lead, cadmium, copper and iron in water, sediment ...

LEAD, CADMIUM, COPPER AND IRON IN WATER, SEDIMENT, GALATEA PARADOXA AND MACROBRACHIUM RARIDENS SAMPLES FROM THE VOLTA ESTUARY AT ADA, GHANA N. K. ASARE-DONKOR1*, J. D. AMENU1 AND A. A. ADIMADO1 1

Department of Chemistry, College of Science, Kwame Nkrumah University of Science and Technology, P.M.B, Kumasi, Ghana.

AUTHORS’ CONTRIBUTIONS This work was carried out in collaboration between all authors. Author NKAD designed the study, wrote the protocol and interpreted the data. Author JDA anchored the field study, gathered the initial data and performed preliminary data analysis. Authors NKAD and AAA managed the literature searches and produced the initial draft. All authors read and approved the final manuscript.

Original Research Article __________________________________________________________________________________ ABSTRACT The concentrations of four heavy metals (Pb, Cd, Cu and Fe) were determined in water, sediments, Galatea paradoxa (clam) and Macrobrachium raridens (Prawn) from Ada fishing site at the Volta Estuary in Ghana using Atomic Absorption Spectrophotometer (AAS). The mean metal concentrations in water were 0.21, 0.02, 1.74 and 0.04 mg/kg for Pb, Cd, Cu and Fe, respectively whilst those in the sediments were found to be 1.18, 2.08, 0.98 and 1336.13 mg/kg for Pb, Cd, Cu and Fe, respectively. The levels of Pb and Cd were above the WHO and EPA permissible limits for water whilst Cd and Fe were found to be above the IAEA permissible limits for sediment metal concentration. The mean metal concentrations in the Galatea paradoxa and Macrobrachium raridens tissues were 2.20, 4.01, 45.25, 104.41 and 4.28, 5.87, 110.03, 64.95 mg/kg for Pb, Cd, Cu and Fe, respectively. The level of concern (LOC) in shell fish consumption for Pb, Cd, Cu and Fe were 2.95, 0.11, 42.11, 736.84 mg/kg, respectively. The risk quotient for Macrobrachium raridens to Galatea paradoxa samples were 1.45 : 0.75, 55.91 : 38.19, 2.61 : 1.08, 0.09 : 0.14 for Pb, Cd, Cu and Fe, respectively. The study established that health risk associated with the consumption of the M. raridens and G. paradoxa species from the Volta estuary at Ada with regards to the four metals (Pb, Cd, Cu, and Fe) is very significant. Keywords: Volta Estuary; health-risk assessment; pollution load; contamination factor; Geoaccumulation index; heavy metals.

1. INTRODUCTION The pollution of the aquatic environment with heavy metals has become a serious environmental problem, which threatens aquatic ecosystems, agriculture, and human health [1]. Heavy metals generally enter the

aquatic environment by atmospheric deposition, erosion of geological matrix or due to anthropogenic activities such as industrial effluents, domestic sewage and mining wastes [2,3]. Over the years, many African countries, have experienced considerable population growth which has resulted in a steep rise in

_____________________________________________________________________________________________________ *Corresponding author: Email: [email protected];

Asare-Donkor et al.; JOBARI, X(X): xxx-xxx, 20YY

urbanization, industrialization and agricultural land use [4]. This has resulted in increases in discharge of pollutants into water bodies, causing undesirable effects on the aquatic environment. Most of these pollutants are heavy metals, which eventually settle in bottom sediments [5]. The danger of heavy metals has been aggravated due to their relative high toxicity, carcinogenic nature and persistent nature in the environment [6, 7, 8].

area and is consumed by people along the Volta lake and beyond. Unusually high inputs of heavy metals into the aquatic environment have resulted in great financial losses, affected commercial fisheries and in some cases, have been hazardous to human health [19]. Heavy metals such as copper and iron are essential metals since they play important roles in biological systems in certain quantities whereas cadmium and lead are non-essential metals, as they are toxic, even in trace amounts [20]. In the normal metabolism of fish, the essential metals are taken up from water, food or sediment and hence end up taking this heavy metals which later accumulate in the tissues through the effects of bio concentration, bioaccumulation and the food chain process [21]. These essential metals can also produce toxic effects when the metal intake is excessively elevated [22].

