2.3.1. Children's drawing tasks A total of 68 (37 males and 31 females) from the 74 children were enrolled and asked to participate in three drawing tasks of common objects that children readily encounter or experience in the study area, though their reproduction varies in complexity: a house, a person, and a donkey. They were provided with a pencil, rubber eraser, drawing pad, table, chair and allowed as much time to draw as they needed to complete their drawings, but no instruction or suppo

Abstract

Highlights

  • Cognitive ability was assessed in children exposed to a range of fluoride levels in drinking water.
  • The study successfully implemented the CANTAB test to children residing in rural Ethiopia.
  • Water fluoride levels were negatively associated with children’s drawing skills, and CANTAB’s memory and learning tests.
  • Children exposed to high fluoride made more errors as CANTAB task difficulty increased.
  • The findings add urgency to further study the potential neurotoxicity of low and high fluoride in drinking water.

Abstract

Fluoride (Fsingle bond) exposure in drinking water may lead to reduced cognitive function among children; however, findings largely remain inconclusive. In this pilot study, we examined associations between a range of chronic Fsingle bond exposures (low to high: 0.4 to 15.5 mg/L) in drinking water and cognition in school-aged children (5–14 years, n = 74) in rural Ethiopia. Fluoride exposure was determined from samples of community-based drinking water wells and urine. Cognitive performance was measured using: 1) assessments of ability to draw familiar objects (donkey, house, and person), and 2) a validated Cambridge Neuropsychological Test Automated Battery’s (CANTAB) Paired Associate Learning (PAL), which examines memory and new learning and is closely associated with hippocampus function of the brain. Associations between Fsingle bond and cognitive outcomes were evaluated using regression analysis, adjusting for demographic, health status, and other covariates. The median (range) of water and urine Fsingle bond levels was 7.6 (0.4–15.5 mg/L) and 6.3 (0.5–15.7 mg/L), respectively; these measures were strongly correlated (r = 0.74), indicating that water is the primary source of Fsingle bond exposure. Fluoride in drinking water was negatively associated with cognitive function, measured by both drawing and CANTAB test performance. Inverse relationships were also found between Fsingle bond and drawing objects task scores, after adjusting for covariates (p < 0.05). Further analysis using CANTAB PAL tasks in the children confirmed that Fsingle bond level in drinking water was positively associated with the number of errors made by children (p < 0.01), also after adjusting for covariates (p < 0.05). This association between water Fsingle bond and total errors made became markedly stronger as PAL task difficulty increased. Fluoride exposure was also inversely associated with other PAL taskssingle bondthe number of patterns reached, first attempt memory score and mean errors to success. These findings provide supportive evidence that high Fsingle bond exposures may be associated with cognitive deficits in children. Additional well-designed studies are critically needed to establish the neurotoxicity of Fsingle bond in children and adults exposed to both low levels known to protect dental caries, as well as excess Fsingle bond levels in drinking water.


Abstract online at https://www.sciencedirect.com/science/article/pii/S0892036223001435#ac0005

Excerpt:

2.3.1. Children’s drawing tasks

A total of 68 (37 males and 31 females) from the 74 children were enrolled and asked to participate in three drawing tasks of common objects that children readily encounter or experience in the study area, though their reproduction varies in complexity: a house, a person, and a donkey. They were provided with a pencil, rubber eraser, drawing pad, table, chair and allowed as much time to draw as they needed to complete their drawings, but no instruction or support was provided other than the name of the items to be produced. All children submitted drawings of each object, such that a total of 204 drawings were collected and scored. Most children took approximately 20–30 min to finish all three drawings. We developed scoring criteria based on the completeness of each object such that a point was given for each part correctly drawn (Table 1). Each object also received an additional score for overall appearance ranging from 0 to 4 (bad (0), poor (1), fair (2), good (3), very good (4)). Similar figure drawing criteria were used in other studies to assess child cognition (Panesi and Morra, 2016; Imuta et al., 2013). All drawings were independently scored by two examiners who were blinded to the Fsingle bond concentrations in well water; the inter-rater reliability was assessed and showed a strong correlation (r > 0.92).

Fig. 2

4. Discussion and conclusion

In this study, we assessed the association between chronic exposure to naturally-occurring Fsingle bond in drinking water and cognitive function in school-aged children, as measured using two distinct types of assessments: a simple drawing task of familiar objects, and the CANTAB PAL tests. The sample was recruited from 8 communities primary exposed to chronic Fsingle bond ranging from 0.41 to 15.5 mg/L in the MER. These communities have relatively homogenous populations with similar lifestyles and stable residency, but the residents of different villages use community-based drinking water sources that vary in their Fsingle bond levels. We hypothesized that measures of cognitive performance would decline with exposure to elevated Fsingle bond concentrations. Accordingly, we found adverse associations of Fsingle bond exposures in drinking water with children’s drawing and CANTAB task performance. The strongest and most significant negative impacts were observed for the more challenging drawing task—a donkey (Fig. 1A). It is observed that children struggled more when drawing a donkey than a house or a person, which may be indicative of a greater challenge accessing memory for this task. In contrast, children appeared to have an easier time drawing a person or a house, and associations between drawing performance and Fsingle bond exposures were correspondingly weaker. Consistent with the negative associations between drawing skill and Fsingle bond exposure, children drinking from wells in communities with higher Fsingle bond levels performed worse in CANTAB PAL tasks that are used to test new learning and memory, and especially the PAL total errors adjusted measure. It was also observed that higher Fsingle bond levels were related to higher deficits in the more difficult PALTEA tasks (i.e., increasing number of boxes from 2 to 8) (Fig. 5). The PAL test targets hippocampal function by measuring visual memory and new learning (Barnett et al., 2016; de Rover et al., 2011). A study by Choi et al. (2015) found that measured working memory using the Wechsler Intelligence Scale for Children-Revised (WISC-IV) in children was negatively associated with dental fluorosis (a marker of early life Fsingle bond exposure during critical periods of tooth development, the first 8 years) and Wechsler’s total and backward digit span tests. Goodman et al. (2022) also reported that visual-spatial and perceptual reasoning abilities may be more impacted by Fsingle bond exposure as compared to verbal abilities.

