There were a bunch of things I noticed during my time at this company which were traits of a toxic work environment and tend to take a toll on the mental health of the employee:
1. The management team are very biased and generally tend to speak very rudely; yelling and being abusive is a part of the routine.
2. One of the co-founders does not think it beneath him to hit under the belt and bring personal matters into a conversation if he thinks it will help his case (which is highly unprofessionally and not expected from anyone in a company let alone the founder).
3. There is a lot of politics and biases which are part of your everyday work environment at this company so I'd suggest you be careful who you talk to and how.
4. There is no value of employees and they are looked at as disposable tissues that can be taken in and thrown out in moment's notice (not what you'd expect from a startup their size and funds you know?)
5. The word of 2-3 people in the company is taken above actual performance and work ethic, so be careful as to who's wrong side you get on. It could cost you your job and definitely your sanity while you stick around.
6. Just an overall place where people in higher roles do not know how to speak to subordinates or understand where to draw the line. I have previous experience working for startups and have never had voices been raised or inappropriate words been thrown around casually(being abusive isn't how companies function in 2019)