John Wasswa

PCDD/Fs and dioxin-like PCBs in surface sediments from Lake Victoria, East Africa.

Surface sediments (<60 cm) from the Napoleon Gulf and Thurston Bay on the northern shore of Lake Victoria were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs). Fifteen PCDD/Fs and eleven dl-PCBs were found in 75.5% of the samples. The maximum concentrations of PCDD/Fs and dl-PCBs were 44.1 and 136 pg g(-1) dry weight (dw), respectively. Octachlorodibenzo-p-dioxin was the predominant PCDD/F congener at the Napoleon Gulf and Thurston Bay area. Regarding the dl-PCBs, a variation in levels was observed between the mono-ortho PCBs and non-ortho PCBs, with the former having higher levels than the latter. The PCDD/F and dl-PCB levels, in the sediments of Napoleon Gulf, which is near urban centers and industrial areas were markedly higher (α ≤ 0.05) than those from the Thurston Bay, which is offshore, suggesting that human activities could be sources of the pollutants to the surrounding water resources. World Health Organization-toxic equivalency quotients (WHO-TEQs) lay in the range of 0.07-5.53 pg g(-1) dw for PCDD/Fs and 0.01-0.23 pg g(-1) dw for dl-PCBs. 23.1% of samples from the Napoleon Gulf had their results above the set WHOPCDD/Fs-TEQ value.

PCDD/Fs and dioxin-like PCBs in fish species from Lake Victoria, East Africa

Two commercially important fish species, Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) belonging to different trophic levels were collected from the Napoleon Gulf and Thurston Bay in Lake Victoria. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) were extracted from the fish muscles and livers using the (13)C isotope dilution method, followed by multiple column chromatography clean-up. Analysis was achieved by a high resolution gas chromatography coupled with a high resolution mass spectrometer. The concentrations of analytes ranged from 0.07 to 0.59pgg(-1) fresh weight (fw) and 0.3-19.0pgg(-1) in L. niloticus and 0.06-0.18 and 0.2-15.7pgg(-1) in O. niloticus, for ∑PCDD/Fs and ∑dl-PCBs, respectively. Differences in congener concentrations were observed between the two fish species and study sites, and this was attributed to differences in feeding habits and trophic levels. World Health Organization-toxic equivalents (WHO-TEQs) were in the range 0.01-0.16pgTEQg(-1) for the PCDD/Fs and 0.001-0.74pgTEQg(-1) for the dl-PCBs. The TEQ values in the present study were lower compared to those of most fish samples reported in literature and were within permissible levels recommended by the European Union, implying that the fish was fit for human consumption.

Heavy metal contamination in vegetables cultivated on a major urban wetland inlet drainage system of Lake Victoria, Uganda

The population of the Ugandan capital, Kampala, located close to Lake Victoria, appears to be exposed to risk of ingesting the heavy metals Cadmium (Cd) and Lead (Pb) through vegetables in their diet. Lake Victoria is responsible for frequent torrential polluted runoffs in the city. The Nakivubo channel, the city’s major wetland drainage system, empties directly into the lake. Vegetables are grown on the urban wetland soils. Heavy metal content in vegetables from the wetland cultivation sites was determined by wet acid digestion, with 87–92% recovery. The results showed that although the heavy metal levels of manganese (Mn), zinc (Zn), cadmium (Cd) and lead (Pb) were significantly higher than those in similar food crops from rural control sites, only Cd and Pb exceeded the World Health Organisation (WHO) maximum permissible levels. Cd and Pb pose serious human health risks. Early pollution control measures are advisable.

Speciation of heavy metals in water from the Uganda side of Lake Victoria

Different forms of copper Cu, zinc Zn, lead Pb and cadmium Cd in water from the Uganda side of Lake Victoria (25°C, pH 6.75–7.18), the second largest inland freshwater lake in the world, have been studied using ion‐exchange, dialysis and atomic absorption spectrophotometry. The results indicate that heavy metals Cu, Zn, Pb and Cd are present mainly in the cationic form (80–83%). Small quantities of anionic (13–22%), non‐ionic, dialyzable (4–8%), and non‐ionic, non‐dialyzable (< 1.3–4.4%) forms were also detected for all metals except Cd. The corresponding concentrations lay in the ranges: cationic, 0.06–0.99; anionic, < 0.001–0.25; non‐ionic, dialyzable, < 0.001–0.08; non‐ionic, non‐dialyzable, < 0.001–0.06 µg ml−1. The existence of the metals in non‐ionic and non‐dialyzable forms is attributable to metal associations with high relative molecular mass (RMM) organic matters.

