Muni Repository (MR)
This repository contains open access publications of Muni University Library.
Objectives:
- To digitally collect, preserve and provide electronic access to scholarly works and research output of Muni University.
- Increase the visibility and impact of our research, making it easy for researchers, students, policymakers and journalists to reference, replicate, and re-use the work.
- Issue permanent, unique and trustworthy identifiers when creating URLs to access the resource without concern that the location of the resource may change.
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- Contact the library through email: libsupport@muni.ac.ug
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Recent Submissions
Development of a green sorbent-based microextraction technique for the determination of trace level aflatoxins in traditionally processed cassava products
(Muni University, 2025-10-14) Yanduru, Mercy
Aflatoxins are a class of naturally occurring mycotoxins that pose a serious threat to food safety and public health due to their potent carcinogenic, mutagenic, and hepatotoxic effects. The detection of aflatoxins in complex food matrices remains challenging due to matrix interferences and the labor-intensive nature of conventional sample preparation techniques. This study aimed at development of a green, sensitive, and efficient analytical method for the quantification of aflatoxins in food samples, employing porous membrane-protected micro-solid phase extraction (µ-SPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). A series of eco-friendly sorbent materials were synthesized from water hyacinth biomass through chemical activation using eggshell-derived calcium carbonate and phosphoric acid. The resulting materials were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM), and subsequently applied in the micro-solid phase extraction of aflatoxins for trace-level determination. The Taguchi orthogonal array design was employed to optimize key extraction parameters including pH, extraction time, sorbent dosage, ionic strength, and desorption time that influence the extraction efficiency of aflatoxins. Under optimized conditions, the developed method exhibited a linear response in the concentration range of 1–50 ng/mL, with a determination coefficient (R²) between 0.9994 and 0.9999. The method also demonstrated good recovery efficiencies ranging from 80.00% to 92.18%. The method achieved limits of detection (LODs) of 0.08, 0.06, 0.09, and 0.07 µg/kg, and limits of quantification (LOQs) of 0.25, 0.20, 0.30, and 0.22 µg/kg for aflatoxins B₁, B₂, G₁, and G₂, respectively. Good precision was demonstrated, with intra-day and inter-day relative standard deviation (RSD) values ranging from 4.10% to 5.45%. The developed method was successfully applied to the trace-level determination of aflatoxins in 30 cassava flour samples collected from Arua City, Uganda. The analysis revealed that 3.30 % of the preconcentrated samples contained aflatoxin concentrations exceeding the Uganda National Bureau of Standards (UNBS) permissible limit of 10 µg/kg. Aflatoxin B₁ concentrations in the samples were found to be below the maximum allowable limits established by both the European Union (2 µg/kg) and the Uganda National Bureau of Standards (5 µg/kg).This study has established a sensitive and efficient micro-solid phase extraction method for trace level aflatoxins detection in cassava products, indicating contamination levels above safety limits and highlighting the necessity for continuous food safety monitoring.
The influence of Allee effects on optimal harvesting of Nile perch, Nile tilapia, and small pelagic fish in Lake Victoria
(Muni University, 2025-11-10) Onekgiu, George
In this dissertation, models for finding the optimal controls of harvesting Nile perch, Nile tilapia, and small pelagic fish within a food chain formulated with and without the Allee effect were presented. The models were based on reaction-diffusion-advection PDEs subject to Robin boundary conditions. The version without the Allee effect employed logistic growth dynamics, while the one incorporating the Allee effect utilised an Alleetype growth function.
The optimality system, comprising the state equations, adjoint equations, and optimality conditions, was derived using the formal Lagrange method. An FBSM based on explicit finite difference schemes was employed to solve the state, adjoint, and control equations in the two models.
In the model without the Allee effect, optimal controls that allowed for continuous opti mal harvesting were determined, with higher yields observed toward the end of the period when fish populations had grown. The results also indicated that diffusion and advection coefficients significantly influenced fish distribution and optimal control of harvesting: low diffusion coefficients promoted fish aggregation and higher economic returns, whereas high advection coefficients dispersed fish and reduced returns. In scenarios where the Allee effect was considered, the optimal controls obtained required no harvesting to prevent population collapse when the initial populations were low (below the Allee threshold). At moderate to high initial biomasses of the three fish species (above the Allee threshold), the optimal controls obtained permitted continuous optimal harvesting across the entire domain and throughout the simulation period. This emphasises the pivotal role of the Allee effect in defining population thresholds that ensure an optimal and sustainable harvesting.
It is recommended that, without the Allee effect, continuous optimal harvesting that targets areas of high population aggregation to maximise yield and economic returns, should be allowed. With the Allee effect, harvesting should cease when populations are below the threshold to allow recovery, while populations above the threshold can be harvested sustainably at optimal rates.
Optimal harvesting of nile perch, nile tilapia, and small pelagic fish populations on lake Albert, Uganda
(Muni University, 2025-11-10) Lubangakene, Geoffrey
In this dissertation, an optimal fish harvesting problem for harvesting small pelagic fish, Nile tilapia, and Nile perch within a food chain, modelled with constant yield and constant effort harvesting, is considered. In particular, the optimal harvesting strategy that ensures both economic benefits and ecological sustainability of fish species was determined. The models were based on nonlinear ordinary differential equations that account for logistic growth, harvest, and species interactions. The problem is motivated by the need to address the concern of decreasing fish populations, resulting from overfishing and unsustainable harvesting practices.
