Fish consumption, mercury exposure, and their associations with scholastic achievement in the Seychelles Child Development Study

doi:10.1016/j.neuro.2010.05.010

NeuroToxicology

Volume 31, Issue 5, September 2010, Pages 439-447

https://doi.org/10.1016/j.neuro.2010.05.010 Get rights and content

Abstract

Studies of neurodevelopmental outcomes in offspring exposed to MeHg from maternal consumption of fish have primarily measured cognitive abilities. Reported associations have been subtle and in both adverse and beneficial directions. Changes in functional outcomes such as school achievement and behavior in exposed children and adolescents have not been examined. We undertook an assessment of school success of children in the Seychelles Child Development Study (SCDS) main cohort to determine if there were any associations with either prenatal or recent postnatal MeHg exposure. The primary endpoints were Seychelles nationally standardized end-of-year examinations given when the cohort children were 9 and 17 years of age. A subgroup (n = 215) from the main cohort was also examined at 9 years of age using a regional achievement test called SACMEQ. Prenatal MeHg exposure was 6.8 ppm in maternal hair; recent postnatal exposure was 6.09 ppm at 9 years and 8.0 ppm at 17 years, measured in child hair. Multiple linear regression analyses showed no pattern of associations between prenatal or postnatal exposure, and either the 9- or 17-year end-of-year examination scores. For the subgroup of 215 subjects who participated in the SACMEQ test, there were significant adverse associations between examination scores and postnatal exposure, but only for males. The average postnatal exposure level in child hair for this subgroup was significantly higher than for the overall cohort. These results are consistent with our earlier studies and support the interpretation that prenatal MeHg exposure at dosages achieved by mothers consuming a diet high in fish are not associated with adverse educational measures of scholastic achievement. The adverse association of educational measures with postnatal exposure in males is intriguing, but will need to be confirmed by further studies examining factors that influence scholastic achievement.

Section snippets

Setting

The study was conducted in the Republic of Seychelles, an Indian Ocean archipelago with about 85,000 inhabitants of mixed African, European, and East Asian origins. The Seychellois diet is varied but high in fish and fruit (Bonham et al., 2008). Human services and education are free and organizationally similar in to educational systems in western societies. The MeHg concentrations in local fish are similar to those of fish commercially available in the US (Robinson and Schroff, 2004) and sea

Methylmercury exposure

The mean prenatal MeHg level in maternal hair for the main cohort was 6.89 ppm (SD = 4.52) and for the 9-year child hair level it was 6.09 ppm (SD = 3.47) (both from Myers et al., 2003). The 17-year child MeHg hair level had a mean of 8.00 ppm (SD = 4.68). We compared the two subgroups, those with and without the SACMEQ scores, using two-sample t-tests. The prenatal MeHg levels were similar between the two groups, 6.77 (SD = 4.21) versus 6.95 (SD = 4.67) ppm respectively. However, the SACMEQ group had a

Discussion

Our results for Primary 6 and Secondary 3 end-of-year examinations indicated no consistent pattern of association between prenatal or recent postnatal MeHg hair levels and any outcome, either at the end of primary school or in mid-high school. In all, we studied 12 end-of-year examination scores, six at the end of Primary 6 and six at the end of Secondary 3. We found one association between prenatal MeHg exposure and 11 out of 12 achievement scores, and no association between recent postnatal

Summary

This study is the first time scholastic achievement scores have been related to either prenatal or postnatal MeHg exposure from fish consumption and we found no consistent pattern of associations. These results are consistent with findings from our earlier studies that reported prenatal MeHg exposure to dosages present in frequent fish consumers are not associated with consistent detectable effects on child development. The adverse associations found with recent postnatal MeHg exposure are

Conflict of interest statement

None.

