Heavy Metals in Urban Lake of Kashmir Himalayas

Abstract

Contaminations by heavy metals in aquatic ecosystems strongly affect foodchain relationships through the process of biomagnification. Heavy metals (i.e. Fe, Cu, Mn, Pb, Zn, Cd, Cr, and Co) were determined from sediment, water and macrophytic species (Ceratophyllum demersum, Phragmites australis, and Potamogeton crispus) of Nigeen lake. The concentration of different heavy metals was determined using atomic absorption spectrophotometer. The concentration of heavy metals was found highest in sediments (viz: Fe- 61.43 ppm, Zn- 56.54 ppm, Cu- 54.77 ppm, Pb- 34.56 ppm, Co- 19.56 ppm, Cr- 14.68 ppm, Mn- 9.09 ppm and Cd- 5.25 ppm), in water (viz: Pb- 198.50 ppm, Fe- 14.70 ppm, Zn- 2.68 ppm, Cd- 2.43ppm, Mn- 1.60 ppm, Cu- 0.07 ppm, Cr- 0.04 ppm and Co- 0.006 ppm) in macrophytes (Ceratophyllum demersum viz: Fe- 306.20 ppm, Zn- 4.58 ppm, Mn- 2.80 ppm, Cd- 0.50 ppm, Cu- 0.29 ppm, Pb- 0.16 ppm; Co- 0.092 ppm and Cr- 0.080 ppm, Phragmites australis viz: Fe- 26.68 ppm, Zn- 3.99 ppm, Mn- 2.93 ppm, Cd- 1.85 ppm, Cu- 0.77 ppm, Pb- 0.58ppm, Cr- 0.27 ppm and Co- 0.134 ppm, Potamogeton crispus viz: Fe- 24.31 ppm, Zn- 4.61 ppm, Mn- 3.83 ppm, Pb- 1.07 ppm, Cd- 0.29 ppm, Cr- 0.29 ppm, Cu- 0.174 ppm, Co- 0.05 ppm).

Introduction

Aquatic ecosystems are nowadays subjected to high anthropogenic pressures especially rapid urbanization, overuse of pesticides, chemical detergents, municipal and industrial discharges (Harper et al. 1999), these anthropogenic activities resulted in heavy metal pollution of natural water resources (Giguene et al. 2004). Due to the persistent nature of heavy metals, they get accumulated in foodchain through the process of biomagnification, posing serious threats to aquatic and human health (Malik et al. 2010). Fe+2, Mn+2, Cu+2 and Zn+2 are considered as essential elements required in low concentrations whereas, many metals, such as Pb+2, Hg+2 and Cd+2, have no known role in biological functioning and can be toxic to organisms at very low concentrations (Nicolau et al. 2006; Kar et al. 2008). Therefore, the release of metals into aquatic ecosystems poses serious threat to the fauna and flora of receiving water courses. Aquatic macrophytes play an important role in functioning of an aquatic ecosystem (Pandit et al. 2010). There has been considerable interest in using aquatic plants for removal of various pollutants, including heavy metals from water bodies because of their fast growth rate and simple growth requirements (Lewis 1995). Heavy metal pollution in the environment especially of aquatic ecosystem is a major global concern which has provoked the development of phytoremediation technologies for cleaning aquatic ecosystems. Uptake of heavy metals by aquatic macrophytes is dependent on the life form of the macrophytes: rooted emergent, floating or submerged (Mishra et al. 2008). For emergent macrophytes, root uptake is the primary source of metals. Floating and submerged species however, can also accumulate metals directly from the water by their shoots, for free-floating macrophytes the water is the only source of metals (Wolverton and McDonald 1978). Monitoring of aquatic ecosystems for heavy metal contaminations is essential because heavy metal content may impart a significant impact on health, reproduction, and survival of organisms living in lakes, as there is no such study which has assessed the heavy metal content of Nigeen lake, thus, the present study has been carried out to evaluate concentration of heavy metals (Fe+2, Zn+2, Cu+2, Mn+2, Co+2, Cr+3, Cd+2 and Pb+2) and their sequestration potential by three macrophytic species (Ceratophyllum demersum, Phragmites australis and Potamogeton crispus) of the Nigeen lake and further to identify the most efficient macrophytic species for heavy metal sequestration.

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Material and Methods

Study area

Nigeen lake is situated in Srinagar city between the geographical coordinates 34º 06′-34º 08′ N and 74º 49′-74º 50′ E at an attitude of 1583 m (a.m.s.l) (Fig 1). It is located at a distance of 9 kms to the north east of Srinagar. Nigeen lake is warm monomictic, with an unstable thermocline having maximum depth of 6 m. The lake is fed by a narrow water channel from Dal Lake at Ashaibagh Bridge in the North East area which contributes significant volume of water to lake. A total of four study sites were selected across the basin and their brief descriptions are given below.