The major tributaries to the Volta Lake such as the White Volta, Black Volta and the Oti River originate outside Ghana, where a lot of agricultural and mining activities take place which are potential sources of heavy metals. The construction of the Akosombo Dam on the lake and perennial flooding of farm lands serves as major contributors of these contaminants in the lake which moves downstream into the estuary. In recent times, there has been an increase in agricultural and industrial activities along the catchment area of the Volta Lake [9]. The increase in agricultural activities such as cultivation of vegetables, fish farming, groundnut cultivation, in areas like Ada, Agave, Aveglo, etc. with application of sewage sludge, sewage water and various agrochemicals such as fertilizers, pesticides on these farms contribute immensely to heavy metal accumulation in top soil layers and also their subsequent transport into rivers through surface run-offs. The smelting activities of the small scale metal fabricating industries activities not only release the target metals but also metals which are associated in the ores [9].

Monitoring programmes and research on heavy metals in aquatic environments have become widely important due to concerns over accumulation and toxic effects in aquatic organisms and to humans through the food chain [23]. Metal concentration in the aquatic environment has been analysed using water samples [24], sediments [6] and aquatic biota [25] taken from study sites. The occurrence of elevated concentrations of trace metals in sediments found at the bottom of the water column can be a good indicator of man induced pollution rather than natural enrichment of the sediment by geological weathering [4]. The ultimate sink for many of these contaminants is the aquatic environment due to discharges or to hydrologic and atmospheric processes [26].

The contamination of this natural waters by heavy metals negatively affects aquatic biota and poses considerable environmental risks and concerns [10, 11]. These may have devastating effects on the ecological balance of the aquatic environment. High discharge of heavy metals into the aquatic environment eventually accumulates in water, sediments and dependent biotic components like fishes and aquatic plants [12]. It is important that the ions released from bulk metallic compounds, their speciation and their toxicity are studied [13, 14, 15] since in such environments, ions released may end up as different chemical species that produce different biological impacts [16, 17, 18]. The discharge of this industrial and sewage waste without adequate treatment often contaminate the estuarine and coastal water with conservative pollutants such as heavy metals, many of which bioaccumulate in the tissues of resident organisms like fishes, clams, crabs, shrimps, prawn, seaweeds etc. G. paradoxa (clam) and M. raridens (volta river prawn) happens to be one of the fishery resources and an important source of nutrition in the

The aquatic environment with its water quality is considered the main factor controlling the state of health and disease in both man and animal [27]. Nowadays, the increasing use of the waste chemical and agricultural drainage systems represents the most dangerous form of chemical pollution particularly heavy metal pollution. The objective of study was therefore to determine the concentrations of some heavy metals (Pb, Cd, Cu and Fe) in G. paradoxa) and M. raridens, harvested from the Volta Estuary at Ada and assess the health effects as well as the pollution levels of the fishing sites. In addition the relationship between sediment metal concentration and tissue metal concentration and the risk of consuming G. paradoxa and M. raridens from the estuary would be assessed.

2. MATERIALS AND METHODS

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2.2 Sampling 2.1 Study Area 40 samples each of M. raridens and G. paradoxa were purchased from local fishermen at the Volta Estuary at Ada in the Greater Accra Region. The samples were transported in ice-chest the same day to the Kwame Nkrumah University of Science Laboratory in Kumasi under iced condition. They were stored on arrival under frozen conditions. Sediments from the Volta estuary at Ada were collected into a clean polyethylene. The samples were stored in frozen condition during transported to the laboratory for further analysis. The water samples were collected at about 10 cm below the surface into 750 ml plastic bottles which had been carefully washed with detergent and soaked in 10% nitric acid to remove any trace of metal in it and rinsed with distilled water and dried. Nitric acid was added to water samples to adjust the pH to 2 to avoid precipitation and/or adsorption to the walls of the vessel and prevent

The study was carried out in Volta Estuary at Ada, Ghana. Ada (Latitude 05°49' 18.6" N and 000°38.46' 1"E) which is an active clam and prawn fishing grounds at the Volta Estuary. The Volta River in Ghana has been known to support substantial local clam and prawn fishery. In addition to over 60 commercially important food fishes, the river supports prawn and clam fisheries at its lower reaches [28]. Before the construction of the Akosombo and Kpong Dams on the Volta River in 1964 and 1981 respectively, areas within Senchi and Atimpoku were noted for their prawn industry while the area between Akuse and Sogakope was considered the centre for the clam industry [29].

Fig. 1. Map showing sampling location at Ada in the Volta Estuary of Ghana

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microbial activities. The acidified water samples were then kept in a refrigerator for further analysis in the laboratory.

in the ratio of 1:1; 5 ml of sulphuric acid H2SO4) to 1 ml of distilled water in a digestion tube. The content was heated for 30 minutes at a temperature of 200 ±5 ºC. The certified Reference Materials (CRMs) were brought into solution following the same analytical procedure and the solution were analysed in the same manner as the samples during the analysis.

