Document ID: EPA-HQ-OPP-2006-0145-0002
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-03-22T05:00Z

Environmental
Fate
and
Ecological
Risk
Assessment
for
the
Reregistration
of
Xylene
Range
Aromatic
Solvents
Prepared
by:

Anita
Pease,
Biologist
James
Wolf,
Ph.
D.,
Environmental
Scientist
U.
S.
Environmental
Protection
Agency
Office
of
Pesticide
Programs
Environmental
Fate
and
Effects
Division
Environmental
Risk
Branch
IV
Ariel
Rios
Building
(
Mail
Code
7507C)
1200
Pennsylvania
Ave.,
NW
Washington,
DC
20460
Reviewed
by:
Brian
Anderson,
Biologist
Stephanie
Syslo,
Risk
Assessment
Process
Lead
Dan
Rieder,
Branch
Chief
October
4,
2005
i
Table
of
Contents
I.
Executive
Summary
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1
A.
Nature
of
Chemical
Stressor
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1
B.
Potential
Risks
to
Non­
Target
Organisms
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1
C.
Conclusions
­
Exposure
Characterization
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3
D.
Conclusions
­
Effects
Characterization
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5
E.
Uncertainties
and
Data
Gaps
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6
II.
Problem
Formulation
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10
A.
Stressor
Source
and
Distribution
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10
1.
Source
and
Intensity
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10
2.
Physical/
Chemical/
Fate
and
Transport
Properties
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11
3.
Pesticide
Type,
Class,
and
Mode
of
Action
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12
4.
Overview
of
Pesticide
Usage
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.12
B.
Receptors
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12
1.
Aquatic
Effects
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13
2.
Terrestrial
Effects
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13
3.
Ecosystems
at
Risk
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13
C.
Assessment
Endpoints
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15
D.
Conceptual
Model
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16
1.
Risk
Hypotheses
.
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16
2.
Diagram
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17
E.
Analysis
Plan
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21
1.
Preliminary
Identification
of
Data
Gaps
and
Methods
.
.
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.
22
2.
Measures
to
Evaluate
Risk
Hypotheses
and
Conceptual
Model
.
.
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.
.
23
a.
Measures
of
Exposure
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23
b.
Measures
of
Effect
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24
c.
Measures
of
Ecosystem
and
Receptor
Characteristics
.
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.
24
III.
Analysis
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25
A.
Use
Characterization
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25
B.
Exposure
Characterization
.
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.
.
27
1.
Environmental
Fate
and
Transport
Characterization
.
.
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.
.
27
a.
Summary
of
Empirical
Data
.
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27
b.
Degradation
and
Metabolism
.
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27
c.
Transport
and
Mobility
.
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27
d.
Field
Studies
.
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28
e.
Bioaccumulation
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.
29
ii
2.
Measures
of
Aquatic
Exposure
.
.
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29
a.
Aquatic
Exposure
Modeling
.
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.
29
b.
Aquatic
Exposure
Monitoring
and
Field
Data
.
.
.
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.
32
3.
Measures
of
Terrestrial
Exposure
.
.
.
.
.
.
.
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.
32
a.
Terrestrial
Exposure
Modeling
.
.
.
.
.
.
.
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.
.
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.
.
.
.
.
.
.
.
32
(
1).
Estimates
for
Exposure
Via
Consumption
of
Contaminated
Water
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
33
(
2).
Estimates
for
Exposure
via
Inhalation
of
Volatilized
Xylenes
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
34
b.
Residue
Studies
.
.
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.
36
C.
Ecological
Effects
Characterization
.
.
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.
.
36
1.
Aquatic
Effects
Characterization
.
.
.
.
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.
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.
.
36
a.
Aquatic
Animals
.
.
.
.
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.
.
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.
.
.
.
.
39
(
1).
Acute
Effects
.
.
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.
.
39
(
2).
Chronic
Effects
.
.
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.
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.
41
(
3).
Sublethal
Effects
.
.
.
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.
.
.
42
(
4).
Field
Studies
.
.
.
.
.
.
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.
.
42
b.
Aquatic
Plants
.
.
.
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.
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.
.
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.
.
42
2.
Terrestrial
Effects
Characterization
.
.
.
.
.
.
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.
.
.
43
a.
Terrestrial
Animals
.
.
.
.
.
.
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.
.
43
(
1).
Acute
Effects
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
43
(
2).
Chronic
Effects
.
.
.
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.
.
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.
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.
.
46
(
3).
Sublethal
Effects
.
.
.
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.
.
.
.
46
(
4).
Field
Studies
.
.
.
.
.
.
.
.
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.
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.
.
.
.
.
.
.
.
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.
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.
.
.
47
b.
Terrestrial
Plants
.
.
.
.
.
.
.
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.
.
47
IV.
Risk
Characterization
.
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.
47
A.
Risk
Estimation
­
Integration
of
Exposure
and
Effects
Data
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
47
1.
Non­
Target
Aquatic
Animals
and
Plants
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
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.
.
.
.
.
.
.
48
2.
Non­
Target
Terrestrial
Animals
.
.
.
.
.
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.
.
.
.
.
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.
.
.
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.
.
.
.
.
50
a.
Acute
Risk
to
Mammals
and
Birds
from
Ingestion
of
Contaminated
Water
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
.
.
.
.
50
b.
Acute
Risk
to
Mammals
Via
Inhalation
Exposure
.
.
.
.
.
.
.
.
.
.
.
50
c.
Acute
Risk
to
Mammals
from
Combined
Exposure
via
Inhalation
and
Contaminated
Water
.
.
.
.
.
.
.
.
.
.
.
.
.
51
B.
Risk
Description
.
.
.
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.
.
.
.
.
.
53
1.
Risks
to
Aquatic
Organisms
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
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.
.
54
2.
Risks
to
Terrestrial
Organisms
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
.
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.
.
.
56
3.
Review
of
Incident
Data
.
.
.
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.
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.
