatica to 25.30 mg∙kg−1 in C. benghalensis. Accumulation of high concentrations of Pb and Cd in plant tissues of C. benghalensis above normal concentrations of 5 mg∙kg−1 Pb and 10 mg∙kg−1 Cd was observed by Zu et al., [
In order to get an idea about the site specific metal uptake ability of individual plant species, the site-wise details for metal concentrations in sediments, shoots and roots of all the plants for Pb (
Metal | Plant | No. of sites present | Metals in shoot (mg∙kg−1) | Metals in root (mg∙kg−1) | ||||
---|---|---|---|---|---|---|---|---|
Min | Max | Median | Min | Max | Median | |||
Lead | Alternanthera philoxeroides | 11 | 16.06 | 27.13 | 17.08 | 46.64 | 91.79 | 70.98 |
Ipomoea aquatica | 6 | 14.29 | 34.49 | 16.97 | 28.64 | 57.50 | 42.18 | |
Eichhornia crassipes | 5 | 18.69 | 26.97 | 24.97 | 34.88 | 80.95 | 61.66 | |
Sedges | 3 | 15.51 | 33.70 | 16.80 | 45.27 | 92.79 | 63.77 | |
Commelina benghalensis | 2 | 17.74 | 33.85 | 25.79 | 60.16 | 92.70 | 76.43 | |
Sagittaria sagittifolia | 2 | 17.12 | 32.53 | 24.83 | 67.25 | 72.71 | 69.98 | |
Enhydra fluctuans | 1 | NA | NA | 25.49 | NA | NA | 59.25 | |
Ludwigia adscendens | 1 | NA | NA | 15.79 | NA | NA | 74.52 | |
Cadmium | Alternanthera philoxeroides | 11 | 2.57 | 5.64 | 3.79 | 8.48 | 45.03 | 15.72 |
Ipomoea aquatica | 6 | 2.65 | 8.00 | 2.80 | 3.88 | 14.30 | 7.89 | |
Eichhornia crassipes | 5 | 3.52 | 5.79 | 5.06 | 8.32 | 30.88 | 14.05 | |
Sedges | 3 | 2.49 | 8.05 | 2.63 | 9.01 | 26.77 | 14.49 | |
Commelina benghalensis | 2 | 3.01 | 7.44 | 5.23 | 12.94 | 37.67 | 25.30 | |
Sagittaria sagittifolia | 2 | 3.06 | 5.69 | 4.38 | 16.58 | 27.24 | 21.91 | |
Enhydra fluctuans | 1 | NA | NA | 5.51 | NA | NA | 13.60 | |
Ludwigia adscendens | 1 | NA | NA | 3.08 | NA | NA | 16.84 | |
Chromium | Alternanthera philoxeroides | 11 | <0.15a | 15.32 | 10.47 | <0.30a | 81.28 | 41.51 |
Ipomoea aquatica | 6 | <0.15a | 4.48 | 2.57 | <0.30a | 43.26 | 19.07 | |
Eichhornia crassipes | 5 | <0.15a | 18.45 | 16.46 | 6.21 | 133.75 | 20.65 | |
Sedges | 3 | <0.15a | 10.74 | 10.74 | 38.34 | 73.39 | 57.63 | |
Commelina benghalensis | 2 | <0.15a | 11.62 | 11.62 | <0.30a | 20.10 | 20.10 | |
Sagittaria sagittifolia | 2 | 9.49 | 15.17 | 12.33 | 10.49 | 18.23 | 14.36 | |
Enhydra fluctuans | 1 | NA | NA | 1.74 | NA | NA | 2.84 | |
Ludwigia adscendens | 1 | NA | NA | 4.27 | NA | NA | 28.59 |
aValues below detection limit. NA: not applicable.
