OBJECTIVE: To explore the effects of pesticide exposure on the auditory system, specifically on hearing status based on auditory brainstem responses.

METHODS: A cohort of pregnant women was identified in several communities in a rural area from April 2002 to February 2003 and followed up until delivery. Mother-infant dyads were assessed for exposure to pesticides. Maternal and fetal exposures to environmental toxic products were determined by measuring levels in maternal hair and blood, and infant cord blood, hair, and meconium, respectively. Hearing status was measured using otoacoustic emissions (OAE) and confirmed by diagnostic auditory brainstem responses (ABR) measured at 80, 60, and 40 decibels. Waves I, III, V were identified and absolute latencies measured, including inter-peak latencies from waves 11III, I-V, and III-V. Pesticide exposure was then correlated with latencies of Waves I, III, V, and interpeak latencies of waves I-III, IIV, and III-V. Hearing loss and pesticide exposures were correlated with Griffiths Mental Development Scores (GMDS).

RESULTS: Significant delays in the ABR wave latencies were noted in the group with exposure to pesticides. Propoxur was the most common toxic product detected in infants and meconium the best substrate for its detection. There was a 1.4% risk of hearing loss with exposure to propoxur (RR=0.52 (0.12-2.30), p = 0.06), a 6.25% risk with cypermethrin exposure (RR= 4.53 (0.61133.64), P = 0.10) and 6.25% risk with pretilachlor exposure (3.13 (0.44-22.30), p = 0.07). Griffith's Mental Developmental Scale scores (GMDS- hearing and speech subscale and general quotient scores) were not significantly different between exposed and unexposed groups. However, three infants with positive exposures and hearing loss had below average, or low to average scores using this scale.

CONCLUSION: Maternal exposure to environmental toxic products may affect the auditory pathway in infants at birth. Pregnant women should limit their exposure to such toxic products in order to avoid neurodevelopmental effects particularly on hearing because this is very important in the critical stage of language and speech development.