In order for toxic substances like heavy metals to cause effects in organisms, they must be bioavailable.[7] For organisms residing in contaminated sediments, the contaminants are most bioavailable when dissolved in the pore water, as opposed to being precipitated as a solid or sorbed to a sediment particle.[8] Metals in the solid metal-sulfide form are thus considered non-bioavailable, and are unlikely to cause toxicity in sediment-dwelling organisms.