Total body burden

The atmospheric movement of pollutants from sources to receptors is only one form of translocation. A second one involves our attempt to control air pollutants at the source. The control of parhculate matter by wet or dry scrubbing techniques 3delds large quantities of waste materials—often toxic—which are subsequently taken to landfills. If these wastes are not properly stored, they can be released to soil or water systems. The prime examples involve the disposal of toxic materials in dump sites or landfills. The Resource Conservation and Recovery Act of 1976 and subsequent revisions are examples of legislation to ensure proper management of solid waste disposal and to minimize damage to areas near landfills (4). 

The presence of air pollutants in the surrounding ambient air is only one aspect of determining the impact on human beings. An air pollution instrument can measure the ambient concentration of a pollutant gas, which may or may not be related to its interaction with individuals. More detailed information about where and for how long we are breathing an air pollutant provides additional informahon about our actual exposure. Finally, how an air pollutant interacts with the human body provides the most useful information about the dose to a target organ or bodily system. 

The human body and other biological systems have a tremendous capacity to take in all types of chemicals and either utilize them to support some bodily function or eliminate them. As analyhcal capabihhes have improved, lower and lower concentrations of chemicals have been observed in various parts of the body. Some of these chemicals enter the body by inhalation. 

The concept of total body burden refers to the way a trace material accumulates in the human system. The components of the body that can store these materials are the blood, urine, soft tissue, hair, teeth, and bone. The blood and mine allow more rapid removal of trace materials than the soft tissue, hair, and bone (5). Accumulation results when trace materials are stored more rapidly than they can be eliminated. It can be reversed when the source of the material is reduced. The body may eliminate the trace material over a period of a few hours to days, or may take much longer— often years. 

The effect of accumulation in various systems depends greatly on the quantity of pollutants involved. Many pollutants can be detected at concentrations lower than those necessary to affect human health. For pollutants which are eliminated slowly, individuals can be monitored over long periods of time to detect trends in body burden the results of these analyses can then be related to total pollutant exposure. Following are two examples of air pollutants that contribute to the total body burden for lead and carbon monoxide. 

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The body excretes tritium with a biological half-life of 8—14 d (10.5 d average) (75), which can be reduced significantly with forced fluid intake. For humans, the estimated maximum permissible total body burden is 37 MBq (1 mCi). The median lethal dose (LD q) of tritium assimilated by the body is estimated to be 370 GBq (10 Ci). Higher doses can be tolerated with forced fluid intake to reduce the biological half-life. 

The absorption, distribution, and accumulation of lead in the human body may be represented by a three-part model (6). The first part consists of red blood cells, which move the lead to the other two parts, soft tissue and bone. The blood cells and soft tissue, represented by the liver and kidney, constitute the mobile part of the lead body burden, which can fluctuate depending on the length of exposure to the pollutant. Lead accumulation over a long period of time occurs in the bones, which store up to 95% of the total body burden. However, the lead in soft tissue represents a potentially greater toxicological hazard and is the more important component of the lead body burden. Lead measured in the urine has been found to be a good index of the amount of mobile lead in the body. The majority of lead is eliminated from the body in the urine and feces, with smaller amounts removed by sweat, hair, and nails. 

The second example of an air pollutant that affects the total body burden is carbon monoxide (CO). In addihon to CO in ambient air, there are other sources for inhalation. People who smoke have an elevated CO body burden compared to nonsmokers. Individuals indoors may be exposed to elevated levels of CO from incomplete combustion in heating or cooking stoves. CO gas enters the human body by inhalation and is absorbed directly into the bloodstream the total body burden resides in the circulatory system. The human body also produces CO by breakdown of hemoglobin. Hemoglobin breakdown gives every individual a baseline level of CO in the circulatory system. As the result of these factors, the body burden can fluctuate over a time scale of hours. 

The baseline level of COHb is—0.5% for most individuals. Uponexposure to elevated levels of atmospheric CO, the percentage of COHb will increase in a very predictable manner. Analytical techniques are available to measure COHb from <0.1 to >80% in the bloodstream, providing a very rapid method for defermining the total body burden. If elevated levels of CO are reduced, the percentage of COHb will decrease over a period of time. 

The collection of air samples using air tubes and/or filters is of value during the course of the field research when performing SDDBM studies. The air tube/air filter data can be used to estimate the portion of the total body burden, which originates from respiratory exposure to the active ingredient. Of course, if an organic vapor respirator is used by the worker as a matter of course, the respiratory exposure component should be backed out of the final exposure calculation. 

In human adults, approximately 94% of the total body burden of lead is found in the bones. In contrast, bone lead accounts for 73% of the body burden in children (Barry 1975). This large pool of lead in adults can serve to maintain blood lead levels long after exposure has ended (Flemming et al. 1997 ... 

Lead is initially distributed throughout the body and then redistributed to soft tissues and bone. In human adults and children, approximately 94% and 73% of the total body burden of lead is found in bones, respectively. Lead may be stored in bone for long periods of time, but may be mobilized, thus achieving a steady state of intercompartmental distribution (see Section 2.3.2). 