The optimality system, comprising the state equations, adjoint equations, and optimality condition, was derived using Pontryagin’s maximum principle. A forward-backward sweep method based on fourth-order Runge–Kutta schemes was employed to solve the optimality system. Peano’s existence theorem and Lipschitz uniqueness theorem were used to prove the existence and uniqueness, respectively, of solutions to the state equations.
Numerical results show that for constant yield harvesting, harvest rates remained constant throughout the simulation period, with the highest harvest rate recorded for Nile perch and the lowest for Nile tilapia. In contrast, under constant effort harvesting, the highest harvest rate is again recorded for Nile perch, while the lowest is for small pelagic fish. Constant effort harvesting strategies allow fish populations to adjust dynamically and support ecological resilience. Whereas, constant yield harvesting risks over exploitation with any slight increase in harvest rates above the optimal level.
The study recommends optimal harvesting strategies for Lake Albert, Uganda, as they promote ecological sustainability by preventing both over exploitation and underutilisation of resources. Fisheries managers should maintain fish populations at a moderate level by enforcing zero harvests when fish biomass is low to ensure faster recovery and reduce the risk of species extinction.
Impact of open waste dumping at Ewuata site on the water quality of Adumini stream, Arua city
(Muni University, 2025-11-10) Egabile, Alfred
Open waste dumping sites, where waste is deposited without proper treatment, are major sources of land, air and water pollution. One of the most serious effects of open dumpsites is water pollution, as waste leachate seeps in to nearby open water bodies, posing risks to human health, aquatic life. The open waste dumping site at Ewuata in Arua City, is located at only approximately 70 meters from Adumini Stream, and it is likely to pose significant environmental risks due poor waste management practices. This study evaluated the impact of open waste dumping site at Ewuata on the water quality of Adumini stream, with emphasis on physicochemical parameters and macrozoobenthic invertebrates as bio indicators, so as to support Sustainable Development Goal 6 for clean water and sanitation. The objectives of this study were to characterize solid wastes, analyze leachate and stream physicochemical parameters (pH, TDS, EC, DO, COD, BOD, Pb, Cr and Cd), and assess biological water quality using the Biological Monitoring Working Party (BMWP) score and Average Score Per Taxon (ASPT). An experimental design was employed. For characterization of solid wastes, 200 kg of solid wastesfrom 10 trucks were randomly sampled, sorted into categories (organic, plastics, metals, glass, fabrics) per ASTM (1998) standards. The physical parameters were analyzed on site whereas, COD, BOD, and heavy metals (Cd, Pb, Cr) were analyzed in the laboratory. Stream water samples were collected from three sites upstream (S1), near-dumpsite (S2) and downstream (S3). Macrozoobenthic invertebrates were sampled using the kick sampling method (ISO, 2012), and were identified to family level, and scored using BMWP and ASPT. Data were analyzed using ANOVA, followed by Tukey’s post hoc and Pearson’s correlation at a 95% confidence interval with SPSS version 20. Results showed that, solid waste was predominantly organic, followed by plastics, with minimal glass and metals. Leachate showed high pollution as parameters such as EC, COD, BOD Cd exceeded WHO standards. Water quality at the S1, S2 and S3 varied significantly, Pb and Cr were below detection limits. BMWP scores indicated good water quality at S1 (62), poor water quality at S2 (12) and S3 (25), with ASPT values of 5.6, 3, and 4.2, respectively, reflecting pollution-tolerant taxa dominance at S2. The leachate had significantly impacted the water quality, posing threat to aquatic ecosystems and community health. There is need for increased solid waste recycling and sorting before dumping, implementation controlled landfills for enhanced waste management practices and need to carry out detailed study on the seasonal variation of the physicochemical parameters of the stream
Assessment of microplastics in selected rivers, fish, and wastewater from car wash bays in Arua city
(Muni University, 2025-10-14) Draku, Sydney Emmanuel
Microplastics (MPs) are increasingly recognised as critical pollutants in freshwater ecosystems, yet data from sub-Saharan urban settings remain limited. This study investigated the occurrence, distribution, and polymer composition of MPs in car wash effluents, receiving river water, and fish in Arua City, Uganda. Five (5) car wash bays and two rivers (Asa and Enyau) were purposively selected. Ten (10) litres of river water, one (1) litre of wastewater, and twenty (20) fish samples were collected and processed via filtration (300–0.45 μm), oxidative digestion, and polymer identification using micro– Fourier Transform Infrared Spectroscopy (μFTIR). One-way ANOVA results revealed significantly higher MP concentrations in bays employing jet washing and exhibiting prolonged wastewater retention (F = 133.98, p < 0.05). Fibres and fragments comprised >80% of particles, with dominant polymers being polyethylene (PE), polypropylene (PP), and ethylene-based copolymer (EPC). Mean MP levels in both rivers were observed to be in the same range, with spatial heterogeneity linked to local anthropogenic activity. Fish from River Asa showed the highest MP loads, positively correlated with body length (r = 0.714, p = 0.000). Findings position car wash facilities as major sources of microplastics, calling for targeted regulatory and infrastructural interventions, alongside public awareness campaigns and further research to mitigate microplastic pollution in Arua City.