David M. K. Ongeri

Trace metals in Lates niloticus and Rastrineobola argentea samples for human consumption at Winam Gulf of Lake Victoria

Trace metals were determined in the two most abundant fish species in the Winam Gulf of Lake Victoria (Lates niloticus and Rastrineobola argentea). The results show that the concentratios of the metals have no significant difference (p < 0.05) among the different sampling sites for each species. This situation was attributed to the mobility trends of fish. The abundance trend of the metals in L. niloticus was Fe>Cu>Pb>Cd, while that of Rastrineobola argentea was Zn>Fe>Cu>Pb>Cd. The difference in the trends was attributed to the fact that Rastrineobola argentea is consumed wholly, while the internal organs of L. niloticus are gotten rid of before consumption. This same reason explains why the concentrations of the metals were significantly higher in Rastrineobola argentea compared to those in L. niloticus. Rastrineobola argentea was found to be a major source of trace metals intake by humans.

Speciation study of trace elements in surface sediment of Winam Gulf, Lake Victoria, by sequential extraction, aqua-regia acid digestion, and ICP-OES

The speciation of trace metals in surface sediment in Kisumu Carwash area of Winam Gulf, was studied and results compared with those found at Usoma beach which was found to be several orders of magnitude less polluted. High proportions of the metals were bioavailable (fractions 1–6) with BA% ranging from 21.7% (Al) to 94.5% (Pb) at Carwash and 19.6% (Al) to ∼100% (for Cd and Pb) at Usoma beach. The readily mobilizable fraction (fractions 1–4) decreased in the order: Pb > Mn > Sn > Cu > Co > Zn > Mg > Cd > Mo > Ni > Cr > Fe > Al at Carwash and Mn > Mo > Sn > Pb > Cd > Mg > Cu > Zn > Co > Ni > Fe > Cr > Al at Usoma beach. The total Zn, Cd, Cr, and Cu sediment concentrations at Carwash were higher than the threshold effect concentrations (TECs), although their bioavailable concentrations were lower than these limits. Both the total and bioavailable concentrations of Pb in surface sediment at Kisumu Carwash area were higher than the TEC threshold limit indicating significant contamination from this heavy metal. Although there was a general good agreement on data obtained by sequential extraction as compared with those obtained by direct aqua-regia digestion, there were large discrepancies for some specific metal analytes which could be accounted for in terms of analytical variations and lack of uniformity in physical and chemical composition of the sediment samples analyzed.

Efficient adsorption of lead (II) and copper (II) from aqueous phase using oxidized multiwalled carbon nanotubes/polypyrrole composite

ABSTRACT Polypyrrole coated oxidized multiwalled carbon nanotubes (oMWCNT/Ppy) were applied to determine the adsorption characteristics of Pb(II) and Cu(II) from their aqueous solutions. Structural and morphological characterization studies using scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopy showed successful preparation of the oMWCNT/Ppy composite. The influence of pH, contact time, and initial metal ion concentration on the adsorption of Pb(II) and Cu(II) was studied. The adsorption processes fitted well with Langmuir isotherm and pseudo-second-order kinetic models. The maximum adsorption capacities for Pb(II) and Cu(II) were determined as 26.32 and 24.39 mg/g, respectively. Desorption studies indicated that the oMWCNT/Ppy composite could be reused for five cycles with minimum loss of its initial adsorption capacity.