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Papers by esther lugwisha

This study investigated the performance of the selected Waste Stabilization Ponds (WSPs) in Dar e... more This study investigated the performance of the selected Waste Stabilization Ponds (WSPs) in Dar es Salaam. The concentrations of heavy metals (Pb, Fe, Cu, Zn, Mn and Cr) in influents, effluents and sludge of University of Dar es Salaam-UDSM, Mabibo, Vingunguti industrial, and Mikocheni (WSPs) as well as the influence of pH on the concentrations of heavy metals in laboratory prepared effluents were determined. The samples of influents and effluents were respectively taken at inlets and outlets of the WSPs, while sludge samples were taken randomly as grab samples from the WSPs then mixed into composite samples. The mean physical parameters; temperature, pH, TDS and EC of the WSPs were also determined and found to be within the working conditions of the WSPs. The mean concentrations of all heavy metals in effluents (0.0013 - 0.4293 mg/L) after treatment in the WSPs were lower compared to that of the influents (0.0037 - 7.11 mg/L) and were within permissible values according to TBS (200...

The levels of formaldehyde and acetaldehyde in bottled drinking water and the effect of storage t... more The levels of formaldehyde and acetaldehyde in bottled drinking water and the effect of storage time and storage conditions on their levels were determined. A total of 144 samples of six brands of bottled drinking water were purchased from Dar es Salaam, Iringa, Mwanza and Arusha regions in Tanzania. Analysis was performed using HPLC on the 1st day and after 14 and 42 days of storage in a refrigerator, at room temperature and exposure to sunlight. The levels of formaldehyde and acetaldehyde in the refrigerated samples ranged from 2.46 to 19.25 μg/L and from not detected (ND) to 58.70 μg/L, respectively. In samples stored at room temperature, the levels of formaldehyde and acetaldehyde were up to 23.26 μg/L and 36.10 μg/L, respectively. The highest levels of formaldehyde and acetaldehyde in samples exposed to sunlight were 46.0 μg/L and 187.0 μg/L, respectively. The lowest levels of the aldehydes were found in refrigerated samples and the highest levels were in samples exposed to su...

The effectiveness of thermal and acid modified locally available kaolin clay in Tanzania (Pugu cl... more The effectiveness of thermal and acid modified locally available kaolin clay in Tanzania (Pugu clay), for removal of cationic dye from water systems were tested. The raw Pugu kaolin (RPK) was thermally-treated at 150oC for 7 hours and acid-leached with 0.2 M H2SO4 under reflux for 3 hours, to obtain thermally-activated Pugu kaolin (TAPK) and acid-activated Pugu kaolin (AAPK), respectively. The raw and modified clays were characterized by XRF, XRD, ATR-FTIR and Porosimeter for their mineralogical compositions, chemical compositions, specific surface areas and pore sizes. A comparative analysis of their respective adsorption efficiencies was carried out using basic blue 9 dye (BB9) as a representative adsorbate. The results revealed that while RPK was mainly composed of 44.18% silica and 26.70% alumina, the modified adsorbents had higher silica content of 46.95% and 58.81%; decreased alumina content of 24.11% and 12.74%, and increased surface areas from 15.36 to 41.07 m2/g and 149.61 ...

Journal of Applied Sciences and Environmental Management, 2017

This study investigated the levels of pesticide residues in selected fruits from major markets in... more This study investigated the levels of pesticide residues in selected fruits from major markets in Dar es Salaam city. Samples of tomatoes and watermelons were analysed for eighteen organochlorine, organophosphorus and pyrethroid pesticide residues. Extraction was performed using acetone followed by dichloromethane: cyclohexane mixture and the extracts were cleanedup using florisil. The compounds were determined by gas chromatography-mass spectrometry (GC-MS). Pesticides and metabolites were detected in 95.8% of the samples. The compounds detected included chlorpyrifos, α-endosulfan, β-endosulfan and cypermethrin and their highest concentrations were 3810 ± 50, 370 ± 20, 120 ± 6 and 50 ± 4 ng/g, respectively. Others were p,p'-DDD, o,p'-DDD, p,p'-DDE and α-HCH with highest concentrations varying from 1 ± 0.5 to 20 ± 1.2 ng/g. There were no significant variations in concentrations of the pesticide residues between the fruits and among the sampling sites, indicating similarities in contamination patterns. The concentrations of the contaminants were above the maximum residue limits (MRLs) in 41.7% to 50% of the tomatoes and watermelons indicating risks and concerns for public health. The Tanzanian agrochemicals and food regulatory agencies (e.g. TPRI, TFDA and TBS) and the government in general should ensure strict applications of laws that regulate pesticides in the country and develop effective educational programmes for farmers to apply good agricultural practices such as reducing the use of pesticides, applying appropriate pesticides and doses, and restrict the spray before harvesting. The consumers should thoroughly wash or process the fruits to reduce the levels. © JASEM

Tanzania Journal of Science, 2011

The effect of glycol and heat on some clay minerals of the eastern southern region of Lake Victor... more The effect of glycol and heat on some clay minerals of the eastern southern region of Lake Victoria in Tanzania has been studied. First, Whole Rock Powder mount XRD analysis was carried out at the measuring range 2 # ranging between 2 o-65 o. Four non-clay minerals found in samples were Na-feldspar, K-feldspar, pyrope and quartz. Oriented clay mineral XRD analysis diffractograms were developed when the air-dried samples were diffracted in measuring range 2# between 2 o-32 o. Main clay mineral groups found in the samples were kaolinite, illite and montmorillonite. After glycolating the samples, it was evident that kaolinite diffractograms were inverted while montmorillonite diffractograms peaks were widened and shifted. But on heating to 550 o C, the peaks for both kaolinite and montmorillonite collapsed. The case was different for illite peaks which showed stability under both treatments. This analysis made it possible to differentiate between kaolinitic and non-kaolinitic clays. IR spectroscopy study was also carried out and the results were presented for comparison to clay minerals identified by XRD analysis. XRD analysis identified kaolinite, illite and montmorillonite as clay minerals in the samples, results which agree with IR. IR absorption bands occurred at 3694, 3825, 694 and ca 430-470 cm-1 are characteristic of kaolinite mineral. While absorption bands which appeared at 3455, 3463, 3600, 3440, 3610 and 532-539 cm-1 are characteristics of illite mineral group, and a band at 3432 cm-1 signifies the presence of both kaolinite and montmorillonite.

