Few infections are toxic. I might worry if I saw something powdery and fuzzy growing all over the sides and lid of the FV. Particularly if greenish black or blackish green.
But as mentioned, just give the stuff between the top and bottom a taste and see if you like it. Infections usually range from a mildly pleasing sour taste to downright nasty. But not a killer. Perhaps maybe a trip to the commode with the runs/squirts at the worst.