Elsevier

Environmental Research

Volume 110, Issue 1, January 2010, Pages 96-104
Environmental Research

Hair mercury levels, fish consumption, and cognitive development in preschool children from Granada, Spain ,,☆☆

https://doi.org/10.1016/j.envres.2009.10.005Get rights and content

Abstract

The main source of human exposure to mercury is the consumption of fish contaminated with methylmercury, which may adversely affect early neurodevelopment. This study assessed mercury levels in hair of preschoolers in Spain, where fish consumption is elevated, with the aim of investigating the influence of their fish intake and other factors on mercury exposure, and evaluating their association with cognitive development. A population-based birth cohort from Granada (Spain) was studied at the age of 4 yr. Total mercury (T-Hg) levels were determined in children's hair, and daily fish intake was assessed by a food frequency questionnaire. The McCarthy Scales of Children's Abilities (MSCA) were used to assess children's motor and cognitive abilities. Complete data were gathered on 72 children, and multivariate analyses were performed to evaluate the influence of mercury exposure and fish intake on MSCA outcomes. Mean concentration of T-Hg in hair was 0.96 μg/g (95% confidence interval=0.76; 1.20 μg/g). T-Hg levels were associated with higher frequency of oily fish consumption, place of residence, maternal age, and passive smoking. After adjustment for fish intake, T-Hg levels ≥1 μg/g were associated with decrements in the general cognitive (−6.6 points), memory (−8.4 points), and verbal (−7.5 points) MSCA scores. Higher mercury exposure in children from this Mediterranean area was associated with cognitive development delay. Studies on the putative benefits of fish intake during early development should consider mercury exposure from different fish species.

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.

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    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.

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