Biosolids and other organic residuals contain traces of chemicals and organic materials, sometimes called “microconstituents.” Water that enters wastewater recycling facilities, from which biosolids are derived, may contain many natural and synthetic chemicals, some of which are toxic in high enough concentrations. These chemicals come from natural sources – households, businesses, and street drains.
There has been growing concern about the potential impacts of traces of synthetic chemicals in the environment. This has been driven by the ability of scientists to measure smaller and smaller amounts (parts per billion, parts per trillion, etc.) Wherever scientists have looked, in surface waters, in soils, in mammals, and even in the arctic, they have found traces of microconstituents. These traces get into the environment directly from homes and businesses and daily activities.
Are traces of synthetic chemicals in biosolids a concern for the environment?
There have been no significant detrimental effects shown from normal biosolids applications to soils in full-scale, field studies using biosolids. Human exposures and human health risks from microconstituents in biosolids and other residuals are likely lower than the much higher levels experienced in daily use of these chemicals. The fact is, not many people are directly exposed to biosolids. On the other hand, many of the trace chemicals people mention in biosolids are in regular use in homes and businesses; that is where human exposure occurs.
The potential risks from microconstituents in biosolids to soil and other environmental receptors continues to be studied, current research indicates potential risks to be very low.
It is worth noting that soils, biosolids and the treatments biosolids go through are effective at reducing concentrations of most microconstituents. Biosolids recycling to soils can be a solution in dealing with such chemicals, helping remove them from aquatic systems and destroying or sequestering them.