Docket Number: EPA–HQ–OPP–2010-0242 

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United States Chemical Safety December 2010 

Environmental Protection and Pollution Prevention 

Agency (7510P)

Chlorine Gas Final Work Plan 

Registration Review December 2010 

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TABLE OF CONTENTS

Chlorine Gas Registration Review Team ................................................................................................... 4

I. INTRODUCTION ..................................................................................................................................... 5

II. COMMENTS RECEIVED ON THE PRELIMINARY WORK PLAN ............................................. 5

III. RISK ASSESSMENT AND DATA NEEDS ........................................................................................ 6

IV. TIMELINE ........................................................................................................................................... 12

V. GLOSSARY of TERMS & ABBREVIATIONS ................................................................................. 14
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Chlorine Gas Registration Review Team

Human Health & Environmental Effects 

Tim McMahon 

Srinivas Gowda 

Risk Management

Monisha Harris 

Lance Wormell 

Office of General Counsel

Philip Ross 
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I. INTRODUCTION 

This is the Environmental Protection Agency’s (EPA or “the Agency”) Final 

Work Plan (FWP) for the registration review of Chlorine Gas. The work plan includes 

the expected registration review timeline. The work plan also addresses public comments 

received concerning the Preliminary Work Plan (PWP) in the Summary Document which 

was posted in the chlorine gas registration review docket, and any other comments 

concerning the initial docket postings. The Summary Document provided information on 

what EPA knows about the pesticide and what additional risk analyses and data or 

information the Agency believes are needed to make a registration review decision. 

 The Agency is implementing the registration review program pursuant to Section 

3(g) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and will review 

each registered pesticide every 15 years to determine whether it continues to meet the 

FIFRA standard for registration. Changes in science, public policy and pesticide use 

practices will occur over time. The registration review program is intended to make sure 

that, as the ability to assess risk evolves and as policies and practices change, all 

registered pesticides continue to meet that statutory standard. The public phase of 

registration review begins when the initial docket is opened for each case. Information 

on this program is provided at: http://www.epa.gov/oppsrrd1/registration_review/. 

 The chlorine gas Preliminary Work Plan was published June 23, 2010. The 60-day 

comment period ended on August 23, 2010. The Preliminary Work Plan document is 

available on www.regulations.gov, docket number EPA-HQ-OPP-2010-0242. 

 

II. COMMENTS RECEIVED ON THE PRELIMINARY WORK PLAN 

 EPA received two comments during the public comment period on the initial 

docket, described below. In the PWP, EPA also solicited comments on three specific 

topics: environmental justice; water body impairment; and trade irritants. No comments 

or information were received during the public comment period concerning these issues. 

The comments received during the initial public comment period did not affect 

the data needs, work plan and timeline described in the PWP and they remain as they 

were presented initially in the PWP. Further, this document makes final the work plan 

for the chlorine gas registration review process. 

Comment: The FIFRA Endangered Species Task Force (FESTF) submitted a 

comment requesting that any technical registrant for chlorine gas who is not a 

member of the FESTF (or a company having met its data compensation 

obligations) be asked to provide a formal offer-to-pay to FESTF for reliance on 

their data. In their comment, FESTF also noted that PPG Industries, Inc, Pioneer 

Americas LLC, Canexus U.S., Inc, Chemical Formulators, Inc., Olin Corporation 

and Brenntag Canada, Inc. are the leading registrants for chlorine gas, and that 

the above mentioned are not FESTF members. Therefore, the technical registrant 
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must offer to pay FESTF to rely on FESTF submitted data or develop substantial 

similar data on their own. 

Response: The Agency thanks FESTF for its comment and will consider this 

information as it conducts the registration review and makes its registration 

review decisions. 

Comment: The Chlorine Institute, Inc. submitted a comment questioning the value 

of obtaining additional plant studies (GLNs 850.4225, 850.4250, 850.4400, 

850.5400) and requesting that EPA review the numerous references sited in the 

Chun, et al paper submitted as part of the Chlorine Institute’s response. The 

Chlorine Institute also requested clarification on how the vegetation listed above 

could potentially be adversely affected by the application of chlorine as an 

antimicrobial pesticide.

Response: EPA thanks the Chlorine Institute for submitting additional open 

literature information that was not available to EPA at the time the summary 

document was completed. The Agency has conducted a preliminary review of 

these data and believes that the information in these articles is not sufficient to 

satisfy the four data requirements cited above. The Agency intends to require 

these four studies as initially presented in the Preliminary Work Plan because 

these data are necessary to conduct a full ecological risk assessment, including an 

endangered species assessment based on chlorine’s use in swimming pool water, 

industrial slimicides used in recirculating and once-through water cooling towers 

and paper mills that potentially pass through water treatment plants and may be 

discharged into terrestrial and aquatic environments. The justification for each of 

these studies is provided in Appendix A of the Summary of Product Chemistry, 

Environmental Fate and Ecotoxicity Data for Chlorine Registration Review 

Decision Document, p. 26-29. 