• Ashaibagh (S1): The site is Situated between (34° 6′ 53.0″ N and 74° 50′ 9.5″ E). The major portion of the area is used for the cultivation of vegetables and acts as the inlet source of Nigeen basin receiving water from other basins of Dal Lake.
• Nallah Amir Khan (S2): The site is situated between (34° 06′ 50.2″ N and 74° 49′ 13.5″ E), this site lies close to the sewage treatment plant and is marked by the presence of human settlements on one side. Free floating and submerged macrophytic communities are abundant.
• Khojyarbal (S3): The site is situated between (34° 6′ 28.1″ N and 74° 49′ 47.3″ E), at this site the lake receives maximum sewage from the neighbouring household drains. The substrate of the area was fine, dark coloured neighbouring rich macrophytic vegetation.
• Boni-Bagh Sadrabal (S4): The site is situated between (34° 7′ 37.33″ N and 74° 49′ 38.2″ E), this site is heavily impacted by direct discharge of sewage from nearby houseboats.

Sampling and Preservation

Sediment samples were collected from four sites using Ekman Dredge sampler. The samples were collected in polyethylene bags and brought to laboratory for analysis. The water samples were collected in 1 litre decontaminated polyethylene bottles, preserved by the addition of 2 ml of nitric acid and stored at 4°C until digestion. While as, plants were transported to laboratory in polythene bags within a period of 24 hours.

Analytical analysis

The sediment samples were air dried under shade in laboratory, grinded in pestle and mortar and passed through 2mm sieve. Analysis of different heavy metals was carried out as per standard methods given by Lindsay and Norvell (1978). Heavy metals in water samples were extracted with a mixture of concentrated HNO3 and H2SO4 and preserved in refrigerator till analysis APHA (1998). Plant samples were thoroughly washed with tap water, filamentous algae and extraneous matter was handpicked from plants. All plant samples were oven dried at 80°C for 24 h and were ground in a pestle-mortar, sieved through the 0.5 mm-mesh sieve. After homogenization, the finely ground material was digested. Plant samples were digested with a mixture of concentrated HNO3 and per chloric acid (1:2 v/v) [9] and preserved in a refrigerator till analysis. Atomic Absorption Spectrophotometer (800 Perkin Elmer, USA) was used to detect the heavy metals. The samples were analyzed in triplicates and their concentrations were expressed as mg/Kg for sediments, mg/L for water and mg/Kg dry weight for plant samples. Statistical analysis was performed using SPSS software version 13 for windows. ANOVA was employed to find the significant relationship between heavy metals and various factors of the lake.

Results and discussion

The results of heavy metals in lake sediments, water and different macrophytes Ceratophyllum demersum, Phragmites australis and Potamogeton crispus are shown in Tables 2, 3, 4, 5 and 6. The highest concentration of heavy metals was found in the sediments of the lake. Among the different samples assessed, Fe+2 was the most abundant metal. Abundance of Heavy metals in sediments of the lake followed the order: Fe+2 > Zn+2 > Cu+2 > Pb+2 > Cr+3 > Mn+2 > Cd+2. The average concentration of the heavy metals in the water samples of the Nigeen lake was in the order Pb+2 > Fe+2 > Zn+2 > Cd+2 > Mn+2 > Cu+2 > Cr+3 > Co+2. The macrophytic plant species of the lake, have shown different orders like in Ceratophyllum demersum the order was Fe+2 > Zn+2 > Mn+2 > Cd+2 > Cu+2 > Pb+2 > Co+2 > Cr+3. Similarly, Phragmites australis showed the distribution pattern: Fe+2 > Zn+2 > Mn+2 > Cd+2 > Cu+2 > Pb+2 > Cr+3 > Co+2 and the heavy metal distribution in Potamogeton crispus followed the order as Fe+2 > Zn+2 > Mn+2 > Pb+2 > Cd+2 > Cr+3 > Cu+2 > Co+2.

The highest concentration of Fe+2 (61.43 ± 0.43 mg/kg) was found in the sediments at S1. The concentration of Fe+2 in water varied from 14.70 at S2 to 0.24 at S2 this is attributed to the weathering of rocks, discharge of sewage effluents, agricultural and domestic wastes into the lake (Moati and Sammak 1997). Ceratophyllum demersum accumulated higher concentrations of Fe+2 than the other two plants studied which could be related to high surface area:volume ratio of Ceratophyllum demersum, makes it a strong competitor for nutrients (Hernandez et al. 1999) and availability of soluble form of Fe+2 and ionic form of Fe+2 to plants also influenced by different factors, mostly by the amounts of soluble oxygen and pH (Goulet and Pick 2001).

