Guidance Values Examples

Various international, federal, and national bodies set guidance values for exposure to chemicals in various media such as air, drinking water, soil, and food. This section will present some examples of guidance values set by the WHO representing an international body, the US-EPA and the EU representing federal bodies, and Denmark representing a national body. 

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Acute toxicity In vitro Mammalian systems Aquatic vertebrates and invertebrates Plants IC/EC50 in appropriate test species Use of appropriate indicators of acute toxicity, for example, EPA guidance values, reference doses, and so on... 

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. 

In the following sections, human exposure factors for ambient air (Section 7.3.1), soil (Section 7.3.2), and drinking water (Section 7.3.3) will be described. These media are used as examples, which serve to illustrate the differences in exposure factors provided by various exposure factor documents. Such differences can have a great impact on the risk characterization (Chapter 8) as well as on the development of regulatory standards and health-based guidance values (Chapter 9), and it is therefore important that the most relevant and reliable values are used for the particular situation. 

Examples of guidance values developed by the WHO include air quality guidelines and drinking water guidelines, and (in collaboration with the FAO) maximum residue limits (MRLs) for pesticides and veterinary dmgs and maximum levels for food additives. 

For example, the guidance value for water is determined from the TDI and known daily intake of water by a standard adult of 60-kg weight drinking the water for 70 years. 

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... 

A.9.2.9.5 The guidance values refer to effects seen in a standard 90-day toxicity study conducted in rats. They can be used as a basis to extrapolate equivalent guidance values for toxicity studies of greater or lesser duration, using dose/exposure time extrapolation similar to Haber s rule for inhalation, which states essentially that the effective dose is directly proportional to the exposure concentration and the duration of exposure. The assessment should be done on a case-by-case basis for example, for a 28-day study the guidance values below would be increased by a factor of three. 

Table 7.3.3 Example mean reference values for uroporphyrin, coproporphyrin I, and coproporphyrin III (these can only be interpreted as a guidance) collected by means of high-performance liquid chromatography (HPLC). The intermediary porphyrins were below the detection limit...

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