57
4.
Endocrine
Effects
.
.
.
.
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.
.
57
iii
5.
Federally
Threatened
and
Endangered
(
Listed)
Species
Concerns
.
.
.
.
.
.
.
58
a.
Action
Area
.
.
.
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.
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.
58
b.
Taxonomic
Groups
Potentially
at
Risk
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
59
(
1).
Discussion
of
Risk
Quotients
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
59
(
2).
Probit
Dose
Response
Relationship
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
59
(
3.)
Data
Related
to
Under­
represented
Taxa
.
.
.
.
.
.
.
.
.
.
.
60
(
4.)
Implications
of
Sublethal
Effects
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
60
c.
Indirect
Effects
Analysis
.
.
.
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.
60
d.
Critical
Habitat
.
.
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.
.
63
e.
Co­
occurrence
Analysis
.
.
.
.
.
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.
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.
.
.
.
.
.
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.
.
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.
.
.
63
C.
Description
of
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
.
.
.
.
.
.
.
.
.
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.
.
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.
.
.
.
.
.
.
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.
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.
.
.
.
.
.
.
.
67
1.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
All
Taxa
.
.
.
.
.
.
.
.
.
.
.
.
.
.
67
2.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
Aquatic
Species
.
.
.
.
.
.
.
.
67
3.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
Terrestrial
Species
.
.
.
.
.
.
68
4.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Effects
Assessment
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
69
5.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
the
Acute
and
Chronic
LOCs
.
.
.
.
.
.
.
.
.
.
.
.
.
70
V.
Literature
Cited
.
.
.
.
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.
.
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.
71
ACKNOWLEDGEMENTS
.
.
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.
75
List
of
Appendices
A.
Environmental
Fate
Studies
.
.
.
.
.
.
.
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.
.
.
.
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.
.
.
.
.
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.
.
.
A1
B.
Estimation
of
Concentration
in
Receiving
Water
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
B1
C.
Data
Requirements
­
Environmental
Fate
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
C1
D.
Environmental
Fate
and
Monitoring
Bibliography
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
D1
E.
Ecological
Effects
Data
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
E1
F.
The
Risk
Quotient
Method
and
Levels
of
Concern
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
F1
G.
Detailed
Risk
Quotients
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
G1
H.
Data
Requirements
­
Ecological
Effects
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
H1
I.
Ecotoxicology
Bibliography
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
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.
.
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.
.
.
.
.
.
.
.
.
.
I1
J.
Summary
of
Endangered/
Threatened
Species
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
J1
iv
List
of
Tables
Table
1.
Physical
and
Chemical
Properties
of
Xylene
Isomers.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
10
Table
2.
Summary
of
Assessment
Endpoints
and
Measures
of
Effect
for
Xylene
Mixtures
and
Xylene
Isomers.
.
.
.
.
.
.
.
.
.
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.
.
.
14
Table
3.
Relationship
Between
Return
Flow
Volume
and
Receiving
Water
Volumes
Used
in
the
Plug
Flow
Model..
.
.
.
.
.
.
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.
.
.
.
.
28
Table
4.
Exposure
Estimates
for
Birds
and
Mammals
via
Consumption
of
Contaminated
Water.
.
.
.
.
.
.
.
.
.
.
.
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.
.
32
Table
5.
Maximum
Estimated
Exposure
for
Volatilized
Xylenes.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
38
Table
6.
Xylene
Toxicity
Reference
Values
(
TRVs)
for
Aquatic
Organisms
.
.
.
.
.
.
.
.
.
.
.
.
.
.
40
Table
7.
Comparison
of
the
Range
of
Acute
Toxicity
Values
for
Mixed
Xylenes
and
Xylene
Isomers
in
Aquatic
Animals.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
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.
.
.
.
.
.
.
.
.
41
Table
8.
Toxicity
Reference
Values
(
TRVs)
for
Mixed
Xylenes
in
Terrestrial
Organisms.
.
.
.
.
.
46
Table
9.
Acute
Toxicity
Values
for
Birds,
Expressed
in
Terms
of
a
Single
Xylene
Dose
(
mg)
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
47
Table
10.
Acute
Toxicity
Values
for
Mammals,
Expressed
in
Terms
of
a
Single
Xylene
Dose
(
mg).
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
48
Table
11.
Acute
RQs
for
Freshwater
Fish,
Freshwater
Invertebrates,
Estuarine/
Marine
Fish,
Estuarine/
Marine
Invertebrates,
and
Algae
Exposed
to
Mixed
Xylenes
or
Xylene
Isomers
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
51
Table
12.
Acute
RQs
for
Birds
and
Mammals
Exposed
to
Mixed
Xylenes
via
Consumption
of
Contaminated
Water.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
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.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
54
Table
13.
Acute
RQs
for
Mammals
Exposed
to
Volatilized
Mixed
Xylenes
Via
Inhalation.
.
.
.
55
Table
14.
Composite
Acute
RQs
for
Mammals
Exposed
to
Mixed
Xylenes
by
Consumption
of
Contaminated
Water
and
Inhalation.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
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.
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.
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.
.
.
.
.
.
.
.
56
Table
15.
Calculated
Xylene
Concentrations
at
which
Acute
RQs
Are
Less
Than
Acute
LOCs
for
Aquatic
Organisms
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
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.
.
.
.
.
59
Table
16.
Time,
Distance,
and
Dilution
for
Xylene
Concentrations
to
Decrease
from
10
ppm
and
1
ppm
to
<
0.04
ppm
Based
on
a
Steady­
State
Plug
Flow
Dilution
Model
.
.
.
.
.
.
.
.
.
.
.
61
Table
17.
Tabulation
by
Taxonomic
Group
and
Crop
of
Listed
Species
That
May
Occur
in
Mixed
Xylene
Use
Areas
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
69
Table
18.
Tabulation
by
Taxonomic
Group
and
State
of
Listed
Species
That
May
Occur
in
Mixed
Xylene
Use
Areas
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
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.
.
.
.
.
.
.
.
69
v
List
of
Figures
Figure
1.
Ecological
Conceptual
Model
for
Screening­
Level
Risk
Assessment
of
Mixed
Xylenes
Applied
to
Irrigation
and
Drainage
Canals
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
18
Figure
2.
Concentration
of
Xylene
in
Receiving
Water
Versus
Dilution
and
Time.
Dilutions
are
none,
10:
1,
20:
1,
and
50:
1
.
.
.
.
.
.
.
.
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.
29
1
I.
Executive
Summary
A.
Nature
of
Chemical
Stressor
Aromatic
emulsifiable
petroleum
solvents
are
used
to
control
weed
growth
in
open
channels
which
carry
water
for
irrigation
(
canals,
ditches)
or
water
for
drainage
(
ditches).
There
is
currently
only
one
registered
product
(
T­
Chem
Aquatic
Weed
Killer
EPA
Reg.
No.
9768­
18),
which
is
used
in
programs
for
the
Bureau
of
Reclamation,
the
U.
S.
Dept.
of
Interior,
and
cooperating
state
water
use
organizations.
The
product
may
be
used
only
in
the
16
states
specified
in
the
Bureau
of
Reclamation
Act.
These
states
include
Arizona,
California,
Colorado,
Idaho,
Kansas,
Montana,
Nebraska,
Nevada,
New
Mexico,
North
Dakota,
Oklahoma,
Oregon,
South
Dakota,
Utah,
Washington,
and
Wyoming.

