Abstract
Introduction: During the past four decades, mercury (Hg) research focused on fish consumption has explained less than 22% of Hg in human blood. One overlooked exposure pathway for infants and young children is the concentration of Hg in soils. Although 75% of the U.S. population lives in urban areas near industrial facilities, minimal data exist regarding the concentration and speciation of Hg in residential soils. Chronic exposure through ingestion of low concentrations of Hg in soils may explain a portion of the blood Hg levels noted in infants. Methods: Three relatively unexposed residential sites in a suburban community were selected. The primary route of contamination was atmospheric deposition. Soils were digested in a nitric acid-hydrofluoric acid solution and analyzed by cold vapor atomic absorption spectrophotometry. Measured concentrations of total Hg in local suburban soil samples were compared to levels measured in a national study of 27 remote and rural sites. The Al-Shahristani pharmacokinetic model, developed after the 1971 Iraqi Methyl Hg poisoning incident, was used to calculate the blood Hg concentration in a hypothetical year-old infant. Results: Soil samples contained Hg concentrations ranging from 0.01 to 0.24 ppmw. The distribution of Hg in the soil samples was non-linear and non-normal. The mean soil Hg concentrations at the three locations were 0.08, 0.05 and 0.08 ppm. Calculated blood Hg concentrations for a 10 kg, year-old infant due to ingestion of soil (200 mg/day) containing 0.2, 0.4 and 0.8 ppm Hg were 0.08, 0.17 and 0.26 μg/L, respectively. Conclusions: The pilot study data appear to support the hypothesis that chronic, low-level soil ingestion may be a significant source of Hg for infants. Further study is warranted.
Highlights
During the past four decades, mercury (Hg) research focused on fish consumption has explained less than 22% of Hg in human blood
Using all 21 samples, the average concentration of Hg in topsoil from site C was 0.044 ppmw (Table 2). This is the first study to propose that measured Hg in soil may have some effect on blood Hg levels in infants
The United States Environmental Protection Agency (USEPA) survey of soils collected in North America reported an average background Hg concentration of 0.022 ppm with a range of 0.0005 to 0.07 ppmw [13]
Summary
During the past four decades, mercury (Hg) research focused on fish consumption has explained less than 22% of Hg in human blood. Chronic exposure through ingestion of low concentrations of Hg in soils may explain a portion of the blood Hg levels noted in infants. Calculated blood Hg concentrations for a 10 kg, year-old infant due to ingestion of soil (200 mg/day) containing 0.2, 0.4 and 0.8 ppm Hg were 0.08, 0.17 and 0.26 μg/L, respectively. A statistical analysis indicates a link between fish consumption and Hg concentrations in infant cord blood, the correlation is weak. A weak dose-response relationship (r2 = 0.21) between fish consumption and infant cord blood Hg was confirmed in another study of pregnancies among women living along the St. Lawrence River who ate an average of 3.5 fish meals/month [10]. Received December 18th, 2012; revised January 9th, 2013; accepted January 31st, 2013 ABSTRACT
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