UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM: 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

August 7, 2013 

SUBJECT: Review of MRID 49190801 "The Quantification and Characterization of Silver 

Released from Textiles Treated with NSPW-L30SS: As a Result of Simulated 

Laundering Conditions", Study Number 110112.0001 Revision 2, 04-30-2013 

PC Code: 072599 DP Barcode: 413873 

Decision No.: 418580 Registration No.: 84610-E 

Petition No.: NA Regulatory Action: Product Registration - Section 3 

Risk Assess Type: NA Case No.: 5042 

TXRNo.:NA CASNo.:NA 

MRID No.: 49019201, 49045301, 40 CFR: NA 

49190801 

FROM: Timothy Dole, CIH, Industrial Hygienist 0\ � � � ])-� 

Risk Assessment and Science Support Branch , . . / 

Antimicrobials Division (7510P) 

THRU: Timothy Leighton, Senior Scientist c:;:;r;

 ""

 .. .._ __ 

Steve Weiss, Chief 

Risk Assessment and Science Support Branch 

Antimicrobials Division (7 51 OP) 

TO: Jed Costanza Ph.D., Environmental Protection Specialist 

Regulatory Management Branch I 

Antimicrobials Division (751 OP) 

Attached is a review of MRID 49190801. This study is the second revision of the original 

studies (MRIDs 49019201 and 49045301) which were revised to correct typographical errors and 

clarify the procedures used for sample preparation and analysis. In addition, the two reports 

(MRIDs 49019201 and 49045301) were combined into one report (MRID 49190801). 

Page 1 of 13 
1.0 Introduction 

This study was submitted by NanoSilva, LLC in support of the textile use for their proposed 

product NanoSilva NSPW-L30SS. This product is proposed for use as a preservative in 

synthetic textiles such as polyester. It will be applied as a master batch marketed under the brand 

name Polyguard. A master batch is a plastic pellet formulation that is added to the plastic 

polymer mixture prior to the production of fibers. The proposed application rate in the final 

treated article is 10 to 30 ppm silver. The study consisted of a washing machine test where 

fabric samples were washed in a simulated washer according to the ISO test method for 

colorfastness. The washing fluid consisted of tap water and detergent to simulate laundering 

conditions that result in down the drain environmental exposures and artificial saliva to simulate 

saliva contact exposures that occur when toddlers suck or mouth treated textiles. 

2.0 Materials Tested 

This study was conducted with polyethylene terephthalate (PET) fabric samples that had 

been manufactured to nominally contain 36 ppm silver. This concentration was obtained by 

using a PET polymer extrusion mix which contained 85 percent untreated PET and 15 percent 

master batch. The master batch contained 98 percent untreated PET and 2 percent Nanosilva 

NSPW-L30 which contains 1.19 percent silver (all percentages are by weight). The analytical 

concentration (listed as the theoretical concentration in the report) was 26.2 ppm based on 

previous analysis of the silver content and recovery rate of 95.1 percent for NSPW-L30SS and 

77.4 percent for the master batch. 

The treated fabric samples were taken from extra-large black knit sport shirts. Control 

samples were taken from a two meter long piece of untreated white fabric composed of 100% 

PET. The fabric samples used for the laundering test were cut to 10 x 20 em and were not 

hemmed. These samples had an average weight of2.75 grams (n=3). The fabric samples for 

the saliva test were cut slightly larger (1 0 x 22 em) and they were hemmed to minimize the 

fraying that was observed during the laundering test. These samples had an average weight of 

3.73 grams (n=3). 

3.0 Testing Methods 

The test method was modeled after the ISO 1 05-C06 test method "Colour fastness to 

domestic and commercial laundering" that was used in Geranio et al. (2009) and Lorenz et al. 

(2012). The ISO test method uses steel balls in a simulated washing machine. The ISO method 

was modified for this study to include the use of plastic balls instead of steel balls to eliminate 

the possibility of silver contamination from the steel balls. Also the fabric samples were 

doubled in size to 8 x 20 em and the amount of washing solution was correspondingly increased 

to 150 ml. 

