Ben Horenstein 

Tri-TAC Chair 

East Bay Municipal Utility District 

375 – 11th Street, MS702 

Oakland, CA 94607 

(510) 287-1846 

bhorenst@ebmud.com

June 28, 2010 

Office of Pesticide Programs (OPP) 

Regulatory Public Docket (7502P) 

U.S. Environmental Protection Agency (U.S. EPA) 

1200 Pennsylvania Ave., NW. 

Washington, DC 20460–0001 

RE: Nanosilver Antimicrobial Pesticide Products; Registration Application 

(Docket Number EPA–HQ–OPP–2010-0325) 

The purpose of this letter is to comment on the application to register nanosilver as 

an antimicrobial and preservative additive. We are pleased to have the opportunity 

to provide U.S. EPA information from our experience and scientific literature, with 

the goal of helping U.S. EPA ensure the environmental risk assessments for 

nanosilver are complete and accurate and informing U.S EPA’s risk management 

decision. Our comments focus specifically on the environmental risks of silver 

discharges to publicly-owned wastewater treatment plants (POTWs). 

Tri-TAC is a technical advisory committee representing the League of California 

Cities, California Association of Sanitation Agencies, and California Water

Environment Association. We seek to improve the effectiveness and accountability 

of environmental programs that affect publicly owned treatment works in California 

by working with regulatory agencies and interest groups on treatment plant-related 

issues. 

Tri-TAC members are very concerned about the water quality impacts from the 

discharge of silver and nanosilver in particular into our municipal wastewater 

systems. These concerns have been expressed in our previous letters to U.S. EPA 

and in letters from our colleagues at the Bay Area Clean Water Agencies (BACWA) 

and the National Association of Clean Water Agencies (NACWA). We appreciated 

U.S. EPA’s decision to regulate silver ion-generating products like the Samsung 

“Silver Wash” washing machine. This decision recognized our concerns about the 

potential water quality impacts of residential pesticide uses—and affirmed U.S. 

EPA’s responsibility to regulate releases of pesticidal silver into the environment. 

Tri-TAC’s Interest in Silver-Based Pesticides 

Silver is highly toxic to aquatic life at low concentrations, is persistent, and can 

bioaccumulate in some aquatic organisms, such as clams. Due to concerns about 

Vice Chair 

Natalie Sierra

San Francisco Public 

Utilities Commission 

1145 Market Street, 5th Floor 

San Francisco, CA 94103 

(415) 934-5772 

nsierra@sfwater.org

Water Committee 

Co-Chairs 

Gail Chesler 

Central Contra Costa 

Sanitation District 

5019 Imhoff Place 

Martinez, CA 94553 

(925) 229-7294

gchesler@ccentralsan.org

Lorien Fono 

Carollo Engineers 

2700 Ygnacio Valley Road, 

Suite 300 

Walnut Creek, CA 94598 

(925) 932-1710

lfono@carollo.com

Air Committee 

Chair 

Jay Witherspoon

CH2M Hill 

155 Grand Avenue, 

Suite 1000 

Oakland, CA 94612 

(510) 251-2888 

jay.witherspoon@ch2m.com

Land Committee 

Co-Chairs 

Greg Baatrup 

Fairfield-Suisun Sewer 

District 

1010 Chadbourne Road 

Fairfield, CA 94534 

(707) 428-9162 

gbaatrup@fssd.com

Matt Bao 

Los Angeles County 

 Sanitation Districts 

1955 Workman Mill Road 

Whittier, CA 90601 

(562) 699-7411 ext. 2809 

mbao@lacsd.org
Docket No. EPA–HQ–OPP–2010-0325 

June 28, 2010 

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A technical advisory committee on POTW regulatory and policy issues

bioaccumulation and the placing of strict silver effluent limits in discharge permits, 

POTWs have implemented pollution prevention programs to identify and reduce 

silver discharges to sanitary sewer systems. These programs have been very 

successful in reducing POTW influent and effluent silver concentrations. These 

programs have also reduced silver concentrations in biosolids (sewage sludge), 

ensuring that silver will not limit options for biosolids reuse. 

As discussed at length in the enclosed BACWA letter, the enclosed report by the 

Woodrow Wilson International Center for Scholars (Luoma 2008), and in enclosed 

scientific papers, ordinary use of silver-containing pesticides releases silver to 

municipal wastewater treatment systems. Widespread use of household products 

that release silver particles into sanitary sewer systems could increase silver 

concentrations in POTW influents, effluents, and biosolids. If silver pesticide 

product use becomes common, wastewater silver discharges could reach levels not 

seen in the last two decades—and could have adverse impacts on our wastewater 

treatment process as well as on the quality of our effluent and biosolids. 

POTWs are subject to National Pollutant Discharge Elimination System (NPDES) 

permits under the Clean Water Act. These permits include toxicity limits and may 

also include quantitative effluent limitations for silver. Exceeding these limitations 

has serious consequences, including monetary fines and penalties and the risk of 

citizen lawsuits. Under California law, our members are liable for daily Mandatory 

Minimum Penalties should violations of their discharge permits occur. 

Nanosilver and POTWs 

Available scientific information indicates that it will be important for the POTW 

discharge assessment to include a special assessment of the wastewater 

discharges from nanosilver products. Silver particle size and form (e.g., zeolite) 

may significantly alter the way silver-containing products affect POTWs. For 

example: 

• The quantity and/or nature of silver discharged to POTWs may be affected 

by the small particle size and large surface area of nanosilver products as 

compared to other silver biocides. For example, Benn and Westerhoff 

(2008) found that for certain products, silver losses during washing were so 

large that most of the silver in these products would be washed into the 

municipal wastewater system during the products’ lifetimes. (A copy of this 

paper is enclosed.) Where small particles occur in products, the entire 

particle could be washed down the drain. 

