title: A population-based case-control study of drinking-water nitrate and congenital anomalies using Geographic Information Systems (GIS) to develop individual-level exposure estimates.
abstract: Animal studies and epidemiological evidence suggest an association between prenatal exposure to drinking water with elevated nitrate (NO3-N) concentrations and incidence of congenital anomalies. This study used Geographic Information Systems (GIS) to derive individual-level prenatal drinking-water nitrate exposure estimates from measured nitrate concentrations from 140 temporally monitored private wells and 6 municipal water supplies. Cases of major congenital anomalies in Kings County, Nova Scotia, Canada, between 1988 and 2006 were selected from province-wide population-based perinatal surveillance databases and matched to controls from the same databases. Unconditional multivariable logistic regression was performed to test for an association between drinking-water nitrate exposure and congenital anomalies after adjusting for clinically relevant risk factors. Employing all nitrate data there was a trend toward increased risk of congenital anomalies for increased nitrate exposure levels though this was not statistically significant. After stratification of the data by conception before or after folic acid supplementation, an increased risk of congenital anomalies for nitrate exposure of 1.5-5.56 mg/L (2.44; 1.05-5.66) and a trend toward increased risk for >5.56 mg/L (2.25; 0.92-5.52) was found. Though the study is likely underpowered, these results suggest that drinking-water nitrate exposure may contribute to increased risk of congenital anomalies at levels below the current Canadian maximum allowable concentration.
authors: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, NS B3H 1V7, Canada. ceholtby@ucalgary.ca.
authors: Caitlin E
authors: CE
authors: Holtby
authors: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, NS B3H 1V7, Canada. jrg@dal.ca.
authors: Judith R
authors: JR
authors: Guernsey
authors: Perinatal Epidemiology Research Unit, Departments of Pediatrics and Obstetrics & Gynaecology, Dalhousie University, 5980 University Avenue, Halifax, NS B3K 6R8, Canada. alexander.allen@dal.ca.
authors: Alexander C
authors: AC
authors: Allen
authors: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE C1A 4P3, Canada. jvanleeuwen@upei.ca.
authors: John A
authors: JA
authors: Vanleeuwen
authors: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, NS B3H 1V7, Canada. victoria.allen@dal.ca.
authors: Victoria M
authors: VM
authors: Allen
authors: School of Environmental Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada. rjgordon@uoguelph.ca.
authors: Robert J
authors: RJ
authors: Gordon
mesh_terms: D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology* / Q000209:etiology; D060766:Drinking Water / Q000032:analysis*; D005260:Female; D040362:Geographic Information Systems; D006801:Humans; D018811:Maternal Exposure / Q000009:adverse effects* / Q000706:statistics & numerical data; D009566:Nitrates / Q000009:adverse effects* / Q000032:analysis; D009674:Nova Scotia / Q000453:epidemiology; D011247:Pregnancy
chemical_list: D060766:Drinking Water; D009566:Nitrates