Secondly, pest species have been exposed to natural toxins for a long time before the onset of human civilization.

Biotoxins - natural toxins produced by organisms, often for use as a defence mechanism.

These natural toxins are highly concentrated (approximately 1400 fold) in river foam.

A natural toxin from plants growing right in these woods.

One theory being explored is that the fish were killed by a toxin, either natural or man-made.

These natural toxins include some of the most poisonous compounds known.

Such plants have even higher levels of natural toxins.

Under certain conditions, some species of marine algae form blooms with can produce natural toxins.

Neither does cooking remove the natural toxins that can contaminate certain fish.

Modified plants may contain higher levels of natural toxins.