![](media/image1.wmf){width="1.3541666666666667in"
height="1.3541666666666667in"}

**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

WASHINGTON D.C., 20460

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

**PC Code:** 018101

> **DP Barcodes:** D336717

**Date**: March 19, 2007

**[MEMORANDUM]{.underline}**

**SUBJECT:** Tier I Drinking Water Assessment for Chlormequat Chloride
in Support of Reregistration Eligibility Decision

**TO:** Tracy Perry, Chemical Risk Manager

Special Review Branch

Special Review and Reregistration Division

Elissa Reaves, Risk Assessor

Donald Wilbur, Risk Assessor

Reregistration Branch II

Health Effects Division

**FROM:** Marietta Echeverria, Environmental Scientist

Environmental Risk Branch IV

Environmental Fate and Effects Division

**THROUGH:** R. David Jones, Ph.D., Senior Agronomist

Environmental Risk Branch IV

Environmental Fate and Effects Division

**APPROVED**

**BY:** Elizabeth Behl, Branch Chief

Environmental Risk Branch IV

Environmental Fate and Effects Division

Attached is the drinking water exposure assessment for chlormequat
chloride in support of the reregistration eligibility decision (RED).
This assessment considers all registered outdoor uses including bedding
plants and ornamentals in shadehouses and nurseries. If additional
refinements are necessary, please contact Marietta Echeverria at
703-305-8578 or echeverria.marietta@epa.gov.

**Tier I Drinking Water Exposure Assessment for the Reregistration
Eligibility Decision (RED) for Chlormequat Chloride**

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**Chlormequat Chloride \[2-chloroethyltrimethyl ammonium chloride\]**

**CAS No. 000999-81-5**

+---------------------------------------+------------------------------+
| *Prepared by:*                        |                              |
+---------------------------------------+------------------------------+
| Marietta Echeverria, Environmental    | U. S. Environmental          |
| Scientist                             | Protection Agency            |
|                                       |                              |
| Environmental Risk Branch IV          | Office of Pesticide Programs |
|                                       |                              |
|                                       | Environmental Fate and       |
|                                       | Effects Division             |
|                                       |                              |
|                                       | Environmental Risk Branch IV |
|                                       |                              |
|                                       | 1200 Pennsylvania Ave., NW   |
|                                       |                              |
|                                       | Mail Code 7507P              |
|                                       |                              |
|                                       | Washington, DC 20460         |
+---------------------------------------+------------------------------+
| *Reviewed by:*                        |                              |
|                                       |                              |
| R. David Jones, Ph.D, Senior          |                              |
| Agronomist                            |                              |
|                                       |                              |
| Elizabeth Behl, Branch Chief          |                              |
|                                       |                              |
| Environmental Risk Branch IV          |                              |
|                                       |                              |
| Environmental Fate and Effects        |                              |
| Division                              |                              |
+---------------------------------------+------------------------------+

# Executive Summary

This document reports the drinking water exposure assessment for
2-chloroethyltrimethyl ammonium chloride (chlormequat chloride) that has
been conducted to support the human health risk assessment for the
rergistration eligibility decision (RED). Chlormequat chloride is a
plant growth regulator used on bedding plants and containerized
ornamentals in greenhouses, shadehouses, and nurseries. Foliar spray
applications and drench applications (greenhouse uses only) are allowed
on the label. Tier 1 surface water and groundwater modeling was
conducted for the labeled shadehouse or container nursery use (EPA Reg.
No. 241-74), which represents the highest use rate of all labeled uses
with an annual application rate of 33.3 lbs. a.i./A/year. The
recommended estimated drinking water concentrations (EDWCs) for the
human health risk assessment are in Table 1. There were no identified
major degradates of chlormequat chloride in the laboratory studies.
However, all transformation products greater than 10% of the applied may
not have been identified in the aerobic soil and aerobic aquatic
metabolism studies.