Thermochimica Acta, 1992

Abstract Under experimental conditions which tend to minimise the effects of heat and mass transf... more Abstract Under experimental conditions which tend to minimise the effects of heat and mass transfer, the kinetics of the decomposition of calcite according to CaCO 3 (s) CaO(s) + CO 2 (g) is split by the restriction of CO 2 transport at the degree of conversion α t when the channels in the CaO(s) surrounding the reactant provide the only diffusion path. Because of the resulting convective cooling beyond α t , the phase boundary reaction proceeds initially with the reaction-only activation energy E a (1) = 192.89 kJ mol −1 up to α t , after which the reaction proceeds with an apparent activation energy of E a (2) = 210.33kJ mol −1 . The diffusion-controlled reaction proceeds with the mean value of the activation energy E a (D 1 ) = 0.5 ( E a (1) + E a (2)) = 201.65 kJ mol −1 . The activation energies differ by the same amount, i.e. E a (D 1 ) − E a (1) = E a (2) − E a (D 1 ) = 8.72 kJ mol −1 , equivalent to the degenerate deformation vibration v 4 = δ(O-C-O) of calcite observed at 706 cm −1 (infrared) and 714 cm −1 (Raman), which for a transition state sensitive to the instantaneous transport of CO 2 , complements the cage effect exercised by the lattice, thus giving strong evidence supporting our mechanistic interpretation of the decomposition kinetics.

Tanzania Journal of Science, 2009

A study of some properties of clays collected from selected sites in Kowak deposit in Tarime Dist... more A study of some properties of clays collected from selected sites in Kowak deposit in Tarime District was carried out in order to assess their suitability as raw materials in ceramic and its related industries. The silica (SiO2) content in the clays is predominant, and is about 66.89% followed by alumina (Al2O3) that is 20.2%. Haematite (Fe2O3) was found to be the third in abundance with an average of 3.58%. Other constituents are present in small proportions. Water loss at 105 o C lies between 2.70% and 2.76%. DTG, TG, XRD techniques and chemical analyses studied by AAS method were used to determine the minerals present in the deposit. Two clay minerals, namely, illite and kaolinite were dominant. The non-clay minerals, referred to as "impurities" found in clays include quartz, pyrope and potash-feldspar (K2O.Al2O3.6SiO2) in the form of microcline. Illite, kaolinite, quartz and potash-feldspar were found in all sites of the deposit while pyrope was revealed in one site only. On the basis of this study, the results obtained from the chemical, thermal and mineralogical analyses, suggest that the clays from the deposit could be exploited for the manufacture of bricks, tiles and some limited ceramic ware.

Tanzania Journal of Science, 2009

Fired properties of talc-clay mixed bodies of different compositions were investigated for cerami... more Fired properties of talc-clay mixed bodies of different compositions were investigated for ceramic applications. Clays from Pugu and Malangali and talcs from two different sites in Kikombo deposits in Dodoma Region were used. Chemical analyses, X-ray analysis and Differential Thermal analysis for clays and talcs were used for the characterisation. Moulded mixed samples of clay and talc dried at room temperature at 110 0 C for 24 hours were fired at 1200, 1250, 1300 and 1350 0 C for 6 hours. Both clay deposits consist mainly of kaolin. Talc1-T1 is of higher purity than Talc-T2. Furthermore, the percentage shrinkage of the fired crisp bodies was found to increase with temperature. Pure talcs showed the lowest amount of shrinkage while body mixes having the highest percentage of clay showed the highest amount of shrinkage. In general, the percentage of water absorption of talc-clay compositions decreased as the firing temperature was increased. Mixed bodies containing Pugu clay and those containing talc1-T1 have higher percentage of water absorption than those containing Malangali clay and talc2-T2. This is due to the higher levels of impurities present in Malangali clays and high propotion of lime in talc2-T2.

Tanzania Journal of Science

Kaolin clay from Moshi, northern Tanzania has been characterized for potential ceramics productio... more Kaolin clay from Moshi, northern Tanzania has been characterized for potential ceramics productions. Clay samples taken from three different levels of the deposit were analysed by XRD and XRF. Firing experiments were carried out on experimental briquettes at a maximum temperature of 1300 °C at the rate of 100 °C/hour. The results revealed dominance of kaolinite and illite in the raw clay. The samples were composed majorly by silica (36.88–41.62%), alumina (30.83–32.40%) and hematite (9.29–12.70%). Granulometric analysis showed that the amount of clay decreased with deposit depth. The physicomechanical properties of the clay fired at the optimal temperature of 1300 °C included shrinkage (22.06–30.72%), water absorption (18.23–20.15%), bulk density (1.834–2.182 g/cm3) and modulus of rupture (2.957–6.313 MPa). Mullite was the key component responsible for mechanical strength. Clay sample from the top level showed the best properties. The parameters were of satisfactory quality and comp...

International Journal of Environmental Science and Technology, 2021

The development of new adsorbent materials exhibiting enhanced properties is recognized as a comp... more The development of new adsorbent materials exhibiting enhanced properties is recognized as a compelling and technologically significant area of materials research. One of such designs involves chemical modification of native clays leading to materials with improved properties. Herein, native Malangali kaolinite was modified by HCl acid to facilitate improvements in its physicochemical properties. The adsorption kinetics, equilibrium and thermodynamics of cadmium and cobalt ions on chemically modified Malangali kaolin were examined during a series of adsorption experiments. Both native and chemically modified kaolin clays were analysed for their compositional, structural, mineralogical and morphological properties. The resulting chemically modified kaolinite recorded a significant increment in pore diameter, pore volume and surface area from 2.99 to 3.60 nm, 0.45 to 0.81 cc/g and 78.69 to 107.27 m/g, respectively. The heavy metals adsorption kinetics was studied using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The pseudo-second-order model demonstrated a better fit to the experimental kinetic data compared to other models. The isothermal equation due to Langmuir model showed good agreement with the equilibrium data when compared to Dubinin–Radushkevich and Freundlich isotherms, indicating monolayer adsorption on homogeneous active sites of the adsorbent. The Langmuir monolayer adsorption capacity of 1.067 and 1.043 mg/g was acquired for cadmium and cobalt ions, correspondingly. Thermodynamic studies indicated an exothermic, spontaneous and physisorption process of heavy metals on the adsorbent. Our findings have demonstrated that chemically modified Malangali kaolinite can be exploited as an affordable, eco-friendly and efficient adsorbent for the adsorption of heavy metals form polluted wastewater.

