Exposures to (and intake of) environmental contaminants depends to a large degree on the characteristics of the people concerned.  These comprise not just their physical characteristics, such as height and weight, which influence the bodily area available for exposure and the mass into which the contaminant can be absorbed, but also the many different aspects of behaviour that help to determine opportunities for exposure and efficiency of intake.  These latter factors involve almost every aspect of lifestyle - e.g. diet, exercise, transport choices, home environment, dress, smoking and patterns of socialisation - and all the many different elements of social and personal context and history that in turn influence these (e.g. age, gender, income, culture).

If exposure and intake assessment are to be reliable, and properly reflect the variations in exposure likely to occur within a study population, they need to take account of these personal and social influences.  This is all the more important in integrated environmental health impact assessments, where concern is often about how exposures will change under different policy scenarios.  These changes are not just a function of changes in the environment; they occur also because of associated changes in behaviour.  Policies aimed at reducing urban air pollution, for example, are often targetted at changing emissions from transport systems and housing.  Achieving either of these almost inevitably involves adaptations in behaviour, both as a deliberate part of the policy itself (e.g. by encouraging a shift from private to public transport, or installation of insultaion in the home) and as a concomittant or incidental response.   Even a simple switch from car to bus or train for the journey to work, for example, may result in a change in travel routes, travel time, journey duration, amount of time spent outdoors and even style of dress, all of which may affect exposure and intake of pollutants and may modify the overall health impact of the policy.  Moreover, many of the behavioural and lifestyle characteristics that modulate exposures and intake in these ways are associated with gender, socio-economic status or ethnicity, and are thus the potential source of social inequalities in risk and so-called environmental injustices.  For this reason, too, they need to be considered in assessments.

Allowing for these effects in any detailed way is difficult, especially in large population studies, where individual level data on time activity, lifestyle and personal characteristics is likely to be sparse.  Because of their social and demographic associations, however, they can be approximated with some degree of confidence at group level - e.g. stratified by age, gender, socio-economic status or occupation.  Behavioural, lifestyle, social and personal data are all extensively collected, for exampe, both as part of national censuses and more targetted social surveys.  Several attempts have also been made to bring together relevant information in the form of databases on exposure factors.  These provide statistics on a wide variety of behaviours and other contextual factors likely to affect exposures.  They can best be used in exposure assessments either deterministically, to adjust estimates of 'average exposure' for specific population sub-groups, or probabilistically to represent the distribution of exposures likely to occur within a group as a consequence of behavioural, lifestyle and personal influences.    

Links to a number of sources are provided under See also, below.