The washing solution for the laundering test consisted of 4 grams per liter of ECE detergent 

in distilled water at pH 10.6. The solution was added to one of three separate stainless steel 

containers and preheated to 40 degrees C. After preheating, one treated textile sample was added 

to each container and washed for 45 minutes at 40 degrees C. The sample was then removed 

Page 2 of 13 
from the container and wrung out by hand into the container and then the contents of the 

contai.tier were poured into an HDPE bottle. The sample, still wet, was placed into a new 

stainless steel container and rinsed with 20 ml of water for 5 minutes using the washing machine. 

This rinse cycle was repeated using a new stainless steel container and the two collected rinsing 

solutions were combined and placed into an HDPE bottle. The samples were then dried and 

placed into plastic bags for analysis. 

The washing solution for the saliva test consisted of simulated saliva that contained a mixture 

of sodium, potassium and amonium salts, potassium thiocyanate, urea, sodium sulfate 

decahydrate, calcium chloride decahydrate, potassium phosphate and sodium bicarbonate. The 

samples were washed in the same manner as the laundering test samples; however, the samples 

were not rinsed after washing and the process was repeated three times for a total of nine 

samples. 

4.0 Sample Preparation Methods 

Wash and Rinse Solutions 

The wash solution samples were filtered using separate 0.45 micron 50 mm diameter filters 

for each sample. The filter membranes were then cut into 3 x 3 mm pieces and were weighed out 

into microwave vessels and digested with 3ml HN03 in a CEM digester. After digestion, the 

sample was diluted to 10 ml with deionized water. 

The filtrate from the wash solution sample was collected, placed into a sealed test tube and 

labeled for direct analysis. 

Textiles 

The textile was cut into 3 x 3 mm pieces (100 to 150 mg) and weighed out into a microwave 

vessel and digested with 3 ml HN03 in a CEM digester. After digestion the control samples 

were diluted to 10 ml and the treated samples were diluted to 25 ml. 

5.0 Sample Analysis 

The samples were analyzed with Inductively Coupled Plasma -Mass Spectrometry (ICPMS). The instrument was calibrated with standards containing 10, 20, 50, 100 and 200 ppb 

silver in 2 percent nitric acid. The resulting calibration line had a correlation coefficient of 

greater than 0.995. 

The limit of quantitation LOQ was reported to be 0.094 ppb for filtrates (i.e. liquids) and 9.4 

ppb for the textiles and filters (i.e. solids). As discussed in Appendix A; however, the Agency 

evaluated the study data and determined that the actual LODs are 10 ppb for filtrates and 1,000 

ppb for solids. 

Page 3 of 13 
6.0 Quality Control 

Quality control (QC) blank samples included the following: 

• One untreated polyester fabric sample used for washing in detergent. 

• Three untreated polyester fabric samples used for washing in saliva. 

• One filtrate each from untreated textile wash and rinse solutions, 

• One filter/residue sample each from untreated textile wash and rinse solutions 

• Three filtrates each from untreated textile saliva solutions, 

• Three filter/residue samples from untreated textile saliva solutions. 

No silver was detected in any of these samples. 

QC samples included initial calibration verification solutions (ICV) and continuing 

calibration verification (CCV) solutions of 100 ppb, a filter spiked with 5000 ppb silver nitrate, 

untreated fabric spiked with a solution of 10 ppm silver nitrate and blank solution spiked with 

5000 ppb silver nitrate. The results of the ICV and CCV samples indicated an average recovery 

of 97.6 ppb (n=14) with a standard deviation of 3.0 ppb. Additional information regarding the 

ICV and CCV samples is included in Appendix A. The results of the spike samples are included 

in Table 1. 

