In many areas of the world, children are regularly exposed to environmental chemicals. During any given period of life, children will experience exposure to many chemicals at the same time. The effects of such mixtures of chemicals on the molecular underpinnings of the disease process, such as oxidative stress (OS) or on functional endpoints such as cognitive functions, are not well understood in children. There is also little understating of the extent to which endogenous antioxidant defenses in children's bodies or exogenous antioxidants buffer the effects of chemical mixtures on children's health. The few studies on this topic to date have been mostly cross-sectional or limited to small numbers of chemicals. To address these gaps, the proposed study will leverage the Salud Ambiental Montevideo (SAM) cohort in Uruguay, which has enrolled 679 1st-grade children between years 2012-19. Currently, children range in age 7-15 years and have been followed-up for 0-5 years, depending on year of enrollment. Exposure to chlorpyrifos and pyrethroids pesticides has been characterized in a sub-sample of children using urinary metabolites of the pesticides. Exposure to metals in this cohort is generally low. In a cross-sectional pilot study of SAM participants, a metal mixture was linked to higher levels of oxidative DNA damage and with lower performance on a test of general cognitive abilities. The proposed study will consist of 3 years of follow-up of SAM children to annually characterize the levels of metals in blood and urine, and metabolites of chlorpyrifos, pyrethroids, and polycyclic aromatic hydrocarbons (PAHs) in urine. Each year, urinary biomarkers of OS (F2-isoprostane and 8-OHdG), serum antioxidant enzymes (GPx and PON1), and serum antioxidant vitamins (vitamin C, carotenoids, retinol, etc). will be measured. A sub-sample of ~100 children will participate in a year-long intensive (monthly) assessment of OS biomarkers to characterize short-term fluctuations in biomarkers and their biological predictors. Children will complete assessments of executive functions (EF) in Y2 and Y3 of the study. Leveraging data collected at enrollment into SAM (T0, ~7y), chemical mixtures will be constructed in statistical machine learning models for four time points: T0 and Y1-3 of the proposed study. These mixtures will be modeled to understand how exposure to mixtures over time is associated with OS and EF. Potential effect modification by antioxidants will be tested. The proposed activities align with the 2018-23 NIEHS strategic plan of research on the exposome to promote human health through the advancement of environmental health sciences. Specifically, they will: 1) advance the basic understanding of short (1 yr) and medium-term (3 yrs) fluctuations in biomarkers of OS and antioxidant defenses, which have not been investigated in children; 2) contribute to understanding of the extent to which chemical mixtures in early-middle childhood affect a molecular process (OS) thought to underlie the development of chronic disease, as well as functional endpoints that underlie children's learning and social interactions.
Throughout their lives, children are exposed to many different chemicals but our understanding of the effects of these mixtures on child health is limited. Our research is relevant to public health: it will inform prevention efforts and communication of risks by creating a deeper understanding of how exposure to chemical mixtures affects oxidative stress and cognition in children and how well the body's antioxidant defenses are able to counteract these effects. Our work is also relevant to the mission of the NIEHS: it will contribute fundamental knowledge on environmental influences on disease.