Thiourea

Thiourea was first used medicinally in the 1940s as an antithyroid drug (before being replaced by propylthiouracil) to treat hyperthyroidism [1]. Industrial uses developed in parallel: thiourea is used in photography as a toning agent, in textile processing as a reducing agent for disulfide bonds in wool, as a chemical intermediate in pharmaceutical synthesis, and as a component of some fire-resistant impregnation treatments [2]. It is also found as a natural metabolite in the human body and as a natural compound in some plant-derived foods (brassica family vegetables — thiourea is related to the naturally occurring goitrogens glucosinolates) [1].

Occupational exposure occurs in photographic chemical production and use, textile processing facilities, and chemical synthesis [1]. Environmental contamination from manufacturing facilities [2]. Dietary exposure from brassica vegetables containing related thiocompounds is background and at physiological levels [1].

Thiourea competitively inhibits thyroid peroxidase (TPO), reducing iodination of thyroglobulin and thereby reducing T3 and T4 synthesis [1]. Chronic TPO inhibition leads to elevated TSH (thyroid-stimulating hormone), which acts as a trophic factor promoting thyroid follicular cell proliferation — ultimately causing thyroid adenomas and carcinomas through indirect (non-genotoxic) hormonal stimulation [2]. EPA classifies thiourea as a Group B2 probable carcinogen based on thyroid tumors in rodents [1]. It also causes hemolytic anemia at higher doses [2].

Photography chemical workers, textile processing workers, chemical synthesis workers [1]. People with iodine deficiency are more susceptible to thiourea's thyroid-disrupting effects [2].

1. Occupational workers should use fume hoods and gloves when handling thiourea [1]. 2. Ensure adequate iodine intake if working with thiourea [2]. 3. Monitor thyroid function (TSH, free T4) for workers with regular thiourea exposure [1].