UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

December 13, 2012 

SUBJECT: Responses to the 60-Day Public Comments on the Product Chemistry, 

Environmental Fate, and Ecological Effects Scoping Document in Support of 

Registration Review of Poly(hexamethylene-biguanide) hydrochloride. 

FROM: 

THRU: 

TO: 

PC Code: 111801 DP Barcodes: 405762 

Decision Nos.: 459677 Registration Nos.: 

Petition No(s).: NA Regulatory Action: Response to 60-

Day Public Comments 

Risk Assessment Type: Single Case No.: 3122 

chemical 

TXRNo.:NA CAS No.: 32289-58-0/27083-27-8 

MRID Nos.: None 40 CFR: None 

Najm Shamim, Ph.D., Chemist ~i1a-_ a/~ F~ Srinivas Gowda, M.S. Microbiologist 1 

Pat Jennings, Environmental Engineer rl ~ \1\..--~ j r-· 

r -PDonna Randall, M.S., Senior Effects Scientist ~ (/l/ ~ 

Risk Assessment and Science Support Branch (RASSB) 

Antimicrobials Division (7 51 OP) 

Steven Weiss, Branch Chief ~ tt/~ Risk Assessment and Science Support Branch (RASSB) 

Antimicrobials Division (7510P) 

Rebecca von dem Hagen, Chemical Review Manager 

Regulatory Management Branch II 

Antimicrobials Division (751 OP) 

The Office of Pesticide Programs' Antimicrobial Division (AD) has reviewed the public 

comments received on the Poly(hexamethylenebiguanide) Registration Review, Case # 3122 

(Docket ID Number EPA- HQ- OPP- 2012- 0341). Comments were received from the Bay Area 

Clean Water Agencies (BACWA); the California Stormwater Quality Association (CASQA); the 

Tri-TAC (the Technical Advisory Committee for the CASQA, the California Water Environment 

Association and the League of California Cities); and the San Francisco Bay Water Quality 

1 
Control Board (SFBWQB). Common comments from multiple submitters were compiled and 

summarized rather than provided verbatim. 

1. Comment: (BACWA, CASQA, SFBWQB, Tri-TAC) The PHMB risk assessment should 

evaluate sewer and stormwater exposure pathways for the swimming pool use. 

Discharge from pools to surface water from storm drains is a major pathway in pesticiderelated TMDL. 

Agency's RespoJse: The Agency has not previously assessed the potential for 

environmental exposures from the discharge of treated swimming pool water. In most 

cases, pesticides used in pools for the purpose of disinfection are dissipated in the process 

of providing the Resticidal effect (e.g., chlorine-based treatments). However, for more 

persistent chemic~ls, such as PHMB, the Agency has determined that such an assessment 

should be included in the registration review assessment. A statement will be added to 

the FWP to clarify that the risk assessment will include evaluation of discharge from 

swimming pool use. 

2. Comment: (BACW A, CASQA, Tri-T AC) Enclosed informational materials that should 

assist EPA with development of a modeling scenario for swimming pools. 

Agency's Response: The information enclosed on swimming pools will be reviewed and 

used to inform decisions on development of a modeling scenario for swimming pools. 

3. Comment: (BACW A, CASQA, SFBWQB, Tri-T AC) Urban storm drainage conveyance 

systems also have distinct physical characteristics that rapidly convey water and 

pollutants from use sites to receiving waters. To correctly evaluate the environmental 

risks of PHMB released in swimming pool discharges, these discharges must be modeled 

as distinct events, rather than on the basis of long-term averages. 

Agency's Response: A scenario used to estimate environmental exposure concentrations 

from storm drain discharge will at a minimum consider peak exposure conditions. 

4. Comment: (BACWA, CASQA, SFBWQB, Tri-TAC) The PHMB risk assessment should 

evaluate storm water exposure pathways for leaching of PHMB from paints or coatings on 

exterior surface structures or facades. Submitted attachments providing results of 

laboratory and field studies on leaching of biocides from facades. 