2.3 Samples Treatment The length and wet weight of the M. raridens and G. paradoxa samples were taken and then grouped into five subsamples based on their weight and lengths. They were dried at 110 °C in an oven until a constant weight was obtained. Each subsample was ground to powder and kept in clean and dry well labelled containers ready for analysis. One gram of sample was placed in a 250 ml digestion tube and 10 ml of concentrated HNO3 was added. The mixture was boiled gently for 30 minutes to oxidize all easily oxidizable matter. After cooling, 5 ml of 70% HClO4 was added and the mixture was boiled gently until dense white fumes appeared. After cooling, 20 ml of deionised water was added and the mixture was boiled further to release any fumes. The solution was cooled, further filtered with a filter paper transferred quantitatively to a 25 ml volumetric flask by adding distilled water [30]. A blank solution was also prepared using the above method.

2.5 Statistical Analysis The data obtained in the study were subjected to statistical analysis using SPSS 17.0 statistical package. One way ANOVA (Analysis of variance) was performed for statistically significant differences in the mean values of heavy metal concentrations in different class sizes of G. paradoxa and M. raridens. Linear regression analysis was conducted using the following variables: concentrations of lead, cadmium, copper, iron, mean length and fresh mean weight of the G. paradoxa and M. raridens samples. The pollution Load Index (PLI), Contamination Factor (CF), Geoaccumulation Index (Igeo) and Bio-sediment Accumulation Factors (BSAFs) were computed using Microsoft Excel for windows 2013 version.

2.6 Health Risk Assessment

The sediment samples were dried at 110°C to constant weight and then powdered in a mortar and pestle. Nitric-perchloric acid digestion was performed, following the procedure recommended by the AOAC (1990) [30]. The acid preserved and well mixed water sample was poured into a beaker and 5 ml conc. HNO3 was added. The mixture was gently boiled and evaporated on a hot plate up to 10-20 ml. the beaker was then wash down with deionized water and the samples were filtered. The filtrate was transferred into a 100 ml volumetric flask and made to the mark [31]. A blank solution was prepared using the same method with double distilled water.

Risk quotient (RQ) was calculated as the ratio between concentration of trace element in the sample and the level of concern (LOC) for that metal [32]. Thus, the level of concern (LOC), which is a threshold concentration of a chemical above which a hazard to human health may exist, was calculated as the ratio of Tolerable Daily Intake (TDI) and the Rate of Shellfish Consumption (RSC) [32]. Data on average national rate of shellfish consumption (RSC) was calculated from the Daily Food Supply per capita from Fish and Fishery Products of the FAO (FAOSTAT 2004) which estimates the daily food supply from fish and fishery products in Ghana to 51 be 62.6 g/person/day. The national daily rate of shellfish consumption was estimated to be 0.95 g/person/day = 0.00095 kg/person/day [9]. The LOC which is a threshold concentration of a chemical above which a hazard to human health may occur were evaluated and compared to the maximum concentrations obtained for the various metals analysed in this study.

2.4 Sample Analysis

The digested samples were analysed using Flame Atomic Absorption Spectrometer (FAAS). The operation conditions for the analysis of the metals are indicated in Table 1.The instrument was calibrated using standard solutions of concentrations 1 ppm, 2 ppm and 4 ppm of the various metals. Analysis of 𝑙𝑒𝑣𝑒𝑙 𝑜𝑓 𝑐𝑜𝑛𝑐𝑒𝑟𝑛 𝐿𝑂𝐶 = Blanc and replicate samples were carried out for 𝑡𝑜𝑙𝑒𝑟𝑎𝑏𝑙𝑒 𝑑𝑎𝑖𝑙𝑦 𝑖𝑛𝑡𝑎𝑘𝑒 𝑇𝐷𝐼 1 quality assurance. Certified reference material DOLT𝑟𝑎𝑡𝑒 𝑜𝑓 𝑠ℎ𝑒𝑙𝑙 𝑓𝑖𝑠ℎ 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑅𝑆𝐶 4 (Dogfish muscle) and TORT-2 from the National Research Council (NCR) in Canada were used to assess 𝑅𝑖𝑠𝑘 𝑄𝑢𝑜𝑡𝑖𝑒𝑛𝑡 𝑅𝑄 the accuracy and precision of the analytical methods. = 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡𝑠 𝑖𝑛 𝑠ℎ𝑒𝑙𝑙 𝑓𝑖𝑠ℎ 2 𝑙𝑒𝑣𝑒𝑙 𝑜𝑓 𝑐𝑜𝑛𝑐𝑒𝑟𝑛 𝐿𝑂𝐶 The blanc solution was prepared by adding 2 ml of nitric acid and perchloric acid (HNO3-HClO4) mixture Table 1. The operational current intensities and wavelengths for the various heavy metals determined 4


