UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

OFFICE OF           

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

MEMORANDUM

	Date:	2/22/06

	Subject:	Dichlobenil.  Use on Rhubarb.  Summary of Analytical Chemistry
and Residue Data. Petition Number 2E6398.

		DP Number: D315266	Decision Number:  354590

		PC Code: 027401	MRID Numbers:  45572201

		40 CFR 180.231	Chemical Class: nitrile herbicide	 

	From:	W. Cutchin, Chemist

		ARIA/TRB

		Registration Division (7505C)

	Through:	P. Shah, Toxicologist

		RAB1

		Health Effects Division (7509C)

	To:	S. Brothers

		MURIEB

		Registration Division (7505C)

Executive Summary

Interregional Research Project No. 4 (IR-4) has submitted field trial
data for dichlobenil (2,6-dichlorobenzonitrile) on rhubarb.  Dichlobenil
is a nitrile herbicide that acts by inhibiting germination of actively
dividing meristems and acts primarily on growing points and root tips. 
Dichlobenil, formulated as the 4% granular product Casoron® 4G (EPA
Reg. No. 400-168), is to be applied at 2.0 lb ai/A to rhubarb.  The
product is applied directly to soil while the target crop is dormant. 
Three field trials were conducted in the United States encompassing
Regions XI (WA) and XII (OR [2]) during the 1999 growing season.  No
specific Regions are indicated in OPPTS 860.1500 guidelines for rhubarb.
 Since Region XII accounts for 72% of the domestic rhubarb production,
the location and number of field trials are adequate.

The qualitative nature of the residue in plants is adequately understood
based on acceptable plant metabolism studies on apples and grapes.  Both
studies indicate that the major residue of concern is
2,6-dichlorobenzamide (BAM).  The parent compound, dichlobenil, was not
detected in either of the studies.  The OPP Metabolism Committee met and
concluded that BAM is the major terminal residue of dichlobenil in
plants, and should be added to the tolerance expression.  Since there
are no rhubarb animal feed items of regulatory concern, a discussion of
the nature of the residues of dichlobenil in livestock commodities is
not germane to this action.  

PAM Vol. II, Method A is a gas-liquid chromatography/electroconductivity
detector (GLC/ECD) method with a detection limit of 0.05 ppm, which can
be used for determination of residues of dichlobenil in/on plant
commodities.  This method was judged adequate for tolerance enforcement.
 However, the registrant was required to revise the method or develop an
alternative method using safer solvents.  The revised method is not
adequate and will require additional modification before it can be
accepted as a tolerance enforcement method.  A GLC/ECD method, L
3-53-71, for determination of residues of BAM in/on fruits and nuts has
undergone a successful independent laboratory validation and has been
validated by the EPA Analytical Chemistry Laboratory (ACL).  However, a
revised method incorporating ACL's comments must be submitted before the
requirements for an analytical method for BAM can be considered
fulfilled.  Dichlobenil is completely recovered using the multiresidue
methods in the Pesticide Analytical Manual (PAM) Vol. I Sections 302 and
304.  BAM is also completely recovered using Section 302.  Since the
multiresidue methods adequately quantitate dichlobenil and BAM, there is
adequate enforcement methodology for this action.  

The analytical methods SOP# Meth-83, Determination of Dichlobenil
Residues in Cherries and SOP# Meth-84, Determination of
2,6-dichlorobenzamide Residues in Cherries, developed by Morse
Laboratories were used with minor modifications for the analysis of
dichlobenil residues on rhubarb.  Dichlobenil residues were extracted
from the raw agricultural commodity (RAC) by extracting with ethyl
acetate/hexane and clean up using a Florisil column.  BAM residues were
extracted from the raw agricultural commodity (RAC) by extracting with
ethyl acetate and clean up using a Florisil column.  Samples were
analyzed using a gas chromatograph with a Hall detector (electrolytic
conductivity detector) in halogen mode.  The analytical method was
validated for rhubarb at 0.05, 0.1, and 0.5 ppm for dichlobenil and
0.01, 0.02, and 0.1 ppm for BAM.  At the range of the fortification
levels, method recoveries were 63-96% dichlobenil and 76-110% for BAM.
The lower limit of method validation (LLMV) was reported for dichlobenil
and BAM as 0.05 ppm and 0.01 ppm, respectively.  The limit of detection
(LOD) was 0.006 ppm for both dichlobenil and BAM.  The method used for
data collection is adequate.  No residues above the LLMV of 0.05 ppm for
dichlobenil or 0.01 ppm for BAM were found in any rhubarb sample.  

	There are no rhubarb processed commodities of regulatory interest. 
Rhubarb is not rotated on a regular basis, therefore inadvertent
residues in rotational crops is not a concern for this action.

