Subchronic Sodium Chlorate Exposure in Drinking Water Results in a Concentration-Dependent Increase in Rat Thyroid Follicular Cell Hyperplasia

Abstract

Chlorine dioxide (ClO 2 ) is an effective drinking water disinfectant, but sodium chlorate (NaClO 3 ) has been identi ed as a potentially harmful disinfection by-product . Studies were performed to describe the developmen t of thyroid lesions in animals exposed to NaClO 3 in the drinking water. Male and female F344 rats and B6C3F 1 mice were exposed to 0, 0.125, 0.25, 0.5, 1.0, or 2.0 g/L NaClO 3 for 21 days. Additional male F344 rats were exposed to 0, 0.001, 0.01, 0.1, 1.0, or 2.0 g/L NaClO 3 for 90 days. Female F344 rats were exposed to 0, 0.5, 1.0, 2.0, 4.0, or 6.0 g/L of NaClO 3 for 105 days. Thyroid tissues were processed by routine methods for light microscopi c examination, and follicular cell hyperplasia was diagnosed using a novel method. Thyroid hormone levels were altered signi cantly after 4 and 21 days. NaClO 3 treatment induced a concentration-dependen t increase in the incidence and severity of thyroid follicular cell hyperplasia. Male rats are more sensitive to the effects of NaClO 3 treatment than females. Follicular cell hyperplasi a was not present in male or female B6C3F 1 mice. These data can be used to estimate the human health risk that would be associated with using ClO 2 , rather than chlorine, to disinfect drinking water.

Toxicity Profiles in Rats Treated with Tumorigenic and Nontumorigenic Triazole Conazole Fungicides: Propiconazole, Triadimefon, and Myclobutanil

“…The lesion scores were: 0 -no lesion present, 1 -centrilobular hypertrophy, 2 -centrilobular and midzonal hypertrophy, 3 -pan lobular hypertrophy, 4 -pan lobular hypertrophy with cytoplasmic vacuolation. The thyroid gland was scored for colloid depletion, follicular cell hypertrophy, and/or follicular cell hyperplasia as previously described (Hooth et al, 2001;Khan et al, 2005).…”

Risks for public health related to the presence of chlorate in food

“…Sodium chlorate treatment induced a statistically significant increase in the incidence and severity of thyroid follicular cell hyperplasia and colloid depletion at doses ≥ 2 000 mg/L. Follicular cell hypertrophy was observed at doses ≥ 2 000 mg/L, but the increase was statistically significant at the highest dose only (Hooth et al, 2001 . Each drinking water sample was completed with sodium chloride to reach the same sodium concentration in each group (48 mM).…”

“…per day) dissolved in deionized water for 105 days. There were no effects on thyroid histology, but no other details were reported (Hooth et al, 2001 (Hooth et al, 2001). …”

“…Significant colloid depletion was diagnosed in most treated animals but the incidences were similar in all groups. Follicular cell hypertrophy was present in most animals, but the incidence did not increase in a concentration manner (Hooth et al, 2001). …”

Detailed Review Paper on Amphibian Metamorphosis Assay for the Detection of Thyroid Active Substances

“…Distinct histopathology is also associated with goiter, including a thickened capsule wall, shrinking of capillaries, fusion of the follicles, increased follicular size, and infiltration of connective tissue (partitions) entering the lobe from the capsule (Wollman, 1980). A possible framework for of analysis for thyroid histopathology is given in Hooth et al (2001). The histological techniques are relatively simple, using thin sections of the thyroid gland and standard light microscopy of hemotoxylin/eosin stained tissue.…”