2 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 reco very assessment on 5/sex/group following termination of exposure.

The CMTF states that d ata from the existing five day study can be used to calculate an LC 50

.

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 wheth er further mitigation is

necessary. T he data will allow the Agency to better assess the risks to these organisms, including the likelihood of potent ial 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 teste d and not the 5

- day exposure timeframe, the number of animals te sted, 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 registratio n 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 seed ling 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 test ing 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 dicoty ledon 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 result3 from vapor moving offsite. C hloropicrin 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 a nd 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 c lean 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 Un iversity. 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 l aboratory 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 p lants 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 randomizat ion 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 t he 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 ex posure testing with terrestrial plants. C omments on the SE and VV

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

formulation.

Seedling E mergence (SE) S tudy : Based on preliminary modeling, the Agency believes that

s oil exposure of seedlings to fumigants vi a 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 soi l, as specified in EFED’s problem formulati on

. 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 V igor (VV) S tudy : 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 par ticular interest is quantification of toxicity endpoints, i.e. , a NOAEC

or EC 05 and an EC 25 that can be used to derive risk quotients for listed and non

- listed species

.4 In the submitted study, the most sensitive endpoint w as dry weight for oilseed rape. T he study author d iscounted this endpoint due to ‘ mechanical damage ’ to the plants incurred during handl ing. However, i nsufficient information was provided to determine the impact of the mechanical damage, and whether growth inhibition was also a factor. T he 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 stu dy 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 mi nimize the concerns detailed in the CMTF

comments.