« Examination of pregnant women’s exposure reveals links between similar compounds.
Human exposure to a chemical is likely to match that of related substances, according to a study of the ‘exposome‘ – the environmental equivalent of the human genome.
The study indicates that results reported for single exposures need to be carefully interpreted in light of correlations to other exposures of related chemicals.
The ‘exposome‘ represents everything that humans are exposed to from conception onwards. It includes:chemicals, diet and social influences.
Exposome studies aim to understand how exposures interact with personal characteristics, such as genetics, to affect health.
Current analytical techniques are not sensitive or flexible enough to identify the components of the exposome in a “single analytical sweep”, say the researchers, led by Oliver Robinson from the Centre for Research in Environmental Epidemiology in Barcelona, Spain. They have adopted a “bottom-up” approach, using exposure assessment tools such as biomonitoring.
The team has used data on chemical exposure for more than 700 women enrolled in the Spanish infancia y medio ambiente (Inma) project. This birth cohort study runs in seven Spanish regions to examine the role of environmental pollutants during pregnancy and early childhood in relation to growth and development.
Women in the survey have their blood analysed for chemicals such as organochlorines and perfluoroalkyl substances (PFAS). Meanwhile breast milk is screened for polybrominated diphenyl ethers, and urine for metals, phthalates and bisphenol A. The women answer questionnaires to assess their home environment, including pesticide use. Researchers also estimate noise exposure levels and building density, including surrounding green spaces.
An exposure heat-map for Inma’s Sabadell group – situated in Catalonia – reveals correlations for groups of chemicals with similar structures or from the same source. Water disinfection byproducts and air pollutants correlated well, as did PFAS, with four PFOA compounds showing the strongest exposure correlation.
“From this analysis it is clear that it is very difficult to know, for instance, which PFAS is having an impact on a health effect such as neurodevelopment,” says Dr Robinson. “Knowledge of correlation is very important in epidemiological analysis since if you only measure one exposure you may actually be detecting a health effect from highly correlated exposures.”
Understanding exposure correlations not only helps when selecting the most suitable statistical approaches, but may also allow the exposome to be characterised using fewer exposures, he adds.
The researchers consider their correlation analysis to provide a “first picture” of the structure of the exposome during pregnancy. “This information will aid interpretation of reported findings from epidemiological studies in general and inform future analyses of the exposome,” they conclude.
The team is currently delving further into Inma data, looking, for example, at diet.
The study is published in Environmental Science and Technology and links to a wider EU “early-life” exposome project called HELIX.”
Journal article : http://pubs.acs.org/doi/ipdf/10.1021/acs.est.5b01782
HELIX project: http://www.projecthelix.eu/
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