HEAVY METAL POLLUTION OF COCHIN BACKWATERS

 

ABSTRACT

Cochin backwater is facing serious threat due to heavy metal pollution caused by rapid urbanization and industrialization. In this paper, literatures on heavy metal sources, level and spatio-temporal distribution in water, sediments and organisms were reviewed for a comprehensive understanding of the status of heavy metal pollution in Cochin backwater. Increased levels of the heavy metals encountered were linked to local industrialization. Northern part of the backwater is more polluted by heavy metals compared to southern and middle part of the backwater. High levels of heavy metals were also found in biota.

INTRODUCTION

Coastal marine ecosystems are vulnerable to adverse impacts from various urban and industrial developmental activities, which could facilitate the disposal of several chemical agents, with consequent degradation in the water quality causing serious health hazards to the aquatic organisms. Among environmental contaminants, heavy metals in effluents emerged as one of the most pressing problems because of their inherent toxicity, vast sources, persistence, and non-degradability. Heavy metals from mining, smelting, agriculture, petrochemical industry, printing, aquaculture, electronic industry and municipal waste discharged to the aquatic environment can be bioaccumulated by the organism and biomagnified through food chain. Metal contamination in aquatic systems is a matter of serious concern from human health point of view as many of the organisms particularly fish forms an integral part of human diet. Therefore, a better understanding of the status of heavy metal pollution is inevitable for a sustainable development of the coastal marine ecosystem.

Kerala’s coastal zone is unique with the presence of a large number of perennial or temporary backwaters (Kayals), endowed with rich biological and genetic diversity. Cochin backwaters, with an area of 256 km² extending from Cochin to Alleppy having two permanent openings, one at Cochin, which forms the main entrance (450 m wide) to Arabian sea and another opening, further north at Azhikode. Six rivers (Achenkovil, Pampa, Manimala, Meenachil and Muvattupuzha in the south and a branch of Periyar in the north) are discharging about 2×1010 m ³ /y of fresh water, ­60% of which is during summer monsoon (June - Sep). This estuary, characterized by high productivity, acts as a nursery ground for many species of marine and estuarine fin fishes, molluscs and crustaceans. The areas of the backwater with fine sediments and rich organic matter supports abundant and diverse benthic fauna. The booming city of Cochin and 60% of the chemical industries of Kerala located in the vicinity of the backwater discharge nearly 0.105 million m³ /d of effluents. Therefore, Cochin backwater is greatly affected due to pollution and toxicity problems particularly from heavy metals, pesticides, PCBs and organotin compounds. Cochin backwater has thus been drawn considerable research interest for the last few decades because of the social and economic importance. Extensive investigations have been conducted on heavy metal abundance, distribution and speciation in dissolved, particulate and sedimented media. The aim of this article is to provide a comprehensive understanding of heavy metal concentration, distribution, and sources in water, sediment and marine organisms in the Cochin backwater system so as to assess any future changes.

HEAVY METAL POLLUTION

Water has become a major threat in today’s world. Collection of heavy metals, a few of them, is potentially toxic and these get distributed to different areas through different pathways. With an increase in the earth’s population, development and industrialization are taking place rapidly and these get the major source of water contamination.

Both anthropogenic activities and geochemical processes are responsible for heavy metal contamination in ecosystems. Elements that have high density and are less noxious are known as heavy metals. Examples of heavy metals are lead, iron, mercury, cadmium, zinc, arsenic, copper, and chromium and the actual volume of these heavy metals is more than 6 g/m³. These heavy metals not only impair the quality of the aquatic ecosystem but also human health . These heavy metals are so dangerous that they cannot be degraded or decomposed and they have the arability to bioaccumulate.

The toxicity of these heavy metals in the human body reduces energy levels; disrupts brain functioning; disturbs the functioning of various other organs such as the brain, lungs, liver, and kidney; and also hinders blood composition. If the contact with heavy metals continues, then it can hinder the physical, neurological, and muscular functioning. And due to these diseases like multiple sclerosis, Parkinson’s disease and muscular dystrophy, and Alzheimer’s disease. Chronic exposure to some of the heavy metals and their compounds may even cause cancer. Pollution of these heavy metals into the river may cause distressing effects on the ecological balance of the aquatic environment, and with the extent of contamination, the diversity of aquatic organisms becomes limited. The fish in the aquatic ecosystem can be used for examining the well-being of biota. Due to pollutants in the food chain of organisms, harmful effects can be seen and the aquaculture can become dead.