Hollowcathode Lamp(HCL) Lead (Pb) Cadmium (Cd) Copper (Cu) Iron (Fe)

2.7 Sediment and Assessment

Current used/mA 10.00 4.00 4.00 5.00

Organism

Detection limit 5.00 x 10-2 1.50 x 10-3

Flame Acetylene Acetylene Acetylene Acetylene

sample and background concentration. The CF‘s for different elements vary at the sampling sites and a site‘s pollution load index may then be calculated by multiplying the contamination factors and deriving the Nth root of the N factors [34]. Pollution Load Index value of 1 indicates heavy metal load close to the background level, and value above 1 indicates pollution [33, 34]. Pollution Load Index is used to find out the mutual pollution effect at different stations by the different elements in soils and sediments [35]. The calculated PLI values were compared to description of sediment quality by Tomlinson et al. [33] to verify the pollution levels of the sampling sites.

Pollution

The pollution intensities in organisms and the environments were estimated using the Contamination Factor (CF), Pollution Load Index (PLI), Geoaccumulation Index (Igeo) and Bio- sediment Accumulation Factors. These indices are used to compare the pollution status of different areas of the environment [33]. The pollution Load Index (PLI), Contamination Factor (CF), Geoaccumulation Index and Bio-sediment Accumulation Factors (BSAFs) were computed using Microsoft Excel 2007 version. Tomlinson et al. [33] and Cabrera et al. [34] method was used in computing the overall pollution load indices (PLIs) of the sediment. The CF‘s for different elements at the sampling site will varyand a site‘s pollution load index may then be calculated by multiplying the contamination factors and deriving the Nth root of the N factors [34]. Pollution Load Index value of 1 indicates heavy metal load close to the background level, and value above 1 indicates pollution [33, 34]. The PLI was calculated using the equations below: PLIsampling site = (CF1 x CF2 x CF3 x CF4)1/n

Wavelength/nm 217.00 228.80 324.75 248.30

Müller’s geochemical Index (Igeo) quantitative approach was used to quantify the degree of anthropogenic contamination in sediments from the Volta Estuary. The Igeo values enable the assessment of pollution by comparing current and pre-industrial concentrations, although it is not always easy to reach pre-industrial sediment layers [37]. The Igeo for each analysed metal was calculated using the formula; Igeo = Log2 (Cn/1.5 x Bn)

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where Igeo is the Geoaccumulation Index, Cn is the measured content of element in sediment, and Bn the element‘s content in average shale (background concentration) [38] and 1.5 is a constant. The world average shale concentrations of elements of interest are either directly measured in texturally equivalent uncontaminated sediments or size fractions or taken from literature [39]. The Igeo is associated with a qualitative scale of pollution intensity and samples were classified as unpolluted ( 0), unpolluted to moderately polluted (0  Igeo  1), moderately polluted (0  Igeo  2), moderately to strongly polluted (2  Igeo  3), strongly polluted (3  Igeo  4), strongly to extremely polluted (4  Igeo  5) and extremely polluted ( Igeo  1) [37, 40, 41].

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Where, n is the number of metals studied and CF is the contamination factor of each metal on the site. The level of contamination of heavy metals in sediments is expressed in terms of a contamination factor (CF). Contamination Factors (CFs) are derived, using background concentrations or baseline or concentration of the element of interest in an unpolluted area [33, 35, 36]. It is expressed by the equation; where the contamination factor CF < 1 means low contamination; 1 ≤ CF < 3 indicates moderate contamination; 3 ≤ CF ≤ 6 represents considerable contamination and CF > 6 means very high contamination. C metal sample concentration and C background is background concentration. (mg/kg) value background C g/kg) metal.

Biota-Sediment Accumulation Factor (BSAFs) is the ratio metal concentrations in an organism to its corresponding sediment metal concentrations, represented by the equation below. The various clam sizes obtained for each sampling period was treated as a unit.