Agency's Response: The Agency appreciates the information documenting that use sites 

like walls on the exteriors of building treated with paints containing biocides like 

titanium dioxide and nanosilver could contaminate the storm drains and wastewater 

streams. The Agency agrees that PHMB use in exterior architectural paints and coatings 

can result in releases to surface water from leaching and wash off from rain, building 

wash water or irrigation overspray contacting these surfaces. A statement will be added 

to the FWP identifying that the risk assessment will include evaluation of leaching from 

use in architectural paints applied to facades and other exterior surfaces. 

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5. Comment: (BACW A, Tri-TAC) Other PHMB uses listed in the Summary Document 

that should be incorporated into Down-The-Drain modeling include surface sanitizers and 

disinfectants for residential, commercial, hospital, veterinary and industrial settings; 

janitorial products for wet mopping; impregnated sponges; fabric treatments; and 

cleaning products for pet kennel and sleeping quarters. Whenever any indoor surface is 

sanitized or disinfected, it is likely that it will eventually be rinsed, washed or wiped 

down in the near future, likely down an indoor drain that flows to a wastewater treatment 

facility. Janitorial and other cleaning products often are concentrates that require mixing 

with water. Lefto er portions of cleaners are commonly poured down drains. 

Impregnated sponges and fabric washing will inherently result in discharges to 

wastewater treatment facilities. 

Agency's Response: The Agency agrees that the modeling plan for PHMB should be 

amended to include discharges to wastewater treatment plants from PHMB uses, 

including but not limited to: swimming pools and spas (as discussed in Response #1); 

surface sanitizers and disinfectants for residential, commercial, hospital, veterinary and 

industrial settings; janitorial products for wet mopping; impregnated sponges; fabric 

treatments; and cleaning products for pet kennel and sleeping quarters. The AD will 

examine these uses in the ecological risk assessment for PHMB. 

6. Comment: (BAOW A, Tri-TAC) EPA also needs to modify the modeling scenarios listed 

in the Scoping document (pp. 20-21) to account for releases ofPHMB not only during 

product formulation, but also during product use. For example, the OECD Emission 

Scenario Documents on Coatings (No. 20) and Adhesives (No. 22) provide only for 

emissions during product formulation. However, certain product uses, such as caulking in 

shower stalls, could also release PHMB to wastewater treatment plants. 

Agency's Response: The Agency agrees that the modeling scenarios listed in the scoping 

document should account for both releases of PHMB during product formulation and 

during in-service rse of the product. The Agency is working to develop conceptual 

models for formulation and in-service use of antimicrobial pesticides that will identify all 

potential pathways of exposure to environmental media and to develop exposure 

scenarios for those exposure pathways that are determined to be of potential concern. 

7. Comment: (BACWA, Tri-TAC) Would like to learn more about the cooling tower 

scenario to be used for PHMB. On the basis of the reference provided in the docket, we 

are uncertain whether the cooling tower use scenario reasonably accounts for likely 

PHMB discharges from cooling water systems into municipal wastewater treatment 

plants. Municipal wastewater treatment plants receive cooling water discharges not only 

from power plants, but also from industrial facilities, office complexes, and even large 

commercial and residential buildings, all of which commonly have water-based cooling 

systems. Our past experience with tributyltin cooling water additives taught us that for 

some biocides, eJ en one or two users among dozens or hundreds of cooling towers in our 

service areas can challenge our ability to comply with our NPDES permits. 

