In a scientific review published on May 11, 2016, in the peer-reviewed journal International Journal of Hygiene and Environmental Health, Martine Vrijheid and colleagues from ISGlobal, Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain, explore the evidence for associations between common environmental contaminants and child health outcomes.
Studies published between 2010 and 2015 were included, with the last search performed on September 1, 2015. Considered exposures included prenatal/maternal intra-uterine exposures or postnatal childhood (0-18 years) to air pollutants, select heavy metals, organochlorine compounds, perfluoroalkyl substances, polybrominated diphenyl ethers, currently used pesticides, phthalates, and bisphenol A (BPA, CAS 80-05-7). Child health outcomes were limited to four areas: fetal growth, neurodevelopment, respiratory and immune health, and childhood obesity. Not included were congenital malformations, genital or pubertal development, cancers, and mortality related outcomes.
For fetal growth and preterm birth, evidence for association with low birth weight was considered “moderate” for perfluorooctanoate (PFOA), and “insufficient” for perfluorooctane sulfonate (PFOS) and other perfluoroalkyl substances (PFASs). For phthalates and BPA, evidence was classified as “inconclusive” due to inconsistencies in the study results.
For neurodevelopment, evidence was classified as “insufficient” for all PFASs due to the low number of available studies and inconsistencies in their results. For phthalates, the authors note that more than ten epidemiological studies have found some associations between higher maternal exposure and poorer neurodevelopmental outcomes. However, evidence was classified as “insufficient” due to inconsistencies “with respect to the different phthalate congeners, the neurodevelopmental domains implicated and the sex-specificity of the effects.” Similarly, evidence for BPA was considered “insufficient” as well due to “discrepancies in the sex-specific directions of the associations, in the specific behavioural domains most affected, and in the time window or exposure.”
For respiratory and immune health, there has been evidence that PFASs exposure may negatively affect the efficiency of vaccination; apart from this, evidence for PFASs association with other child health outcomes was considered “insufficient”. For phthalates and BPA, despite some studies finding positive associations with the development of respiratory and allergic diseases, the evidence was considered “insufficient” due to the low number of studies and inconsistency of results.
For childhood growth and obesity, despite several studies finding positive associations with exposure to PFASs of phthalates, overall evidence was “insufficient”. For BPA, a large number of studies in children and adults has found “generally consistent positive cross-sectional associations” between BPA content in urine and diabetes, obesity and hypertension; however, less consistent results were obtained in five prospective studies. This led the authors to classify the overall evidence as “insufficient”.
The authors note that phthalates and BPA pose unique challenges in estimating the exposure levels. Because of their short biological half-lives, any single-time measurement provides only a snapshot of a very recent exposure, not permitting any conclusions on long-term exposure trends. This may be one reason for the existence of large inconsistencies in the study results. This view is also supported by Vandenberg and Prins in their commentary published on May 17, 2016 in the peer-reviewed journal Andrology. They go even further, suggesting that a stronger focus on inconsistencies rather than positive findings delivered by numerous studies on BPA is promoted by industry whose strategy is to ‘manufacture doubt’ in order to delay definitive regulatory action.
References
Vrijheid, M., et al. (2016). “Environmental pollutants and child health – A review of recent concerns.” International Journal of Hygiene and Environmental Health (published online May 11, 2016)
Vandenberg, L. N., and Prins, G. S. (2016). “Clarity in the face of confusion: new studies tip the scales on bisphenol A (BPA).” Andrology (published online May 17, 2016)
