15
CHAPTER 2
REVIEW OF LITERATURE
2.1
COASTAL ECOSYSTEMS - INDIA
Indian coastal zone comprises (i) east and west coasts of the mainland (ii) coast of two groups of islands, Lakshadweep in the southern part of Arabian Sea, Andaman and Nicobar island groups in the eastern part of Bay of Bengal. India has an extensive coastline of 7516 km, the mainland accounts for 5422 km, Lakshadweep coast extends 132 km and Andaman and Nicobar Islands stretches to 1962 km (Venkataraman 2008). India has 14 major, 44 medium and 162 small rivers with a total catchment area of 3.12×106 km2 (Desai and Achuthankutty 2000). Major estuarine areas are located along the Indian coastal region extending up to an area of 2.6 million hectares (Gouda and Panigraphy 1999).
India is one among the 12 mega biodiverse countries and more than 25 hotspots of the richest and highly endangered eco-regions of the world with a vast Exclusive Economic Zone (EEZ) of 2.02 million km2 adjoining the continental regions. The offshore islands, wide range of rocky coasts, coral reefs, lagoons, estuaries, mangroves, backwaters, salt marshes and sandy stretches are characterized by unique biotic and abiotic properties and processes (Venkataraman 2005).
16
2.1.1
Coastal Pollution in India Indian coastal ecosystems are sensitive towards changes occurring
in the environment and a few areas are now struggling to maintain their diversity due to extensive human activity and other factors (Fikirdesici et al 2012; Metcalfe et al 2011). In addition, coastal ecosystems continue to be threatened and disturbed by problems such as pollution, erosion, flooding, salt water intrusion and storm surges (Nirmalie 2010). Waste disposal into coastal waters comes from three main sources viz., direct discharge of waste into the oceans, runoff due to rain, and pollutants from the atmosphere. The major sources of pollution in Indian coasts are urban sewage, drilling for and shipping of crude oil, effluents from industries including chemicals, radioactive wastes and heat discharges. All these have resulted in the deterioration of the coastal ecosystem (Verlecar et al 2006). 2.2
POLLUTION ALONG CHENNAI COAST Chennai is an important metropolitan coastal city in India, and it is
located in Tamil Nadu along the Bay of Bengal. Chennai’s coastal waters have been receiving a large amount of industrial, agricultural and domestic effluents through waterways that flow through or near the city: Ennore estuary, Coovum river, Adyar river, Buckingham canal and Muttukatu backwaters as shown in Figure 2.1 and Table 2.1. Of the various components of effluents that reach coastal areas, heavy metals are widely distributed and are considered as an important toxic constituent (Jayprakash et al 2009; Shanmugam et al 2007). Overall assessment of heavy metal pollution in coastal regions of Chennai reveals that the accumulation of heavy metals has increased in all compartments viz. sediment, biota and water. Specifically an increasing trend is observed during the past few decades (Ramanibai and Santhi 2012; Seshan et al 2012; Venkatachalapathy et al 2011; Laxmi Priya et al 2011; Solai et al 2010; Sundararajan and Usha Natesan 2010; Batvari et al
17
2008; Jonathan et al 2008; Muthuraj and Jayaprakash 2007; Shanmugam et al 2007; Selvaraj et al 2004). Sometimes the presence of heavy metals causes such a massive change in the environment that returning back to earlier, pristine conditions is impossible.
Figure 2.1 Major Pollution conduits to Chennai’s coastal waters
18
S. No.
Name of the Industry
Total Discharge ( KLD)
1
EID Parry Ltd.
4.83
2
Balmer Lawrie and Company Ltd. (Leather)
12.83
3 4 5 6 7 8 9 10
ICI India Ltd. (Pharmaceutical) CETEX Petro Chemicals Royal Enfeild Motors Corborundum Universal Ltd Eveready Industries (India)Ltd. Tamilnadu Minerals Ltd. Madras Petrochemicals Division Spic Heavy Chemicals Division
42 75 130 131.5 132.7 133 210 300
11
Kothari Sugars and Chemicals Ltd.
320.5
12 13 14 15
India Additive Ltd. Sriram Fibers Ltd. Ashok Leyland Tamilnadu Petro Products Ltd.
342 678.5 850 1254
16
Indian Organic Chemicals Ltd.
1600
17
Madras Rubber Factory
2000
18
Manali Petrochemicals Ltd.
3415
19 20 21
Madras Fertilizers Ltd. Spic Organic Chemicals Ltd. Madras Refineries Ltd.
