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Health surveillance data

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Administrative data

Endpoint:
health surveillance data
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Data source

Reference
Reference Type:
publication
Title:
Ethylene thiourea: thyroid function in two groups of exposed workers.
Author:
Smith D.
Year:
1984
Bibliographic source:
Br. J. Ind. Med. 41: 362-366

Materials and methods

Study type:
health record from industry
Endpoint addressed:
repeated dose toxicity: inhalation
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Heath records of workers which have been exposed to ETU (ethylenethiourea) dust in 2 factories.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Other name : Ethylenethiourea (ETU)
ETU is produced by reacting ethylene diamine with carbon disulphide in a closed reactor. This is followed by various processes to produce a dust suppressed powder that is bagged off under local exhaust ventilation.

Method

Type of population:
occupational
Details on study design:
Workers have been exposed to ethylenethiourea dust in 2 factories.
All the exposed workers at both factories agreed to take part in the survey. They were all male with an age range of 26 to 62 at factory 1 and 28 to 56 at factory 2.
Control populations were obtained from volunteer male workers on processes not involving ETU or related to compounds at factory 1, and from other male chop floor workers and management at factory 2. As some contamination of factory 2 with ETU powder was suspected originally, male controls from two metal working factories in the same area were also obtained. Controls were matched for age and ethnic origin.
In each subject a clinical history was taken and a medical examination performed. Blood was colIected by venepuncture and taken to the laboratory the same day. All groups were dosed for T4.

Results and discussion

Results:
Over a period of 3 years, five workers involved in mixing ETU (ethylenethiourea) into monomer rubber showed decreased serum concentrations (by approximately 23%) of T4: 80.5 nmol/l vs 105.7 nmol/l  in control group. One had an increased concentration of thyroid-stimulating hormone on two occasions [about 10-fold], but he was found to have premyxoedema.

Any other information on results incl. tables

Table 1 : Comparison of T4 results groups

Group

No. Of observations

Geometric mean (nmol/l)

Mean (on log10 scale)

Variance

Mixers

22

80.5

1.906

0.0117

Process workers

23

96.4

1.984

0.0200

Controls

40

105.7

2.024

0.0054

Table 2 : test statistic and p values for difference between group means

Contrast

v

Degrees of freedom

Variance estimates ratio

p

Controls : process workers

1.26

40.23

0.16

>0.10

Controls : mixers

4.57

40.22

0.61

<0.01

Process workers : mixers

2.08

23.22

0.25

>0.05

Applicant's summary and conclusion

Conclusions:
There is no evidence that thyroid function is severely affected by exposure to ETU at the levels experienced by these workers, nor was there any clinical evidence of any effect. Only one worker was considered to be hypothyroid on biological testing.
Executive summary:

In 1984, Smith performed a cross-sectional study of workers at one ETU production plant and at one rubber production factory in the United Kingdom. The value of this study is somewhat limited because of the small number of workers and the intermittent nature of the working with rubber in 1980 and 1981 (due to economic recession). At the ETU production factory, ETU levels of up to 330 mg/m3 were found in personal air samples; the environmental monitoring levels were in the range of 10 to 240 mg/m3. The average length of exposure of these workers was ten years with a range

of five to twenty years. At the mixing factory, levels between 120 and 160 mg/m3 were recorded on personal samplers. The studied population was made up entirely of males, ranging in age from 26 to 62 years at the production factory (N = 23) and 28 to 56 years at the mixing factory (N = 22). A control group (N = 40) matched in age and ethnic origin was also obtained. This group contained other production workers and managerial staff. The thyroid function of each worker was determined by measuring the T4, TSH and thyroid binding globulin (TBG) in serum. The geometric means of T4 levels were 80.5 nmol/l for mixers, 96.4 nmol/l for process workers and 105.7 nmol/l for controls (normal reference range is 65 to 155 nmol/l according to Mos90). No exposed workers or controls had a history of thyroid illness or of taking thyroid medication, and no clinical symptoms of thyroid disease were found. The concentrations of T4 from the mixers were clearly lower than those from the control group. The difference between the

controls and the process workers was slight, and was entirely due to one individual having a particularly low level. The difference between the mixers and the process workers lay on the borderline of statistical significance. The TSH levels were within normal limits in all the controls and process workers (range 2.1 to 5.4 nmol/l). In one mixer the levels on two occasions were extremely high (21.8 nmol/l and 17.0 nmol/l); he was investigated further and was found to have premyxoedema. The TBG levels and the T4/TBG ratios did not differ among the groups and were within normal limits.