Assessment of heavy metals (Cd, Cr and Pb) in water, sediment and seaweed (Ulva lactuca) in the Pulicat Lake, South East India
Introduction
The ever growing list of chemical contaminants released into the environment on a large scale including numerous aliphatic and aromatic compounds, heavy metals, radionucleotides and phthalate esters. Among these innumerable contaminants, pollution by heavy metals in coastal environment has become a global phenomenon because of its toxicity, persistence for several decades in the aquatic environment, bioaccumulation and biomagnification in the food chain (Valls and Lorenzo, 2002, Gochfeld, 2003).
Toxic heavy metals are usually present at low concentration in aquatic ecosystem, but deposits of anthropogenic origin have raised the heavy metal concentration, creating environmental problems in coastal zones, lakes and rivers. The concentrations above the tolerable level are a disturbing factor for species survival and stability of the ecosystem. Many studies have already been reported that the use of different species of Ulva and Enteromorpha as bio-indicators of metal contamination (Ho, 1990, Haritonidis and Malea, 1999, Giusti, 2001, Conti and Cecchetti, 2003). In addition, reasonable size of the algae and sedentary mode of living habitat appear to be a suitable aquatic fauna for assessing the contamination level in an ecosystem. Since metals such as Cd, Cr, Pb and Hg are associated with the industrial wastes released in the North Chennai Coastal region, the common green algae Ulva lactuca, which is wide spread along the Pulicat Lake shores, were found to be a suitable aquatic fauna for evaluating the contamination level.
Pulicat Lake in the North Chennai coastal region is a typical brackish water ecosystem of great importance with regards to its biodiversity and their aesthetic value. Due to its morphological and brackish water characteristics, it is the best suitable habitat for breeding and nursing ground for fishes. And now it is being considered as a “Ramsar Site” by The International Union for the Conservation of Nature and Natural Resources (IUCN) and The World Wide Fund for Nature (WWF) – India, including the Ministry of Environment and Forests. In addition, it is the home site for nearly 50 different species of water birds and also a breeding site for white and tiger prawns, mud and lagoon crabs, mullets, catfishes and clam varieties.
Over exploitation, mismanagement and improperly treated industrial effluents from more than 25 industries were continuously discharged into North Chennai Coastal region, which brings the great challenge for the ecosystem balance. Studies earlier in Pulicat Lake recorded an elevated level of Cd, Cr and Pb concentrations in water, sediment and plant samples. Cadmium concentration in water samples was 0.01 mg l−1 in both the seasons. The average concentration of Cd in sediments during premonsoon was 6.25 μg g−1 and in postmonsoon it was 7.38 μg g−1 (Padma and Periakali, 1998, Periakali and Padma, 1998). Whereas, in plants the mean concentration observed for Cd, Cr and Pb were 1.06, 0.63 and 0.171 μg ml−1 respectively (Kamala-Kannan et al., 2007). Therefore the present investigation is aimed to study the levels of Cd, Cr and Pb in U. lactuca, sediment and water samples of Pulicat Lake primarily to generate data on seasonal variations of Cd, Cr and Pb concentration in U. lactuca of Pulicat Lake, and secondly to evaluate the degree of contamination in the study area in comparison with other areas.
Section snippets
Study area – Pulicat Lake
The study area is restricted to the lake waters of Pulicat, which is the second largest brackish water lagoon in India running parallel to the Bay of Bengal, bordering the east coast of Andhra Pradesh with a portion of it extending into the northern part of Tamil Nadu (Fig. 1). The lake is about 360 sq km in size, and its depth (water column) varies from 1 to 6 m. The point source of pollution are mainly from North Chennai Thermal Power Plant, Ennore port activities, Manali Petrochemical
Concentration of metals in water
The abundance of metals in the lake water (regardless of seasons and sampling station) decreased in the following order: Cr > Pb > Cd (Table 2). Chromium concentration in water samples was in the range between 1.4 and 11.4 μg l−1. The minimum level of chromium 1.4 μg l−1 was recorded in station five during monsoon and maximum level 11.4 μg l−1 was recorded in station three during premonsoon. In general, the highest mean value (7.78 μg l−1) in water was observed during premonsoon and lowest (3.53 μg l−1)
Discussion
The results presented in this study comprise an attempt to report the seasonal variations and degree of heavy metals contamination (Cd, Cr and Pb) in water, sediment and U. lactuca samples collected from Pulicat Lake, Southeast coast of India. To compare the seasonal variations, six different localities were chosen for the present study. Sampling station one is a boat house and station two is a place were anthropogenic wastes are released by local fisherman communities, station three is located
Conclusion
Pulicat Lake is one of the most important wetland in the southeast coast of India. Based on the present study, it is concluded that the degree of contamination and seasonal variation of heavy metals were high in water, sediment and U. lactuca. Efforts should be needed to protect Lake Pulicat from pollution and also to reduce environmental risks. This study and the valuable data will pave the way for future research on Pulicat Lake.
Acknowledgements
The author S.K.K. is grateful to the Chonbuk National University for the Postdoctoral Grant 2007. The author B.P. is grateful to the University of Madras for the research fellowship under the “UGC- UWPFE” programme. The authors acknowledge the DST-FIST-AAS Instrumentation facility at the Department of Applied Geology, University of Madras. Authors also acknowledge Dr. M.P. Jonathan, Professor Investigator, Centro de Investigaciones en Ciencias de la Tierra,Universidad Autónoma del Estado de
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