This study determined the level of mercury, lead, and zinc in baby teeth of children with autism spectrum disorder (n = 15, age 6.1 +/- 2.2 yr) and typically developing children (n = 11, age = 7 +/- 1.7 yr). Children with autism had significantly (2.1-fold) higher levels of mercury but similar levels of lead and similar levels of zinc. Children with autism also had significantly higher usage of oral antibiotics during their first 12 mo of life, and possibly higher usage of oral antibiotics during their first 36 mo of life. Baby teeth are a good measure of cumulative exposure to toxic metals during fetal development and early infancy, so this study suggests that children with autism had a higher body burden of mercury during fetal/infant development. Antibiotic use is known to almost completely inhibit excretion of mercury in rats due to alteration of gut flora. Thus, higher use of oral antibiotics in the children with autism may have reduced their ability to excrete mercury, and hence may partially explain the higher level in baby teeth. Higher usage of oral antibiotics in infancy may also partially explain the high incidence of chronic gastrointestinal problems in individuals with autism.

Children with autism were examined to determine amounts of mercury (Hg) in their baby hair and the factors that might affect Hg body burden. US children with autism (n ¼ 78) and matched controls (n ¼ 31) born between 1988 and 1999 were studied. Hg in first-cut baby hair was determined using cold vapor atomic fluorescence spectrometry (CVAFS). Twenty samples were split and also measured with Neutron Activation Analysis (NAA). Logistic regression analysis showed that compared to children with higher levels of mercury (above 0.55 mcg g À1 ), children with lower levels of mercury in their hair (below 0.55 mcg g À1 ) were 2.5-fold more likely to manifest with autism. Children with autism had similar mercury exposure as controls from maternal seafood and maternal dental amalgams. Children with autism also had 2.5-fold higher incidence of oral antibiotic use during their first 18 months of life. Their mothers were possibly more likely to use oral antibiotics during pregnancy or nursing. The amount of Hg in the baby hair of children with autism showed a significant correlation with the number of maternal dental amalgams. The lower level of Hg in the baby hair of children with autism indicates an altered metabolism of Hg, and may be due to a decreased ability to excrete Hg. This is consistent with usage of higher amounts of oral antibiotics, which are known to inhibit Hg excretion in rats due to alteration of gut flora, and may exert a similar effect in humans. Higher usage of oral antibiotics in infancy may also partially explain the high incidence of chronic gastrointestinal problems seen in individuals with autism.