Microconstituents /Trace Chemicals
Biosolids and other organic residuals contain traces of chemicals, sometimes called "microconstituents." Wastewater, 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.
Since 2000, 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, in the arctic – they have found traces. 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?
NEBRA has long tracked this issue, to continually improve our understanding of the biosolids and residuals products we manage. So far, researchers have found some impacts of certain trace chemicals - pharmaceuticals, for example – to aquatic organisms living downstream of wastewater treatment facilities.
But there have been no significant detrimental effects shown from normal biosolids applications to soils in full-scale, field studies using actual biosolids. This is likely due to the fact that healthy soils are biologically active media that break down and/or sequester trace synthetic chemicals, reducing the potential exposure of biological organisms.
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 biota and other environmental receptors have not been studied as much, but also appear to be low. And it makes sense for research to continue.
In the meantime, 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, as noted in this 2014 presentation, which provides advice on what biosolids managers can do to mitigate potential concerns, even as scientific understanding continues to improve.
McCarthy and Loyo-Rozales, 2015: Risks Associated with Application ofMunicipal Biosolids to Agricultural Lands in a Canadian Context – Literature Review. The most comprehensive literature review to date regarding trace organic chemicals and pathogens in biosolids.
Biosolids and Soil: Remarkable Media for Managing Trace Organic Chemicals of Potential Concern, slides from a webinar presented by Ned Beecher for the NEWEA Microconstituents Committee, March 24, 2016
- How Likely is Your Exposure to MCs Via Biosolids? A Risk Analysis Brochure from NW Biosolids, 2016. Download from here (scroll down the page).
Organic Contaminants in Biosolids - video - Dr. George O'Connor (Univ. of Florida)
PPCPs in Wastewater & Biosolids, in the New York Water Environment Association journal Clearwaters, Fall 2008.
WEF Technical Practice Updates (look for "Microconstituents" section)
The NEBRA office has additional information, references, and referrals.