Microplastics (MPs) are ‘emerging’ contaminants that threatens freshwaters and may have negative impact on the aquatic organisms. However, despite plastic waste being a major source of these contaminants, there is no data available on the plastic and microplastics pollution in Botswana’s freshwater systems even though it is slowly becoming an eyesore. Therefore, the role of this study was to assess the distribution of microplastics in surface water, the amount of MPs ingested by freshwater species (Tilapia sparrmanii, Oreochromis niloticus, Coregonus kiyi, Coptodon rendalli and Corbicula fluminea) as well as characterize MPs based on their morphologies. This study was done in three study areas, the Okavango Delta which is the largest inland wetland hosting wildlife, tourism, and supporting the socio-economic lifestyle of inhabitants, the Gaborone dam and the Dikgatlhong dam as the two largest major reservoir of freshwater in the country. Samples were strategically collected from the Okavango delta, Gaborone dam and Dikgatlhong dam, such that they represent the whole study areas. The samples were analyzed for microplastic contents by wet peroxide oxidation, potassium hydroxide for aqua fauna, density separation, extraction, and visual identification with microscope. Results showed that the weight of MPs for surface water samples from Okavango delta were the lowest between study location, varying from 138.18 to 381.67 µg m−3 and abundance of 10 to 23 particles L−1, with significant difference observed between sampling sites in both variables. Microplastics recovered from the Tilapia sparrmanii of the delta had MPs of 0.3 to 0.6 count per site and mostly present in intestines>gills >stomach. Fibers were mostly discovered in water while fragments were dominant in fish samples with translucent color dominant in both sample matrices. The MPs in size 1-2 mm and 2-3 mm were prevailing both in water and fish samples. In Gaborone dam, the abundance and weight of MPs were slightly higher than those in Okavango delta and Dikgatlhong dam. Surface water had MPs ranging from 36 to 76 particles L−1 while their weight varied from 760 to 1943 µg m-3 . The significantly high abundances were found in deep areas (S3 and S6) located near the boundary wall of the dam than in shallow areas (S1 and S5). The MPs were also discovered in fishes (Oreochromis niloticus and Coregonus kiyi) samples which varied from 1.0 to 3.5 count per sampling site, and Oreochromis niloticus ingested more microplastics than the other fish species. The dominant forms of MPs in Gaborone dam are the translucent and red colors in the form of fibers and fragments, in size ranges of 1-2 mm and 2-3mm. In Dikgatlhong dam, the weight of MPs varied from 400 to 1500 µg m-3 while abundance ranged from 16 to 46 particles L−1, with S5 (dam tower, towards the boundary wall) having the highest in both variables for surface water. The highest counted MPs in Coptodon rendalli fish samples differed from 0.3 to 2.2 count per sampling site. The dominant forms of MPs are translucent and small sized (1-2 mm) in fish while fibers were the most common shape discovered in surface water. Overall, the findings of this study clearly indicate that geographical location, population density, hydrodynamics and economic activity have contributed significantly to the abundance of MPs within freshwater systems. In this case, Gaborone dam which is about 11km away from the capital city had high levels of microplastics recovered than in Okavango delta and Dikgatlhong dam. These two study areas are less exposed to more human activities like the Gaborone dam hence they had low microplastic levels. The Okavango delta is 930 km away from the capital city in north-west direction while Dikgatlhong dam is 457 km in north-east direction. Further, the population around the two dams (Okavango delta- 130 000, Dikgatlhong dam is closest to Robelela village- 924) are much smaller compared to the numbers in the proximity of Gaborone dam (more than 500 000 people in the city and surrounding). With these differences in the population density, a significant variation in terms of microplastics generated and reaching the freshwater system is expected to be high as proven by the results. In addition, the hydrodynamics experienced as the delta has inflow from the highlands of Angola, continuous flow in most of the years and it empties into Lake Ngami. Meanwhile, the Dikgatlhong dam is at the downstream of Shashe and Tati Rivers but its overflow drifts into the Ramokgwebana River through Shashe River into Limpopo River and empties into Indian Ocean. Therefore, this could be attributing to the low microplastic accumulation in these areas. The data has shown that indeed there are microplastics present in major water bodies but their abundance are lower than those in other areas of Africa. Nonetheless, this baseline information will provide insights on the loads of microplastics in surface water and the quantities ingested by fishes in the Okavango delta, Gaborone dam and Dikgatlhong dam, hence the need for monitoring. In addition, in the dam, accumulation of MPs in the downstream implied that the dams may serve as sink f or the MPs. The data will guide in developing evidence based and effective policies that address plastic and microplastic pollution in freshwater systems.

Thesis (MSc in Environmental Science)---Botswana International University of Science and Technology, 2023