Silver Nanoparticles in Sewage Sludge Found to Disrupt Ecosystems

Washington, DC–(ENEWSPF)–March 5, 2013. Low concentrations of silver nanoparticles can cause significant disruptions to natural ecosystems, find scientists at Duke University. This research, published in the journal PLOS ONE, provides a “real-world” look at the effects of this increasingly ubiquitous material in our environment.

Although nanotechnology may have great potential to provide critical breakthroughs in medicine and electronics, one specific material, silver nanoparticles or nanosilver, is particularly suspect in terms of human and environmental health due to its antimicrobial properties and a lack of thorough testing. Nanosilver is found in a wide range of consumer products, including sun screen, children’s toys and pacifiers, toothpaste, and disinfectants. After the material is used, it often makes its way down our drains and into our wastewater treatment plants. Because of the material’s small size, treatment plants are unable to filter out the nanosilver. This causes them to be concentrated in the wastewater treatment plant’s sewage sludge, which is subsequently dried and marketed as a fertilizer under the innocuous label “biosolids.” Sewage sludge represents the primary pathway for nanosilver’s entry into our environment, as an estimated 60% of the average 5.6 million tons of biosolids produced each year in the U.S. are land applied.  While nanosilver is rapidly added to consumer goods and processed into sewage sludge, the emerging science surrounding this substance reinforces the need for a precautionary approach with stringent government regulation and oversight.

In order to get an idea of the real-world effects of nanosilver, the researchers created a number of mesocosms -small structures containing various plants and microorganisms intended to mimic the natural environment. Sewage sludge was then applied to the mesocosms in varying concentrations and compared after 50 days. Notably, the researchers included a positive control by creating a mesocosm with high levels of silver nitrate. Their expectations were that lower levels of nanosilver would not cause the same adverse effects as the high levels of silver nitrate. However, the scientists found a number of negative effects that were as large or larger than the effects of silver nitrate. Both microorganisms and plants were affected by the presence of low levels of nanosilver. One of the plants studied, a common grass known as Microstegium vimeneum, produced 32% less biomass in nanosilver treated mesocosms compared to the control. While both M. vimineum and another plant, Lobelia cardinalis, concentrated the nanosilver in their tissue, only M. vimineum showed reduced growth, indicating that the effects of nanosilver may vary from plant to plant.

Microorganism communities were significantly disturbed by the nanosilver treatment. Researchers observed changes in their abundance, function, and community composition. Enzymes that indicate a microbial community’s ability to decompose organic matter, and are also associated with a microbes’ ability to handle external stress showed marked decreases which fell in accord with the loss of overall microbial biomass. Along with the 35% drop in biomass was a decline in microbial diversity which occurred on the first day after the nanosilver application. This indicates that nanosilver may cause acute non-target effects on microbial communities, which jeopardizes an important aspect of maintaining healthy soil.

“Our results show that silver nanoparticles in the biosolids, added at concentrations that would be expected, caused ecosystem-level impacts,” notes lead author Benjamin Colman, Ph.D. “Specifically, the nanoparticles led to an increase in nitrous oxide fluxes, changes in microbial community composition, biomass, and extracellular enzyme activity, as well as species-specific effects on the above-ground vegetation.”

The scientists’ note that their next step is to look at the longer term effects of silver nanoparticles, and to examine another increasingly common nanoparticle, titanium dioxide.

This study comes on the heels of a Dutch study published early last month which revealed the harmful effects of silver imbued sewage sludge on earthworm health. With growing evidence that sewage sludge containing nanosilver damages soil and ecosystem health. Beyond Pesticides urges consumers to contact their representatives about this issue demand they tell the U.S. Environmental Protection Agency to regulate these substances.

Currently, the chemical testing methodologies for nanotechnology are outdated, manufacturers do not fully disclose the nanoparticles that are incorporated in their products, and there is a critical lack of governmental oversight and regulation. As there are no requirements for labeling nanoparticles in the U.S., consumers are largely in the dark. Many of the products containing nanomaterials on the market now are for skin care and cosmetics, but nanomaterials are also increasingly being used in products ranging from medical therapies to food additives to electronics. In 2009, developers generated $1 billion from the sale of nanomaterials, and the market for products that rely on these materials is expected to grow to $3 trillion by 2015.

USDA organic certified products are the last refuge for consumers wanting to avoid nanomaterials. The National Organic Standards Board imposed a general ban over nanotechnology in its fall 2010 meeting, although USDA’s National Organic Program has never initiated rulemaking on the subject. Overall, little is being done to review, regulate, or safety test nanotechnology that is currently being used in conventional agriculture and food processing, ingredients and packaging. Avoid biosolids that are marketed as “organic” fertilizers, as they can contain ecosystem damaging nanosilver.

Speakers at the 31st Annual Pesticide Forum will address the wide range of regulatory failures perpetuated by our current system of government oversight. Join us in Albuqueque, New Mexico from April 5-6 for a discussion on the alternatives already present and strategies we all can take to promote a future with Sustainable Families, Farms and Food.

Sources:  Duke University, Futurity,