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

Abstract

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.