Assessment of Heavy Metal Pollution of the Iture ... - Springer Link

Environ Monit Assess (2007) 131:467–473 DOI 10.1007/s10661-006-9492-2

Assessment of Heavy Metal Pollution of the Iture Estuary in the Central Region of Ghana J. R. Fianko & S. Osae & D. Adomako & D. K. Adotey & Y. Serfor-Armah

Received: 24 March 2006 / Accepted: 15 September 2006 / Published online: 14 December 2006 # Springer Science + Business Media B.V. 2006

Abstract A detailed study has been presented on heavy metal content of the Iture Estuary. Waters of the Sorowie and Kakum rivers that supply water into the Estuary were investigated to ascertain heavy metal pollution levels due to anthropogenic activities. Concentration s of Cd, Zn, Se and Pb were measured. The study shows pre-occupying pollution levels that constitute a threat to both terrestrial and aquatic ecosystems. The abundance of metals in the Estuary is in the order Zn>Pb>Cd>Se. The level of Cd in the Iture Estuary ranged between 0.011 mg/l and 0.041 mg/l while Se was in the range 0.018 mg/l to 0.029 mg/l, Pb 0.020 mg/l to 0.075 mg/l and Zn 0.040 to 2.45 mg/l. The impact of contaminated water from the Sorowie River on the Iture Estuary was outstanding and the study points out the importance of the Sorowie River as a primary pollution source to the Iture Estuary. The pollution of the Iture Estuary was found to be connected to human activities in its catchments. J. R. Fianko (*) : S. Osae : D. K. Adotey : Y. Serfor-Armah Department of Chemistry, National Nuclear Research Institute, Ghana Atomic Energy Commission, P.O. Box LG 80, Legon – Accra, Ghana e-mail: [email protected] D. Adomako Department of Physics, National Nuclear Research Institute, Ghana Atomic Energy Commission, P.O. Box LG 80, Legon – Accra, Ghana

Keywords Iture Estuary . Heavy metals . Pollution . Toxicity . Agrochemicals

1 Background The Kakum and Sorowie rivers flow through a rapidly urbanized and industrialized region of the central region and forms an integral part of the Iture estuary. The estuary is a valuable recreational and ecological asset but owing to the rapidly expanding urban areas, it is subject to the effects and influences of these developments. The Kakum and Sorowie catchment is the area where greater diversity of urban users is found and where population growth is most rapid. High-density low-income housing is developing in the catchment with a concomitant increase in quality and quantity of storm water runoff. It is estimated that about 90% of particulate matter carried by rivers settles in estuaries and coastal areas (Karen & Baird, 2001; Martin & Whitfield, 1983). The sea and more particularly the aquatic systems e.g. Estuaries are the ultimate repositories of man’s waste. The highly dynamic nature of the marine environment allows for very rapid assimilation of these materials by processes such as dilution, oxidation or sequestration into sediments. However, the capacity for such assimilation is limited.

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The existence of heavy metals in aquatic environments has led to much concern over their influence on plants and animals life in these environments and indeed on man’s need for wholesome water. The occurrence of elevated levels of trace metals in water can be a good indication of man-induced pollution and high levels of heavy metals can often be attributed to anthropogenic influences rather than natural enrichment of the sediment by geological weathering (Karen & Baird, 2001). The effect of metals in water and wastewater ranges from beneficial through troublesome to dangerously toxic. The elevated levels can have detrimental effects on both the biota inhabiting the aquatic environment as well as people who utilize this environment for food, recreation and potable water. Through the natural process of biomagnification, minute quantities of metals become part of the various food chains and concentration become elevated to levels, which can prove to be toxic to both human and other living organisms. The accumulation of these elements, many of which are highly toxic to animal life by aquatic plant life and the lower forms of marine animals is one of man’s less praise-worthy influences on the biosphere. Heavy metals are stable and persistent environmental contaminants of coastal water and sediment. The level of toxicity in water can be measured in relation to metallic elements present. Since the effect of these elements is cumulative, drinking water should contain none of these toxic metals. Apart from health hazards, water pollution could lead to serious economic and social consequences including fish production, recreation, paralysis and civil disorder. The accumulation of metals in the aquatic ecosystem has direct consequence to man and to the ecosystem. Interest in metals like Zn and Se, which are required for metabolic activity in living organisms, lies in the narrow “window” between their essentiality and toxicity (Fatoki, Lujiza, & Ogunfowokon, 2002). Others like Cd and Pb exhibit extreme toxicity even at trace levels (Merian, 1991) thus necessitating regular monitoring of sensitive aquatic environments. Zinc, lead, cadmium and selenium are common pollutants, which are widely distributed in the aquatic environment. Their sources are mainly from weathering of minerals and soils, atmospheric deposition, industrial and domestic effluents as well as urban storm water runoffs.