Site No. | Plant species | Lead concentration (mg∙kg−1) | Translocation factor (TF) | Bioaccumulation factor | |||
---|---|---|---|---|---|---|---|
Sediment | Shoot | Root | Shoot (BAFs) | Root (BAFr) | |||
1 | A. philoxeroides | 56.36 | 16.06 | 51.09 | 0.31 | 0.29 | 0.91 |
E. crassipes | 18.69 | 34.88 | 0.54 | 0.33 | 0.62 | ||
I. aquatica | 16.76 | 41.32 | 0.41 | 0.30 | 0.73 | ||
Sedges | 16.80 | 45.27 | 0.37 | 0.30 | 0.80 | ||
2 | A. philoxeroides | 52.44 | 16.31 | 57.59 | 0.28 | 0.31 | 1.10 |
E. crassipes | 24.97 | 61.66 | 0.41 | 0.48 | 1.18 | ||
I. aquatica | 17.17 | 57.50 | 0.30 | 0.33 | 1.10 | ||
3 | A. philoxeroides | 40.64 | 25.75 | 84.45 | 0.31 | 0.63 | 2.08 |
I. aquatica | 32.08 | 28.64 | 1.12 | 0.79 | 0.71 | ||
4 | A. philoxeroides | 36.15 | 27.13 | 91.79 | 0.30 | 0.75 | 2.54 |
I. aquatica | 15.93 | 35.98 | 0.44 | 0.44 | 1.00 | ||
C. benghalensis | 17.74 | 60.16 | 0.30 | 0.49 | 1.66 | ||
5 | A. philoxeroides | 41.06 | 18.17 | 85.00 | 0.21 | 0.44 | 2.07 |
I. aquatica | 34.49 | 43.05 | 0.80 | 0.84 | 1.05 | ||
Sedges | 33.70 | 92.79 | 0.36 | 0.82 | 2.26 | ||
C. benghalensis | 33.85 | 92.70 | 0.37 | 0.82 | 2.26 | ||
6 | A. philoxeroides | 37.35 | 16.19 | 46.64 | 0.35 | 0.43 | 1.25 |
I. aquatica | 14.29 | 50.47 | 0.28 | 0.38 | 1.35 | ||
7 | A. philoxeroides | 38.89 | 17.08 | 62.48 | 0.27 | 0.44 | 1.61 |
E. crassipes | 26.97 | 60.78 | 0.44 | 0.69 | 1.56 | ||
S. sagittifolia | 32.53 | 67.25 | 0.48 | 0.84 | 1.73 | ||
8 | A. philoxeroides | 50.71 | 17.57 | 71.56 | 0.25 | 0.35 | 1.41 |
E. crassipes | 19.94 | 69.34 | 0.29 | 0.39 | 1.37 | ||
9 | A. philoxeroides | 18.80 | 20.34 | 70.98 | 0.29 | 1.08 | 3.78 |
E. crassipes | 26.84 | 80.95 | 0.33 | 1.43 | 4.31 | ||
10 | A. philoxeroides | 28.85 | 16.74 | 59.91 | 0.28 | 0.58 | 2.08 |
S. sagittifolia | 17.12 | 72.71 | 0.24 | 0.59 | 2.52 | ||
E. fluctuans | 25.49 | 59.25 | 0.43 | 0.88 | 2.05 | ||
11 | A. philoxeroides | 21.88 | 14.45 | 75.38 | 0.19 | 0.66 | 3.45 |
Sedges | 15.51 | 63.77 | 0.24 | 0.71 | 2.92 | ||
L. adscendens | 15.79 | 74.52 | 0.21 | 0.72 | 3.41 |
Bold values indicate values > 1 for (TF) and (BAF).
