Population level effects assessment practices

It is an accepted practice when assessing the environmental effects of pollution on man and his place of abode to use a divisor of 40 (some agencies may divide by 30) against the long-term exposure level in the Occupational Health and Safety Act (OSHA). Much lower exposure limits are necessary due to the much longer term of exposure in the domestic situation. The section of the population most likely to spend long periods of time in the home are those most susceptible to the detrimental effects of pollutants, i.e. the young, the elderly or the infirm. For short-term exposure the known data can be used directly from the list or from animal-exposure data. 

Risk assessment of chemicals does not, in practice, estimate the incidence and severity of the adverse effects likely to occur in the human population or environmental compartment due to actual or predicted exposure to a substance — the definition of risk characterization in Article 2 of Directive 93/67/EEC. The assessment process hinges on being able to say that there is a threshold below which the chemical has no adverse effects, in other words on being able to derive a no-effect level. Recent debates, discussed later, challenge the idea that there normally is such a threshold. 

Although dose-response assessments for deterministic and stochastic effects are discussed separately in this Report, it should be appreciated that many of the concepts discussed in Section 3.2.1.2 for substances that cause deterministic effects apply to substances that cause stochastic effects as well. The processes of hazard identification, including identification of the critical response, and development of data on dose-response based on studies in humans or animals are common to both types of substances. Based on the dose-response data, a NOAEL or a LOAEL can be established based on the limited ability of any study to detect statistically significant increases in responses in exposed populations compared with controls, even though the dose-response relationship is assumed not to have a threshold. Because of the assumed form of the dose-response relationship, however, NOAEL or LOAEL is not normally used as a point of departure to establish safe levels of exposure to substances causing stochastic effects. This is in contrast to the common practice for substances causing deterministic effects of establishing safe levels of exposure, such as RfDs, based on NOAEL or LOAEL (or the benchmark dose) and the use of safety and uncertainty factors. 

We have reviewed current conceptual and modeling approaches in mixture eco-toxicology as well as current experimental evidence to derive practical risk assessment protocols for species and species assemblages. From the review of conceptual approaches in mixture ecotoxicology, it appears that there is a difference between a mechanistic view of joint action from a compound mixture and a probabilistic perspective on combined toxicity and mixture risk. A mechanistic view leads to emphasis on the distinction of modes of action and physicochemical properties first, then on the choice of the appropriate joint toxicity model, followed by a comparison of the models prediction with experimental observations. A probabilistic orientation leads to the observation that concentration addition often yields a relatively satisfactory quantitative prediction of observations for the integral level of effects as observed in individual organisms or populations. In these applications, concentration addition is frequently connected with a slight bias to conservatism, especially for compounds with different modes of action (Backhaus et al. 2000,2004 Faust et al. 2003). 

The main diagnostic practices with radiopharmaceuticals are the procedures for bone, cardiovascular, lung perfusion, lung ventilation, thyroid scan, thyroid uptake, renal, liver/ spleen, and brain examinations. The effective doses per procedure are considerably higher and are 4.5 mSv, 8 mSv, 1.5 mSv, 1 mSv, 3.4 mSv, 15 mSv, 1.9 mSv, 1.7 mSv, and 6 mSv, respectively, and the number of procedures per 1,000 population are 4.5, 2.7, 1.8, 0.34, 4.1, 0.92, 0.89, 2.1, and 1.3, respectively for countries at health-care level I. But patients near to the end of their lives receive many of these exposures, and thus the doses are not distributed evenly among the population. Therefore, these doses should not be used for the assessment of detrimental effects of radiation exposure. 

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