This
product
is
used
to
control
a
variety
of
aquatic
nuisances
such
as
surface
pond
scum
(
filamentous
algae),
and
submerged
weeds
such
as
American
pondweed
(
Potamogeton
nodosus
Poir),
horned
pondweed
(
Zannichellia
palustris),
leafy
pondweed
(
Potamogeton
foliosus
Raf
),
Richardson's
pondweed
(
Potamogeton
richardsonii),
curly
leaf
pondweed
(
Potamogeton
crispus),
coon
tail
water
weed
(
Ceratophyllum
demers)
and
water
star
grass
(
Heteranthera
dubia).
This
registered
product
consists
of
98%
mixed
xylene
isomers,
but
may
also
contain
small
quantities
of
ethylbenzene
and
emulsifiers
to
aid
in
the
dispersal
of
the
xylenes
throughout
the
canal
or
drainage
ditch.
It
is
applied
to
canals
and
drainage
ditches
when
the
weed
growth
begins
to
interfere
with
water
flow
or
delivery.
To
minimize
the
risk
of
effects
to
human
health,
the
label
indicates
that
water
from
the
treated
drainage
ditch
should
not
flow
into
receiving
waters
if
the
concentration
of
xylene
exceeds
10
ppm.
The
10
ppm
(
mg/
L)
represents
the
concentration
that
the
EPA
has
set
as
an
enforceable
standard
called
a
Maximum
Contaminant
Level
(
MCL)
for
safe
drinking
water
(
USEPA,
OW).

