A review of heavy metals research in Tanzania (2000–2024)

Heavy metal contamination is an increasing environmental and public health concern in Tanzania due to rapid urbanization, mining, industrialization, and intensified agriculture. This scoping review synthesizes 177 peer-reviewed studies published between 2000 and 2024 on heavy metals in environmental, food, cosmetic, medicinal, aquatic, and human matrices in Tanzania. The findings show a steady rise in research, with peak publications between 2015 and 2019. Atomic absorption spectroscopy was the most commonly employed analytical method, followed by ICP-based techniques, XRF, and other spectroscopic approaches. The most studied heavy metals are Pb, Cd, Cu, Zn, Cr, Hg, and As, while Co, Ni, Mn, Al, Ag, and V appear occasionally, mainly in sediments or biota, and trace elements such as Th, U, and other rare elements are detected rarely, often near mining or uranium deposits. Across environmental matrices, reported concentration ranges vary widely among studies, with particularly high levels in sediments and soils near mining and industrial areas, where some individual studies reported concentrations exceeding international guideline values. Elevated concentrations were also observed in food, beverages, cosmetics, medicinal plants, water, and aquatic biota, highlighting potential exposure pathways through dietary, dermal, and environmental contact. However, these findings are derived from heterogeneous studies and should not be interpreted as nationally representative quantitative estimates. Patterns of bioaccumulation reported in several individual studies, particularly in plants and aquatic organisms, further underscore ecological and human health concerns; however, this review summarizes reported observations rather than performing a quantitative meta-analysis of bioaccumulation factors. This review is nationally and internationally relevant, given Tanzania’s extensive mining activities and long Indian Ocean coastline, linking environmental contamination to broader regional and global ecosystems. The study identifies key research gaps, including limited monitoring of highly toxic elements, underrepresented marine ecosystems, and uneven geographic distribution of studies across the country. The study also recommends the use of advanced analytical techniques, such as ICP-MS, for analyzing trace and ultra-trace metals. The findings provide a critical reference for environmental monitoring, public health interventions, and sustainable management of heavy metal pollution in Tanzania.