3 
Agency's Response: The Agency is developing scenarios for recirculating and oncethrough cooling towers and will be making these publicly available once a thorough 

review is completed. The scenario for recirculating cooling towers is adapted from 

Generic Scenarios developed by the Chemical Engineering Branch of 

EP A/OCSPP/OPPT. The approach for the once-through cooling tower scenario will 

employ the probabilistic dilution model (PDM) option ofthe General Population and 

Ecological Exposures from Industrial Releases Module ofEPA/OPPT's Exposure and 

Fate Assessment Screeing Tool (E-F AST) to determine the number of days of 

exceedance of concentrations of concern (COCs) for species selected to represent 

freshwater fish, freshwater invertebrates and aquatic plants would be exceeded 

downstream of facilities with once-through cooling tower uses, such as steam electric 

power plants. 

8. Comment: (BAd w A, CASQA, SFBWQB, Tri-TAC) The work plan should be refined 

by incorporating specific problem formulations, risk hypotheses, conceptual models and 

analysis plans similar to those that appear in most Environmental Fate & Effects Division 

(EFED) environmental assessment work plans. 

Agency's Response: The Agency agrees that a key purpose of work plans for 

antimicrobial pesticides undergoing registration review is to complete the problem 

formulation phase of the risk assessment process which is described in chapter 3 of the 

Agency's "Guidelines for Ecological Risk Assessment" (EPA/630/R-95/002F). The 

Antimicrobials Division (AD) also believes that additional refinements to future work 

plans such as conceptual models and analysis plans similar to those that appear in most 

EFED environmental assessment work plans would help provide clarity to the public on 

the environmental risk assessments AD plans to perform. Beginning with the work plan 

for para-tertiary amyl phenol, which was published earlier this year, the AD changed the 

format and scope of their work plans and began incorporating the key elements of the 

problem formulation phase of ecological risk assessment (i.e. , selecting assessment 

endpoints, developing conceptual models, and preparing an analysis plan) into this and all 

future work plans for antimicrobial pesticides undergoing registration review. The work 

plan for PHMB preceded this change and these changes will not be made to historic work 

plans which includes the existing PHMB work plan. 

9. Comment: (BACWA, CASQA, SFBWQB, Tri-TAC) Disagree with the Agency's 

proposal to waive acute and chronic toxicity tests for estuarine and marine species. 

These data are necessary because the use of freshwater species data to estimate effects on 

marine/estuarine species in an acute-to-chronic ratio (ACR) approach is not scientifically 

justified. In fact, this approach is not approved by EPA- the EPA OW does not allow 

fresh water ACRs to be used in the development of salt water quality criteria. Finally, 

available aquatic toxicity data are insufficient to justify extrapolating data from 

freshwater species to marine/estuarine species. 

Agency's Response: The PHMB work plan does not waive acute toxicity data for 

estuarine/marine species. In the PHMB environmental fate and effects scoping document 

and work plan acute data is required for an estuarine/marine fish, shrimp, and mollusk 

4 
species for both TGAis. Regarding the OW not using ACRs derived from freshwater 

species to calculate chronic values for saltwater species the OW guidance for 

development of national criteria 1

, which is Appendix H of the Water Quality Standards 

Handbook cited by commentors, states: 

" ... Even though absolute toxicities might be different in fresh and salt waters, such 

relative data as acute-chronic ratios and bioconcentration factors often appear to be 

similar in the two waters. When data are available to indicate that these ratios and 

factors are probably similar, they are used interchangeably ... " (page 7 of the 

criteria development guideline) 

and the guidance for calculation of an ACR for use in deriving a saltwater chronic value 

provides for two of the three required ACRs being from freshwater species (page 13 of the 

criteria developmahent guideline). The Agency does recognize, that given PHMB does not 

have a structural alog to verify that ACRs for freshwater and saltwater species in this 

case will not differ, at least one chronic saltwater study with the more sensitive 

estuarine/marine acute fish or shrimp will be required to provide confirmation. The need 

for an additional saltwater ACR in this case would be a higher tier requirement and is only 

needed if findings indicate that ACRs for freshwater and saltwater differ. 