  -----------------------------------------------------------------------
  **Table 1. Tier I EDWCs for chlormequat chloride for ground boom spray
  applications (EPA Reg. No. 241-74)**
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

+--------------------------+---------------------+---------------------+
| Drinking Water Source    | Use rate (lbs       | EDWC (ppb)          |
| (Model)                  | ai/A/year)          |                     |
+--------------------------+---------------------+---------------------+
| **Surface water          | 33.3                | 2574                |
| (FIRST)**                |                     |                     |
|                          |                     | 91                  |
| \- Acute (peak)          |                     |                     |
|                          |                     |                     |
| \- Chronic (annual mean) |                     |                     |
+--------------------------+---------------------+---------------------+
| **Groundwater            | 33.3                | 24                  |
| (SCI-GROW)**             |                     |                     |
+--------------------------+---------------------+---------------------+

# Problem Formulation

This is a Tier I drinking water assessment that uses modeling and
available monitoring data to estimate the groundwater and surface water
concentrations in drinking water sources (pre-treatment) resulting from
pesticide use on sites that are vulnerable. This initial tier screens
out chemicals with low potential risk and allows OPP to focus resources
on more refined risk assessments for chemicals which potentially present
more significant risks. This drinking water assessment reports potential
exposure concentrations for the human health dietary risk assessment and
provides a description of how those concentrations were determined.

## Previous Assessments

EFED completed a Tier I drinking water assessment for the only
registered outdoor use of chlormequat chloride (on ornamentals and
bedding plants in nurseries and shadehouses) in August 2006 (018101
D322925 DWA). This assessment relies on the previous assessment. During
the registration process the maximum use pattern decreased from 49.5 lbs
ai/A/year to 33.3 lbs ai/A/year. This assessment is based on the maximum
rate of the registered uses of Cycocel® (EPA Reg. No. 241-74; 33.3 lbs
ai/A/year). The previous assessment only considered exposure to parent
chlormequat chloride. However, since there were unidentified residues in
the metabolism studies that may be of risk concern, a total toxic
residue approach that assumes all uncharacterized extractable residues
are of equal toxicity to chlormequat chloride was used to estimate
exposure in the current assessment. This results in an increase in
aerobic soil metabolism half-life of \~200% for surface water modeling
and \~27% for groundwater modeling.

# Analysis

## Use Characterization

Chlormequat chloride is a plant growth regulator (PGR) for use on
bedding plants and containerized ornamentals in greenhouses,
shadehouses, and nurseries as the formulated product Cycocel® (EPA Reg.
No. 241-74). In open production areas not under cover, Cycocel® use is
restricted to containerized ornamentals only. Application to field-grown
ornamentals is not allowed by the label. The label allows foliar spray
applications and drench applications. Drench applications are only
allowed for the indoor greenhouse uses. This assessment does not
consider the indoor greenhouse uses because environmental exposures are
expected to be limited to greenhouse discharge which is regulated under
the National Pollutant Discharge Elimination System (NPDES).

For the outdoor (shadehouse and nursery) uses, spray volume providing
thorough plant coverage will vary with plant size and foliage coverage
and application rates will vary according specific crop type. However,
the label states that a single application cannot exceed a rate of 3.7
lbs. ai/A, and the total annual rate can not exceed 33.3 lbs ai/A/year.
The label also limits the number of applications to 3 per crop cycle.
For this assessment, 3 production cycles per year are assumed, resulting
in a maximum of 9 applications per year. The interval between repeat
applications to the same crop can range from 5 to 21 days. Table 2
summarizes the maximum application rates used in this assessment.

