EWG gives this a 10 on the toxicity scale as it is a mercury-based preservative. Might be a good idea to adjust toxicity ratings here as this looks pretty dangerous:
https://www.ewg.org/skindeep/ingredient/706528/THIMEROSAL/

FDA does not allow mercury in drugs or in cosmetics, except under very specific conditions where there are no other safe and effective preservatives available – conditions that these products do not meet. Check the label. If the words “mercurous chloride,” “calomel,” “mercuric,” “mercurio,” or “mercury” are listed on the label, you should stop using the product immediately.