Environ Monit Assess (2007) 131:467–473

Cadmium is a non-essential metal that is toxic even when present in very low concentrations. The toxic effect of cadmium is exacerbated by the fact that it has an extremely long biological half-life and is therefore retained for long periods of time in organisms after bioaccumulation (Webb, 1975). Cadmium has been found to be toxic to fish and other aquatic organisms. Its effect on man includes kidney damage and severe pain in bones (itai-itai in Japan) (Tsuehiya, 1978). The detection and determination of these trace metals in natural waters are of considerable importance not only as a means of establishing their influence on various ecosystems but also for monitoring and controlling the pathways by which they reach the hydrosphere. This study reports the levels of dissolved Cadmium, Lead, Selenium and Zinc in the Iture estuary in Ghana. It also aims at assessing the impact of potential pollution sources mainly from the Iture communities’ formal disposal to the Estuary, and from agricultural activities along the Sorowie and Kakum rivers supplying water to the Estuary. The catchment supports a rapidly growing population and there are concerns regarding the water quality of the Sorowie and Kakum rivers supplying water to the estuary. The main uses of water in the catchment are domestic, agriculture involving almost all the indigenous people, which are mostly fishermen, aquatic ecosystem use and recreation.

2 Materials and Methods 2.1 The study area The Iture Estuary is situated on the Cape Coast– Takoradi trunk road and is about 5 km from Cape Coast, the Central Regional capital of Ghana and about 7 km from Elmina (Figure 1). The study area lies between latitude 5°30′N and 5°47′N and longitudes 0°12′W and 0°35′W. The Central Region belongs to the coastal savanna vegetation and the geological formation of the area is referred to as Dahomeyan. IT is underlain by the Cape Coast basintype granitoids which have wide range of chemical and mineralogical composition (Junner, 1940). The rock types include ortho and para gneisses, schist and magmatites many of which are rich in garnet,


469

Figure 1 Overview of sampling area.

conc. (mg/l)

hornblende and biotite. The soil consists mainly of coastal savanna and coastal sand. The Iture community constitutes part of the Cape Coast–Elmina coastal plain. Its morphology and surficial geology bear characteristic signatures of Cape Coast granites, which have wide range of chemical and mineralogical composition (Junner, 1940).

0.045 0.04 0.035 0.03 0.025 0.02 0.015 0.01 0.005 0

0.038

0.041

0.033 0.029

KA

KB SA sampling site

Figure 2 Mean Cd level in Iture Estuary.

SB

3 Sampling The samples for analysis were all surface water obtained twice weekly from December to June at four sites which spans both the dry and wet seasons. The sampling stations were chosen based on accessibility and closeness to major population centers. Two were located in the Sorowie River (SA and SB) and the other two on river Kakum (KA and KB) which supply water to the estuary. Site SB and KB were located in the estuarine region of the rivers while SA and KA were located above the tidal head in the freshwater reaches of the rivers (Figure 1). Water samples were taken from mid stream at a depth of 20–30 cm in 1-l plastic bottles, which have been conditioned and adequately washed with detergents and rinsed several times with de-ionized water. Two sets of samples were taken at each sampling site. The water samples were acidified on site to pH less than 2 with 5 ml analytical grade concentrated HNO3. After collection the samples were placed in coolers with ice bags whilst been transported to the laboratory and kept at about 4 °C until analyzed. Temperature

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3 2.45

conc.(mg/l)