III. RISK ASSESSMENT AND DATA NEEDS 

A Reregistration Eligibility Decision was completed for chlorine gas in 1999. However, 

to complete registration review, additional data are anticipated to be needed to conduct 

the human health and ecological risk assessments. 

Human Health Risk Assessment Status

The Agency has reviewed all the available information on toxicology and human 

exposure regarding chlorine gas. The toxicology and exposure databases for chlorine gas 

are considered adequate. Therefore, the Agency anticipates that no additional toxicity or 

exposure data will be needed for the chlorine gas registration review case. 

Further human health information is available in the document titled “Chlorine 

Gas: Human Health Effects Scoping Document for the Registration Review Decision,” 

dated June 4, 2010. 
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Dietary and Drinking Water Exposure and Risk

Dietary Food Exposure

Food exposure to chlorine gas and aqueous chlorine is not expected to occur 

because there is not a reasonable expectation that residues significantly above naturally 

occurring background levels would occur. Due to the high reactivity and water solubility 

of chlorine and chlorine salts, residues are also not expected to accumulate or 

bioaccumulate in the food chain. Therefore, a dietary food risk assessment is not 

anticipated as being needed for chlorine gas in support of this registration review. 

Dietary Drinking Water Exposure

The registered uses of chlorine gas and aqueous chlorine include disinfection of 

municipal drinking water. The EPA's Office of Water has conducted a risk assessment 

for the use of chlorine in disinfection of municipal drinking water as well as disinfection 

byproducts resulting from the use of chlorine in municipal drinking water disinfection 

(Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR: 63 FR 69390 - 

69476, December 16, 1998, Vol. 63, No. 241). As a result of this assessment, a 

Maximum Residual Disinfectant Level of 4 mg/L for chlorine in municipal drinking 

water was determined as a safe level for human exposure 

(http://www.epa.gov/safewater/mdbp/dbp1.html). Maximum contaminant levels of 

disinfection byproducts were also established as a result of this assessment. As the other 

registered uses of chlorine gas/aqueous chlorine are not likely to result in contamination 

of surface or groundwater, and as the EPA's Office of Water has already assessed the 

drinking water use, the Office of Pesticide Programs does not anticipate conducting a 

drinking water assessment for chlorine gas/aqueous chlorine. 

Tolerances

There is a tolerance exemption for chlorine gas (40 CFR 180.1095) “when used 

preharvest or postharvest in solution on all raw agricultural commodities.” There are also 

tolerance exemptions for both sodium hypochlorite (40CFR 180.1235) and calcium 

hypochlorite (40CFR 180.1054). 

Aggregate and Cumulative Exposure and Risk

In examining aggregate risk, the Agency takes into account the available and 

reliable information concerning exposures to pesticide residues in food, drinking water, 

and non-occupational pesticide exposures. For the registered uses of chlorine gas, there 

is no expectation that residues above background levels will occur to chlorine in the diet 

from food contact or food uses. Therefore, there is no expectation that exposure in the 

diet from food contact or food uses of chlorine gas will result in an exposure that would 

be considered in an aggregate risk assessment, because this level would be no different 

than background levels that humans are exposed to on a daily basis. With respect to the 

disinfection of municipal drinking water, a maximum residual disinfectant level of 4mg/L 
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for chlorine residue has been established by the Agency’s Office of Water which has 

been determined to be a safe level for human exposure. Therefore, this exposure would 

not contribute to an increased aggregate risk, as it has already been pointed out that there 

is no increased dietary exposure over background, and the drinking water disinfectant 

level of 4 mg/L for chlorine had been determined to be a safe level for human exposure. 

Together then, dietary and drinking water exposures do not contribute to an increased 

risk. Non-dietary residential dermal and incidental oral exposures could result from use 

of chlorine gas in swimming pools. The Agency will need to consider the magnitude of 

these exposures, the health effects that have been reported from dermal and incidental 

oral exposures to chlorine, the dose levels at which these effects have been reported, and 

the relationship of these effects to actual human exposures to determine whether an 

aggregate assessment is appropriate. It should be noted that use of proper application 

methods and use of trained personnel in the use of chlorine gas would likely result in 

minimal to no exposure from this use. 