Site No. | Plant species | Cadmium concentration (mg∙kg−1) | Translocation factor (TF) | Biaccumulation factor | |||
---|---|---|---|---|---|---|---|
Sediment | Shoot | Root | Shoot (BAFs) | Root (BAFr) | |||
1 | A. philoxeroides | 22.30 | 2.57 | 8.48 | 0.30 | 0.12 | 0.38 |
E. crassipes | 3.52 | 8.32 | 0.42 | 0.16 | 0.37 | ||
I. aquatica | 2.87 | 5.46 | 0.53 | 0.13 | 0.25 | ||
Sedges | 2.63 | 9.01 | 0.29 | 0.12 | 0.40 | ||
2 | A. philoxeroides | 5.49 | 2.93 | 12.72 | 0.23 | 0.53 | 2.32 |
E. crassipes | 5.06 | 9.61 | 0.53 | 0.92 | 1.75 | ||
I. aquatica | 2.74 | 13.45 | 0.20 | 0.50 | 2.45 | ||
3 | A. philoxeroides | 7.38 | 5.01 | 18.94 | 0.26 | 0.68 | 2.57 |
I. aquatica | 7.37 | 5.99 | 1.23 | 1.00 | 0.81 | ||
4 | A. philoxeroides | 5.28 | 5.64 | 12.03 | 0.47 | 1.07 | 2.28 |
I. aquatica | 2.65 | 3.88 | 0.68 | 0.50 | 0.74 | ||
C. benghalensis | 3.01 | 12.94 | 0.23 | 0.57 | 2.45 | ||
5 | A. philoxeroides | 9.48 | 3.79 | 32.72 | 0.12 | 0.40 | 3.45 |
I. aquatica | 8.00 | 14.30 | 0.56 | 0.84 | 1.51 | ||
Sedges | 8.05 | 26.77 | 0.30 | 0.85 | 2.82 | ||
C. benghalensis | 7.44 | 37.67 | 0.20 | 0.79 | 3.97 | ||
6 | A. philoxeroides | 7.84 | 2.74 | 10.01 | 0.27 | 0.35 | 1.28 |
I. aquatica | 2.70 | 9.78 | 0.28 | 0.34 | 1.25 | ||
7 | A. philoxeroides | 9.39 | 3.86 | 15.72 | 0.25 | 0.41 | 1.67 |
E. crassipes | 5.36 | 14.05 | 0.38 | 0.57 | 1.50 | ||
S. sagittifolia | 5.69 | 27.24 | 0.21 | 0.61 | 2.90 | ||
8 | A. philoxeroides | 6.81 | 4.56 | 32.47 | 0.14 | 0.67 | 4.77 |
E. crassipes | 5.05 | 30.88 | 0.16 | 0.74 | 4.54 | ||
9 | A. philoxeroides | 3.92 | 4.31 | 45.03 | 0.10 | 1.10 | 11.50 |
E. crassipes | 5.79 | 18.20 | 0.32 | 1.48 | 4.65 | ||
10 | A. philoxeroides | 5.33 | 3.48 | 13.77 | 0.25 | 0.65 | 2.58 |
S. sagittifolia | 3.06 | 16.58 | 0.19 | 0.57 | 3.11 | ||
E. fluctuans | 5.51 | 13.60 | 0.41 | 1.03 | 2.55 | ||
11 | A. philoxeroides | 3.96 | 3.32 | 16.55 | 0.20 | 0.84 | 4.19 |
Sedges | 2.49 | 14.49 | 0.17 | 0.63 | 3.66 | ||
L. adscendens | 3.08 | 16.84 | 0.18 | 0.78 | 4.26 |
Bold values indicate values > 1 for (TF) and (BAF).