Table 1 - Quality Control Spiked Samples 

Sample Type Sample ID * Flask# Measured Expected 

(ppb) (ppb) 

Silver nitrate solution spike onto fabric Textile Spike SM 3889-3 9,600 10,000 

Silver nitrate solution spike onto fabric Textile Spike SM 3889-4 9,800 10,000 

Blank solution spiked with silver nitrate - 9a SM 3389-2 4,877 5,000 

before filtration 

Blank solution spiked with silver nitrate - 9b SM 3889-1 4,885 5,000 

after filtration 

*The results of the above samples are hsted on pages 116 to 118 of the study report. 

7.0 Results 

Silver Content of Textiles 

The silver content of the textiles was analyzed in duplicate for each sample before and after 

washing. A listing of the results is included in Table 2 for the samples washed in detergent and 

in Table 3 for the samples washed in saliva. 

The silver concentration in the textiles prior to washing in detergent ranged from 23,637 to 

24,931 ppb with a mean of 24,198 ppb (i.e. 24.2 ppm) which was similar to what was expected 

(26.2 ppm) given the application rate and recovery rates observed in previous studies. The 

average concentration of silver in the textile after washing ranged from 21,594 ppb to 24,047 ppb 

with a mean of 23,182 ppb (23.1 ppm). The change in the silver content of the textile samples 

ranged from a loss of 0.61% to a loss of -8.6% with a mean loss of 4.3%. The study author 

noted that some of this loss might have been due to fiber release from the edges of the samples 

which were not hemmed. 

Page 4 of 13 
The silver concentration in the textiles prior to washing in saliva ranged from 24,072 to 

26,109 ppb with a mean of 25,413 ppb (i.e. 25.4 ppm). The average concentration of silver in 

the textile after washing ranged from 24,065 ppb to 26,742 ppb with a mean of 25,314 ppb (25.3 

ppm). The change in the silver content of the textile samples ranged from a loss of 6.8 % to a 

gain of 5.9% with a mean of -0.34%. These samples were hemmed. 

Silver Content of the Laundering Solution and Rinse Water 

The results for the filter and filtrate samples of the wash water are given in Table 4 and they 

indicate that 1.6 percent of the silver in the textile was released. All of the results were less than 

the LODs and values of one half the LOD were used in accordance with OPP Policy (US EPA, 

2000) to calculate the amount of silver released. 

Silver Content of Saliva Wash Solution 

The results for the filter and filtrate samples of the saliva are given in Table 5 and they 

indicate that 0.9 percent of the silver was released. All of the results were less than the LODs 

and one half the LOD was used in the calculations. 

8.0 Conclusions 

The study indicates that 1.6 percent of the silver in NanoSilva treated polyester fabric is 

released during washing in detergent and 0.9 percent of the silver is released during washing in 

simulated saliva. The study is acceptable and can be ).lsed for risk assessment. 

References 

Geranio, 2009. The Behavior of SilverNanoparticles during Washing. Geranio, L., Heuberger, 

M., Nowack, B., Environmental Science and Technology 43:8113-8118, September, 2009. 

Lorenz, C., Windler, L., von Goetz, N. et al. 2012. Characterization of silver release from 

commercially available functional (nano) textiles. Chemosphere 89:817-824. 

US EPA, 2000. Assigning Values to Nondetected!Non- Quantified Pesticide Residues in Human 

Health Food Exposure Assessments, Office of Pesticide Programs, U.S. Environmental 

Protection Agency, March 23, 2000 

Page 5 of 13 
Table 2- Silver Content of Textile Samples Washed in Detergent 

Change in Silver 

Before Washin2 (Addendum 4) After Washing (Addendum 6) Content 

Sample ID Sampl Flask# Silver in Textile Silver in Sampl Flask# Silver in Textile Silver in ugH Percentc 