  --------------- --------------- ------------- ------------- -------------
  **Table 2.                                                  
  Maximum use                                                 
  patterns for                                                
  Cycocel on                                                  
  bedding plants                                              
  and                                                         
  containerized                                               
  ornamentals**                                               

  **Uses**        **App. type**   **Max app.    **Max \# of   **Min app.
                                  Rate (lbs     app./ year**  Interval
                                  ai/A)**                     (days)**

  Bedding plants, Foliar spray;   3.7           9             5
  containerized   mechanized                                  
  ornamentals     ground boom                                 
                  sprayer                                     
  --------------- --------------- ------------- ------------- -------------

## Environmental Fate and Transport Characterization

There are a number of data gaps in the chlormequat chloride
environmental fate and transport dataset. In the absence of data,
assumptions made regarding chlormequat chloride were compared to and
supported by the environmental fate and transport data of
didecyl-dimethylammonium chloride (DDAC, PC code 69149, CAS No.
007173-51-5). DDAC and chlormequat chloride are both quaternary ammonium
compounds that have been classified according to the Agency's PR Notice
88-2 (February 26, 1988) as Group I, alkyl or hydroxyalkyl (straight
chain) substituted quaternary ammonium compounds.

Chlormequat chloride has variable mobility in the environment. Batch
equilibrium studies resulted in Freundlich sorption coefficients ranging
1.13 -- 9.12 ml/g with corresponding 1/N values ranging 0.511 -- 0.955
(MRIDs 46715228, 46715229). Even though chlormequat chloride is a
cation, the correlation between cation exchange capacity (CEC) and
sorption was not significant in the batch equilibrium studies. In a
*supplemental* aged column leaching study 0.3-0.5 % of the applied
radioactivity was found in the leachate after 48 hours of leaching with
4 pore volumes of 0.01 M CaCl~2~ in a loamy sand soil (MRID 46715230).
In another *supplemental* aged column leaching study 2.5% of the applied
radioactivity was found in the leachate following 45 days of leaching
with 0.5 inches of distilled water daily through a 15 inch column filled
with a clay loam soil (MRID 124061). In a *supplemental* unaged column
leaching study \< 0.1 % of applied radioactivity was found in the
leachate after leaching with 20 inches of distilled water at a rate not
exceeding 1 inch/hour through a 15 inch column filled with a sand, sandy
loam, silt loam and clay loam soil (MRID 124062). In both of these
studies distilled water was used which could lead to dispersion of clays
that could affect soil structure.

Depending on soil, site and meteorological conditions chlormequat
chloride may be transported off-site via runoff, leaching and/or
erosion.

Overall, the major route of dissipation for chlormequat chloride appears
to be microbial degradation. A *supplemental* aerobic soil metabolism
study showed that chlormequat chloride degraded with half-lives of 30-43
days in two sandy loam and two silt loam soils (MRID 46715225). In the
study, up to 43.7% and 10.7% of the applied radioactivity in the soil
extracts was unaccounted for in two soils. No attempt was made to
identify these transformation products and it is not known whether or
not the residues consisted of one or more components. Consequently, all
transformation products detected at \>10% of the applied may not have
been identified. Using a total residue approach that assumes all
uncharacterized extractable residues are of equal toxicity to
chlormequat chloride results in half-lives of 32 -- 132 days. A
*supplemental* aerobic aquatic metabolism study showed that chlormequat
chloride degraded with total system half-lives of 5-9 days in a river
water-sandy loam sediment and pond water-silt loam sediment system (MRID
46715227). There were no available acceptable data for degradation of
chlormequat chloride by hydrolysis or photolysis. Comparison to DDAC
data, however, suggests that chlormequat chloride may be hydrolytically
and photolytically stable (MRID 411758-01, 411758-02). There are also no
data for chlormequat chloride under anaerobic conditions. DDAC has,
however, been shown to be persistent under anaerobic conditions (MRID
422538-02). **Table 3** summarizes the registrant-submitted
environmental fate and transport properties of chlormequat chloride.

Major degradates (excluding CO~2~) were not identified in the available
metabolism studies. In the aerobic aquatic metabolism study, an
unidentified polar compound reached a maximum of 4.8 and 13.4 % in the
total systems. Choline-chloride was also detected in the aerobic aquatic
metabolism study at a maximum of 2.0 and 5.5% in the total systems.

