Background: Disinfection by-products (DBPs) constitute a complex mixture of prevalent chemicals in drinking water and there is evidence of neurotoxicity for some of them. Objectives: We evaluated the association between estimates of DBP exposure during pregnancy and child neuropsychological outcomes at 1 and 4–5 years of age. Methods: We conducted a population-based mother-child cohort study in Spain with recruitment at first trimester of gestation (INMA Project, 2003–2008). Neuropsychological development was measured at 1 year of age using the Bayley Scales of Infant Development and at 4–5 years with the McCarthy Scales of Children's Abilities. Modeled tap water concentrations of trihalomethanes (THM) were combined with personal ingestion, showering and bathing habits to estimate exposure as ingestion uptake, all route (showering, bathing, ingestion) uptake (μg/day) and crude levels (μg/l) in the residence. Chloroform, brominated THMs (bromodichloromethane, dibromochloromethane, bromoform) and total THMs (chloroform and brominated THMs) were analysed separately. Nine haloacetic acids levels were available in one of the areas. Linear regression was used to estimate associations in 1855 subjects adjusting for covariables. Results: The median concentration of total THMs, chloroform, brominated THMs, total haloacetic acids, dichloroacetic acid, and trichloroacetic acid were, respectively 30.3 μg/L, 9.4 μg/L, 11.6 μg/L, 10.5 μg/L, 2.7 μg/L, and 3.1 μg/L. The associations between THM exposure and neuropsychological outcomes were null, except for total and brominated THM uptake though all routes and the general cognitive score at 4–5 years, with a decrease in − 0.54 points (95%CI − 1.03, − 0.05) and − 0.64 (95%CI − 1.16, − 0.12), respectively, for doubling total and brominated THM uptake. A positive association found between dichloroacetic acid and the mental score at 1 year did not persist at 4–5 years. Conclusions: Minor associations observed between DBP exposure during gestation and child neuropsychological development at 1 year disappeared at 4–5 years. Although a suggestive association is identified for exposure to brominated THMs and the cognitive score at 4–5 years, chance cannot be ruled out.

This study was funded by Grants from UE (FP7-ENV-2011 cod 282957 and HEALTH.2010.2.4.5-1), and from Spain: Instituto de Salud Carlos III (Red INMA G03/176, CB06/02/0041, FIS-FEDER 03/1615, 04/1509, 04/1112, 04/1931, PI041436, FIS-PI042018, 05/1079, 05/1052, 06/1213, FIS-PI06/0867, 07/0314, 081151, 09/02647, 09/02311, 09/00090, 11/0178, 11/02591, 11/02038, 13/1944, 13/2032, 13/02429, 13/02187, 14/0891, 14/1687, CP14/00108, CP16/00261 and Miguel Servet-FEDER MS15/0025, MS13/00054, CP0610034, MS14/00108), CIBERESP (Ref. AA08_012), the Conselleria de Sanitat de la Generalitat Valenciana, Generalitat de Catalunya (CIRIT 1999SGR 00241), Fundació La Marató de TV3 (090430), Obra Social Cajastur/Fundación Liberbank, Universidad de Oviedo, Department of Health of the Basque Government (2005111093, 2009111069, 2013111089 and 2015111065), and the Provincial Government of Gipuzkoa (DFG06/002, DFG08/001 and DFG15/221). Annual agreements with the city council of the study area in Gipuzkoa (Zumarraga, Urretxu, Legazpi, Azkoitia y Azpeitia y Beasain). ISGlobal is a member of the CERCA Programme, Generalitat de Catalunya.