Termites: a potentially large source of atmospheric methane, carbon dioxide, and molecular hydrogen.

Termites may emit large quantities of methane, carbon dioxide, and molecular hydrogen into the atmosphere. Global annual emissions calculated from laboratory measurements could reach 1.5 x 10(14) grams of methane and 5 x 10(16) grams of carbon dioxide. As much as 2 x 10(14) grams of molecular hydrogen may also be produced. Field measurements of methane emissions from two termite nests in Guatemala corroborated the laboratory results. The largest emissions should occur in tropical areas disturbed by human activities.

The effects of Mn2+, Ni2+, Cu2+, Co2+ and Zn2+ ions on pesticide adsorption and mobility in a tropical soil.

The adsorption behaviour of DDT in a tropical silt-clay soil from Kenya showed that addition of increasing metal ion concentrations from 10 to 100 microg/g of soil, reduced the % DDT adsorption in the soil by factors ranging from 6.1% to 15.4% depending on the type of metal ion. The inhibition of adsorption by metal ions was most observed in the lower ranges of metal ion concentrations in soil, i.e. up to 100 microg/g, beyond which additional increase in metal ion concentration did not result in any further increase in % adsorption. In the standard adsorption test procedure with different soil samples saturated with 100 microg/g of metal ions, the rate of adsorption of the pesticide varied with the type of metal ion and the equilibrium maximum adsorption of DDT was lowered with addition of metal ions, with the % adsorption of 78.4% (control) being reduced to lower values in the range of 67%-77.4%, depending on the type of metal ion. The data for control and samples fitted well into the Freundlich adsorption model and showed that addition of metal ions lowered the K(f) values compared with control. The results suggested that in the natural soil-water environments where there was no disturbance, aggregation of humic substances-pesticide molecule complexes altered the observed lowering of adsorption caused by inhibition by metal ions, and enhanced binding to solid soil phase occurred instead. In the leaching experiments, DDT was found to leach more extensively in soils with lower %OC content and the extent of leaching in soil columns saturated with metal ions at 100 microg/g was found to be inhibited compared with control and depended on the type of metal ion.

Anthropogenic sources of heavy metals in the Indian Ocean coast of Kenya.

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 microg/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 reported in rivers in South Africa but the sediment concentrations 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.

Levels of toxic metals in multisectoral samples from Winam Gulf of Lake Victoria.

In this study, the distribution and sources of inputs of trace metals including Cd, Cu, Zn and Pb from various sources as well as Fe which is widely used in the construction industry, into Winam Gulf of Lake Victoria were investigated. The sampling sites were located up streams and down streams of four rivers (Sio, Nyamasaria, Nyando and Sondu-Miriu), in four beaches along the lake (Port Victoria, Kisumu Car Wash, Dunga and Hippo point beaches) and in three estates (Nyamasaria, Migosi and Nyawita) in Kisumu city, covering potential agrochemical and industrial sources and drinking water points, respectively. The concentrations (in microg/L) of trace metals analysed in the lake and river waters ranged from <1.79 (Cd), <3.83 (Pb), <1.53-3.86 (Cu), 4.37-11.6 (Zn), 11.8-2,440 (Fe). The sediment concentrations (in microg/kg x 10(3)) ranged from 0.19 to 1.91 (Cd), 6.86-138 (Pb), 18-100 (Cu), 36.2-443 (Zn) and 960-73,200 (Fe), with highest concentrations of all metals being recorded at Kisumu Car Wash area. The study confirmed that the concentrations of the metals accumulate downstream in the rivers both in water and sediment and these rivers are major sources of the heavy metal load into Winam Gulf of Lake Victoria.

The effects of aflatoxin exposure on Hepatitis B-vaccine induced immunity in Kenyan children.

