Distribution of Heavy Metals in the Coastal Marine Surficial Sediments in the Msasani Bay-Dar es Salaam Harbour Area

In Tanzania, a large amount of domestic and industrial wastes are daily released to the aquatic environment without prior treatment. The demographic pressure resulting from the about 2.5 million people in the Dar es Salaam region (according to the 2002 National Census) is the major driver of amounts of waste released. Heavy metals such as arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn), some of which are toxic, are among the wastes being released. The present study documents the levels of the above-mentioned metals in sediments recovered from the Msasani Bay-Dar es Salaam harbour area. Heavy metal concentrations in the collected coastal marine surfical sediments were determined using atomic absorption spectrophotometery. The concentration of most of the heavy metals in sediments is higher in the Dar es Salaam harbour than outside the habour area. These metals are derived from the industrial areas through rivers and storm water outflows. The concentration of Cd, Ni, and Pb increase northward from the Dar es Salaam harbour to the Msasani-Kunduchi area. Also the concentration of these three metals increases with increasing distance offshore to the boundary of the study area. Concentrations of Cd, Ni, and Pb in sediments above background level indicate that these sediments are polluted. Although the current concentration of most heavy metals in sediments is low, suggesting low levels of pollution in the study area, the increasing trend in dumping untreated wastes, driven by the demographic pressure, might change the future scenario. This calls for attempts to treat waste before it enters the marine environment, to reduce contamination, accompanied by regular monitoring work. land near residential areas or dumped at roadsides and in streams. A large proportion (76%) of the inhabitants of the Dar es Salaam city use pit latrines, while 13% are served by a central sewerage system and 11% use septic tanks (Mgana and Mahongo, 1997; Dar es Salaam City Council, 2004). Furthermore, sewage from the central sewerage system is discharged untreated to the Indian Ocean from the screenhouse. Sludge from septic tanks is periodically removed using cesspit emptier or vacuum trucks, which in turn empty their contents either into the stabilization ponds or into a screen-house where the INTRODUCTION According to the 2002 National Census, the city of Dar es Salaam has a population of about 2.5 million. With this level of population there is a significant amount of waste generated daily. For example, municipal solid wastes generated in the city of Dar es Salaam amounts to 1,770 tonnes/day (Mgana and Mahongo, 1997). Only 8.1% of the waste generated is disposed in the official open dumpsite, a practice that is common in many developing countries (Soto-Jiménez et al., 2001; Sarkar et al., 2004). Uncollected refuse is mainly stockpiled on vacant