Materials Today: Proceedings, 2020

Abstract The occurrence, toxicity and hazardous nature of heavy metals have prompted researchers ... more Abstract The occurrence, toxicity and hazardous nature of heavy metals have prompted researchers to search for affordable and efficient adsorbents for their removal from the environment. Malangali kaolin clay is an abundant and eco-friendly local adsorbent material which can offer sustainable and cost-effective solution towards heavy metal remediation. Raw kaolin clay has the ability to scavenge heavy metals by improvement to its surface chemistry and adsorption capacity through modification. In this study, the feasibility of physically activated Tanzanian Malangali kaolin clay to sequester cobalt and cadmium ions from simulated wastewater was examined under batch process. The physical activation of pristine kaolin clay was carried out by thermal treatment at 300 °C to influence its adsorption efficiency and physicochemical properties. The clay sample was characterized by Fourier Transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Nitrogen adsorption–desorption and chemical analysis by atomic absorption spectrometer (AAS). After thermal treatment of the pristine kaolinite, the specific pore volume and surface area amplified significantly from 0.454 − 0.813 cc/g and 78.69–83.046 m2/g, respectively. The heavy metal removal efficiency of thermally activated Malangali kaolinite (TAMK) was evaluated by investigating cobalt (Co2+) and cadmium (Cd2+) ions as potential water pollutants. The results obtained from batch experiments showed the elimination of heavy metal ions is greatly influenced by the initial concentration, adsorbent amount, contact time and solution pH. Adsorption isotherm studies revealed that Langmuir isotherm (R2 = 0.988 for Cd2+ and 0.979 for Co2+) presented the best fit to the equilibrium data than Freundlich isotherm (R2 = 0.965 for Cd2+ and 0.953 for Co2+) with cadmium ions being favourably adsorbed on TAMK compared to cobalt ions. Owing to improved surface area and porosity characteristics, TAMK displayed higher removal efficiency for both Co2+ and Cd2+ ions in simulated polluted water.

Journal of Applied Sciences and Environmental Management, 2018

This study assessed the levels of seventeen pesticides and metabolites residues in chicken feeds ... more This study assessed the levels of seventeen pesticides and metabolites residues in chicken feeds and raw eggs as well as the effects of processing methods on the levels in eggs in samples obtained from six poultry farms in Ilala and Kibaha districts, Tanzania. Extraction was performed by solid dispersion method and the extracts were cleaned-up by adsorption column chromatography. The analytes were determined by Gas Chromatography-Mass Spectrometry (GC-MS). The highest mean concentrations of the contaminants in feeds and eggs were as follows, respectively: aldrin 0.62 and 2 mg/kg, dieldrin 0.71 and 1.3 mg/kg, total DDT 6.68 and 8.14 mg/kg, total endosulfan 3.53 and 3.74 mg/kg, total HCHs 0.91 and 1.21 mg/kg, chlorpyrifos 12.2 and 0.59 mg/kg, fenitrothion 4.9 and 0.64 mg/kg and pirimiphos methyl 22.11 and 1.6 mg/kg. Chicken feeds were found to be the most contaminated followed by raw eggs and finally cooked eggs. Most of the concentrations were above the maximum residue limits (MRLs) indicating risks and concerns. Proper selection and preparation of poultry feeds could reduce the levels in the feeds and eggs.

Chemosphere, 2018

The concentrations of organochlorine and organophosphorus pesticides and metabolites were investi... more The concentrations of organochlorine and organophosphorus pesticides and metabolites were investigated in chicken kidney, liver and muscle samples obtained from chickens collected from four poultry farms in Dar es Salaam and Pwani regions in Tanzania. The samples were extracted by solid dispersion using cyclohexane:ethyl acetate. The extracts were cleaned by adsorption column chromatography. The analytes were determined using gas chromatography-mass spectrometry (GC-MS). The concentrations of total DDT, total endosulfan and total HCHs in the samples ranged from 0.71 to 26, 0.3 to 7.9 and 0.02-10.4 mg/kg lipid weight (lw), respectively. The highest concentrations of aldrin, dieldrin, chlorpyrifos, fenitrothion and pirimiphos methyl were 5.5, 4.8, 9.7, 5.6 and 7.8 mg/kg lw, respectively. The highest concentrations of the contaminants were found in the kidney and liver samples. The sites in Dar es Salaam showed the highest concentrations of the compounds. Most of the concentrations were above the maximum residue limits (MRLs) indicating risks and concerns for livestock and public health.

International Journal of Analytical Chemistry, 2017

This study investigated the levels of pesticides and metabolites in vegetables from major markets... more This study investigated the levels of pesticides and metabolites in vegetables from major markets in Dar es Salaam city, Tanzania. Samples of fresh cabbage, spinach, and onions from the markets were analysed for pesticide residues. Extraction was performed using acetone followed by dichloromethane : cyclohexane mixture and the extracts were cleaned up using Florisil. The compounds were determined by gas chromatography-mass spectrometry (GC-MS). Pesticides and metabolites were detected in 72.2% of the samples. The detected pesticide residues and their highest mean concentrations were p,p′-DDT 4.00 × 10−3 mg/kg, p,p′-DDD 6.40 × 10−1 mg/kg, o,p′-DDD 1.00 × 10−2 mg/kg, α-endosulfan 6.00 × 10−1 mg/kg, β-endosulfan 2.10 × 10−1 mg/kg, chlorpyrifos 3.00 mg/kg, and cypermethrin 4.00 × 10−2 mg/kg. The most frequently detected compounds were p,p′-DDD and chlorpyrifos. The order of contamination was spinach > cabbage > onions. Generally, there were no significant variations in concentrati...

