Sources of Heavy Metal Input Into Winam Gulf, Kenya

Abstract

Water and surface sediment from rivers Kisat, Nyamasaria, Nyando, Sondu-Miriu, Kuja, Awach, Yala, and Nzoia, which flow into Winam Gulf, were analyzed for heavy metals in order to assess the influence of the catchment activities on heavy metal input into the lake. Sampling was done both upstream and at river mouths where the rivers entered in to the lake. The mean sediment concentration of exchangeable cations (in microg/g) for Ag, Cd, Co, Cu, Mn, Ni, Pb, Sn, and Zn ranged from 0.01 to 263 (for Mn at Kuja). Ag, Cr, and Cd were poorly leachable with 0.1 MHCl but the other cations were found to be fairly exchangeable. Most exchangeable cations in sediment ranged between 2% and 20% of the total heavy metal content obtained by digestion with strong acid. The mean total dissolved metal (0.45 microm filter cut-off) and mean total sediment concentrations ranged from nd-16 (Ag), nd-8 (Cd), nd-23.3 (Co), nd-50 (Cr), 5-157.5 (Cu), 50-3276 (Mn), nd-54.1 (Ni), 7-93.6 (Pb), 25-219.5 (Zn) in microg/L and from nd-8.34 (Ag), 0.48-1.75 (Co), nd-1.78 (Cd), 2.92-5.36 (Cr), 3.90-150.2 (Cu), 133.5-7237 (Mn), 4.33-42.29 (Ni), 3.09-66.06 (Pb), 23.39-7.83 (Sn) and 23.39-350.8 (Zn) in microg/g dry weight, respectively. The rivers analyzed were found to be non-polluted in terms of sediment loads except river Kisat which was found to be polluted because of elevated levels of Pb, Mn, Cu, and Zn. Nyamasaria and Nyando were also found to have higher concentrations of Pb, Cu, and Zn than those reported previously in the lake sediment. The dissolved metal concentrations were acceptable by WHO maximum limits in drinking water except Mn which was above WHO limit in Kisat, Nyando, and Nyamasaria waters. Enrichment of Cd and Pb was found in all the river sediment samples with factors ranging from 2.12 at Kisat river mouth to 4.41 at Awach (for Cd) and from 1.49 (at Kisat river mouth) to 2.38 (at Nyando river mouth).

Chromium Distribution and Spatial Variations in the Finer Sediment Grain Size Fraction and Unfractioned Surficial Sediments on Nyanza Gulf, of Lake Victoria (East Africa)

“…For lake and river bottom sediments, the following values were obtained: Nyanza Gulf (sediments: 0.42 ± 0.05 to 1.12 ± 0.11 mg/kg) [19,20]; Winam Gulf (21.0 ± 0.70 mg/kg [18]; nd to 0.275 ppm) [22]; L. Kanyaboli (lake, 3.7 to 7.73 g/g) [23]; inflowing rivers of Nyanza Gulf (2.92 to 5.36 g/g) [24]; Nyanza Gulf and inflowing rivers (rivers = nd to 125 mg/kg; lake = nd to 85.7 mg/kg) [62,108,109] …”

“…However, sediment cores collected from the deep offshore areas of the main Lake Victoria show peaks of total Hg from the early 1960s [17]. In the Nyanza Gulf, studies on trace metals exist but only very few of them include Cr metal [18][19][20][21][22][23][24]. The Nyanza gulf watershed is known for the presence of gold mines [25][26][27] and also serves as an important agroindustrial zone.…”

Analytical Relevance of Trace Metal Speciation in Environmental and Biophysicochemical Systems

“…The weathering of rocks and volcanic eruptions are among the natural sources, while aerial deposition from automotive traffic and power plants, mining, industrial activities, urbanization, and agricultural activities constitute human-induced sources [41][42][43]. Human-induced emissions and inputs into freshwater, estuarine, seawater or ocean systems can give rise to higher concentrations of the metals relative to the natural threshold concentrations.…”

“…In the estuaries, partitioning studies are particularly important because metal speciation is influenced by the constantly changing environmental conditions including salinity, pH and sediment redox potential [43,50,51]. The speciation of dissolved metals in seawater is relatively well understood.…”

Metal partitioning in sediment pore water from the Ondo coastal region, Nigeria

“…Metals are a class of important anthropogenic inorganic pollutants and due to their various health-related problems and widespread environmental occurrences, they have garnered much attention around the world (Paulson et al 2006;Yalcin, Narin, and Soylak 2007;Lalah, Ochieng, and Wandiga 2008;Liu et al 2009;Hiller, Jurkovic, and Utriepka 2010;Uluturhan 2010). Certain trace elements, Cr, Cu, Ni, and Zn, are essential micronutrients required for the normal growth and function of organisms.…”