Assessment of an integrated environmental exposure index

Health Council of the Netherlands: Standing Committee Environmental Factors
and Health. Assessment of an integrated environmental exposure index. The
Hague: Health Council of the Netherlands, 1995; publication no. 1995/05

An integrated environmental exposure index (abbreviated in the English text IEI; the Dutch abbreviation is MBI for milieubelastingsindex) is intented to serve as a tool for spatial planners in areas where activities like housing and industry compete for space. The idea behind an IEI is to be able to express in one number or qualification an assessment of various aspects of the quality of the environment. This report concerns the question whether such an IEI can be realised, and in particular whether a certain procedure is correct that was proposed for derivation of an IEI. The IEI concerned was developed by the Institute for Environmental Research of the Free University in Amsterdam (IER-IEI, in Dutch: IVM-MBI Instituut voor Milieuvraagstukken - Milieubelastingsindex). The IER-IEI aims at being a measure for the health risk of the population in a given area that is affected by air pollutants, sound and the possibility of accidents, all caused by surrounding installations. For calculation of the IEI a number of rules of combination are applied to measured or estimated data obtained for the area. It is important for the assessment that the IER-IEI contains steps that can be verified more or less empirically, as well as steps that are based on a value judgement.
This report is produced by a committee of the Health Council of the Netherlands on request of the Minister of Health, Welfare and Sports and the Minister of Housing, Spatial Planning and Environment.

The committee considered to what extent, in general, an IEI can represent the integrated human health risk at a given site, in so far it is caused by sources of detrimental influences in the vicinity.
An IEI-procedure can be verified in part by empirical research or by establishing whether certain decision rules are in agreement with existing knowledge, however a calculated IEI number for a given location can not be verified by the study of adverse health effects in the population. To do so, one would need to study a very large, homogenous population thoroughly and for a prolonged period of time and compare it to a suitable control group. Besides the adverse effect on health caused by most environmental factors is minor compared to the effects of other determinants such as life style, profession, housing or genetic status and thus difficult to measure.
The IER-IEI implies the assumption that exposure of humans at the particular location is relatively constant and equal for all members of the population. This assumption implies a severe simplification of reality. Even for a population that has lived at the site for a long period of time, exposure to factors from the environment will vary from minute to minute and from year to year. Also the composition of the population will change, and as a confounding factor exposure to environmental factors may play a role. These factors can complicate or even make impossible a reliable estimate of the exposure and its health effects.
The IER-IEI did not take into account all types of exposures to environmental factors when established, although these factors may affect health adversely. In this respect air pollution from sources beyond the region under consideration can be mentioned, e.g., fine dust or nitrogen dioxide. Considering routes of exposure (of substances), the IER-IEI confines itself to inhalation; uptake by soil or food is not included. Vibrations, and biological agents are types of pollution that are neglected in the IER-IEI. In addition, several health effects are not taken into account by the IER-IEI, e.g., illness due to exposure to carcinogens, non-lethal injuries due to accidents and feelings of insecurity in industrial environments.

The adverse factors to be combined, e.g., air pollutants, sound and accident risk, must be given a common denominator. Considering the intended character of the IER-IEI, as a measure of risk to health, the denominator must be a health effect.
The committee considers it possible to establish an index for odour and sound, based on empirical data of hindrance, their common denominator, as suggested by the NIPG-TNO and included as the first step of the IER-IEI. The committee does not consider it possible to produce a combined index based on empirical data for carcinogenic effects and for accident risk (external safety) although both factors can cause death. If it is presumed that a kind of 'model population' stays on a certain location for such a long time that any health effect due to environmental influences is realised, a common index for death could be thought of. Carcinogens and accidents can also cause illness. On a scientific or medical basis, illness and death cannot be given a common denominator. The committee also does not consider it possible to construct a single index for substances causing toxic but non-carcinogenic effects, considering the great differences in the nature of the effects. In principle, only a combined toxicity index for similar effects is possible.

The committee concludes that it is not possible to construct, on a scientific or medical basis, one measure for health damage or risk that would include hindrance, illness and death. In administrative decision-making knowledge from the social sciences about value judgment and decision models could be helpful.