Why are the combined effects of indoor air pollutants hard to measure?
Indoor air is a complex mixture of pollutants (chemical substances, allergens and microbes) from various sources that changes with time. At present, however, relevant data and established methods to evaluate the health effects of such mixture of air pollutants are rare and risk assessments of air pollution mostly deal with exposure to single substances. In addition, the few findings available on interactions among more than two chemicals usually do not address issues of long-term toxicity at realistic concentrations. Data from studies on individual chemicals can be used directly if the components of the mixture act independently. However, some of the chemicals in the air may influence each other. Indeed, several chemicals acting together may cause more (or less) harmful effects than the sum of the effects caused by each chemical separately. For example, potentially harmful combined effects of mixtures of pesticides have been observed at concentrations of each single component at which,