10. Comment: (BACWA, CASQA, SFBWQB, Tri-TAC) Registrants should be required to 

develop environmental chemistry analysis methods. The analytical methods for 

commodity residue measurements that registrants are required to develop lack sufficient 

analytic sensitivity to evaluate pesticides at environmentally relevant concentrations for 

environmentally relevant matrices, such as water column, sediment, wastewater effluent 

and biosolids. Such analytical methods exist for very few pesticides. Surface water 

quality monitoring programs, which include surveillance monitoring conducted by state 

and federal agen9ies, and compliance monitoring conducted by local agencies subject to 

NPDES stormwater and wastewater permits, need analytical methods for pesticides with 

sufficiently low detection limits that are practicable in commercial and government 

analytical laboratories. Where such methods do not exist, public agencies sometimes are 

forced to develop them at public expense. We believe it is more efficient and equitable 

for the manufacturer to develop these methods at the time of initial registration of its 

product. We request that EPA adopt the approach used by the DPR to specify pesticide 

analysis method development during the registration review process. 

Agency's Response: For environmental fate and effects assessments the Agency requests 

registrants to provide chemistry analysis methods that meet the data quality objectives of 

the laboratory study or field study for which the analytical method is needed. 

Additionally environmental chemistry methods used to generate data associated with a 

field or monitoring study must include results of a successful confirmatory method trial 

by an independent laboratory. At this time the Agency is not planning to ask registrants 

to develop additional laboratory analytical methods not connected with conduct of studies 

supporting the risk assessment. 

1 http://water.epa.gov/scitech/swguidance/standards/criteria/aglife/upload/85guidelines.pdf 

5 
11. Comment: (BAOWA, CASQA, SFBWQB, Tri-TAC) Monitoring data would be 

invaluable for registration review, and we urge EPA to require registrants to conduct 

monitoring for their products in the environment, particularly in urban creeks and 

municipal wastewater. California DPR has required registrants to conduct a one-time 

survey ofthe concentrations of eight pesticides (not including PHMB) in wastewater 

influent, effluent and biosolids. EPA should issue similar requirements for other 

pesticides where water monitoring data are lacking. 

Agency's Response: Monitoring is a higher tier refinement for a risk assessment and 

such studies are required where information is needed to address a specific risk concern 

that cannot be answered using information from a lower tier study or model and/or to 

reduce uncertainty for the decision being made. This approach ensures that the data 

quality objectivd and resultant study design of such a monitoring study including type 

and number of locations, media to be monitored, and frequency of monitoring provide 

robust information for the intended use of the data in the risk assessment. At this time, 

the Agency believes the data requested, which does not include any environmental 

monitoring, will provide a robust risk assessment. If at the conclusion of the risk 

assessment decision makers identify that the uncertainties for uses rise to a level of 

needing refinement to address label changes or mitigation the decision to require 

monitoring may be reconsidered at that time. 

12. Comment: (BAQWA, SFBWQB, Tri-TAC) We request that documents for PHMB 

registration revief be modified to indicate OPP's intent to work with OW and a timeline 

by which it will utilize the outcomes of the common effects assessment methodology 

project. 

Agency's Response: Currently the Agency does not have a fixed timeframe but are 

actively working with OW and ORD on follow-up actions that will advance the 

harmonized methodologies discussed at the SAP. The Agency's web page 

www.epa.gov/oppefedl/cwa fifra effects methodology/scope.html will be updated as 

the effort progresses. A statement addressing this effort will be added to the scoping 

document. 

13. Comment: (BACWA, SFBWQB, Tri-TAC) Modeling Average Periods: To facilitate 

integration with OW regulatory programs, we request that the work plan be modified to 

provide exposure estimates for time periods consistent with those used by OW, in 

addition to the time periods ordinarily used by OPP. 

Agency's Response: The Agency has agreed to harmonize with the OW in regard to 

utilizing a common database for the purpose of deriving effects endpoints for pesticides. 