BACKGROUND: Globally, approximately three million children die each year from vaccine preventable infectious diseases mainly in developing countries. Despite the success of the expanded immunization program, not all infants and children around the world develop the same protective immune response to the same vaccine. A vaccine must induce a response over the basal immune response that may be driven by population-specific, environmental or socio-economic factors. Mycotoxins like aflatoxins are immune suppressants that are confirmed to interfere with both cell-mediated and acquired immunity. The mechanism of aflatoxin toxicity is through the binding of the bio-activated AFB1-8, 9-epoxide to cellular macromolecules. METHODS: We studied Hepatitis B surface antibodies [anti-HBs] levels to explore the immune modulation effects of dietary exposure to aflatoxins in children aged between one and fourteen years in Kenya. Hepatitis B vaccine was introduced for routine administration for Kenyan infants in November 2001. To assess the effects of aflatoxin on immunogenicity of childhood vaccines Aflatoxin B1-lysine in blood serum samples were determined using High Performance Liquid Chromatography with Fluorescence detection while anti-HBs were measured using Bio-ELISA anti-HBs kit. RESULTS: The mean ± SD of AFB1-lysine adducts in our study population was 45.38 ± 87.03 pg/mg of albumin while the geometric mean was 20.40 pg/mg. The distribution of AFB1-lysine adducts was skewed to the right. Only 98/205 (47.8%) of the study population tested positive for Hepatitis B surface antibodies. From regression analysis, we noted that for every unit rise in serum aflatoxin level, anti-HBs dropped by 0.91 mIU/ml (-0.9110038; 95% C.I -1.604948, -0.21706). CONCLUSION: Despite high coverage of routine immunization, less than half of the study population had developed immunity to HepB. Exposure to aflatoxin was high and weakly associated with low anti-HBs antibodies. These findings highlight a potentially significant role for environmental factors that may contribute to vaccine effectiveness warranting further research.

Use of complexing ligands in the determination of antimony and tin by atomic-absorption spectrometry.

The atomic-absorption spectrophotometric determination of antimony is best achieved in the presence of either an ammonium fluoride, hydrochloric acid, nitric acid mixture, or one of the following complexing agents: tartaric acid, citric acid, oxalic acid, 2-mercaptopropanoic acid. The interference of the 29 metals tested is least in the ammonium fluoride-hydrochloric acid-nitric acid mixture and is similar in tartaric acid, citric acid and 2-mercaptopropanoic acid media. However, the interference is pronounced in oxalic acid. Tin can be determined if any of the complexing agents or 6M hydrochloric acid is present.

The distribution of organochlorine pesticides in marine samples along the Indian Ocean coast of Kenya.

The concentrations of organochlorine residues of lindane, aldrin, alpha-endosulfan, dieldrin, endrin, p,p'-DDE, p,p'-DDD and p,p'-DDT in samples of seawater, sediment, fish and seaweed from different locations along the coast of Kenya are discussed in relation to the geographical location of the sampling sites and potential sources of residue over a period of two years. All sediment samples were found to contain very low levels of organic carbon except those sampled from Sabaki River that had high (4.7%) organic carbon due to greater primary activity. Most of the pesticides residues (112 samples analysed in 1997 and 258 analysed in 1998/99) were detected in fish, water, sediments and seaweed. The concentration of some residues was higher during the wet season than the dry season in 1997, but no marked seasonal variation was observed in 1998/99. Lindane, aldrin, p,p'-DDT and p,p'-DDE were the most frequently observed residues in all samples while alpha-endosulfan, dieldrin, p,p'-DDD and endrin were either present low concentrations or absent in most samples. Water samples had the lowest concentrations of residues (range 0.503 - 9.025 ng g(-1)). Sediments had the second highest levels of pesticides residues with a range of 0.584 - 59.00 ng g(-1) while fish lipid content had the highest levels of residues in 1989/99 with p,p'-DDT concentration of 1011 ng g(-1) and 418 ng g(-1) p,p'-DDD in Siganus rivulatus.

Accumulation, distribution and metabolism of 14C-1,1,1-trichloro-2, 2-, bis-(p-chlorophenyl)ethane (p,p'-DDT) residues in a model tropical marine ecosystem.

Accumulation, distribution and metabolism of ring labelled, 14C-1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT) in a model marine aquatic ecosystem consisting of seawater, sediment, oysters (Isognomonon alatus) and Humbug fish (Dascillus aruanus) were studied in the laboratory. 14C-p,p'-DDT distributes rapidly in the ecosystem immediately after application on the water surface with reduction of its concentration in the water phase from 1.18 ng g(-1) to 0.71 ng g(-1) after 2 hours and an increase in its content in the sediment and oysters. The bioconcentration factor reached a maximum of 19 x 10(3) in oysters, and 1657 in Humbug fish after 24 hours. The sediment concentration reached 117 ng g(-1) after 168 hours from start of application. A peak bioconcentration factor of 111 x 10(3) was calculated after 120 hours when 0.24 mg kg(-1) of 14C-p,p'-DDT was maintained through dosing every 24 hours with 0.002 mg kg(-1) of a mixture of labelled and non-labelled pesticide. The rate of depuration of accumulated 14C-p,p'-DDT sediment residues was up to 78.3% after 24 hours while oysters lost only 14.0% during the same period. The loss in Humbug fish was only 22.2% in three days. Volatilisation and sorption losses from seawater alone (without sediment/biota) were found to be very high in the range of 73.8 - 91.5% over 24 h for p,p'-DDT in aerated and nonaerated ecosystem. Gas chromatograph and TLC analysis of water, sediment and oyster samples revealed presence of p,p'-DDT and substantial amounts of p,p'-DDE and p,p'-DDD three days after pesticide dosage.

