The association between urinary concentrations of organophosphate metabolites and asthma-related outcomes at 12-month follow-up among children from informal settlements in Western Cape, South Africa

Abstract

BACKGROUND AND AIM: There is limited evidence on the relationship between pesticide exposure and child respiratory outcomes in non-agricultural settings. This study investigated the association between organophosphate pesticide (OP) exposure and child asthma-related outcomes among children from four informal settlements. METHODS: This study was a longitudinal study of 590 schoolchildren, with a 12-month follow-up period. A standardised questionnaire adopted from the International Study of Asthma and Allergies in Childhood (ISAAC) was administered to caregivers on child’s respiratory symptoms and household characteristics. Spirometry and fractional-exhaled nitric oxide (FeNO), including a phadiatop test (atopy status) and urinary concentrations of dialkyl phosphate (DAP) metabolites diethylphosphate (DEP), dimethylthiophosphate (DMTP)] were measured at baseline and follow-up. Dimethylphosphate (DMP) was measured only at baseline. RESULTS: The mean age of schoolchildren were 9.9 ± 0.91 years and median sum DAP was 32.9 ng/ml (18.4 – 52.9 ng/ml) at baseline. Incidence proportions of new asthma outcome cases at 12-months were 2.2 % doctor diagnosed asthma, 17.8 % asthma-symptom score ≥ 2, 14.5 % forced expiratory volume 1< lower limit of normal, and 5.9 % airway inflammation across all areas. In the linear mixed and fixed effect model, no consistent patterns of increased risk of new asthma-associated outcomes at the 12-month was found. However, there was a significant increase in airway inflammation (β:2.99 (95% CI: 0.48 - 5.50) in the 3rd DEP quintile (1.9 – 3.0 ng/mL) compared to the reference quintile (1.10 ng/ml). CONCLUSION: DAP concentrations were higher than those of children in other settings. However, the study did not find consistent associations between urinary concentrations of DAP metabolites and asthma related outcomes over a 12-month follow-up period among schoolchildren. Future studies with a longer follow-up period and repeated OP pesticide biomonitoring are recommended. KEYWORDS: Pesticides, organophosphates, asthma, children, informal settlements, dialkyl phosphates, South Africa