The PLI of the sampling areas were obtained by deriving Contamination Factors (CFs), using background concentrations or baseline or concentration of the element of interest in an unpolluted area [33, 35, 36]. Contamination Factor (CF) is the ratio of concentration of an element in a 5


BASF =

𝑪𝒐𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏 𝒐𝒇 𝒉𝒆𝒂𝒗𝒚 𝒎𝒆𝒕𝒂𝒍 𝒊𝒏 𝒐𝒓𝒈𝒂𝒏𝒊𝒔𝒎 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏 𝒐𝒇 𝒎𝒆𝒕𝒂𝒍 𝒊𝒏 𝒆𝒏𝒗𝒐𝒓𝒐𝒏𝒎𝒆𝒏𝒕

(clam) samples from the Volta Estuary in Ada were Pb - 2.2 mg/kg, Cd - 4.01 mg/kg, Cu - 45.25 mg/kg and Fe -104.41 mg/kg.

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Where BSAF = Biota-Sediment Accumulation Factor in kilogram tissue per kilogram sediment (kgtiss/kgsed). Concentration of metal in the organism tissues reported in milligrams per kilogram tissue (mg/kgtiss); and Concentration of the same metals in the ambient environment, sediment in this case reported in milligrams per kilogram sediment (mg/kgsed) [33].

The concentrations of Pb, Cd, Cu and Fe in G. paradoxa were all above the WHO permissive levels in fish whilst with the exception of Fe, which was within the IAEA permissible values in fish Pb, Cd, and Cu in the clam samples were above (Table 3). Figs. 2 and 3 also show plots of the heavy metals as against the various classes of M. raridens and G. paradoxa in accordance with Table 2. These plots give the relative levels of the various metal in each class of M. raridens and G. paradoxa. It was observed that all the classes of M. raridens recorded values of Pb, Cd, Cu and Fe which were above the WHO values and on the other hand all classes recorded values above the IAEA values with the exception of Fe which fell below. It was also observed that all the classes of G. paradoxa recorded values of Pb, Cd, Cu and Fe above the WHO values while four classes with the exception of class B recorded values within the IAEA values. The high heavy metal levels in M. raridens (Volta River prawn) and G. paradoxa (clam) would pose health hazards to the consumers. Bioaccumulation occurs as a result of the uptake, storage and accumulation of organic and inorganic contaminants by organisms from their environment [44].

3. RESULTS AND DISCUSSION The results of the analysis are given in Tables 2-5 and Figs. 2 and 3. Table 2 gives the mean fresh body lengths and the corresponding mean weights of the M. raridens and G. paradoxa sub samples. The mean concentration of heavy metals in the M. raridens samples from the Volta Estuary in Ada were Pb - 4.28 mg/kg, Cd -5.87 mg/kg, Cu - 110.03 mg/kg and Fe - 64.95 mg/kg. The concentration of Pb, Cd, Cu and Fe obtained in the prawn samples were all above the WHO standard limits of the metals in fish. The concentrations Pb, Cd, and Cu were also above the IAEA permissive levels in fish while only Fe was within the permission level (Table 3). The mean concentration of heavy metals in the G. paradoxa

Table 2. Mean lengths of M. raridens and G. paradoxa sub-samples and their corresponding mean fresh weights

Sample PR A PR B PR C PR D PR E

M. raridens Length (mc) 5.70 6.70 8.00 9.40 11.20

Weight (g) 2.30 3.50 6.80 10.20 19.20

G. paradoxa Length (cm) 5.30 5.60 6.00 6.40 7.40

Sample CL A CL B CL C CL D CL E

Weight (g) 5.70 6.40 6.70 9.30 12.40

Table 3. Mean concentration of Pb, Cd, Cu and Fe in M. raridens and G. paradoxa in the Volta Estuary at Ada (mg/kg dry weight) Element

Pb Cd Cu Fe

Macrobrachum raridens Concentration Mean RSD range concentration % ± STD 1.10-10.10 4.28±3.59 84.3 9 5.35-6.20 5.87±0.38 6.39 99.15-116.10 110.03± 6.81 6.19 40.60-102.20 64.95±24.58 37.8 4

Galatea paradoxa Concentration Mean RSD range concentration % ± STD 0.05-5.35 2.20±2.39 108.59

a

WHO /mg/k g

b

0.05

0.12

3.20-4.70 41.95-51.75 61.45-165.05

0.03 1.00 0.30

0.18 3.28 146.00

a

4.01±0.69 45.25±4.14 104.4±38.24

Wyse et al. [42]; bAckacha et al. [43]