Water quality and trace metal distribution in a pristine Lake in the Lake basin in Kenya.

Water and surface sediment samples taken from various locations within Lake Kanyaboli in the Lake Victoria basin were analysed to determine the concentration and distribution of heavy metals. There were wide ranges in concentrations of the metals among the sampling points analysed. Sediment concentrations (microg/g dry weight) ranged from n.d.-2.54 (Ag), 0.25-1.08 (Cd), 0.89-1.64 (Co), 3.7-7.73 (Cr), 1.80-30.27 (Cu), 1073-2627 (Mn), 22.61-55.60 (Ni), 11.42-153.9 (Pb), 40.46-154.7 (Sn) and 65.0-146.5 (Zn). Dissolved metal concentrations (microg/L) ranged from n.d.-9.22 (Ag), n.d.-5.54 (Cd), n.d.-8.30 (Co), 5.26-60.82 (Cr), 10.96-43.11 (Cu), 184.7-375.9 (Mn), 1.84-38.3 (Ni), 5.98-47.77 (Pb), n.d.-540.6 (Sn) and 14.5-55.9 (Zn). Compared with WHO standards and other freshwaters worldwide, this lake was found to be unpolluted, with all metals, except Mn, being detected at concentrations lower than the highest desirable levels and maximum permissible levels. Some of the toxic metals, Cu, Zn, Pb and Cd (in sediment) and Ag, Co and Pb (in water) were detected at lower concentrations than those found in the polluted Kisumu Pier in Winam Gulf in the Lake basin, which confirms the anthropogenic influence on the latter.

Sources of heavy metal input into Winam Gulf, Kenya.

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).

Copper binding by dissolved organic matter in freshwaters in Kenya.

The binding of Cu2+ to dissolved organic matter in eight different natural water samples obtained from different locations in Kenya was studied by potentiometric titration method. The DOC contents of the eight natural water samples ranged from 2.71 to 374 mg/L. The water samples were adjusted to a uniform background electrolyte concentration of 0.5 M NaNO(3) and pH 6 and the temperature maintained at 20 degrees C during the assay. A Nernst equation E (mV) = -32.175 pCu + 305.5 (R (2) = 0.9996) obtained for the Cu2+ calibration standards (10(-4)-10(-6) M) was used to determine the concentration of free and bound Cu2+, respectively. The bound [Cu2+] varied by a factor of 2, ranging from 2.67 x 10(-3) mol/kg DOC (in a high DOC alkaline lake water sample) to 3.2962 x 10(-1) mol/kg (in a low DOC river water sample). The binding constants (Log K) varied by a factor of 2 and ranged from 3.43 to 5.57. The percentage binding ranged from 87% to almost 100% in the eight natural water samples. A Suwannee River Fulvic Acid standard sample (40 mg/L DOC) was used for comparison and for validation of the method.

Analysis of heavy metals in water and surface sediment in five Rift Valley lakes in Kenya for assessment of recent increase in anthropogenic activities.

The concentrations of heavy metals Ag, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sn and Zn were analysed in water and surface sediments of five Rift Valley lakes Nakuru, Elementaita, Naivasha, Bogoria and Baringo in Kenya. The dissolved mean concentration levels (mug/L) in water ranged within 13.0-185.0 (Ag), 2.0-43.0 (Cd), 5.0-316.0 (Co), 25.0-188.0 (Cr), 4.7-100.0 (Cu), 50.0-282.0 (Mn), 19.0-288.0 (Ni), 25.0-563.0 (Pb), 300.0-1050.0 (Sn) and 29.0-235.0 (Zn). The mean sediment concentrations (in mug/g (dry weight)) ranged within 0.1-0.35 (Ag), 0.05-1.18 (Cd), 0.17-1.38 (Co), 1.94-4.91 (Cr), 1.46-20.95 (Cu), 667.7-3946.8 (Mn), 11.69-39.72 (Ni), 10.92-38.98 (Pb), 17.21-56.52 (Sn) and 96.2-229.6 (Zn). The data indicate that some of the sites analysed, especially in Lake Nakuru, had relatively higher concentration levels of heavy metals Cd, Co, Cu, Pb, Ni, and Zn in the water which points to anthropogenic addition. However, potential influence of geochemical processes on the concentration levels in sediment is also shown in Co, Ni, and Cu which were more concentrated in the remote Lake Baringo sediment as well as in Pb and Mn which were more concentrated in the remote Lake Bogoria sediment. Data on some important limnological parameters including pH, salinity, electrical conductivity and temperature are also presented.