Full length articleChanges in water manganese levels and longitudinal assessment of intellectual function in children exposed through drinking water
Introduction
Manganese (Mn) is an essential element that occurs naturally in soil, air, as well as in all living organisms. This metal is also commonly present in groundwater, sometimes in high concentrations, due to local geological characteristics. High Mn concentration have been reported in drinking water in many countries around the world where groundwater is used for human consumption (Frisbie et al., 2012), including Canada (Barbeau et al., 2011). Mn is an essential nutrient, but in large dose can also be a potent neurotoxicant, with effects on cognition, behavior, and neuromotor function (Dobson et al., 2004). Early studies depicting the neurotoxic effects of Mn were conducted in occupationally exposed groups (Mergler et al., 1994, Rodier, 1955, Roels et al., 1987), and more recently increased efforts were made to investigate Mn neurotoxicity in environmentally exposed children (O'Neal and Zheng, 2015).
Epidemiological evidence suggests that Mn exposure from drinking water could be associated with lower intelligence quotient (IQ) scores in children (Bouchard et al., 2011, Wasserman et al., 2006). Drinking water Mn concentrations has also been associated with poorer memory, attention, motor functions (Oulhote et al., 2014a), mathematics achievement scores (Khan et al., 2012), perceptual reasoning, working memory (Nascimento et al., 2016, Rahman et al., 2016, Wasserman et al., 2011, Wasserman et al., 2016), as well as behavior problems (Bouchard et al., 2007, Khan et al., 2011, Rahman et al., 2016). Although these studies vary greatly in terms of levels of exposure, they support the hypothesis that Mn exposure might adversely affect the developing brain.
We previously reported that elevated water Mn concentration (MnW) was associated with lower IQ in a group of school-age children aged 6–13 years (Bouchard et al., 2011). In this study, children in the highest quintile of Mn concentration had IQ scores 6 points lower than those in the lowest quintile. The association between MnW and IQ was stronger for girls than for boys. Hair Mn concentrations were also associated with lower IQ scores. Importantly, these results were observed at levels of exposure currently considered low and safe since and only 3% of participants had drinking water exceeding the World Health Organization guideline of 400 μg Mn/L (World Health Organization, 2004) (before this guideline it was discontinued altogether in 2011; World Health Organization, 2011).
The present study follows up the above cohort, and was conducted approximately four years after the initial study, depending on participants. The first objective was to re-assess the relation between water Mn concentration and cognition in this cohort around adolescence. The second objective was to monitor changes in Mn concentration in participants’ drinking water and to investigate how it might relate to change in IQ scores.
Section snippets
Study design and recruitment
Participants of the baseline epidemiological study in southern Quebec (Canada) carried out by Bouchard et al. in 2007–2009 were contacted for the present follow-up study, conducted in 2012–2013. Details on selection and recruitment of the baseline study participants are reported elsewhere (Bouchard et al., 2011). Of the initial 380 participants (mean age, 9.3 years; standard deviation [SD], 1.8), 287 children (mean age, 13.7 years; SD, 1.8) participated in the follow-up study. Mean time elapse
Descriptive statistics
Participants' characteristics and Mn levels in water and hair, as well as TAWMn are shown in Table 1. Seventy-eight percent of mothers had at least some college education, 64% had family income above $50,000, and 99% of children were white. More details on the characteristics of the initial cohort are available in Bouchard et al. (2011).
At follow-up examination, tap water Mn ranged from 0.2 to 961 μg/L (arithmetic mean, 57.6; geometric mean [GM], 14.5). Forty percent of children were exposed to
Discussion
The results from this follow-up study suggest that Mn concentration in drinking water is negatively associated with IQ during childhood, and that this negative association remains present at adolescence among girls. Higher water Mn concentration was rather associated with higher IQ in boys at the follow-up examination. Similar results were observed for MnH levels, i.e., lower Performance IQ scores in girls and opposite findings in boys, although associations were not significant. It is
Conclusion
Exposure to Mn from drinking water was associated with lower IQ in girls, whereas it was rather associated with higher IQ in boys. This adds to the mounting number of studies reporting sex-related differences in Mn toxicity. Also, for participants whose water Mn increased at follow-up, IQ scores decreased significantly compared with scores at baseline examination. Further studies are needed to better understand underlying mechanisms for sex differences in Mn neurotoxicity.
Competing financial interests’ declaration
We have no financial interests to declare.
Acknowledgments
We wish to acknowledge participants and families of participants who gave their time and help us carry out the study. We would like to thank Marie-Eve Brodeur for recruiting participants; her experience with this cohort was of great help. We are grateful for the SickKids Foundation for funding this study (grant #NI12-065). The Canadian Institutes of Health Research (CIHR) funded the original epidemiological study (NRF-82899).
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2021, Environmental PollutionCitation Excerpt :In the brain, excess of Mn can alter central nervous system (CNS) functions in developing fetus, post-natal periods and adult life (Lucchini et al., 2017; Miah et al., 2020). Recent epidemiological studies reported that early-life Mn exposure may cause abnormal neuronal development that leads to sub-clinical toxicity and long-term consequences (Aschner and Aschner, 1990; Lucchini et al., 2014; Haynes et al., 2015; Bauer et al., 2017; Bjørklund et al., 2017; Chiu et al., 2017; Dion et al., 2018; Ntihabose et al., 2018). Excessive Mn is also able to cause aberration of neurogenesis reducing survival of immature cells and compromising their differentiation into neurons (Wang et al., 2012; Fu et al., 2016).