Hair mercury levels, fish consumption, and cognitive development in preschool children from Granada, Spain ,☆,☆☆
Introduction
Mercury is a heavy metal from both natural and anthropogenic sources that is widespread and persistent in the environment (ATSDR, 1999). Once released into the environment, inorganic mercury is deposited in aquatic media and becomes methylmercury (MeHg), its most toxic organic form, which bioaccumulates in marine organisms and is biomagnified through the food chain (Boening, 2000). Humans can be affected by mercury from amalgam fillings, thermometers, fossil-fuel emissions, preservative vaccines, and cosmetic products, among others (Counter and Buchanan, 2004), but the main source of human exposure is consumption of MeHg-contaminated fish (US Environmental Protection Agency, 2009)
MeHg is highly and selectively toxic to the central nervous system, especially in the foetus (Díez, 2009). Thus, chronic prenatal exposure to MeHg may results in neurological disabilities (Jedrychowski et al., 2006; Oken et al., 2005), including language, learning, and attention deficits and, to a lesser degree, motor and visual-spatial impairment (Castoldi et al., 2008). In two longitudinal-cohort studies in the Faroe Islands and New Zealand neurodevelopmental deficits in school-age children were associated with prenatal exposure to MeHg from maternal fish consumption (Crumpt et al., 1998; Grandjean et al., 1997). However, a study in the Seychelles Islands found no adverse effect on children's cognitive development (Myers et al., 2003; Palumbo et al., 2000). Hence, the effects of chronic prenatal exposure to MeHg remain unclear and controversial (Oken et al., 2005, Oken et al., 2008). Fish is the primary source of nutrients considered to improve child development, such as omega-3 fatty acids (Cohen et al., 2005; Domingo et al., 2007a, Domingo et al., 2007b), and the balance between the benefits and risks of fish consumption has yet to be fully elucidated (Davidson et al., 2008; Oken et al., 2008). Three US studies reported that greater fish consumption in pregnancy was related to higher infant cognition but that higher prenatal mercury levels were associated with lower cognition (Lederman et al., 2008; Oken et al., 2005, Oken et al., 2008).
Based on the studies in Faroe, New Zealand, and the Seychelles, the US Environmental Protection Agency (EPA) adopted a reference dose (RfD) for MeHg of 0.1 μg/kg bw/day (USEPA, 2001). This RfD is based on neurodevelopmental effects associated with in utero exposure to MeHg from the maternal diet and is related to a maternal hair mercury concentration of 1.0 μg/g (NRC, 2000). Among the few studies addressing postnatal exposure and potential neurodevelopmental impairment, contradictory results were published by two cross-sectional studies from Brazil (Grandjean et al., 1999; Tavares et al., 2005), and another study in the Faroe Islands found no association between higher hair mercury levels in children and delayed neurodevelopment (Murata et al., 2002).
Scalp hair has been widely used as a biomarker of human mercury exposure (McDowell et al., 2004). Mercury in the hair correlates with mercury in the brain, and MeHg accounts for approximately 70–80% of total mercury (T-Hg) in hair (Cernichiari et al., 1995). Although investigations of mercury exposure and postnatal neurodevelopment have largely relied on concentrations in maternal hair, it has been suggested that children's hair mercury levels reflect exposure to the same dietary mercury sources as the mother (Marques et al., 2007).
Spain is considered one of the largest consumers of fish in Europe (Welch et al., 2002) and the second in the world (Ministerio de Sanidad y Consumo, 2009). The Mediterranean basin contains important cinnabar deposits, and long-lived predatory fish have higher mercury content in the Mediterranean than elsewhere (Renzoni et al., 1998).
The potential sub-clinical effects on neurodevelopment of low-level exposure to MeHg from contaminated fish remain unclear. The objectives of this study were to investigate exposure to mercury in preschool children from Granada, Spain, by quantifying hair T-Hg levels, to examine the influence of fish intake during infancy and other factors on this T-Hg exposure, and to evaluate their combined effect on cognitive and motor development at 4 yr of age in a cross-sectional analysis of a birth cohort.
Section snippets
Study area and population
The study sample was drawn from a cohort established in the province of Granada in South-eastern Spain (Freire et al., 2009, Freire et al., in press) within the INMA (Environment and Childhood) study (Ribas-Fitó et al., 2006). The survey was conducted in the area served by the San Cecilio University Hospital (population, 512 000 inhabitants; 50 municipalities). The study area is located in a Mediterranean province with little industrial activity that is mostly devoted to agriculture practices
Results
Mean age of the children at testing was 51 months (range=48–57 months). T-Hg and MeHg were quantified in all hair samples (n=72 and 23, respectively). GM of T-Hg concentrations was 0.96 μg/g (95% CI=0.8; 1.2 μg/g) and median was 1.04 μg/g. Mean MeHg concentration was 1.81 μg/g (95% CI=1.4; 2.3 μg/g). Spearman test showed that T-Hg and MeHg levels in the paired samples were highly correlated (r=0.88; p<0.001). Fried and boiled/grilled white fish were the most frequently consumed (76% and 65% of
Mercury exposure
Levels of T-Hg in the hair of these children from Granada, Spain, were higher than those reported in other young populations from North-eastern Spanish areas with important chemical and fishing-industry activities (Batista et al., 1996; Nadal et al., 2005; Torrente et al., 2005), much higher than concentrations found in children from US and Germany (Pesch et al., 2002; McDowell et al., 2004), but lower than levels reported in heavily exposed children from Brazil, Faroe, and Seychelles Islands (
Acknowledgments
The authors are grateful to Richard Davies for editorial assistance. The results would not have been achieved without the selfless collaboration of the study participants and staff at the Pediatrics Department of the San Cecilio University Hospital.
