Based on the extremely low Ksp values for heavy metal sulfides, if [SEM]/[AVS] is less than 1 ([SEM < [AVS]), then all the extractable metals in the sediment should be in their solid sulfide form and non-bioavailable; above this value, the pool of sulfide is "exhausted" and heavy metals are more likely to be present in the sediment pore water, their bioavailable form.[1] In theory, then, an [SEM]/[AVS] value of 1 represents a cutoff between a "no-effects" range and a "possible effects" range.