Journal of Food and Nutrition Sciences, 2014

The physicochemical composition of harvested soursop (Annona muricata L.) fruits from Coast regio... more The physicochemical composition of harvested soursop (Annona muricata L.) fruits from Coast region, Tanzania, during open-air storage was determined. The ash, titratable acidity, crude fat, crude fiber, moisture and sugars content were determined by proximate analysis. Ascorbic acid contents were determined using the 2,6-dichlorophenol-indophenol dye method while macro-nutrients and heavy metals were determined by Flame Atomic Absorption Spectrophotometry (FAAS). The fruits were harvested at the mature ripe stage and kept in open air storage over several days. The determinations were done immediately after fruit arrival at the laboratory and thereafter at intervals of two days from the day of harvest. The results showed that soursop fruits had high moisture content (73.1%-82.1%), low titratable acidity (0.10-1.25% ca), low crude fat (0.42 mg/100 g-fw), moderate ash content (0.87 mg/100 g-fw) and crude fibre content (6.09 mg/100 g-fw), high ascorbic acid content (34.0-19.7 mg/100 g-fw), high total sugars content (34.3%-45.3%), reducing sugar content (18.9%-39.2%) and sucrose content (15.5%-30.0%). Of the macroelements Na, Ca and K, the average content were 895.6, 870.3 and 367.5 mg/100 g-fw respectively. Heavy metals (Fe, Zn, Cu, Pb and Cd) content was very low in the soursop fruits, ranging between <0.0015 mg/100 g-fw for Cd and 0.82 mg/100 g-fw for Fe. During storage, the moisture content, titratable acidity level and sugars content in the fruit were all increasing whereas the ascorbic acid content was decreasing. There were no significant changes during storage for levels of crude fat, fiber, ash, mineral elements and heavy metals. The findings from this study suggest that this fruit from coast region of Tanzania can contribute nutritionally to the health of the consumer.

International Journal of Science, Technology and Society, 2014

International Journal of River Basin Management, 2013

This study investigated concentration profiles of trace, rare earth and platinum group metals in ... more This study investigated concentration profiles of trace, rare earth and platinum group metals in fluvial sediments from the Pangani river basin (43,650 km 2), one of the largest river basins in Tanzania, to assess its environmental quality. Sediment samples were collected in two distinct seasons from 12 representative sites of diverse land-use practices and characterised by ICP-MS after optimised microwave digestion. Ecological risks were assessed by evaluation of pollution index and comparison with legislated sediment quality guidelines (SQG). The results revealed contamination by some trace metals (e.g. Pb, V, Cu, Cr, Ni, Cd, As, Co, Mn and Zn) in concentrations ranging from 0.7 to 2940 mg kg −1 , and four rare earth elements (Y, Ce, Nd, Yb) in concentrations ranging from 0.9 (Yb) to 500 mg kg −1 dry weight (Ce), which significantly exceeded the estimated background values at some stations. Palladium was the only platinum group element that was detected in quantifiable concentrations (0.3-3.5 mg kg −1). Concentrations of some trace metals exceeded the SQGs at some localised areas. Principal component analysis and multivariate correlations indicated geochemical characteristics of the area as the major control of metal concentrations and spatial variability. Organic matter and clay contents also played a significant role in metal distributions. Assessment of land-use practices upstream of the sampling locations was used to trace potential anthropogenic sources of metal enrichments, where highest levels were found in areas close to urban centres and agricultural activities. The study provides baseline data for future monitoring programs, and highlights the need for more comprehensive analysis involving a wider spatio-temporal scale and ecotoxicological risk assessment.

International Journal of Environmental Analytical Chemistry, 2013

Tanzania Journal of Science, 2018

The suitability of raw Malangali kaolin (RMK) clay for the removal of cadmium and cobalt ions fro... more The suitability of raw Malangali kaolin (RMK) clay for the removal of cadmium and cobalt ions from water was investigated using a batch technique whereas the characterization of adsorbent material was performed by XRD, XRF, ATR-FTIR and N 2 physisorption techniques. Various experimental parameters were tested for the effectiveness of RMK in removing heavy metals whereby quantitative determination of both Cd 2+ and Co 2+ ions has shown that, the factors such as adsorbent particle size, solution pH, contact time, adsorbent dose as well as initial metal ion concentration had significant effects on the adsorption processes. The equilibrium data described by Langmuir and Freundlich isotherms were used in this study. It was shown that Langmuir isotherm displayed a better fitting model than that of Freundlich because of its higher correlation coefficient, thus, demonstrating the occurrence of monolayer coverage of Cd 2+ and Co 2+ ions on the surface of RMK clay. The results obtained in thi...

Kaolin and quartz from Pugu and feldspar from Morogoro were used to produce feldspathic dental po... more Kaolin and quartz from Pugu and feldspar from Morogoro were used to produce feldspathic dental porcelain bodies. Mineralogical results from XRD revealed the presence of kaolinite, illite, microcline and clinochlore in the kaolin samples; albite, microcline, sanidine in the feldspar samples and only silica in the quartz samples. The chemical results studies by XRF revealed the presence of in varying proportions. Particle size distribution of all the raw materials were determined and particles &lt;63 μm were used for preparation of batches. The batches of different compositions with ranges: quartz (12-22%), feldspar (75-88%) and kaolin (3-5%) were fired at 1100, 1200 and 1250 o C, and the developed properties were tested. The physico-mechanical properties studied exhibited volumetric shrinkage between 2 and 55.17%, open porosity between 6.67 and 40.00%, water of absorption between 7.1 and 40%, bulk densty of 1.43 – 5.68 g/cm 3 , and compressive strength at 0.13-32.25 MPa. The optimal firing temperature for the best results was found to be 1250 o C. The results obtained indicate that kaolin and quartz from Pugu and feldspar from Morogoro are potential raw materials for the production of dental porcelain.