Copper normally occurs in drinking water from copper pipes, utensils, copper sulphate as a common fungicide. Binning and Baird (2001) reported higher values of Cu from the aquatic system of industrial areas. In sediments the concentration of Cu+2 varied from 54.77at S1 to 18.10 at S2. In water, Cu+2concentration varied from 0.09 at S3 to 0.02 at S2. High levels of Cu+2 in sediments at all the sites could be related to discharge of sewage, domestic and agriculture wastes (Aksoy et al. 2005). Phragmites australis accumulated highest content of Cu+2 as compared to other two macrophytes

The chromium content in the sediment varied from 14.68 at S2 to 3.23 at S1. Similar results were obtained by Baligar and Chavadi (2005) in the freshwater ecosystems. The high concentration of Cr+3found in water was (0.04 mg L−1) at S2 could be related to high sewage load as the sites are located near sewage treatment plant and floating gardens. Further, it has been reported that the enrichment of Cr+3 in waters is due to domestic and commercial waste inputs (Bragato et al. 2006, Strivastava et al. 2008). The macrophyte Potamogeton crispus showed the highest concentration of Cr+3 (0.70 mg L−1) at S2, this is due to the fact that submerged aquatic plants accumulates heavy metals (Cr+3 and Cu+2) 4-5 times higher than the riverside vegetation.

Lead in aquatic ecosystems results from leaded petrol wastes, paints and lead batteries. Lead concentration was found highest in sediments (34.56 mg kg−1) at S4. The concentration of Pb+2 in the surface water varied from (198.50 mg L−1) at S4 to (0.07 mg L−1) at S3. Among the macrophytes, Potamogeton crispus showed the highest concentration of Pb+2 (1.07 mg kg−1). Baldantoni et al. (2004) reported that the shoots of Najas marina show higher concentrations of lead. Babovic et al. (2010) observed that the leaves of Phragmites communis accumulated less concentrations of lead. The main sources of lead to the lake being agricultural discharge and spill of leaded petrol from fishing boats and leachates/runoff from mechanical garages located in the immediate vicinity (Hardman et al. 1994).

Cadmium concentration was found highest in sediments (5.25 mg kg−1) at S1. In water concentration of Cd+2 varied from 2.43 mg L−1) at S4 to 0.22 mg L−1) at S1. Among the macrophytic plants, maximum accumulations of Cd+2 (1.85 mg/Kg), was found in Phragmites australis at S1 and lowest (0.08 mg/Kg in Potamogeton crispus at S3. Cadmium concentrations in the lake samples can be linked to sewage runoff and other domestic wastes from the households and use of fertilizers in the floating gardens located near the sites. It has been found that urban sewage, fertilizers and road traffic are a source of Cd+2 (Chaney 1989, Baldantoni et al. 2004).

Zinc concentration in sediments varied from 56.54 at S2 to 12.89 at S3. In water Zn varied from 2.68 at S4 to 0.55 at S1. Among macrophytes, highest concentration of zinc was found in Potamogeton crispus at S4. It has been experimented that macrophytes accumulate 2.5 Kg of Zn+2 from 1 hectare of surface waters (Fritioff and Greger 2001), thus playing important role in purification of contaminated waters naturally.

Cobalt concentration in sediments varied from a maximum of 19.560 at S2 to 6.450 at S1. In water cobalt varied from 0.005 to 0.002 ppm. However, in comparison to other macrophytes, the highest concentration of Co+2 was found in 0.134 Phragmites australis. The study have revealed that macrophytes are potential source for sequestering of heavy metals from polluted water bodies (Vardanyan et al. 2007) and should be an integral part of sustainable development of the aquatic ecosystems and pollution control programmes.

Conclusion

The study revealed that the Fe+2, Zn+2 and Mn+2 were in high levels throughout the study period. While as, accumulation of heavy metals in the macrophytes reduces the pollution load of an aquatic ecosystem. In this respect, all the three plants play an important role in sequestration of heavy metals but Ceratophyllum demersum emerged as the strong competitor as compared to other two macrophytes Phragmites australis and Potamogeton crispus to sequester more heavy metals. These results could be very useful for environmental monitoring and restoration management tool of aquatic ecosystems. The present study is not limited to the above three macrophytes but to identify other macrophytes capable of phytoremediation.

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