Relation Between Cord Blood Mercury Levels and Early Child Development
Relation Between Cord Blood Mercury Levels and Early Child Development
Objective: This study was designed to determine whether prenatal mercury exposure, including potential releases from the World Trade Center (WTC) disaster, adversely affects fetal growth and child development.
Methods: We determined maternal and umbilical cord blood total mercury of nonsmoking women who delivered at term in lower Manhattan after 11 September 2001, and measured birth outcomes and child development.
Results: Levels of total mercury in cord and maternal blood were not significantly higher for women who resided or worked within 1 or 2 miles of the WTC in the month after 11 September, compared with women who lived and worked farther away. Average cord mercury levels were more than twice maternal levels, and both were elevated in women who reported eating fish/seafood during pregnancy. Regression analyses showed no significant association between (ln) cord or maternal blood total mercury and birth outcomes. Log cord mercury was inversely associated with the Bayley Scales of Infant Development psychomotor score [Psychomotor Development Index (PDI) ] at 36 months (b = -4.2, p = 0.007) and with Performance (b = -3.4, p = 0.023) , Verbal (b = -2.9, p = 0.023) , and Full IQ scores (b = -3.8, p = 0.002) on the Wechsler Preschool and Primary Scale of Intelligence, Revised (WPPSI-R) , at 48 months, after controlling for fish/seafood consumption and other confounders. Fish/seafood consumption during pregnancy was significantly associated with a 5.6- to 9.9-point increase in 36-month PDI, and 48-month Verbal and Full IQ scores.
Conclusions: Blood mercury was not significantly raised in women living or working close to the WTC site in the weeks after 11 September 2001. Higher cord blood mercury was associated with reductions in developmental scores at 36 and 48 months, after adjusting for the positive effects of fish/seafood consumption during pregnancy.
Mercury can be present in the body as inorganic mercury (mostly Hg), metallic mercury (elemental, Hg), and organic mercury (mostly methylmercury). Common inorganic sources include air and water pollution, some skin creams, and herbal medicines. Seafood (including fish) consumption is a major contributor of methylmercury to blood total mercury; metallic mercury typically comes from amalgam dental fillings and industrial exposure. Although inhaled metallic mercury is a less common source of blood mercury, in humans about 80% of inhaled metallic vapor is retained by the body [World Health Organization (WHO) Task Group 1991]. It has a half-life in blood of about 60 days (range, 31-100) (Counter and Buchanan 2004). Like methylmercury, after crossing the blood-brain barrier, metallic mercury can be oxidized to inorganic mercury, which does not freely return to the circulation, resulting in accumulation in the brain. Much more mercury ends up in the brain of mice and monkeys after inhalation of the metallic form than after injection of the inorganic form (WHO Task Group 1991).
The collapse of the World Trade Center (WTC) towers on 11 September 2001 resulted in the dispersion of many potentially harmful pollutants, including heavy metals (Lioy et al. 2002; McGee et al. 2003; Offenberg et al. 2003). Hundreds of thousands of gallons of airplane fuel, stored diesel fuel, and gasoline in vehicles parked beneath the buildings burned there, releasing some mercury into the air. Metallic mercury was also released with the crushing of tens of thousands of fluorescent light bulbs, major brands of which contain 3.5-15 mg of metallic mercury in a 4-foot bulb (Inform, Inc. 2003). In addition, nearly half of the demolished automobiles would have contained at least one hood or trunk light, or antilock braking system switch bearing metallic mercury (Adsit et al. 2002), each containing about 1,000 mg of metallic mercury [U.S. Environmental Protection Agency (EPA) 2005]. Other possible mercury sources included cathode ray tubes, such as those used for computer screens, and industrial switches and relays, which can contain from 1 to 91,000 g of metallic mercury (U.S. EPA 2002).
