ABSTRACT:Tubifex tubifex has been shown to survive in organic polluted environments, however, not much has been done on its inorganic pollution tolerance. Samples of T. tubifex and their respective sewage sludge were taken from Soche wastewater treatment plant in Blantyre City, Malawi during July 2007 to November 2008. The total number of sludge samples taken was fifty one which was made into seventeen composite samples. A total of seventeen T. Tubifex samples were also collected. The samples were analyzed for copper, lead, manganese, zinc and cadmium using standard methods from American Public Health Association and Association of Official Analytical Chemists. The concentrations of metals in sewage sludge and T. tubifex were on dry weight basis and the metals determined were acid extractable. In general, heavy metals concentration was lower in T. tubifex than in sewage sludge. The range of heavy metals concentrations were (in sludge and (T. tubifex)): zinc 275.3 -361.5 mg/kg (45.0 -82.2 mg/kg), manganese 293.7 -230.1 mg/kg (1.21 -3.69 mg/kg), copper 86.5 -120.1 mg/kg (1.6 -4.7 mg/kg), lead 11.2 -22.4 mg/kg (Below detection limit -0.95 ) and cadmium 1.12 -2.31 mg/kg (1.08 -2.18 mg/kg). The results showed significant differences between the concentrations of manganese, copper, lead and zinc in sewage sludge and T. tubifex (p < 0.05). However there was no significant difference between the concentrations of cadmium in sewage sludge and T. tubifex (p > 0.05). T. tubifex did not show the ability to accumulate heavy metals (attributed to its high defecation and metabolic rate) except for cadmium hence cannot be used as a bioindicator for heavy metal pollution in sludge.

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Abattoir effluent is known to degrade the quality of receiving water bodies. This study assesses the impact of effluent from Shire Valley Abattoir on the physico-chemical parameters of Mchesa Stream in Blantyre. Water samples were collected from five sampling sites along Mchesa Stream located at progressive distances from the discharge point. Sampling was done three times over a period of four months (June to September 2008). The physico-chemical parameters tested were: pH, biochemical oxygen demand (BOD), dissolved oxygen (DO), suspended solids (SS) and electrical conductivity (EC). The mean values of the measured parameters were as follows: BOD (381.1 mg L-1); DO (3.6 mg L-1); SS (312.8 mg L-1); pH (7.6); and EC (105.6 µs cm-1). The highest concentrations of BOD and SS were 612.3 mg L-1 and 477.3 mg L-1 respectively and were obtained at a point of effluent discharge into Mchesa stream. One-way ANOVA showed significant deviation from WHO standards for BOD, SS and DO (p < 0.05). This study shows that effluents from the Shire Valley Abattoir have partially contributed to the pollution of Mchesa Stream to levels which pose health and environmental hazards to the surrounding communities.

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