home edit2 whole TSD November 2002 PDF format - OEHHA

involved in 2,4,5-T production between 1951 and 1971. The authors determined each worker's vital
status through 1976, resulting in a median length of time since first exposure of about 20 years. Only
one malignancy (a respiratory cancer) was recorded vs. 3.6 expected from US population rates. This
cancer death occurred among the employees with 20 or more years of latency; in this group 0.9 deaths
were expected.
Besides the small sample size, there are other problems with using this study for risk assessment. The
exposure to TCDD may have been minimal. Environmental sampling of the breathing zone in 1969
revealed 2,4,5-T concentrations between 0.2 and 0.8 mg/m 3 . Product specifications at that time called
for a maximum TCDD concentration of 1 ppm. Assuming the maximum level of both 2,4,5-T in the
breathing zone, and TCDD in the 2,4,5-T, the concentration of TCDD in the breathing zone would have
been 10 -6 of the concentration of 2,4,5-T, or 0.8 ng/m 3 . Ott et al. also noted that 157 of the 204
workers (77%) were exposed for less than one year. Furthermore, a review of medical records of the
cohort uncovered no cases of chloracne.
A further analysis of Dow employees was presented by Bond et al. (1983), who reported a morbidity
survey on the combined cohorts previously described by Cook et al. (1980) and Ott et al. (1980).
Bond et al. found few differences between the morbidity of these workers and a matched control group
of workers from other locations in the plant. There were, however, more ulcers and diseases of the
digestive system (excluding liver) in the 2,4,5-T cohort, at roughly twice the prevalence in the controls.
However, because the investigators only studied cohort members who participated in company medical
programs between 1976 and 1978, only 69% of the original cohort was included. The study did not
include workers who had died, retired, or left the company, raising the possibility that the most affected
workers might have been missed.
Following the publication of the four US mortality studies, reports began to appear in Lancet of four
additional cases of STS among these cohorts, bringing the apparent total to seven (Honchar and
Halperin 1981, Cook 1981b, Moses and Selikoff 1981, Johnson et al. 1981). The proportion of
deaths in these merged cohorts due to STS appeared to be far greater than would be expected
(Fingerhut and Halperin 1983), although there is great difficulty in estimating expected rates of STS
using general population statistics (Cook and Cartmill 1984). Fingerhut (cited in VA 1984) had the
diagnoses of the seven cases reviewed by two pathologists. The pathologists could only agree on a
diagnosis of STS for three of the seven, another three being reclassified, and the last diagnosis being
disputed. Of the three definite cases, only two had frank chloracne to corroborate exposure. The VA
review (1984) concluded that the occurrence of even two cases of STS among these relatively small
cohorts warranted continued surveillance.
Other cohort studies of occupational exposures have come from Great Britain, West Germany, and the
Netherlands. May (1973 and 1982) only briefly described the aftermath of a 1968 accidental release of
TCP with a "higher than normal" concentration of TCDD. A total of 79 cases of chloracne were
recorded, but May did not specify how many workers were exposed, so that an attack rate cannot be
calculated. A survey of 46 of these workers, who were still with the company 10 years later, revealed
that roughly half still had some chloracne (May, 1982). There were no other clinical problems reported,
171