+---------------------+----------+----+----+----+-------------------+
| **Table 3. Summary  |          |    |    |    |                   |
| of environmental    |          |    |    |    |                   |
| chemistry and fate  |          |    |    |    |                   |
| properties of       |          |    |    |    |                   |
| chlormequat         |          |    |    |    |                   |
| chloride**          |          |    |    |    |                   |
+=====================+==========+====+====+====+===================+
| **Parameter**       | *        |    |    |    | **Ref             |
|                     | *Value** |    |    |    | erence/Comments** |
+---------------------+----------+----+----+----+-------------------+
| ***Selected         |          |    |    |    |                   |
| Physical/Chemical   |          |    |    |    |                   |
| Parameters***       |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| PC code             | 018101   |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| CAS No.             | 999-81-5 |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Physical state      | Liquid   |    |    |    | Product chemistry |
+---------------------+----------+----+----+----+-------------------+
| Chemical name       | 2-       |    |    |    | Product chemistry |
|                     | chloro-N |    |    |    |                   |
|                     | ,N,N-tri |    |    |    |                   |
|                     | methylet |    |    |    |                   |
|                     | hylethan |    |    |    |                   |
|                     | ammonium |    |    |    |                   |
|                     | chloride |    |    |    |                   |
|                     | salt     |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Chemical formula    | C~5~H~1  |    |    |    | Product chemistry |
|                     | 3~Cl~2~N |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Molecular weight    | 158.1    |    |    |    | Product chemistry |
|                     | g/mol    |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Water solubility    | 10^6^    |    |    |    | Product chemistry |
|                     | mg/L     |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Density             | 1.14     |    |    |    | Product chemistry |
|                     | g/mL     |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Boiling point       | Not      |    |    |    | Product chemistry |
|                     | reported |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Vapor pressure (20  | 7.5 x    |    |    |    | Product chemistry |
| °C)                 | 10^-8^   |    |    |    |                   |
|                     | mm Hg    |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| log K~OW~           | 2.51     |    |    |    | Product chemistry |
+---------------------+----------+----+----+----+-------------------+
| ***Persistence***   |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Hydrolysis t~1/2~   |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| pH 5                | No data  |    |    |    | Likely stable per |
|                     |          |    |    |    | comparison to     |
| pH 7                |          |    |    |    | DDAC (MRID        |
|                     |          |    |    |    | 411758-01)        |
| pH 9                |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Photolysis t~1/2~in | No data  |    |    |    | Likely stable per |
| water               |          |    |    |    | comparison to     |
|                     |          |    |    |    | DDAC (MRID        |
|                     |          |    |    |    | 411758-02)        |
+---------------------+----------+----+----+----+-------------------+
| Photolysis t~1/2~   | No data  |    |    |    | Likely stable per |
| in soil             |          |    |    |    | comparison to     |
|                     |          |    |    |    | DDAC (MRID        |
|                     |          |    |    |    | 411758-02)        |
+---------------------+----------+----+----+----+-------------------+
| Soil metabolism     | 43.4,    |    |    |    | MRID 46715225     |
| aerobic t~1/2~      | 29.7,    |    |    |    |                   |
|                     | 31.5,    |    |    |    |                   |
| \[Total             | 43.0 d   |    |    |    |                   |
| residues\]^1^       |          |    |    |    |                   |
|                     | \[43.4,  |    |    |    |                   |
|                     | 32.9,    |    |    |    |                   |
|                     | 36.3,    |    |    |    |                   |
|                     | 132.3    |    |    |    |                   |
|                     | d\]      |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Soil metabolism     | No data  |    |    |    | Likely stable per |
| anaerobic t~1/2~    |          |    |    |    | comparison to     |
|                     |          |    |    |    | DDAC (MRID        |
|                     |          |    |    |    | 422538-02)        |
+---------------------+----------+----+----+----+-------------------+
| Aquatic metabolism  | 4.9, 8.7 |    |    |    | MRID 46715227     |
| aerobic t~1/2~      | d        |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Aquatic metabolism  | No data  |    |    |    | Likely stable per |
| anaerobic t~1/2~    |          |    |    |    | comparison to     |
|                     |          |    |    |    | DDAC (MRID        |
|                     |          |    |    |    | 422538-02)        |
+---------------------+----------+----+----+----+-------------------+
| ***Mobility***      |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Batch equilibrium   | Soil     | K  | 1  | K~ | MRIDs 46715228,   |
|                     | Type     | ~f | /N | oc | 46715229          |
|                     |          | ~^ |    | ~^ |                   |
|                     |          | 2^ |    | 3^ |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Loamy    | 1. | 0  | 55 |                   |
|                     | sand     | 25 | .5 |    |                   |
|                     |          |    | 11 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Sandy    | 4. | 0  | 2  |                   |
|                     | loam     | 57 | .6 | 91 |                   |
|                     |          |    | 91 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Silt     | 1. | 0  | 81 |                   |
|                     | loam     | 13 | .7 |    |                   |
|                     |          |    | 02 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Sand     | 1. | 0  | 93 |                   |