Section 408(b)(2)(D)(v) of FFDCA requires that, when considering whether to 

establish, modify, or revoke a tolerance, the Agency consider “available information” 

concerning the cumulative effects of a particular pesticide's residues and “other 

substances that have a common mechanism of toxicity.” EPA has not yet determined 

whether chlorine gas has a common mechanism with other compounds; consequently, a 

cumulative assessment will not be performed at this time. 

Occupational and Residential Exposure and Risk

An occupational and/or residential exposure assessment is required for an active 

ingredient if (1) certain toxicological criteria are triggered and (2) there is potential 

exposure to handlers (mixers, loaders, applicators, etc.) during use or to persons entering 

treated sites after application is complete. Because chlorine gas is metered into water 

through closed systems in manufacturing processes or from large stationary containers 

such as tank cars, tank trucks, and cylinders, the Agency believes that occupational and 

post-application exposure to chlorine gas, including exposure of pool service operators 

and bystanders is not significant provided proper application methods are followed. 

These application methods are presented in pamphlets published by the Chlorine 

Institute, available at: 

http://www.chlorineinstitute.org/Bookstore/content.cfm?ItemNumber=3637&navItemNu

mber=3638). 

Anticipated Physical/Chemical Property Data Needs

All product chemistry data requirements have been fulfilled for chlorine gas. 

Therefore, it is anticipated that additional product chemistry data will not be needed for 

the active ingredient chlorine gas. 

Further information is available in the “Summary of Product Chemistry, 

Environmental Fate, and Ecotoxicity Data for the Chlorine Gas Registration Review 

Decision Document,” dated June 3, 2010. 
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Environmental Fate and Ecological Risk Assessment and Data Needs

The Agency has reviewed the environmental fate and ecological hazard databases 

for chlorine gas. Based on its review, EPA believes risk assessments are needed to ensure 

that the chlorine gas registration review case meets FIFRA standards. The Agency will 

complete the environmental fate and ecological hazard risk assessments presented below. 

• Environmental Fate 

• Ecological hazard 

• Endangered species assessment 

Further information is available in the “Summary of Product Chemistry, 

Environmental Fate, and Ecotoxicity Data for the Chlorine Gas Registration Review 

Decision Document,” dated June 3, 2010. 

The Agency needs to conduct ecological risk assessments for chlorine used in 

once-through water cooling towers for control of microbiological growth and that likely 

would be discharged into effluents and surface waters. Therefore, the Agency anticipates 

needing ecotoxicity data for chlorine that is of potential concern for once-through water 

cooling towers uses of chlorine. The following ecotoxicity data are needed to conduct an 

ecological risk assessment: 

Anticipated Ecological Data Needs 

o (GLN 850.4225) seedling emergence, Tier II - dose response study on rice 

(Oryza sativa); 

o (GLN 850.4250) vegetative vigor, Tier II - dose response study on rice 

(Oryza sativa); 

o (GLN 850.4400) aquatic plant growth (aquatic vascular plant toxicity), 

Tier II - dose response study on floating macrophyte Lemna gibba; and 

o (GLN 850.5400) aquatic plant growth (algal toxicity), Tier II - dose 

response studies on (Selenastrum capricornutum (green algae), Anabaena 

flos- aquae (blue-green cyanobacteria), Navicula pelliculosa (freshwater 

diatom), and Skeletonema costatum (marine diatom). 

Endangered Species

 The Agency has not conducted a risk assessment that supports a complete 

endangered species determination for chlorine gas. The ecological risk assessment 

planned during registration review will allow the Agency to determine whether chlorine 

gas use has “no effect” or “may affect” federally listed threatened or endangered species 

(listed species) or their designated critical habitats. When an assessment concludes that a 

pesticide’s use “may affect” a listed species or its designated critical habitat, the Agency 

will consult with the U.S. Fish and Wildlife Service and/or National Marine Fisheries 

Services (the Services), as appropriate. 
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Incidents

 The toxicological review of chlorine by the Agency for Toxic Substances and 

Disease Registry (ATSDR, 2002) summarizes an extensive database regarding human 

exposure to chlorine gas by the inhalation, oral, and dermal routes of exposure. 

