Bioavailability ingestion

Human subjects cannot be used in dosing studies for ethical reasons. Therefore, appropriate animal models are often used to determine bioavailability of As in contaminated soil. Recently reviewed in vivo models used to measure bioavailable As include juvenile swine, monkey, rabbit, and dog (17,18). In these in vivo dosing trials, soil As bioavailability is evaluated by measuring As in urine, blood, feces, and/or storage tissues (bone, skin, nails, hair). Most As is measured in urine following oral or intravenous doses of soluble As considered 100% bioavailable. Ingestion of soluble As by human volunteers resulted in 64-69% of dosed As received in urine. Similar As recoveries of highly soluble forms of dosed As have been reported in monkey (19), juvenile swine (20), and dog... 

Bioavailability from Environmental Media. Endosulfan can be absorbed following inhalation of contaminated workplace air and ingestion of insecticide-contaminated food (Ely et al. 1967). Dermal contact with or ingestion of endosulfan that is tightly bound to soil particles is an exposure route of... 

Klienfeld and Tabershaw 1954 Prout et al. 1985 Stephens 1945 Stevens et al. 1992 Templin et al. 1993 Withey et al. 1983), or dermal (Bogen et al. 1992 Jakobson et al. 1982 McCormick and Abdul-Rahman 1991 Sato and Nakajima 1978 Steward and Dodd 1964 Tsuruta 1978) exposure. All these routes of exposure may be of concern to humans because of the potential for trichloroethylene to contaminate the air, drinking water, food, and soil. More information on the absorption of trichloroethylene following ingestion of contaminated soil and plants grown in contaminated soil near hazardous waste sites are needed to determine bioavailability of the compound in these media. 

Such evidence indicates that it might be unnecessary to reach the same intake of soy products as Japanese or other Asian populations to reach the same plasma levels of isoflavones. The rationale for such a difference could be a different bioavailability of the ingested isoflavones. Indeed, in most Asians a deficiency of an intestinal lactase, responsible for P-glucosides hydrolysis, might explain the lower isoflavones concentrations in the blood of the Japanese (Day et ai, 2000). 

A major drawback of this study was that we measured lipid peroxidation ex vivo, but not in vivo using the latest and most promising methods such as F2 isoprostanes (Roberts and Morrow, 2000). However, we are planning to do that soon, so hopefully future studies will bring us more detailed information about the effects of phloem on lipid peroxidation. In conclusion, our study showed that lignans are bioavailable from the wood matrix, that long-term consumption of phloem is safe and that ingestion of phloem can inhibit lipid peroxidation in humans. 

In the total plasma response approach, the bioavailability of a compound is determined by measuring its plasma concentration at different times (up to weeks) after single or long-term ingestion of the compound from supplements or food sources. Generally, a plasma concentration-versus-time plot is generated, from which is determined the area-under-curve (AUC) value used as an indicator of the absorption of the componnd. Here, the term relative bioavailability is more appropriate since AUC valnes of two or more treatments are usually compared. This is in contrast to absolnte bioavailability for which the AUC value of the orally administered componnd is compared to that obtained with intravenous administration taken as a reference (100% absorption). 

This approach can be used only for fat-soluble compounds that follow the same lymphatic route to be transported to the liver as carotenoids. The bioavailability of the compound of interest is determined by monitoring the appearance of the compound and its newly formed intestinal metabolites in the postprandial chylomicron fraction of plasma [also called the density < 1.006 kg/L fraction or triglyceride-rich lipoprotein (TRL) fraction because it is generally a mixture of chylomicrons (CMs) and very low density lipoproteins (VLDLs)] as a function of the time after ingestion. 