Site No. | Plant species | Chromium concentration (mg∙kg−1) | Translocation factor (TF) | Biaccumulation factor | |||
---|---|---|---|---|---|---|---|
Sediment | Shoot | Root | Shoot (BAFs) | Root (BAFr) | |||
1 | A. philoxeroides | 488.76 | <0.15a | 81.28 | - | - | 0.17 |
E. crassipes | 7.58 | 20.65 | 0.37 | 0.02 | 0.04 | ||
I. aquatica | <0.15a | 19.07 | - | - | 0.04 | ||
Sedges | 10.74 | 73.39 | 0.15 | 0.02 | 0.15 | ||
2 | A. philoxeroides | 115.52 | <0.15a | 9.07 | - | - | 0.08 |
E. crassipes | 18.45 | 6.21 | 2.97 | 0.16 | 0.05 | ||
I. aquatica | 4.48 | <0.30 a | - | 0.04 | - | ||
3 | A. philoxeroides | 100.85 | 5.97 | <0.30 a | - | 0.06 | - |
I. aquatica | 0.65 | <0.30 a | - | 0.01 | - | ||
4 | A. philoxeroides | 96.17 | <0.15a | <0.30 a | - | - | - |
I. aquatica | <0.15a | <0.30a | - | - | - | ||
C. benghalensis | <0.15a | <0.30a | - | - | - | ||
5 | A. philoxeroides | 138.66 | 14.97 | 35.62 | 0.42 | 0.11 | 0.26 |
I. aquatica | <0.15a | 14.55 | - | - | 0.11 | ||
Sedges | <0.15a | 57.63 | - | - | 0.42 | ||
C. benghalensis | 11.62 | 20.10 | 0.58 | 0.08 | 0.15 | ||
6 | A. philoxeroides | 511.17 | <0.15a | 44.12 | - | - | 0.09 |
I. aquatica | <0.15a | 43.26 | - | - | 0.09 | ||
7 | A. philoxeroides | 196.39 | 15.32 | 38.17 | 0.40 | 0.08 | 0.19 |
E. crassipes | <0.15a | 14.05 | - | - | 0.07 | ||
S. sagittifolia | 15.17 | 18.23 | 0.83 | 0.08 | 0.09 | ||
8 | A. philoxeroides | 169.66 | <0.15a | 72.58 | - | - | 0.43 |
E. crassipes | 17.89 | 133.75 | 0.13 | 0.11 | 0.79 | ||
9 | A. philoxeroides | 69.86 | 2.14 | 38.89 | 0.06 | 0.03 | 0.56 |
E. crassipes | 15.02 | 49.92 | 0.30 | 0.22 | 0.72 | ||
10 | A. philoxeroides | 82.00 | <0.15a | <0.30a | - | - | - |
S. sagittifolia | 9.49 | 10.49 | 0.91 | 0.12 | 0.13 | ||
E. fluctuans | 1.74 | 2.84 | 0.61 | 0.02 | 0.04 | ||
11 | A. philoxeroides | 113.82 | <0.15a | 49.07 | - | - | 0.43 |
Sedges | <0.15a | 38.34 | - | - | 0.34 | ||
L. adscendens | 4.27 | 28.59 | 0.15 | 0.04 | 0.25 |
aValues below detection limit. Bold values indicate values > 1 for (TF).
