From exposure to dose

To determine whether and to what extent humans may be harmed (suffer toxicity) from a chemical exposure, it is necessary to know the dose created by the exposure. The concept of dose is so important that it needs to be treated in detail. 

Exposure, as we have seen, refers to an individual s contact with an environmental medium containing a chemical or, in some cases, with the chemical itself. The amount of chemical that enters the body as a result of the exposure is called the dose. 

The magnitude of the dose is a function of the amount of chemical in the medium of contact, the rate of contact with the medium, the route of exposure, and other factors as well. Experts in exposure analysis use various means to estimate the dose incurred by individuals exposed to chemicals. Exposure analysis is one of the critical steps in toxicological risk assessment. 

Note - and this is quite important - that if a 20 kg child (about 44 lbs) were to take the same four tablets on one day, the child s dose would be more than three times that of the adult, as follows 1300 mg aspirin/20 kg b.w. = 65 mg/(kg b.w. day). For the same intake of aspirin (1300 mg), the smaller person receives the greater dose. 

First we calculate the weight oiFCE (inmg) getting into their bodies. 

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Chemistry will play a large role in the research areas of our own strategic plan. For example, work on particulate matter will allow us to understand the nature of the particles and their behavior in the atmosphere, develop the modeling that will predict their fate and transport along with the resulting human exposure, and understand the transition from exposure to dose that will enable health assessment work. 

The primary objective of CICADs is characterization of hazard and dose-response from exposure to a chemical. CICADs are not a summary of all available data on a particular chemical rather, they include only that information considered critical for characterization of the risk posed by the chemical. The critical studies are, however, presented in sufficient detail to support the conclusions drawn. For additional information, the reader should consult the identified source documents upon which the CICAD has been based. 

In view of this neurotoxicity, we will review some data relevant to this process. First, we will review data showing that methamphetamine (METH), a prototypic psychomotor stimulant, which has been widely used for nonmedical purposes at doses often a good deal higher than therapeutie doses, is neurotoxic to dopamine (DA) and serotonin (5-hydroxytryptamine (5-HI)) systems. Second, we will examine the evidence that other substituted phenethylamines are also neurotoxic to certain transmitter systems. Last, we will examine the behavioral and pharmacological consequences of neurotoxicity that result from exposure to some of these amphetamine-related drugs. 

Collective dose—The sum of the individual doses received in a given period of time by a specified population from exposure to a specified source of radiation. Collective dose is expressed in units such as man-rem and person-sievert. 

Early in the program, critical components (e.g.,the turbomolecular pump) and circuit boards were tested for their ability to survive neutron and gamma irradiation rates and doses similar to those that would be received from exposure to the detonation of a tactical nuclear device. All components were powered up at the start of the gamma irradiation tests but not during the neutron irradiation tests. Circuit boards were protected by circumvention circuits that powered down critical circuits in 10 to lOOps upon detecting radiation. All components survived the nuclear radiation tests. This unusual performance was noted with positive commendations by the staff at the White Sands Missile Range, where the tests were performed. Tests of the fully integrated CBMS II system, installed in a reconnaissance vehicle, will be conducted in the future. 

The average annual effective dose equivalent received by a member of the UK population is currently estimated to be 2150 ySv. Of this total, 87% arises from exposure to radiation of natural origin, the largest single contributor being inhalation of the short-lived decay products of radon. This exposure occurs predominantly in the home. 

The risk of lung cancer from exposure to radon daughters in homes is derived by assessing lung dose, either absolutely by evaluating an effective dose equivalent (UNSCEAR, 1982 NEA, 1983) or by scaling the... 

Table II. Reference Values of Mean Bronchial Dose from Exposure to 1 WLM Potential Alpha-energy in Homes...

However, results obtained from lung dose modelling still show a large range of values for the conversion of Rn-d exposure to dose for the following reasons ... 

This material is hazardous through inhalation, skin absorption (high doses), penetration through broken skin, and ingestion. Delayed effects from exposure to high concentrations include disintegration of red blood cells. Symptoms include drowsiness, weakness, vomiting, respiratory distress, diarrhea, convulsions, shock, low body temperature, and death. 

Toxic effects of expositions are calculated for a variety of exposures and effect combinations, assuming a probabilistic dose-effect relationship. Lethal and incapacitating responses (e.g. respiratory effects, topical skin effects or incapacitating eye effects) of varying degrees of severity are addressed. The model also distinguishes between effects resulting from vapour exposure and from exposures to liquid droplets. These primary effect probabilities are subsequently combined to afford overall casualty probabilities for lethality, severe incapacitation and incapacitation due to topical eye effects. 

No studies have shown yet humans can develop cancer from exposure to sweeteners. ACSH the enormous doses necessary for such experiments. .. may overwhelm the animal s natural defenses. Saccharin still available, but its use has decreased since 1983 (aspartame approval s year)... 

Harmful effects from exposure to //-hexane have mainly occurred in adults. This is because most known cases have occurred in workers. However, it is probable that if children were exposed to //-hexane at levels that cause harmful effects in adults, similar effects would occur. We do not know whether children differ from adults in their susceptibility to health effects from //-hexane exposure. Only a few animal studies have compared the effects of //-hexane between adults and young animals. In these studies, the young animals were somewhat less likely to have harmful effects on their nervous system from breathing //-hexane than the adults, but more likely to die from a large oral dose. 

Long-term health effects from exposure to low-to-moderate doses of radiation include cancer of the thyroid, prostate, kidney, liver, salivary glands, and lungs Hodgkin s disease leukemia and increased numbers of stillbirths and genetic defects. Concerns about potential long-term health effects often lead to anxiety and depression problems among those exposed to radiation. 

So, with this larger social context in mind, we return to the technical discussion, and move from exposure to what is a principal determinant of risk the dose. 

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