References (61)
- et al.
Mercury in hair for a child population from Tarragona Province, Spain
Sci. Total Environ.
(1996) Ecological effects, transport, and fate of mercury: a general review
Chemosphere
(2000)- et al.
Human developmental neurotoxicity of methylmercury: impact of variables and risk modifiers
Regul. Toxicol. Pharmacol.
(2008) - et al.
Qualitative assessment of visuospatial errors in mercury-exposed Amazonian children
Neurotoxicology
(2009) - et al.
Neurodevelopmental investigations among methylmercury-exposed children in French Guiana
Environ. Res.
(2002) - et al.
Mercury exposure in children: a review
Toxicol. Appl. Pharmacol.
(2004) - et al.
Neurodevelopmental effects of maternal nutritional status and exposure to methylmercury from eating fish during pregnancy
Neurotoxicology
(2008) - et al.
Determination of methylmercury in human hair by ethylation followed by headspace solid-phase microextraction-gas chromatography-cold-vapour atomic fluorescence spectrometry
J. Chromatogr. A
(2002) - et al.
Benefits and risks of fish consumption Part I. A quantitative analysis of the intake of omega-3 fatty acids and chemical contaminants
Toxicology
(2007) - et al.
Benefits and risks of fish consumption Part II. RIBEPEIX, a computer program to optimize the balance between the intake of omega-3 fatty acids and chemical contaminants
Toxicology
(2007)
Urinary 1-hydroxypyrene and PAH exposure in 4-year-old Spanish children
Sci. Total Environ.
Pilot study of intrauterine exposure to methylmercury in Eastern Aegean islands, Greece
Sci. Total Environ.
Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury
Neurotoxicol. Teratol.
Effects of in utero exposure to polychlorinated biphenyls and related contaminants on cognitive functioning in young children
J. Pediatr.
Effects of prenatal exposure to mercury on cognitive and psychomotor function in one-year-old infants: epidemiologic cohort study in Poland
Ann. Epidemiol.
Hair mercury concentrations of children and mothers in Korea: implication for exposure and evaluation
Sci. Total Environ.
Organochlorine pesticides in placentas from Southern Spain and some related factors
Placenta
Changes in children hair-Hg concentrations during the first 5 years: maternal, environmental and iatrogenic modifying factors
Regul. Toxicol. Pharmacol.
Intake of chemical contaminants through fish and seafood consumption by children of Catalonia, Spain: health risks
Food Chem. Toxicol.
Improvements in the methylmercury extraction from human hair by headspace solid-phase microextraction followed by gas-chromatography cold-vapour atomic fluorescence spectrometry
J. Chromatogr. A
Mercury speciation in the hair of pre-school children living near a chlor-alkali plant
Sci. Total Environ.
Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study
Lancet
Association between prenatal exposure to methylmercury and cognitive functioning in Seychellois children: a reanalysis of the McCarthy Scales of Children's Ability from the main cohort study
Environ. Res.
Prenatal exposure to mercury in a prospective mother–infant cohort study in a Mediterranean area, Valencia, Spain
Sci. Total Environ.
Mercury levels along the food chain and risk for exposed populations
Environ. Res.
Mercury in waters from South-eastern Spain: possible sources of pollution
Ars. Pharm.
The biological monitoring of mercury in the Seychelles study
Neurotoxicology
A quantitative analysis of prenatal methyl mercury exposure and cognitive development
Am. J. Prev. Med.
Influence of prenatal mercury exposure upon scholastic and psychological test performance: benchmark analysis of a New Zealand cohort
Risk Anal.
Cited by (176)
Bioaccessibility data of potentially toxic elements in complementary foods for infants: A review
2023, Food Research InternationalExposure to mercury among Spanish adolescents: Eleven years of follow-up
2023, Environmental ResearchNeuropsychological effects and cognitive deficits associated with exposure to mercury and arsenic in children and adolescents of the Mojana region, Colombia
2023, Environmental ResearchCitation Excerpt :The action of metal ions violates antioxidant protection, thus making possible the development of diseases in different body systems, among which the nervous system stands out, due to the neurological disorders caused by the action of neurotoxicity (Jomova and Valko, 2011; Sharma et al., 2014; Rice et al., 2014; Antunes dos Santos et al., 2016). At the neuropsychological and cognitive skills functioning level, it has been found that mercury exposure (E-Hg) is negatively related to memory and delays in cognitive development, in the verbal-language (expressive) component, in the development of motor function, in attentional function and in visuospatial organization, both in prenatal and postnatal exposure (Cordier et al., 2002; Counter et al., 2006; Debes et al., 2006; Freire et al., 2010; Hsi et al., 2014; Snoj et al., 2017). It has also been shown that Hg may be adversely related to some IQ functions through dose-responses (Axelrad et al., 2007; Bellinger et al., 2016).
The EAT–Lancet reference diet and cognitive function across the life course
2022, The Lancet Planetary Health
- ☆
Funding: This study was supported by grants from the Consejería de Salud de la Junta de Andalucía [SAS 07/0133], the Spanish Ministry of Health [FIS 07/0252], Spanish Ministry of Science and Innovation (FPU-Program to C.F.; Juan de la Cierva Program-FSE to M.J.L.E.), and the European Commission [CONTAMED FP7-ENV-212502].
- ☆☆
Approval by committee for human subjects: Written informed consent was obtained from parents before the study, which was approved by the Ethics Committee of the San Cecilio University Hospital.