Exposure dose, definition

For the inhabitants of the exclusion zone, situated in a forested region without well-developed economic and social infrastructures, it is of interest to estimate the relative contributions to internal exposure of forest food (berries and mushrooms) and conventional agricultural food (potatoes and milk). Some specialist studies have assumed that forest food represents only a small part of the diet of inhabitants of the exclusion zone, but we would suggest that in fact, it plays a major role. Typically, the consumption of forest food contributes 50% of the internal exposure dose, while for some critical population groups, it can exceed 80%. The definition of the spatial variation in pollution, the prevailing ecological conditions, and the diet should allow a scientifically-based prediction to be made of the internal exposure dose to the local population, and will help to identify the major risk factors within a certain time period following the Chernobyl catastrophe. 

A related term is the margin of safety. According to the OECD/IPCS definitions listed in Annex 1 (OECD 2003), the margin of safety, for some experts, has the same meaning as the Margin of Exposure, while for others, the margin of safety means the margin between the RfD and the actual exposure dose or concentration. 

Several terms are used differently by toxicologists and epidemiologists, so definitions are provided for terms as they are used here. Dose is the amoimt of a substance to which a person is exposed over some period. An exposure dose is how much of a substance is encoimtered in the environment. An absorbed dose or internal dose is the amount of a substance that gets into the body through the eyes, skin, stomach, intestines, or lungs. One needs to differentiate exposure (lead outside the body) from the internal dose. 

Several additional terms related to the absorption of x-radiation require definition energy of a x-ray photon is properly represented in joules but more conveniently reported in eV fluence is the sum of the energy in a unit area intensity or flux is the fluence per unit time and the exposure is a measure of the number of ions produced in a mass of gas. The unit of exposure in medicine is the Rn ntgen, R, defined as the quantity of radiation required to produce 2.58 x C/kg of air. The absorbed dose for a tissue is a measure of energy dissipated per unit mass. The measure of absorbed dose most... 

Tb allium, which does not occur naturaHy in normal tissue, is not essential to mammals but does accumulate in the human body. Levels as low as 0.5 mg/100 g of tissue suggest thallium intoxication. Based on industrial experience, 0.10 mg /m of thallium in air is considered safe for a 40-h work week (37). The lethal dose for humans is not definitely known, but 1 g of absorbed thallium is considered sufficient to kHl an adult and 10 mg/kg body weight has been fatal to children. In severe cases of poisoning, death does not occur earlier than 8—10 d but most frequently in 10—12 d. Tb allium excretion is slow and prolonged. For example, tb allium is present in the feces 35 d after exposure and persists in the urine for up to three months. 

Typical units for LDjq values are milligrams or grams of material per kilogram of body weight (mg/kg or g/kg, recall that 1 kg = 2.2 pounds). Never be exposed to an LD50 dose of a hazardous chemical- by definition, there is a 50% chance this will kill you and if you survive you are not going to be in good shape. Pay close attention to the permissible exposure level (PEL) instead. This is a more realistic determination of the maximum safe exposure to a material and is usually based on the known effects of the chemical on humans, rather than laboratory animals. 

Hazard identification is defined as tlie process of determining whetlier human exposure to an agent could cause an increase in the incidence of a health condition (cancer, birtli defect, etc.) or whetlier exposure to nonliumans, such as fish, birds, and otlier fonns of wildlife, could cause adverse effects. Hazard identification cliaracterizes tlie liazard in terms of tlie agent and dose of the agent. Since tliere are few hazardous chemicals or hazardous agents for wliich definitive exposure data in humans exists, tlie identification of health hazards is often characterized by the effects of health hazards on laboratory test animals or other test systems. ... 

Much of the initial development of Gaussian modeling and definition of dispersion paramenters was done during and after World War I in addressing the problem of poison gas dispersal. These studies involved the definition of risk factors, such as exposure and dose. The next intensive development effort came during and after World War II with the nuclear weapons program. 

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