|                     |          | 73 | .5 |    |                   |
|                     |          |    | 43 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Sandy    | 2. | 0  | 89 |                   |
|                     | loam     | 14 | .7 |    |                   |
|                     |          |    | 68 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Loam     | 9. | 0  | 9  |                   |
|                     |          | 12 | .8 | 12 |                   |
|                     |          |    | 49 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     | Silt     | 8. | 0  | 3  |                   |
|                     | loam     | 08 | .9 | 85 |                   |
|                     |          |    | 55 |    |                   |
+---------------------+----------+----+----+----+-------------------+
|                     |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Column leaching --  | 0.3-0.5  |    |    |    | MRIDs 46715230,   |
| aged residues       | %        |    |    |    | 124061            |
|                     | applied  |    |    |    |                   |
|                     | radio    |    |    |    |                   |
|                     | activity |    |    |    |                   |
|                     | in       |    |    |    |                   |
|                     | leachate |    |    |    |                   |
|                     | after 48 |    |    |    |                   |
|                     | hours of |    |    |    |                   |
|                     | leaching |    |    |    |                   |
|                     | with 4   |    |    |    |                   |
|                     | pore     |    |    |    |                   |
|                     | volumes  |    |    |    |                   |
|                     | of 0.01  |    |    |    |                   |
|                     | M        |    |    |    |                   |
|                     | CaCl~2~  |    |    |    |                   |
|                     | in a     |    |    |    |                   |
|                     | loamy    |    |    |    |                   |
|                     | sand     |    |    |    |                   |
|                     | soil;    |    |    |    |                   |
|                     |          |    |    |    |                   |
|                     | 2.5% of  |    |    |    |                   |
|                     | applied  |    |    |    |                   |
|                     | radio    |    |    |    |                   |
|                     | activity |    |    |    |                   |
|                     | in       |    |    |    |                   |
|                     | leachate |    |    |    |                   |
|                     | f        |    |    |    |                   |
|                     | ollowing |    |    |    |                   |
|                     | 45 days  |    |    |    |                   |
|                     | of       |    |    |    |                   |
|                     | leaching |    |    |    |                   |
|                     | with 0.5 |    |    |    |                   |
|                     | acr      |    |    |    |                   |
|                     | e-inches |    |    |    |                   |
|                     | of       |    |    |    |                   |
|                     | d        |    |    |    |                   |
|                     | istilled |    |    |    |                   |
|                     | water    |    |    |    |                   |
|                     | daily in |    |    |    |                   |
|                     | a clay   |    |    |    |                   |
|                     | loam     |    |    |    |                   |
|                     | soil;    |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Column leaching -   | \< 0.1 % |    |    |    | MRID 124062       |
| unaged              | of       |    |    |    |                   |
|                     | applied  |    |    |    |                   |
|                     | radio    |    |    |    |                   |
|                     | activity |    |    |    |                   |
|                     | in       |    |    |    |                   |
|                     | leachate |    |    |    |                   |
|                     | after    |    |    |    |                   |
|                     | leaching |    |    |    |                   |
|                     | with 20  |    |    |    |                   |
|                     | acr      |    |    |    |                   |
|                     | e-inches |    |    |    |                   |
|                     | of       |    |    |    |                   |
|                     | d        |    |    |    |                   |
|                     | istilled |    |    |    |                   |
|                     | water at |    |    |    |                   |
|                     | a rate   |    |    |    |                   |
|                     | \< 1     |    |    |    |                   |
|                     | inch/hr  |    |    |    |                   |
|                     | in a     |    |    |    |                   |
|                     | sand,    |    |    |    |                   |
|                     | sandy    |    |    |    |                   |
|                     | loam,    |    |    |    |                   |
|                     | silt     |    |    |    |                   |
|                     | loam and |    |    |    |                   |
|                     | clay     |    |    |    |                   |
|                     | loam     |    |    |    |                   |
|                     | soil.    |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Laboratory          | NA       |    |    |    |                   |
| volatility          |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| ***Field            |          |    |    |    |                   |
| Dissipation***      |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Terrestrial field   | No data  |    |    |    |                   |
| dissipation         |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Aquatic field       | NA       |    |    |    |                   |
| dissipation         |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| **                  |          |    |    |    |                   |
| *Bioaccumulation*** |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+
| Accumulation in     | No data  |    |    |    |                   |
| fish, BCF           |          |    |    |    |                   |
+---------------------+----------+----+----+----+-------------------+

