Abstract

This study assessed the ability of filamentous green algae (Spirogyra aequinoctialis) and earthworms (Aporrectodea icteria) to accumulate heavy metals from water and soils, respectively. Samples of S. aequinoctialis, A. icteria and their respective water and soil environments were taken from designated sampling points in the City of Blantyre in Malawi during the rainy and dry season in order to capture seasonal variations. The samples were analyzed for pH, organic matter and the heavy metals cadmium, chromium, copper, iron, lead, nickel and zinc using standard methods (APHA, AOAC and Walkley -Black). The concentrations of metals in soils, algae and earthworms were on dry weight basis and the metals determined were acid extractable.In general, the concentration of metals in S. aequinoctialis were higher than in the corresponding water environment in both seasons, but lower in the rainy season than the dry season. In the rainy season the concentrations were (in S. aequinoctialis and (water)): Mn 0.432 - 5.641 mg/L (ND - 0.530 mg/L), Cd ND - 0.016 mg/L (0.07 - 0.111 mg/L), Cu 0.002 - 0.826 mg/L (ND), Fe 30.75 - 81.36 mg/L (ND - 3.209 mg/L), Zn 0.202 - 3.270 mg/L (0.502 - 2.614 mg/L), Pb ND - 0.965 mg/L (0.011 - 0.098 mg/L), Cr ND – 0.431 mg/L (ND) and Ni ND - 0.443 mg/L (0.305 - 0.49 mg/L). In the dry season the concentrations were: Mn 0.281 - 16.132 mg/L (0.035 - 0.626 mg/L), Cd 0.22 - 0.912 mg/L (0.014 - 0.111 mg/L), Cu 0.056 - 2.302 mg/L (ND - 0.076 mg/L), Fe 13.825 -96.641 mg/L (0.372 - 2.282 mg/L), Zn 0.203 - 6.188 mg/L (0.102 - 0.403 mg/L), Pb ND - 0.972 mg/L (ND - 0.23 mg/L), Cr ND - 0.663 mg/L (ND - 0.419 mg/L) and Ni ND -0.421 mg/L (0.101 - 0.578 mg/L). The concentration of metals in soils was found to be higher than in A. icteria, except for cadmium. In both soils and A. icteria the levels of metals were generally higher in the dry season than the rainy season. In the rainy season the concentrations were (in A. icteria and (soil)): Mn 1.005 - 9.623 mg/kg (10.255 - 17.894 mg/kg), Cd 0.108 - 0.144 mg/kg(ND - 0.041 mg/kg), Cu ND - 0.413 mg/kg (ND - 0.041 mg/kg), Fe 14.67 - 54.82 mg/kg(61.283 - 67.560 mg/kg), Zn 0.664 - 5.274 mg/kg (1.372 - 17.45 mg/kg), Pb ND - 0.796mg/kg (0.512 - 2.945 mg/kg), Cr ND (ND - 6.832 mg/kg) and Ni 0.291 - 0.869 mg/kg v (ND - 2.891 mg/kg). In the dry season the concentrations were: Mn 1.603 - 7.582 mg/kg (8.995 - 31.43 mg/kg), Cd 0.155 - 0.551 mg/kg (ND - 0.179 mg/kg), Cu 0.005 - 0.916 mg/kg (0.119 - 10.134 mg/kg), Fe 13.697 - 63.727 mg/kg (11.827 - 82.824 mg/kg), Zn 0.461 - 5.109 mg/kg (0.255 - 14.463 mg/kg), Pb ND - 0.476 mg/kg (0.031 - 3.485 mg/kg), Cr ND - 0.031 mg/kg (0.053 - 8.191 mg/kg) and Ni 0.043 - 0.93 mg/kg (0.026 - 4.319 mg/kg). There were no significant differences (p > 0.05) in organic matter content in soils for rainy (0.588 - 9.266%) and dry season (0.559 - 9.357%). There were also no significant differences (p > 0.05) in water pH for rainy (5.99 - 10.13) and dry season (5.98 - 9.68).However, there were significant differences (p < 0.05) in soil pH between the rainy (6.47 - 8.37) and the dry season (6.27 - 7.75). This study has therefore shown that S. aequinoctialis has the capability of accumulating Mn, Cd, Cu, Fe, Zn, Pb and Cr and can be used as a biological indicator for long term metal water pollution monitoring. However A. icteria showed the ability to accumulate Cd only and therefore cannot be used as a biological indicator for metal soil pollution monitoring. The high concentration of metals in the dry season unlike the rainy season was mainly attributed to dilution and soil deposition as a result of surface runoff.

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School	: School of Natural and Applied Sciences
Issued Date	: 2007

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