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
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.