This study investigated the performance of the selected Waste Stabilization Ponds (WSPs) in Dar e... more This study investigated the performance of the selected Waste Stabilization Ponds (WSPs) in Dar es Salaam. The concentrations of heavy metals (Pb, Fe, Cu, Zn, Mn and Cr) in influents, effluents and sludge of University of Dar es Salaam-UDSM, Mabibo, Vingunguti industrial, and Mikocheni (WSPs) as well as the influence of pH on the concentrations of heavy metals in laboratory prepared effluents were determined. The samples of influents and effluents were respectively taken at inlets and outlets of the WSPs, while sludge samples were taken randomly as grab samples from the WSPs then mixed into composite samples. The mean physical parameters; temperature, pH, TDS and EC of the WSPs were also determined and found to be within the working conditions of the WSPs. The mean concentrations of all heavy metals in effluents (0.0013 - 0.4293 mg/L) after treatment in the WSPs were lower compared to that of the influents (0.0037 - 7.11 mg/L) and were within permissible values according to TBS (200...

The levels of formaldehyde and acetaldehyde in bottled drinking water and the effect of storage t... more The levels of formaldehyde and acetaldehyde in bottled drinking water and the effect of storage time and storage conditions on their levels were determined. A total of 144 samples of six brands of bottled drinking water were purchased from Dar es Salaam, Iringa, Mwanza and Arusha regions in Tanzania. Analysis was performed using HPLC on the 1st day and after 14 and 42 days of storage in a refrigerator, at room temperature and exposure to sunlight. The levels of formaldehyde and acetaldehyde in the refrigerated samples ranged from 2.46 to 19.25 μg/L and from not detected (ND) to 58.70 μg/L, respectively. In samples stored at room temperature, the levels of formaldehyde and acetaldehyde were up to 23.26 μg/L and 36.10 μg/L, respectively. The highest levels of formaldehyde and acetaldehyde in samples exposed to sunlight were 46.0 μg/L and 187.0 μg/L, respectively. The lowest levels of the aldehydes were found in refrigerated samples and the highest levels were in samples exposed to su...

The effectiveness of thermal and acid modified locally available kaolin clay in Tanzania (Pugu cl... more The effectiveness of thermal and acid modified locally available kaolin clay in Tanzania (Pugu clay), for removal of cationic dye from water systems were tested. The raw Pugu kaolin (RPK) was thermally-treated at 150oC for 7 hours and acid-leached with 0.2 M H2SO4 under reflux for 3 hours, to obtain thermally-activated Pugu kaolin (TAPK) and acid-activated Pugu kaolin (AAPK), respectively. The raw and modified clays were characterized by XRF, XRD, ATR-FTIR and Porosimeter for their mineralogical compositions, chemical compositions, specific surface areas and pore sizes. A comparative analysis of their respective adsorption efficiencies was carried out using basic blue 9 dye (BB9) as a representative adsorbate. The results revealed that while RPK was mainly composed of 44.18% silica and 26.70% alumina, the modified adsorbents had higher silica content of 46.95% and 58.81%; decreased alumina content of 24.11% and 12.74%, and increased surface areas from 15.36 to 41.07 m2/g and 149.61 ...

Journal of Applied Sciences and Environmental Management, 2017

This study investigated the levels of pesticide residues in selected fruits from major markets in... more This study investigated the levels of pesticide residues in selected fruits from major markets in Dar es Salaam city. Samples of tomatoes and watermelons were analysed for eighteen organochlorine, organophosphorus and pyrethroid pesticide residues. Extraction was performed using acetone followed by dichloromethane: cyclohexane mixture and the extracts were cleanedup using florisil. The compounds were determined by gas chromatography-mass spectrometry (GC-MS). Pesticides and metabolites were detected in 95.8% of the samples. The compounds detected included chlorpyrifos, α-endosulfan, β-endosulfan and cypermethrin and their highest concentrations were 3810 ± 50, 370 ± 20, 120 ± 6 and 50 ± 4 ng/g, respectively. Others were p,p'-DDD, o,p'-DDD, p,p'-DDE and α-HCH with highest concentrations varying from 1 ± 0.5 to 20 ± 1.2 ng/g. There were no significant variations in concentrations of the pesticide residues between the fruits and among the sampling sites, indicating similarities in contamination patterns. The concentrations of the contaminants were above the maximum residue limits (MRLs) in 41.7% to 50% of the tomatoes and watermelons indicating risks and concerns for public health. The Tanzanian agrochemicals and food regulatory agencies (e.g. TPRI, TFDA and TBS) and the government in general should ensure strict applications of laws that regulate pesticides in the country and develop effective educational programmes for farmers to apply good agricultural practices such as reducing the use of pesticides, applying appropriate pesticides and doses, and restrict the spray before harvesting. The consumers should thoroughly wash or process the fruits to reduce the levels. © JASEM

Tanzania Journal of Science, 2011

The effect of glycol and heat on some clay minerals of the eastern southern region of Lake Victor... more The effect of glycol and heat on some clay minerals of the eastern southern region of Lake Victoria in Tanzania has been studied. First, Whole Rock Powder mount XRD analysis was carried out at the measuring range 2 # ranging between 2 o-65 o. Four non-clay minerals found in samples were Na-feldspar, K-feldspar, pyrope and quartz. Oriented clay mineral XRD analysis diffractograms were developed when the air-dried samples were diffracted in measuring range 2# between 2 o-32 o. Main clay mineral groups found in the samples were kaolinite, illite and montmorillonite. After glycolating the samples, it was evident that kaolinite diffractograms were inverted while montmorillonite diffractograms peaks were widened and shifted. But on heating to 550 o C, the peaks for both kaolinite and montmorillonite collapsed. The case was different for illite peaks which showed stability under both treatments. This analysis made it possible to differentiate between kaolinitic and non-kaolinitic clays. IR spectroscopy study was also carried out and the results were presented for comparison to clay minerals identified by XRD analysis. XRD analysis identified kaolinite, illite and montmorillonite as clay minerals in the samples, results which agree with IR. IR absorption bands occurred at 3694, 3825, 694 and ca 430-470 cm-1 are characteristic of kaolinite mineral. While absorption bands which appeared at 3455, 3463, 3600, 3440, 3610 and 532-539 cm-1 are characteristics of illite mineral group, and a band at 3432 cm-1 signifies the presence of both kaolinite and montmorillonite.

