Chromosome damage in peripheral lymphocytes from American thorium workers.

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.