AD continues to evaluate exposure and risk quotients consistent with the following 

documents: 

USEPA. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, 

Office of Research and Development, Washing, D.C. EPA/630/R-95/002F. April1998. 

http://cfuub.epa.gov/ncea/cfm/recorddisplay.cfm?deid=30759 

6 
USEPA, 2004. Overview ofthe Ecological Risk Assessment Process in the Office of 

Pesticide Progr~s. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides and Toxic Substances, Office ofPesticide Programs, Washington, D.C. 

January 23, 2004

1 

14. Comment: (BAGWA, SFBWQB, Tri-TAC) We encourage EPA to use DPR sales data 

for PHMB, whic~ indicate that over 35,000 pounds ofPHMB were sold in 2010. These 

data are more use~l than pesticide reporting data, because most PHMB products are used 

by entities (residents and pool maintenance companies) that are not required to report 

pesticide usage. 

Agency's Response: The Agency agrees that when sales data for a pesticide are 

available, these should be used whenever they are available to prevent underestimates of 

pesticides that may potentially be released to the environment. Some states, however, do 

not have sales data available for all their registered pesticides and the best available data 

on amounts used · n those states must be used in lieu of sales data. 

15. Comment: (BACWA, Tri-TAC) Because data in the supplemental studies cited (Scoping 

Document, pp. 1 0-11) indicate that PHMB poses a threat to the treatment process, we 

request that EPA seek to obtain all data necessary to complete a careful review of 

PHMB' s potentia;l impacts on wastewater facilities and their critical microorganisms. 

Based on EPA's description of the sludge respiration inhibition test from the 1970s as 

being "supplemental", we are not confident that EPA has the information necessary for a 

thorough quantitative risk assessment. If EPA has any scientific questions about the 

supplemental study's estimate that sludge respiration is not inhibited at PHMB 

concentrations less than 40 mg/L, we request that EPA require a sludge respiration 

inhibition test (EPA OPPTS Guideline 850.6800). 

Agency's Response: The Agency agrees with the commenter that an Activated Sludge 

Respiration Inhibition (ASRI) test should be conducted following current Agency 

guidelines (OECD 209, OCSPP 850.3300). Upon reexamination ofthe 1970s study the 

Agency has concluded that this study which was characterized as supplemental does not 

provide adequate information that can be used to ascertain a dose-response curve of the 

relationship between concentration of PHMB and respiration inhibition effects to 

activated sludge microorganisms. Although a quantitative assessment of risks to 

activated sludge microorganisms is not currently within the scope of ecological risk 

assessments for antimicrobial pesticides, consideration of potential adverse effects to 

wastewater treatment plant microorganisms is included in conceptual models. An 

important application of information that can be obtained from a dose-response curve of 

the relationship between concentration of PHMB and respiration inhibition effects to 

activated sludge microorganisms exposed to PHMB is discussed in the Agency response 

to comment 17. 1 

7 
In conclusion, the Agency will require an ASRI test to be performed according to either 

OECD 209 or OCSPP 850.3300 and will include this additional data requirement in the 

final work plan for PHMB. 

16. Comment: (BACW A, Tri-TAC) Encourage EPA to consider available open literature, if 

any, to assess the potential for wastewater treatment process interference. 

Agency's Response: To assess the potential for wastewater treatment process 

interference, the Agency uses results from an acceptable ASRI test performed according 

to OECD 209 or OCSPP 850.3300 guidelines. An ASRI test performed according to 

these guidelines would be expected to provide results that would be adequate to develop a 

dose-response relationship between concentration ofPHMB and respiration inhibition 

effects to activated sludge microorganisms exposed to PHMB. In the absence of an 

acceptable ASRI test, the Agency would review open literature for information on the 

potential for wastewater treatment plant interference as a result of PHMB entering 

wastewater treatment plants. 