2.5

2.13

2

1.59

1.47

1.5 1 0.5 0 KA

KB SA sampling site

SB

Figure 3 Mean Zn level in Iture Estuary.

and pH of the water were determined on-site with portable Metrolin model 691-pH meter and mercuryin-glass thermometer, respectively

The acidified water samples (100 ml) after filtration with preconditioned plastic Millipore filter unit equipped with a 0.45 μm filter membrane (Gelman Inst. Co., London) were digested with 1:10 mixture of conc. HNO3 and 30% H2O2 to concentrate and convert metals associated with particulate to the free metal. The metals levels were then measured using the Perkin Elmer model 3110 Atomic Absorption spectrophotometer (AAS). A blank determination using the same procedure was performed. For quality control, double deionized water samples were spiked with known amounts about 1 mg each of Zn as zinc metal, Cd as cadmium metal, Pb as Pb(NO3)2 and Se as Na2SeO3 respectively and the recovery of Zn, Cd, Pb and Se were measured using standard analysis protocol as adopted for the water samples. Three replicate addition experiments were performed for the water sample.

5 Results and Discussion 4 Laboratory Analyses Water samples were analyzed by both classical and automated instrumental methods as appropriated in standard methods for analysis of water and waste water (APHA, 1998, and EPA, 1983). All reagents used were of analytical grade and instruments pre-calibrated appropriately prior to measurement. Replicate analyses were carried out for each determination to ascertain reproducibility and quality assurance.

0.075

0.08

0.025

0.022 0.02

0.07

0.02 0.018

0.054

0.06 conc.(mg/l)

0.02 conc.(mg/l)

Percentage recoveries of the elements from spiked water samples were Zn 75%±0.2%, Cd 78%±0.3%, Pb 86%±0.1% and Se 83%±0.2%, which validate the experimental procedure used for the chemical analyses. Since pH and temperature affects the solubility and toxicity of metals in the aquatic ecosystems, this pH and temperature range were used to access the metal toxicities in the estuary for the use of the aquatic ecosystem. Metals such as Cd, Pb, Zn, Al and Mn are most likely to have increased detrimental environmental effects as a result of a lowered pH (Fatoki et al.,

0.015 0.01

0.05 0.033

0.04 0.03

0.02

0.02

0.005

0.01 0

0 KA

KB

SA

sampling site Figure 4 Mean Se level in Iture Estuary.

SB

KA

KB SA sampling site

Figure 5 Mean Pb levels in Iture Estuary.

SB


471

0.08

Cd

0.07

Se

3

Pb

conc.(mg/l)

0.06 conc. (mg/l)

3.5

0.05 0.04 0.03

2.5 2 1.5

0.02

1

0.01

0.5

0

0

Dec

Feb

Apr

Dec

Jun

a. Cd, Se, Pb

Feb

Apr

Jun

b. Zn

Figure 6 Seasonal variation of a Cd, Se, Pb and b Zn in Iture Estuary.

2002). The mean pH values of water samples in the estuary varied between 6.8 and 7.7 while temperature ranged between 26.50°C and 29°C and falls within the WHO recommended values for pH and temperature in water for domestic use. Elevated levels of metals (Cd, Se, Pb and Zn) were detected in the estuary. The abundance of metals in the estuary is in the order Zn>Pb>Cd>Se. The heavy metal concentrations in the freshwater reaches are generally lower than in the estuarine region. The metal concentrations in the estuary do not show any particular trend and this indicate that the source might be diffused. The probable source is from natural sources due to geological formation of the catchment’s soil, agricultural, domestic and industrial runoffs. The metal concentration is related to nonpoint source inflows from the two major rivers discharging directly into the estuary. Sites KB and SB recorded higher values of all the metals. The higher concentrations at these sites might be due to contributions from agricultural farms and fishing communities dotted along the banks of these rivers that contain agrochemicals. The estuary is a recipient of domestic waste from the Iture community and several informal settlements along the Kakum and Sorowie rivers. Sampling points in the Sorowie river especially site SB contains the highest concentration of all the metals. Apart from the fact that SB is close to the sea and cottage industries, the Sorowie River support a rapidly growing population upstream for their entire domestic, industrial and

