This is a question that we get every so often. There are warnings for TCA [tricyclic antidepressants such as Nortriptylinetm referred to as "TCA's" and also water safety], and have been for many years. The state of California [proposition 65]* has stated that it can cause cancer in humans if it is ingested in too high a percentage. There are studies to back this -- BUT -- they are ingesting it!
Luckily we never ingest TCA and we suggest that you never do either ... like they do with the rats in the study. Unfortunately you will find that just about any ingredient (including pure water) used/ingested in excess will cause death. This is true and exactly why all ingredients are tested and used in moderation to find their safe levels.
Do a bit of research on that and you will find what I am trying to explain here. Look at the studies for parabans... that is a great one. Parabens are used in microscopic levels...and truly nothing works better at such a small amount. Yet, with studies they are dosing parabens in more-than-several-lifetimes amounts .... and feeding that to a small rodent (not a human) to test that if we gorge ourselves with an ingredient meant to be used at .0001% then we will cause cancer. ... Well, I would think so. Misuse of an ingredient should not be a study.
Certainly, at the end of the day, you do not have to purchase TCA, but don't be so alarmed about all the "fear mongering" out there. It is in excess and you can probably find something on every ingredient out there - including essential oils. Read over this article as well: https://www.platinumskincare.com/blog/do-you-have-a-preservative-phobia/
*Proposition 65 requires California to publish a list of chemicals known to cause cancer, birth defects or other reproductive harm. This list, which must be updated at least once a year, has grown to include approximately 900 chemicals since it was first published in 1987.
The Office of Environmental Health Hazard Assessment (OEHHA) within the California Environmental Protection Agency is adding chloral (CAS No. 75-87-6), chloral hydrate (CAS No. 302-17-0), 1,1,1,2-tetrachloroethane (CAS No. 630-20-6), and trichloroacetic acid (CAS No. 76-03-9) to the list of chemicals known to the State of California to cause cancer for purposes of the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 651). The listing of these four chemicals is effective September 13, 2013.
TCA is in this list because it is ingested - not topically applied! TCA is one of the major by-products of the disinfection of water by chlorination. Concentrations measured in drinking water supplies in one study in the U.S. ranged from 4 to 103 mg/L, with a mean concentration of 38 mg/L, while another study reported quarterly median values of TCA ranging from 4.0 to 6.0 mg/L (Bull and Kopfler, 1991). IARC (1995) reported that TCA occurs in chlorinated drinking water at levels up to 200 mg/L.
No Significant Risk Level (NSRL): 9.9 micrograms per day (oral) https://oehha.ca.gov/proposition-65/chemicals/trichloroacetic-acid