Maternal exposure to methylmercury has been associated with decrements in cognitive function in the child (Budtz-Jorgensen et al. 2007; Grandjean et al. 1997, 2005; Jedrychowski et al. 2006; Oken et al. 2005). The developmental effects of maternal inhalation of low levels of metallic mercury vapor during pregnancy have been explored primarily in animals [reviewed by Counter and Buchanan (2004)]; however, in a study of women in Tagum, the Philippines, a fish-eating community using metallic mercury in gold mining/processing, cord blood total mercury was associated with developmental and language deficits at 2 years of age (Ramirez et al. 2003). A few studies have shown a relationship between occupational mercury exposure and various adverse reproductive outcomes using work setting or hair levels to define exposure (Seidler et al. 1999; Sikorski et al. 1986). Less is known about the relation to birth outcomes of lower-level, nonoccupational, metallic mercury exposure. A study, using questionnaires to assess exposure, of pregnant women having mercury dental fillings replaced during pregnancy showed no reductions in newborn birth weight (Hujoel et al. 2005).
To evaluate the relation of blood total mercury to birth outcomes and child development, we used data collected in a study of the effects of the WTC attack of 11 September 2001 on women delivering several months after the event. We measured total mercury in maternal and cord blood, a measurement that reflects methylmercury from fish consumption, as well as inorganic and metallic mercury. We explored the relation of blood total mercury to proximity to the WTC and hypothesized that higher blood total mercury levels, whatever their source, would be associated with differences in birth outcomes and adversely affect child development, as measured by the Bayley Scales of Infant Development (2nd ed., BSID-II) (Bayley 1993) at 12, 24, and 36 months, and the Wechsler Preschool and Primary Scale of Intelligence, Revised (WPPSI-R) (Wechsler 1989), at 48 months.
Although consumption of fish has been shown to be associated with higher maternal and/or cord mercury concentrations (Daniels et al. 2004; Jedrychowski et al. 2006), significantly higher infant scores on the MacArthur Communicative Development Inventory at 15 months and on the Denver Developmental Screening Test at 18 months have been associated with increasing fish intake during pregnancy (Daniels et al. 2004). Therefore, we also evaluated whether maternal fish/seafood consumption would have a protective effect on the child's cognitive development and whether, by including it in the analyses, we would more clearly detect detrimental effects of prenatal mercury exposure.
Objective: This study was designed to determine whether prenatal mercury exposure, including potential releases from the World Trade Center (WTC) disaster, adversely affects fetal growth and child development.
Methods: We determined maternal and umbilical cord blood total mercury of nonsmoking women who delivered at term in lower Manhattan after 11 September 2001, and measured birth outcomes and child development.
Results: Levels of total mercury in cord and maternal blood were not significantly higher for women who resided or worked within 1 or 2 miles of the WTC in the month after 11 September, compared with women who lived and worked farther away. Average cord mercury levels were more than twice maternal levels, and both were elevated in women who reported eating fish/seafood during pregnancy. Regression analyses showed no significant association between (ln) cord or maternal blood total mercury and birth outcomes. Log cord mercury was inversely associated with the Bayley Scales of Infant Development psychomotor score [Psychomotor Development Index (PDI) ] at 36 months (b = -4.2, p = 0.007) and with Performance (b = -3.4, p = 0.023) , Verbal (b = -2.9, p = 0.023) , and Full IQ scores (b = -3.8, p = 0.002) on the Wechsler Preschool and Primary Scale of Intelligence, Revised (WPPSI-R) , at 48 months, after controlling for fish/seafood consumption and other confounders. Fish/seafood consumption during pregnancy was significantly associated with a 5.6- to 9.9-point increase in 36-month PDI, and 48-month Verbal and Full IQ scores.
Conclusions: Blood mercury was not significantly raised in women living or working close to the WTC site in the weeks after 11 September 2001. Higher cord blood mercury was associated with reductions in developmental scores at 36 and 48 months, after adjusting for the positive effects of fish/seafood consumption during pregnancy.