With respect to inhalation exposure, death from chlorine gas used as a chemical 

weapon in World War I was noted. Causes of death from this exposure were bronchopneumonia, lobar pneumonia, purulent pleurisy, and tuberculous meningitis. The 

concentration of exposure causing death was not known in this circumstance. More 

recent incidents involving exposure to chlorine gas as a result of rail car accidents in 

which chlorine gas was released also did not note actual levels producing lethality, but as 

noted in the ATSDR review, “Prater (1990) indicates that concentrations of 400 ppm can 

be lethal to humans in 30 minutes and that immediate death follows inhalation of a 

concentration of 1,000 ppm. Concentrations between 1,000 and 1,200 ppm for 30 

minutes are lethal to humans according to a review of earlier data from various American 

authors by Withers and Lees (1985b).” As might be expected, the respiratory tract is the 

primary target of inhalation exposure to chlorine gas, and toxicity resulting from such 

exposure is manifest upon the tissues and organs of the respiratory tract. 

From oral exposure, death in humans has been reported from ingestion of 200 mL 

of a solution containing 3–6% chlorine (as sodium hypochlorite) (ATSDR, 2002). 

Regarding accidental ingestion, only minor effects on the gastrointestinal tract were 

observed in data compiled by Pike et al. (1963), who reviewed 129 cases of children who 

ingested Clorox® and reported that no complications of consequences were found. Sixtyfive cases were examined by esophagoscopy within 96 hours of the ingestion and only 2 

showed evidence of esophageal injury. The children were between 12 month and 7 years 

old and the amounts of bleach ingested ranged from “1⁄2 ounce to 1 cup (ATSDR, 2002). 

With respect to dermal exposure, the ATSDR review notes that “No studies were 

located regarding respiratory, cardiovascular, gastrointestinal, hematological, 

musculoskeletal, hepatic, renal, endocrine, and body weight effects in humans or in 

animals following dermal exposure to aqueous chlorine.” However, it is known that 

dermal exposure to chlorine is extremely irritating to skin. 

 From OPP’s Incident Data System, the following information was obtained on 

chlorine gas. The reported routes of exposure for the 324 incident cases involving 

chlorine gas-specific incidents were inhalation (99.7%), ocular (38%), and dermal (10%). 

It should be noted that in many cases, more than one route of exposure applied for an 

individual incident case (e.g., inhalation and ocular). The most common symptoms 

reported for the routes of exposure are listed below: 

• Inhalation exposure ( headache (26%), difficulty breathing/shortness of breath 

(24%), sore throat/throat irritation (22%), coughing (21%), respiratory irritation 

(14%), nausea (11%), chest pain/tightness (10%), nasal irritation (8%), 
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asthma/wheezing (7%), vomiting (6%), and dizziness/lightheadedness (6%). In 

many cases more than one symptom was reported for each exposure route. 

• Ocular exposure (eye irritation/burning/pain )(100%). 

• Dermal exposure (skin irritation/burning) (100%). 

Aqueous Chlorine Related Incidents 

 The reported routes of exposure for the 17 incidence cases involving aqueous 

chlorine incidents were inhalation (59%), ingestion (29%), dermal (18%) and ocular 

(12%). It should be noted that in many cases, more than one route of exposure applied 

for an individual incident case (e.g., inhalation and dermal). The most common 

symptoms reported for the routes of exposure are listed below: 

• Inhalation exposure (difficulty breathing/shortness of breath (50%), respiratory 

irritation (30%), skin irritation/burns (30%), sore throat/throat irritation (20%), 

digestive system irritation (20%), headache (20%), coughing (20%), impaired 

cognitive ability/psychological effects (20%), nausea (6%), chest pain/tightness 

(10%), nasal irritation (10%), asthma/wheezing (10%), dizziness/lightheadedness 

(10%), and weakness (10%)). In many cases more than one symptom was 

reported for each exposure route. 

• Ingestion exposure (vomiting (100%), sore throat/throat irritation (60%), and 

digestive system irritation (20%)). 

• Dermal exposure (skin irritation/burns (100%)) 

• Ocular exposure (eye irritation/burning/pain (100%)). 

Adverse Ecological Incidents 

The Agency maintains a database system (Ecological Incident Information System or 

EIIS) to track and evaluate accidental kills associated with pesticide use. The likelihood that 

a particular pesticide caused the incident is classified as “highly probable”, “probable”, 

“possible”, or “unlikely”, based on the information contained in the incident report. A 

review of the EIIS database for ecological incidents involving chlorine (PC Code 020501) 

was completed on 05/12/2000. A summary of the results are presented below. 

For chlorine, one incident report was filed in which unknown species of fish were 

killed in a lake upon a spill of chlorine from a water treatment plant. The number of fish 

killed were unknown. The certainty index was highly probable for the incident and a 

substantial spill of chlorine will kill fish. The report was filed in 2000. 

This incident data is consistent with the available acute toxicity data indicating that 

chlorine is very highly toxic to fish. 

