ABSTRACT

The distribution and occurrence of heavy metals in the sediment, water column and fish Heterotis niloticus, Labeo senegalensis, Synodontis clarias, Hyperopisus bebe, Alestes baremose, Chrysichthys nigrodigitatus, Tilapia mariae, Parachanna obscura, Pharactolaemus ansorgii, Clarias gariepinus, Protopterus annectens, Auchenoglanis occidentalis, Gymnarchus niloticus, Sarotherodon galilaeus, Mugil cephalus, Schilbe mystus, Cynoglossus senegalensis and Clarias walkeri of the Anambra River were investigated over a year period in five locations adopting standard ecological and

chemical methods. Following the establishment of the presence and concentration of the heavy metals As, Cd, Cr, Cu, Fe, Pb and Zn and physicochemical properties in the principal media and fish, the biological effects of the most hazardous heavy metals in the media were investigated in laboratory bioassays on single and multiple mixtures on the basis of 96h LC50 index. Bioaccumulation studies of sub lethal concentration of the heavy metals were evaluated over 28day duration in laboratory bioassay. The ranges of concentration of heavy metal types measured in the Anambra River environment in both rainy season and dry season were as follows: Sediment : AS: not detected, rainy season, and not detected, dry season; Cd: 0.00250.001mg/kg 0.0060 0.001mg/kg, rainy season and 0.00200.000 mg/kg 0.00600.000 mg/kg, dry season; Cr: 0.00100.000

mg/kg 0.00650.006 mg/kg, rainy season and 0.00100.000 mg/kg 0.00300.000mg/kg, dry season; Cu: 0.05050.013 mg/kg 0.12550.021mg/kg, rainy

season and 0.04150.001mg/kg0.1250 0.000mg/kg, dry season; Fe: 0.03100.006mg/kg0.0880 0.018mg/kg, rainy season and 0.20600.001mg/kg

0.17500.000mg/kg, dry season; Pb: 0.00150.0010mg/kg0.00600.007mg/kg rainy season, and 0.00100.000mg/kg0.00500.000mg/kg, dry season; Zn: 0.19550.127mg/kg0.42200.154mg/kg, rainy season and 0.52000.000mg/kg

0.93000.000mg/kg, dry season. Water: AS: not detected, rainy season and not detected, dry season; Cd: not detected, rainy season and not detected, dry season; Cr: 0.00100.001mg/L 0.00400.001mg/L, rainy season and not detected, dry season; Cu: 0.00150.0010.02700.024mg/L, rainy season and 0.00400.000mg/L 0.02000.000mg/L, dry season; Fe: 0.00350.001mg/L0.04100.001mg/L, rainy season and 0.01500.000mg/L 0.06000.000mg/L, dry season; Pb: 0.00100.000mg/L 0.00300.000mg/L, rainy season and 0.00200.000mg/L0.00400.000mg/L, dry season;

Zn: 0.03600.004mg/L 0.25850.036mg/L, rainy season and 0.14800.000mg/L 0.41000.000mg/L, dry season. Fish: AS: not detected, rainy season and not detected,

dry season; Cd: 0.00160.001mg/kg0.00530.001mg/kg rainy season, and 0.00100.000mg/kg0.00450.001mg/kg, dry season; Cr: 0.00100.000mg/kg

0.00430.0042mg/kg, rainy season and 0.00100.000mg/kg0.00500.000mg/kg, dry season; Cu: 0.01620.006mg/kg0.04080.017mg/kg, rainy season and 0.00400.001mg/kg 0.08110.064mg/kg, dry season; Fe: 0.00320.002mg/kg

0.03680.007mg/kg, rainy season and 0.00500.001mg/kg 0.16600.119mg/kg, dry season; Pb: 0.00100.000mg/kg0.00700.007mg/kg, rainy season and

