Industries are required to remove toxic metals from the wastewater prior to discharging wastewater into sanitary sewers (see
Pretreatment Program). Since the adoption of the Pretreatment Program in the early 1980's industries within the City of Appleton have stepped up to meet regulatory compliance requirements. Furthermore, outreach, education, and awareness efforts have advanced the commitment by industry, commercial, and residential users to seek out environmentally responsible or friendly alternatives to "hazardous" or "toxic" products whenever possible. This commitment has translated into a biosolids product that consistently meets state and federal standards for metals concentrations.
It is important to remember that not all metals are "toxic" or "hazardous". Toxic elements found in the environment like arsenic, cadmium, mercury, and lead are generally the result of undesirable or unintentional anthropogenic activities (e.g. mining, coal burning, combustion engines, and dumping). When found in excessive quantities or elevated concentrations these elements are unsafe to human or environmental health. However, others like copper, iron, manganese, and zinc are naturally occurring elements found in the environment and necessary for the growth of plants, animals, and humans. These elements are unsafe in large quantities, and the City's biosolids concentrations are well below those concentrations.