Thermochimica Acta, 1992

Abstract Under experimental conditions which tend to minimise the effects of heat and mass transf... more Abstract Under experimental conditions which tend to minimise the effects of heat and mass transfer, the kinetics of the decomposition of calcite according to CaCO 3 (s) CaO(s) + CO 2 (g) is split by the restriction of CO 2 transport at the degree of conversion α t when the channels in the CaO(s) surrounding the reactant provide the only diffusion path. Because of the resulting convective cooling beyond α t , the phase boundary reaction proceeds initially with the reaction-only activation energy E a (1) = 192.89 kJ mol −1 up to α t , after which the reaction proceeds with an apparent activation energy of E a (2) = 210.33kJ mol −1 . The diffusion-controlled reaction proceeds with the mean value of the activation energy E a (D 1 ) = 0.5 ( E a (1) + E a (2)) = 201.65 kJ mol −1 . The activation energies differ by the same amount, i.e. E a (D 1 ) − E a (1) = E a (2) − E a (D 1 ) = 8.72 kJ mol −1 , equivalent to the degenerate deformation vibration v 4 = δ(O-C-O) of calcite observed at 706 cm −1 (infrared) and 714 cm −1 (Raman), which for a transition state sensitive to the instantaneous transport of CO 2 , complements the cage effect exercised by the lattice, thus giving strong evidence supporting our mechanistic interpretation of the decomposition kinetics.

Tanzania Journal of Science, 2009

A study of some properties of clays collected from selected sites in Kowak deposit in Tarime Dist... more A study of some properties of clays collected from selected sites in Kowak deposit in Tarime District was carried out in order to assess their suitability as raw materials in ceramic and its related industries. The silica (SiO2) content in the clays is predominant, and is about 66.89% followed by alumina (Al2O3) that is 20.2%. Haematite (Fe2O3) was found to be the third in abundance with an average of 3.58%. Other constituents are present in small proportions. Water loss at 105 o C lies between 2.70% and 2.76%. DTG, TG, XRD techniques and chemical analyses studied by AAS method were used to determine the minerals present in the deposit. Two clay minerals, namely, illite and kaolinite were dominant. The non-clay minerals, referred to as "impurities" found in clays include quartz, pyrope and potash-feldspar (K2O.Al2O3.6SiO2) in the form of microcline. Illite, kaolinite, quartz and potash-feldspar were found in all sites of the deposit while pyrope was revealed in one site only. On the basis of this study, the results obtained from the chemical, thermal and mineralogical analyses, suggest that the clays from the deposit could be exploited for the manufacture of bricks, tiles and some limited ceramic ware.

Tanzania Journal of Science, 2009

Fired properties of talc-clay mixed bodies of different compositions were investigated for cerami... more Fired properties of talc-clay mixed bodies of different compositions were investigated for ceramic applications. Clays from Pugu and Malangali and talcs from two different sites in Kikombo deposits in Dodoma Region were used. Chemical analyses, X-ray analysis and Differential Thermal analysis for clays and talcs were used for the characterisation. Moulded mixed samples of clay and talc dried at room temperature at 110 0 C for 24 hours were fired at 1200, 1250, 1300 and 1350 0 C for 6 hours. Both clay deposits consist mainly of kaolin. Talc1-T1 is of higher purity than Talc-T2. Furthermore, the percentage shrinkage of the fired crisp bodies was found to increase with temperature. Pure talcs showed the lowest amount of shrinkage while body mixes having the highest percentage of clay showed the highest amount of shrinkage. In general, the percentage of water absorption of talc-clay compositions decreased as the firing temperature was increased. Mixed bodies containing Pugu clay and those containing talc1-T1 have higher percentage of water absorption than those containing Malangali clay and talc2-T2. This is due to the higher levels of impurities present in Malangali clays and high propotion of lime in talc2-T2.

Tanzania Journal of Science

Kaolin clay from Moshi, northern Tanzania has been characterized for potential ceramics productio... more Kaolin clay from Moshi, northern Tanzania has been characterized for potential ceramics productions. Clay samples taken from three different levels of the deposit were analysed by XRD and XRF. Firing experiments were carried out on experimental briquettes at a maximum temperature of 1300 °C at the rate of 100 °C/hour. The results revealed dominance of kaolinite and illite in the raw clay. The samples were composed majorly by silica (36.88–41.62%), alumina (30.83–32.40%) and hematite (9.29–12.70%). Granulometric analysis showed that the amount of clay decreased with deposit depth. The physicomechanical properties of the clay fired at the optimal temperature of 1300 °C included shrinkage (22.06–30.72%), water absorption (18.23–20.15%), bulk density (1.834–2.182 g/cm3) and modulus of rupture (2.957–6.313 MPa). Mullite was the key component responsible for mechanical strength. Clay sample from the top level showed the best properties. The parameters were of satisfactory quality and comp...

International Journal of Environmental Science and Technology, 2021

The development of new adsorbent materials exhibiting enhanced properties is recognized as a comp... more The development of new adsorbent materials exhibiting enhanced properties is recognized as a compelling and technologically significant area of materials research. One of such designs involves chemical modification of native clays leading to materials with improved properties. Herein, native Malangali kaolinite was modified by HCl acid to facilitate improvements in its physicochemical properties. The adsorption kinetics, equilibrium and thermodynamics of cadmium and cobalt ions on chemically modified Malangali kaolin were examined during a series of adsorption experiments. Both native and chemically modified kaolin clays were analysed for their compositional, structural, mineralogical and morphological properties. The resulting chemically modified kaolinite recorded a significant increment in pore diameter, pore volume and surface area from 2.99 to 3.60 nm, 0.45 to 0.81 cc/g and 78.69 to 107.27 m/g, respectively. The heavy metals adsorption kinetics was studied using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The pseudo-second-order model demonstrated a better fit to the experimental kinetic data compared to other models. The isothermal equation due to Langmuir model showed good agreement with the equilibrium data when compared to Dubinin–Radushkevich and Freundlich isotherms, indicating monolayer adsorption on homogeneous active sites of the adsorbent. The Langmuir monolayer adsorption capacity of 1.067 and 1.043 mg/g was acquired for cadmium and cobalt ions, correspondingly. Thermodynamic studies indicated an exothermic, spontaneous and physisorption process of heavy metals on the adsorbent. Our findings have demonstrated that chemically modified Malangali kaolinite can be exploited as an affordable, eco-friendly and efficient adsorbent for the adsorption of heavy metals form polluted wastewater.