e# (uglkg) Textile (ug)A e# (uglkg) Textile (ugt 

3092012-Al I M0544-l 24,199 66.6 2 M3889-35 24,197 66.5 

Duplicate M0544-2 23,851 65.6 M3889-36 23,614 64.9 

Average 24,025 66.1 23,906 65.7 0.40 -0.61 

3092012-A2 2 M0544-7 24,158 66.4 3 M3889-37 23,793 65.4 

Duplicate M0544-8 25,703 70.7 M3889-38 24,301 66.8 

Average 24,931 68.6 24,047 66.1 2.5 -3.6 

3092012-A3 3 M0544-13 24,076 66.2 4 M3889-40 21,594 

Duplicate M0544-14 23,198 63.8 N/A 

Average 23,637 65.0 21,594 59.4 5.6 -8.6 

Average (n=3) 24,198 66.6 23,182 63.7 2.8 -4.3 

A. Silver in textile (ug) =Silver in Textile (uglkg) *weight of textile (2.75 gm)* 0.001 gm!kg 

B. Silver Released (ug) =Silver in textile before washing (ug)-Silver in textile after washing (ug) 

C. Silver Released (percent)= [Silver released (ug) I Silver in textile before washing (ug)] * 100 

Page 6 of 13 
Table 3- Silver Content of Textile Samples Washed in Saliva Solution 

Before Washine (Addendum 7) After Washine (Addendum 9) 

Sampl Flask# 

e# 

Textile ID 

3092012-A1-1 1 M2422-1 

Duplicate M2422-2 

Average 

3092012-A1-2 2 M2422-3 

Duplicate M2422-4 

Average 

3092012-A1-3 3 M2422-5 

Duplicate M2422-6 

Average 

3092012-A2-1 4 M2422-7 

Duplicate M2422-8 

Average 

3092012-A2-2 5 M2422-9 

Duplicate M2422-10 

Average 

30920 12-A2-3 6 M2422-11 

Duplicate M2422-12 

Average 

3092012-A3-l 7 M2422-13 

Duplicate M2422-14 

Average 

3092012-A3-2 8 M2422-15 

Duplicate M2422-16 

Average 

3092012-A3-3 9 M2422-17 

Duplicate M2422-18 

Average 

Average (n=9) 

Silver in 

Textile 

(ug/kg) 

25,232 

25,372 

25,302 

26,831 

26,262 

26,547 

26,207 

25,371 

25,789 

23,178 

24,967 

24,073 

25,289 

26,781 

26,035 

25,776 

23,106 

24,441 

26,897 

25,322 

26,110 

26,278 

23,628 

26,391 

24,862 

26,504 

25,683 

25,597_± 850 

Silver in 

TextileA (ug) 

94.1 

94.6 

94.4 

100.1 

98.0 

99.0 

97.8 

94.6 

97.1 

86.5 

93.1 

89.8 

94.3 

99.9 

97.1 

96.1 

86.2 

91.2 

100.3 

94.4 

97.4 

98.0 

88.1 

93.1 

92.7 

98.9 

94.1 

94.8 + 3.1 

Sampl Flask# 

e# 

4 Mag 7 

MagS 

5 Mag 9 

Mag 10 

6 Mag 11 

Mag 12 

7 Mag 13 

Mag 14 

8 Mag 15 

Mag 16 

9 Mag 17 

Mag 18 

10 Mag 19 

Mag 20 

11 Mag 21 

Mag 22 

12 Mag 23 

Mag 24 

A. Silver in textile (ug) =Silver in Textile (ug/kg) *weight of textile (3.73 gm)* 0.001 gmlkg 

Silver in 

Textile (ug/kg) 

25,116 

23,014 

24,065 

24,834 

26,327 

25,581 

25,325 

23,198 

24,262 

24,293 

26,204 

25,249 

26,984 

26,499 

26,742 

23,758 

24,840 

24,299 

25,351 

23,715 

24,533 

26,563 

26,373 

26,468 

26,415 

26,841 

26,628 

25,314 + 1,090 

B. Silver Released (ug) = Silver in textile before washing (ug)-Silver in textile after washing (ug) 

C. Silver Released (percent)= [Silver released (ug) I Silver in textile before washing (ug)] * 100 

Page 7 of 13 

Silver in 

Textile (ug) 

