Heavy Metals (Trace Elements) in Biosolids & Other Organic Residuals
"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.