Threshold guidance values

At a wipe test a sample is taken with a tissue or a swab from a surface, after it has been cleaned. The tissue must be moistened with a liquid in which the substance to be expected will dissolve. The sample is then analysed for example for radioactivity or traces of substances used. Results of wipe tests may be in the order of 0.1 nanograms/cm, very much depending on the method of sampling and method of analysis. A reference value (threshold guidance value) can therefore (Mily be set in relation to a specific method of sampling and analysis. A general consensus isn t available yet... 

Table 26.7 Threshold Guidance values for 5-fluorouracil and Platinum in hospital pharmacies (Adapted from Schierl et al. [58])...

Reference should be made to Threshold Limit Values, Guidance Note EHl7/78, issued by the Health and Safety Executive (HSE), or Industrial Ventilation (American Conference of Governmental Industrial Hygienists). In all cases, proposals should be reviewed by and submitted to the relevant local authority agencies. 

Default Assessment Factors Used or Suggested for the Establishment of a Regulatory Standard or Health-Based Guidance Value for Threshold Effects... 

Guidance values are developed from a standard such as, e.g., an Acceptable/Tolerable Daily Intake (ADI/TDI), and Reference Dose/Concentration (RfD/RfC). For threshold effects, the standard is derived by dividing the No-Observed-Adverse-Effect Level (NOAEL) or Lowest-Observed-Adverse-Effect Level (LOAEL), or alternatively a Benchmark Dose (BMD) for the critical effect (s) by an overall assessment factor, described in detail in Chapter 5. For non-threshold effects, the standard is derived by a quantitative assessment, described in detail in Chapter 6. 

Technical Guidance Document Threshold Limit Values Technical Notes for Guidance... 

BMD models are used to estimate human health guidance values for environmental substances. QSARs are used to provide data estimates for chemicals that lack adequate experimental documentation. The ATSDR uses two commercial computational toxicology models to make toxicity predictions based on QSARs. To increase confidence in the models predictions, ATSDR used the models similarity search features and established a minimum threshold similarity distance value of 0.25 to increase the probability that predicted toxicity values are close to nearest analog chemicals. 

A common misconception is that health guidance values, such as the MRL, represent a level above which toxicity is likely to occur. This misconception has occasionally led to unwarranted concern and public apprehension about relatively benign exposures to environmental substances. The MRL is neither a threshold for toxicity, nor a level beyond which toxicity is likely to occur. MRLs are established solely as screening tools for public health officials to use when determining whether further evaluation of potential exposure at a hazardous waste site is warranted. The relevance of the MRL to public health is discussed further in the following sections concerning the derivation of the respective mercury MRLs. 

Health and Safety Executive, Guidance Note EH 15/80, Threshold Limit Values, HMSO, London (1980)... 

Authorities from several countries publish recommended standards for airborne gases, vapours, dusts, fibres and fume. The two main sources are the Health and Safety Executive in the UK who publish occupational exposure limits (OELs) in their Guidance Note Series No EH40 and the American Conference of Governmental Industrial Hygienists who publish threshold limit values (TLVs). Both these sources update annually. 

Reliable quantitative data are a prerequisite for evaluating the contribution of a single odorant to a positive aroma or off-flavor. They are needed to calculate odor activity values (OAV) that are defined as the ratio of the concentration to the sensory threshold of a given compound in a matrix (Rothe and Thomas, 1963 Acree et al., 1984). These values give guidance in the evaluation of the impact of an odorant to the overall aroma profile. 

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