Materials Today: Proceedings, 2020

Abstract The occurrence, toxicity and hazardous nature of heavy metals have prompted researchers ... more Abstract The occurrence, toxicity and hazardous nature of heavy metals have prompted researchers to search for affordable and efficient adsorbents for their removal from the environment. Malangali kaolin clay is an abundant and eco-friendly local adsorbent material which can offer sustainable and cost-effective solution towards heavy metal remediation. Raw kaolin clay has the ability to scavenge heavy metals by improvement to its surface chemistry and adsorption capacity through modification. In this study, the feasibility of physically activated Tanzanian Malangali kaolin clay to sequester cobalt and cadmium ions from simulated wastewater was examined under batch process. The physical activation of pristine kaolin clay was carried out by thermal treatment at 300 °C to influence its adsorption efficiency and physicochemical properties. The clay sample was characterized by Fourier Transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Nitrogen adsorption–desorption and chemical analysis by atomic absorption spectrometer (AAS). After thermal treatment of the pristine kaolinite, the specific pore volume and surface area amplified significantly from 0.454 − 0.813 cc/g and 78.69–83.046 m2/g, respectively. The heavy metal removal efficiency of thermally activated Malangali kaolinite (TAMK) was evaluated by investigating cobalt (Co2+) and cadmium (Cd2+) ions as potential water pollutants. The results obtained from batch experiments showed the elimination of heavy metal ions is greatly influenced by the initial concentration, adsorbent amount, contact time and solution pH. Adsorption isotherm studies revealed that Langmuir isotherm (R2 = 0.988 for Cd2+ and 0.979 for Co2+) presented the best fit to the equilibrium data than Freundlich isotherm (R2 = 0.965 for Cd2+ and 0.953 for Co2+) with cadmium ions being favourably adsorbed on TAMK compared to cobalt ions. Owing to improved surface area and porosity characteristics, TAMK displayed higher removal efficiency for both Co2+ and Cd2+ ions in simulated polluted water.

Journal of Applied Sciences and Environmental Management, 2018

This study assessed the levels of seventeen pesticides and metabolites residues in chicken feeds ... more This study assessed the levels of seventeen pesticides and metabolites residues in chicken feeds and raw eggs as well as the effects of processing methods on the levels in eggs in samples obtained from six poultry farms in Ilala and Kibaha districts, Tanzania. Extraction was performed by solid dispersion method and the extracts were cleaned-up by adsorption column chromatography. The analytes were determined by Gas Chromatography-Mass Spectrometry (GC-MS). The highest mean concentrations of the contaminants in feeds and eggs were as follows, respectively: aldrin 0.62 and 2 mg/kg, dieldrin 0.71 and 1.3 mg/kg, total DDT 6.68 and 8.14 mg/kg, total endosulfan 3.53 and 3.74 mg/kg, total HCHs 0.91 and 1.21 mg/kg, chlorpyrifos 12.2 and 0.59 mg/kg, fenitrothion 4.9 and 0.64 mg/kg and pirimiphos methyl 22.11 and 1.6 mg/kg. Chicken feeds were found to be the most contaminated followed by raw eggs and finally cooked eggs. Most of the concentrations were above the maximum residue limits (MRLs) indicating risks and concerns. Proper selection and preparation of poultry feeds could reduce the levels in the feeds and eggs.

Chemosphere, 2018

The concentrations of organochlorine and organophosphorus pesticides and metabolites were investi... more The concentrations of organochlorine and organophosphorus pesticides and metabolites were investigated in chicken kidney, liver and muscle samples obtained from chickens collected from four poultry farms in Dar es Salaam and Pwani regions in Tanzania. The samples were extracted by solid dispersion using cyclohexane:ethyl acetate. The extracts were cleaned by adsorption column chromatography. The analytes were determined using gas chromatography-mass spectrometry (GC-MS). The concentrations of total DDT, total endosulfan and total HCHs in the samples ranged from 0.71 to 26, 0.3 to 7.9 and 0.02-10.4 mg/kg lipid weight (lw), respectively. The highest concentrations of aldrin, dieldrin, chlorpyrifos, fenitrothion and pirimiphos methyl were 5.5, 4.8, 9.7, 5.6 and 7.8 mg/kg lw, respectively. The highest concentrations of the contaminants were found in the kidney and liver samples. The sites in Dar es Salaam showed the highest concentrations of the compounds. Most of the concentrations were above the maximum residue limits (MRLs) indicating risks and concerns for livestock and public health.

International Journal of Analytical Chemistry, 2017

This study investigated the levels of pesticides and metabolites in vegetables from major markets... more This study investigated the levels of pesticides and metabolites in vegetables from major markets in Dar es Salaam city, Tanzania. Samples of fresh cabbage, spinach, and onions from the markets were analysed for pesticide residues. Extraction was performed using acetone followed by dichloromethane : cyclohexane mixture and the extracts were cleaned up using Florisil. The compounds were determined by gas chromatography-mass spectrometry (GC-MS). Pesticides and metabolites were detected in 72.2% of the samples. The detected pesticide residues and their highest mean concentrations were p,p′-DDT 4.00 × 10−3 mg/kg, p,p′-DDD 6.40 × 10−1 mg/kg, o,p′-DDD 1.00 × 10−2 mg/kg, α-endosulfan 6.00 × 10−1 mg/kg, β-endosulfan 2.10 × 10−1 mg/kg, chlorpyrifos 3.00 mg/kg, and cypermethrin 4.00 × 10−2 mg/kg. The most frequently detected compounds were p,p′-DDD and chlorpyrifos. The order of contamination was spinach > cabbage > onions. Generally, there were no significant variations in concentrati...