3435 4550 7680
Table 2.1 Industrial Discharges along Coast Overall, anthropogenic pressure on the sea’s resources is increasingly affecting the health of many organisms, leading to changes in the food web structure and resulting in bioaccumulation and biomagnification in marine organisms. Surveys of coastal (ecological) communities indicated that the density and diversity of aquatic organisms have changed over time in Chennai’s coastal areas. However, there is very little data available on aquatic toxicity of heavy metals on marine organisms; and available data does not clearly confirm if the impact is related to toxic contamination or other contributing factors. The following sections describe the major waterways that act as pollution conduits. 2.2.1
Pulicat Lagoon
Pulicat lagoon is the second largest brackish water lake in India running parallel to the Bay of Bengal. It has an area of 481 km2 with long
19
intertidal zone. The length of the lagoon is 60 km and the width is 0.2-17.5 km. At the southern end, it opens into the Bay of Bengal through a shallow mouth of 200 m. Input to the Pulicat lagoon is through the Arani River at southern tip, Kalangi River from northwest Swarnamukhi River at the northern end. Over-exploitation, mismanagement and improperly treated industrial effluents discharged into North Chennai Coastal region, threaten the lagoon ecosystem. Several threats to the lagoon have been identified in parts of the Pulicat lagoon which fall in Andhra Pradesh viz., sewage, agricultural chemicals and industrial effluents, wastes from numerous fish processing units, oil spills from the mechanized boats, salt manufacturing industry and shrimp farming from Arani and Kalangi rivers draining into the Pulicat lagoon (Laxmi Priya et al 2011; Batvari et al 2008). 2.2.2
Ennore Creek Ennore creek is a backwater located at Ennore, Chennai along the
Coromandel Coast of the Bay of Bengal. It is located in the zone comprising lagoons with salt marshes and backwaters, submerged under water during high tide and forming an arm of the sea with the opening to the Bay of Bengal at the creek. The creek receives wastewater from numerous sources including untreated wastewater and treated effluents from industrial sources in the surrounding area by a couple of rivers, namely, Arani River flowing in the north and Kosasthalaiyar River. Ennore coast receives untreated sewage from Royapuram sewage outfall, untreated/treated industrial effluents from Manali Industrial Belt, as well as from chemical industries like fertilizer, oil refineries and sugar. Apart from this, it receives fly ash and thermal discharges from the nearby Ennore Thermal Power Station. In addition to that, fishing and navigational activities take place in the area. The dredging activities in Ennore area have resulted in changes in the landscape, sediment transport and dust pollution to the coast by quarrying process (Seshan et al 2012; Padmini and Vijaya Geetha 2007).
20
2.2.3
Chennai Port
Chennai Port is considered as the eastern gateway of south India. It handles nearly 50 million tonnes per year of different commodities such as coal, iron ore, chemical manures, machineries, chemicals including acids, cement, granite blocks, furnace oil, diesel oil, vegetable oil etc. Apart from these, there are also containers and passenger traffic in the harbour. As of 2011, cargo movements to the port were increased by 21%. Over 5,000 container trucks move through the port every day. However, the number of containers coming into the port has dropped by 30 per cent in the same year. On an average, 3000 vessels move around the harbour area (sources: Chennai Port http://www.chennaiport.gov.in/; Shanmugam et al 2007). The sources of pollution at harbours and landing jetties include organic waste, litter, petroleum hydrocarbon and toxic chemicals (Mukerjee 2002). Water used for washing down ships can be contaminated, even when no chemicals are used. Mukerjee (2002) stated that the port might be contaminated with oil debris, heavy metals or sediments. These cause contamination or pollution of aquatic environment and constitute a hazard to public health (Agbagwa and Okpokwasili 2011).
2.2.4
Cooum River
Cooum River flows towards eastern direction in the Chennai city. The major portion of city’s treated/untreated sewage is channelized through this river to the sea. This river also serves as a conveyor of storm water from the city’s sewage drain network. Nearly 30 per cent of the estimated 55 million litres of untreated sewage being let into the waterways of Chennai daily, including water from the Chennai metropolitan water supply and Sewerage board, gets into the Cooum river. About 60 per cent of the untreated sewage gets into the Buckingham Canal and the Adyar River takes the rest. In
21
2010, about 340 sewage outfalls into the waterways were identified. Of them, more than 130 sewage outfalls were in the Cooum River and a majority of them were between Aminjikarai and Nungambakkam. In some of the spots in areas such as Maduravoyal, more than seven tonnes of municipal solid waste is being dumped into the river every day.
The bed slope of the river is very mild. This, together with the formation of sand bar at the river mouth and a tidal range below 1.2 m prevent the effective flushing of the river during the ebb tide. As a result, for periods other than monsoon, the stagnant river is anoxic and very rich in organic matter. There is periodic reversal of this trend only at the river mouth due to weak tidal effect (Venkatachalapathy et al 2011; Shanmugam et al 2007)
2.2.5
Adyar River
Adyar river originates near the Chembarambakkam Lake in Chengalpattu district. It also flows in an easterly direction. Despite the high pollution levels, boating and fishing activities take place in this river. The river collects surplus water from about 200 tanks and lakes, small streams and the rainwater drains in the city, with a combined catchment area of 331 sq miles. Most of the waste from the city is drained into this river between Chembarambakkam and Thiru.Vi.ka. Bridge.
The problem of sedimentation was not severe as the Adyar's width near Thiru.Vi.Ka. Bridge is nearly 480 m that enables tidal effect into the waterway for about 4 km. However, it was found essential to provide groynes to keep the river mouth open for adequate width and prevent inundation during monsoon (Venugopal et al 2009; Achyuthan et al 2002).
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2.2.6
Buckingham Canal The Buckingham Canal is a 421.55 km long fresh water navigation
canal, running parallel to the Coromandel Coast of South India from Vijayawada in Andhra Pradesh to Villupuram District in Tamil Nadu. The canal connects most of the natural backwaters along the coast to the coastal area of Chennai. The Coovum and Adyar rivers connect to the Bay of Bengal in heart of Chennai city whereas Muttukadu backwater connects at outskirts of Chennai city.
Within the Chennai city, the Buckingham canal is heavily polluted by sewage and industrial effluents, and the silting up of the canal has left the water stagnant, creating an attractive habitat for malaria-spreading mosquitoes. The North Chennai Thermal Power Station (NCTP) discharges hot water and fly ash into the canal as well. Buckingham Canal is the most polluted of the three major waterways in the city with nearly 60 per cent of the estimated 55 million litres of untreated sewage being let into it daily, including the water by Chennai Metropolitan Water Supply and Sewerage Board (Ravichandran and Manickam 2012; Seshan et al 2012).
