Washington: Exposure to lead in early childhood impairs performance on reading tests among minority and low-income children, according to a new study.

The analysis showed that children already at the low end of the test-score curve were more greatly affected by lead exposure - the greater the exposure, the greater the impact on their scores.

"We found a clear dose-response pattern between lead exposure and test performance, with the effects becoming more pronounced as you move from children at the high end to the low end of the test-score curve," said lead investigator Marie Lynn Miranda, director of the Children's Environmental Health Initiative (CEHI) at Duke University.

The study linked data on blood-lead levels from the North Carolina Childhood Lead Poisoning Prevention Program surveillance registry to reading test scores for 4th graders in all 100 of the states counties.

The study's analysis revealed that early childhood exposure to lead, the family's poverty status and parental education all account for a decline in test-scores. On average, exposure to lead accounts for between seven percent and 16 percent of the decline, with a larger decline associated with higher blood-lead levels.

By comparison, they found the family's poverty status, as indicated by enrolment in a free or reduced-price school lunch programme, accounts for 25 percent to 28 percent of a decline in test results.

And parental education accounts for the largest portion of the drop in test scores, between 58 percent and 65 percent of the total, a Duke release said.

"This demonstrates the particular vulnerabilities of socio-economically and environmentally disadvantaged children," said Miranda, a professor of paediatrics also.

These details were published online in NeuroToxicology. IANS