Guideline value

The health effects of different pollutants vary according to the Intensity and duration of exposures and the health status of the persons exposed. A sumnary of these effects Is provided In Table II, together with the WHO (1979) guideline values for the protection of human health. The WHO European office has reviewed these guidelines, WHO (1987), and has recommended additional values for SOj In the presence of particulate matter. 

Table II. WHO Air Quality Guideline Values and Health Effects...

Figure 6 shows a cumulative probability plot of both the maximum dally and hourly NO2 averages In cities for the 1980-84 time period. The plotted values can be directly compared to the WHO guideline values of 150/tg/m3 for the maximum 24-hour level and 400/tg/m3 for the maximum 1-hour level. In both cases, about 25% of the cities worldwide exceed the guideline values. Based on these proportions of cites with NO2 concentrations above the short-term guideline values. It Is estimated that approximately 15-20 percent of urban residents In North America and Europe are at Increased risk to short-term high NO2 exposures. 

Figure 7 provides a cumulative frequency distribution of the maximum 8-hour standard In 15 cities In 1980-84. Shown on the graph Is the 10 mg/m3 WHO guideline value. It can be seen that the average maximum 8-hour level Is exceeded In about 50% of the cities. 

Table V. Cities Reporting Site-Year Averages In Excess of WHO Guideline Values, In Percent...

WHO (2004) concluded that The mono- and disubstituted compounds that may leach from PVC water pipes for a short time after installation are primarily immunotoxins although they appear to be of low general toxicity, some are developmental toxins in rodents. The data available are insufficient to permit the proposal of guideline values for individual dialkyltins or the mono derivatives, although the concentrations observed in drinking-water are several orders of magnitude lower than the doses reported to cause developmental effects in rats and mice. ... 

WHO Drinking-water guideline values for health-related organics None WHO 1984... 

WHO Guideline value for drinking water is not detectable by consumers No WHO 1984... 

Meat consumption rate)(Fraction fat in meat)(guideline value)... 

For comparison, we have calculated the health effects for typical residential properties (4 occupants each) based on 1) the naturally occurring background radiation levels and radionuclide concentrations in four cities across the U.S. (see Table V) and 2) the EPA (CFR, 1981) guideline values (20 yR/h, 0.02 WL, 5 pCi Ra-226/g of soil) for cleanup at inactive uranium processing sites (see Table VI). 

On the other hand, the estimated risk for occupants of residential structures cleaned up to the EPA guideline values was about a factor of 3 higher than for residents exposed to natural background levels. 

WHO Drinking-water guideline values-chemlcals of health significance 300 g/L WHO 1996... 

The most widely used of the many mathematical models proposed for extrapolation of carcinogenicity data from animal studies to low-dose human exposures (i.e., low-dose extrapolation) is the LMS model. This has, in effect, become the default approach for quantitative risk assessment and has been used by, e.g., the US-EPA for many years as well as by the WHO in relation to derivation of drinking-water guideline values for potential carcinogens (WHO 1996) (see Section 9.2.1.2 for drinking-water guideline values). 

The WHO considers in its drinking-water quality guidelines, in relation to genotoxic carcinogens, that a lifetime cancer risk for consumers of less than 10 represents a tolerable risk (WHO 1996). Guideline values associated with excess lifetime cancer risks of 10 and 10 are also presented for the genotoxic carcinogens to emphasize the fact that each country should select its own appropriate risk level. 

The WHO emphasized that guideline values for carcinogenic substances computed using mathematical models must be considered at best as a rough estimate of the cancer risk, as these models do not usually take into account a number of biologically important considerations, such as toxicokinetics, DNA repair, or immunological protection mechanisms. However, the models used are conservative and probably err on the side of caution. 

In order to account for differences in metabolic rates between experimental animals and humans, a surface area to body weight correction (Section 5.3.2.2) is sometimes applied to quantitative estimates of cancer risk derived by low-dose extrapolation. The WHO stated that incorporation of this factor increases the risk by approximately one order of magnitude, depending on the species upon which the estimate is based, and increases the risk estimated on the basis of studies in mice relative to that in rats. The WHO considered incorporation of this factor to be overly conservative, particularly in view of the fact that linear extrapolation more likely overestimates risk at low doses. Therefore, the guideline values for carcinogens were developed on the basis of quantitative estimates of risk that were not corrected for the ratio of surface area to body weight. 

The introductory Chapter 2 of the Air Quality Guidelines (WHO 2000) gives a very detailed and comprehensive description of the criteria used in establishing the guideline values including criteria for selection of NOAEL/LOAEL, adverse effect, benchmark approach, and uncertainty factors. These criteria are comparable to the principles outlined in Chapters 4 and 5 in this book. There are also criteria for selection of averaging times and for consideration of sensory effects (malodorous... 

In some instances, provisional guideline values have been set for constiments for which there is some evidence of a potential hazard but where the available information on health effects is limited. Provisional guideline values have also been set for substances for which the calculated guideline value would be below the practical quantification level, or below the level that can be achieved through practical treatment methods, as well as for certain substances when it is likely that guideline values will be exceeded as a result of disinfection procedures. 

It is stated that thousands of chemicals have been identified in drinking-water supplies around the world, many in extremely low concentrations. The chemicals selected for the development of guideline values include those considered potentially hazardous to human health, those detected relatively frequently in drinking water, and those detected in relatively high concentrations. 

Chapter 12 of Volume 2, second edition (WHO 1996), gives a detailed and comprehensive description of the principles used in estabfishing the guideline values. 

The assessment of the toxicity of drinking-water contaminants has been made on the basis of published reports from the open literamre, information submitted by governments and other interested parties, and unpublished proprietary data. In the development of the guideline values, existing international approaches to developing guidelines were carefully considered. Previous risk assessments developed by the WHO/IPCS in EHC monographs (see Section 3.6.1.1), lARC (see Section 3.6.1.2), JMPR (see Section 3.6.1.3), and JECFA (see Section 3.6.1.3) were reviewed. These assessments were relied upon except where new information justified a reassessment. The quality of new data was critically evaluated prior to their use in risk assessment. 

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