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**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

WASHINGTON D.C., 20460

> OFFICE OF
>
> PREVENTION, PESTICIDES AND
>
> TOXIC SUBSTANCES

**PC Code:** 031301

> **DP Barcodes:** D294452

**Date**: 24 January 2006

**[MEMORANDUM]{.underline}**

**SUBJECT:** **DCNA (Dicloran):** Revised Tier I Drinking Water EDWC's
for Use in the Human Health Risk Assessment.

**TO:** Christine Olinger, Chemist

RRBI/HED (7509C)

**FROM:** Cheryl A. Sutton, Ph.D., Environmental Scientist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507C)

**APPROVED**

**BY:** Elizabeth Behl, Branch Chief

ERB IV/EFED (7507C)

This memo summarizes the revised Tier I estimated drinking water
concentrations (EDWC) for DCNA in surface water for use in the human
health risk assessment. The revision is due to the submission of new
aerobic aquatic metabolism data by the registrant. The EDWC's are
summarized in **Table 1**. EFED used the screening model FIRST (FQPA
Index Reservoir Screening Tool) to calculate the surface water EDWC. The
groundwater EDWC (1.3 ug/L ppb) reported in the initial DWA has not
changed. Both surface water (acute and chronic) and groundwater EDWC's
are based on DCNA use on apricots at 4.0 lb a.i./A/application applied
in a single application.

**Table 1. Tier I surface water EDWCs for DCNA for the drinking water
assessment.**

+-----------------------------------+-----------------------------------+
| Surface water drinking water      | 1-in-10-year acute: 172.8 ug/L    |
| sources                           | (ppb)                             |
|                                   |                                   |
|                                   | 1-in-10-year chronic: 1.8 ug/L    |
|                                   | (ppb)                             |
+-----------------------------------+-----------------------------------+

An additional degradate, **2,6-dicholorbenzoic acid (DCBA)**, was
identified in the newly submitted aerobic aquatic metabolism study at
maximum concentrations of 9.2-9.3% of the applied in the water phase (7
days) and 3.3-5.8% of the applied in the sediment phase (14 days). By
study termination, DCBA had decreased to 1.0-1.7% of the applied in the
water phase. There were no major degradates of DCNA detected in the
previously reviewed laboratory studies (i.e. none accounted for as much
as 10% of radioactivity measured at any point in the studies), with the
exception of the transformed chemical present as nonextractable
residues. The minor degradates of DCNA expected in the environment are:
2,6-dichloro-p-phenylenediamine (DCPD); 4-amino-3,5-dichloroacetanilide
(DCAA); and 2,6-dichloro-4-hydroxyaniline (DCHA); and
3,5-dichloro-4-hydroxyacetanilide (3,5HA).

***Estimated Drinking Water Concentrations***

To estimate the surface water concentrations, the application rates for
apricots (a single application of 4.0 lb a.i./A/application) was used,
which represents the maximum label rate across all crops. While there
are several different types of applications to apricots listed on the
labels at that rate, an aerial application was modeled, as it yields the
highest EDWC's due to the higher levels of spray drift associated with
that application type. Because the Tier I model is not dependent on crop
type (other than for a percentage crop area factor), the EDWC's
determined for apricots are also applicable to other crops receiving 4
lb a.i./A by aerial application.

A summary of the model input parameter values used in FIRST is presented
in Table 2. The FIRST output file is located in Attachment 1. The
modeling input value for the aerobic aquatic metabolism half-life was
decreased to 3.7 days from the initially used value of 1828 days based
on the newly submitted data. A table of the source data used to
determine input parameter values is located in Attachment 2.

