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Pollution of water and soils arises from overburdens of mines, application of fertilizers and pesticides, industrial effluents and sewage sludge (Alloway & Ayres, 1997), among others. In heavily contaminated soils and water, there is a decrease in the population, growth and function of biota. In most cases all biological indices of environmental health (fish, invertebrates and algae) decline as pollution intensity increases (Cuffney et al., 2000; Hill et al., 2000; Khan, 1990). The identification of plant and animal species with the ability to accumulate metals is therefore of interest for the purposes of environmental monitoring (Chukwuma, 1998; Manly, 1996). Earthworms and periphyton (attached algae) have been utilized as indicators of pollution of soils and water with metals (Ireland, 1983; Holan et al., 1993; McCormick & Cairns, 1994; Ramelow, 1987; Jin-fen et al., 2000). Despite being very small, experiments unequivocally demonstrate that algae sequester heavy metals by complexation to phytochelatins (Gekeler et al., 1988), which is an identical mechanism as higher plants. In the context of biomonitoring, earthworms act as quantitative monitors of total-soil metal and also estimators of ecologically significant soil metal concentration (Morgan & Morgan, 1988). Earthworms are important components of the soil system mainly because of their favourable effects on soil structure and function which include increasing soil fertility by formation of an organic matter layer in topsoil. The most widely studied earthworm species are Eisenia fetida, Eisenia Andrei, Lumbricus terrestris and Lumbricus rubellus (Georgescu & Weber, 2007). In Malawi, several studies have confirmed the presence of heavy metals in water and soils. Kadewa et al. (2001) found levels of copper, cadmium and chromium in soils fertilized by sewage sludge from Soche waste water treatment plant in Blantyre to be higher than the range for critical concentration for sludge amended soils. Sajidu et al. (2007) found that the levels of lead, cadmium, iron, manganese, zinc, chromium and nickel in streams in the city of Blantyre were much higher than World Health Organisation (WHO) safe limits for drinking water in all sampled streams after they had passed through industrial areas. Lakudzala et al. (1999) found that at some points on Mudi, Likhubula and Shire Rivers, the iron and lead levels exceeded WHO guideline limits. However, not much has been done on the use of biological indicators to assess the state of the environment. In addition, studies that assess levels of heavy metals in biota are lacking because they only target either

Periphyton and Earthworms as Biological Indicators of Metal Pollution in Streams of Blantyre City, Malawi