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Section 18 Emergency Exemption Application 

TYPE OF EXEMPTION BEING REQUESTED

 SPECIFIC

 QUARANTINE

 PUBLIC HEALTH

CONTACT PERSON(S) AND QUALIFIED EXPERT(S) (166.20(a)(1))

CONTACT PERSON:

Name: David Hickens 

Title: Chief, NASA JSC Environmental 

Office 

Organization: NASA JSC 

Address: 

 

Phone: 281-483-3120

QUALIFIED EXPERT:

Name: Mark E. Wilson

Title: Boeing Associate Technical Fellow

Organization: Boeing 

Address: 3100 space Center Blvd., MC HB3-

20, Houston TX 77059-3556 

Phone: 281-226-6966 

DESCRIPTION OF PESTICIDES REQUESTED (166.2O(a)(2))

Common Chemical Names

(Active Ingredients): o-phthalaldehyde (OPA) CAS Number 643-79-8

Trade Names and EPA Reg. Nos.:

Formulations: Immobilization of OPA on a Porous Resin (P/N SV1012327-2) % Active 

Ingredient: 0.25 g OPA/cm3of resin; Resin Loading factor based on 84% elution efficiency = 

210 mg OPA/cm3resin

Manufacturers: o-phthalaldehyde – Sigma Aldrich; OPA Resin (P/N SV1012327-2) –

Hamilton Sundstrand

DESCRIPTION OF PROPOSED USE (166.20(a)(3))

Sites to be Treated: International Space Station Internal Active Thermal Control System

(IATCS) coolant including the US Laboratory including Node 1 and Airlock (249 liters), 
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Japanese Experiment Module (213 liters), Columbus (160 liters), and Node 3 (194 liters).

Method of Application: Elution of OPA from the OPA Resin (P/N SV1012327-2) into the 

IATCS coolant volume through the use of an antimicrobial applicator canister (P/N 683-

63436) placed in a by-pass line at a payload rack location and initiating flow at 400 lb/hr for 

16 hours.

Rate of Application (in terms of a.i. and product): Approximately 250 mg/L OPA added to 

each loop approximately 1/year.

Maximum Number of Applications: Approximately 1 application/year for each loop, 

determined by measuring OPA concentration every 90 days and utilization of the quantity of 

OPA Resin necessary to increase the as circulated in flight hardware OPA concentration to 

300 ppm based on degradation of OPA to 50 – 100 ppm.

Total Acreage (or other units) to be Treated: US Laboratory - 272 liters, Japanese 

Experiment Module – 213 liters, Columbus – 150 liters, and Node 3 – 194 liters for a total 

volume of 829 liters. 

Total Amount of Pesticide to be Used (in terms of a.i. and product): VR = Volume Resin 

Required; VL = Volume of IATCS (L); [OPA] = Desired OPA Concentration (mg/L); FOPA = 

OPA Resin Loading factor = 210 mg OPA/cm3-Resin; Therefore VR = (VL * [OPA])/ FOPA ; 

VR = (829 L * 250 mg/L)/210 mg OPA/cm3= 987 cm3 OPA Resin/year.

Use Season (period of time for which use of chemical is requested): As required through 

the life of the International Space Station to maintain the OPA concentration as circulated in 

flight hardware between 25 – 500 ppm OPA as specified in Table 4.1-2.8 “Heat transport fluid 

(IATC)” Revision E of SSP-30573 “Space Station Program Fluid Procurement and Use 

Control Specification”.

Additional Restrictions, User Precautions and Requirements, Qualifications of 

Applicators, etc.: The method to deliver OPA to the IATCS coolant was an immobilization 

of the active biocide to a solid substrate. The immobilization process involved a solvent 

evaporation technique that allowed the OPA to be physically constrained in a porous 

methacrylate resin material. Once the resin material was exposed to the coolant fluid, the OPA 

effectively eluted from the resin material into the aqueous phase. This implementation was 

selected due to system requirements and the use of pre-existing flight hardware. System

requirements included limits on the initial and final OPA concentration observed eluting from 

the canister (reactor) and compatibility with the coolant loop chemistry (i.e. no leachate, 

particles, adverse effects to chemistry/system materials). The flight hardware used for the 

OPA delivery was a stainless steel canister with an approximate volume of 2.0 L with flex 

hoses and quick disconnects to connect the canister to a payload rack location. 
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ALTERNATIVE METHODS OF CONTROL (166.20(a)(4)) (Efficacy data and/or other 

information included as a separate attachment)

Registered Alternative Pesticides: An extensive evaluation of biocides was conducted to 

down-select to several candidates for test trials (see Appendix A). Criteria for that down-select 

included: the need for safe, non-intrusive implementation and operation in a functioning 

system; the ability to control existing planktonic and biofilm residing micro-organisms; a 

negligible impact on system wetted materials of construction; and a negligible reactivity with 

existing coolant additives. A five-point ordinal rating scale from 5 (excellent) to 1 

