Diversity and quantity of macro-and microplastics in irrigation farms sourcing water from an urban river: a case of Arusha Tanzania

Increased concentration of plastics in urban rivers and agricultural farms causes degradation of river system functionality and reduces the productivity of agricultural soils, respectively. This study assessed the quantity and types of macro-and microplastics found in dependent smallholder irrigation farms downstream of Arusha city in Tanzania. The microplastics' concentration from the sites was visualized using dissecting microscope 40X, enumerated and categorized based on the shape, color, and sizes for soil samples. Then the suspected materials’ spectral were determined using the Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR). Afterwards, the confirmations and identifications of the polymers' types from spectral were confirmed using SiMPle Software. The average microplastic from the water column was 0.57 ± 0.27 items L-1 , sediment 0.17± 0.07 items g-1, while in the irrigation farms ranged from 102 to 728 items with a mean of 0.69 ± 0.35 items g-1 . However, no international standards have been developed to ascertain the pollution level, but the reported values are unsafe to the environment. Other studies conducted in similar conditions reported mean values within the range of values found in this study and more. Polyethylene was the dominating type of macroplastics evaluated from riverbanks and irrigation farms with a frequency of occurrence 100 %, while polystyrene was abundant in all microplastics samples. Farms adjacent to the irrigation canal had a greater number of microplastics and macroplastics. Thus this study reveals urban rivers as the primary sources of plastics pollution in the irrigation farms situated in flood-prone zones.