Trihalomethanes, chlorite, chlorate in drinking water and risk of congenital anomalies: a population-based case-control study in Northern Italy

Background Epidemiological evidence of an association between disinfection by-products (DBPs) exposure via drinking water and reproductive outcomes is still inconclusive. Objective The aim of this study was to investigate the association between trihalomethanes (THMs), chlorite and chlorate exposure and congenital anomalies. Methods A case-control study was carried out in Emilia-Romagna Region (Italy). Data on 1917 different congenital anomalies (neural tube, cardiac, diaphragm and abdominal wall, oesophagus, cleft lip and palate, respiratory, urinary tract and chromosomal anomalies) observed in the period 2002–2005 were extracted from the Regional Malformation Registry. Four controls (newborns without anomalies) were randomly selected form the Regional Birth Register and frequency matched to cases according to pregnancy period. The network supplying water during the first trimester of pregnancy was identified on the basis of mother's address: DBPs data, technical and structural information were linked to each subject. Results Overall, THMs exposure was very low (mean: 3.8±3.6 μg/l), and no risk excess was observed. Chlorite and chlorate values were fairly high (mean: 427±184 μg/l and 283±79 μg/l, respectively). Women exposed to chlorite level >700 μg/l were at higher risk of newborns with renal defects (OR: 3.30; 95% IC: 1.35–8.09), abdominal wall defects (OR: 6.88; 95% IC: 1.67–28.33) and cleft palate (OR: 4.1; 95% IC: 0.98–16.8); women exposed to chlorate level >200 μg/l were at higher risk of newborns with obstructive urinary defects (OR: 2.88; 95% IC: 1.09–7.63), cleft palate (OR: 9.60; 95% IC:1.04–88.9) and spina bifida (OR: 4.94; 95% IC:1.10–22). Conclusions This was the first study showing an excess risk of different congenital anomalies related to chlorite and chlorate exposure via drinking water: further research is needed to confirm the observed relationships in large datasets, specifically for chlorate, an unregulated DBP.