Bioavailability and bioaccessibility

Bioaccessibility testing of metals using the physiologically based extraction test (PBET) or the simplified bioaccessibility extraction test (SBET) has gained popularity in recent years in the UK (Nathanail McCaffrey 2002). The aim of the tests is to simulate the extraction of metals into solution in the juices in the stomach, upper and lower intestine (PBET) and in the stomach (SBET). The empirical test results should only be applied to the ingestion of soil or dust pathways. The tests have been calibrated for lead, and to a lesser degree for arsenic. Risk assessors should be satisfied that the health criteria 

This is illustrated in a paper by Oomen etal. (2002). This paper described a multi-laboratory comparison and evaluation of five in vitro digestion models. The experimental design and the results of a round robin evaluation of three soils, each contaminated with arsenic, cadmium and lead were presented and discussed. A wide range of bioaccessibility values were found for the three soils  

Details of the five in vitro methods used [SBET (BGS) DIN method (RUB) in vitro digestion model (RIVM) SHIME method (LabMET/Vito) and TIM method (TNO)] are given in the paper. 

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Semple KT, Doick KJ, Jones KC et al (2004) Defining bioavailability and bioaccessibility of contaminated soil and sediment is complicated. Environ Sci Technol 38 228A-231A... 

More investigations are needed to explore the benefits of Brazil nut and its by-products for human health. Studies on the bioavailability and bioaccessibility of the known Brazil nut bioactive compounds as well as their potential allergenic reactions are required. Although very few publications have reported the TPC content of Brazil nut, more research work is necessary to determine the types of phenolics present in Brazil nut. 

Cashew nut and its coproducts provide a complex food rich in macronutrients and micronutrients, as well as small quantities of various antioxidants and bioactive compounds that are relevant to many health beneficial attributes. These bioactive compounds include MUFA, PUFA, phenolics, phytosterols, phytostanols, tocopherols, and phytates. While benefits of cashew nut and its coproducts for human health appear promising, further research on bioavailability and bioaccessibility of cashew bioactive compounds as well as potential allergenic reaction is required for a better understanding of the role of cashew nut and its coproducts in human health. 

Drexler J., Mushak P., 1995. Health risks from extractive industry wastes characterization of heavy metal contaminants and quantification of their bioavailability and bioaccessibility. Third International Conference on the Biogeochemistry of Trace Elements, May 15—19, 1995, Paris, France. 

The release of a compound from the food matrix in which it is incorporated is a determining process for its bioavailability and is largely influenced by the physicochemical characteristics of the compound, the type of food matrix, the subcellular location of the compound in plant tissues, and the food processing. The, food matrix type greatly influences the compound bioaccessibility. 

Sediments can also serve as potential exposure routes for aquatic food chains through the bioaccumulation of contaminants by benthic organisms. The potential of sediment contaminants to expose organisms in sediments and the water column is determined by their bioavailability. The bioavailability or bioaccessibility of nonpolar organic contaminants is determined by how strongly they are bound to organic matter in soil and sediment [31, 32]. This fact should be taken into account in a realistic assessment of the environmental risks of these contaminants (Fig. 13). 

A chemical interaction is the combined effect of two chemicals resulting in a greater (synergistic, potentiation, or supra-additive) or lesser (antagonistic, inhibitive, sub-additive, or infra-additive) effect than expected based on additivity (see [24]) Bioaccessibility, bioavailability, and bioaccumulation, three chemical-specific properties, play a key role in their potential interactions. The co-occurrence and exposure of various chemicals in the environment can lead... 

The principle goal of electrobioremediation is therefore to make bioaccessible compound, nutrient, and TEA fractions bioavailable and consequently increase biotransformation rates (Fig. 18.3). The following chapter will specify the impact of DC fields on bacterial mobilization in and deposition to subsurface matrices (Fig. 18.1b). 

The bioaccessibility of a compound can be defined as the result of complex processes occurring in the lumen of the gut to transfer the compound from a non-digested form into a potentially absorbable form. For carotenoids, these different processes include the disruption of the food matrix, the disruption of molecular linkage, the uptake in lipid droplets, and finally the formation and uptake in micelles. Thus, the bioaccessibility of carotenoids and other lipophilic pigments from foods can be characterized by the efficiency of their incorporation into the micellar fraction in the gut. The fate of a compound from its presence in food to its absorbable form is affected by many factors that must be known in order to understand and predict the efficiency of a compound s bioaccessibility and bioavailability from a certain meal. ... 

The degree of linkage of a compound may also affect its bioaccessibility in the gut. It is generally admitted that a compound linked with other molecules (e.g., via esterification, glycosylation, etc.) is not absorbed as well as its free form and thus it must be hydrolyzed in the gut in order to be taken up by enterocytes. Due to the presence of hydroxyl or keto groups on their molecules, the xanthophylls (lutein, zeaxanthin, and P-cryptoxanthin) are found in both free and esterified (monoester or diester) forms in nature, but few studies have been conducted to date to assess the bioavailabilities of these esters. 

Physical and Chemical Properties. The physical and chemical properties of lead and its compounds are sufficiently well defined to allow an estimation of the environmental fate of lead to be made (Howe 1981 HSDB 1996 Lide 1996 Merck 1989 Sax 1984 Sax and Lewis 1987). Availabilities of the various forms need to be modeled and the connectivities to bioaccessabilities and bioavailabilities determined. 