93.7 

85.8 

89.8 

92.6 

98.2 

95.4 

94.5 

86.5 

90.5 

90.6 

97.7 

94.2 

100.7 

98.8 

99.7 

88.6 

92.7 

90.6 

94.6 

88.5 

91.5 

99.1 

98.4 

98.6 

98.5 

100.1 

99.3 

94.4 + 4.0 

Change in Silver 

Content 

ugl:j Percentc 

-4.6 -4.9 

-3.6 -3.6 

-6.6 -6.8 

+4.4 +4.9 

+2.6 +2.7 

-0.6 -0.7 

-5.9 -6.1 

+5.5 +5.9 

+5.2 +5.5 

-0.4+ 4.9 -0.34 + 5.2 
Table 4- Amount of Silver Released following Washing in Detergent 

Silver in Textile Water (LOD = 10 uglliter) Filter/Residue (LOD = 1000 uwk�:) Silver Released 

Sample I.D. Before WashingA Sample Flask# Silver Silve�·c Sample Flask# Silver Filter Silver"· u ugE Percenr 

# (\lgL

 (ug) # (uglkg) (gm) (ug) 

Wash Water (Addendum 5 

3092012-A1 66.1 ug 2a 3889-5 <LOD 0.75 2c M3889-7 <LOD 0.10 0.05 0.80 

3889-6 <LOD 0.75 M3889-8 <LOD 0.10 0.05 0.80 

3092012-A2 68.6 ug 3a 3889-9 <LOD 0.75 3c M3889-11 <LOD 0.10 0.05 0.80 

3889-10 <LOD 0.75 M3889-12 <LOD 0.10 0.05 0.80 

3092012-A3 65.0 ug 4a 3889-13 <LOD 0.75 4c M3889-15 <LOD 0.10 0.05 0.80 

3889-14 <LOD 0.75 M3889-16 <LOD 0.10 0.05 0.80 

Rinse Water (Addendum 5 

3092012-Al 66.1 ug 6a 3889-21 <LOD 0.20 6c M3889-23 <LOD 0.10 0.05 0.25 

3889-22 <LOD 0.20 M3889-24 <LOD 0.10 0.05 0.25 

3092012-A2 68.6 ug 7a 3889-25 <LOD 0.20 7c M3889-27 <LOD 0.10 0.05 0.25 

3889-26 <LOD 0.20 M3889-28 <LOD 0.10 0.05 0.25 

3092012-A3 65.0 ug 8a 3889-29 <LOD 0.20 8c M3889-31 <LOD 0.10 0.05 0.25 

3889-30 <LOD 0.20 M3889-32 <LOD 0.10 0.05 0.25 

Total Amount of Silver Measured in Wash and Rinse Water 

3092012-Al 1.05 1.6 

3092012-A2 1.05 1.5 

3092012-A3 1.05 1.6 

Average 1.6 

A. Average of two replicate analyses as listed in Table I of this review. 

B. Results were less than the LOD. Used LOD/2 for silver content calculations. 

C. Silver in Wash Water (ug) =Wash Water Silver (ug/liter) *Flask Volume (0.15 liter for wash water samples and 0.040 liter for rinse water samples) 

D. Silver in Filter/Residue (ug) =Silver in Filter/Residue (uglkg) *Filter Weight (gm) * 0.001 kg/gm 

E. Silver Released (ug) =Wash Water Silver (ug) +Filter/Residue Silver (ug) 

F. Percent Silver Released= Silver Released (ug) I Silver in Fabric Samples (ug). 

Page 8 of 13 
Table 5- Amount of Silver Released following Washing in Saliva 

Water (LOD = 10 uglliter Filter/Residue (LOD = 1000 ug/k2] Silver Released 

Silver in Textile Sample Flask# Silver Silve� Sample Flask# Silver Filter wt Silver'- ugu Percent"' 

Sam_Q_le I.D. Before WashingA # (ug/ liter) (ug) # (uglkg) (gm) (ug) 

Wash Water (Addendum 8) 

