As municipal wastewater treatment facilities and systems have improved during the past 20 years and as trade waste discharge licences have become increasingly strict, pollutant concentrations in biosolids have decreased dramatically and are typically well below national and State and Territory Guidelines.
Many of the trace metals in biosolids, including cadmium, lead, copper and zinc, enter wastewater from industrial drains and metal pipes in homes and businesses. Some of these metals, known as micronutrients, are essential in small amounts for plant survival. Others such as cadmium (which is a common ingredient in toothpaste) are monitored very closely in biosolids to ensure they remain well below the Guideline values.
Organic compounds, including pesticides, polychlorinated biphenyls (PCBs) and dioxins, can be found in some biosolids in concentrations near the lowest detectable limits. Studies have found the risks associated with these to be negligible and as many of these compounds are no longer used by the community the risk is diminishing.
In Australia and New Zealand biosolids Guidelines developed or endorsed by State and Territory and national environmental and health-related departments define strict contaminant classifications for heavy metals to ensure sustainable, appropriate uses in Australia and New Zealand.