Internal dose

Dose-Response Cune A graphical representation of the quantitative relationship between the administered, applied, or internal dose of a chemical or agent, and a specific biological response to that chemical or agent. 

Plutonium has a much shorter half-life than uranium (24.000 years for Pu-239 6,500 years for Pu-240). Plutonium is most toxic if it is inhaled. The radioactive decay that plutonium undergoes (alpha decay) is of little external consequence, since the alpha particles are blocked by human skin and travel only a few inches. If inhaled, however, the soft tissue of the lungs will suffer an internal dose of radiation. Particles may also enter the blood stream and irradiate other parts of the body. The safest way to handle plutonium is in its plutonium dioxide (PuOj) form because PuOj is virtually insoluble inside the human body, gi eatly reducing the risk of internal contamination. 

Calculation of dermal exposure and internal dose using DDBM data... 

The calculation of potential total dermal exposure of mixer-loaders and re-entry workers using dosimetry data and calculation of the internal dose using biological monitoring data is complex but will be discussed briefly. 

The internal dose (ID) for workers can be calculated by using the analytical data from the urine collection carried out simultaneously with the dosimetry. The calculation of the ID using urine data is complex and will not be dealt with in detail. However, there are several references, that can help guide one through such calculations. Nolan et al have addressed this subject in great detail, as have other researchers. 

Shiraishi K, Yamamoto M. 1996. Internal dose from ingestion for Japanese adult males. Health Phys 71(5) 700-704. 

Unchanged compounds or metabolites in blood and urine can be used to monitor human exposure to some carbamates. Table 5 shows some biological indices of internal dose used to monitor carbamate exposure. Urine carbamate metabolites may provide a good estimate of the internal dose because the half-life of most compounds is very short, samples collected soon after the end of the exposure are preferable for analysis (WHO, 1986). 

Pyrethroid insecticides are rapidly metabolized to their inactive acids and alcohol components, which are excreted primarily in urine. A small portion of the absorbed compounds is excreted unchanged. Occupational exposure to pyrethroid insecticides can be assessed by measuring intact compounds or their metabolites in urine. Biological indicators of internal dose in exposed subjects are reported in Table 7. Due to their rapid metabolism, determination of blood concentrations can only be used to reveal recent high-level exposures. 

The relationship between exposure and internal dose is known only for a few pyrethroids. Human volunteer studies have shown that, after a single oral administration, pyrethroids and the respective metabolites are excreted in urine within 24 hr and do not accumulate in the body. In field workers exposed to cypermetrin through the dermal route, urine excretion of the intact compound and its metabolites peaked 36 hr after exposure had ceased (WHO, 1989). 

Pentachlorophenol concentrations in urine and serum can be used as biomarkers of internal dose (Colosio et al., 1993a). PCP concentrations up to about 30 mg/L were detected in urine samples of exposed workers, while concentrations lower than 0.3 mg/L were detected in the general population. The presence of PCP in biological samples of the general population is attributable to indoor exposure to the compound released from treated materials (furniture, leather, paints, etc.). 

There is a growing need to better characterize the health risk related to occupational and environmental exposure to pesticides. Risk characterization is a basic step in the assessment and management of the health risks related to chemicals (Tordoir and Maroni, 1994). Evaluation of exposure, which may be performed through environmental and biological monitoring, is a fundamental component of risk assessment. Biomarkers are useful tools that may be used in risk assessment to confirm exposure or to quantify it by estimating the internal dose. Besides their use in risk assessment, biomarkers also represent a fundamental tool to improve the effectiveness of medical and epidemiological surveillance. 

In this part of the study, the internal dose of propoxur was assessed for HV applicators (n = 9) and harvesters (n = 18) using biological monitoring in two trials. In the first trial, workers wore their normal work clothing, followed by a trial where the same workers wore additional protective clothing. The minimum period between the two trials was 5 days. 

The internal dose of propoxur was measured by assessing the total amount of 2-isopropoxyphenol (IPP) excreted in the urine, collected over a period of 24 hr from the start of exposure, and described in detail in previous studies (Brouwer et al., 1993 Meuling et al., 1991). Volunteer kinetics studies revealed a one-to-one relationship of absorbed propoxur and excreted IPP on a mole basis. Based on the results by Machemer et al. (1982), a pulmonary retention of 40% was used to calculate the relative contribution of the respiratory exposure to the internal exposure. To estimate the contribution of the dermal exposure, the calculated respiratory portion was subtracted from the total amount of IPP excreted in urine. 

Relation between external exposure, skin moisture, and internal dose... 

Bonithon-Kopp et al. (1986b) investigated another potential marker for lead exposure. Maternal and infant hair lead levels, determined from hair samples taken at birth, were found to be correlated inversely with results on neurobehavioral tests (McCarthy Scales of Children s Abilities) when the children were tested at 6 years of age. Other studies have also reported associations between hair lead levels and behavioral or cognitive test scores, but measures of lead in hair may not accurately reflect internal body burden of lead, and such data should not be used to evaluate internal dose-response relationships (EPA 1986a). 

Studies in rodents, dogs, and non-human primates have demonstrated all of the major types of health effects of lead that have been observed in humans, including cardiovascular, hematological, neurodevelopmental, and renal effects (EPA 1986a). These studies also provide support for the concept of blood lead concentration as a metric of internal dose for use in dose-response assessments in humans. 

Gatsonis and Needleman (1992) identified a different set of statistical and methodological issues that have contributed to the inconsistencies (1) selection of adequate markers of exposure or internal dose,... 

The most significant information given in Table I is that the radon daughter ions do contribute to the total internal dose if only at about 3% in this study. The effect of free ions in contrast with daughters attached to aerosols is substantial when the mechanics of deposition in the bronchial tree and lungs are taken into account. The dose from "unattached" Po-218, which includes the Po-218 positive ions as a major component, can be from 3 to 40 times that of the attached Po-218 (NCRP, 1984). Current dosimetry models allow for the important role played by Po-218 in small-ion form. Hence, their effect is significantly greater than the 3% contribution to the PAEC (WL) shown in Table I. 

Radon daughter ions and the ionization caused by the decay chains of radon and thoron in indoor air play important roles both from the contribution made by the daughter product positive ions to internal dose and from the effects of ion-pair production on the indoor atmospheric electrical parameters. 

These results, however, cannot be used to establish a dose-effect curve, because of inadequate dose estimates. For this purpose it is necessary to calculate the individual accumulated external and internal doses of all persons involved into the investigation,... 

Average internal dose from natural radioactivity, United States 0.25... 

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