No abstract

NHANES II audiometry data were used to confirm a previously observed link between blood lead (PbB) level and hearing threshold. Other indicators of neurological development, such as age at which a child first sat up, walked, and spoke, and the presence of speech difficulties and hyperactivity were also examined to determine if they were significantly related to lead exposure. The probability of elevated hearing thresholds at 500, 1000, 2000 and 4000 Hz increased significantly (p less than .0001) with increasing PbB for both ears. PbB levels were also significantly related to delays in the age at which children first sat up, walked, and spoke and to the probability that a child was hyperactive. Lead was not related to the probability of a child having a previously diagnosed speech impairment.

We examined data recorded for 3,545 subjects aged 6-19 y who participated in the Hispanic Health and Nutrition Survey. We sought to confirm a relationship between blood lead levels and elevated hearing thresholds that we previously reported in a similar study in which data from the Second National Health and Nutrition Examination Survey was used. Lead was associated with an increased risk of hearing thresholds that were elevated above the standard reference level at all four frequencies (i.e., 500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz). Lead was also associated with hearing thresholds when they were treated as a continuous outcome. The relationships appeared to continue at blood lead levels less than 10 micrograms/dl. An increase in blood lead, from 6 micrograms/dl to 18 micrograms/dl, was associated with a 2-dB loss in hearing at all frequencies, and an additional 15% of children had hearing thresholds that were below the standard at 2,000 Hz.