• Nanosilver particle may have extraordinary effects on POTW treatment 

processes. In two related studies, Choi and Hu (2008) and Choi et al. (2008) 

found that silver particles less than 5 nanometers in diameter are uniquely 

toxic to nitrifying bacteria, which are critical to biological nutrient removal at 

POTWs. (Copies of both papers are enclosed). 
Docket No. EPA–HQ–OPP–2010-0325 

June 28, 2010 

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A technical advisory committee on POTW regulatory and policy issues

• Differing removal efficiencies. POTWs tend to be most efficient at removing 

larger particles from wastewater. Tiny particles and zeolites may have 

different potential to pass through POTWs than other forms of silver. 

• Particle size is known to modify silver’s aquatic toxicity. For example, see 

Griffitt et al. 2008, enclosed. 

Widespread Use of Silver-Based Pesticides Is Not Sustainable 

It is distressing to POTWs to observe the increasing prevalence of household 

products that use silver and other toxic chemicals for general antimicrobial 

purposes. POTWs are proud of our history of taking effective actions that reduce 

discharges of toxic pollutants to the environment. While POTWs have the authority 

to regulate industrial and commercial sources of silver and other toxic pollutants, we

have little or no control over the discharge of pollutants from the thousands of 

households we serve. Silver is a toxic metal that cannot degrade in the environment 

and is registered for use as a pesticide in numerous products. To allow the 

unrestricted usage of products that intentionally release silver into the environment 

would be an irresponsible neglect of the principles of environmental sustainability 

that should strongly influence U.S. EPA’s decisions. 

Thank you for your consideration of our comments on the application to register 

nanosilver as an antimicrobial and preservative additive. If you have any questions, 

please contact Gail Chesler, at (925) 229-7294 or chesler.gail@gmail.com. 

Sincerely, 

Ben Horenstein 

Tri-TAC Chair 

Enclosures:

1. Pla, M. Bay Area Clean Water Agencies (2009). Comment letter – petition 

for Rulemaking Requesting U.S. EPA Regulate Nanoscale Silver Products 

as Pesticides. Letter to Nathanael R. Martin, U.S. EPA. March 19. 

2. Luoma, S. N. (2008). Silver Nanotechnologies and the Environment: Old 

Problems or New Challenges? Woodrow Wilson International Center for 

Scholars, Project on Emerging Nanotechnologies. Publication PEN 15. 

September.

3. Benn, T. M. and P. Westerhoff (2008). "Nanoparticle silver released into 

water from commercially available sock fabrics." Environmental Science & 

Technology 42(11): 4133-9 (published correction is included). 

4. Blaser, S. A., M. Scheringer, et al. (2008). “Estimation of cumulative aquatic 

exposure and risk due to silver: Contribution of nano-functionalized plastics 

and textiles.” Science of the Total Environment 390 (2-3): 396-409. 
Docket No. EPA–HQ–OPP–2010-0325 

June 28, 2010 

Page 4 

5. Choi, O. and Z. Hu (2008). "Size dependent and reactive oxygen species 

related nanosilver toxicity to nitrifying bacteria." Environmental Science & 

Technology 42(12): 4583-8. 

6. Choi, O., K. K. Deng, et al. (2008). “The inhibitory effects of silver 

nanoparticles, silver ions, and silver chloride colloids on microbial growth.” 

Water Research 42: 2066-2074. 

7. Griffitt, R. J., J. Luo, et al. (2008). "Effects of particle composition and 

species on toxicity of metallic nanomaterials in aquatic organisms." 

Environmental Toxicology & Chemistry 27(9): 1972-8. 

8. Pesticide Transport to POTWs – conceptual model diagram and diagram of 

examples of direct and indirect pathways between pesticide uses and 

POTWs 

Note: Enclosures 3 through 7 are copyrighted materials that cannot be posted in 

the public docket. These have been submitted via email to Heather Garvie. We 

request that U.S. EPA provide these materials to all staff that are reviewing these 

comments. 

cc: Steve Owens, Assistant Administrator, Office of Preventing, Pesticides, and Toxic Substances 

Steven Bradbury, Acting Director, U.S. EPA Office of Pesticide Programs 

William R. Diamond, Director, Field and External Affairs Division 

Jack Housenger, Director, Biological and Economic Analysis Division 

Lois Rossi, Director, Registration Division 

Joan Harrigan-Farrelly, Director, Antimicrobials Division 

Betty Shackleford, Associate Director, Antimicrobials Division 

Norm Cook, Branch Chief, Antimicrobials Division 

Demson Fuller, U.S. EPA Office of Pesticide Programs 

Peter Silva, Assistant Administrator, U.S. EPA Office of Water 

Ephraim King, Director, U.S. EPA Office of Water, Office of Science and Technology

James A. Hanlon, Director, U.S. EPA Office of Water, Office of Wastewater Management 

Jared Blumenfeld, Administrator, U.S. EPA Region 9 

Alexis Strauss, Director, Water Division, U.S. EPA Region 9 

Patti TenBrook, Life Scientist, U.S. EPA Region 9 

Syed Ali, California State Water Resources Control Board 

Nan Singhasemanon, California Department of Pesticide Regulation

Jeff Wong, Chief Scientist, California Department of Toxic Substances Control 

Kelly D. Moran, Urban Pesticides Pollution Prevention Project 

Chris Hornback, Senior Director, Regulatory Affairs, National Association of Clean Water Agencies 

Preeti Ghuman, Los Angeles County Sanitation District 

Gail Chesler, Central Contra Costa Sanitary District 

Lorien Fono, Carollo Engineers 

 

A technical advisory committee on POTW regulatory and policy issues