(unacceptable) was used to score each biocide against 10 weighted assessment criteria: 

Material Compatibility 4x; Chemical Compatibility 3x; Safety/Toxicity 3x; Disinfection 

Effectiveness 2x; Stability 2x; Byproduct Acceptability 2x; On-orbit Implementation 1x; Cost 

1x; In-Flight Monitoring 1x; and Technology Readiness 1x. All oxidizing biocides and 

halogens were eliminated due to increased corrosion of nickel brazes on cold plates and heat 

exchangers. Phenols were eliminated due to instability in the coolant. Quaternary

ammoniums were eliminated due to their reduction of surface tension which increases gas trap 

leakage. Trade studies and rapid screening assays were used to develop a prioritized list of 

acceptable antimicrobial agents including glutaraldehyde, ortho-phthalaldehyde (OPA), and 

methyl isothiazolone. Glutaraldehyde at greater than 25 ppm was eliminated due to NASA 

concerns with safety and toxicity and methyl isothiazolone was eliminated from further 

consideration due to its ineffectiveness against biofilms and toxicity at higher concentrations. 

Therefore, OPA, an aromatic dialdehyde compound with the formula C6H4(CHO)2 was 

selected for qualification testing for use as a biocide in the IATCS.

Alternative Control Practices: Lowering the water activity of the coolant by increasing salt 

concentration was ruled out due to requirements for surface tension specified in SSP-30573 

Revision B, Space Station Program Fluid Procurement and Use Control Specification. 

Requirement specifications included chlorides less than 1.0 ppm and a surface tension of 72–

77 dynes/cm at 20C. 

EFFICACY OF USE PROPOSED UNDER SECTION 18 (166.20(a)(5)) (Efficacy data 

and/or other information included as a separate attachment)

EXPECTED RESIDUE LEVELS IN FOOD (166.20(a)(6)) (Residue data included as 

separate attachment) Not Applicable Due to Removal by ISS ECLSS

DISCUSSION OF RISK INFORMATION (166.20(1)(7))

(Potential risks to human health, endangered or threatened species, beneficial organisms, 

and the environment)

Description of application sites, including proximity to residential areas, aquatic systems, 

endangered or threatened habitats, soil types, etc.: Elution of OPA from the OPA Resin 

(P/N SV1012327-2) into the IATCS coolant volume through the use of an antimicrobial 

applicator canister (P/N 683-63436) placed in a by-pass line at a payload rack location in the 

U.S. Laboratory Module, Columbus Module, Japanese Experiment Module, and/or Node 3 

and initiating flow at 400 lb/hr for 16 hours. 
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Possible risks posed by use: Evaluations of the toxicity of OPA were conducted by Martin 

E. Coleman, Ph.D., Wyle Toxicology Consultant, and the results were reported in Memo 632 

dated March 4, 2005, Memorandum TOX-MC-2007-Draft dated August 27, 2007 and 

Memorandum TOX-MC-2008-Draft dated March 24, 2008. Circulated concentrations of OPA 

up to 500 ppm were determined to be Toxicity Hazard Level 0 (Nonhazard) defined as slight 

irritation that lasts <30 minutes and will not require therapy for all toxicology parameters. 

Initial effluent concentrations of OPA greater than 1000 ppm introduced into a payload bypass stream from the antimicrobial applicator were determined to be a Toxicity Hazard Level 

1 (Critical) defined as slight to moderate irritation that lasts >30 minutes and will require 

therapy due to irritation of soft tissues such as the eye. If coolant containing OPA leaks and 

the water evaporated until OPA became saturated, the resulting concentrate would be a severe 

eye irritant classified as a Toxicity Hazard Level 2 defined as moderate to severe irritation that 

has the potential for long-term performance decrement and will require therapy. Solid OPA 

was determined to be a Toxicity Hazard Level 2 (Catastrophic) for eye and skin irritancy and a 

Toxicity Hazard Level 1 (Critical) for inhalational and systemic toxicity. OPA in rare 

instances has caused allergic reactions from repeated skin contact with residual liquids or 

solids. OPA loaded resin beads containing 0.25 g/cm2 OPA in the antimicrobial applicator 

was assessed as a Toxicity Hazard Level 0 (Nonhazard).

JSC Toxicology provided additional assessment of the risk of solid OPA from IATCS fluid in 

Memo Tox-HG-2009-09 dated April 30, 2009. This memo documents the JSC Toxicology

Group's assessment of dry OPA from evaporated ITCS fluid as a Toxicity Hazard Level 0, 

rather than a Toxicity Hazard Level 2. Although solid OPA could cause catastrophic eye 

damage if it were to contact the eye, consideration of the behavior of liquids under the specific 

spaceflight conditions expected on ISS led to the conclusion that contact with the eyes of dry

OPA from evaporated ITCS fluid is not credible. Thus, dried OPA films from evaporated 

ITCS fluid should not be considered Toxicity Hazard Level 2 eye hazards.