2.2.7
Muttukadu Backwater The Muttukkadu backwater extends for a distance of 20 km from
the mouth. The backwater runs at a right angle to the coast for a distance of about 3 km and branches into southern and northern wings. Muttukadu backwater forms a complex system of shallow estuarine network spread over an area of 215.36 acres (87.190 hectares) used for fishing and boating activities. The backwater extends northward and southward for about 15 km and opens into the Bay of Bengal at its eastern end. During the northeast monsoon period flood waters are collected from the surrounding areas and
23
Buckingham canal. During October-December due to inundation by the water from the upper reaches, the sand bar gets eroded and the connection with the sea is restored.
There are several aquafarms in this region growing prawns which are mainly exported. These farms not only draw water from Muttukadu, but also discharge nutrient-enriched wastewater back into the estuary. The unimpeded dumping of effluents by one and all, from Metro water authorities to corporate houses to star hotels that have sprung up in the southern suburbs makes Muttukadu a highly polluted region (Ravichandran and Manickam 2012).
2.3
HEAVY METAL POLLUTION STATUS IN CHENNAI
Estuaries and coastal areas receive significant amount of anthropogenic inputs from both point and non-point sources and from metropolitan areas, tourism activities and industries located along the estuarine edges (Shanmugam et al 2007; Caeiro 2005). Dural (2007) stated that the heavy metal pollution in estuaries and coastal areas has been recognized as a serious environmental concern. Among the various contaminants, heavy metals are serious pollutants of aquatic ecosystems because of their environmental persistence, toxicity and ability to be incorporated into food chains (Nikulina and Dullo 2009; Santos et al 2005), occurring both in sediment and water (Akcali and Kucuksezgin 2011; Wu et al 2007). The following sections describe the high concentrations of heavy metals in the marine matrices, water, sediment and biota in Chennai.
24
2.3.1
Heavy Metals in Coastal Waters
Solai et al (2010) investigated the physical parameters and trace elements in surface water off Pondicherry, Bay of Bengal, and Southeast Coast of India. Overall investigation revealed that metal enrichment was observed close to the major urban areas in the Pondicherry coast which were associated with industrialized areas. Compared to Veerampatnam, high concentrations of Zn and Pb in the coastal waters and sediments were observed in the Pondicherry region due to high inputs of domestic and industrial wastes.
The distribution of dissolved and particulate heavy metals (Cd, Cu, Ni, Zn, Fe, Pb, Cr and Mn) in Chennai coastal was studied by Shanmugam et al (2007). Results clearly indicated that higher concentrations of toxic metals were found in the coastal waters mainly due to the influence of industrial effluents and sewage waste.
Jonathan et al (2008) investigated the dissolved trace elements (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn and Cd) and physico-chemical parameters from Uppanar River and coastal waters off Cuddalore, Southeast Coast of India. The result clearly showed that the physico-chemical parameters did not exhibit significant relationship with trace metals. Enrichment of Pb was due to external input and excess levels of Cu, Zn, Cr, Cu and Ni were identified.
Kuppusamy and Giridhar (2006) examined the water quality characteristics including trace metal speciation in Ennore, East Coast of India. They reported higher levels of trace metals, especially Cu and Pb, in the off shore waters. An earlier study by Jayaprakash et al (2005) in the same area showed that higher concentrations were found in lower salinity zones that
25
were significantly influenced by inputs from land based sources and regions of industrial catchments.
Senthilnathan and Balasubramanian (1999) investigated select heavy metals (Cu, Zn, Cd and Pb) in water, sediment and plankton from Pondicherry harbour and found higher metal concentrations during monsoon and lower during summer.
2.3.2
Heavy Metals in Sediment
Ravichandran and Manickam (2012) measured the concentrations of Cd, Co, Cu, Cr, Ni, Pb and Zn in the Chennai coastal sediments and reported high metal concentrations along Chennai coast. The metal concentrations were high in the nearshore stations due to closer proximity to industrial outlets.
Venkatachalapathy et al (2011) carried out statistical analysis on heavy metal distribution using 21 surface sediment samples collected from Chennai coast, to examine the extent of heavy metal pollution using magnetic susceptibility.
High pollution load index in the off shore stations were
associated with anthropogenic activities such as harbour activities, sewage and industrial effluents.
Seshan et al (2012) estimated heavy metals in the sediment of Buckingham canal, Ennore, south east coast of India. High metal concentrations were observed and all the pollution indices classify Ennore as moderately contaminated. The results indicated that the industrial activities and nearby municipal dumping were responsible for the higher metal concentrations in Ennore estuary.
26
Sundararajan and Natesan (2010) studied the geochemistry of core sediments from Mullipallam creek, south east coast of India. Normalization with Al values had been done for all the major and trace elements and enrichment factors were calculated. The calculated enrichment factors and comparison indicated that the trace metals Mn, Cr, Cu, Ni, Co, Pb, Zn (especially Pb) were enriched mainly due to the external (anthropogenic) activities in the land as well as in the coastal zone (Palk Strait).
Muthuraj and Jayaprakash (2007) estimated the concentration of heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Zn, Co and Cd) in sediment of Ennore shelf, Southeast Coast of India. The result showed that the major sources of metal contamination in Ennore are land-based anthropogenic sources such as discharge of industrial wastewater, municipal sewage and runoff through the Ennore estuary. The intermetallic relationship revealed the identical behaviour of metals during their transport in the marine environment. Acid leachable trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn and Cd) in the sediments were analyzed from Ennore Creek of Chennai Southeast Coast of India by Jayaprakash et al (2008). They reported that the enrichment of metals in the sediments is mainly attributed to the intense industrial activities around Chennai.
