Social factors associated with nitrogen dioxide (NO2) exposure during pregnancy: The INMA-Valencia project in Spain

Numerous studies have focused on the effects of exposure to air pollution on health: however, certain subsets of the population tend to be more exposed to such pollutants depending on their social or demographic characteristics. In addition, exposure to toxicants during pregnancy may play a deleterious role in fetal development as fetuses are especially vulnerable to external insults. The present study was carried out within the framework of the INMA (Infancia y Medio Ambiente or Childhood and the Environment) multicenter cohort study with the objective of identifying the social, demographic, and lifestyle factors associated with nitrogen dioxide (NO2) exposure in the subjects in the cohort. The study comprised 785 pregnant women who formed part of the INMA cohort in Valencia, Spain. Outdoor levels of NO2 were measured at 93 sampling sites spread over the study area during four different sampling periods lasting 7 days each. Multiple regression models were used for mapping outdoor NO2 throughout the area. Individual exposure was assigned as: 1) the estimated outdoor NO2 levels at home, and 2) the average of estimated outdoor NO2 levels at home and work, weighted according to the time spent in each environment. The subjects' socio-demographic and life-style information was obtained through a questionnaire. In the multiple linear analyses, the outdoor NO2 levels assigned to each home were taken to be the dependent variable. Other variables included in the model were: age, country of origin, smoking during pregnancy, parity, season of the year, and social class. These same variables remained in the model when the dependent variable was changed to the NO2 levels adjusted for the subjects' time-activity patterns. We found that younger women, those coming from Latin American countries, and those belonging to the lower social strata were exposed to higher NO2 levels, both as measured outside their homes as well as when time-activity patterns were taken into account. These subgroups also have a higher probability of being exposed to NO2 levels over 40 mu g/m(3), which is the annual limit for maximum safe exposure, as established by European Directive 2008/50/EC. (C) 2011 Elsevier Ltd. All rights reserved.