B.
Potential
Risks
to
Non­
Target
Organisms
The
focus
of
this
screening­
level
assessment
was
to
evaluate
risks
associated
with
exposure
to
mixed
xylenes
applied
underwater
for
use
in
the
control
of
aquatic
weeds
in
two
different
types
of
habitat
including:
1)
canals
and
ditches
which
contain
xylene­
treated
irrigation
water,
and
2)
receiving
water
bodies
(
i.
e.,
streams,
rivers,
and/
or
lakes)
which
receive
return
flow
from
xylenetreated
irrigation
water.
Return
flow
is
the
portion
of
irrigation
water
that
finds
its
way
back
to
a
stream
channel
either
as
surface
flow
or
subsurface
flow.
The
treated
canals
and
ditches
of
the
irrigation
systems
contain
water
only
during
the
growing
season
when
they
are
delivering
water
to
crops
and
can
be
dry
from
3
to
6
months
out
of
the
year,
depending
on
the
area
and
the
crops
being
irrigated.
Given
this
use
pattern,
potential
exposures
pathways
exist
for
aquatic
and
terrestrial
ecosystems
via
direct
exposure
and
potential
ingestion
of
contaminated
water
and
from
inhalation
exposure
of
xylenes
that
volatilize
from
contaminated
water.
Since
mixed
xylenes
are
applied
directly
below
the
surface
of
the
water,
terrestrial
exposure
pathways
typically
considered
(
i.
e.,
exposure
of
terrestrial
animal
food
sources
and
exposure
of
terrestrial
plants
via
direct
2
application
or
spray
drift)
were
not
addressed
in
this
assessment.
Given
the
rapid
volatilization
of
xylenes
from
water
(
half­
lives
range
from
less
than
2
days
in
a
shallow
flowing
water
body
to
6
days
in
a
pond),
chronic
exposure
of
aquatic
and
terrestrial
ecosystems
is
also
not
expected.