Srinivasalu et al (2008) estimated trace metals (Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn) in the surface sediments along a 60 km coastal zone area in the central part of Tamil Nadu from Injambakkam (south of Chennai City) to Cuddalore, near the River Palar. High values of trace metals in the southern part of the study area are due to the large-scale industries along the coast and anthropogenic activities that cause serious environmental problems.
Kannan et al (2008) estimated the heavy metals Cd, Cr, and Pb in water, sediment and seaweed from the Pulicat Lagoon, North Chennai Coastal
27
region. Results showed that the Pulicat Lagoon received the effluents from industries located in North Chennai Coastal region. The concentrations of heavy metals were found to be the highest in sediment.
Prasath and Khan (2008) investigated the heavy metals (Zn, Cu, Fe, Mn, Co, Pb, Cd, Ni) in water, sediment and fish from Poompuhar Coast, Southeast Coast of India. The results clearly showed significant variations in the accumulation of heavy metals in water, sediment and fish.
Sujatha et al (2008) investigated trace elements (Cd, Co, Cr, Cu, Ni, Pb, and Zn) in the sediment samples from inner shelf region along the coastal belt of Nagapattinam, Tamil Nadu, India, after the 2004 tsunami. They pointed out that higher concentration of metals was brought in by tsunami through the clayey sediment from sea-bottom that were settled for years together in inland areas as well as from the offshore sediment and domestic waste discharges.
2.3.3
Heavy Metals in Biota
Vasanthi et al (2013) studied bioaccumulation of heavy metals and its associated histological perturbations in various tissues of Mugil cephalus collected from Ennore estuary and compared with the fish collected from offshore region. The concentration of Cu, Pb, Zn, Cd, Mg
and Fe were
quantified in gills, liver and muscle. Overall, the highest metal concentrations were found in the fish collected from Ennore estuary. The accumulation in the gills and liver of M. cephalus was found to be quite high in comparison with the muscle.
A number of studies have been carried out on the biota of Pulicat lagoon. Most recently, Laxmi Priya et al (2011) estimated the concentration
28
of heavy metals (Cu, Cr, Zn, Cd, Pb and Ni) in water, sediments and organisms from two locations in Pulicat lagoon, which receives considerable quantity of effluents from industries located in North Chennai coastal region. The effect of pollution was studied by evaluating metal bioaccumulation and correlation obtained between metal level in water, sediment and organisms. The results indicated high concentration of Cu, Pb and Zn in liver and tissue of the organisms. Liver and gill are preferred areas for accumulation of metals in fish.
The concentration of heavy metals were determined in marine fishes from Parangipettai coast, south east coast of India (Raja et al 2009). The result clearly pointed out that heavy metals showed increased levels in the gills and alimentary canal of all organisms.
Batvari et al (2008) estimated the concentration of Cr, Cd, Zn, Pb and Fe in four fish organs (gills, liver, intestine and muscle) in two fish species from Pulicat lagoon. They reported that the metal concentrations in the fish muscle showed low Pb and Fe, while higher concentrations were observed in the liver and gills of the two fish species.
Padmini and Vijaya Geetha (2007) estimated the concentration of heavy metals in fish species Grey Mullet (Mugil cephalus) from Ennore estuary. The highest metal concentrations were found in the tissues of the fish species which lead to oxidative stress and shorter lifespan. The source of the heavy metals was attributed to the discharge of effluents from industries situated in the vicinity of the Ennore estuary.
Kumar and Achyuthan (2005) studied heavy metal accumulation in certain marine animals like fish, prawn, crab and mussel along the coastal
29
waters of Chennai, Tamil Nadu, India. The report clearly showed that the concentration of heavy metals Pb, Zn, Cu and Cr are high.
2.4
TOXIC BEHAVIOR OF HEAVY METALS IN MARINE ENVIRONMENT
High levels of metals in the tissues of the aquatic organisms traceable to human activities, especially waste disposal into aquatic ecosystems, are currently a major environmental problem all over the world (Laxmi Priya et al 2011; Wang et al 2009). In recent years, there has been a growing awareness of the need to improve the ability to detect and assess adverse effects of contaminants in marine biota. Towards this, various studies to monitor and control metal contamination in coastal environments are being carried out around the globe.
Elevated heavy metal concentrations in aquatic systems are often toxic to animals living in those environments. Most of the trace metals are considered as essential micronutrients but are also toxic at concentrations higher than the amount required for normal growth. Other metals like Pb, Cd and Cr have unknown roles in living organisms and are toxic even at low concentration (Siwela et al 2009).
The toxic effects of heavy metals on marine organisms depend on various factors. Some heavy metals are relatively more toxic than other metals (Jakimska et al 2011). For example, the relative toxicity of Cd, Pb, Cu and Zn have been grouped in descending order from high toxicity to low toxicity as Cd > Pb > Cu > Zn (Jakimska et al 2011; Wang et al 2007; Grosell et al 2006). Even low concentrations of heavy metal in the environment have harmful effects due to the accumulation of metals within the body tissues of aquatic animals. Filter feeders such as bivalves, can absorb heavy metals
30
either directly from water or indirectly from their food. Biomagnification is another problem induced by contaminants within the body tissues of animals along the food chain (Hariharan et al 2012; Laxmi Priya et al 2011). Biomagnification is the process by which contaminants are accumulated along the food chain. As a result, humans and other predators belonging to the higher levels of the food chain may have more heavy metal pollutants in their body tissues than the animals at lower levels (Gabr et al 2008; Lodhi et al 2006).
Several studies revealed that heavy metal pollutants affect the biology and ecology of the aquatic environment (Jakimska et al 2011; Presley et al 2003). The ecological effects of heavy metal pollution on aquatic organisms depend on the type of pollutant, the concentration and the duration of exposure to the pollutant. Toxicity can change the community structure and population of organism. Also, toxicity may be expressed at the organism, cellular or sub-cellular levels (Van der Oost et al 2003).
