Nontoxic neonates: babies avoid chemical's effects. (Science Selections).

In the late 1950s, porphyria cutanea tarda killed more than 1,000 Turkish babies when they developed a secondary soft tissue infection known as pembe yara. The babies had been exposed to the toxic chemical hexachlorobenzene (HCB) through breast milk. Researchers realized during that outbreak that breast-fed babies are particularly vulnerable to the effects of this fat-bound contaminant. Scientists have also known that HCB is transferred from mother to fetus through the placenta. Yet until recently, they knew little about the impact of prenatal exposure. In this issue, researchers find that infants exposed prenatally to high concentrations of HCB appear to escape the adverse effects associated with the pollutant [EHP 110:205-209]. However, metabolism might be affected in babies exposed in utero to both maternal cigarette smoke and HBC.

The porphyrias, of which porphyria cutanea tarda is only one, are disorders characterized by excessive excretion of porphyrins, pigments formed during the production of hemoglobin and excreted naturally in urine and feces. Elevated porphyrin excretion can also indicate subclinical metabolic abnormalities. University of Barcelona researcher Dolores Ozalla and colleagues studied porphyrin excretion among Spanish neonates born at a Mora d'Ebre hospital between 1997 and 1999. They chose the hospital for its proximity to Flix, a rural village of 5,000 where residents have the highest atmospheric (35 [micro]g/[m.sup.3]) and serum (36.7 ng/mL) concentrations of HCB ever reported. Villagers are exposed to HCB through emissions from a nearby electrochemical factory.

The researchers studied the effects of prenatal exposure to HCB by measuring porphyrin concentrations in the infants' urine. They took urine samples from 68 neonates, 38 of whose mothers were from Flix (the exposed population) and 30 of whose mothers were from neighboring villages (the nonexposed population). To assess the infants' exposure to HCB, the researchers analyzed concentrations of the chemical in both maternal serum and cord blood.

Children of mothers from Flix had the highest HCB concentrations in their cord blood. These infants, however, did not excrete unusual amounts of urinary porphyrins. All were within normal range, although the researchers did note higher excretion of one type of porphyrin, CPIII, among exposed infants than among the exposed group. When Ozalla adjusted for maternal cigarette smoking during pregnancy, which for reasons unknown occurred more among mothers exposed to HCB, the difference between the two infant groups disappeared. This indicates that maternal smoking alone seemed to account for the difference in porphyrin excretion. Total porphyrin excretion was approximately 34% higher in infants whose mothers smoked, with the biggest difference occurring in excretion of CPIII, which was 116% higher.

An unexpected finding was that infants in the highest tertile of HCB exposure excreted the lowest levels of two types of porphyrins, CPI and CPIII. Ozalla discounts the negative association, claiming the number of subjects is too small to draw conclusions. Her data overall suggest that, although HCB levels in Flix are among the highest in the world, they're too low to affect porphyrin metabolism in infants exposed prenatally. The only cause Ozalla found for higher excretion in infants was mothers' cigarette smoking during pregnancy. She emphasizes that her study did not measure tobacco exposure, and suggests future studies examine this link more closely.