In
evaluating
the
possible
risks
of
mixed
xylenes
to
aquatic
and
terrestrial
receptors,
this
assessment
focuses
on
a
range
of
water
concentrations
that
include
the
recommended
allowable
exposure
limits
for
xylenes
(
the
maximum
label
rate
of
11
gallons
product
for
each
1
cfs
flow)
in
treated
irrigation
canals
and
drainage
ditches,
that
is,
an
initial
concentration
of
approximately
740
mg/
L,
which
will
decline
with
time
and
over
distance
from
point
of
application.
However,
since
the
maximum
allowable
concentration
of
740
mg/
L
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
o­
xylene
of
178
mg/
L
(
the
highest
solubility
limit
reported
for
the
three
xylene
isomers).
According
to
the
current
label,
xylene
concentrations
in
return
flows
from
treated
irrigation
(
i.
e.,
portion
of
water
applied
as
irrigation
that
flows
into
receiving
rivers,
streams,
lakes,
and
ponds)
can
not
exceed
10
mg/
L;
therefore,
this
concentration
was
also
evaluated
as
a
potential
exposure
concentration.
It
is
recognized
that
the
concentration
of
xylene
in
the
return
flow
may
be
less
than
10
mg/
L
due
to
dissipation
that
occurs
while
the
water
is
used
to
irrigate
fields,
prior
to
being
released
into
a
receiving
water
body.
In
addition,
it
is
expected
that
xylene
concentrations
will
further
decrease
via
dilution
with
the
volume
of
water
in
the
receiving
water
body.

The
results
of
this
Tier
I
screening­
level
(
deterministic)
risk
assessment
show
that
exposure
of
aquatic
animals
and
plants
to
mixed
xylenes
under
the
conditions
of
recommended
use
pose
acute
risk
to
listed
(
i.
e.,
endangered)
and
non­
listed
freshwater
and
estuarine/
marine
fish
and
invertebrates
(
including
amphibians),
as
well
as
aquatic
non­
vascular
plants.
Acute
risks
to
vascular
aquatic
macrophytes
were
not
assessed
due
to
lack
of
quantitative
toxicity
data;
however,
since
mixed
xylenes
are
used
to
control
unwanted
aquatic
vegetation
and
risks
are
predicted
for
algae,
the
potential
for
risk
to
listed
and
non­
listed
vascular
aquatic
plants
is
assumed.
Acute
risk
quotients
exceeded
all
acute
LOCs
for
the
range
of
water
concentrations
considered
in
this
assessment
(
10
to
740
mg/
L).
Thus,
exposure
of
aquatic
species
to
xylenes
at
the
recommended
water
concentrations
in
the
treated
irrigation
water
(
canals
and
ditches)
can
be
expected
to
reduce
survival
of
aquatic
organisms.
In
addition,
available
data
indicates
that
reproductive
effects
may
also
occur
in
estuarine/
marine
invertebrates
following
short­
term
exposures.
If
listed
fish,
amphibians,
and/
or
aquatic
invertebrates
are
present
in
the
irrigation
canals
or
ditches,
the
potential
for
direct
and
indirect
effects
to
these
species,
through
loss
of
food
and
habitat,
is
expected.
Because
acute
risks
to
all
aquatic
species
were
observed
at
the
allowable
xylene
concentration
(
10
mg/
L)
in
the
return
flows
of
treated
irrigation
into
receiving
rivers
and
streams,
risk
to
listed
and
non­
listed
aquatic
receptors
may
not
be
restricted
to
drainage
and
irrigation
ditch
habitats,
but
may
extend
to
receiving
water,
depending
upon
environmental
conditions.
Based
on
acute
risk
for
freshwater
and
estuarine/
marine
fish
and
invertebrates,
indirect
effects
to
listed
species
(
i.
e.,
fish,
mammals,
birds,
reptiles,
and
amphibians)
that
eat
freshwater
and
estuarine/
marine
fish
and
invertebrates
may
occur.
The
potential
for
adverse
effects
to
those
listed
obligate
and
general
species
that
rely
on
aquatic
plants
for
food
and/
or
habitat
and
shelter
also
exists.
3
Based
upon
the
available
toxicity
data,
xylene
concentrations
in
return
flows
should
not
exceed
0.04
mg/
L
for
freshwater
environments
and
0.05
mg/
L
for
estuarine/
marine
environments
to
be
protective
of
listed
aquatic
species.
Therefore,
additional
dissipation
(
i.
e.,
volatilization,
degradation,
and
dilution)
is
required
at
the
10
mg/
L
level
to
achieve
concentrations
that
are
not
harmful
to
listed
aquatic
receptors
in
receiving
water
bodies.
Depending
on
the
dilution
and
distance
downstream
where
listed
aquatic
species
may
occur
in
receiving
water
bodies,
exposure
to
xylene
is
expected
to
exceed
the
endangered
species
LOCs.

