Absorption studies ingestion

The site and mechanism of absorption of ingested americium are not known. Based on studies of plutonium, it is likely that americium absorption occurs, at least to some extent, in the small intestine. Studies of the absorption of plutonium in preparations of in situ isolated segments of small intestine of immature miniature swine indicate that absorption of actinides can occur along the entire small intestine, with the highest rates of absorption occurring in the duodenum (Sullivan and Gorham 1982). 

Children s Susceptibility. No studies were located in which comparisons were made between the sensitivity of children and adults to the toxicity of americium. Animal studies indicate that juvenile dogs are less susceptible than adults to americium-induced bone cancer (Lloyd et al. 1999). No direct evidence was located to indicate that the pharmacokinetics of americium in children may be different from that in adults. Based on dosimetric considerations related to differences in the parameters of available models, as well as studies in animals, it seems likely that children may be more susceptible to americium toxicity than are adults by virtue of age-related differences in pharmacokinetics. Absorption of ingested americium may be as much as 200 times greater in neonatal animals than in adults. (Bomford and Harrison 1986 David and Harrison 1984 Sullivan et al. 1985). 

The lethal oral dose in humans is estimated to be 0.3-0.5 g/kg. Symptoms of inhalation, absorption, or ingestion in humans (inferred mostly from animal studies) may include numbness of oral mucous membranes, nausea, vomiting, abdominal pain, muscle tremor, incoordination, clonic convulsions, and stupor. 

Methods for Reducing Toxic Effects. There are no established methods for reducing absorption of DEHP or metabolites because the mechanism of absorption is not known. There have been no studies of compound-specific techniques for reducing DEHP body burden. External contact with DEHP can be treated by thoroughly washing the affected area. Activated carbon, possibly combined with a cathartic, will diminish absorption of ingested DEHP from the gastrointestinal tract (HSDB 2000). 

No studies were located that quantitated the absorption of ingested 1,1-dichloroethane in humans or animals. However, when 700 mg [ C]-1,1-dichloroethane/kg was orally administered to rats and mice, absorption was evidenced by the presence of radiolabel in expired air and the presence of radiolabeled metabolites in urine, though there was no quantitative assessment made of the extent or rate of absorption (Mitoma et al. 1985). 

Aromatic EC>9-EC16 Fraction. No data regarding the extent or rate of absorption of ingested naphthalene or monomethyl naphthalenes were available, except for a report that 80% of an oral dose of 2-methyl naphthalene was recovered as metabolites in the urine of rats within 24 hours (ATSDR 1995e). Studies with animals indicate that orally administered isopropylbenzene (cumene) rapidly appeared in the blood and that 90% of the administered dose was accounted for in urinary metabolites (EPA 1987a, 1997b). 

Absorption, Distribution, Metabolism, Excretion. Absorption data for humans exposed to nitrobenzene via inhalation and the dermal route indicate that it is efficiently absorbed by these routes. Although absorption studies using the oral route have not been located for humans, the available case studies suggest that it can also be absorbed via ingestion. However, quantitative data are lacking. Similarly, in animals, quantitative absorption studies using inhalation or dermal... 

The real availability of fruit and vegetable phenolics ready to be absorbed in the intestinal tract should also be studied. Analysis of the flavonoid and phenolic content of fruit and vegetables does not provide a real picture of the compounds which may be released from plant tissues after ingestion and which may be available for absorption. Studies concerning the real availability of food phenolics should be carried out. 

The general consensus, until recently, has been that the average fractional gastrointestinal absorption of ingested lead is ca. 8% [6,7]. However, Chamber-lain and co-workers [10] have related the results of their detailed studies of the metabolism of lead to various data used to derive the above average and conclude that a more realistic average absorption of 13-18% should be applied for adults. These higher values appear necessary to account for the concentrations of lead found in blood and urine. 

Because copper has only two stable isotopes, only one tracer isotope is available, which limits the choice of techniques for metabolic studies substantially. In most human studies, Cu has been used to determine apparent absorption, as the difference between the amount of isotope ingested and the amount recovered in feces. To check for completeness of fecal collection, holmium has been suggested and successfully used as a non-absorbable, quantitative elemental marker in copper absorption studies [259]. Studies comparing copper absorption of foods intrinsically or extrinsicaUy labeled with Cu are limited. Johnson and co-workers [260, 261] found no statistically significant difference in copper absorption from intrinsically and extrinsicaUy labeled goose fiver, goose breast, peanut butter, and wheat. Harvey et al. [262] observed significant differences in copper absorption between intrinsically and extrinsicaUy labeled sunflower seeds and soy beans. 

It is also recognized that co-ingested dietary fat improves carotenoid bioavailability (Dimitrov et al. 1988 Prince and Frisoli, 1993 Reddy etal. 1995 Jayarajan et al. 1980). Because of their hydrophobic nature the carotenoids are constrained to the hydrophobic domains of plant tissues where they may be present as part of the photosynthetic mechanism in leaf chloroplasts (CogdeU 1988), as semicrystalline bodies in fruit and roots (Thelander et al. 1985) or dissolved in lipid droplets within plastids in ripe fruit (de Pee et al. 1998). Absorption studies would indicate that carotenoid present as semicrystalline bodies is most difficult to absorb, followed by carotenoids in leaves, with fruit carotenoids dispersed in oil droplets being most easily absorbed. 

The acute toxicity of DMF is relatively low. The LD q by oral ingestion ia rats is 2800 mg/kg and the LC for mice is 9400 mg/(2 h). Skin absorption is also an important route by which DMF can be iatroduced iato the body, and an LD q of 4720 mg/kg has been observed ia rabbit-skia exposure studies. 

Health and Safety Factors. Animal-feeding studies of DMPPO itself have shown it to be nontoxic on ingestion. The solvents, catalyst, and monomers that are used to prepare the polymers, however, should be handled with caution. Eor example, for the preparation of DMPPO, the amines used as part of the catalyst are flammable toxic on ingestion, absorption, and inhalation and are also severe skin and respiratory irritants (see Amines). Toluene, a solvent for DMPPO, is not a highly toxic material in inhalation testing the TLV (71) is set at 375 mg/m, and the lowest toxic concentration is reported to be 100—200 ppm (72). Toxicity of 2,6-dimethylphenol is typical of alkylphenols (qv), eg, for mice, the acute dermal toxicity is LD q, 4000 mg/kg, whereas the acute oral toxicity is LD q, 980 mg/kg (73). The Noryl blends of DMPPO and polystyrene have PDA approval for reuse food apphcations. 

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