The shoot DM values were higher for most plants growing naturally (excepting E. crassipes and E. flutuans) when compared to an earlier study which was conducted in less contaminated sites [
Pb exhibits long residence time, is sparingly soluble as a result of rapid conversion to PbSO4 at the soil surface and forms relatively stable organo-metal complexes or chelates with organic matter in soil making it the least phytoavailable amongst all toxic heavy metals. Only 1% of the total Pb in soil is water soluble and exchangeable for uptake by plants [
Shoot concentration of Pb for all plants (
In some of the sites, native species like I. aquatica, C. benghalensis, S. sagittifolia and the sedges exhibited high shoot Pb concentrations which were above critical values (>30 mg∙kg−1). Of the four plants present in Site 5, which was near an iron industry, three native species had greater than critical shoot Pb concentrations. Steel and iron manufacturing industries are a potential source of Pb [
Except for all plants in Site 1 and I. aquatica in Site 3, all plants indicated high accumulation potential of Pb in roots (BAFr > 1), while in plants present in Sites 9 to 11 (with lowest sediment Pb contents) the bioaccumulation factors in roots were close to ≥3. From the translocation factors in
Cd enters aquatic systems as effluents mainly through electroplating, pigments, plastic stabilizers and batteries [
The sedges exhibited minimum and maximum shoot Cd levels of 2.49 mg∙kg−1 in Site 11 and 8.05 mg∙kg−1 in Site 5 respectively (
Of concern is the transfer factor of 1.23 in I. aquatica and high bioaccumulation of Cd in shoots of both I. aquatica and E. fluctuans. The leaves and stems of I. aquatica (water spinach) and the young shoots of E. fluctuans (water cress or marsh herb) are commonly used as green leafy vegetables in Southeast Asia, India and China [
Most of the plants in the study sites also showed a high bioaccumulation for Cd in their roots (BAFr > 1), except in Site 1 where none of the plants present could accumulate the element. Site 1 also had the with the highest sediment concentration among sites. In Site 9, A. philoxeroides exhibited exceedingly high accumulation of Cd in its roots (BAFr 11.5) compared to E. crassipes (BAFr 4.65) while its accumulation in shoots (BAFs 1.10) was less than that of E. crassipes (BAFs = 1.48), thereby showing its potential to limit transfer of Cd to its above ground tissues. Moreover, it appears that the two invasive plants present in Site 9 bioaccumulated large amounts of Pb and Cd in their shoots (BAF > 1) as well as in roots (BAF ≥ 4). The production of organic acids by fungi and bacteria present in sewage, which was a constituent of Site 9, promotes solubilization, mobility and bioavailability of metals in sediments by lowering pH through the process of nitrification and microbial carbon dioxide production [
Cr occurs in several oxidation states with trivalent and hexavalent states being the most stable. Hexavalent Cr (Cr6+) is the principal species in surface waters and aerobic soils and has a long residence time and is very mobile [
Despite higher than background levels of Cr in sediments at most sites, it is evident from
For most other plants, shoot concentration of Cr was above the normal levels (0.1 to 0.5 mg∙kg−1) suggested for plants [
Efficient translocation of elements from roots to shoots in plants was not evident from this study as has been reported for wetland plants which only depend on metal exclusion for their metal tolerance due to reduced translocation [
In urban areas where heavy metal pollution of freshwater ecosystems is constantly on the rise, this study highlights the ability of some emergent rooted plants to phytostabilize contaminants in the sediments by accumulation in roots thereby reducing the risk to human health and the environment. Both invasive as well as some native plants were equally capable of accumulating Pb and Cd into their roots. However with regard to the widespread consumption and distribution of I. aquatica across large parts of the Asian sub-continent, this native species needs to be carefully monitored due to its ability to accumulate Pb and Cd in its above ground parts without any obvious visible symptoms. On the other hand, A. philoxeroides, being a cosmopolitan species shows considerable promise not only as an efficient accumulator of Pb and Cd in its roots but its ability to rapidly uptake heavy metals even at very low ambient levels could also make it an efficient indicator of the aquatic ecosystem quality. Moreover, due to its restricted transfer of metals to its above ground parts, the plant can additionally be promoted for feed/
food use. Repeated harvesting of A. philoxeroides plant parts from water bodies would doubly contribute to its use as well as restrict its spread potential, a negative aspect of all invasive plants. The potential of A. philoxeroides as a metal excluder needs to be explored since it translocates less to its shoots as compared to E. crassipes and I. aquatica.
This project was supported financially by the Indian Statistical Institute, Kolkata. We would like to acknowledge Sandip Chatterjee, Susant Mahankur and Jahira Begam for technical and field assistance. We would like to thank the anonymous Reviewers’ for their helpful suggestions.
Jha, P., Samal, A.C., Santra, S.C. and Dewanji, A. (2016) Heavy Metal Accumulation Potential of Some Wet- land Plants Growing Naturally in the City of Sciences, 7, 2112-2137. http://dx.doi.org/10.4236/ajps.2016.715189