CHAPTER ONE
INTRODUCTION
1.1 Background
Water is one of the most abundant and essential resources of man and occupies about 70% of the earth surface (Eja, 2002). Water pollution occurs when a body of water is adversely affected due to addition of large amounts of materials to the water, making it unfit for intended use. Such water is considered polluted. However it must be mentioned that some heavy metals are naturally present in some natural water sources. Some of them are essential for health of living organisms, but when their concentrations are very high, beyond tolerable limits they become toxic. Marine pollution is however a critical environmental issue of concern across the globe when growing human population increases, the intensities of anthropogenic threat it exerts on the environment increases as a result of industrialization and agricultural activities (Raga et al. 2009). Heavy metals can enter a water body by industrial and consumer waste or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers and groundwater.
Heavy metals or trace elements is the term refer to those elements that occur at very low levels of few parts per million in a given system (Kalu et al. 2015). They are among the most harmful of the elemental pollutants. Metals such as mercury, cadmium, lead and nickel has no biological function in the human system and ispotentially toxic even at trace concentrations. Some of them like Pb, Sn, Hg, Zn and Cu can be very toxic to the system (Bhatia, 2006). Heavy metals include essential elements like iron as well as toxic metals like Cd and Hg. Heavy metals are highly persistent and can easily enter a food chain and accumulate until they reach toxic levels. These may eventually kill fish, birds and mammals (USEPA, 1999). Water, sediments and biota are generally metal reservoirs in aquatic environment. Researchers have revealed that nearly all metal content in aquatic environment reside in water and sediments (Ademoroti, 1996). (Bower 1979) found that sediments are the major depository of metals, in some cases holding up to 99% of the total amount in the system. The concentration of harmful and toxic substances is of many orders of magnitude higher in water, sediments and biological tissues than in water itself. Aquatic ecosystem is the ultimate recipient of almost everything including heavy metals. This has long been recognized as a serious pollution problem (Farombi et al. 2007). The input of heavy metal in sediments is particularly of concern due to its toxic nature. Previous studies have shown that 30-90% of heavy metals in rivers are transported in sediments associated form (Wang et al. 2011). Sediments particularly are regarded as any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of body of water or other liquid. The contamination of aquatic system by heavy metals, especially in sediments has become one of the most challenging pollution issues owing to itstoxicity, abundance, persistence and subsequent bio-accumulation (Fu et al. 2014). When discharged into aquatic ecosystems heavy metals can be absorbed by suspended solids, then strongly accumulated in sediments and bio-magnified along aquatic food chains. Moreover, these sediments act as sink and may in turn acts as sources of heavy metals.
Many aquatic organisms for example periwinkles have the ability to accumulate and biomagnifies contaminants like heavy metals, polycyclic aromatic hydrocarbons and PCB in the environment (Davies et al. 2006). Heavy metals are accumulating by marine organisms to very high concentrations in their tissue and hence their bodies are easily measured. The periwinkle (Tympanotonus Fuscatus) is a mollusk (gastropods) of high commercial and economic value in the Niger delta region of Nigeria. It is commonly distributed and found in the mangroves swamps and intertidal zones of estuarine and marine waters of the Niger delta. The periwinkle is a small sea snail, a marine gastropod mollusk that has gills and is classified within the kingdom animalia. (Reid et al.2011). It is a robust intertidal species with a dark and sometimes banded shell.
1.2 Water Pollution
Since the second part of the 20th century, there has been growing concerns over the diverse effects of heavy metals on human and aquatic ecosystems (Baysal et al. 2011).Water is a transparent and colorless chemical substance. Water plays a significant role in maintaining the human health and welfare. It’s also a vital commodity (NBS, 2012) and its sources include rivers, stream, lakes, wells etc. Rivers are among the oldest water bodies in the world (Higler, 2012).Water covers 71% of the earth surface and is considered to be neutral with a pH (the negative log of the hydrogen ion concentration) of 7.
Naturally water and sediments particles are not pure, but partly contaminated on a daily basis and most times influenced by natural and artificial conditions such as anthropogenic activities .Some of these anthropogenic activities include mining, disposal of effluents from industries and indiscriminate use of fertilizers and pesticides in cultivation (Amman, 2002).In recent years developed and developing countries have enacted strict environmental laws to curb the menace of metals emissions.
