Exposure and bioavailability of Cerium through the ingestion of soil (Uganda)

The UK Department For International Development (DFID) Technical Development and Research (TDR) programme funded a three-year project between 1995 and 1998 entitled “Cerium & Endomyocardial Fibrosis in Tropical Terrains” (Project R6228). The presence of elevated levels of dietary Ce, and deficient levels of dietary Mg in southern India have been assigned as potential environmental cofactors in the aetiology of Endomyocardial Fibrosis, which is also endemic in certain areas of Uganda. One of the aims of the project is to assess the relative importance of various exposure scenarios for the Ugandan population to Ce to define protective measures if required. Initial assessments of dietary intakes of Ce in Ugandan soils and foodstuffs have indicated that soils are a significant exposure pathway. A review is presented of exposure to soil and its ingestion both world-wide and specifically in Uganda. The deliberate consumption of soil by pregnant women and children (during the crawling stage of their development and between the ages of 4 and 8) is common in Uganda. However, prior to this study no information was available concerning the bioavailability of Ce in ingested soil or soil contaminated food. A Physiologically Based Extraction Test (PBET) has been used to determine the bioaccessibility of Ce in soil and dust samples from two districts in Uganda. The PBET incorporates gastro-intestinal tract parameters representative of a human for predicting the bioaccessibility of metals from an ingested solid matrix . Results showed there was a large degree of variation in Ce bioaccessibility between the samples, and between the different size fractions of individual samples. There was a marked increase in bioaccessibility when the pH was increased between the stomach and small intestine phases of the PBET for the smaller size fractions between >20 and <1 μm. Variations in mineralogy are considered to have caused the variations in Ce bioacessibility, although it was not possible to accurately determine specific mineral phases due to the small size of the minerals in the finest soil fractions.