Regulatory Recommendations and Residue Chemistry Deficiencies

Pending receipt of the corrected Section F and the forthcoming human
health risk assessment, TRB recommends for the proposed tolerance for
the combined residues of the herbicide dichlobenil (2,6-
dichlorobenzonitrile) and its metabolite 2,6-dichlorobenzamide in
rhubarb at 0.06 ppm. 

Background

Dichlobenil is a nitrile herbicide that acts by inhibiting germination
of actively dividing meristems and acts primarily on growing points and
root tips.

TABLE 1.  Test Compound Nomenclature.

Compound	Chemical Structure



Common name	dichlobenil

Company experimental name	DCBN

IUPAC name	2,6-dichlorobenzonitrile

CAS name	2,6-dichlorobenzonitrile

CAS #	1194-65-6

End-use product/(EP)	Casoron® 4G (EPA Reg. No. 400-168)



TABLE 2.  Physicochemical Properties of Dichlobenil.  

Parameter	Value	Reference

Melting point/range	145°C	RED Chapter, 6/29/95 

pH	NA

	Density	1.3 g/cm3	IPS Inchem, 4/05

Water solubility ( 25°C)	0.0021g/100mL	RED Chapter, 6/29/95

Solvent solubility (g/100mL at 25°C)	xylene 5.3 

ethanol 1.5 

cyclohexane 0.37   

	Vapor pressure at 20°C	5.5 x 10-4 mmHg	IPS Inchem, 4/05

Dissociation constant (pKa)	NA

	Octanol/water partition coefficient Log(KOW)	2.64	IPS Inchem, 4/05

UV/visible absorption spectrum	NA

	

860.1200  Directions for Use

Table 3.  Summary of Directions for Use of Dichlobenil.



Applic. Timing, Type, and Equip.	

Formulation

[EPA Reg. No.]	

Applic. Rate 

(lb ai/A)	

Max. No. Applic. per Season	

Max. Seasonal Applic. Rate

(lb ai/A)	

PHI

(days)	

Use Directions and Limitations



Rhubarb



Apply while crop is dormant using granular applicator	

Casoron® 4G [400-168]	

2	

1	

2	

NA	





Conclusions.  The label is adequate to allow evaluation of the residue
data relative to the proposed use.

860.1300 Nature of the Residue - Plants

Dichlobenil RED, 10/98

The qualitative nature of the residue in plants is adequately understood
based on acceptable plant metabolism studies on apples and grapes.  Both
studies indicate that the major residue of concern is
2,6-dichlorobenzamide (BAM).  The parent compound, dichlobenil, was not
detected in either of the studies.  On June 8, 1992, the OPP Metabolism
Committee met and concluded that BAM is the major terminal residue of
dichlobenil in plants, and should be added to the tolerance expression. 
Because dichlobenil plant metabolism studies demonstrate that
2,6-dichlorobenzoic acid (2,6-DCBA) is not a plant metabolite, the
Committee has recommended removing 2,6-DCBA from the tolerance
expression for dichlobenil.  Therefore, residue data for 2,6-DCBA are no
longer required.  All conclusions specified here regarding the status of
residue chemistry data requirements and the adequacy of the established
tolerances reflect the Metabolism Committee's determination to add BAM
to the tolerance expression and remove 2,6-DCBA from the tolerance
expression.

Conclusions.  The residues of concern in plants are the parent
dichlobenil and the metabolite BAM. 

860.1300 Nature of the Residue - Livestock

Since there are no rhubarb animal feed items of regulatory concern, a
discussion of the nature of the residue of dichlobenil is not germane to
this action.

860.1340 Residue Analytical Methods

Dichlobenil RED, 10/98 

45572201.der.doc, W. Cutchin, in process

PAM Vol. II, Method A is a gas-liquid chromatography/electroconductivity
detector (GLC/ECD) method with a detection limit of 0.05 ppm, which can
be used for determination of residues of dichlobenil in/on plant
commodities.  This method was judged adequate for tolerance enforcement;
however, Method A uses benzene as a solvent.  The registrant was
required to revise the method or develop an alternative method using
safer solvents.  The revised method (MRID 43805301) is currently under
review.  However, this method is not adequate and will require
additional modification before it can be accepted as a tolerance
enforcement method.  The Dichlobenil Guidance Document required
development of an analytical method for the detection and quantitation
of BAM in plant commodities.  The former basic producer, Solvay Duphar,
submitted a GLC/ECD method (L 3-53-71) for determination of residues of
BAM in/on fruits and

nuts.  This method has undergone a successful independent laboratory
validation and has been validated by the EPA Beltsville Analytical
Chemistry Laboratory (ACL).  However, a revised method incorporating
ACL's comments must be submitted before the requirements for an
analytical method for BAM can be considered fulfilled.  