The biological effects of heavy metals on aquatic animals that are manifested as various pathological conditions depend on the toxicity of the heavy metal compounds. Patel and Bahadur (2010) and Kennish (1997) showed that the chemical nature of heavy metal compounds were more important in the determination of the toxicity of heavy metals than the total concentration or the exposure time of the animal to the heavy metal compound. However, animals living in environments contaminated with heavy metals can often regulate metal contents in their bodies within a limited range. Excess heavy metals ingested by animals are excreted, detoxified or accumulated inside the animal bodies. All heavy metal contaminants above a threshold concentration in water have harmful effects on marine animals. The exposure of marine animals to higher levels than the threshold results in various pathological and physiological responses, such as tissue inflammation
31
and degeneration, genetic derangement and growth retardation (Oliva et al 2009).
2.5
LEAD (Pb)
Lead is one of the oldest metal known to mankind and has been used since medieval times and has also been widely studied. Not required for normal physiology in animals, it is potentially toxic to most of the aquatic organisms even when present in lower concentrations. It is a dense, highly malleable metal that is resistant to corrosion. Pb has become important due to increasing environmental contamination. The main sources of Pb are atmospheric lead, paint chips, used ammunition, fertilizers, pesticides and lead-acid batteries and other industrial activities.
The principal uses of Pb today are in storage batteries as metallic lead and lead oxide (35%), in water distribution systems, food, and lead used in hobby activities (10%), cable coverings (10%), solders (10%), chemicals such as lead carbonate and lead chromate in pigments and paints (15%). Other uses are in ammunition, alloys such as brass and steel, corrosive liquid containers, glassware and radiation shielding. Tri-basic lead sulphate is used as a stabilizer in polyvinyl chloride (PVC) plastics. The availability and sources of lead may be classified as natural and anthropogenic.
2.5.1
Natural Sources of Lead
Lead occurs as an important constituent of more than 200 minerals. The most common lead mineral is galena (lead sulphide) which contains zinc minerals and small amounts of copper, iron and cadmium. Other ores are anglesite (lead sulphate); cerussite (lead carbonate) and plattnerite (lead [IV] oxide). Small quantities of metallic lead are occasionally found in nature. The
32
average concentration of lead in the Earth’s crust is 1.6 g Pb per 100 kg of soil. Therefore lead is a relatively rare metal (AMAP 2005 and 1999; Pain 1995).
Natural sources of lead are attributed to weathering of rocks, especially lead minerals. Rocks such as basalt and granite contain traces of lead. Igneous activity and radioactive decay also contribute to natural levels of lead found in the environment. AMAP (2005 and 1999) estimated the worldwide annual emission of lead from natural sources to be 24.5 x 103 tonnes; of this, eroded soil particles made up about 65% of the natural lead emissions while contributions from forest fires and sea salt spray were less than 5%.
2.5.2
Anthropogenic Sources of Lead
From various studies, it is evident that anthropogenic output outweighs all natural sources (Libes 1992). The total lead production in the world was estimated to be more than 1.5 bilion tonnes (U.S. Geological Survey 2012). Most anthropogenic inputs of lead result from mining, smelting and refining of lead and other metal ores (Harrison and Laxen, 1981). Tetraethyl lead was till recently, mixed with petrol, as an anti-knock compound. Vehicle emissions from the combustion of tetra alkyl lead released inorganic lead into the atmosphere. This use of a lead compound was phased out in most countries in the early 2000 because of concerns over air and soil lead levels and the accumulative neurotoxicity of lead. Industrial emissions resulting from the production, use, recycling and disposal of lead containing products also play a major part by contributing lead into the environment. The initial recipient of these emissions is the atmosphere from which lead may be dispersed to other environmental media such as water and
33
soil.
There
is
inter-compartmental
exchange
between
the
various
environmental matrices.
2.5.3
Behaviour of Lead in Environment
Pb appears ubiquitous in aquatic ecosystems, bioaccumulates in aquatic organisms and is deposited in bed sediment in association with particulate matter (Ahmed and Bibi 2010; Harte et al 1991).Generally, Pb occurs in the environment in a wide range of physical and chemical forms that greatly influence its behaviour and its effects on the ecosystem. Most of the Pb in the environment is in the inorganic form and exists in several oxidation states (0, I, II and IV). According to Nussey et al (2000), Pb (II) is the most stable ionic species present in the environment, and is thought to be the form in which most Pb was bio-accumulated by aquatic organisms. In addition, Pb is also present in the organic form, such as alkyl Pb from auto emissions (Ahmed and Bibi 2010; Nussey et al 2000).
Seymore et al (1995) reported that Pb appears to be metabolized via the Ca metabolic pathway and therefore accumulates in the skeletal tissues. However, Pb is known to accumulate in the tissues of fish, including skeletal bones, gills, kidneys, liver and scales (Spokas et al 2006; Fabris et al 2006). Seymore et al (1995) stated that the uptake of aqueous Pb2+ across the gills into the blood stream is the primary mode of uptake in freshwater fish. According to Nussey et al (2000) the toxicity of Pb is dependent upon the life stage of the fish, pH and hardness of the water, in addition to the presence of organic materials. The uptake and toxicity of Pb in aquatic organisms generally decreases with increasing water hardness and alkalinity (Markich and Jeffree (1994). According to Seymore et al (1995), as the pH of the water decreases, the ionic state of the metal becomes more prevalent and toxicity increases acutely.