Water is polluted when contaminants are discharged into water bodies. Over the years the world has experience devastating effects of water pollution. The search for good domestic water has been man utmost concern since the beginning of civilization and thus, scarcity of clean freshwater is one of the world most pressing environmental problems. It is very important and vital to test the water before it is used for any purpose what so ever. Water (sediments inclusive) must be tested with different physicochemical parameters. Water most especially from the riverine area contains a lot of dissolved, suspended, microbiological impurities. Physical as well as chemical test is necessary to ascertain the state of the water. Due to the very low concentration of heavy metals and other impurities present in water and sediments particles, highly sophisticated analytical instruments and a well-trained manpower respectively. Water, sediments and biota are generally metal reservoirs in aquatic environment. Researchers have revealed that nearly all metal content in aquatic environment reside in water and sediments (Ademoroti, 1996). (Bower 1979) found that sediments are the major depository of metals, in some cases holding up to 99% of the total amount of metal present in the system. The concentration of harmful and toxic substances is of many orders of magnitude.
1.3 Heavy Metals
The pollution of the aquatic environment with heavy metals has become a worldwide problem and of scientific concern because the metals are indestructible and most of them have toxic effects on organisms (MacFarlane and Burchett, 2000; Censi et al. 2006; Oronsaye et al. 2010). Heavy metals enter rivers and lakes from a variety of sources that include the rocks and soils directly exposed to surface water, in addition to the discharge of various treated and untreated liquid wastes to the water bodies (APHA et al. 2005., Alaa and Osman, 2010).
Heavy metals are chemical elements with a specific gravity at least 5 times that of water. Some well known toxic metals have a specific gravity of 5 or more than that of water. Examples include cadmium (8.65), lead (11.34) etc. Metals like nickel, cadmium and lead have no known physiological activity, but have been proven to be detrimental to human health beyond certain levels (Marschner, 1995).Pollution of heavy metals not only affects water bodies and the quality of the atmosphere, it also threatens the health and life of animals by virtue of the food chain. The pollution caused by heavy metals is a long term and irreversible process. Such metals are not required for routine functioning of the human body and therefore are toxic even at low concentrations having mainly excessive amounts of heavy metals (e.g. lead, cadmium and nickel as well as heavy metals). Industrial processes are of special concern because they generate contaminated effluents which when discharged into the marine environment leads to chronic poisoning of aquatic animals (Ellis, 1989). There are over ten (10) heavy metals such as cobalt (Co), lead (Pb), mercury (Hg), arsenic (As), thallium (Tl), nickel (Ni),manganese (Mn), zinc (Zn), cadmium (Cd) and chromium (Cr) that have a particular significance in ecotoxicology, since they are highly persistent (Storelli, et al., 2005). The levels of metals such as Mn, Zn, and Cr are toxic beyond a certain limit, whereas Pb, Ni and Cd are toxic even in trace amounts (Bury, et al; 2003;Fernandes, et al; 2008). Toxicity is realized when these heavy metal levels are higher than the recommended limit which is different for individual elements in drinking water. These heavy metals: Pb, Ni, Mn, Zn, Cd and Cr have the following WHO recommended limits: 0.01 mg/l, 0.07 mg/l, 0.4 mg/l, 3.0 mg/l, 0.003 mg/l and 0.05 mg/l respectively for drinking water and 2.0 mg/kg in fish for Pb and Ni (WHO, 2008).Heavy metal concentrations in aquatic ecosystems are also monitored by measuring their concentrations in sediments, water and plants, since for the normal metabolism of the aquatic life, metals are taken up from water, food or sediment (WHO, 2000; Miller et al., 2002; Tüzen, 2003; Canlý and Atlý, 2003;Agatha, 2010; Anim et al., 2010).
1.3.1 Effects of Heavy Metals
Lead
Lead is the second on the Agency for Toxic Substances and Diseases Registry’s (ATSDRs) list of hazardous substances. Lead occurs naturally in the earth crust in the concentration of about 13mgkg-1(ATSDR, 2005). It can be present in the air, water and soil through human activities. Lead when discharged into water, pollutes the water. It can trigger both acute and chronic symptoms of poisoning. It target organs are the bones, brain, blood, kidney and thyroid glands (WHO, 1992). Acute lead poisoning is rare and is from ingestion of soluble lead salt or inhalation of lead vapor. It causes abdominal collie, vomiting and diarrhea (Duffus, 1980).