activities. Sewage and urban waste water from town and several settlements, constitute other discharges that are negatively affecting the water quality in the region (Koukal et al., 2004). The mean concentration of Cd in the estuary varied between 0.011 mg/l and 0.041 mg/l. Site KA in the freshwater region recorded the least level of Cd (Figure 2). Cadmium is extremely toxic and the primary use of water high in Cd could cause adverse health effect to consumers such as renal disease and cancer (Fatoki et al., 2002; Friberg, Elinder, Kjellstroem, & Nordberg, 1986). The WHO and EPA has established a human health based guideline of 0.003 mg/l for drinking water (USEPA, 1996; WHO, 1996). These guidelines were exceeded at all the sampling sites. In view of the fact that major use of the water is domestic, high levels of Cd in the estuary is of great concern. The probable source of Cd in the estuary are from natural sources due to the geology of the catchment soils and runoffs from agricultural soils where phosphate fertilizers have often been used since Cd is a common impurity in phosphate fertilizers. Other probable sources include leachates from disused nickel–cadmium based batteries and cadmium-plated items that are disposed at refuse dumps by the communities. Zn and Se concentrations do not meet the criterion of maximum concentration (CMC) established by EPA of 0.12 mg/l for Zn (DeZuane, 1977) and 0.01 mg/l for Se (WHO, 1996). Mean levels of Zn in the estuarine waters ranged between 0.40 mg/l and 2.45 mg/l (Figure 3). The WHO recommended value

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for Zn in water for domestic supply is 3 mg/l (WHO, 1996) and should not be a problem if the water is used for domestic purpose. However, Zn could be a problem in water for other users especially in the aquatic ecosystem. Zn cans in garbage moulds, rusty and unwanted galvanized scraps disposed by communities along the banks of Kakum and Sorowie finds their way into the estuary. The presence of Se in the estuary could be attributed to runoff from poultry and livestock farms as well as fossil fuel, domestic sewage and agrochemicals. The mean levels of Se recorded varied between 0.018 mg/l and 0.029 mg/l (Figure 4) which happen to be above the 0.01 mg/l limit recommended by WHO for domestic water (WHO, 1996). The mean Pb levels in the estuary ranged from 0.020 mg/l to 0.075 mg/l with highest recorded at SB (Figure 5). Adverse chronic effects may occur at 0.5 mg/l to 1.0 mg/l Pb. At levels greater than 0.1 mg/ l, possible neurological damage in foetuses and children may occur (DWAF, 1996). These levels were exceeded in the estuary and the direct use of water from the rivers supplying water into the estuary for domestic use without treatment could be detrimental to pregnant women and young children. Possible sources of Pb in the estuary could be from domestic sewage and effluent discharge from rural and highway and seepage from waste disposal sites as well as the geology of the catchments. There was significant seasonal variation in the metal concentration within the period. The dry season registered elevated levels of the metals as compared to the wet season. The metal concentration increased gradually from December to April (Figure 6a and b) which represent the dry season. Dilution effect of the rainy season due to storm run-off into receiving rivers and excessive evaporation of the surface water with its attendant pre-concentration of most of the metals may be responsible for the observed trend. The impact of contaminated water from the Sorowie River on the water quality in the Iture Estuary can be followed by comparing sampling sites SB and KB. The data points out the importance of the Sorowie River as a primary pollution source to the Iture Estuary. The continuous increase in heavy metal contamination of estuaries and coastal waters is a cause of concern as these metals have the ability to bioaccumulate in the tissues of various biotas and may also


affect the distribution and density of benthic organisms as well as the composition and diversity of faunal communities.

6 Conclusion Cadmium, Zinc, Lead and Selenium levels in the Iture Estuary have been determined in this study. The results of the study have indicated gross pollution of the Iture Estuary especially as regards heavy metals. This poses a health risk to several communities in the catchments who rely on the Estuary primarily for their domestic sources without treatment. An elevated level of heavy metals in the waters is a good indication of man-induced pollution as a result of sewage discharge into the estuary. The gross pollution of Sorowie and Kakum rivers are impacting negatively on the Iture Estuary.

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