Anthropogenic Sources of Heavy Metals in the Indian Ocean
Coast of Kenya
E. Z. Ochieng Æ J. O. Lalah Æ S. O. Wandiga
Received: 28 November 2008 / Accepted: 22 June 2009 / Published online: 7 July 2009
Ó Springer Science+Business Media, LLC 2009
Abstract Water and surface sediment samples from
Rivers Sabaki, Ramisi and Vevesi that flow into the Indian
Ocean coast of Kenya were analysed for heavy metals. The
sediment concentrations of exchangeable cations (in lg/g)
for Co, Cu, Mn, Ni, Pb, Sn and Zn ranged from 0.10 to
506.75 (for Mn at Sabaki), constituting between 2% and
20% of the total metal concentrations obtained by digestion
with strong acid. Cu, Mn, Ni, Pb and Zn were more
leachable with 0.1 N HCl. The total dissolved metal in
water and the total sediment concentrations for Ag, Cd, Co,
Cr, Cu, Mn, Ni, Pb, Sn and Zn are given in the text. For
dissolved metals, the metal/Mn ratios indicated higher
concentrations of Ag in Sabaki River, Cd in Ramisi, Ni in
Sabaki and Pb in Ramisi, respectively. In sediments, the
metal/Mn ratios showed higher enrichment of Ag in
Ramisi, Cd in Sabaki and Vevesi, and Zn in Sabaki,
respectively. Enrichment factors showed elevated levels of
Cd, Pb and Zn in sediment in River Sabaki and River
Vevesi that were due to anthropogenic inputs through Athi
River. The total dissolved metal concentration ranges for
the three rivers were comparable with those ranges repor-
ted in rivers in South Africa but the sediment concentra-
tions were below those of rivers in Europe and Asia where
anthropogenic addition of some of the toxic elements such
as Cu, Pb and Cd is evidently higher.
Keywords Water, surface sediment Á Heavy metals Á
Rivers Á Indian Ocean Coast of Kenya Á Enrichment factors
Studies on heavy metal pollution of river systems have
recently attracted a lot of attention due to the need for
acceptable drinking water quality and better understanding
of environmental pollution of freshwater resources (Lee
et al. 1998; Neal et al. 2000; Huang and Lin 2003; Powell
and Alexander 2003; Reimann et al. 2003; Jain 2004;
Adamo et al. 2005; Nyangababo et al. 2005; Okonkwo
et al. 2005; Demirak et al. 2006; Deheyn and Latz 2006;
Grosbois et al. 2006; Nicolau et al. 2006). Inland rivers and
streams are also important sources of anthropogenic metal
deposits into the seas and oceans (Everaarts and Nie-
uwenhuize 1995; Milward and Lin 2003; Adamo et al.
2005; Nicolau et al. 2006). Unlike organic contaminants,
natural processes of decomposition do not remove heavy
metals; instead heavy metals can be enriched by aquatic
organisms and can therefore be converted to organic
complexes that may even be more toxic (Jain 2004).
Although fractionation is useful in determining the bio-
availability and toxicity of heavy metals, the total content
of heavy metals in water and sediment is useful in mapping
out various hot spots as well as for identification of
anthropogenic inputs (Lee et al. 1998; Huang and Lin
2003). Apart from human and industrial effluents, weath-
ering of soil and rocks and volcanic eruptions are also other
main sources of heavy metals discharging into the marine
environment.
Since metal solubility is principally controlled by envi-
ronmental pH, its concentration, its various types of species
and oxidation states, the organic ligands and the redox
environment of the aquatic system (Lee et al. 1998; Huang
and Lin 2003; Davis and Leckie 1978; Jeon et al.
2003;
E. Z. Ochieng Á S. O. Wandiga
Department of Chemistry, College of Biological and Physical
Sciences, University of Nairobi, P.O. Box 30197, Nairobi,
Kenya
J. O. Lalah (&)
Department of Chemistry, Maseno University,
P.O. Box 333 Maseno, Kenya
e-mail: josephlalah57@yahoo.com
123
Bull Environ Contam Toxicol (2009) 83:600–607
DOI 10.1007/s00128-009-9807-4