Sources of contamination:

The presence of these heavy metals on the surface of the water can be due to natural or anthropogenic activities.

a)     Natural sources:

    Trace metals are found in excess levels in the environment, they are formed by geographical processes such as volcanic eruptions, weathering of rocks, and leaching into rivers, lakes, and oceans due to the action of water. The presence of heavy metals in water depends on the local geology, hydrogeology, and geochemical characteristics of the aquifer.

      One of the main sources of pollution is weathering. The weathering of the sedimentary rocks such as limestone or dolomite or shale makes the water contaminated or polluted. When there is an interaction of water with rock element, it also leads addition of these elements into the water; thus, contamination occurs. Examples of such elements are granite, syenite, basalt, gabbro, nepheline, and andesite.

b)    Anthropogenic sources:

Anthropogenic events, in which human settlement replaced the natural forest and agricultural activities have increased the environmental impacts. The maximum of forest land is converted into human settlement and agriculture. The water carrying capacity has decreased with the rapid increase in industrialization and urbanization. Hg concentration in water has increased with agriculture activities and human activities. Activities like domestic sewage into the water, solid waste burning, coal and oil combustions, and pyrometallurgical processes and mining are the main reason for this. The source of Ni is the corroded metal pipes and containers. The major source of lead in water majorly comes from additives of paints and petrol and aerosol precipitation. Chemical industries are some industrial activities through which Hg pollutes the water system and these activities are the largest contributor to Hg contamination in the environment

• Domestic sewage: huge amount of untreated sewage from domestic is thrown into the river. This untreated waste from domestic has the presence of toxins. Domestic untreated water is thrown directly into the water resource and this majorly causes pollution inside the water and harms the ecosystem. When these toxic metals get inside the water, they decrease the quality of the water. The presence of nitrite and nitrate anions leads to a major threat to the exposed organisms; examples of such threats are methemoglobinemia. Water sources that get deposited by this sewage also become anions rich, due to the presence of chlorine in urine, and NaCl is used in the human diet.
• Industrial source: Residue from the industry is the major source through which these heavy metals get into the aquatic ecosystems, and their accumulation in water varies with the type of wastewater treatment used. Plants have the presence of these metals in water. Through the food chain, fish contaminants can reach man. Disposed of heavy metals and waste from industries they get accumulated in rivers and lakes thus causing harmful impacts on animals and humans. There is direct damage to plant or animal nutrition at that time human health is affected. The pollutants that are polluting the water are killing marine organisms such as mollusks, marine birds, fishes, and other organisms that live in the sea.
• Urbanization: An increase in the population leads automatically leads to more generations of solid waste. Both solid waste and liquid waste are deposited into the water without any treatment. Human excreta also contaminate the water. Thus, contaminated water leads to a generation of a large number of bacteria, which is a threat to human well-being.
• Agriculture source: When it rains the water from the surface runoff and that rainwater enters the nearby water resource and thus pollutes the existing water. Agricultural runoff cases freshwater bodies’ eutrophication. Phosphate has one of the major contributions to eutrophication. Fertilizers that are too enriched with nitrogen decrease the dissolved oxygen in rivers and coastal zones thus bringing hazardous effects to the biota. Pesticides leach into groundwater, thus polluting groundwater.
• Atmospheric source: Small pollutants particles which are present in the air, get into the water stream through the rain, when it rains these particles come down and then with the flow of water enters into the sea, thus polluting the water there. These pollutants that are present in the air usually get from the burning of fossil fuels e.g. is CO₂, which combines with water and produces sulfuric acid. Just like this nitrogen dioxide also combines with the water and forms the nitric acid. And with the help of rainwater, they enter the water resources 
• Mining source: Heavy metals are present on the earth and thus they can enter the water system through various pathways and one of them is through mining sources. When it rains or through flowing water, it leaches heavy metals out from their geological formation. These processes get disturbed when manmade economic activities such as mining are done. Through these processes, the area that is already mined out gets exposed to water and air and this leads to the acid mine drainage (AMD). The low pH conditions associated with AMD mobilize heavy metals, including radionuclides where these are present

