Browsing by Author "Mwalongo, Dennis"

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Influence of phosphate fertilizers on the radioactivity of agricultural soils and tobacco plants in Kenya, Tanzania, and Uganda
(Springer Berlin Heidelberg, 2023-06-20) Mwalongo, Dennis; Haneklaus, Nils; Carvalho, Fernando; Lisuma, Jacob; Kivevele, Thomas; Mtei, Kelvin
Three brands of NPK fertilizers that contain variable concentrations of natural radioactivity are commonly used in tobacco plantations in Kenya, Tanzania, and Uganda. Tobacco plants are known for hyper-accumulation of natural radionuclides, particularly 238U. This study investigated if the elevated radioactivity in phosphate fertilizers could enhance radioactivity in soils and tobacco plant leaves. The 232Th, 238U, and 40K radionuclide levels in NPK-fertilized soils and tobacco leaves were measured using gamma-ray spectroscopy. The research included a one-year reference experiment with tobacco growing in plots, a ten-year semi-controlled experiment in well-managed tobacco farms, and a field survey of radioactivity in soils and tobacco leaves at three traditional tobacco fields in Migori (Kenya), Urambo (Tanzania), and Kanungu (Uganda). The findings demonstrated that soils and tobacco leaves exposed to NPK fertilizers with increased radioactivity had activity concentrations of 232 Th, 238 U, and 40 K that were considerably higher (at all sites) than in the control samples (with no use of NPK fertilizers). As the continued application of NPK fertilizers raises concentrations of 232Th, 238U, and 40K in agricultural soils, the study assessed radiological risks for humans from exposure to agricultural soils enriched with phosphate fertilizers, and it was found to be below the exposure limit of 1 mSvy-1 suggested by the International Commission on Radiological Protection (ICRP). However, tobacco consumers, both by snuffing and smoking, may face significant radiological risks, as the snuffing and smoking resulted in effective doses that were 2.41 to 6.53 and 1.14 to 2.45 times greater than the average yearly dose that the general public receives from inhalation of natural radionuclides (United Nations Scientific Committee on Atomic Radiations estimates). Furthermore, the results indicate that the lifetime excess cancer risk for tobacco snuffers and smokers ranged from 5 × 10 -5 to 24.48 × 10 -3 and 2.0 × 10 -5 to 9.18 × 10 -3 , respectively. The influence of phosphorus-derived fertilizer containing relatively high natural radioactivity, potential human radiation exposure, and radiological risk due to gamma radionuclides is estimated and discussed. The results reveal that applying phosphate fertilizers enhances natural radioactivity in soil and is subsequently influenced by soil to tobacco plant uptake. Therefore, the study recommends that countries use fertilizers with lower radionuclide content to conserve soil quality and reduce gamma-emitting radionuclides in tobacco plants.
Investigation of uranium derived from phosphate fertilizers on plants uptakes and bacterial diversity in selected agricultural soils of east africa
(NM-AIST, 2024-08) Mwalongo, Dennis
Different types of phosphate fertilizers (PFs) used in agriculture to increase soil fertility contain uranium (U) as an accompanying element. Uranium is both toxic and slightly radioactive. This study investigated the concentrations of U in phosphate rocks (PRs) and PFs used in growing tobacco (Nicotiana tabacum L.) and maize (Zea Mays L) plants from Burundi, Kenya, Rwanda, Tanzania, and Uganda. The results showed that the concentrations of U in phosphates from Burundi, Kenya, Tanzania and Uganda were statistically significant (P ≤ 0.01). The lowest U concentration was 10.7 mg kg−1 found at the Mrima Hill deposit in Kenya and the highest was 631.6 mg kg−1 found at the Matongo deposit in Burundi. Uranium concentrations for local and imported PFs was also statistically significant (P ≤ 0.01). Uranium concentration from PFs ranged from 107.88 ± 9.60 and 281.57 ± 15.82 mg kg−1 . The study also assessed the influence of U from PFs on the radioactivity of agricultural soils and uptake by tobacco plants. The results showed that applications of PFs in agricultural soils increased radioactivity in agricultural soil and tobacco crops. Tobacco smoking and snuffing behaviors resulted in an annual effective dose that was 2.41-6.53 and 1.14-2.45 times greater than annual recommended effective doses for snuffers and smokers. This work also investigated the influence of fertilizer derived U on maize plant uptake and bacterial diversity in soil after application of fertilizers with varying U concentrations. The pilot field experiments showed that application of PFs with different U concentrations influenced bacteria abundance and diversity in maize crops. Applications of Nafaka plus (NP) (3.93 mg kg-1 ) and Minjingu Powder (MP) (3.06 mg kg-1 ) PFs in soil increased bacteria abundance and diversity. Some bacteria were abundant on NP treated soil (high U content) because of their ability to tolerate higher U concentrations. Uptake from soil to crop for maize after applications of PFs of varying U concentrations was investigated by amending soil with Eucalyptus globulus ssp maideii bark and kaolin clay. The soil amendments in reduced U uptake from soil to plant in pot experiments. It is believed that the reduced U uptake is associated with eucalyptus globulus ssp maideni carboxyl groups that can reduce mobile hexa-uranyl ions to immobile tetra uranyl ions that can be absorbed by the kaolin clay. The study recommends further work in understanding the mechanisms of Eucalyptus ssp maidenii bark powder and kaolin U uptake reduction in soil complex matrix.
