The sources and chemical content of edible soil sticks sold in markets in Tanzania: a cross-sectional analytical study.

Geophagy, or eating soil, is common in various countries including Tanzania. Studies have reported on the levels of different chemicals in consumed soil, some of which can be harmful to the health of individuals practicing geophagy. Dried soil sticks for eating, referred to as pemba, are commercially available in many markets in sub-Saharan Africa, but few studies have established the sources of the soils. The purpose of the current study was to: (1) systematically document the sources of the soils used in pemba commonly sold in regional markets throughout Tanzania using a global positioning system (GPS) to establish the supply chain flow of pemba to markets, and (2) assess the chemical element content of the soil sources for both water-extractable chemical element (WEC) and total chemical element (TC) contents. Surveys were conducted at regional markets across mainland Tanzania to identify the sources of soils commonly used in commercially available soil sticks. Then, soil samples were collected from identified sources in 12 regions across Tanzania and analyzed for WEC and TC content using an inductively coupled plasma mass spectrometry laboratory technique. Mining of the pemba soil was localized in 12 regions. Analysis of the supply chain flow revealed a well-established distribution network that ensured transportation and marketing of the soil sticks to regions throughout the country. WEC and TC of essential and trace elements (Ca, Fe, K, Mg, Na, Mn, Co, Cr, V, Mo, Cu, and Zn) and toxic elements (Al, As, Ba, Cd, Ni, and Pb) were detected at varying concentrations. Most of the trace and toxic elements were above the normal range, based on the oral maximum tolerable limits designated by the World Health Organization and US Agency for Toxic Substance and Disease Registry. This is the first study in Tanzania to document and examine the source soil locations for commercially available soil sticks at the macroscale across the entire country. The findings suggest that geophagy could be a significant exposure pathway for toxic elements.