They can be when they are converted into nitrosamines, which appears to happen in the absence of plants. In the presence of phytonutrients, nitrates are converted to nitrites, which have several health benefits. In the absence of phytonutrients, nitrates can be converted into nitrosamines, which are a potent carcinogen.

See: https://nutritionfacts.org/topics/nitrates/

Thanks. I'm looking at the articles in these replies. I see that maybe I should be taking Vitamin C and E to help balance things.