Despite their potential health-promoting effects as dietary antioxidants, the fate of betalains in humans has been poorly studied. Betalain bioavailability was first demonstrated in humans by the appearance of betacyanins in urines after ingestion of beetroot extract" and red beet juice," indicating that these compounds are indeed absorbed. Although intact betacyanins (betanin and isobetaiun) appeared rapidly in human urine with a maximum excretion rate observed within 2.5 to 8 hr," betacy-anin recoveries in human urine were usually low (< 1% of the dose) over 24 hr postdose, suggesting that either the bioavailabifity of betacyaiuns from red beetroot is low or that renal clearance is a minor excretion route for these compounds. 

After ingestion of cactus pear fruit pulp, both betanin and indicaxanthin were found in human plasma (with AUCo i2 h values of 0.46 and 29.2 lunol/hr/mL, respectively), partly associated with LDL, and in urine (3 and 76%, respectively, of the ingested compounds)," indicating that indicaxanthin was better absorbed than betanin. The bioavailability of indicaxanthin from prickly pear fruit pulp was 20 times that of betanin, suggesting differences in the fates of the two classes of betalains (betacyanin and betaxanthins) in the human body. In rats, betanin appeared to be... 

Bioavailability from Environmental Media. The absorption and distribution of americium as a result of inhalation and ingestion exposures have been discussed in Sections 3.3.1 and 3.3.2. EPA lists identical uptake factors for inhaled and ingested americium (and all the other transuranics other than plutonium) regardless of compound solubility, indicating that the knowledge base for americium is not sufficiently developed to quantify the differences that are recognized for most other elements. 

Exposures of Children. Children will be exposed to americium in the same manner as adults in the general population (i. e., ingestion of food and water and inhalation of air). Americium is potentially found at hazardous waste sites at elevated levels. Since children may have oral exposure to soil through hand-to-mouth activity, bioavailability studies of americium in soil via the oral route may be useful to assess the risk of this type of exposure. 

Colorants do not contribute to therapeutic activity, nor do they improve product bioavailability or stability. Indeed, they increase the cost and complication of the manufacturing process. Their main role is to facilitate identification and to enhance the esthetic appearance of the product. In common with all material to be ingested by humans, solid dosage forms are severely restricted in the coloring agents that are allowable. This situation is complicated by the lack in international agreement on an approved list of colorants suitable for ingestion. 

Bioavailability from Environmental Media. Additional information on absorption following dermal contact with, or ingestion of, contaminated soil and water would also be helpful in determining the importance of this route of exposure for populations of concern. 

Adult subjects who ingested soil (particle size less than 250 im) from the Bunker Hill NPL site absorbed 26% of the resulting 250 pg/70 kg body weight lead dose when the soil was ingested in the fasted state and 2.5% when the same soil lead dose was ingested with a meal (Maddaloni et al. 1998). There are no reported measurements of the absorption of soil-bome lead in infants or children. Additional evidence for a lower absorption of soil-bome lead compared to dissolved lead is provided from studies in laboratory animal models. In immature swine that received oral doses of soil from one of four NPL sites (75 or 225 ig Pb/kg body weight), bioavailability of soil-bome lead ranged from 50% to 82% of that of a similar... 

The bioavailability of ingested soluble lead in adults has been found to vary from less than 10% when ingested with a meal to 60-80% when ingested after a fast (Blake and Mann 1983 Blake et al. 1983 ... 

Exposures Of Children. Estimates are available for intake by children through ingestion of contaminated soils, dust, paint chips (EPA 1989c), and breast milk (Wolff 1983). However, some of these estimates are not current or well understood. To better understand the sensitivity of the nursing infant to chemicals such as lead, epidemiological studies, chemical monitoring, and model development and application are needed (Byczkowski et al. 1994). The bioavailability of lead from soil or dust on the hand after mouthing activity needs to be modeled. 

Exposure and Bioavailability Issues. Primary routes of exposure to lead are via inhalation and ingestion. Lead exposure occurs through inhalation of airborne lead particles with deposition rates in adults of 30%-50% depending on factors such as particle size and ventilation rate (EPA 1986). Once deposited in the lower respiratory tract, lead appears to be almost completely absorbed (Morrow et al. 1980). 

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