References (36)

M.P. Bonham et al.
Habitual fish consumption does not prevent a decrease in LCPUFA status in pregnant women (the Seychelles child development nutrition study)
Prostaglandins, Leukotrienes and Essential Fatty Acids
(2008)
C. Borras et al.
Mitochondria from females exhibit higher antioxidant gene expression and lower oxidative damage than males
Free Radical Biology and Medicine
(2003)
Y. Cao et al.
Does background postnatal methylmercury exposure in toddlers affect cognition and behavior?
NeuroToxicology
(2010)
C. Cox et al.
Dose–response analysis of infants prenatally exposed to methylmercury: an application of a single compartment model to single-strand hair analysis
Environmental Research
(1989)
P.W. Davidson et al.
Neurodevelopmental effects of maternal nutritional status and exposure to methylmercury from eating fish during pregnancy
NeuroToxicology
(2008)
P. Grandjean et al.
Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury
Neurotoxicology and Teratology
(1997)
J.R. Hibbeln et al.
Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study
Lancet
(2007)
G.J. Myers et al.
Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study
Lancet
(2003)
G.J. Myers et al.
Postnatal exposure to methyl mercury from fish consumption: a review and new data from the Seychelles child development study
NeuroToxicology
(2009)
G. Olivieri et al.
The effects of beta-estradiol on SHSY5Y neuroplastoma cells during heavy metal induced oxidative stress, neurotoxicity and beta-amyloid secretioin
Neuroscience
(2002)

J.J. Strain et al.

Associations of maternal long chain polyunsaturated fatty acids, methyl mercury, and infant development in the Seychelles Child Development and Nutrition Study

NeuroToxicology

(2008)

D.J. Thomas et al.

Sexual differences in the distribution and retention of organic and inorganic mercury in methyl mercury-treated rats

Environmental Research

(1986)

D.J. Thomas et al.

Sexual differences in the excretion of organic and inorganic mercury in methyl mercury-treated rats

Environmental Research

(1987)

M. Vahter et al.

Gender differences in the disposition and toxicity of metals

Environmental Research

(2007)

D.A. Axelrad et al.

Dose–response relationship of prenatal mercury exposure and IQ: an integrative analysis of epidemiologic data

Environmental Health Perspectives

(2007)

E. Cernichiari et al.

The biological monitoring of mercury in the Seychelles study

NeuroToxicology

(1995)

E. Cernichiari et al.

Monitoring methylmercury during pregnancy maternal hair predicts fetal brain exposure

NeuroToxicology

(1995)

T.W. Clarkson et al.

The toxicity of mercury and its chemical compounds

Critical Reviews of Toxicology

(2006)

Cited by (58)