3092012-A1-1 94.4 ug 4a 1219-12 <LOD 4c Ml220-7 <LOD 0.130 0.065 

1219-16 <LOD Ml220-8 <LOD 0.122 0.061 

<LOD 0.75 <LOD 0.063 0.81 0.86 

30920 12-A 1-2 99.0 ug Sa 1219-17 <LOD Sc Ml220-9 <LOD 0.122 0.061 

1219-18 <LOD M1220-10 <LOD 0.109 0.055 

<LOD 0.75 <LOD 0.058 0.81 0.82 

3092012-Al -3 97.1 ug 6a 1219-21 <LOD 6c Ml220-l l <LOD 0.123 0.062 

1219-22 <LOD Ml220-12 <LOD 0.128 0.064 

<LOD 0.75 <LOD 0.063 0.81 0.83 

30920 12-A2-l 89.8 ug 7a 1219-25 <LOD 7c Ml220-13 <LOD 0.118 0.059 

1219-26 <LOD Ml220-14 <LOD 0.111 0.056 

<LOD 0.75 <LOD 0.058 0.81 0.90 

3092012-A2-2 97.1 ug 8a 1219-29 <LOD 8c Ml220-15 <LOD 0.115 0.058 

1219-30 <LOD Ml220-16 <LOD 0.113 0.057 

<LOD 0.75 <LOD 0.058 0.81 0.83 

3092012-A2-3 91.2 ug 9a 1219-33 <LOD 9c Ml220-17 <LOD 0.109 0.055 

1219-34 <LOD Ml220-18 <LOD 0.110 0.055 

<LOD 0.75 <LOD 0.055 0.81 0.89 

3092012-A3-1 97.4 ug lOa 1219-37 <LOD lOc Ml220-19 <LOD 0.112 0.056 

1219-38 <LOD Ml220-20 <LOD 0.111 0.056 

<LOD 0.75 <LOD 0.056 0.81 0.83 

3092012-A3-2 93.1 ug lla 1219-41 <LOD llc Ml220-21 <LOD 0.120 0.060 

1219-42 <LOD Ml220-22 <LOD 0.115 0.058 

<LOD 0.75 <LOD 0.059 0.81 0.87 

3092012-A3-3 94.1 ug 12a 1219-45 <LOD 12c Ml220-23 <LOD 0.117 0.059 

1219-46 <LOD Ml220-24 <LOD 0.118 0.059 

<LOD 0.75 <LOD 0.059 0.81 0.86 

Overall Mean ± SD {n=9) 0.81 0.85_±0.029 

A. Average of two replicate analyses as listed in Table 3 of th1s review. 

B. Silver in Wash Water (ug) =Wash Water Silver (ug/liter) *Flask Volume (150 ml) * 0.001liter/ml 

C. Silver in Filter/Residue (ug) =Silver in Filter/Residue (uglkg) *Filter Weight (gm) * 0.001 kg/gm 

D. Silver Released (ug) =Wash Water Silver (ug) +Filter/Residue Silver (ug) 

E. Percent Silver Released= Silver Released (ug) I Silver in Fabric Samples (ug). 

F. All results were less than the LOD. Used LOD/2 for silver content calculations. 

Page 9 of 13 
Appendix A- Calculation of the Detection Limit for the NanoSilva Study: The Quantification and 

Characterization of Silver Released from Textiles Treated with NSPW-L30SS as a Result of 

Simulated Laundering Conditions 

This appendix documents how the detection limit included in the Nanosilva study is not valid and 

calculates a recommended level of detection. These calculations are based on a review of the 

procedures detailed in the OPP Position Paper: Assigning Values to Non-Detected/Non- Quantified 

Pesticide Residues in Human Health Food Exposure Assessments (US EPA, 2000). 

1. MDL of0.0094 p.g/L is Not Valid 

In Section 8.1.2 of the Nanosilva Study, the method detection level (MDL) for silver is stated as 0.0094 

J.g/L for liquid samples and 0.94 J.g/kg for solid samples. As stated in Section 7.2.2 of the Nanosilva 

Study, the MDL represents the minimum concentration of silver that can be identified and reported with 

99% confidence that the silver concentration is greater than zero, which is consistent with the definition 

at 40 CFR 136. In Section 8.1.3 of the Nanosilva Study, it is stated that the limit of quantitation (LOQ) 

is 0.094 J.g/L for liquid samples and 9.4 J.g/kg for solid samples. The LOQ is defined in Section 7.2.3 as 

being I 0 times the MDL, which was previously communicated to Nanosilva in a phone call on January 

25, 2013. 

