Human exposure to environmental contaminants and congenital anomalies: a critical review

Abstract

Congenital anomalies are an important cause of infant mortality and disability. Developmental exposure to environmental contaminants is thought to increase the risk for congenital anomalies. Herein, we describe a critical review of the literature conducted between February and March 2014 yielding 3057 references from which 97 unique relevant articles published from 2003 through 2014 were evaluated. Common congenital anomalies including hypospadias, cryptorchidism, anogenital distance (AGD), congenital heart defects and oral clefts were well represented in the literature whereas other outcomes such as neural tube defects, limb deficiency defects and gastroschisis were rarely described. While definitions used for congenital anomalies and methods of ascertainment were usually consistent across studies, inconsistencies were frequently found in grouping of different congenital heart defects. Despite strong links between some congenital anomalies and parental occupation, these studies are unable to provide clear insight into the specific chemicals responsible owing to lack of direct measures of exposure. In comparison, data are mixed for contaminant exposures at concentrations representative of results from contemporary biomonitoring studies. Of the environmental contaminants studied, the association between phthalate exposures and developmental abnormalities of the male reproductive tract received the greatest attention. Important limitations of the literature studied relate to adequacy of sample size, absence of or weaknesses in exposure assessment methodologies, failure to account for biological plausibility and grouping of congenital anomalies with divergent mechanisms. We conclude that the literature is inadequate at this time to support a conclusion that exposure to environmental contaminants are or are not associated with increased risks for congenital anomalies in the general population.

Keywords:

• Birth defects
• congenital anomalies
• contaminants
• environment
• toxicants

Acknowledgements

The authors are grateful for the administrative and technical support provided by Ms. Margaret Talbot during the conduct of this review. The authors gratefully acknowledge the review comments provided by reviewers selected by the Editor and anonymous to the authors. These comments were useful in improving the manuscript.

Declaration of interest

The employment affiliation of the authors is as shown on the cover page. This review was sponsored by a contract from the Public Health Agency of Canada (WGF) for preparing a review of the literature on the state-of-the-science linking exposure to environmental contaminants and congenital anomalies. The coauthors serve as external science advisors to the Public Health Agency of Canada and received no compensation for their role in the preparation of this manuscript. The review of the literature and the interpretation of the literature was the exclusive work product of the authors and the interpretations of the data presented in this review are not necessarily those of any sponsors. While the sponsor was provided with a copy of the final draft of the manuscript, the sponsor did not provide comment or input on the paper prior to submission to CRT. Finally, the authors have not appeared in any regulatory or legal proceedings related to the material covered in the review paper.