Relationship of mercury and selenium in ocean fish frequently consumed in the Seychelles: A comparison to levels in ocean fish consumed in the US
2023, NeuroToxicology
We characterized mercury and selenium in the fish consumed in the Seychelles Islands to determine if their levels are similar to fish consumed in the US. A secondary aim was to examine whether fish weight and species predict mercury and selenium in fish consumed in the Seychelles. We measured total mercury (THg) and selenium (Se) content of 10 samples from each of the 19 most frequently consumed fish species in Seychelles and for each calculated the Se:Hg molar ratios and the Selenium Health Benefit Value Index (HBV Se). Linear regression models examined associations with weight and species. Average MeHg levels in fish ranged from less than 0.01 ppm (streamlined spinefoot) to 0.7 ppm (bludger trevally) with an overall mean of 0.21 ± 0.23 ppm. Average Se levels ranged from 0.34 ppm (blue-barred parrot fish) to 0.93 ppm (blue-lined large-eye bream) with a mean of 0.54 ± 0.23 ppm. All fish species had a mean Se:Hg molar ratio > 1 and positive mean HBV Se index values. Weight was strongly predictive of MeHg and Se:Hg molar ratio, both across and within most species, but was less predictive of Se and HBV Se. Our study demonstrated that fish consumed in Seychelles have mercury and selenium content similar to that of fish consumed in the US. Fish in both countries have favorable positive values for Se:Hg molar ratios and HBV Se indexes. Because mercury and selenium concentrations in fish are similar to those in the US but fish consumption is substantially higher in Seychelles, the Seychellois make an ideal population in which to determine if there are adverse effects of prenatal, postnatal, and lifetime low dose MeHg exposure from fish consumption.
Prenatal and concurrent blood mercury concentrations and associations with IQ in canadian preschool children
2023, Environmental Research
Prenatal and childhood mercury (Hg) exposures have been associated with negative impacts on child neurodevelopment. It is unclear if associations persist at the low Hg exposures typical in Western countries.
To examine associations between prenatal/childhood blood Hg concentrations and child IQ in Canadian male and female children while considering the potential modifying role of prenatal fish consumption.
We analyzed data from the Maternal-Infant Research on Environmental Chemicals study. Hg was measured in first trimester (n = 527), cord (n = 430), and child (at 3–4 years of age, n = 355) blood and examined sex-stratified associations between blood Hg and children's Full Scale IQ (FSIQ), Verbal IQ (VIQ), Performance IQ (PIQ), and General Language Composite (GLC) scores (assessed with WPPSI-III). Prenatal Hg analyses were further stratified by prenatal fish consumption (low: 0–2, moderate: 3–7, or high: ≥8 times/month).
Higher cord blood Hg concentrations were associated with lower PIQ (ß = −3.27; 95%CI: 6.44, −0.09) in male children with the lowest prenatal fish consumption. Progressively stronger positive associations were observed with PIQ in male children for moderate (ß = 1.08; 95%CI: 0.10, 2.26) and high (ß = 3.07; 95%CI: 1.95, 4.19) prenatal fish consumption. Cord blood Hg concentrations were positively associated with female children's FSIQ (ß = 1.29; 95% CI: 0.77, 1.81) and PIQ (ß = 2.01; 95% CI: 1.19, 2.83); however, when stratified only in the highest fish consumption subgroup. Among female children, higher child blood Hg concentrations were associated with an approximately 1-point increase in FSIQ, VIQ, and GLC.
Prenatal exposure to low levels of Hg was associated with lower PIQ scores in male children with low prenatal fish intake. Positive associations between cord and child blood Hg concentrations and IQ were primarily observed in female children and may be due to beneficial effects of prenatal fish intake.
Exposure to mercury among Spanish adolescents: Eleven years of follow-up
2023, Environmental Research
The toxic effects of mercury exposure on human health are a public health concern. The most important source of this exposure is the consumption of fish and marine mammals. This study aims to describe hair mercury concentrations and their evolution from birth until eleven years of age in adolescents from the INMA (Environment and Childhood) birth cohort study, and to assess the association of hair mercury concentrations at eleven years of age with sociodemographic and dietary factors.
The sample comprised 338 adolescents from the sub-cohort of Valencia (in eastern Spain). Total mercury (THg) was measured in hair samples collected at 4, 9 and 11 years old and in cord blood at birth. The equivalent of hair for cord-blood THg concentrations was calculated. Fish consumption and other characteristics at 11 years old were collected through questionnaires. Multivariate linear regression models were conducted to explore the association between THg concentrations, fish consumption and covariates.
