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in Rats and the OCSPP guideline for Acute Avian Oral Testing. The study varies from the 

guidelines in the following ways:

1. the study utilizes 5 repeated exposures of 4 hours instead of a single 4 hour exposure;

2. 15 animals of each sex are tested instead of 5; and

3. examination of animal effects included sublethal effects such as histopathological 

examination of respiratory tissue and other internal organs on all animals, organ weight 

analysis on all animals, and a recovery assessment on 5/sex/group following termination 

of exposure.

The CMTF states that data from the existing five day study can be used to calculate an LC50.

EFED Response: The Agency requested an acute avian inhalation study for the purpose of

assessing acute risk to birds associated with the inhalation route of exposure. Results of this 

study would be used to calculate acute risk quotients for birds from exposure to chloropicrin 

and to identify whether current labeling is appropriate and whether further mitigation is 

necessary. The data will allow the Agency to better assess the risks to these organisms, 

including the likelihood of potential risks to endangered species.

As there was no mortality observed in the previously submitted study and test concentrations 

were lower than estimated environmental concentrations (EECs), the study is not particularly 

useful for risk assessment. This limitation is due to the exposure levels tested and not the 5-

day exposure timeframe, the number of animals tested, or the examination of sublethal 

effects. However, higher exposure levels may be more manageable in a study with a single 4 

hour exposure. Exposure levels in studies of acute toxicity for terrestrial animals are typically 

requested up to 10 times the EEC. The submitted study tested exposure up to 0.0044 mg/L in 

air, equal to or below previously calculated EECs. Maximum EECs in air calculated for 

previous ecological risk assessments were 0.019 mg/L using the Industrial Source Complex: 

Short-Term Model (ISCTS3) with a 24-hour time-weighted average and 0.0042 mg/L using 

the Probabilistic Exposure and Risk model for Fumigants (PERFUM) with a 4-hour 

averaging period. For the registration review risk assessment, the PERFUM model will be 

used to generate EECs using the most recent flux data obtained from field volatility studies.

CMTF Comment 2: Seedling Emergence and Vegetative Vigor Studies

In response to the Agency’s request for a seedling emergence (SE) guideline study and for 

testing of additional species in a vegetative vigor (VV) vapor exposure study, the CMTF 

provided additional details on the previously submitted studies (MRID 48442802). These studies 

used vapor exposure for both SE and VV assessment and were designed to closely follow 

relevant OECD guidelines and, to the extent possible, OCSPP testing guidelines. 

The guidelines for SE and VV studies require 10 plant species to be tested. Five dose levels are 

to be used, and testing is to be performed in a greenhouse or small field. The submitted studies 

were performed with 6 plant species instead of 10 and 3 treatment levels instead of 5. The test 

species did include corn and soybean, but not a root crop. Monocotyledon and dicotyledon 

species were included.

Chloropicrin is applied directly into the soil of fallow fields, so nontarget plants will only be 

found offsite of the chloropicrin application. Exposure to those nontarget plants could only result 
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from vapor moving offsite. Chloropicrin field application studies demonstrate that peak offsite 

vapor exposure occurs during a 12 hour window following initiation of treatment. 

Controlled vapor exposures are only possible in dynamic inhalation chambers and the scope of 

the work was limited by the availability of large inhalation chambers. Chambers with a 2000 liter 

capacity, the largest available, were used and these chambers could accommodate only 6 plant 

species given required number of replicates. An effect and a no-effect level were generated in the 

study for seedling and plants exposed to chloropicrin vapor for 6 hours per day on 2 consecutive 

days. Pilot chamber studies showed that control plants exposed to an airflow for more than 6 

hours per day of only clean air developed deleterious leaf drying.

A modified Horsfall and Barratt rating scale was used to assess plant damage or phytotoxicity. 

The work was conducted under the direction of Dr. Daniel Voltz, Associate Professor of 

Horticulture at Ohio State University. EPA noted mechanical damage to plants identified in the 

report and had questions regarding the damage. As envisioned in the OCSPP and OECD 

guidelines, vegetative vigor and seedling emergence studies are greenhouse or field studies. They 

are not laboratory studies and are not dynamic inhalation chamber studies. Standard care and 

observation of treated and control plants pre- and especially post-exposure appeared to have a 

greater impact on plant growth and vigor than chloropicrin vapor. Since the plants could not be 

watered or observed while in the chamber, transfer of all plants into and out of the exposure 

chambers was necessary. This transfer of plants into and out of the chambers and into controlled 

environment growth rooms as well as randomization of individual pot location within the 

chamber took a toll on plant structure. Of great interest was the observation (in pilot studies) that 

the constant flow of clean, humidified air over untreated plants produced signs of pathology 

(chlorosis). Even the minimum air flow necessary to deliver and distribute the lowest 

concentration of chloropicrin within the chamber was detrimental to vegetation.

EFED Response: The Agency appreciates the additional details regarding study design and 

conduct for vapor exposure testing with terrestrial plants. Comments on the SE and VV 

studies are addressed separately below, based on the data needs identified in the problem 

formulation.

Seedling Emergence (SE) Study: Based on preliminary modeling, the Agency believes that

soil exposure of seedlings to fumigants via runoff is a potential concern for non-tarped 

applications. Therefore, the Agency is requesting a guideline SE study with application of 

chloropicrin directly to the soil, as specified in EFED’s problem formulation. Registrants are 

encouraged to contact the Agency with any questions or concerns regarding the test protocol

prior to study initiation. No SE toxicity data using vapor exposure is requested.

Vegetative Vigor (VV) Study: The Agency concurs that vapor exposure is the primary 

exposure pathway of concern for vegetative vigor of terrestrial plants. Data from a VV vapor 

exposure study will be used to determine the potential for chloropicrin to affect non-target 

terrestrial plants. Of particular interest is quantification of toxicity endpoints, i.e., a NOAEC 

or EC05 and an EC25 that can be used to derive risk quotients for listed and non-listed 

species. 
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In the submitted study, the most sensitive endpoint was dry weight for oilseed rape. The 

study author discounted this endpoint due to ‘mechanical damage’ to the plants incurred 

during handling. However, insufficient information was provided to determine the impact of 

the mechanical damage, and whether growth inhibition was also a factor. The data followed a 

clear dose-response pattern. Because these effects were seen at the lowest concentration 

tested and these effects may have been due to handling rather than chloropicrin toxicity, 

EFED recommends that oilseed rape be retested in a new study along with the additional two 

monocot and two dicot species requested to complete the requirement for a VV study. 

Registrants are encouraged to contact the Agency with any questions or concerns regarding 

the test protocol prior to study initiation to minimize the concerns detailed in the CMTF 

comments.