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Background: Podoconiosis, non-filarial elephantiasis, is a non-infectious disease found in tropical regions such as Ethiopia, localized in highland areas with volcanic soils cultivated by barefoot subsistence farmers. It is thought that soil particles can pass through the soles of the feet and taken up by the lymphatic system, leading to the characteristic chronic oedema of the lower legs that becomes disfiguring and disabling over time. Methods: The close association of the disease with volcanic soils led us to investigate the characteristics of soil samples in an endemic area in Ethiopia to identify the potential causal constituents. We used the in vitro haemolysis assay and compared haemolytic activity (HA) with soil samples collected in a non-endemic region of the same area in Ethiopia. We included soil samples that had been previously characterized, in addition we present other data describing the characteristics of the soil and include pure phase mineral standards as comparisons. Results: The bulk chemical composition of the soils were statistically significantly different between the podoconiosis-endemic and non-endemic areas, with the exception of CaO and Cr. Likewise, the soil mineralogy was statistically significant for iron oxide, feldspars, mica and chlorite. Smectite and kaolinite clays were widely present and elicited a strong HA, as did quartz, in comparison to other mineral phases tested, although no strong difference was found in HA between soils from the two areas. The relationship was further investigated with principle component analysis (PCA), which showed that a combination of an increase in Y, Zr and Al2O3, and a concurrent increase Fe2O3, TiO2, MnO and Ba in the soils increased HA. Conclusion: The mineralogy and chemistry of the soils influenced the HA, although the interplay between the components is complex. Further research should consider the variable biopersistance, hygroscopicity and hardness of the minerals and further characterize the nano-scale particles. [ABSTRACT FROM AUTHOR]

Many Plio-Pleistocene lake basins in eastern Africa associated with early hominins contained waters that were alkaline, enriched in silica due to weathering of volcaniclastics and hydrothermal activity, and evaporatively concentrated. Such conditions are favorable for the formation of silicate minerals precipitated from solution, or neoformed through alteration of detrital parent material. The most common authigenic silicates thus produced include the zeolite family of minerals and a number of clay minerals, particularly 2:1 clays of the illite and smectite families. Particularly in the absence of well-preserved paleoecological records, these minerals may provide important evidence of paleoenvironmental conditions. Stratigraphic variations in lacustrine authigenic silicates can give an indication of changes in cation proportions in paleolake waters over time. For example, in Pliocene deposits of the Baringo Basin, Kenya, fluctuations between phillipsite (K-rich) and analcime (Na-rich) facies suggest changing salinity levels because more saline waters have greater Na/K ratios. In one interval in the Chemeron Formation, analcimic muds are interbedded with freshwater diatomites, suggesting a link between high amplitude of environmental variability and peak orbital eccentricity ~2.6 Ma. In the Lake Magadi basin in southern Kenya, marked increases in zeolite abundance and greater dominance of Na-rich phases indicate hydrological closure and enhanced evaporative concentration suggesting a long-term increase in aridity accelerating ~380 ka. In short cores of the Chew Bahir basin of southern Ethiopia, greater analcime abundances and incipient low-temperature illitization of smectite (indicating greater K uptake in more saline waters) are associated with Late Pleistocene arid episodes such as the Younger Dryas. In the Olduvai Basin of northern Tanzania, fluctuations in the Al/Mg ratio of authigenic clay minerals record changes in salinity, as greater Mg is incorporated into clays during saline episodes. These clay mineral changes are accompanied by shifts in the oxygen isotope composition of structural oxygen, indicating equilibrium with variably saline waters. Both elemental and isotopic changes fluctuate over precessional timescales, suggesting orbital control of hydrologic balance ~1.8 Ma.Authigenic silicates can be an important source of paleolimnological data, particularly over the range of salinities between the relatively freshwater conditions under which biological proxies readily accumulate, and the extreme salinities associated with evaporites such as halite and trona (Na-carbonate). [ABSTRACT FROM AUTHOR]