Epidemiological data
Administrative data
- Study result type:
- experimental result
- Study period:
- No data
- Reliability:
- other: not applicable for non-standard epidemiological studies
Data source
Reference
- Reference Type:
- publication
- Title:
- Thyroid function of newborns and exposure to chlorine dioxide by-products
- Author:
- Ouhoummane, N.; Levallois, P. and Gingras, S.
- Year:
- 2004
- Bibliographic source:
- Activities of Environemntal Health, 559(11):582-587
Materials and methods
Test guideline
- Qualifier:
- no guideline available
- Principles of method if other than guideline:
- Thyroid function of newborns from 11 municipalities where drinking water was disinfected by chlorine dioxide with that of newborns from 15 municipalities using chlorine disinfection. Mean neonatal blood thyroid stimulating hormone (TSH) levels and proportion of congenital hypothyroidis cases susing the results of the Quebec neonatal screening for congenital hypothyroidism for 32,978 newborns over the period 1993 - 1999.
- GLP compliance:
- no data
Endpoint addressed
- Endpoint addressed:
- toxicity to reproduction / fertility
Test materials
- Identity of test material same as for substance defined in section 1 (if not read-across):
- yes
Test material identityopen allclose all
- Details on test material:
- No data
Method
Type of population
- Type of population:
- general
- Details on study design:
- Newborn thyroid function was assessed using the results of the provincial neonatal screening for congenital hypothyroidism. The newborn screening program was started in 1974 and covers 99% of births. It is based on the systematic measurement of blood TSH level. All blood analyses were carried out in a single laboratory, which had a very effective quality control and monitoring system. The validity of the program is shown by the sensitivity (97%) and specificity (96%) of the screening test. A double data entry system was used, as well as validation of the coherence of the data by programming and revision to compensate for missing data. All screening procedures and action criteria were similar during this period. The covariables in the screening database taken into account in the analysis were: age at screening, birth weight and sex.
- Details on exposure:
- Infants were grouped into two groups:
(a) The exposed group - Infants included those whose mothers resided in any of the 11 municipalities using ClO2 as a primary household water disinfectant, and were born between 1993 and 1999, in any of the above municipalities. For each municipality, the water treatment plant confirmed the use of a single disinfectant for the complete period under study (1993 - 1999).
(b) The reference group - Newborns whose mothers resided in any of 15 municipalities using Cl as a primary household water disinfectant and not using ClO2. The choice of the reference group was based on the municipalities' similarities to those using ClO2 to treat household water in the following variables: population size, annual birth rate and rate of employment. - Statistical methods:
- Data was analysed using SAS, version 8.2 (SAS Institute, Inc., Cary, NC). The distribution of variables for the newborns of the two groups were compared using a chi-square test for proportions and t test for means. Analysis of variance was used to compare arithmetic mean TSH concentrations at birth. These analyses were adjusted for potentially confounding variables in the screening database and stratified them by birth weight. Numbers of infants with elevated TSH levels in exposed and reference groups were compared using a chi-square test. We calculated and compared prevalence of the various types of congenital hypothyroidism (confirmed primary hypothyroidism and transitory hypothyroidism) using the Fisher exact test, using p < 0.05 to determine statistical significance.
Results and discussion
- Results:
- Sex ratio was similar in both groups, but low birth weight was slightly more frequent in the exposed group (p = 0.023) and the proportion of the births for which blood samples were taken between 0 and 1 day was slightly higher in the reference group.
- Confounding factors:
- No data
- Strengths and weaknesses:
- The main limitation of this study was the assessment of exposure, with little information on individual exposure such as level of water contamination and among of water consumed by mothers during pregnancy.
- Any other information on results incl. tables:
- Sex ratio was quite similar in both groups, but low birth weight (<2.5 kg) was slightly more frequent in the exposed group (p = 0.023), and the proportion of the births for which blood samples were taken between 0 and 1 day was slightly higher in the reference group (p < 0.0001). Adjusted mean TSH level was significantly higher in the exposed group (2.43 mU/L) than in the reference group (2.21 mU/L) (p = 0.048). Elevated TSH levels (>=15 mU/L) were quite rare (0.15%) and their occurrence was similar in the two groups (p = 0.32). For newborns with low birth rate, elevated TSH levels were found more frequently in the exposed group, but the difference was not statistically significant (p = 0.37) and the number of cases was very small (n = 4). Nine confirmed cases of hypothyroidism for the entire group of newborns was observed, with a prevalance of 3.9/10,000 for the exposed group and 1.7/10,000 for the reference group (p = 0.32). Two transitory cases of hypothyoidism in the exposed group were observed, with a prevalance of 1.3/10,000 (p = 0.22).
Applicant's summary and conclusion
- Conclusions:
- No evidence that ClO2 in drinking water suppressed thyroid function in newborns with normal weight. No statistical differences in TSH levels or prevalence of congenital hypothyroidism between exposed and reference groups. The results of the study raise the possibility of a subtle effect of ClO2 on low birth weight babies. Because of the sensitive nature of the fetus, the potential for adverse health effects of exposure to ClO2 merits further epidemiological research.
- Executive summary:
- In an epidemiological study, thyroid function of newborns from 11 municipalities where drinking water was disinfected by chlorine dioxide with that of newborns from 15 municipalities using chlorine disinfection, was assessed.Mean neonatal blood thyroid stimulating hormone (TSH) levels and proportion of congenital hypothyroidis cases used the results of the Quebec neonatal screening for congenital hypothyroidism for 32,978 newborns over the period 1993 - 1999.Infants were grouped into two groups: the exposed group, where infants included those whose mothers resided in any of the 11 municipalities using ClO2 as a primary household water disinfectant and the reference group where newborns whose mothers resided in any of 15 municipalities using Cl as a primary household water disinfectant and not using ClO2.Sex ratio was quite similar in both groups, but low birth weight (<2.5 kg) was slightly more frequent in the exposed group (p = 0.023), and the proportion of the births for which blood samples were taken between 0 and 1 day was slightly higher in the reference group (p < 0.0001). Adjusted mean TSH level was significantly higher in the exposed group (2.43 mU/L) than in the reference group (2.21 mU/L) (p = 0.048). Nine confirmed cases of hypothyroidism for the entire group of newborns was observed, with a prevalance of 3.9/10,000 for the exposed group and 1.7/10,000 for the reference group (p = 0.32). Two transitory cases of hypothyoidism in the exposed group were observed, with a prevalance of 1.3/10,000 (p = 0.22).No evidence that ClO2 in drinking water suppressed thyroid function in newborns with normal weight. No statistical differences in TSH levels or prevalence of congenital hypothyroidism between exposed and reference groups. The results of the study raise the possibility of a subtle effect of ClO2 on low birth weight babies. Because of the sensitive nature of the fetus, the potential for adverse health effects of exposure to ClO2 merits further epidemiological research.
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