No solid evidence that biosolids are safe to disperse

September 7, 2011

Originally posted at The Chronicle Herald on August 27, 2011.
By Murray McBride

As a soil chemist with many years of experience in conducting research on the behaviour of pollutants in soils, I am compelled to take issue with some of the assertions made by proponents of sewage sludge (biosolids) application to farms in the Aug. 4 article by Aaron Beswick.

While it is true that Nova Scotia has relatively strict guidelines for those contaminants that are regulated in the province, the regulations cover only toxic metals and a few pathogens, providing no regulations or guidelines for the large group of biologically active and potentially toxic organic chemicals (including, but by no means restricted to, dioxins, PAHs, pharmaceuticals, plasticizers, antimicrobial agents, and brominated fire retardants).

All of these chemicals, and many more, are present in sludges generated by sewage treatment plants, as demonstrated, for example, by the U.S. EPA 2009 Targeted National Sewage Sludge Survey. The contaminants of concern in sludges are a moving target, and regulations have not adjusted to this fact.

Many of the contaminants of most concern today were not present (or known to be present) in sludges at the time the rules were developed. The recent discovery of nanoparticles (such as nanosilver), a new class of toxins, in some sludges is one example. The reality is that regulations focused on a handful of toxic metals are today very badly out of date.

Specifically, the persistent organic pollutants (POPs) are conspicuous by their absence from the Nova Scotia guidelines. But the statement by Gordon Price, chairman of innovative waste management research for the Nova Scotia Agricultural College, about organic compound breakdown in soils implies that we need not be concerned about the accumulation of any synthetic organic chemicals in soils because the microbes will break them down quickly.

This may be the case for many contaminants, but is certainly not true for the POPs (including the brominated fire retardants) which accumulate in agricultural soils more or less in proportion to the cumulative sludge loading rate. In cases where surface application on pastures without incorporation is done, there is a danger of contaminating the human food chain via grazing livestock.

Even when we consider the large group of organic chemicals referred to as personal care products (PCPs) and pharmaceuticals, which are present in all municipal sludges, research has now shown that their breakdown in the soil may not be rapid enough to prevent their transfer into food crops or into drainage water and runoff.

It is claimed by Dr. Price that there are 50 years of scientific research to support the practice of farm application of sewage sludge products. This claim creates the false impression that there is presently a good understanding of the behaviour and toxicity of the many chemicals presently found in sludges.

In actual fact, very few of the contaminants in sludges have been studied in detail to determine their fate in soils and their tendency to transfer into surface and drainage water, into crops, or into livestock.

Furthermore, for alkali-treated sludges such as N-Viro, there has been even less research done on the impacts of this highly alkaline material on soil fertility or the behaviour of metals and other contaminants in soils. However, the very high pH of this material (11-12) actually renders some contaminant metals more soluble and available for plant uptake and leaching.

The claim is commonly made by promoters of sludge application on farms that there haven’t been any observed problems or toxic effects observed after decades of application, and therefore these chemicals cannot be doing any harm. This argument is disingenuous and self-serving. I would challenge anyone promoting land application as a sustainable practice to explain how they would be made aware of harm if it were occurring to humans from toxic chemicals in sludge applied to land; any effects of carcinogenic or endocrine-disrupting chemicals will not be immediately obvious, and in any event there is no regular monitoring of health effects in farming areas where sludges are being applied.

In fact, in my experience, those individuals who have reported that their soils and livestock were harmed by sludge, or have claimed to be harmed personally by direct exposure to sludges and sludge aerosols, have had regulatory agency officials quickly dismiss their claims as not credible.

In conclusion, I disagree with environmental consultant Lise Leblanc’s statement that anti-sludge activists such as Dr. Marilyn Cameron are “fear-mongering” by making public the evidence for a multitude of synthetic chemicals in sludge products, chemicals whose behaviour in the environment and combined toxicity to animals and humans is largely unknown. In the face of this high level of uncertainty, it is only prudent to avoid applying sludge materials to farmland on which we grow our food.

Dr. Murray McBride is professor of soil chemistry, and director, Cornell Waste Management Institute.

Filed under: Sewage Sludge

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