Endocrine Disruptor Screening Program 

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the 
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Administrator may designate.” The EDSP employs a two-tiered approach to making the 

statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to 

identify the potential of a chemical substance to interact with the estrogen, androgen, or 

thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and 

are found to have the potential to interact with E, A, or T hormonal systems will proceed 

to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests 

are necessary based on the available data. Tier 2 testing is designed to identify any 

adverse endocrine related effects caused by the substance, and establish a dose-response 

relationship between the dose and the E, A, or T effect. Between October 2009 and 

February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, 

which contains 58 pesticide active ingredients and 9 inert ingredients. This list of 

chemicals was selected based on the potential for human exposure through pathways such 

as food and water, residential activity, and certain postapplication agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors. 

Chlorine gas is not among the group of 58 pesticide active ingredients on the initial list to 

be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all 

pesticide chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data 

call-ins for all pesticide active ingredients. 

For further information on the status of the EDSP, the policies and procedures, the list of 

67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/.

IV. TIMELINE 

The EPA has created the following estimated timeline for the completion of the 

chlorine gas registration review case. The Agency anticipates requiring additional data 

and residential, occupational and ecological exposure assessments for this registration 

review case. 

Anticipated Schedule

Activities 

Estimated 

Month/Year 

Phase 1: Opening the docket 

Open Public Comment Period for Chlorine Gas Docket Completed June 2010 

Close Public Comment Period Completed August 2010

Phase 2: Case Development 

Develop Final Work Plan (FWP) Completed December 

2010 

Issue DCI November 2011 

Data Submission November 2012 

Open Public Comment Period for Preliminary Risk Assessments March 2014 

Close Public Comment Period June 2014 
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Phase 3: Registration Review Decision 

Open Public Comment Period for Proposed Reg. Review Decision September 2015 

Close Public Comment Period December 2015 

Final Decision and Begin Post-Decision Follow-up 2016 

Total (years) 6 

Next Steps

The Agency plans to develop a Data Call-In for this pesticide and expects to issue 

it in November 2011. 
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V. GLOSSARY of TERMS & ABBREVIATIONS

ai Active Ingredient 

AR Anticipated Residue 

ASTM American Society for Testing and Materials 

AWPA American Wood Preserver’s Association 

CBI Confidential Business Information 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

CSF Confidential Statement of Formula 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DFR Dislodgeable Foliar Residue 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison 

EC Emulsifiable Concentrate Formulation 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EP End use Product 

EPA Environmental Protection Agency 

EUP End-Use Product 

FDA Food and Drug Administration 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FFDCA Federal Food, Drug, and Cosmetic Act 

FQPA Food Quality Protection Act 

FOB Functional Observation Battery 

GENEEC Tier I Surface Water Computer Model 

IR Index Reservoir 

LC50 Median Lethal Concentration. A statistically derived concentration of a 

substance that can be expected to cause death in 50% of test animals. It is 

usually expressed as the weight of substance per weight or volume of water, air 

or feed, e.g., mg/l, mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be expected to 

cause death in 50% of the test animals when administered by the route indicated 

(oral, dermal, inhalation). It is expressed as a weight of substance per unit 

weight of animal, e.g., mg/kg. 

LOC Level of Concern 

LOAEL Lowest Observed Adverse Effect Level 

μg/g Micrograms Per Gram 

μg/L Micrograms Per Liter 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording and tracking 

submitted studies. 

MUP Manufacturing-Use Product 

NA Not Applicable 

NAWQA USGS National Ambient Water Quality Assessment 

NPDES National Pollutant Discharge Elimination System 

NR Not Required 

NOAEL No Observed Adverse Effect Level 

OPP EPA Office of Pesticide Programs 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 
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PAIRA Pure Active Ingredient Radiolabelled 

PCA Percent Crop Area 

PDP USDA Pesticide Data Program 

PHED Pesticide Handler's Exposure Data 

PHI Preharvest Interval 

phr Pounds Per Hundred 

ppb Parts Per Billion 

PPE Personal Protective Equipment 

ppm Parts Per Million 

PRZM/EXAMS Tier II Surface Water Computer Model 

Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer 

Risk Model 

RAC Raw Agriculture Commodity 

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RQ Risk Quotient 

RTU Ready to Use 

SCI-GROW Tier I Ground Water Computer Model 

SAP Science Advisory Panel 

SF Safety Factor 

SLN Special Local Need (Registrations Under Section 24©) of FIFRA) 

TGAI Technical Grade Active Ingredient 

TEP Typical End-Use Product 

USDA United States Department of Agriculture 

UF Uncertainty Factor 

WPS Worker Protection Standard