In previous related studies, drawing (e.g., a person) has often been used as a nonverbal screening measure of cognitive ability that may indicate visual sensory input and neuromuscular output (Imuta et al., 2013; Reynolds and Hickman, 2004; Kamphaus and Pleiss, 1991; Kamphaus and Pleiss, 1991; Reynolds and Hickman, 2004; Abell et al., 1996, Abell et al., 2001). A study by Panesi and Morra (2016) assessed dog drawing in relation to executive function and working memory and found that these two parameters jointly accounted for 58.3% of the variance of dog drawing skill. Moreover, working memory individually accounted for the largest variance (15.4%), whereas executive function accounted for 4.4%. The interaction of these two predictors was then responsible for the remaining 38.5% of this joint variance. Evidence of the role of working memory and executive function in drawing flexibility was also reported by Morra, 1994 and Barlow et al., 2003. Moreover, environmental factors can impede these aspects of cognition and drawing. For example, a study by Guillette et al. (1998) observed impairments in memory, social interaction, creativity, drawing ability, and motor skills in a population of Mexican children exposed to pesticides relative to a comparable group living in an unexposed area. Most dramatically, pesticide exposed children scored more poorly in a “draw a person” task, which may indicate lower cognitive ability or poor visuomotor coordination.

In our study, grade level (or age) was positively associated with drawing ability, which is also consistent with prior literature (Panesi and Morra, 2016). Owing to our sampling approach, however, which aimed to balance sex and age within and across communities, the children in each community are similar, such that sex- and age-related effects cannot explain the variation in observed outcomes across communities. Other possible confounders include As and Pb, which are known to be neurotoxic contaminants, but these were found at low levels in drinking water from the sample communities and in samples of children’s urine. The concentrations of As and Pb in drinking water ranged between 0.92 and 21.9 ?g/L (mean:7.3 ± 6.83 ?g/L), and 0.001 to 0.73 ?g/L (mean: 0.23 ± 0.27 ?g/L), respectively. Anemic appearance, as diagnosed from clinical signs of anemia (e.g., pallor on conjunctiva), was observed in 45.5% of the children, and is known to impair motor and mental development in infants, children, and adolescents (Lam and Lawlis, 2017; Burden et al., 2007; Lazoff, 2007). In regression analysis the association of anemic appearance, and As and Pb in water and urine did not significantly correlate with performance measures, however, this exploratory study relied on a relatively small sample and used cross sectional data to proxy for long-term exposure. In addition, the purposeful recruitment of children to obtain representative age and sex distributions around specific community wells limits the representativeness of the sample. As a result, the study may not be viewed as providing a definitive analysis of Fsingle bond’s neurotoxicity in children. Nonetheless, the similar sociodemographic and lifestyles in these communities minimizes the risk of confounding by variables that may be correlated with exposures and cognitive performance measures. An important additional limitation was the small number of sample communities and wells. In particular, when adjusting the standard errors for clustering within wells/communities, the statistical significance of the association between water Fsingle bond and the PALTEA task performance scores was reduced from p = 0.034 to p = 0.09, emphasizing the need to increase the number of wells and study participants to obtain greater statistical power.

Other limitations include a lack of control of parental variables such as maternal age, educational level of parent, socio-economic status, and assessment of chemical mixture models for better exposure and effect characterization other potential neurotoxicants (e.g., As, Pb), and elemental deficiencies such as iodine and iron that may modify cognition (Lam and Lawlis, 2017). For some urine biomarker measures that were collected as spot samples, we accounted for dilution using urine SG, to reflect actual Fsingle bond exposure from drinking water.

5. Conclusion

Our findings suggest that there are cognitive impairments among children exposed to higher Fsingle bond concentrations, evaluated using figure drawing performance and validated CANTAB cognitive tools. This study also successfully demonstrated the use of language and culture neutral CANTAB testing in a rural Ethiopian sample of children for the first time. Thus, CANTAB can feasibly be administered in this and other similar rural African contexts (as also shown by Chetty-Mhlanga et al., 2022, Chetty-Mhlanga et al., 2018; Nkhoma et al., 2013). While this exploratory study adds evidence and concern about the potential neurotoxicity of elevated Fsingle bond exposure, more studies are critically needed to better establish neurodevelopmental impacts of a range of Fsingle bond exposures from gestation to adulthood, using rigorous study designs and advanced methodologies including mixture models for exposure and effect characterization. Such studies would help provide concrete evidence to inform leaders and policy makers on the need for effective approaches to mitigate environmental exposures to Fsingle bond, including in Fsingle bond endemic geographic settings such as the study areas where alternative water sources are limited, or to establish the threshold levels at which such exposures become toxic, and specifically, inform the growing controversy over the safety of water fluoridation.


Funding sources from the PI’s Internal Institutional Start-up Fund, and National Institute of Environmental Health Sciences (NIEHS’s) career development grant (K99/R00 ES023472) that made the research possible.