Bioavailability issues have been reviewed previously (Mihelcic etal. 1993 Boesten 1993 Baveye and Bladon 1999 Ehlers and Luthy 2003). In this review, we discuss specifically the bioavailability of soil- or sediment-sorbed organic contaminants to pollutant-degrading bacteria. Direct uptake of sorbed contaminants is perhaps the most controversial and least understood process. The definition of bioavailability given by Alexander (2000) will be used in this review. The term bioaccessibility encompasses what is immediately available plus that which may become available, whereas bioavailability refers to what is available immediately. 

Oral bioavailability of soil-borne contaminants is defined as the contaminant fraction that reaches systemic circulation and derives from the combined result of soil ingestion, bioaccessibility, absorption and the first-pass effect (Fig. 9.4) (Oomen et al., 2003 Wragg and Cave, 2003). The bioaccessible fraction is defined as the contaminant fraction that is mobilised from soil into the digestive juice chyme and represents the maximum amount of contaminant available for intestine absorption (Ruby et al., 1996, 1999). 

Bioaccessibility, and therefore oral bioavailability of soil contaminants, depends on soil type and contaminant (Davis et al., 1997 Gr0n and Anderson, 2003 Hamel et al, 1998 Ruby et al., 1999). PTMs occur in soil as a complex mixture of solid-phase chemical compounds of varying particle size and morphology, characterised by variable metal bioavailability. Mineral phases that form under acidic conditions (e.g. lead sulphate, iron-lead sulphate) will tend to be more stable in the acidic conditions of the stomach and hence less bioaccessible. By contrary, mineral phases... 

Figure 9.Z) Oral bioavailability of soil contaminants as the combined result of soil ingestion, bioaccessibility, absorption and first-pass effect (modified from Oomen et al., 2003).

Sequential Enzymatic Extractions for the Evaluation of the Bioaccessibility of Metals in Foodstuffs Some attention has been paid to the analysis of enzymatic digests of foodstuffs in the quest for molecular information to contribute to the knowledge of the bioavailability of some elements. Sequential enzymolyses in simulated gastric and gastrointestinal juice were proposed for an estimation of bioavailability of heavy metal species from meat [46] and cocoa samples [47, 48]. The soluble fractions of the stomach and upper intestinal... 

Oomen et al. (2003) defined 4 steps in the oral bioavailability of chemicals present in contaminated soils to man soil ingestion, mobilization from soil during digestion (i.e., bioaccessibility), absorption from the intestinal lumen, and first-pass effect. An in vitro model of the human digestive system was used to study the uptake of chemicals from ingested soil. When an artificial soil, spiked... 

Peijnenburg WJGM, Jager T. 2003. Monitoring approaches to assess bioaccessibility and bioavailability of metals matrix issues. Ecotoxicol Environ Safety 56 63-77. 

A variety of terms have been established to help constrain the relative availability of toxins that can be readily released from administered substances into body fluids. Bioavailability is defined by toxicologists as the fraction of an administered dose of a substance that is absorbed via an exposure route and actually reaches the bloodstream (Ruby et al, 1999 Lioy, 1990 Hamel, 1998). The bioaccessibility of a substance is the fraction that can be dissolved by body fluids (i.e., in the... 

Bioaccessibility tests (also called bioavailability or physiologically based extraction tests) have been used extensively to measure the short-term solubihty of and metal extraction from earth materials and other substances in simulated gastric, intestinal, and lung fluids (Ruby et al, 1992, 1996, 1999 Hamel, 1998 Battelle and Exponent, 2000 Oomen et al, 2002 Mullins and Norman, 1994). Biodurability tests have been used extensively to measure the long-term solubility of earth materials and other substances such... 

Contaminants in the soil can adversely impact the health of animals and humans when they ingest, inhale, or touch contaminated soil, or when they eat plants or animals that have been affected by soil contamination. The exposure of an organism to a carcinogen or other ecotoxic compound in soil is not related to the total concentration of that substance in soil but rather to the amount that is actually available (bioavailability) [34]. Most chemical extraction methods reported in literature were studied in terms of their ability to recover all the contaminants (PAH, pesticides, etc.) from a soil matrix [30,35]. In this chapter we propose the use of a fast and simple analytical extraction method to mimic the bioaccessibility determined by pollution of benzene, naphthalene and anthracene chloride, amino and sulfonate derivatives. The method, based on an ultrasonic extraction [36,37], was performed within a short time (2 minutes) and with a little amount of solvent (10 mL) [31]. 

The capacity of an environment to provide a chemical at a constant rate may become limited due to depletion of labile pools of the chemical. This has inspired the differentiation of an immediate bioavaUability [the freely dissolved compound immediately ready for uptake (Reichenberg and Mayer, 2006)] from a potential bioavailability, which has been named bioaccessibility (the compound that may become bioavailable by, e.g. dissolution, or desorption over time) (Semple et ai, 2004). In this concept, the bioaccessible compound is a fraction of the total compound and appears to be an appropriate descriptor of the possible degradation end point. 

Ravel B, Newville M (2005) ATHENA, ARTEMIS, HEPHAESTUS data analysis for X-ray absorption spectroscopy using IFEFFIT. J Synchrotron Radiat 12 537-541 Reeder RJ, Schoonen MAA (2006) Metal speciation and its role in bioaccessibility and bioavailability. In Sahai N, Schoonen MAA (eds) Medical mineralogy and geochemistry. Reviews in mineralogy and geochemistry, vol 64. Mineralogical Society of America, VA, pp 59-113... 

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