Human bioaccessibility of potentially toxic elements in soils using three in-vitro extraction methods

Pollution of soils with potentially toxic elements (PTE) is a major global concern. Analytical methods are required to assess not only total PTE concentrations, but also the fraction that is bioaccessible to humans following ingestion. This thesis compares methods for measuring bioaccessible PTE concentrations in soils, and applies these to locations in UK, Spain and Oman to assess risk to human health. The simple bioaccessibility extraction test (SBET), physiologically based extraction test (PBET) and the unified Bioaccessibility Research Group of Europe (BARGE) method (UBM) were the three methods used in this study. The SBET method was used to assess the risk of urban metals (Cu, Pb and Zn) in allotment soils that can be released from the soil and absorbed in the body. The findings showed that mean human percent bioaccessibility values were found to be 61% for Cu, 86% for Pb and 86% for Zn. These values were compared to plant uptake (phytoavailability) which was measured by using EDTA. The percent mean phytoavailability for plants were found to be lower than the human bioaccessibility values. The original PBET method in this study was modified slightly to simplify and speed up the method and also to minimise loss of sample during extraction. The new approach showed no difference to the original PBET which was checked by applying student t-test. The SBET, modified PBET and UBM methods were compared using different soils. This was done to get information that can contribute to the decision making process on methods to study the bioaccessibility of contaminants in soils for the seven PTE (As, Cd, Cr, Cu, Ni, Pb, Zn). The current work demonstrates that bioaccessibility is not the same for each metal within a given soil, nor between the soils. However, Principal Component Analysis (PCA) data analysis showed that the difference between the three methods in the stomach phase was small especially between PBET and SBET methods. The soil from the industrial area in Sohar, Oman, showed that it is highly contaminated with Cr and Ni. The three extraction methods SBET, PBET and UBM showed low mobilisation of Cr and Ni in stomach and intestine. This finding was confirmed by applying BCR sequential extraction which showed that Cr and Ni were mainly associated with the residual fraction.Pollution of soils with potentially toxic elements (PTE) is a major global concern. Analytical methods are required to assess not only total PTE concentrations, but also the fraction that is bioaccessible to humans following ingestion. This thesis compares methods for measuring bioaccessible PTE concentrations in soils, and applies these to locations in UK, Spain and Oman to assess risk to human health. The simple bioaccessibility extraction test (SBET), physiologically based extraction test (PBET) and the unified Bioaccessibility Research Group of Europe (BARGE) method (UBM) were the three methods used in this study. The SBET method was used to assess the risk of urban metals (Cu, Pb and Zn) in allotment soils that can be released from the soil and absorbed in the body. The findings showed that mean human percent bioaccessibility values were found to be 61% for Cu, 86% for Pb and 86% for Zn. These values were compared to plant uptake (phytoavailability) which was measured by using EDTA. The percent mean phytoavailability for plants were found to be lower than the human bioaccessibility values. The original PBET method in this study was modified slightly to simplify and speed up the method and also to minimise loss of sample during extraction. The new approach showed no difference to the original PBET which was checked by applying student t-test. The SBET, modified PBET and UBM methods were compared using different soils. This was done to get information that can contribute to the decision making process on methods to study the bioaccessibility of contaminants in soils for the seven PTE (As, Cd, Cr, Cu, Ni, Pb, Zn). The current work demonstrates that bioaccessibility is not the same for each metal within a given soil, nor between the soils. However, Principal Component Analysis (PCA) data analysis showed that the difference between the three methods in the stomach phase was small especially between PBET and SBET methods. The soil from the industrial area in Sohar, Oman, showed that it is highly contaminated with Cr and Ni. The three extraction methods SBET, PBET and UBM showed low mobilisation of Cr and Ni in stomach and intestine. This finding was confirmed by applying BCR sequential extraction which showed that Cr and Ni were mainly associated with the residual fraction