EXPOSURE TO MIXTURES OF CHEMICAL-SUBSTANCES - IS THERE A NEED FOR REGULATIONS

The setting of standards for individual substances is an important too l in the protection of human health. However, it has been a topic of d iscussion for many years whether only this type of standard-setting wi ll meet common goals for health protection, since humans are exposed t o a large variety of chemical substances from many different sources i n variable concentrations and by different routes of exposure. The com plexity of this problem makes it difficult to answer this question and almost impossible to quantify the answer. It is common knowledge that combined exposure to chemical substances may cause synergism. However , these examples are referring to relatively high levels of exposure. In present environmental and occupational practice, exposure to indivi dual chemicals has usually been reduced to acceptable levels. The key question is whether exposure to mixtures at levels of the single compo nents near or below no-observed-adverse-effect levels can still cause adverse effects. Few countries have incorporated procedures concerning combination toxicity in their policy regarding chemical substances. I f so, the uncertainty in these procedures is considerable because of l ack of relevant data. This usually leads to a conservative approach. R oughly two approaches can be distinguished for systemic toxicants: int roduction of an (extra) uncertainty factor or application of the addit ivity principle. In The Netherlands, for systemic toxicants a safety f actor was introduced in 1989 to account for combination effects. Probl ems related to this approach have led to adaptations in procedures and a reconsideration of the chosen safety factor. Copyright 1997 Elsevie r Science Ltd.