Examining Potential Spatial Planning Influences on Nitrate Contamination in Urban Agriculture: A Cross-Sectional Study in Dar es Salaam, Tanzania

In existing scientific literature, numerous investigations have elucidated the correlation between nitrate contamination within groundwater and the corresponding agricultural zones above them. However, a discernible dearth of studies exists concerning the association between these agricultural domains and the resultant products derived therefrom. This cross-sectional study, conducted between 2021 and 2023 in Dar es Salaam, Tanzania, investigated the toxicity of vegetables from urban agriculture (UA) concerning nitrate contamination. Recognizing that excess nitrates pose carcinogenic risks and noting a lack of studies linking urban spatial morphology to UA nitrate contamination, geolocated samples were collected from specific planting locations. Nitrate levels were assessed using the Greentest® device, and a regression statistical model was employed for analysis, incorporating spatial and farm characteristics alongside GIS for visualization. The findings revealed that Dar es Salaam exhibits an institutionally planned UA and a very low vegetable contamination. Furthermore, a positive correlation emerged between nitrate levels and farm plot surface—the larger the area, the greater the contamination. The most contaminated vegetables are found on the outskirts of the city and on land that can be cultivated and built on, and these vegetables grow more on plants outside the ground than those in tuber form or lying on the ground. This study highlights the positive correlation between urban spatial characteristics and UA product toxicity. It underscores the inadequacy of current UA practices in African cities as a standalone solution to food insecurity, emphasizing the need for integrated urban planning and architecture in UA. The results suggest that careful consideration of spatial planning can serve as a crucial lever in mitigating nitrate contamination and addressing public health inequalities associated with UA in Dar es Salaam.