[Pharmwaste] FW: [Sludge] Study: Impact of Silver Nanoparticle Effects at ThresholdLevels

Sue Dayton sdayton at swcp.com
Fri Feb 5 13:02:35 EST 2010

Posted on our sludge listserve....


Sue Dayton

Blue Ridge Environmental Defense League

North Carolina Healthy Communities Program


Saxapahaw, NC 27340

(336) 525-2003

sdayton at swcp.com




Our lives begin to end the day we become silent about things that matter.
-  Martin Luther King Jr.





From: sludge-bounces at lists.ibiblio.org
[mailto:sludge-bounces at lists.ibiblio.org] On Behalf Of Jeffrey G. White
Sent: Friday, February 05, 2010 10:52 AM
To: Sludge
Subject: [Sludge] Study: Impact of Silver Nanoparticle Effects at


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Impact of Silver Nanoparticle Effects at Threshold Levels

Silver nanoparticles (AgNPs) are a frequently used nanomaterial with a wide
range of industrial and consumer applications, including fiber coating,
detergents, and hydrogels and plastics to prevent bacterial and fungal
growth. Nanoparticles released from various nanotechnology-enhanced consumer
products will inevitably enter our sewers and wastewater treatment plants
(WWTPs). What effects, if any, they have on treatment processes is the
subject of an ongoing WERF research project, Impact of Silver Nanoparticles
on Wastewater Treatment (U3R07).

Researchers from the University of Missouri are evaluating how silver
nanoparticles will affect bacterial growth during wastewater treatment. The
team, led by Dr. Zhiqiang Hu, assistant professor of civil and environmental
engineering, has set up several lab-scale wastewater treatment modular units
using activated sludge processes designed to remove organic matter and
nutrients in wastewater. After a prolonged period of operation (>300 days),
the researchers took the activated sludge samples for nanotoxicity testing.

Results to date demonstrate that nitrifying bacteria are especially
susceptible to inhibition by silver nanoparticles. Researchers found that at
a concentration of 0.4 mg/L total Ag, a mixture of positively charged silver
ions and AgNPs inhibited the growth of nitrifying bacteria by 11.5 percent.
In an experiment on shock loading of 100% AgNPs (lasting for 12 hours),
researchers detected a peak concentration of 0.75 mg/L total Ag in the
activated sludge basin, and about 50% nitrifying bacterial growth inhibition
(or nitrification inhibition) accompanied with a slight accumulation of
nitrite concentration in wastewater effluent was observed.

The results suggest the accumulation of silver could have a detrimental
effect on wastewater treatment, if the concentration reaches threshold
levels. Preliminary results from parallel studies of anaerobic digestion, a
commonly used solid stabilization process in wastewater treatment plants,
indicate that AgNPs at concentrations of 19 mg/L (19,000 ppb) or above in
biomass started to inhibit anaerobic microbial activities. Because most of
the silver particles are in the activated sludge or biosolids, the
researchers will continue to examine the impact of these nanoparticles on
anaerobic digestion.

The U.S. Environmental Protection Agency has instituted a secondary drinking
water standard for silver of 100 ppb. Though typical silver effluent
concentrations from sewage plants are low (at ppb levels or below),
increased use of nanosilver products poses new threats to sensitive water
bodies. U.S. EPA has set water quality criteria values for silver in salt
and fresh water at 1.9 and 3.2 ppb, respectively. The research team will
provide a summary that identifies threshold levels of silver nanoparticles
in various treatment processes. Awareness of these threshold levels will
directly benefit wastewater treatment operators and state regulatory
officials in making informed decisions with regard to silver nanoparticles
in wastewater treatment plants.

Look for the final published report Impact of Silver Nanoparticles on
Wastewater Treatment (U3R07) in May 2010.

February 4, 2010

Jeffrey G. White, Ph.D.
Associate Professor
Dept. of Soil Science
3207 Williams Hall
North Carolina State University
Campus Box 7619
Raleigh, NC  27695-7619
Tel: 919-515-2389 Fax: 919-515-2167
email: jeff_white at ncsu.edu
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