Milder FL Applied Biomedical Corp., Danvers, MA Use x-ray fluorescence in a transmission geometry to measure the total body-burden of lead, in vivo, noninvasively HHS... 

Human foods that are particularly rich in copper (20 to 400 mg Cu/kg) include oysters, crustaceans, beef and lamb livers, nuts, dried legumes, dried vine and stone fruits, and cocoa (USEPA 1980). In humans, copper is present in every tissue analyzed (Schroeder et al. 1966). A 70-kg human male usually contains 70 to 120 mg of copper (USEPA 1980). The brain cortex usually contains 18% of the total copper, liver 15%, muscle 33%, and the remainder in other tissues — especially the iris and choroid of the eye. Brain gray matter (cortex) has significantly more copper than white matter (cerebellum) copper tends to increase with increasing age in both cortex and cerebellum. In newborns, liver and spleen contain about 50% of the total body burden of copper (USEPA 1980). Liver copper concentrations were usually elevated in people from areas with soft water (Schroeder et al. 1966). Elevated copper concentrations in human livers are also associated with hepatic disease, tuberculosis, hypertension, pneumonia, senile dementia, rheumatic heart disease, and certain types of cancer (Schroeder et al. 1966). 

Dodds-Smith, M.E., M.S. Johnson, and D.J. Thompson. 1992a. Trace metal accumulation by the shrew Sorex araneus. I. Total body burden, growth, and mortahty. Ecotoxicol. Environ. Safety 24 102-117. 

Patterson, J. and T.V. Fernandez. 1995. Influence of salinity on the total body burden of fish Etroplus maculatus exposed to Ni, Cu and their mixture. Indian Jour. Mar. Sci. 24 211-214. 

Half-time persistence of zinc in the prawn (Palaemon elegans) is about 17 days (Nugegoda and Rainbow 1988b), and between 30 and 270 days for five other crustacean species (NAS 1979). Differences in half-time persistence are finked to differences in excretion rates of ionic zinc and complexed zinc. In general, ionic zinc in crustaceans is excreted first, then complexed zinc surface-adsorbed zinc is turned over faster than internally adsorbed zinc molting accounts for 33 to 50% loss of the total body burden in crabs (Eisler 1981). 

Residues highest in liver and Gl tract all other tissues contributed <4% of total body burden (USEPA 1980)... 

During the first day after each dose, 20% was excreted into urine, 0.5% into feces, and 20% into bile. The addition of 4% cholestyramine to diets for 6 days resulted in increased fecal excretion by a factor of 18 and increased total body burden excretion by 1.4 times (Rozman etal. 1982)... 

Excretion. Chloroform is largely excreted either in the parent form or as the end metabolite (carbon dioxide, CO2) in the bodies of both laboratory animals and humans. Corley et al. (1990) demonstrated that mice exposed to 10 or 89 ppm of chloroform by inhalation excreted 99% of the chloroform body burden as CO2 in exhaled air. As the chloroform concentrations in the air rose however, the amount of chloroform metabolized to CO2 decreased and the amount of unchanged chloroform rose in the exhaled air, indicating that chloroform metabolism in mice is a saturable process. Rats exposed in a similar manner to 93, 356, and 1,041 ppm chloroform excreted 2, 20, and 42.5%, respectively, of the total body burden of chloroform as unchanged parent compound, indicating that chloroform is metabolized to CO2 in rats but to a lesser degree than in mice. 

Substances that can be inhaled include gases, vapors, liquid aerosols (both liquid and solid substances in solution), and finely divided powders/dusts (dust aerosols). Such substances may be absorbed from the respiratory tract or, through the action of clearance mechanisms, may be transported out of the respiratory tract and swallowed. This means that absorption from the gastrointestinal tract will contribute to the total body burden of substances that are inhaled. 

Exposure should normally be understood as external exposure, which can be defined as the amount of substance ingested, the total amount in contact with the skin (which can be calculated from exposure estimates expressed as mg/cm or mg/cm ), or either the amount inhaled or the concentration of the substance in the atmosphere, as appropriate. In cases where a comparison needs to be made with systemic effects data (e.g., when inhalation or dermal toxicity values are lacking or when exposures due to more than one exposure route need to be combined) the total body burden has to be estimated. Since the assessment of the amount that is absorbed after ingestion, by inhalation or by the skin is usually done in the effects assessment (section on toxicokinetics), this calculation of the total body burden is often placed in the section on risk characterization. 

Exposure of the general population to chemicals present in the environment is an example of long-term exposure on a local or regional spatial scale. The general population is mainly exposed to environmental chemicals via oral exposure through food and drinking water and via inhalation from ambient and indoor air. The total body burden can, e.g., be expressed as a total oral intake (the outcome of the exposure assessment). This intake should be compared with a POD derived from preferably long-term studies or at least subchronic studies (outcome of the hazard (effects) assessment). 

Chronic renal failure/dialysis During sucralfate administration, small amounts of aluminum are absorbed. Concomitant use with other aluminum-containing products may increase the total body burden of aluminum. Patients with chronic renal failure or receiving dialysis have impaired excretion of absorbed aluminum, and aluminum is not dialyzed. Aluminum accumulation and toxicity have occurred. 

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