Risk of congenital anomaly in relation to residence near hazardous waste landfill sites
The main aim of this thesis is to investigate whether residence near hazardous waste landfill sites is associated with an increased risk of congenital anomaly. The thesis reports results of a multi-centre case-control study carried out in 10 regions in 6 European countries. Cases were live births, stillbirths, and induced abortions with major congenital anomalies resident at birth within a 7 km area around hazardous waste landfill sites. Controls, two per case, were non-malformed births resident in the same area. A total of 1089 cases of non-chromosomal anomaly, 270 cases of chromosomal anomaly, and 2508 controls were selected around 26 landfill sites. A 3 km zone around sites was defined as the zone of most likely exposure. An expert panel of four landfill specialists scored each landfill site according to their potential to cause exposure of nearby residents. A statistically significant 33% excess in risk of non-chromosomal anomalies was found for living within 3 km of a hazardous waste landfill site. The risk of non-chromosomal anomaly declined steadily with increasing distance from a site. Confounding factors or biases do not readily explain these findings. Risk of chromosomal anomalies was raised near sites but did not reach statistical significance. There was little evidence for relative risk of congenital anomaly (non-chromosomal or chromosomal) close to landfill sites to be associated with hazard potential of landfill sites, adding little support to a possible causal relationship. However, in the absence of a 'gold-standard' for the classification of hazard potential, misclassification of sites may have occurred. Lack of information on exposure of residents near the study sites or near landfill sites in general, limits interpretation of the results. Socio-economic status is a potential confounding factor in the current study but little is known in the literature about socio-economic status as a risk factor for congenital anomaly. This study finds a higher risk of non-chromosomal congenital anomaly and certain specific malformation groups in more deprived populations. These findings require follow-up in studies with larger geographical coverage.