As
previously
mentioned,
EFED
acknowledges
that
xylene
concentrations
in
return
flows
to
receiving
water
bodies
are
likely
to
be
less
than
10
mg/
L,
following
application
of
treated
irrigation
water
onto
fields.
As
discussed
in
the
following
exposure
characterization,
EFED
has
used
a
simple
steady­
state
plug
flow
model
to
estimate
the
amount
of
dissipation
that
would
be
required
to
achieve
a
concentration
of
0.04
mg/
L
that
is
protective
of
listed
aquatic
species
in
receiving
water
bodies.
EFED
has
considered
a
number
of
scenarios
where
the
irrigation
canals
or
ditches
flow
into
different
sized
receiving
bodies.
Specifically,
the
model
was
used
to
predict
the
length
of
time
and/
or
dissipation
distance
required
for
xylene­
treated
water
to
decrease
from
a
concentration
of
10
mg/
L
(
as
specified
in
the
current
label),
as
well
an
alternative
concentration
of
1
mg/
L,
to
a
concentration
of
0.04
mg/
L
required
to
be
protective
of
listed
aquatic
animal
and
plant
species
in
receiving
water
bodies.

For
terrestrial
species,
results
of
this
assessment
show
that
birds
and
mammals
are
not
at
acute
risk
from
exposure
to
xylenes
via
ingestion
of
contaminated
water.
Additionally,
mammals
do
not
appear
to
be
at
acute
risk
from
inhalation
exposure
or
from
combined
exposure
via
ingestion
of
contaminated
water
and
inhalation.
Due
to
lack
of
inhalation
toxicity
data
in
birds,
acute
risks
of
exposure
to
birds
via
inhalation
of
volatilized
xylenes
and
combined
exposure
via
contaminated
water
and
inhalation
could
not
be
assessed.

C.
Conclusions
­
Exposure
Characterization
The
environmental
fate
and
transport
properties
of
xylenes
(
from
other
sources
and
uses
without
the
addition
of
emulsifiers)
are
well
known.
Assuming
that
the
emulsifiers
have
no
significant
effect
on
fate,
other
than
transport
(
solubility),
xylene
and
its
metabolites
do
not
persist
in
surface
water
for
long
periods
of
time
due
to
rapid
volatilization
and
degradation.
These
compounds
do
not
contain
functional
groups
that
are
susceptible
to
hydrolysis
under
environmental
conditions,
nor
do
they
absorb
light
in
the
environmental
UV
region
(
 
>
290
nm);
therefore,
abiotic
degradation
via
hydrolysis
and
photolysis
are
not
important
fate
mechanisms.
Xylenes
are
highly
volatile
compounds,
and
tend
to
evaporate
readily
from
water
surfaces.
These
compounds
also
biodegrade
fairly
rapidly
under
aerobic
aquatic
conditions,
but
appear
to
be
more
stable
under
anoxic
aquatic
conditions.
Xylene
metabolites
include
the
methylated
homologs
of
benzylsuccinic
acid,
benzylfumaric
acid,
and
E­
phenylitaconate.
Other
degradation
products
identified
are
toluic
acid,
phthalic
acid,
and
benzoic
acid,
which
ultimately
degrade
to
carbon
dioxide.