The MDL and LOQ described above differ from the detection limits described in the OPP position paper 

on assigning values to non-detected results for pesticide residues in human health food exposure 

assessments (US EPA, 2000). In this position paper, EPA introduced the term limit of detection (LOD) 

as: 

Limit of Detection (LOD) is defined as the lowest concentration that can be determined to be 

statistically different from a blank. This concentration is recommended to be three standard 

deviations above the measured average difference between the sample and blank signals which 

correponds to the 99% confidence level. 

This value is calculated based on the expected instrument response for calibration samples. The 

Inductively Coupled Plasma Mass Spectrometer (ICP-MS) responses to silver calibration samples 

analyzed on December 1, 2012 (page 59 of the Nanosilva Study) are shown in Table 1. 

Page 10 of 13 
Table 1- Estimated LOD and LOQ Based on Calibration Results from 1 2/01/ 201 2 

Concentration ICP-MS Response Expected (CPS- Expected CPS) (CPS- Expected CPS)"'2 

(Jlg/L) (CPS) CPS 

0 697.81 -99008.43 99706.24 9941334226.02 

10 354265.00 360540.16 -6275.16 39377663.10 

20 805784.43 820088.75 -14304.32 204613697.89 

50 2186578.84 2198734.53 -12155.69 147760813.94 

100 4352969.14 4496477.49 -143508.35 20594646764.41 

200 9168500.70 9091963.41 76537.29 5857956552.45 

Slope 45954.86 Sum 36785689718 

Intercept -99008.43 RMSE 110733 

Based on the OPP position paper, the LOD is determined from the root mean square error (RMSE) from 

the observed vs. expected ICP-MS response. The LOD is estimated as 3 times the R MSE or: 

3 X 110733 + 99008.43 

Liquid LOD = 45954.86 = 9.4Jlg/L 

The concentration of 9.4 J.lg/L is the lowest concentration of silver that can be determined to be 

statistically different from the sample that did not contain silver (i.e., 0 J.lg/L). The equivalent 

concentration for silver in a filter sample is: 

9.4 Jlg silver 10 mL L 1000 g 

Filter LOD (llgfkg) = - 940 Jlg/kg L water digest 1000 mL 0.1 g filter kg -

The OPP position paper also introduces the limit of quantitation (LOQ), which is defined as the level 

above, which quantitative results may be obtained. This is estimated as 10 times the RMSE or: 

10 X 110733 + 99008.43 

LOQ = 45954.86 = 26·2 Jlg/L 

According to the OPP position paper, these estimates for LOD and LOQ form the basis for determining 

the method detection limit and method quantitation limit which would involve analyzing seven samples 

containing silver at 9.4 or 26.2 J.lg/L, respectively. This step was not done for the Nanosilva Study 

because they established the MDL according to Consumer Product Safety Commission Method CPSCCH-£1002-08.1. In the CPSC method, the instrument detection limit (IDL) is first determined from the 

analysis of calibration samples that do not contain silver (i.e., calibration blank). From this analysis, an 

IDL of0.012 J.lg/L was reported (Table 8 of the Nanosilva Study). The IDL was validated by analyzing 

a sample with silver concentration of0.012 J.lg/L seven times with a reported a MDL of0.0094 !J.g/L. 

However, there was no comparison between the ICP-MS response for the 0.012 !J.g/L sample to the ICPMS response for the 10 silver calibration blanks. 