17. Comment: (BACWA, Tri-TAC) In designing its process interference risk assessment, 

EPA should use a quantitative approach. Quantification of risks will provide the basis for 

future risk management. Wastewater facility operators would benefit from specific 

guidance on how to calculate how much PHMB-containing pool water may be safely 

discharged to a wastewater collection system each day. This would ideally be a 

"maximum allowable headworks loading" formula that would provide a simple formula 

to calculate the maximum daily quantity ofPHMB-containing pool water that can be 

discharged while protecting the treatment facility microorganisms and preventing 

interference with the treatment process. 

Agency's Response: Using the dose-response curve from an Activated Sludge 

Respiration Inhi9ition Study (ASRI) study, plant operators can select a respiration 

inhibition percent that would be considered to be an upper bound that would be 

adequately protective to prevent interference with the treatment process and determine 

from this plot a corresponding concentration of PHMB that must not be exceeded. This 

concentration along with wastewater treatment plant influent flow data can be used as the 

basis of a formula to calculate the maximum daily amount of PHMB-containing pool 

water that can be discharged while protecting the activated sludge microorganisms and 

preventing interference with the treatment process. The Agency is planning to provide 

guidance on performing such calculations. 

18. Comment: (BACWA, Tri-TAC) With approximately fifty percent ofwastewater 

treatment costs allocated to biosolids handling, there is particular concern that pesticide 

residues in biosolids may impact biosolids management options, especially land 

application to agricultural areas. Therefore, we urge the OPP, Water (Offices of 

Wastewater Management and Science and Technology), and Research and Development 

to work together to develop a methodology that evaluates potential impacts of pesticides 

to biosolids land application whenever Down-The-Drain assessments indicate that 

pesticides would partition into biosolids. 

8 
Agency's Response: An Intra-Agency Biosolids Workgroup was convened in early 

2012. This workgroup includes members from OPP, and OW Offices of Wastewater 

Management and Science and Technology who are working in consultation with 

members of EPA's Office ofResearch and Development. Two key purposes ofthis 

workgroup are to develop criteria for determining whether a pesticide that is released 

down-the-drain might have the potential to partition to biosolids and subsequently lead to 

exposures of potential concern to humans and ecological organisms from land-application 

ofbiosolids and to develop a screening-level model that can be used to estimate potential 

exposures of humans and ecological organisms to chemical substances in biosolids that 

are land applied. 

19. Comment: (BACWA, Tri-TAC) It should be noted that such evaluations (i.e., of 

potential impacts of pesticides to biosolids land application whenever Down-the-Drain 

assessments indicate that pesticides would partition into biosolids (refer to topic 

introduced in Comment 18)) should focus on fate, transport, and toxicity factors 

specifically applicable to the biosolids matrix. The existing OPP guidelines for the study 

of chemicals in the terrestrial environment could be modified to address biosolidsamended soil systems. In addition, the evaluation should include an analysis of 

bioaccumulation, toxicity to microbes, and toxicity to worms. This will entail requiring 

the registrant to conduct the studies such as a soil microbial community toxicity test 

(OPPTS Guideline 850.3200) and an earthworm subchronic toxicity test (OPPTS 

Guideline 850.31 00). 

Agency's Res onse: Assessing toxicity to microbes and worms is generally not within 

the scope of the Agency's current risk assessment methodologies. For instance, in the 

current version of the Biosolids Core Risk Assessment Model (BCRAM) developed by 

EPA's Office of Water, pathways of ecological exposure to chemicals in biosolids that 

are considered include contact with water, soil, and sediment and ingestion of 

contaminated aquatic and terrestrial species. Although uptake of chemicals in biosolids 

by the soil invertebrate community as a result of contact with soil is considered, this 

methodology does not consider toxicity to microbes and worms. In addition, assessment 

of toxicity to microbes and worms is not within the scope of ecological risk assessment 

for conventional pesticides. Although the Agency occasionally receives data on toxicity 

to earthworms, the Agency does not require such data and does not quantitatively assess 

risk based on this information. The Agency does, however, use this information in 

characterizing risks to conventional pesticides. 

