There are a number of bioassay tools and techniques available. They study LC50, LD 50 (for 24, 48, 96, ....hours). We also do EC studies. I think, mother Nature can provide some hidden physical clues showing toxic effects of toxicants. Different organisms show some defensive or biochemical struggling signals in the form of secretions that can be detected through chemosensing. If we detect the early warning signals by reading the physical or catching the chemical clues mitigation or removal of toxicants could be done  in due time.