Associations between prenatal and recent postnatal methylmercury exposure and auditory function at age 19years in the Seychelles Child Development Study

Abstract

Objectives To determine if prenatal or recent postnatal methylmercury (MeHg) exposure from consuming ocean fish and seafood is associated with auditory deficits in young adults. Some investigators have reported adverse associations while others have found no associations. Ocean fish is an important nutrient source for billions of people around the world. Consequently, determining if there is an adverse association with objective auditory measures is important in assessing whether a risk is present or not. Design The peripheral and central auditory function of 534 subjects in the Seychelles Child Development Study (SCDS) Main Cohort was examined at age 19 years. The auditory test battery included standard pure-tone audiometry, tympanometry, Auditory Brainstem Response (ABR) latencies, and both click-evoked and distortion-product Otoacoustic Emissions (OAE). Associations with MeHg were evaluated with multiple linear regression models, adjusting for sex, recent postnatal MeHg exposure, and hearing loss. Results Bilateral hearing loss (defined as a mean pure-tone threshold of greater than 25 dB) was present in 1.1% of the subjects and was not associated with prenatal or recent postnatal MeHg exposure. As expected, absolute and interwave ABR latencies were shorter for women as compared to men, as the stimulus presentation rate decreased from 69.9 to 19.9 clicks/sec and as the stimulus intensity increased from 60 to 80 dBnHL. Similarly, larger OAE amplitudes were elicited in women as compared to men and in the right ears as compared to the left. There was no association of prenatal MeHg exposure with hearing loss, ABR absolute and interwave latencies or OAE amplitudes. As recent postnatal MeHg increased, some associations were found with a few ABR absolute and interwave latencies and a few OAE amplitudes. However, the direction of these associations was inconsistent. As recent postnatal MeHg levels increased the wave I absolute latencies were shorter at 80 dBnHL for all 3 click rates, but the interwave I-V latency was longer for males for the 80 dBnHL 19 clicks/sec and for the III-V interwave latencies for males and females for the dBnHL 69 clicks/sec. Similarly, smaller OAE amplitudes were found at 1500, 2000, and 4000 Hz for males while larger OAE amplitudes were found for females at 1500 and 2000 Hz as the recent postnatal MeHg levels increased. Conclusions No consistent associations were present in this study between prenatal MeHg exposure from consumption of oceanic fish and seafood during pregnancy and auditory functions at 19 years of age. Given the level of prenatal exposure to MeHg, the number of audiologic measures tested, and the presence of the expected sex, click rate, and level dependent findings, it seems unlikely that an association was present and not detected. As recent postnatal MeHg exposure increased, a few associations with ABR latencies and OAE amplitudes were found. The direction of these associations was inconsistent as some showed improved performance as MeHg exposure levels increased ...

Quantitative estimation of mercury intake by toxicokinetic modelling based on total mercury levels in humans

“…Within such social groups, exposure to MeHg in the womb and/or soon after birth has been associated with issues such as altered memory, attention and language development in children (reviewed by Grandjean and Landrigan (2014)). However, it should be stressed that this connection has not been made in other studies (Myers et al, 2003;Nieminen et al, 2015;Orlando et al, 2014).…”

Evidence on Neurotoxicity after Intrauterine and Childhood Exposure to Organomercurials

“…The implication of genetic factors in MeHg-induced neurotoxicity might probably resolve at least some discrepancies between numerous epidemiological studies of human early-life MeHg exposure in fish-consuming populations around the world, including the Faroe Islands [130], Brazil [131,132], Seychelles [133], Quebec [134], Madeira and Japan [135]. Interestingly, the genetic polymorphism in apolipoprotein E (APOE), a major protein transporter in the brain, was significantly correlated with Hg cord blood concentrations and neurodevelopmental impairment in children in Taiwan, where MeHg from fish was assumed as the main source of Hg [136].…”

Recommandations de bonne pratique sur la prise en charge des femmes enceintes exposées au mercure organique et leurs enfants à naître. Recommandations de la Société de toxicologie clinique, associée à la Société française de toxicologie analytique, à la Société française de santé publique, à la Société francophone de santé environnement, à la Société française de pédiatrie, à la Société française de néonatalogie, au Collège national des gynécologues obstétriciens

“…Chez l'enfant, en cas d'exposition in utero, des altérations des performances dans les tests psychométriques, corrélées à la concentration de mercure dans le sang total ou les cheveux, sont détectables dans des cohortes exposées au MeHg au-delà de respectivement 40 µg/L et 10 µg/g. En-deçà de ces seuils, certaines études épidémiologiques mettent en évidence de discrètes altérations cognitives dont la fréquence et/ou l'intensité augmentent avec la concentration de mercure dans le sang ou les cheveux (32), mais d'autres études, aussi nombreuses, ne montrent pas d'effet nocif ou sont même en faveur d'une amélioration des performances cognitives avec la dose interne de mercure (26). Ces contradictions apparentes sont explicables par des facteurs de confusion mal contrôlés (fenêtres d'exposition variables, précision de l'évaluation de l'exposition, âge au moment de l'évaluation neurologique, type de test utilisé, prise en compte des autres facteurs nutritionnels, modélisation des relations dose-réponse…).…”

“…Il s'agit en particulier d'études de cohorte dans les îles Seychelles et les îles Féroé(4). Elles ont fait l'objet de plusieurs revues systématiques récentes dont les conclusions sont convergentes (3), y compris avec celles des quelques suivis d'études ou des nouvelles études épidémiologiques publiées depuis(22)(23)(24)(25)(26). L'exposition in utero au MeHg est responsable d'altérations des fonctions cognitives: ralentissement psychomoteur, diminution des performances visuo-spatiales, ainsi que des capacités d'attention et de traitement de l'information (niveau 1)(23,27,28).…”