The geometric mean of hair THg concentrations at 11 years of age was 0.86 μg/g (95%CI: 0.78–0.94) and 45.2% of the participants presented concentrations above the equivalent RfD proposed by the US EPA (1 μg/g). Consumption of fish such as swordfish, canned tuna and other large oily fish was associated with higher levels of hair mercury at 11 years of age. Swordfish had the highest effect with an increase of 125% in hair mercury (95%CI: 61.2–214.9%) given a 100 g/week increase in its consumption, and, taking into account the frequency of consumption, canned tuna was the main contributor to Hg exposure among our population. The hair THg concentrations at 11 years of age represented a reduction of around 69% with respect to that estimated at childbirth. Even though THg exposure shows a sustained decreasing trend, it can still be considered elevated. INMA birth cohort studies provide a longitudinal assessment of mercury exposure in a vulnerable population, its associated factors and temporal trends, and this information could be used to adjust recommendations about this issue.
HBM4EU-MOM: Prenatal methylmercury-exposure control in five countries through suitable dietary advice for pregnancy – Study design and characteristics of participants
2023, International Journal of Hygiene and Environmental Health
Seafood is a major source of vital nutrients for optimal fetal growth, but at the same time is the main source of exposure to methylmercury (MeHg), an established neurodevelopmental toxicant. Pregnant women must be provided with dietary advice so as to include safely fish in their diet for nutrition and mercury control. The aim of this work is to present the design of a multicentre randomized control trial (RCT), which combines human biomonitoring (HBM) with dietary interventions using seafood consumption advice to pregnant women for MeHg control, and to collect information about other possible sources of exposure to mercury. It also presents the materials developed for the implementation of the study and the characteristics of the study participants, which were self-reported in the first trimester of pregnancy.
The “HBM4EU-MOM” RCT was performed in the frame of the European Human Biomonitoring Initiative (HBM4EU) in five coastal, high fish-consuming European countries (Cyprus, Greece, Spain, Portugal and Iceland). According to the study design, pregnant women (≥120/country, ≤20 weeks gestational age) provided a hair sample for total mercury assessment (THg) and personal information relevant to the study (e.g., lifestyle, pregnancy status, diet before and during the pregnancy, information on seafood and factors related to possible non-dietary exposures to mercury) during the first trimester of pregnancy. After sampling, participants were randomly assigned to “control” (habitual practices) or “intervention” (received the harmonized HBM4EU-MOM dietary advice for fish consumption during the pregnancy and were encouraged to follow it). Around child delivery, participants provided a second hair sample and completed another tailored questionnaire.
A total of 654 women aged 18–45 years were recruited in 2021 in the five countries, primarily through their health-care providers. The pre-pregnancy BMI of the participants ranged from underweight to obese, but was on average within the healthy range. For 73% of the women, the pregnancy was planned. 26% of the women were active smokers before the pregnancy and 8% continued to smoke during the pregnancy, while 33% were passive smokers before pregnancy and 23% remained passively exposed during the pregnancy. 53% of the women self-reported making dietary changes for their pregnancy, with 74% of these women reporting making the changes upon learning of their pregnancy. Of the 43% who did not change their diet for the pregnancy, 74% reported that their diet was already balanced, 6% found it difficult to make changes and 2% were unsure of what changes to make. Seafood consumption did not change significantly before and during the first trimester of pregnancy (overall average ∼8 times per month), with the highest frequency reported in Portugal (≥15 times per month), followed by Spain (≥7 times per month). During the first-trimester of pregnancy, 89% of the Portuguese women, 85% of the Spanish women and <50% of Greek, Cypriot and Icelandic women reported that they had consumed big oily fish. Relevant to non-dietary exposure sources, most participants (>90%) were unaware of safe procedures for handling spillage from broken thermometers and energy-saving lamps, though >22% experienced such an incident (>1 year ago). 26% of the women had dental amalgams. ∼1% had amalgams placed and ∼2% had amalgams removed during peri-pregnancy. 28% had their hair dyed in the past 3 months and 40% had body tattoos. 8% engaged with gardening involving fertilizers/pesticides and 19% with hobbies involving paints/pigments/dyes.
The study design materials were fit for the purposes of harmonization and quality-assurance. The harmonized information collected from pregnant women suggests that it is important to raise the awareness of women of reproductive age and pregnant women about how to safely include fish in their diet and to empower them to make proper decisions for nutrition and control of MeHg, as well as other chemical exposures.
