 Based on the chemical interactions between heavy metals (SEM) and acid-volatile sulfide (AVS), the concentrations of these two components can be used to assess the potential for toxicity to sediment-dwelling organisms.A number of heavy metals, such as cadmium and lead, are toxic to various forms of life, particularly when dissolved in water as metal ions.Toxic heavy metals are often present in surface water as a result of natural processes, such as the weathering of metal-containing rocks, or due to human activity, such as mining and smelting.