Dose and Exposure

If possible, there should be measurement of the toxic effect in order quantitatively to relate the observations made to the degree of exposure (exposure dose). Ideally, there is a need to determine quantitatively the toxic response to several differing exposure doses, in order to determine the relationship, if any, between exposure dose and the nature and magnitude of any effect. Such dose—response relationship studies are of considerable value in determining whether an effect is causally related to the exposure material, in assessing the possible practical (in-use) relevance of the exposure conditions, and to allow the most reasonable estimates of hazard. 

Variability arises from true heterogeneity in characteristics such as dose-response differences within a population, or differences in contaminant levels in tlie enviromiient The values of some variables used in an assessment change witli time and space, or across tlie population whose exposure is being estimated. Assessments should address tlie resulting variability in doses received by members of the target population. Individual exposure, dose, and risk can vary widely in a large population. The central tendency and high end individual risk descriptors are intended to capture tlie variability in exposure, lifestyles, and other factors tliat lead to a distribution of risk across a population. 

Table 2 Fate and effects of metals in a stream receiving a point-source of metals (upper part of the table) or diffuse input via urban runoff (lower part of the table). Summary of the expected influence of four different hydrological situations base-flow in a rainy period a flood after a rainy period low-flow after a long period of low rainfall (water scarcity) and a flood produced after this drought. Metal concentration (M) metal retention efficiency (measured on the basis of the nutrient spiraling concept) exposure (dose and duration) bioaccumulation (in fluvial biofilms) and metal sensitivity (of biofihns)...

Ecotoxicology deals with the study of the harmful effects of chemicals in ecosystems. This includes harmful effects upon individuals, although the ultimate concern is about how these are translated into changes at the levels of population, commnnity, and ecosystem. Thns, in the conclnding sections of the chapter, emphasis will move from the distribntion and environmental concentrations of pollutants to conseqnent effects at the levels of the individnal, population, community, and ecosystem. The relationship between environmental exposure (dose) and harmful effect (response) is fundamentally important here, and full consideration will be given to the concept of biomarkers, which is based on this relationship and which can provide the means of relating environmental levels of chemicals to consequent effects npon individuals, populations, communities, and ecosystems. 

Organism, Route of Exposure, Dose, and Other Variables Effect Reference8... 

The conditions of exposure (dose and duration) under which the chemical s toxicity can be produced. 

D to wheat. The resultant data were used to calculate exposure doses and urinary excretion relationships. 

There are numerous caveats in the use of pre-existing risk assessments to interpret biomonitoring datasets, especially if it is not possible to relate the biomonitoring result to the exposure dose and if the population that the... 

This chapter provides an overview of the exposure, dose, and risk assessments for atrazine and simazine. The underlying databases and detailed algorithms used to produce the numerical results presented herein have been submitted to the USEPA (Sielken et al., 1996). 

The method used in the present work to obtain action spectra of wood pulps is analogous to that developed to construct the erythema action spectrum for human skin [7]. In order to evaluate the action spectra for the photochemical discoloration of the pulps, the spectral irradiance at the sample position must be measured and the response of the exposure, e.g. in terms of the reflectance at 457 nm, has to be analyzed. Thus, an action spectrum takes into account both the exposure dose and the character of the chromqphores that are photoactive in the pulp. The action spectrum for the yellowing is then obtained by plotting the reciprocal of the exposure dose necessary to produce a certain predetermined degree of yellowness versus wavelength. 

OPs have been in use for several decades as important chemicals for the control of crop pests. With their chemical and biochemical reactions, OPs have been well established as extremely poisonous chemicals. This classification is due to the inhibition of the marker enzyme ChE, which is produced in the liver. Blood enzymes provide an estimate of tissue enzyme activity. After acute exposure to OPs or a nerve agent, the erythrocyte enzyme activity most closely reflects the activity of the tissue enzyme. Once the OPs inhibit the tissue enzyme, it cannot hydrolyze ACh, and the accumulation stimulates the affected organ. Based on the manner of exposure (dose and duration) to different OPs, a series of toxicity signs and symptoms set in the organism, leading to death. These are important aspects to be closely monitored among pest control operators and occupational workers exposed to OPs. 

Data regarding metabolism of benzene in humans have come primarily from studies using inhalation exposures. Benzene is excreted both unchanged via the lungs and as metabolites in the urine. The rate and percentage of excretion via the lungs are dependent on exposure dose and route. Qualitatively, the metabolism and elimination of benzene appear to be similar in humans and laboratory animals, but no directly comparable studies are available (Henderson et al. 1989 Sabourin et al. 1988). 

THERdbASE contains two major modules, namely a Database Module and a Model Base Module. The Database Module relates information from exposure, dose and risk-related data files, and contains information about the following population distributions, location/activity patterns, food-consumption patterns, agent properties, agent sources (use patterns), environmental agent concentrations, food contamination, physiological parameters, risk parameters and miscellaneous data files. The Model Base Module provides access to exposure dose and risk-related models. The specific models included with the software are as follows Model 101, subsetting activity pattern data Model 102, location patterns (simulated) Model 103, source (time application) Model 104, source (instantaneous application) Model 105, indoor air (two zones) Model 106, indoor air (n zones) Model 107, inhalation exposure (BEAM) Model 108, inhalation exposure (multiple chemicals) Model 109, dermal dose (film thickness) Model 110, dose scenario (inhalation/dermal) Model 201, soil exposure (dose assessment). 

This chapter describes and illustrates probabilistic approaches to aggregate and cumulative assessments of exposure, dose and risk. Aggregate assessments account for multiple sources (e.g. food, water, residence and occupation) and multiple routes (ingestion, dermal and inhalation) of exposure for a single pesticide. Cumulative assessments combine exposures for chemicals that share a... 

This chapter illustrates probabilistic approaches to residential and occupational exposnre assessment and their incorporation into aggregate and cumulative assessments of exposure, dose and risk. 

A common understanding of the terminology used in occupational and residential exposure assessment is an important prerequisite to effective harmonization. For example, inconsistent use of terms such as exposure/dose and upper bound/ worst-case is confusing and can be an impediment to effective harmonization. 

Only some of the pathways can be considered critical, that is that they contribute most to the exposure dose and may approach the dose upper bound. This depends on the site-specific parameters and on the physico/chemical behaviour of individual radionuclides. For example ... 

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