The analytical methods SOP# Meth-83, Determination of Dichlobenil
Residues in Cherries and SOP# Meth-84, Determination of
2,6-dichlorobenzamide Residues in Cherries, developed by Morse
Laboratories were used with minor modifications for the analysis of
dichlobenil residues on rhubarb.  Dichlobenil residues were extracted
from the raw agricultural commodity (RAC) by homogenizing the samples
with ethyl acetate/hexane and rotovaping the supernatant almost to
dryness.  The residue is then redissolved in hexane and cleaned up using
a Florisil column.  The dichlobenil residues are eluted with ethyl
acetate/hexane, rotovaping the eluant almost to dryness, and the sample
redissolved in hexane for analysis.  BAM residues were extracted from
the raw agricultural commodity (RAC) by homogenizing the samples with
ethyl acetate and taking the supernatant almost to dryness.  The residue
is then redissolved in hexane and cleaned up using a Florisil column. 
The BAM residues are eluted with ethyl acetate/hexane, taking the eluant
almost to dryness, and the sample redissolved in hexane for analysis.  A
gas chromatograph with a Hall detector (electrolytic conductivity
detector) in halogen mode was used for the analysis.  The analytical
method was validated for rhubarb at 0.05, 0.1, and 0.5 ppm for
dichlobenil and 0.01, 0.02, and 0.1 ppm for BAM.  At the range of the
fortification levels, method recoveries were 63-96% dichlobenil and
76-110% for BAM.  The petitioner presented adequate sample chromatograms
and calibration curves.  The LLMV was reported for dichlobenil and BAM
as 0.05 ppm and 0.01 ppm, respectively.  The LOD was 0.006 ppm for both
dichlobenil and BAM.

Conclusions.  The previously submitted methods proposed for tolerance
enforcement for dichlobenil and BAM on plants are not adequate for the
reasons described above.  However, as the multiresidue methods
adequately quantitate dichlobenil and BAM (see, 860.1360, below), there
is no deficiency for this action.  The method used for data collection
is adequate.

860.1360 Multiresidue Methods

Dichlobenil RED, 10/98 

The FDA PESTDATA database dated 1/94 (PAM Vol I, Appendix I) indicates
that dichlobenil is completely recovered (>80%) using multiresidue
methods PAM Vol. I Sections 302 (Luke method) and 304 (Mills fatty food
method), and has partial recovery (50-80%) using Section 303 (Mills,
Onley, Gaither method).  The database also indicates that BAM is
completely recovered (>80%) using Section 302.

860.1380 Storage Stability

45572201.der.doc, W. Cutchin, in process

Since the rhubarb samples were store for only 34 days at -18ºC between
harvest and analysis, storage stability data is not required for this
action.

860.1480 Meat, Milk, Poultry, and Eggs

Since there are no rhubarb livestock feed items of regulatory concern, a
discussion of dichlobenil residues in livestock commodities is not
germane to this action. 

860.1500 Crop Field Trials

45572201.der.doc, W. Cutchin, in process

TABLE 4.  Summary of Residue Data from Crop Field Trials with
Dichlobenil.

Commodity	Total Applic. Rate

 (lb ai/A)

 (g ai/ha)	PHI (days)	Residue Levels

 (ppm)



	n	Min.	Max.	HAFT*	Median

(STMdR)	Mean

(STMR)	Std. Dev.

Dichlobenil

Rhubarb	2.0

(2240)	64-83	3	<0.05	<0.05	<0.05	<0.05	<0.05	NA

BAM

Rhubarb	2.0

(2240)	64-83	3	<0.01	<0.01	<0.01	<0.01	<0.01	NA

* HAFT = Highest Average Field Trial.

	Interregional Research Project No. 4 (IR-4) has submitted field trial
data for dichlobenil on rhubarb.  Three field trials were conducted in
the United States encompassing Regions XI (WA) and XII (OR [2]) during
the 1999 growing season.  No specific Regions are indicated in OPPTS
860.1500 guidelines for rhubarb.  Since Region XII accounts for 72% of
the domestic rhubarb production, the location and number of field trials
are adequate.