Table 2 contains the average and standard deviation for the ICP-MS response from 7 samples fortified 

with silver at 0.012 J.lg/L and the 10 calibration blank samples. This comparison shows that the ICP-MS 

Page 11 of 13 
response for samples containing 0.012 J.

g/L silver were not statistically different from the 10 calibration 

blank samples (students-t = 0.28). Therefore, these results canot be used to establish the LOD or LOQ 

based on the OPP position paper on assigning values to non-detected results for pesticide residues in 

human health food exposure assessments (US EPA, 2000). 

Table 2- ICP-MS Response for Silver Free and Silver Containing Samples 

Samples that do not contain ICP-MS Response Samples fortified ICP-MS Response 

silver (i.e., calibration blank) (CPS) with 0.012 p.g/L silver (CPS) 

Blank1 768.94 R-Blank1 720.03 

Blank2 727.26 R-Blank2 662.81 

Blank3 916.16 R-Blank3 621.14 

Blank4 773.92 R-Blank4 826.15 

BlankS 852.82 R-Blank5 858.93 

Blank6 763.92 R-Blank6 811.15 

Blank7 542.80 R-Blank7 823.37 

BlankS 415.01 

Blank9 396.13 

Blank10 616.69 

Average ± Sta ndard Deviation 677±178 761±92 

2. Determining the LOD 

To establish an LOD, Nanosilva should have analyzed a sample with silver concentration of 9.4 J.g/L at 

least seven times and reported the recovery of silver at this concentration. Since this step was not 

performed, EPA is establishing an LOD based on the seven calibration sample analysis results available 

in the Nanosilva Study. Determining the RMSE for the calibration sample analysis results reveals that 

the LOD ranges from 0.6 to 24.4 J.g/L (Table 3) where the average LOD is 10 J.g/L, which also is the 

lowest calibration sample concentration. 

Table 3 - LOD and LOQ Determined from Eight Calibration Results 

Date of Calibration Sample Analysis LOD Jtg/L) LOQ Jtg/L) 

12/112012 9.4 26.3 

11112/2012 0.6 4.8 

1116/2012 3.7 12.5 

11120/2012 3.3 12.6 

12/20/2013 11.6 32.5 

12/21/2012 24.4 65.9 

12/2112012 16.4 45.2 

Average (J.g/L) 10 29 

Concentration for solids samples (J.g/kg) 1000 2900 

Although no independent samples with concentration of 10 J.g/L were analyzed to validate the LOD of 

10 J.g/L, independently prepared calibration-check samples with concentration of 100 J.g/L were 

Page 12 of 13 
analyzed. Table 4 shows that the analysis of the I OO J.

g/L samples had recoveries between 93.6 and 

I 02. 7%, which are well within the goal of 70 to II 0% according to the OPP position paper. Based on 

the strength of the recovery for the I 00 J.g/L calibration check samples, EPA is setting the LOD as I 0 

J.g/L for liquid samples and I 000 J.g/kg for solids samples. In accordance with the OPP position paper, 

EPA will replace any silver concentration that is below I 0 J.g/L with the value of 5 J.g/L and any solids 

concentration of less than I 000 with the value of 500 J.g/kg. 

Table 4 - Analysis of Calibration Check Samples 

Date of Analysis Sample Name Concentration Recovery (%) 

(f.lg/L) 

I I /I2/20I2 CCV I 01.5 I 01.5 

I 11I2/20I2 rev I 02.7 I 02.7 

11120/20I2 CCVI I 00.7 I 00.7 

I I /20/20I2 CCV4 93.6 93.6 

11/20/20I2 CCV2 95.7 95.7 

I 2/ I8/20I2 rev 95.0 95.0 

I 2/I8/20I2 CCV 95.3 95.3 

I 2/I8/20I2 CCV2 93.9 93.9 

I 2/20/20I2 CCV2 I 00.4 I 00.4 

I 2/20/20I2 CCV3 99.4 99.4 

I 2/20/20I2 CCV4 98.9 98.9 

I 2/2I /20I2 rev 94.9 94.9 

I 2/21120I2 CCVI 97.7 97.7 

I 2/21120I2 CCV2 97. I 97. I 

Average ± standard deviation 97.6 ± 3.0 97.6 

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