Chromosome damage in peripheral lymphocytes from American thorium workers.

Abstract

An analysis of the frequency of chromosome aberrations in lymphocytes from 47 thorium workers and three external controls is presented. Thirty-seven of these cases were divided into three age-matched groups based upon the means of the sums of their emanating radium-224 and bismuth-212 (Ra + Bi) burdens. The low burden group (mean Ra + Bi burden = -0.06 +/- 0.03 nCi) had two two-break chromosome aberrations in 1200 cells, the moderate burden group (mean Ra + Bi burden = 0.21 +/- 0.03 nCi) had three such aberrations in 1000 cells and the high burden group (mean Ra + Bi burden = 0.99 +/- 0.21 nCi) had five such aberrations in 1500 cells. While there is a two-fold increase in the two-break aberration frequency in pooled data from the two higher exposure groups (8/2500 cells) as compared with the lowest exposure group (2/1200 cells), the difference between these subsamples is not statistically significant (p = 0.32). The frequency of dicentrics and centric ring chromosomes (8/3300 cells) in the pooled higher body burden groups from the total sample (mean Ra + Bi burden = 0.56 +/- 0.09 nCi) does however show a very highly significant increase over the historical control frequency. A similar analysis based on total months of employment in the thorium-processing industry did not show a positive relationship between duration of employment and aberration frequency. In broad outline, our results are compatible with those from similar studies on Brazilian thorium workers and Thorotrast patients.