Guidelines for Metals and Metalloids in Ambient ... - ARCHIVE: Defra

Expert Panel on Air Quality Standards
20. In this report, the effects of individual pollutants have been considered
separately. However, the Panel recognises that ambient air in the
vicinity of industrial plant contains a complex mixture of pollutants at
differing concentrations. The effects of exposure to more than one
pollutant may be additive (i.e., the sum of the individual pollutant
effects), synergistic (i.e., greater than the sum of the individual
pollutant effects) or antagonistic (i.e., less than the sum of the
individual pollutant effects).
21. There is a paucity of information on the patterns of exposure of
populations to various mixtures of pollutants and on the effects of
these mixtures. Whether effects are additive, synergistic or antagonistic
will depend on the pollutants involved, their likely mechanisms of
effect and their concentrations.
22. In general, the default assumption is that the effects of multiple
pollutants are additive unless there is evidence to the contrary.
23. Much of the information on the harmful effects of metals on humans
comes from studies of populations whose exposures have occurred at
work. Where there is exposure to more than one toxic metal then it
may be difficult to distinguish the effects of one from the other; the
same is true for simultaneous exposures to other harmful substances
such as noxious fumes at work or, commonly, cigarette smoke. Failure
to account for such ‘confounding’ exposures may lead to an
overestimate of the risk attributed to the metal under study.
24. The application of guideline values is outside the scope of the Panel’s
remit. However Agencies making use of these recommendations
should be aware that in deriving recommended values, the Panel
considered each of the pollutants in isolation. It is recognised
that there are similarities in the range of effect seen for each of the
individual metals considered. For some responses, notably
hypersensitivity, the individual metals are unlikely to show
cross-reactivity but in other cases, for example when an irritant effect
is seen, responses can be anticipated to be additive. These factors
should be taken into account by external Agencies when applying
the values in environments where mixed exposures are likely.
The Panel recommends that in case of doubt a precautionary
approach is appropriate.
1.2.4 Susceptible and vulnerable groups
25. Children are at increased risk of adverse health effects from any inhaled
toxin. The factors that contribute to this increased vulnerability are
discussed in detail in Appendix I of the Halogens and Hydrogen
Halides report (EPAQS, 2006a). In general, children spending more
6