Effect on living organisms

a)  a) Effect on aquatic environment

    One of the most noticeable signs of metal toxicity in fish larvae is growth inhibition. As a result, the length and bulk of fish are indications of environmental conditions. A decrease in pH of water either due to acid rain or any other acidic incidents, due to the heavy metal’s deposition into the water column, causes aquatic biota to become poisonous. Heavy metals get into the fish through three routes: the first is via the fish gills, the second is through the digestive tract of the fish and the last one is through the body of the fish. The gills of fish are the area that is known for the primary metal intake from the contaminated water. The harmful effects of heavy metals have the greatest impact on the death rate, reproduction, individual development rates, and physiological capacity of fish. There have been effects on physical functioning and chemical parameters in the tissues and blood of fish living in water that is polluted via metals. It has been reported that fish exposed to metals developed immune system defects, making them more susceptible to infectious infections and increasing their chances of dying

b)  b)Effects on aquatic plants

    Heavy metals are poisonous and phytotoxic to plants, resulting in diseases such as chlorosis, poor plant development, and yield depression, as well as decreased nutrient absorption, plant metabolic problems, and a reduced capacity to fix molecular nitrogen in leguminous plants. Seed germination was gradually reduced in the presence of increasing levels of lead, it may be due to exposure to lead for a longer duration, some methods, such as leaching, chelation, metal binding, or microbe accumulation, have resulted in the neutralization of lead’s harmful effects. Heavy metals such as Cd, Pb, and Ni even their small concentration in plants can be hazardous to them. Pb poisoning also inhibits enzyme action, creates an imbalance of the water, alters membrane permeability, and disrupts mineral feeding

HEAVY METAL POLLUTION SEEN IN COCHIN BACKWATERS

            Extensive investigations have been conducted on heavy metal abundance, distribution and speciation in dissolved, particulate and sedimented media. Concentration of Iron (Fe), Copper (Cu), Lead (Pb), Zinc (Zn), Cadmium (Cd), Mercury (Hg), Nickel (Ni) and Manganese (Mn) in water samples from Cochin backwaters were 1.67-662.77%, 0.87-50µg/L, 0.12-82µg/L, 1.0-257.92µg/L, 0.02-24µg/L, 0.09-0.17µg/L. However, very high levels of Cu, Zn, Pb and Cd in the suspended particles of Cochin estuary indicate that in the estuarine environment, the suspended particles play a vital role by acting simultaneously as a source and sink for heavy metals. High concentrations of dissolved Zinc, Cadmium, Iron and Mercury was recorded at industrial belt located towards the northern side of the backwater (Ouseph, 1978 Saraladevi et al., 1979, Kaladharan et al., 2011 and Anju et al., 2011).

It was also reported that, in Cochin estuary as well as in Cochin inshore waters, cadmium level has reached critical point, while copper and lead have attained levels of caution (Kaladharan et al., 2011). Temporal trends of heavy metal in Cochin backwater indicated higher concentration of almost all trace metals during premonsoon (February to May) and postmonsoon (September to January) (Nair et al., 1990; Anju et al., 2011). Enrichment of heavy metals due to industrialization and urbanization in Cochin backwater was recorded by several investigators (Remani et al., 1983; Ouseph, 1992). Industrial pollution poises the most serious threat in lower reaches of Periyar i.e., about 15 Kms upstream from the backwaters of Cochin, where a cluster of small and big industries are operating (Joseph, 1984; Paul and Pillai, 1976). Elevated levels of Hg, Cu, Zn and Cd, particularly near industrial areas were observed in this area (Paul and Pillai, 1976). Geochemical analysis of sediment in the estuary revealed that the concentration of toxic metals (Cd, Co, Cr, Cu and Pb) were higher at Vallarpadam, near International Container Transshipment Terminal (ICTT) project and the distribution follows the order Cr > Cu > Cd >Co= Pb (Nair Manju and Sujatha, 2013).