Journal of Food and Nutrition Sciences, 2014

The physicochemical composition of harvested soursop (Annona muricata L.) fruits from Coast regio... more The physicochemical composition of harvested soursop (Annona muricata L.) fruits from Coast region, Tanzania, during open-air storage was determined. The ash, titratable acidity, crude fat, crude fiber, moisture and sugars content were determined by proximate analysis. Ascorbic acid contents were determined using the 2,6-dichlorophenol-indophenol dye method while macro-nutrients and heavy metals were determined by Flame Atomic Absorption Spectrophotometry (FAAS). The fruits were harvested at the mature ripe stage and kept in open air storage over several days. The determinations were done immediately after fruit arrival at the laboratory and thereafter at intervals of two days from the day of harvest. The results showed that soursop fruits had high moisture content (73.1%-82.1%), low titratable acidity (0.10-1.25% ca), low crude fat (0.42 mg/100 g-fw), moderate ash content (0.87 mg/100 g-fw) and crude fibre content (6.09 mg/100 g-fw), high ascorbic acid content (34.0-19.7 mg/100 g-fw), high total sugars content (34.3%-45.3%), reducing sugar content (18.9%-39.2%) and sucrose content (15.5%-30.0%). Of the macroelements Na, Ca and K, the average content were 895.6, 870.3 and 367.5 mg/100 g-fw respectively. Heavy metals (Fe, Zn, Cu, Pb and Cd) content was very low in the soursop fruits, ranging between <0.0015 mg/100 g-fw for Cd and 0.82 mg/100 g-fw for Fe. During storage, the moisture content, titratable acidity level and sugars content in the fruit were all increasing whereas the ascorbic acid content was decreasing. There were no significant changes during storage for levels of crude fat, fiber, ash, mineral elements and heavy metals. The findings from this study suggest that this fruit from coast region of Tanzania can contribute nutritionally to the health of the consumer.

International Journal of Science, Technology and Society, 2014

International Journal of River Basin Management, 2013

This study investigated concentration profiles of trace, rare earth and platinum group metals in ... more This study investigated concentration profiles of trace, rare earth and platinum group metals in fluvial sediments from the Pangani river basin (43,650 km 2), one of the largest river basins in Tanzania, to assess its environmental quality. Sediment samples were collected in two distinct seasons from 12 representative sites of diverse land-use practices and characterised by ICP-MS after optimised microwave digestion. Ecological risks were assessed by evaluation of pollution index and comparison with legislated sediment quality guidelines (SQG). The results revealed contamination by some trace metals (e.g. Pb, V, Cu, Cr, Ni, Cd, As, Co, Mn and Zn) in concentrations ranging from 0.7 to 2940 mg kg −1 , and four rare earth elements (Y, Ce, Nd, Yb) in concentrations ranging from 0.9 (Yb) to 500 mg kg −1 dry weight (Ce), which significantly exceeded the estimated background values at some stations. Palladium was the only platinum group element that was detected in quantifiable concentrations (0.3-3.5 mg kg −1). Concentrations of some trace metals exceeded the SQGs at some localised areas. Principal component analysis and multivariate correlations indicated geochemical characteristics of the area as the major control of metal concentrations and spatial variability. Organic matter and clay contents also played a significant role in metal distributions. Assessment of land-use practices upstream of the sampling locations was used to trace potential anthropogenic sources of metal enrichments, where highest levels were found in areas close to urban centres and agricultural activities. The study provides baseline data for future monitoring programs, and highlights the need for more comprehensive analysis involving a wider spatio-temporal scale and ecotoxicological risk assessment.

International Journal of Environmental Analytical Chemistry, 2013

Tanzania Journal of Science, 2018

The suitability of raw Malangali kaolin (RMK) clay for the removal of cadmium and cobalt ions fro... more The suitability of raw Malangali kaolin (RMK) clay for the removal of cadmium and cobalt ions from water was investigated using a batch technique whereas the characterization of adsorbent material was performed by XRD, XRF, ATR-FTIR and N 2 physisorption techniques. Various experimental parameters were tested for the effectiveness of RMK in removing heavy metals whereby quantitative determination of both Cd 2+ and Co 2+ ions has shown that, the factors such as adsorbent particle size, solution pH, contact time, adsorbent dose as well as initial metal ion concentration had significant effects on the adsorption processes. The equilibrium data described by Langmuir and Freundlich isotherms were used in this study. It was shown that Langmuir isotherm displayed a better fitting model than that of Freundlich because of its higher correlation coefficient, thus, demonstrating the occurrence of monolayer coverage of Cd 2+ and Co 2+ ions on the surface of RMK clay. The results obtained in thi...

Kaolin and quartz from Pugu and feldspar from Morogoro were used to produce feldspathic dental po... more Kaolin and quartz from Pugu and feldspar from Morogoro were used to produce feldspathic dental porcelain bodies. Mineralogical results from XRD revealed the presence of kaolinite, illite, microcline and clinochlore in the kaolin samples; albite, microcline, sanidine in the feldspar samples and only silica in the quartz samples. The chemical results studies by XRF revealed the presence of in varying proportions. Particle size distribution of all the raw materials were determined and particles &lt;63 μm were used for preparation of batches. The batches of different compositions with ranges: quartz (12-22%), feldspar (75-88%) and kaolin (3-5%) were fired at 1100, 1200 and 1250 o C, and the developed properties were tested. The physico-mechanical properties studied exhibited volumetric shrinkage between 2 and 55.17%, open porosity between 6.67 and 40.00%, water of absorption between 7.1 and 40%, bulk densty of 1.43 – 5.68 g/cm 3 , and compressive strength at 0.13-32.25 MPa. The optimal firing temperature for the best results was found to be 1250 o C. The results obtained indicate that kaolin and quartz from Pugu and feldspar from Morogoro are potential raw materials for the production of dental porcelain.