Rare earth elements and uranium in Minjingu phosphate fertilizer products: Plant food for thought
(ELSEVIER, 2024-08-01) Haneklaus, Nils; Mwalongo, Dennis; Lisuma, Jacob; Amasi, Aloyce; Mwimanzi, Jerome; Bituh, Tomislav; Ćirić, Jelena; Nowak, Jakub; Ryszko, Urszula; Rusek, Piotr; Maged, Ali; Bilal, Essaid; Bellefqih, Hajar; Qamouche, Khaoula; Brahim, Jamal; Beniazza, Redouane; Mazouz, Hamid; Merwe, Elizabet; Truter, Wayne; Kyomuhimbo, Hilda; Brink, Hendrik; Steiner, Gerald; Bertau, Martin; Soni, Raghav; Patwardhan, Ashwin; Ghosh, Pushpito; Kivevele, Thomas; Mtei, Kelvin; Wacławek, Stanisław
Minjingu phosphate ore is Tanzania's sole domestic supply of phosphorus (P). The ore contains medium to high concentrations of naturally occurring P2O5 (20–35 %) and relevant concentrations of uranium and rare earth elements (REEs) are also suspected to be present. Currently, neither uranium nor REEs are recovered. They either end up in mine tailings or are spread across agricultural soils with fertilizer products. This work provides a first systematic review of the uranium and REE concentrations that can be expected in the different layers of Minjingu phosphate ore, the way the ore is presently processed, as well as a discussion on alternative processing pathways with uranium/REE recovery. The study analyzed ten distinct Minjingu phosphate ore layers, four mine tailings, and five intermediate and final mineral fertilizer products from the Minjingu mine and processing plant located in northern Tanzania. The results confirm that the uranium concentrations and to a lesser degree, the REE concentrations are indeed elevated if compared to concentrations in other phosphate ores. The study does not identify a significant risk resulting from this. The development of techno-economic solutions for more comprehensive utilization of Minjingu ore is, however, strongly encouraged and suggestions on such processes are provided.
Uranium Dissemination with Phosphate Fertilizers Globally: A Systematic Review with Focus on East Africa
(MDPI, 2024-01-09) Mwalongo, Dennis; Haneklaus, Nils; Lisuma, Jacob; Mpumi, Nelson; Amasi, Aloyce; Mwimanzi, Jerome; Chuma, Furaha; Kivevele, Thomas; Mtei, Kelvin
Growing concern has been expressed about uranium (U) accumulation in agricultural soils caused by the long-term application of mineral fertilizers. More than 80% of naturally occurring U transfers from phosphate rock (PR), the raw material used in mineral fertilizer production, to phosphorus (P) fertilizers. These fertilizers are then distributed on agricultural soils, where the U could accumulate over time and become a risk to the environment. The objective of this work was to review the reported content of U in P fertilizers, its potential dispersion in soils, and its uptake by plants in different countries in the world as reported in the literature. The articles for this systematic review were selected from the Scopus database published between 2003 and 2022. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) protocol were used. A total of 54 articles were assessed based on the standard inclusion and exclusion criteria. U concentrations in P fertilizers, agricultural soil dissemination, and plant uptake for available data were obtained and assessed. In order to compare a set of related data from the collected articles, box and whisker plots showing the distribution of U in P fertilizers are presented by region. The results from the reviewed articles show that the U concentrations in P fertilizer were in the range of 0.1–653 mg kg−1. Interestingly, Minjingu P fertilizers from Tanzania, which are used in six East African countries, showed the highest U concentrations (159 to 653 mg kg−1, average 390 mg kg−1). The reported U concentrations for these fertilizers are, in fact, comparable to those of conventional low-grade uranium deposits mined in Namibia and elsewhere. Additionally, approximately 96% of the reviewed articles indicate that fertilized soil has higher U concentrations than non-fertilized soils, hinting at a measurable effect of mineral fertilizer use. The review recommends U extraction during mineral fertilizer production so that potential environmental risks can be reduced and U resources that would otherwise be lost can be recovered and used to substitute conventional U mining elsewhere.
Uranium in phosphate rocks and mineral fertilizers applied to agricultural soils in East Africa
(Springer Link, 2022-12-11) Mwalongo, Dennis; Haneklaus, Nils; Lisuma, Jacob; Kivevele, Thomas; Mtei, Kelvin
Phosphate rock, pre-concentrated phosphate ore, is the primary raw material for the production of mineral phosphate fertilizer. Phosphate rock is among the fifth most mined materials on earth, and it is also mined and processed to fertilizers in East Africa. Phosphate ore can contain relevant heavy metal impurities such as toxic cadmium and radiotoxic uranium. Prolonged use of phosphate rock powder as a fertilizer and application of mineral fertilizers derived from phosphate rock on agricultural soils can lead to an accumulation of heavy metals that can then pose an environmental risk. This work assesses the uranium concentrations in four major phosphate rocks originating from East Africa and four mineral phosphate fertilizers commonly used in the region. The concentration measurements were performed using energy-dispersive X-ray fluorescence spectrometry. The results showed that the uranium concentration in phosphate rock ranged from as low as 10.7 mg kg−1 (Mrima Hill deposit, Kenya) to as high as 631.6 mg kg−1 (Matongo deposit, Burundi), while the concentrations in phosphate fertilizers ranged from 107.9 for an imported fertilizer to 281.0 mg kg−1 for a local fertilizer produced from Minjingu phosphate rock in Tanzania. In this context, it is noteworthy that the naturally occurring concentration of uranium in the earth crust is between 1.4 and 2.7 mg kg−1 and uranium mines in Namibia commercially process ores with uranium concentrations as low as 100–400 mg kg−1. This study thus confirms that East African phosphate rock, and as a result the phosphate fertilizer produced from it can contain relatively high uranium concentrations. Options to recover this uranium are discussed, and it is recommended that public–private partnerships are established that could develop economically competitive technologies to recover uranium during phosphate rock processing at the deposits with the highest uranium concentrations.