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Tagum study II: follow-up study at two years of age after prenatal exposure to mercury.

OBJECTIVES
To correlate the presence and levels of total mercury (THg) in cord blood and meconium indicating prenatal exposure with developmental milestones at 2 years and to compare these subjects with controls of comparable age using cognitive adaptive test and clinical linguistic auditory milestone scale (CAT/CLAMS).


METHODS
In 48 of the original Tagum (T) subjects, cord blood and meconium Hg levels, head circumference (HC) at birth, and duration of breastfeeding were correlated with CAT/CLAMS at 2 years. At 2 years, THg levels using cold atomic vapor absorption spectrometry were determined in the hair of 46 T subjects and 88 Saranggani (S) controls; THg levels in blood were tested in 48 T subjects and 45 S controls. These levels were correlated with CAT/CLAMS. Both groups had standard physical and neurologic examinations, hearing screen using transitory evoked otoacoustic emissions, serum glutamate pyruvate transaminase, and routine urinalysis. A prevalidated Socioeconomic Means Test was given to both groups.


RESULTS
The Hg level in cord blood was negatively correlated with CAT/CLAMS at 2 years. The HC at birth was negatively correlated with levels of Hg in hair of T subjects 2 years later. HC at birth and 2 years hence were positively correlated with CAT/CLAMS. The following were significantly higher in S controls than in T subjects: expressive language quotient 82.569 +/- 2.21 versus 71.57 +/- 2.61; CLAMS 87.96 +/- 2.43 versus 77.67 +/- 2.51; CAT 90.57 +/- 2.22 versus 83.15 +/- 1.43; and full-scale developmental quotient 89.31 +/- 2.14 versus 80.56 +/- 1.86. Fifteen percent of T subjects had global delay (full-scale developmental quotient <or=70) versus 5.48% in S controls. Hg levels in hair and blood in both T subjects and S controls at 2 years showed no correlation with CAT/CLAMS. The duration of breastfeeding in both groups likewise showed no correlations with CAT/CLAMS.


CONCLUSION
The study suggests that prenatal Hg exposure is correlated with lower scores in neurodevelopmental screening, but more so in the linguistic pathway. Other confounding factors cannot be eliminated.