Effects of low-level mercury exposure on brain-derived neurotrophic factor in preschool children
2021, Ecotoxicology and Environmental Safety
Mercury (Hg), a ubiquitous heavy metal, could affect the neurodevelopment of the children, however, these associations are still equivocal. Brain derived neurotrophic factor (BDNF) plays an essential role in the central nervous system development in children. This study aimed to investigate the effects of low-level mercury exposure on serum BDNF levels and the influence of sex and dietary intake on these relationships in children.
In this cross-sectional study, a total of 541 pre-school children were recruited, the blood mercury concentrations and serum BDNF levels were measured. The background information on demographic characteristics and dietary habits of the children was collected through questionnaires. Multivariable linear models after adjustment for potential confounders were used to evaluate the associations between mercury exposure and levels of BDNF in children.
The GMs of blood mercury concentrations and serum BDNF levels were 1.06 μg/L, 20.4 ng/mL, respectively. A significant positive association between blood mercury concentrations and serum BDNF levels was found. After stratification by sex, the blood mercury concentrations in children were positive associated with serum BDNF levels in girls but not in boys. However, these associations were attenuated when we further adjusted the children’s dietary intake variables.
Our findings suggest that low-levels of mercury exposure may have sex-specific effects on BDNF levels in young children and that dietary intake may be potential confounders in these relationships. However, further studies are warranted to investigate the role of BDNF in the effects of mercury on neurodevelopment.
Human-induced pluripotent stems cells as a model to dissect the selective neurotoxicity of methylmercury
2019, Biochimica et Biophysica Acta - General Subjects
Citation Excerpt :
Importantly, there have been conflicting results in the epidemiological literature as to the association between MeHg exposure and neurodevelopmental outcomes. Of note, the longitudinal studies conducted in the Seychelles Islands have found little evidence of such association [6–11], while the studies conducted in the Faroe Islands have associated MeHg with neurobehavioral deficits including motor function, learning, attention, and memory [12,15,18]. These conflicting results may be due to differences in developmental stage of exposure, genetics, and environmental modifiers, which influence background disease occurrence and impose differential sensitivity to MeHg [19–21].
Methylmercury (MeHg) is a potent neurotoxicant affecting both the developing and mature central nervous system (CNS) with apparent indiscriminate disruption of multiple homeostatic pathways. However, genetic and environmental modifiers contribute significant variability to neurotoxicity associated with human exposures. MeHg displays developmental stage and neural lineage selective neurotoxicity. To identify mechanistic-based neuroprotective strategies to mitigate human MeHg exposure risk, it will be critical to improve our understanding of the basis of MeHg neurotoxicity and of this selective neurotoxicity. Here, we propose that human-based pluripotent stem cell cellular approaches may enable mechanistic insight into genetic pathways that modify sensitivity of specific neural lineages to MeHg-induced neurotoxicity. Such studies are crucial for the development of novel disease modifying strategies impinging on MeHg exposure vulnerability.

View all citing articles on Scopus

^☆: This project was supported by grants R01-ES-08442, T32-ES-007271 and P30-ES-001247 from the National Institute of Environmental Health Sciences to the University of Rochester. The authors wish to thank the Government of Seychelles, Ministry of Education for facilitating the conduct of this research.

View full text

Fish consumption, mercury exposure, and their associations with scholastic achievement in the Seychelles Child Development Study☆

Abstract

Section snippets

Setting

Methylmercury exposure

Discussion

Summary

Conflict of interest statement

Prostaglandins, Leukotrienes and Essential Fatty Acids

Free Radical Biology and Medicine

NeuroToxicology

Environmental Research

NeuroToxicology

Neurotoxicology and Teratology

Lancet

Lancet

NeuroToxicology

Neuroscience

NeuroToxicology

Environmental Research

Environmental Research

Environmental Research

Dose–response relationship of prenatal mercury exposure and IQ: an integrative analysis of epidemiologic data

Environmental Health Perspectives

The biological monitoring of mercury in the Seychelles study

NeuroToxicology

Monitoring methylmercury during pregnancy maternal hair predicts fetal brain exposure

NeuroToxicology

The toxicity of mercury and its chemical compounds

Critical Reviews of Toxicology