Heavy Metals (Trace Elements) in Biosolids & Other Organic Residuals
Biosolids are mostly made up of natural, common, essential elements, which is why they are an excellent "multi-vitamin" fertilizer.
"What about the heavy metals?" is one of the most common questions people ask when they hear about use of biosolids as soil amendments and fertilizers. This was once a concern in the 1960s and 1970s when industrial pollutants were discharged to wastewater treatment facilities without consideration and the resulting sewage sludges were used on farms. Some farm fields built up high levels of cadmium, lead, mercury, and other elements.
But all that has changed. Since the 1980s, there have been increasingly stringent requirements on what can be discharged to sewers. Society has scrutinized the substances and products it uses. Many elements (e.g. lead) and chemicals (e.g. dioxins) have been banned or restricted. Today, industrial pretreatment is required and pollution prevention is a way of life. Today's wastewater contains lower amounts of potentially harmful pollutants, the potential impacts of pollutants are better understood, and the biosolids resulting from wastewater treatment contain minimal traces (parts per million or less) of contaminants of concern. Biosolids are now one of the most scrutinized substances on the planet, and research and risk assessments have led to regulations that make biosolids safe. Those who manage biosolids today are bemused with the "heavy metals question," because that question has long been answered.
In 2015, NEBRA completed a review of literature on metals in biosolids, other soil amendments, fertilizers, and soils. The report is available below, along with a large spreadsheet that shows actual averages and ranges of concentrations in various materials, for comparison.
See:
Metals in Biosolids, Other Soil Amendments, & Fertilizers (NEBRA, August 2015)
Spreadsheet Table Comparing Metals in Biosolids, Soil Amendments, & Fertilizers (NEBRA, August 2015)
Video: Rufus Chaney, PhD, U.S. Dept. of Agriculture presents the science on metals (trace elements) in biosolids, July 27, 2012
Leading research scientists continue to discuss this topic....
“There is simply no information which shows that, after long term use of biosolids as a fertilizer, foods grown on the amended soil would comprise risk to highly exposed individuals based on the home garden model (which gives much more potential for exposure than the general agricultural market model).”