At this time, the Agency has no plans to require registrants to conduct studies such as a 

soil microbial community toxicity test (OPPTS Guideline 850.3200) or an earthworm 

subchronic toxicity test (OPPTS Guideline 850.31 00). 

20. Comment: (BACWA, Tri-TAC) Supports the AD's intention to estimate environmental 

concentrations from wastewater discharges using theE-FAST model's Down-The-Drain 

module. However, there are concerns with the way that E-F AST has been set up and used 

9 
by OPP. Support OPP's previously stated plan to work with EPA's Office of Water and 

stakeholders to refine the way E-F AST is used. 

Agency's Response: To obtain the full context of this comment, the Antimicrobials 

Division reviewed the comment, "Publicly Owned Treatment Works (POTW) Removal 

Efficiency and Improvements ofMethodology About EFAST2" presented in the 

memorandum, "Response to Public Comments on the EFED Registration Review 

Problem Formulation for Bifenthrin" dated December 22,2010 (EPA-HQ-OPP-2010-

0384-0034). 

The approach that the AD presented in its work plan and plans to use in its ecological risk 

assessment for PHMB is not the same as that EFED presented in problem formulations 

for conventional pesticides, such as bifenthrin. Bifenthrin belongs to a class of 

chemicals, synthetic pyrethroids, which have been detected in surface waters, aquatic 

sediments, and biosolids throughout the United States. Consequently, the approach for 

problem formulation EFED proposed for bifenthrin is designed for a higher tier exposure 

and risk assessment than the approach for problem formulation for PHMB, which is 

designed for a screening level exposure and risk assessment. For antimicrobial pesticides 

that have uses and environmental fate characteristics that may result in releases to 

domestic wastewater treatment plants, AD performs a screening-level assessment using 

the Down-the-Drain module ofE-FAST to determine potential concerns for exposure of 

aquatic organisms to an antimicrobial pesticide and/or its degradates. When results from 

this screening level aquatic exposure and risk assessment indicate a potential concern for 

aquatic organisms exposed to an antimicrobial pesticide and/or its degradates 

downstream of domestic WWTPs, AD requires data on antimicrobial pesticides and/or 

their degradates that will provide information on potential removal of pesticide during 

wastewater treatment, toxicity to activated sludge microorganisms, and acute and 

measurement endpoints for aquatic organisms. Wastewater treatment plant studies may 

include: 

• Activated Sludge Respiration Inhibition (ASRI, OECD 209) or Modified ASRI 

test (850.3300); 

• Ready biodegradability (GLN 835.3110), or Porous Pot Test (GLN 835.3220), or 

Simulation Tests to Assess the Biodegradability of Chemicals Discharged to 

Wastewater (GLN 835.3280), or Simulation Test- Aerobic Sewage Treatment: 

A. Activated Sludge Units (GLN 835.3240) 

• Activated Sludge Sorption Isotherm (GLN 835.1110) 

The results ofthe Activated Sludge Respiration Inhibition Test (ASRI) determine which 

of these biodegradation tests are required. If the ASRI test EC5o is less than or equal to 

20 mg/L, then either the Biodegradation in Activated Sludge Study or the Porous Pot Test 

is required. If the ASRI test EC50 is greater than 20 mg/L, then the applicant must choose 

either: (i) Ready Biodegradability or (ii) Biodegradation in Activated Sludge or the 

Porous Pot Test. If the antimicrobial passes the ready biodegradability study, then no 

further testing is required. If, however, the antimicrobial fails the ready biodegradability 

study, then the Biodegradation in Activated Sludge or the Porous Pot study is required. 

10 
Data from these tests would then be used to refine the screening level exposure and risk 

assessment. 

The AD is working to develop a tiered approach for using E-F AST to assess exposures 

and risks to ecological organisms and to develop a plan to distribute this approach for 

review and comment. 

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