34
Davies et al (1976) reported that the 19 month LOEC for rainbow trout (Oncorhynchus mykiss) was 4.1í7.6 µg L-1 in soft water (with hardness 28 mg L-1 as CaCO3; alkalinity- 26 mg L-1 as CaCO3; pH, 6.65í7.34) in contrast;, in hard water it was 18í32 µg L-1 (hardness- 350 mg L-1 as CaCO3; alkalinity- 240 mg L-1 as CaCO3; pH- 7.64í8.25). There is a disproportional inverse relationship between the bioaccumulation of lead and increased calcium concentration (Markich and Jeffree 1994; Varanasi and Gmur 1978). An exponential, inverse relationship has been demonstrated between water hardness and the uptake and toxicity of lead (Barelli and Romeo 1993).
2.5.4
Toxicity of Lead to Marine Organisms
The chemical and physical properties of Pb and biogeochemical processes within the environment influence the movement of lead through ecosystems. Pb was found to affect all components of the environment and moved through the ecosystem until it reached equilibrium. Pb accumulated in the environment, but in certain chemical environments it was transformed in such a way to increase its solubility. Adverse biological effects for Pb in the aquatic environment include increased mortality, population diversity, increased susceptibility, decreased benthic invertebrate abundance and diversity; and abnormal development of benthic organisms (Rainbow 1995).
Pb was found to biologically concentrate in the skin, bones, kidneys, and liver of fish rather than in muscle and did not magnify up the food chain. This makes lead less problematic via this route of exposure. However, people who eat whole fish can be potentially exposed to high concentrations of lead (Wright and Welbourn 2002). When Pb concentrations in algae exceeded 500 µg L-1, enzymes needed for photosynthesis were inhibited. When less photosynthesis takes
35
place, the algae produce less food and therefore the growth is reduced. Decreased algal growth means less food for animals; this has repercussions for the entire ecosystem (Taub 2004).
Fish are more sensitive to Pb than algae. When lead concentrations exceeded 100 µg L-1, gill function was affected. Embryos and young ones are more sensitive to the toxic effects of Pb than adults (Wong and Tan 1999). Pb is more toxic at lower pH and in soft water (Taub 2004; Wright and Welbourn 2002). Similar to other metals, the toxicity of Pb on fish depends in part on the species. Goldfish are relatively resistant because they can excrete Pb via their gills (Landis and Yu 2003).
According to Eisler (1985), in aquatic environments, waterborne Pb is the most toxic form. Adverse effects were noted on Daphnid reproduction at 1.0 µg L-1 of Pb2+, on rainbow trout survival at 3.5 µg L-1 of (CH3CH2)4 Pb and on growth of marine algae at 5.1 µg L-1 of Pb2+. High bioconcentration factors were recorded for filter-feeding bivalve molluscs and freshwater algae at 5.0 µg L-1 of Pb2+.
Pb is also a well-known reproductive toxicant and has been reported to have the potential to inhibit reproduction in aquatic animals at extremely low levels. Pb concentration as low as 0.08 mg L-1was found to severely decrease the offspring population of Diaphanosoma birgei (Garcia et al 2006). Pb toxicity has been reported to be associated with oxidiative stress (Zhang et al 2007). During oxidative stress, ROS impair cells by oxidizing the membrane lipids and proteins as well as DNA. DNA damage is consistent with a facilitative role for Pb in carcinogenesis and even cell death (Zhang et al 2007).
36
2.6
TOXICITY STUDIES
2.6.1
Acute Toxicity Test
Acute toxicity tests are used to determine toxic effects during short-duration exposures (typically 96 h or less). The most common acute test end point is mortality, measured by LC50, the lethal concentration that kills 50% of test organisms in a given time, usually 96 h for higher organisms and 24 or 48 h for some invertebrates (NAS/NAE 1973; Portmann 1972; Sprague 1969; Sprague 1973). The effective concentration (EC50) is usually used when it is difficult to accurately determine mortality and some surrogate end-point such as immobility is measured under the assumption that if the test was extended, it would lead to mortality.
As the LC50 measures a clearly defined effect and calculations are from the middle of the dose-response curve, LC50 data are seen to be more robust than data from chronic exposure studies. However, the lethal threshold concentration of a toxicant may be more appropriate to characterize toxicity, since it represents a common point of lethal physiological response (Sanchez Bayo 2006; Brown 1973; Sprague 1969; Sprague 1973).
In general, determination of lethal concentrations, such as the median lethal concentrations (LC50) is recognized as the first step for risk assessment of synthetic and natural chemicals (Hunt et al 2002; Thorp and Lake 1974; Eisler 1971; Sprague 1969; Sprague 1973).
2.6.2
Chronic Toxicity Test
Chronic toxicity tests are more complex and the effects are studied for longer periods of time. The aim of these tests is to determine the concentration of a test material/ substance (e.g., a chemical, or effluent) that
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produces an adverse effect on a group of test organisms during long term exposure under controlled conditions. Usually, chronic tests are conducted with a set of species of different phylogenetic classification level and at different stages of development (Muyssen et al 2006). Unlike acute toxicity tests, chronic toxicity studies evaluate not only mortality but also endpoints such as individual growth, growth rate, abnormal development, hatching time, reproduction success (the total number of young individuals) and vitality of offspring, behaviour of individuals, physiological parameters and histology.
Using these methods, NOEC and LOEC are calculated. NOEC is the highest concentration of the test substance that does not cause any observed and statistically significant adverse effects on the exposed organisms compared to controls. LOEC is the lowest concentration of the substance used in a test that has statistically significant adverse effect on the exposed population of test organisms compared with controls (Vosyliene 2007; Van Leeuwen and Hermens 1995). As legislation aims at reducing the amount of chemicals released into the environment and thereby preventing adverse effects, NOECs play a major role in applied ecotoxicology. Obtained results were used to estimate the Chronic / MATC (Maximum Allowable Toxic Concentration) and geometric mean of LOEC and NOEC (Wang et al 2009; Wang et al 2007; Valenti et al 2005; Hunt et al 2002; Van Leeuwen and Hermens 1995).