1\. Total residue approach assumes uncharacterized extractable residues
are of similar toxicity as parent chlormequat chloride.

2\. Units of (mg/kg)/(mg/L)^1/N^, where 1/N is the Freundlich exponent.

3\. Approximation calculated from the Freundlich coefficient, per
standard EFED guidance.

## Drinking Water Exposure Modeling

Tier 1 modeling was used to estimate the drinking water exposure for use
in the dietary risk assessment of chlormequat chloride. The following is
a description of the models used, the selection of the model input
parameters, and a characterization of the output from these simulations.

### Models

Tier 1 EDWCs for surface water were generated using FIRST, dated August
5, 2001. FIRST is a screening model designed by the Environmental Fate
and Effects Division (EFED, 2001a) of the Office of Pesticide Programs
to estimate the concentrations found in drinking water from surface
water sources for use in human health risk assessment. As such, it
provides upper bound values on the concentrations that might be found in
drinking water due to the use of a pesticide. FIRST is a single-event
model (one runoff event), but can account for spray drift from multiple
applications. FIRST is hardwired to represent the Index Reservoir, a
standard water body used by the Office of Pesticide Programs to assess
drinking water exposure (Office of Pesticide Programs, 2002). It is
based on a real reservoir, Shipman City Lake in Illinois, which is known
to be vulnerable to pesticide contamination. The single runoff event
moves a maximum of 8% of the applied pesticide into the reservoir. This
amount can be reduced due to degradation on the field and the effects of
binding to soil in the field. FIRST also uses a Percent Cropped Area
(PCA) factor to adjust for the area within the watershed that is planted
to the modeled crop. A PCA of unity (the most protective) was applied in
this assessment because there is no PCA for nurseries and shadehouses
and these uses are not included in the "all agricultural land"
classification on which the default PCA of 0.87 was based.

Tier 1 EDWCs for groundwater were generated with SCIGROW 2.3, dated July
29, 2003 (EFED, 2001b). SCIGROW is a regression model used as a
screening tool for ground water used as drinking water. SCIGROW was
developed by regressing the results of Prospective Ground Water studies
against the Relative Index of Leaching Potential (RILP). The RILP is
function of aerobic soil metabolism and the soil-water partition
coefficient. The output of SCIGROW represents the concentrations that
might be expected in shallow unconfined aquifers under sandy soils.

### Modeling Approach and Input Parameters

Tables 4 and 5 summarize the model input parameter values used in FIRST
and SCIGROW, respectively. These parameters were selected in accordance
with EFED's input parameter guidance (Environmental Fate and Effects
Division, 2002).

