Guidance value, definition

These two definitions reflect two sides of the same situation. In this book, the term critical effect(s) will be used for the hazard/effect considered as being the essential one(s) for the purpose of the risk characterization, e.g., for the establishment of a health-based guidance value, permissible exposure level, or Reference Dose. It should be noted that the critical effect could be a local as well as a systemic effect. It should also be recognized that the critical effect for the establishment of a tolerable exposure level is not necessarily the most severe effect of the chemical substance. For example, although a substance may cause a serious effect such as liver necrosis, the critical effect for the establishment of, e.g., an occupational exposure limit could be a less serious effect such as respiratory tract irritation, because the irritation occurs at a lower exposure level. 

MRLs are, by definition (Chou et al. 1998), substance-specific and do not include effects attributable to interaction (whether additive, synergistic, or antagonistic) with other chemicals or environmental substances. Their relevance to the mission of ATSDR is to assist public health officials in the identification of chemicals/elements of potential health concern at hazardous waste sites. The ATSDR MRL is not intended to be used in the regulatory or site clean-up process, but is instead intended to serve as a basis of comparison with actual measured levels of environmental exposure. Further, the role of informed biomedical judgment is crucial in the application of any MRL, or the media-specific health guidance values (HGVs) derived from them, in any given exposure scenario (Risher and De Rosa 1997). MRLs for a particular substance are based upon the most sensitive effect/endpoint in that portion of the human population considered to be most susceptible to injury from exposure to that substance. Thus, the... 

These are definitive even if the detailed kinetics is not known. While the results of the derivation of the dimensionless functions is limited to the specified conditions, the derivatives are of general value and give experimental guidance. 

The advent of NICE heralds a new era in which evidence about cost-effectiveness is formally required to help determine whether new interventions should be made available at public expense, ffowever, definitive yes/no decisions about market access have major implications for pharmaceutical companies. Economic information available at launch can only provide initial guidance about value for money. Further evidence on cost-effectiveness in real-world use will also be required. 

Measurement uncertainty characterizes the extent to which the unknown value of the measurand is known after measurement, taking account of the information given by the measurement. Compared with earlier, more complicated definitions, the current definition of measurement uncertainty is quite simple, although it does not give much guidance on how it is to be estimated. What information should be used, and how should one use it ... 

In the absence of other guidance governing the cleanliness classification and acceptable levels of microbial contamination of the clean room, the values presented in Table 1 may be used. The room grades presented are from most critical (A) to least critical (E). The definition of criticality is left to the clean-room user organization. 

Although MEPAS applications are often data intensive, the MEPAS documentation provides both application guidance (5) and definitions and sources of information for all input parameters (6). When available, site-specific data are used. Alternative procedures are provided for estimating emission, transport, and exposure parameter values for sites using local, regional, state, and federal information sources. 

The second part of this definition, taken at face value, enables a clean-up approach to be adopted that focusses solely on dealing with the contaminant. However, this option is closed down, except in specific circumstances, by the statutory guidance in Chapter C. The provision was included largely for the avoidance of any potential doubt as to the extent of the remediation requirements of the Part IIA regime. For example, a similar restoration to its former state definition is used under water legislation to require the re-stocking of watercourses with fish after pollution incidents the drafters of Part IIA did not wish to find that this kind of requirement could not be imposed, should it be necessary. 

In summary, the BSS provide radiological criteria to serve as a basis for the derivation of clearance levels but provide no definitive quantitative guidance on clearance levels. The activity concentration values developed in the following section for use in making decisions on the exemption of bulk materials may find use by regulatory bodies as a basis for the clearance of such materials. 

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