0.00100.000mg/kg0.00550.001mg/kg, dry season; Zn: 0.03620.035mg/kg 0.87000.099mg/kg, rainy season and 0.00600.001mg/kg 0.44600.009mg/kg, dry season. There was no season and location variations Pgt;0.05 in the heavy metal concentrations sampled for water and sediment, but in fish, concentrations exhibited

variation Plt;0.05 in Clarias gariepinus, Mugil cephalus, Heterotis niloticus and Protopterus annectens over the sampling regimes. In the water column, only pH and temperature varied significantly Plt;0.05 over the season. A toxicity ranking within limits of variations, showed Cd to be most toxic to Clarias gariepinus followed by Cr and Pb in a decreasing order of toxicity in single action toxicity test. The 96h LC50 values for the single action were obtained as 8.280mg/L, 70.183mg/L and 63.546mg/L for Cd, Pb and Cr, respectively. The binary mixture in predetermined ratio 1:3, 1:5 and 5:3 of the test heavy metals CdPb, CdCr and CrPb showed the 96h LC50 values to be 17.699mg/L, 61.444mg/L and 26.263mg/L, respectively. The resultant toxicity levels of the 96h LC50 values based on the computed synergistic ratio S.R were in conformity with the model of synergism S.R 1.0343.965 except in few cases where the interaction was in agreement with model of antagonism SR 0.468 and 0.135 for CdPb and CdCr, respectively. The triple action studies CdPbCr of the ratio 1:3:5 with 96h LC50 value of 17.878mg/L on equiwild interactions of the single element conformed mostly with the model of synergism SR 3.534 3.926 except the antagonistic interaction of Cd SR 0.463. Laboratory bioaccumulation studies in Clarias gariepinus exposed to sub lethal concentration equivalent to 1/10th and 1/100th of 96h LC50 of Cd, Cr and Pb in single and joint mixtures revealed that the test animal bioaccumulated in their tissues varying amount of the metals depending on the type of metal, length of exposure time and the concentration of the metals in test media. During the single and joint action tests, the test animal increasingly accumulated the metals steadily with time exposure over the 28day experimental duration. In the joint metallic mixtures CdPb, CdCr, CrPb and CdPbCr, it was found that the level of Cd, Cr and Pb bioaccumulated over a 28day period was significantly reduced compared to the concentration of respective metals accumulated during the single action studies. The ecotoxicological implications of the measured levels of heavy metals in the principal media of the Anambra River water, sediment and fish and the results of laboratory bioassays with respect to environmental protection strategies were discussed. Recommendations were outlined to minimize and properly manage heavy metal polluted water bodies.

CHAPTER ONE

1.0 INTRODUCTION.

It is well established that industrial wastes are a complex admixture of

several classes of pollutants such as synthetic chemicals of various types,

hydrocarbons and heavy metals Oyewo, 1998; Otitoloju, 2003. Heavy

metals which are elements having densities greater than 5g cm3 and atomic

number greater than that of calcium 20 are particularly important sources

of pollution, not just because they are toxic at relatively low concentrations

but because they are nondegradable, remaining in the environment long

after the source of pollution or emission has been removed. Several

scientific observations have shown that heavy metals are bioconcentrated or

bioaccumulated in one or several compartments across food webs Chukwu,

1991; Bryan and Langston, 1992; Kiffney and Clement, 1993. In addition,

many metals are transformed into organometallic compounds, which are

more toxic than their elemental or ionic form in the environment Reimer,

1989. Due to the relatively high risk of biological damage posed by heavy

metals from industrial and domestic sources over long periods in aquatic and

terrestrial ecosystems, a lot of research on metal pollution has taken place in

the industrialized countries of Europe, America and Asia Khangarot et al.,

1983; Bryan and Langston, 1992. However, in the developing countries, including Nigeria such researches are more recent with considerable information gaps in their range of occurrence, rate of discharge, distribution patterns and biological effects on local plant and animal species Otitoloju, 2002.

In spite of the known situation in which most human activities including irrigation, pest control, industrial and domestic production and utilization results in the introduction of multiple chemicals or pollutants into ...Get Complete Material.