*For the surface water and groundwater assessments, the maximum
application rate, 3.7 lb a.i./A/application, was used and the maximum
number of applications per year was assumed to be 9 (3 applications per
crop cycle and 3 crop cycles per year). Based on registrant-submitted
data for chlormequat chloride, an aerobic soil metabolism and aerobic
aquatic metabolism half-life of 100 and 12.6 d (the upper 90th
percentile confidence bound on the mean) was used for surface water
modeling with FIRST. It was assumed that chlormequat chloride was stable
to photolysis. For groundwater modeling with SCIGROW, the median of the
four values, 39.9 d, was used as the aerobic soil metabolism input. The
soil-water partitioning coefficient used in FIRST and SCIGROW was 1.1
ml/g and 55 ml/g~oc~, respectively, the lowest non-sand K~d~/K~oc~ of
seven values. The lowest K~oc~ value was used in SCIGROW because there
was greater than 3-fold variability in the available data.*

  -----------------------------------------------------------------------------
  **Table 4. FIRST (v                                  
  1.0) input parameter                                 
  values for chlormequat                               
  chloride applied by                                  
  ground boom spray**                                  
  ----------------------- ----------- ---------------- ------------------------
  **Parameter**           **Value**   **Source**       **Comments**

  Application Rate (lb    3.7         EPA Reg. No.     
  a.i./A)                             241-74           

  Number of Applications  9           EPA Reg. No.     
                                      241-74           

  Interval between        5           EPA Reg. No.     
  Applications (d)                    241-74           

  Soil Partitioning       1.1         MRIDs 46715228,  lowest non-sand value
  Coefficient (K~d~;                  46715229         
  ml/g)                                                

  Aerobic Soil Metabolism 100         MRID 46715225    90^th^ percentile upper
  t~1/2~ (d)                                           confidence bound on the
                                                       mean (43.4, 32.9, 36.3,
                                                       132.3 d) based on total
                                                       residues^1^

  Wetted in?              No          foliar applied   

  Depth of Incorporation  0           foliar applied   
  (inches)                                             

  Method of Application   ground      EPA Reg. No.     
                          spray       241-74           

  Percent Cropped Area    1           Most protective  No PCA for nurseries

  Solubility in Water     10^6^       Product          
  (mg/L)                              chemistry data   

  Aerobic Aquatic         12.6        MRID 46715227    90^th^ percentile upper
  Metabolism t~1/2~ (d)                                confidence bound on the
                                                       mean (4.9, 8.7 d)

  Aquatic Photolysis      0           \--              Assumed stable to
  t~1/2~ (d)                                           photolysis (no data)
  -----------------------------------------------------------------------------

1\. Total residue approach assumes all unidentified extractable residues
are of similar toxicity to parent chlormequat chloride.

  --------------------------------------------------------------------------
  **Table 5. SCIGROW 2.3                                   
  input parameter values                                   
  for chlormequat                                          
  chloride applied by                                      
  ground boom.**                                           
  ---------------------- ----------- --------------------- -----------------
  **Parameter**          **Value**   **Source**            **Comments**

  Maximum Application    3.7         EPA Reg. No. 241-74   
  Rate (lb                                                 
  a.i./A/application)                                      

  Maximum Number of      9           EPA Reg. No. 241-74   
  Applications per Year                                    

  Aerobic Soil           39.9        MRID 46715225         median values
  Metabolism Half-life                                     (43.4, 32.9,
  (days)                                                   36.3, 132.3 d)
                                                           based on total
                                                           residues^1^

  Organic Carbon         55          MRID 46715228,        lowest value; \>
  Partition Coefficient              46715229              3-fold
  (K~oc~, ml/g~oc~)                                        variability in
                                                           K~oc~ data
  --------------------------------------------------------------------------

1\. Total residue approach assumes all unidentified extractable residues
are of similar toxicity to parent chlormequat chloride.

### Modeling Results

The FIRST and SCI-GROW output files are located in Appendix A. Based on
the results of these simulations, EFED recommends an acute surface water
EDWC of **2574 µg/L** and a chronic EDWC of **91 µg/L** for use in the
human health risk assessment. These recommendations are based on the use
of chlormequat chloride to ornamentals in nurseries or shadehouses at an
annual application rate of 33.3 lb a.i./A/year. The recommended EWDC for
groundwater is **23.6 µg/L** and is also based on the use of chlormequat
chloride to ornamentals in shadehouses and nurseries at the previously
stated rate.