Chronic lead poisoning can arise through the regular consumption of food stuffs that are slightly contaminated with lead, inhalation or ingestion of small amount over a small period (Ademoroti, 1996; Etim, 1991). Since lead has high affinity for proteins, their ion forms bonds with the hemoglobin (red blood pigment) and the plasma protein of the blood(Klaasen, 1990). Thus, the synthesis of the blood cells and the vital transport is inhibited. Accumulated lead is toxic in most of its chemical forms, whether it is inhaled or ingested in water or food. It is distributed in all parts of the environment in three main forms through metallic lead, lead salts, and organic lead containing carbon.
Cadmium
Effects of cadmium on the human health are a major health concern. It is one of the most toxic elements to which man can be exposed to in the environment(Kalu, et al 2015). Once it’s absorbed, Cadmium is efficiently retained in the human body, in which it’s accumulates throughout life. Cadmium is primarily toxic to the kidney .It produces a number of health problems and is a known carcinogen. In the industry, it’s regulated by the environment protection agency (EPA) and it has a very low permissible exposure level .Exposure to this toxic metals affects the fetus in the womb (Wikipedia, 2018). The negative effects of cadmium on the body are numerous and can impact nearly all systems in the body, including cardiovascular, reproductive, kidneys, eyes and even the brain. Normal permissible limit is 2.0ppm (Wang Y. et al 2011).
Nickel
Effects of nickel are very crucial and serious harmful health effects from exposure to nickel such as chronic bronchitis, reduced lung function and cancer of the lung and nasal sinus (ATSDR, 2016). It is a chemical element and abundant on earth. When ingested through water in small amounts is harmless to human and in most cases necessary in our diet. However for human it may also present significant health hazards. The inorganic chemicals hold a greater portion as contaminants in water and sediments particles compared to organic chemicals (MDG, 2010). A part of inorganic are in mineral form of heavy metals Heavy metals tends to accumulate in human organs and nervous system and interfere with their normal functions.
1.4 Periwinkle (Tympanptonus fuscatus)
Tympanotonus Fuscatus are aquatic mollusks that are segmented, soft bodied and externally covered by hard calcareous shell that is unsegmented. It belongs to Kingdom: Animalia Phylum: Mollusca Class: Gastropoda Super Family: Gerithoidea Family: Potamididae Genius: Tympanotonus Species: T. Fuscatus (Linnaeus, 1758). Periwinkles are marine gastropod mollusks known as edible sea snails. The adults are benthic and their larval forms are plank tonic. They are usually found on mudflats in the mangrove swamp and are 6cm in length, and dark gray in color. Like mudskipper fish periwinkle are valuable commercially, as their collection and marketing forms an important industry in the Niger Delta. Their nutritive value compares favorably with those of domestic livestock and fish and the estimated crude protein of periwinkle (Tympanotonus Fuscatus) to be 21.04% (Ogundiran. et al 2015). It is an important component of the human diet. Heavy metals are highly persistent and can easily enter a food chain and accumulate until they reach toxic levels. These may eventually kill fish, birds, and mammals (USEPA, 1999). Water, sediments and biota are generally metal reservoirs in aquatic environment.
1.5 Statement of Problem
Pollution and food safety are concerning issues in the past and recent years. Many activities such as oil bunkering, agriculture, man-made activity etc are ongoing in the riverine area. Contaminants in the water can affect the water quality and consequently the human health in general. Contaminants can persist for many years in sediments in both freshwater and marine systems where they hold the potential to affect human health and the environment (Mackevičiene, et al; 2002). Sediments are an important sink of a variety of pollutants, particularly heavy metals and may serve as an enriched source for benthic organisms (Wang, et al; 2002) especially in estuarine ecosystems. Consequently, sediments accumulate contaminants and may act as long-term stores for metals in the environment (Spencer, et al, 2002). Tympanotonos Fuscatus (periwinkle) are deposit feeders and bio-indicators of heavy metals and total hydrocarbon pollution in the aquatic environment. Deposit feeding has to do with sediment and benthic dwellers. This implies the organisms have the ability to bio-accumulate heavy metals in their tissues in the process of deposit-feeding and so integrate the environmental conditions of the water and sediment over time. For this reason this research seeks to determine the levels of heavy metals (lead, cadmium and nickel) in water, sediments and periwinkle and to compare the present values with WHO acceptable (permissible) limits respectively.