2.6.3
Importance of Water Quality Safe Limit
In developing and developed countries, industrial discharge and urban waste disposal into estuarine and coastal regions are the major sources of aquatic pollution. India is a developing country and hence information on water quality safe limit along the Indian coast is essential for protection of
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aquatic ecosystems. However, literature surveys have indicated that there are no prescribed water quality safe limits for metals in seawater for India.
Toxicity information is generally used in two ways: firstly, to compare the sensitivities of different species and potencies of chemicals using toxicity values (acute and chronic results), and secondly to derive "safe" environmental concentrations using toxicity values and application factors in the absence of chronic toxicity information on the tested species.
Toxicity
data
provide
guidelines
for
biological
and
physicochemical indicators of water quality that will protect the ecological health of aquatic ecosystems (Wang et al 2009; Wang et al 2007; Valenti et al 2005; Hunt et al 2002). Therefore, the best approach for protection of aquatic ecosystems from toxic substances is by the derivation of water quality safe limits. Various countries have already derived safe limits for water quality for their coasts. These countries include Canada, United Kingdom, United States, Malaysia, Thailand, Australia and New Zealand (ANZECC and ARMCANZ 2000; Wong and Tan (AMWQC) 1999).
2.6.4
Biomarker Studies as a Tool for Environmental Pollution Monitoring
In the last few decades, the use of biomarkers in aquatic organisms has become a major tool for environmental quality evaluation and risk assessment (Hagger et al 2010; Amiard et al 2006; Regoli et al 2004) Biomarkers are defined as biochemical, cellular, physiological or behavioural variations in the tissue or body fluids or at the level of whole organism that provides evidence of exposure to chemical pollutants and may also indicate a toxic effect (Long et al 2004).The term ‘biomarker’ has been adopted in the context of environmental monitoring, and in the process has expanded widely
39
beyond its original constraints to encompass almost any response indicative of a biological effect (Zoheir et al 2009).
Heavy metal pollution is one of the reasons for disease incidence in marine organisms caused due to adverse effects of pollutants on organisms (Thiagarajan et al 2006). Some species (include bivalves, crustaceans and fishes) are commonly used as bioindicators for marine pollution and as well as for observing impacts on biochemistry and histology (Funes et al 2006; Wester et al 2002).
Chronic contamination by heavy metals particularly in the marine environment is a severe problem. Environmental contamination may alter the structure of the cell membranes by stimulating the lipid per-oxidation process with consequent complex sequences of biochemical reactions (Dabas et al 2012; Varo et al 2007; Verlecar et al 2006). Figure 2.2 depicts flow chart of environmental contaminants and their antioxidants activity.
Figure 2.2
Flowchart of Environmental Contaminants and their Antioxidants Activity
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Heavy metals have significant ability to generate ROS. The first level of cellular response shown against the free radicals is the antioxidant defence and repair systems to minimize the damage that actually occurs. A disturbance in the free radical and antioxidant systems in favour of the former leads to the condition termed oxidative stress (OS). The non-enzymatic antioxidant glutathione and enzymatic antioxidants such as SOD and CAT provide protection against ROS by catalytically converting the oxidants to less reactive species.
GST is a family of phase II enzymes involved in detoxification of potentially genotoxic chemicals by catalysing the conjugation of several xenobiotics with GSH (Thom et al 2001). They also play an important role in the detoxification of reactive oxygen species in the cells (Edwards et al 2008) by protecting lipids from peroxidation. They play a pivotal role in mitigating oxidative stress in all life forms (Lee et al 2008; Company et al 2010).
GSH is often used in biomarker studies, as it is an overall modulator of cellular homeostasis (Ringwood et al 1999). GSH is a low molecular weight scavenger of oxygen radicals (Puerto et al 2011). The reduced form conjugates with electrophilic xenobiotics used for transforming them into water soluble forms making those easily extractable products (Nusetti et al 2001). Often, GSH concentrations have been found to be depleted in contaminant-exposed organisms (Sun et al 2008; Fu and Xie 2006).
Metallothioneins (MT) are proteins rich in the amino acid cysteine and consequently exhibit a high affinity for soft, polarisable metal cations. As a result, MT play a dominant role in the regulation of essential metals (Cu, Zn) and in the sequestration and detoxification of non-essential metals (Cd, Pb) in a wide variety of animals (Trinchella et al 2006; Riggio et al 2003).
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Hepatic MT synthesis is induced by a number of metals, cytokines and stress hormones as well as by a wide range of chemicals, many of which act indirectly via stress or inflammatory response (Patrizia et al 2010). MT transcript were induced in fish by a variety of bivalent metals, including Cd, Zn, Cu, Pb and Hg (Yudkovski et al 2008; Alvarado et al 2006; Eroglu et al 2005). Therefore, MTs have become of great interest for assessing pollution in the marine environment and are seen as potential biomarkers of metal exposure in fish (Patrizia et al 2010; Fernandes et al 2008; Nesto et al 2007; Sarkar et al 2006).
2.6.5
Aquatic Organisms as Indicators for Environmental Pollution
The water quality of the coastal aquatic environment is considered as the main factor controlling the state of health and disease in aquatic organisms. Excess concentrations of heavy metals in the aquatic environment are likely to be toxic and cause several biochemical effects (Funes et al 2006; Gaetke and Chow 2003).