In each trial, dichlobenil was applied to rhubarb with a granular
applicator as a single soil surface broadcast application at 2.0 lb
ai/A.  Applications were made at pre-emergence or when the crop was just
breaking ground.  In each trial, marketable rhubarb was harvested at 64
to 83 days PHI.  The analytical methods SOP# Meth-83, Determination of
Dichlobenil Residues in Cherries and SOP# Meth-84, Determination of
2,6-dichlorobenzamide Residues in Cherries, developed by Morse
Laboratories were used with minor modifications for the analysis of
dichlobenil residues on rhubarb.  Dichlobenil residues were extracted by
homogenizing the samples with ethyl acetate/hexane and cleaned up using
a Florisil column.  The metabolite 2,6-dichlorobenzamide (BAM) residues
were extracted by homogenizing the samples with ethyl acetate and
cleaned up using a Florisil column.  A gas chromatograph with a Hall
detector (electrolytic conductivity detector) in halogen mode was used
for the analysis.  Method recoveries were 63-96% dichlobenil and 76-110%
for BAM.  The LLMV was reported for dichlobenil and BAM as 0.05 ppm and
0.01 ppm, respectively.  The LOD was 0.006 ppm for both dichlobenil and
BAM.  No residues above the LLMV of 0.05 ppm for dichlobenil or 0.01 ppm
for BAM were found in any rhubarb sample.  

Conclusions.  The crop field trials were conducted according to the
proposed use pattern.  The studies were supported by adequate storage
stability data and analytical methods suitable for data gathering
purposes.  No residues above the LLMV of 0.05 ppm for dichlobenil or
0.01 ppm for BAM were found in any rhubarb sample.  The proposed
tolerance of 0.15 ppm for dichlobenil residues is too high.  The
expected residues of dichlobenil on rhubarb when treated according to
the proposed use pattern will not exceed the combined LLMV of 0.06 ppm
for rhubarb; therefore, a tolerance at that level would be appropriate. 
TRB recommends for the establishment of a tolerance for dichlobenil
residues on rhubarb at 0.06 ppm.  A revised Section F is required.

Because there were so few samples submitted and no residues were found
above the LLMV, no MRL spreadsheet analysis was conducted for this
proposed use.  

860.1520 Processed Food and Feed

45572201.der.doc, W. Cutchin, in process

Since there are no rhubarb processed food items of regulatory concern, a
discussion of dichlobenil residues in processed commodities is not
germane to this action. 

860.1650 Submittal of Analytical Reference Standards

No analytical reference standards are available in the Agency=s
Pesticide Repository.  However, both dichlobenil and BAM are available
as reference standards in the commercial market place.

860.1850 & 860.1900 Confined and Field Accumulation in Rotational Crops

	Rhubarb is a perennial crop; therefore a discussion of residues in
rotational crops is not germane to this action.

860.1550 Proposed Tolerances

Dichlobenil residues of concern are parent dichlobenil and the
metabolite BAM (2,6-dichlorobenzamide) as stated in 40 CFR §180.231. 
There are no international harmonization issues associated with this
action.

Table 5.  Tolerance Summary for Dichlobenil



Commodity	

Established/Proposed Tolerance (ppm)	

Recommended Tolerance (ppm)	

Comments (correct commodity definition)



Rhubarb	

0.15	

0.06	





Template Version November 2003



INTERNATIONAL RESIDUE LIMIT STATUS



Chemical Name: 	

Common Name:  Dichlobenil	

   Proposed tolerance

 Reevaluated tolerance

 Other	

Date: 2/7/06



Codex Status 

(Maximum Residue Limits)	

U. S. Tolerances



 No Codex proposal step 6 or above

 No Codex proposal step 6 or above for the crops requested	

Petition Numbers:  2E6398

DP Barcodes:  D315266

Other Identifier:  



Residue definition (step 8/CXL): N/A	

Reviewer/Branch: W. Cutchin

	

Proposed Residue definition:  Combined residues of dichlobenil and
metabolite 2,6-dichlorobenzamide 



Crop (s)	

MRL (mg/kg)	

Crop(s) 	

Tolerance
瀨浰ܩഇഇഇ桲扵牡ݢ」ㄮܵഇഇഇഇ܇܍܍܍܍ഇഇഇഇ܇
܍܍܍܍ഇ楌業獴映牯䌠湡摡ݡ䰍浩瑩⁳潦⁲敍楸潣܇

Ç

烰

à

à

à

à

à

H*

à

à

à

à

à

à

à

à

à

à

à

à

à

à

à

à

à

à

à

愀Ĥ

à

ᶐ

à

à

à

à

à

à

à

ó开

开

ࠀ  No Limits

  No Limits for the crops requested	

   No Limits

  No Limits for the crops requested



Residue definition: N/A	

Residue definition: N/A



Crop(s)	

MRL (mg/kg)	

Crop(s)	

MRL (mg/kg)



	

	

	





	

	

	





Notes/Special Instructions:S.Funk, 02/09/2006.





Dichlobenil	Summary of Analytical Chemistry and Residue Data	Barcode:
D315266

 PAGE  8  of   NUMPAGES  8 

