TPS 731: Neurological effects in children, Exhibition Hall, Ground floor, August 26, 2019, 3:00 PM - 4:30 PM Organochlorine pesticides (OCPs) are environmental contaminants that persist in the environment, and previous studies have shown associations between prenatal OCP exposure and subsequent neurodevelopment. However, it is still not clear how long this association could be prolonged. A prospective birth cohort study was conducted to examine the associations between prenatal OCP exposure and intelligence at 7 years children. Blood samples were analyzed using gas chromatography/mass spectrometry techniques to quantify 29 OCPs. The Wechsler Intelligence Scale for Children 3rd edition (WISC-III) was used to assess intelligence of children, which provided Verbal IQ (VIQ), Performance IQ (PIQ), and Full Scale IQ (FIQ). The test also has four subscales to represent more narrow domains of cognitive functions. We analyzed data from 95 singleton children without congenital anomalies, and who had both maternal OCP levels and WISC-III data. After multiple regression analysis adjusted by maternal age, education, parity, blood sampling period, children sex, we found OCPs had negative association with FIQ and PIQ, and positive association with VIQ. When prenatal total dioxin TEQ level was added to adjustment, however, positive associations between OCPs and VIQ disappeared, and negative association between FIQ and p.p’-DDD (β= -10.8: 95% Confidence Interval: -18.6 -2.9), p.p’-DDT (-19.26: -31.4 -7.1), and between PIQ and p.p’-DDD (-10.8: -18.6 -2.9), p.p’-DDT (-19.3: -31.4 -7.1) were remained. In the same analysis for subscale, the Perceptual Organization Index decreased with p.p’-DDD (-12.2: -20.2 -4.3), p.p’-DDT (-22.4: -34.6 -10.2), and Parlar-26 (-11.2: -21.7 -0.7). Additionally, Freedom from Distractibility Index, which reflects attention or working memory, decreased with p.p’-DDD level (-8.8: -16.8 -0.8). Although careful consideration is needed regarding other influential factors, and causal relationship between prenatal exposure to low-level OCPs and cognitive function of school aged children, prenatal OCP level may have prolonged effect on the children’s intelligence, especially perception, and attention or working memory.