Within any aquatic system, both water and sediment can be analysed to quantify contaminant concentrations. However, there are inherent problems associated with the analysis of both media (Rainbow 1995). Contaminant concentrations in water are typically low, often below detection limits, and can vary greatly over time and space (Villares et al 2001). Contaminants accumulate in sediments, and so are easy to measure and can provide a degree of time integration not found in water analysis (Rainbow and Phillips 1993). However, both in sediment and in water, contaminant concentrations determined by chemical analysis cannot be reliably used to assess the likely toxicity of contaminants to biota (Rainbow 1995). Aquatic organisms have, therefore, become increasingly used as a tool for assessment of contamination (Jose et al 2007).
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Several species have been used in aquatic biomonitoring surveys. However, only a few species can fulfil the prerequisites of an ideal organism (biomonitor) as suggested by Butler (1971) and Haug et al (1974). Specifically, biomonitors employed in biomonitoring surveys should possess the following attributes (Connell et al 1999; Phillips and Rainbow 1994): x
x
Contaminants should be accumulated without lethal impacts. Biomonitors should be sedentary in order to represent the area in which they grow.
x
x
x
Biomonitors should be abundant throughout the area. Biomonitors should be relatively long lived. Biomonitors used should be easy to sample, resilient to survive under laboratory conditions and should provide sufficient tissue for contaminant analysis.
x
Biomonitors should tolerate brackish waters, which are often the most contaminated areas in coastal waters.
x
A simple correlation should exist between contaminant concentration in the biomonitor and the ambient environment.
Based on the above features, some species fulfil most of the above-mentioned characteristics. Bivalves and some invertebrates and select fish are commonly used in biomonitoring surveys. The use of bivalves or gastropod molluscs looks attractive as these organisms take up metals from all environmental compartments: from the aqueous medium or through ingestion from food and inorganic particulate materials and concentrate them (Putri 2012; Gupta and Singh 2011). Fish and crustaceans are also widely used as sentinels of contamination in the aquatic environment. Some fish species, in particular, may accumulate metals upto many orders of magnitude above
43
background concentrations and thus, demonstrate their potential as bioindicators of heavy metal pollution (Fang et al 2008; Storelli and Marcotrigiano 2005).
2.6.5.1
Molluscs
In marine environments, bivalves are common, highly visible, and ecologically and commercially important on a global scale as food and non-food resources. Many of these such as mussels are sessile and this means that they are constantly exposed to
environmental pollution and
bioaccumulate pollutants. Therefore, such bivalves have been usually used as models in the field of environmental toxicology (Almeida et al 2007; Rittschof and McClellan Green 2005).
The green mussel, P. viridis, widely distributed in tropical and subtropical Asia, forms a good and cheap source of animal protein. It is also an important cultivable species in China and southeast Asian countries, such as Philippines, Singapore and Thailand besides India (Tanabe 2000). It occurs as small beds in the intertidal zone to a depth of 15m along the east and west coasts of India. This sessile bivalve also occurs naturally in the estuaries where salinity ranges from 27 to 33 and temperature from 26°C to 32°C (Murugan et al 2008).
Green mussels can accumulate many contaminants in their tissues and concentrations measured to provide a time integrated estimate of bioavailable contaminant concentrations (Verlecar et al 2007; Lau et al 2004). Green mussels are suspension feeders and take up metals both directly from seawater and from suspended particles collected during feeding (Verlecar et al 2007; Rainbow 1995). Dissolved metals (dissolved ions and colloidal particles) are taken up through the gills (Laodong et al 2002). However,
44
dietary sources (which can include phytoplankton and re-suspended sediment particles) tend to account for a large proportion of the metal intake by green mussels (Nicholsona and Lamb 2005; Olivier et al 2002). Due to their ability to accumulate contaminants, mussels have been successfully used for biomonitoring in many pollution assessment studies (Muhammed et al 2008; Mussel watch contaminant monitoring
- http://ccma.nos.noaa.gov/about/
coast/nsandt/musselwatch.aspx).
2.6.5.2
Fishes
Coastal fish have been proposed as sentinel species to assess the possible effect of anthropogenic activities in coastal areas and for monitoring marine environment pollution (Mariottini et al 2006; Eastwood and Couture 2002). Fishes commonly act as suitable bioindicators, because fish species are close to the top of aquatic food web (Padmini et al 2004; Pedrajas et al 1995).
In addition, fish species such as M. cephalus and T. jarbua are selected as sentinel species because of their wide geographic distribution, availability throughout the year, capability of living in a wide range of salinities and temperatures. They are available in coastal waters and enter estuaries, harbours and rivers that are frequently subjected to pollution (Fatemeh and Shahab 2011; Padmini et al 2004; Pascual et al 2003). These fish species are capable of concentrating the contaminants and are therefore considered suitable for biomarker studies.
2.6.5.3
Crustaceans
Pollutants are, in general, permanently immobilized in sediment. However, bioturbation and resuspension constitute a potential danger and significant risk to estuarine fauna, particularly crustaceans (Key et al 2006).
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Crustaceans are major components of aquatic ecosystems that provide a variety of ecological and economic services. Among crustacean species tiger prawn (P. monodon) is the most abundant and ecologically important species. These species play a major role in energy transfer in ecosystems (Leight et al 2005).
P. monodon is one of the most common marine and estuarine crustacean species and abundant throughout the Indian coasts. P. monodon form an important link in the marine aquatic food web because of their opportunistic feeding habits, high abundance levels and tolerance of salinity. It is widely used as food and feed supplement and is considered as an important shell fishery product. Due to its abundance and the fact that the P. monodon is consumed by a large number of people especially those living around the coast, the public health risk associated with its consumption needs to be monitored continually (Emerson and Rajalakshmi 2002).