Contamination by heavy metals in silver fish (Rastreneobola argentea) caught from Lakes Kyoga and Victoria, Uganda.

Little information exists on heavy metal contamination in silver fish (Rastreneobola argentea) caught from Lake Victoria. A large number of Ugandans consume the species. Sun‐dried silver fish were collected from 10 landing sites on Lake Victoria, and from five control sites along Lake Kyoga. The finely ground fish was digested with analytical reagent grade nitric acid. Analyses were performed by atomic absorption spectrophotometry. The specimens were found to contain significantly higher levels (p ≤ 0.05) of zinc, Zn (86.1%), copper, Cu (99.1%), cadmium, Cd (99.3%) and lead, Pb (94.6%) compared with those from the control sites. The fish contamination was attributed to discharge into Lake Victoria of untreated industrial and anthropogenic effluent. Although mean Zn, Cu and Pb concentrations were still below, those of Cd were higher than the maximum permissible levels recommended by the World Health Organization (WHO). Overconsumption of the silver fish could pose Cd‐related health risks.

Characterization of sorption of endosulfan isomers and chlorpyrifos on container walls using mixed solvent systems.

The reliability of sorption data for organic contaminants with low water solubility has generated great concern because of the variability in the literature of the soil-water partition coefficient (K(OC)) values for these compounds. In particular, sorption on container walls in aqueous systems when measuring the sorption coefficient, K(D) (used to calculate K(OC) values), for strongly hydrophobic compounds (SHOCs) is a potential source for discrepancies in the K(OC) values. In this study, we eliminated sorption on container walls when measuring sorption of three halogenated compounds (alpha-endosulfan, beta-endosulfan, and chlorpyrifos) using mixed solvents. Various mixtures of methanol and water were used. Sorption experiments were designed using polytetrafluoroethylene (Teflon)-lined centrifuge tubes and a high-performance liquid chromatography (HPLC) syringe. Solution sample analysis was performed using HPLC equipped with a UV diode array detector and C-18 column at a wavelength of 214 nm, with acetonitrile/water (80:20, v/v) as the mobile phase. The solvophobic model was used to calculate the percent recovery (% R(M)) in water of the test compounds. Our results show that there is considerable sorption on container walls for the three chemicals at volume fractions of methanol (f(c) < 0.4). The data show that, in aqueous systems, percent recoveries for alpha-endosulfan, beta-endosulfan, and chlorpyrifos are 48, 45, and 61, respectively. Thus, to generate reliable sorption data for alpha-endosulfan, beta-endosulfan, and chlorpyrifos and other SHOCs, experiments may be conducted using Teflon-lined centrifuge tubes and HPLC syringes at volume fractions of methanol (f(c) >or= 0.5).

Organochlorine pesticide residues in skin, flesh and whole carrots (Daucus carota) from markets around Lake Victoria basin, Uganda

Residual concentrations of organochlorine pesticides in vegetables cause concern because of their adverse health effects. Pesticides have been applied in agricultural production and vector control in Uganda. Vegetables may absorb high residual levels of cyclodienes necessitating regular monitoring. Carrots are commonly consumed in Uganda as raw salads or components of different dishes. A gas chromatograph with electron capture detector was used to quantify organochlorine pesticides. Pesticide residues were confirmed by gas chromatography with a mass spectrometer. Trace amounts of 4,4′-dichlorodiphenyltrichloroethane (DDT), 2,4′-DDT, 2,4′-dichlorodiphenylchloroethane (DDE), α- endosulphan, β-endosulphan, α-lindane, γ-lindane and dieldrin were detected in carrots. Levels of organochlorine residues in carrots were below the maximum residue limits considered safe for human consumption by Codex Alimentarius and the European Union Commission.