JSC Toxicology recommended that leaks from the antimicrobial applicator and the IATCS 

should be quickly removed before evaporation occurs. Leakage detection on-orbit is primarily

based on thermal control system accumulator quantities.

Proposals to mitigate risks: A removal resin was developed to be able to remove OPA from 

the IATCS in the event of a sustained leak to preserve crew health and safety or if adverse 

system effects were detected from OPA utilization. Ambersorb 572® was chosen as the flight 

candidate since it had approximately twice the capacity for OPA than the activated carbon. 

The resin material has a much more porous structure, resulting in higher surface area to 

facilitate organic adsorption. The resin was also shown to remove greater than 95% of OPA 

degradation products from IATCS coolant but it has a higher affinity for free OPA. The 

removal resin canister may be attached at a payload rack location similar to antimicrobial 

applicator.

COORDINATION WITH OTHER AFFECTED FEDERAL, STATE, AND LOCAL 

AGENCIES (166.20( a)(8)) 

Not Applicable
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NOTIFICATION OF REGISTRANT (166.20(a)(9))

ENFORCEMENT PROGRAM (166.20(a)(10)) (Explanation of legal authority and 

program resources for enforcement)

REPEAT USES (166.20(a)(11)) (If use being requested is a repeat use, and final report 

has not been filed, interim final report included as a separate attachment)

PROGRESS TOWARD REGISTRATION (166.25(b)(2)(ii) (Information from registrant 

concerning the current status ) (Not Required for Request for a Quarantine Exemption)

NASA is beginning the registration process.

NAME OF PEST (166.20(c)(I))

Scientific Name: Cupriavidus metallidurans, Variovorax paradoxus, Acidovorax sp., 

Sphingomonas parapaucimobilis, Stenotrophomonas maltophilia, Methylobacterium 

extorquens, and Unidentified Gram Negative Rods

Common Name: Aerobic/Microaerophilic Water Bacteria

ORIGIN OF INTRODUCED PEST (166.20(c)(2))

Origin of pest, means of its introduction, and spread into the area (if known): 

The primary source of bacteria was from the deionized water used to make the coolant for the 

Internal Active Thermal Control System. Also, the equipment was chemically cleaned with 

isopropanol, rinsed with deionized water and dried prior to assembly. The bacteria may also 

have been introduced during handling and assembly. A silver salt biocide, silver sulfate, 

initially used as an additive in the coolant formulation at a concentration of 0.1 – 3 parts per 

million (ppm) to control growth and proliferation of microorganisms rapidly decreased below 

detection limits within a few hours. Silver ions rapidly underwent an oxidation reduction 

reaction with nickel. The rapid reduction of silver ions in the coolant created a favorable 

environment for the growth and proliferation of microorganisms. Counts of heterotrophic 

bacteria increased from <10 colony forming units (CFU)/100 milliliters (ml) to greater than 

1.0E+06 CFU/100 ml.
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IMPACT OF THE PEST (166.20(C)(3))

Anticipated impact of not controlling the pest, and other information pertinent to 

economic importance of this pest:

Uncontrolled microbiological growth in the IATCS can deteriorate the performance of the 

system and potentially impact human health if opportunistic pathogens become established in 

the system. Microorganisms are capable of degrading the coolant chemistry, attaching to 

surfaces and forming biofilm, subsequent biofouling of filters, tubing, and pumps, decreasing 

flow rates, reducing heat transfer, initiation and acceleration of corrosion, and enhanced 

mineral scale formation. Disinfection to control microbiological growth and biofilm 

formation is necessary to maintain tolerable risk levels for the ISS IATCS due to the required 

operational life of the ISS IATCS for over 15 years without the ability to periodically flush 

and replace coolant, sterilize the system, and/or replace system equipment. 

Information Required for a Final Report

SAMPLE SECTION 18 EMERGENCY EXEMPTION FINAL REPORT FORMAT (40 CFR 

166.32)

(1) Total acreage, number of structures or other units treated, and the total quantity of the 

pesticide used (either actual or estimated);

(2) A discussion of the effectiveness of the pesticide in dealing with the emergency condition;

the minimum inhibitory concentration (MIC) for OPA against the bacteria in the IATCS is 10 

– 20 ppm. The minimum lethal concentration (MLC) for OPA against most of the identified 

bacteria in the IATCS is 30 – 50 ppm. However, the MLC of OPA against Methylobacterium 

extorquens was determined to be 150 – 200 ppm. Expected use concentration of 300 ppm 

OPA is more than ten times higher than the MIC. And provides effective disinfection and 

microbiological growth control.

(3) A description of any unexpected adverse effects which resulted from use of the pesticide 

under the exemption;

(4) The results of any monitoring required and/or carried out under the exemption;

(5) A discussion of any enforcement actions taken in connection with the exemption;

(6) Method(s) of disposition of a food or animal feed, if required to be destroyed under an 

exemption; and

(7) Any other information requested by the Administrator, such as the type of PPE worn by 

applicators.