Toxicology and carcinogenesis studies of malachite green chloride and leucomalachite green. (CAS NOS. 569-64-2 and 129-73-7) in F344/N rats and B6C3F1 mice (feed studies).

Background: Malachite green chloride is a dye used to prevent fungus infections in commercial fisheries. Leucomalachite green is formed from malachite green and remains in the tissues of exposed fish. We studied the effects of malachite green on female rats and female mice, and the effects of leucomalachite green on male and female rats and female mice, to identify potential toxic or cancer-related hazards to humans.

Methods: For each study we mixed the dye into the feed of rats and mice. The doses of malachite green chloride given were 100, 300, or 600 parts per million (ppm) for female rats and 100, 225, or 450 ppm for female mice. Doses of leucomalachite green were 91, 272, or 543 ppm for male and female rats and 91, 204, or 408 ppm for female mice. There were 48 animals in each dose group. Control animals received the same feed with no chemical added. The study lasted for two years. Tissues from more than 40 sites were examined for every animal.

Results: Rats, but not mice, exposed to malachite green chloride or leucomalachite green weighed less on average than the control animals. In rats exposed to the dyes, there were very slight increases in a few types of tumors: cancers of the thyroid gland, liver, and mammary gland in females exposed to malachite green chloride; of the thyroid gland and testes in males exposed to leucomalachite green; and of the thyroid gland and liver of females exposed to leucomalachite green. We saw no increase in cancers in female mice given malachite green chloride, but there was an increase in liver tumors in female mice given to leucomalachite green.

Conclusions: We conclude that tumors of the thyroid gland, liver, or mammary gland in female rats might have been caused by malachite green chloride, but the malachite green chloride did not cause cancer in female mice. We conclude that leucomalachite green might have caused cancers of the thyroid gland in male and female rats, and of the testes in male rats and liver in female rats. Leucomalachite green caused an increase in cancer of the liver in female mice.