Sudhanandh et al. (2011) reported that coastal sediments of Kochi have high heavy metal accumulation and seemed to be under stress. Priju et al. (2007) reported enrichment of Cu, Ni, Co, Zn and Cd in sediment cores recovered from the Vembanad Lake and their concentrations, when compared with other Indian rivers suggested that the Periyar River and Cochin estuary are showing heavy anthropogenic contamination. A long-term assessment of the metal pollution levels in sediments of the northwest part of Cochin backwaters showed an increase in concentrations of Zn from 70 to 1266 mg/kg (18-fold) and Cd from 1.7 to 14.94 mg/kg (9-fold) over the past 24 years (1976-2000). The geochemical fractions of trace metals in the sediments revealed that even though a large quantity of anthropogenic input of metals like Zn, Cd, Pb etc. have been detected in the Cochin estuarine system, the partition patterns showed the retentivity of the inputs in and around the sites of discharge itself, through the geochemical transformation of the metal species (Rajamani, 1994). Analysis of various fractions of mercury in the sediments of Vembanad wetland system showed bioavailability of mercury is very high (Ramaswamy et al., 2011). Increased levels of Cu, Zn, Fe and Mn in gills and alimentary canal compared to the muscle were reported from fishes of Cochin area by Martin et al. (2008).

Jiya et al. (2011) reported that high concentrations of Zn (2758mg/kg) and Nickel (259mg/kg) at geographical location close to industrial belt and metal accumulation at this level in the sediment ultimately resulted in adaptation/reduction in bacterial distribution, diversity and enzyme expression profile, thereby by emergence of resistant strains. Lakshman et al. (1989) reported the ability of Perna viridis to concentrate substantial quantities of heavy metals like mercury, copper, zinc and lead from the environmental water in their tissues especially in gills. High concentrations of Zn, Cu, Fe, Mn, and Hg in oyster (Crassostrea madrasensis) tissues from Cochin harbor indicated that the concentrations were higher during breeding period and also when the estuary experiencing higher salinity (Oct-April) (Ouseph et al., 1987). Accumulation of trace metals (Cu, Cd, Zn, Pb, Fe and Mn) in biota under natural conditions in four common species of fish samples and one prawn sample from the Cochin estuary were analysed by Rajamani et al., 1994. Very high levels of Zn in the flesh of fish sample (16.43-42.25 µg/g) and prawn samples (44.21- 57.12µg/g) observed was reported to pose a threat.

 

Measures that are recommended for conserving the ecosystem are as follows:

• Developing pollution baseline and monitoring studies of the pollutant level, the source of these heavy metals and its pathway
• Adequate management strategies/protocol should be made to control metal discharges in water bodies, thereby lessening the loading of contaminants in the estuarine sediment
• Evaluation of various methods currently used for collection, storage, pretreatment and analysis of samples and selection of optimum method for pollution assessment
• Increase public awareness on the need of marine environmental protection to maintain sustainable development

CONCLUSION

Water pollution is a global problem, and the world’s population is suffering the consequences of tainted water. Living organisms are also affected by the polluted water very much and it is very harmful to the environment. Acute and choric illnesses are caused by heavy metal concentrations in drinking water that exceed the permissible limits set by several national and international organizations. These can range from nonfatal, such as muscle and physical weakness, to fatal, such as brain, nervous system, and even cancer. Water quality testing is necessary for the protection of human health and the environment.

Cochin backwater is presently facing serious challenges because of heavy metal contamination. The concentrations of heavy metals in the water as well as sediment at different locations in the backwater system are consistent with the local industrialization levels. Northern part of the estuary is found to be the most polluted compared to other part of the estuary. Heavy metal levels in some aquatic organisms exceeded the safety limit. Therefore, it is necessary to give more attention to accumulation of heavy metals in organisms as far as the seafood industry and public health is concerned. More precise environmental protection measures should be taken to control the discharge heavy metals from anthropogenic sources

 

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