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17.29 9.15 36.63

IAEA/ mg/kg


160

CONCENTRATION mg/kg

140 120 100 80 60 40 20 0 A

B

C

D

E

WHO

IAEA

MACOBRACHIUM RARIDENS SAMPLES Pb

Cd

Cu

Fe

Fig. 2. Graph showing heavy metal concentration in mg/kg in the five M. raridens sub-samples (A, B, C, D, E) 180 160

concentration mg/kg

140 120 100 80 60 40 20 0 A

B

C

D

E

WHO

IAEA

GALATEA PARADOXA SAMPLES Pb

Cd

Cu

Fe

Fig. 3. Graph showing heavy metal concentration in mg/kg in the five G. paradoxa sub-samples (A, B, C, D, E)

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Table 4. Mean concentration of Pb, Cd, Cu and Fe in water in the Volta Estuary at Ada (mg/kg dry weight) Element Pb Cd Cu Fe

Concentration range 0.19-0.22 0.01-0.03 0.40-3.71 0.03-0.05

Mean concentration ± STD 0.21 ± 0.02 0.024 ± 0.01 1.74 ± 1.44 0.04 ± 0.01

RSD % 7.11 34.31 82.62 25.26

a

b

WHO/mg/l 0.05 0.01 2.00

EPA/mg/l 0.05 0.01 1.30 0.30

a

WHO, [39 ]; bEPA, [40 ]

Table 5. mean concentration of Pb, Cd, Cu and Fe sediments in the Volta Estuary at Ada (mg/kg dry weight) Element Pb Cd Cu Fe

Concentration range 0.60 – 2.05 1.25 – 2.85 0.20 – 2.30 771.00 – 2214.50

Mean concentration ± STD 1.18 ± 0.63 2.08 ± 0.66 0.98 ± 0.95 1336.13 ± 619.35

RSD % 53.21 31.57 97.08 46.35

a

IAEA/mg/kg 26.00 0.15 30.80 40.80

a

Wyse et al. [ 42]

The study of bioaccumulation of heavy metals in the aquatic environment is of a keen interest as a result of its direct toxic effect to aquatic organisms and as human diet and water is concern it is has a potential health hazard on humans. The concentration of these heavy metals obtained by bioaccumulation had being reported as having a relationship with the weight and length of the fish samples [45]. Different fish species use and hold on to heavy metals differently. The risk of heavy metal contamination must therefore be considered on a species by species basis [46].

the natural environment and may come from background levels in the sediments and also the erosion and weathering of soils and parental rocks in the surrounding catchment as well as mobilization of metals from the sediments. The use of agrochemicals in Ada Foah and the other surrounding agricultural communities is not widespread, but the major users of these agrochemicals are small holders who have had little, if any training or skills in application, use, storage or disposal. The amount of chemicals entering the estuarine environment although presently insignificant might have adverse environmental effects in future due to bioaccumulation.

The mean concentration of the heavy metals in the water samples from the Volta Estuary in Ada were Pb: 0.208 mg/l, Cd: 0.0235 mg/l, Cu: 1.7385 mg/l and Fe: 0.036 mg/l. The concentration of Pb and Cd in the water are above the recommended levels while the concentration of Cu and Fe in water are within the WHO and EPA permissive levels (Table 4) [47, 48].

It is generally agreed that heavy metal uptake occurs mainly from water, food and sediment. However, effectiveness of metal uptake from these sources may differ in relation to ecological needs and metabolism of animals and concentrations of the heavy metals in water, food and sediment as well as some other factors such as salinity, temperature and interacting agents [49].

The mean concentration of the heavy metals in the sediment samples from the Volta Estuary in Ada were determined to be Pb-1.175 mg/kg, Cd-2.075 mg/kg, Cu-0.975 mg/kg and Fe-1336.125 mg/kg. The concentration Cd and Fe in sediments were is above the IAEA recommended levels whiles Pb, Cu are within the permissive levels (Table 5).

3.1 Relationship between Heavy Metal Concentrations in the Tissues of the M. raridens and G. paradoxa and Fresh Body Weight and Size

There was an increase in the levels of the heavy metals determined in the fish samples compared to water and sediments except for Fe where the concentration in the sediment were far higher than that of fish samples gives an indication of bioaccumulation of the heavy metals.

The correlation between the mean weight and length were determined in accordance to reports from Canpolat [45]. Comparing the different M. raridens and G. paradoxa size classes (A, B, C, D and E) Table 2 from this sampling stations using one way ANOVA, significant differences (p