Are there any food/drinks that, if consumed regularly over a long period of time, would have a permanent negative effect on the throat, and especially the singing voice?
Permanently? Not really; there's nothing that would be generally called "food" or "drink" that would immediately and permanently have a detrimental effect on your singing voice.
However, avoid cigarette smoking (really any type of smoking or tobacco use) and alcohol, as these can have a cumulative effect that builds up over time. If you stop now, before any change becomes noticeable, your body will heal. However, once the effects of these things reaches a critical mass, they will become permanent, and while they may improve, your career as a singer will likely be over.
I would also caution against regularly eating very spicy foods. The capsaicin will actually irritate and erode the mucous membranes of the mouth and throat, which in the extreme can cause permanent damage. They can also cause acid reflux which can damage the pharynx in other ways. I don't mean cut out spicy food entirely; I love jalapenos and chili and you probably couldn't get me to stop eating them entirely. Just cut back on the heat, and don't eat these things every day.