Mercury can be present in the body as inorganic mercury (mostly Hg), metallic mercury (elemental, Hg), and organic mercury (mostly methylmercury). Common inorganic sources include air and water pollution, some skin creams, and herbal medicines. Seafood (including fish) consumption is a major contributor of methylmercury to blood total mercury; metallic mercury typically comes from amalgam dental fillings and industrial exposure. Although inhaled metallic mercury is a less common source of blood mercury, in humans about 80% of inhaled metallic vapor is retained by the body [World Health Organization (WHO) Task Group 1991]. It has a half-life in blood of about 60 days (range, 31-100) (Counter and Buchanan 2004). Like methylmercury, after crossing the blood-brain barrier, metallic mercury can be oxidized to inorganic mercury, which does not freely return to the circulation, resulting in accumulation in the brain. Much more mercury ends up in the brain of mice and monkeys after inhalation of the metallic form than after injection of the inorganic form (WHO Task Group 1991).
The collapse of the World Trade Center (WTC) towers on 11 September 2001 resulted in the dispersion of many potentially harmful pollutants, including heavy metals (Lioy et al. 2002; McGee et al. 2003; Offenberg et al. 2003). Hundreds of thousands of gallons of airplane fuel, stored diesel fuel, and gasoline in vehicles parked beneath the buildings burned there, releasing some mercury into the air. Metallic mercury was also released with the crushing of tens of thousands of fluorescent light bulbs, major brands of which contain 3.5-15 mg of metallic mercury in a 4-foot bulb (Inform, Inc. 2003). In addition, nearly half of the demolished automobiles would have contained at least one hood or trunk light, or antilock braking system switch bearing metallic mercury (Adsit et al. 2002), each containing about 1,000 mg of metallic mercury [U.S. Environmental Protection Agency (EPA) 2005]. Other possible mercury sources included cathode ray tubes, such as those used for computer screens, and industrial switches and relays, which can contain from 1 to 91,000 g of metallic mercury (U.S. EPA 2002).
Maternal exposure to methylmercury has been associated with decrements in cognitive function in the child (Budtz-Jorgensen et al. 2007; Grandjean et al. 1997, 2005; Jedrychowski et al. 2006; Oken et al. 2005). The developmental effects of maternal inhalation of low levels of metallic mercury vapor during pregnancy have been explored primarily in animals [reviewed by Counter and Buchanan (2004)]; however, in a study of women in Tagum, the Philippines, a fish-eating community using metallic mercury in gold mining/processing, cord blood total mercury was associated with developmental and language deficits at 2 years of age (Ramirez et al. 2003). A few studies have shown a relationship between occupational mercury exposure and various adverse reproductive outcomes using work setting or hair levels to define exposure (Seidler et al. 1999; Sikorski et al. 1986). Less is known about the relation to birth outcomes of lower-level, nonoccupational, metallic mercury exposure. A study, using questionnaires to assess exposure, of pregnant women having mercury dental fillings replaced during pregnancy showed no reductions in newborn birth weight (Hujoel et al. 2005).
To evaluate the relation of blood total mercury to birth outcomes and child development, we used data collected in a study of the effects of the WTC attack of 11 September 2001 on women delivering several months after the event. We measured total mercury in maternal and cord blood, a measurement that reflects methylmercury from fish consumption, as well as inorganic and metallic mercury. We explored the relation of blood total mercury to proximity to the WTC and hypothesized that higher blood total mercury levels, whatever their source, would be associated with differences in birth outcomes and adversely affect child development, as measured by the Bayley Scales of Infant Development (2nd ed., BSID-II) (Bayley 1993) at 12, 24, and 36 months, and the Wechsler Preschool and Primary Scale of Intelligence, Revised (WPPSI-R) (Wechsler 1989), at 48 months.
Although consumption of fish has been shown to be associated with higher maternal and/or cord mercury concentrations (Daniels et al. 2004; Jedrychowski et al. 2006), significantly higher infant scores on the MacArthur Communicative Development Inventory at 15 months and on the Denver Developmental Screening Test at 18 months have been associated with increasing fish intake during pregnancy (Daniels et al. 2004). Therefore, we also evaluated whether maternal fish/seafood consumption would have a protective effect on the child's cognitive development and whether, by including it in the analyses, we would more clearly detect detrimental effects of prenatal mercury exposure.