FIRST (v1.0) is a screening-level model designed to estimate the
pesticide concentrations found in surface water for use in drinking
water assessments. The model provides upper bound estimates of
environmental concentrations (acute and chronic) in surface water
drinking water sources (untreated) that might occur following the use of
a pesticide. FIRST uses basic environmental fate data and pesticide
label use and application information to estimate the EDWCs following
the treatment of a 10-hectare field with subsequent runoff into a
reservoir (an Index Reservoir, based on Shipman City Lake in Illinois, a
13-acre lake 9-feet deep with a watershed area of 427 acres or 172.8
hectares) that undergoes two full turnovers annually. FIRST also uses a
Percent Cropped Area (PCA) factor to adjust for the area within the
watershed that is planted to the modeled crop. In the model, a single
runoff event occurs two days after the last application and can move a
maximum of 8% of the applied pesticide into the reservoir, with the
amount dependent on the degradation and adsorption of the pesticide
which occurs in the field prior to the event, any incorporation of the
pesticide at the time of application, and the PCA. The model also
accounts for degradation and binding to sediment which may occur in the
reservoir following the runoff event. Spray drift (resulting in direct
deposition of the pesticide into the reservoir or indirect loading from
spray drift landing on the feeding stream) in the model is equivalent to
16% of the applied for aerial application, 6.3% for orchard air blast
application, and 6.4% for other ground spray application.

For use in the human health risk assessment, EFED recommends a revised
1-in-10-year acute surface water EDWC of **172.8 ppb** (decreased from
182 ppb) and a revised 1-in-10-year chronic EDWC of **1.8 ppb**
(decreased from 35 ppb), both based on the use of DCNA on apricots at a
rate of a single application of 4 lb a.i./A. The recommended EWDC for
groundwater, also based on the use of apricots at the previously stated
rate, remains at **1.3 ppb**.

**Table 2. FIRST (v1.0) input parameter values for DCNA applied to
apricots by aerial application.**

  -------------------------- -------------------- -----------------------
  **Parameter**              **Value**            **Source/Comments**

  Application Rate (lb       4                    EPA Reg. No. 10163-188
  a.i./A)                                         

  Number of Applications     1                    EPA Reg. No. 10163-188

  Interval between           Not Applicable       --
  Applications (days)                             

  Organic Carbon             660                  MRID 40538202; lowest
  Partitioning Coefficient                        non-sand value of four
  (K~oc~; mL/g)                                   values, per input
                                                  parameter guidance

  Aerobic Soil Metabolism    914                  MRID 40894801; input
  Half-life (days)                                value represents the
                                                  90^th^ percentile of
                                                  the upper confidence
                                                  bound on the average of
                                                  two half-life values,
                                                  per input parameter
                                                  guidance

  Wetted in?                 No                   Input parameter
                                                  guidance

  Depth of Incorporation     0                    Input parameter
  (inches)                                        guidance

  Method of Application      aerial spray         EPA Reg. No. 10163-188

  Percent Cropped Area       0.87 (default value) Input parameter
                                                  guidance

  Solubility in Water (mg/L  7 @ 20 ^o^C          Product chemistry data
  or ppm)                                         

  Aerobic Aquatic Metabolism 3.7                  MRID 46657101; input
  Half-life (days)                                value represents the
                                                  90^th^ percentile of
                                                  the upper confidence
                                                  bound on the average of
                                                  two half-life values,
                                                  per input parameter
                                                  guidance

  Hydrolysis Half-life @ pH  stable               ACC No. 253963
  7 (days)                                        

  Aquatic Photolysis         1.97                 MRID's 43891901,
  Half-life @ pH7 (days)                          45575001
  -------------------------- -------------------- -----------------------

**[ATTACHMENT 1: FIRST File]{.underline}**

RUN No. 1 FOR dcna ON apricotr \* INPUT VALUES \*

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

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

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

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

4.000( 4.000) 1 1 660.0 7.0 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

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

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

914.00 2 N/A 1.97‑ 244.28 3.70 3.64

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONCENTRATION

‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑

172.801 1.839

**[ATTACHMENT 2: General fate and physical-chemical property source data
used for DCNA aquatic exposure modeling.]{.underline}**

