I used google to find the following. Bing, Yahoo, Ask yeilded similar results and any of those will let you see what follows the ....

Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...

Fumaric acid is an organic acid widely found in nature. In humans and other mammals, Fumaric acid is a key intermediate in the tricarboxylic acid cycle for ...

Tartaric acid is a white crystalline diprotic organic acid. It occurs naturally in many plants, particularly grapes, bananas, and tamarinds, and is one of the main ...

They are not dangerous and they are all naturally occurring.

Usually the citric acid and fumaric acid are used together in a specific ratio to get a certain sour profile. I believe tartaric acid is a byproduct of the wine making industry and gives a tart taste (hence, tartaric acid?). I believe it also helps prevent spoilage, to some degree.

On a side note, if you ever see some crystals on a wine cork after you open it up, those are tartaric acid salts. Cream of tartar is also a derivative.