## Monitoring Data

There were no national-scale monitoring data available for this
assessment.

## Drinking Water Treatment

There is no available information on the drinking water treatment
effects on chlormequat chloride.

# conclusions

The estimated concentrations provided in this assessment were generated
from Tier 1 models and are conservative estimates of chlormequat
chloride concentrations in untreated drinking water. Major sources of
uncertainty include the inadequate identification of degradates in the
metabolism studies, assumptions regarding application intervals, the
appropriate PCA for nursery/shadehouse ornamentals, and the
applicability of the standard Tier 1 models to the nursery/shadehouse
use.

In the aerobic soil and aerobic aquatic metabolism studies all
transformation products greater than 10% of the applied may not have
been identified. A total residue approach, which conservatively assumed
that all unidentified extractable residues are of similar toxicity to
parent chlormequat chloride, was used for modeling.

The application interval was assumed to be 5 days (which is the minimum
permitted by the label) for all 9 applications. Since there are only 3
allowed applications per crop cycle, it is likely that the interval
between applications of subsequent crop cycles will be greater than 5
days, and thus the 5-day interval was likely a protective assumption.
Also, since there is no standard PCA for nurseries/shadehouses, this
assessment is based on the assumption that an entire 178-ha watershed
consists of containerized nursery/shadehouse ornamentals all of which
are treated simultaneously with chlormequat chloride, again a likely
conservative assumption. Finally, the standard Tier 1 models used in
this assessment were developed to simulate pesticide applications in
open agricultural fields and not specifically for containerized
ornamentals in nurseries/shadehouses. The impact of rainfall and
corresponding pesticide transport is likely dampened due to the use of
containers and/or shade covers relative to open agricultural fields,
which also leads to a protective assessment.

If dietary risks require refinement, higher tiered models and modeling
scenarios can be utilized upon request.

**Appendix A: Input/Output Modeling Files**

**FIRST File**

RUN No. 1 FOR chlormequat chlo ON nurseries \* INPUT VALUES \*

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

3.700( 29.106) 9 5 1.1\*\*\*\*\*\*\* GROUND( 6.4) 100.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

100.00 2 N/A .00- .00 12.60 12.60

UNTREATED WATER CONC (MILLIGRAMS/LITER (PPM)) Ver 1.1.0 DEC 12, 2005

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONCENTRATION

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

2.574 .091

**SCIGROW File**

SCIGROW

VERSION 2.3

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL

FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:chormequat chloride

time is 3/ 9/2007 12:43:57

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

3.700 9.0 33.300 5.50E+01 39.9

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

groundwater screening cond (ppb) = 2.36E+01

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

**References**

Environmental Fate and Effects Division. 2001a. FIRST (F)IFRA (I)ndex
(R)eservoir (S)creening (T)ool. Tier 1 Model for Drinking Water
Exposure: User\'s Manual.
<http://www.epa.gov/oppefed1/models/water/first_users_manual.htm>

Environmental Fate and Effects Division. 2001b. SCI-GROW - (S)creening
(C)oncentration (I)n (GRO)und (W)ater: User\'s Manual.
<http://www.epa.gov/oppefed1/models/water/scigrow_users_manual.htm>

Environmental Fate and Effects Division. 2002. Guidance for Selecting
Input Parameters in Modeling the Environmental Fate and Transport of
Pesticides, Version II. U. S. Environmental Protection Agency.
Washington, D.C. [http://www.epa.gov/oppefed1/models
water/input_guidance2_28_02.htm/](http://www.epa.gov/oppefed1/models/)

Office of Pesticide Programs. 2000. Part A. Guidance for Use of the
Index Reservoir in Drinking Water Assessments.
<http://www.epa.gov/oppfead1/trac/science/reservoir.pdf>