+------------------------------+-------------------+-------------------+
| **PARAMETER**                | **VALUE**         | **SOURCE OF       |
|                              |                   | INFO./COMMENTS**  |
+==============================+===================+===================+
| **Chemical Name**            | 2,6-dichlo        | --                |
|                              | ro-4-nitroaniline |                   |
|                              | (IUPAC)           |                   |
|                              |                   |                   |
|                              | 2,6-dichloro-4    |                   |
|                              | -nitrobenzenamine |                   |
|                              | (CAS)             |                   |
+------------------------------+-------------------+-------------------+
| **Molecular Weight**         | 207.06 g/mole     | \--               |
+------------------------------+-------------------+-------------------+
| **Solubility (20 ^o^C)**     | 7 mg/L (ppm) @ 20 | Registrant        |
|                              | ^o^C              |                   |
+------------------------------+-------------------+-------------------+
| **Dissociation Constant      | 3.31              | Registrant        |
| (pKa)**                      |                   |                   |
+------------------------------+-------------------+-------------------+
| **Vapor Pressure**           | 1.96 x 10^-6^     | Registrant        |
|                              | mmHg @ 25 ^o^C    |                   |
|                              |                   |                   |
|                              | 1.2 x 10^-6^ mmHg |                   |
|                              | @ 20 ^o^C         |                   |
+------------------------------+-------------------+-------------------+
| **Hydrolysis Half-life (pH   | stable at pH 5,   | Accession No.     |
| 5, 7, 9; 25 ^o^C)**          | 7, 9              | 253963            |
+------------------------------+-------------------+-------------------+
| **Aqueous Photolysis         | 47.2 hours (1.97  | MRID's 43891901,  |
| Half-life (pH 7)**           | days)             | 45575001          |
+------------------------------+-------------------+-------------------+
| **Soil Photolysis            | 263.2 hours       | MRID 43893601     |
| Half-life**                  |                   |                   |
+------------------------------+-------------------+-------------------+
| **Aerobic Soil Metabolism    | 18 months         | MRID 40894801     |
| Half-life**                  | (approx. 540      |                   |
|                              | days) in sandy    |                   |
|                              | loam soil,        |                   |
|                              |                   |                   |
|                              | 6 months (approx. |                   |
|                              | 180 days) in sand |                   |
|                              | soil              |                   |
+------------------------------+-------------------+-------------------+
| **Anaerobic Soil Metabolism  | 38 days in sandy  | MRID 40894801     |
| Half-life**                  | loam soil,        |                   |
|                              |                   |                   |
|                              | 24 days in sand   |                   |
|                              | soil              |                   |
+------------------------------+-------------------+-------------------+
| **Anaerobic Aquatic          | 0.45 days^1^      | MRID 43866501     |
| Metabolism Half-life**       |                   |                   |
+------------------------------+-------------------+-------------------+
| **Aerobic Aquatic Metabolism | 3.4, 3.5 days     | MRID 46657101     |
| Half-life**                  |                   |                   |
+------------------------------+-------------------+-------------------+
| **Organic Carbon Partition   | 660, 735, 760,    | MRID 40538202     |
| Coefficient (K~oc~)**        | 1062              |                   |
+------------------------------+-------------------+-------------------+
| **Soil Partition Coefficient | 3.7, 9.7, 13.6,   | MRID 40538202     |
| (K~d~, mL/g)**               | 15.4 mL/g         |                   |
+------------------------------+-------------------+-------------------+
| **Log K~ow~**                | 2.76              | MRID 41176202     |
+------------------------------+-------------------+-------------------+
| **Henry's Law Constant       | 7.78 x 10^-8^     | Registrant        |
| (atm\*m^3^/mol)**            |                   |                   |
+------------------------------+-------------------+-------------------+
| **Bioconcentration Factors   | 136X whole fish   | MRID 43782001     |
| (BCF) in Fish**              | tissue            |                   |
|                              |                   |                   |
|                              | 49X edible tissue |                   |
|                              |                   |                   |
|                              | 264X nonedible    |                   |
|                              | tissue            |                   |
+------------------------------+-------------------+-------------------+

^1^The half-life was determined in a high organic matter (13.4%)
sediment which may not be respresentative of the soils on which DCNA
will be used. In sandy loam (3.1% o.m.) and sand (1.6% o.m.) soils
treated and flooded simultaneously, and then anaerobically incubated as
part of another study (MRID 40894801), respective anaerobic aquatic
metabolism half-lives of 10.1 and 5.6 days were determined. In an aged
soil column leaching study (MRID 43809001) where the soil was treated
and aged anaerobically prior to placement on the columns, the half-lives
of DCNA in sandy loam (2.8% o.m.), sand (0.59% o.m.), silt loam (0.54%
o.m.) and clay (1.41% o.m.) soils, respectively, were 0.8, 8.5, 9.2 and
5.9 days.