 Thus, sediments with the same quantity of metals in them may have vastly different toxic effects, depending on the quantity of sulfide available to bind with them and render them non-bioavailable.For this reason, the SEM-AVS approach was developed to account for differences in sulfide and refine methods for predicting heavy metal toxicity in sediments.Because sulfide is quickly degraded in the presence of oxygen, sediment samples for SEM/AVS analysis must be kept under rigorously anoxic conditions from the moment they are sampled.