Three
exposure
estimates
were
initially
used
to
assess
risks
of
mixed
xylenes
to
non­
target
aquatic
4
animals
(
i.
e.,
fish,
invertebrates)
and
plants
(
i.
e.,
algae):
10
mg/
L
(
maximum
allowable
xylene
concentration
released
to
receiving
waters),
740
mg/
L
(
estimated
maximum
xylene
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Any
water
coming
off
the
irrigated
fields
as
return
flow
would
be
expected
to
have
xylene
concentrations
less
than
10
ppm.
Limited
monitoring
data
(
Walsh
et
al.,
1977)
of
irrigation
canals
shows
that
initial
xylene
concentrations
of
approximately
500
to
more
than
800
ppm
at
the
point
of
application
decrease
to
100
to
200
ppm
five
to
ten
miles
downstream
from
application.
A
repeat
application
resulted
in
similar
concentrations
more
than
fifteen
miles
downstream
from
the
point
of
application.
The
monitoring
results
show
that
xylene
concentrations
in
the
treated
irrigation
canals
and
ditches
may
exceed
the
10
ppm
release
concentration.
However,
monitoring
of
xylene
residues
in
return
flow
in
the
same
study
showed
a
decrease
in
concentration
from
500
ppm
in
the
water
removed
from
lateral
ditches
for
irrigation
to
less
than
0.2
ppm
(
200
ppb)
(
study
detection
limit)
in
return
flow
after
flowing
through
irrigation
fields
(
length
of
irrigation
rills
750
to
1320
feet).
Similar
findings
were
summarized
in
a
Bulletin
publish
by
the
Bureau
of
Reclamation
(
USDI­
BR,
1969).
Recently,
the
Agency
obtained
some
monitoring
from
the
Washington
State
Department
of
Ecology
(
WDE,
2005).
These
data
reported
xylene
concentrations
in
irrigation
waste
water
(
prior
to
release)
to
range
between
0.004
and
10.9
ppm.
There
were
67
detections
out
of
108
samples.
The
mean
value
was
0.862
ppm.
About
25
percent
of
the
detections
were
less
than
0.04
ppm
and
about
80
percent
of
the
detections
were
less
than
1.0
ppm.
These
data
suggest
that
significant
dissipation
of
xylene
occurs
within
the
field
during
the
irrigation
process.
The
amount
of
water
coming
off
the
field
is
expected
to
vary
due
to
different
management
practices
and
type
of
irrigation.
For
example,
sprinkler
irrigation
systems
would
likely
result
in
increased
dissipation
of
xylene
in
treated
irrigation
water
as
compared
to
flood
irrigation.

Currently,
the
Agency
has
not
adopted
a
specific
model
to
estimate
environmental
concentrations
of
a
pesticide
applied
to
a
transient
flowing
water
body
(
treated
irrigation
water
canal),
where
dissipation
processes
are
functioning
as
water
flows
downstream
in
the
irrigation
canal
and
is
removed
and
subsequently
applied
to
a
crop
as
irrigation
water.
Based
on
concentration
estimates
and
monitoring
data,
it
is
assumed
that
treated
irrigation
water
in
the
canals
and
ditches
exceed
the
endangered
species
LOCs
for
aquatic
animals
and
plants.
It
is
expected
that
xylene­
treated
irrigation
water
will
undergo
dissipation
in
the
field,
with
the
excess
treated
irrigation
water
released
as
return
flow.
Allowable
xylene
concentrations
(
10
mg/
L)
in
the
water
released
as
return
flow
exceed
the
LOC;
however,
actual
concentrations
are
likely
to
be
lower
due
to
in­
field
dissipation
(
additional
volatilization,
degradation,
and
leaching).
The
Agency
modeled
the
dissipation
of
xylene
in
the
return
flow
from
the
point
of
release
to
several
sized
water
bodies,
assuming
the
maximum
release
concentration
(
10
mg/
L),
and
a
simple
steady­
flow
mixing
model
to
estimate
a
distance
or
time
for
the
concentration
to
drop
below
the
LOC
for
aquatic
listed
species.

Using
a
simple
steady­
state
plug­
flow
model
(
PC
030001,
D313280,
Corbin,
2005),
the
dissipation
of
xylene
in
return
flow
with
a
flow
rate
of
1
cfs
and
a
concentration
of
10
mg/
L
(
10000
ppb)
into
a
receiving
water
body
was
considered
for
several
different
dilution
ratios
(
1:
1,
10:
1,
20:
1,
and
50:
1)
(
assuming
a
constant
flow
rate
of
1
cfs,
mixing
during
dilution,
and
a
volatilization
half­
life
of
2
days).
Release
into
a
dry
channel
is
approximated
by
the
zero
(
0)
dilution
estimate.
As
5
expected,
the
time
and
distance
required
for
xylene
to
dissipate
to
concentrations
that
are
protective
of
listed
aquatic
species
in
receiving
water
decreases
with
increasing
dilution
(
i.
e.,
larger
receiving
water
bodies).
Depending
on
the
dilution
factor,
which
is
a
function
of
the
geometry
of
the
receiving
water
body,
the
time
required
for
xylene
to
dissipate
from
10
mg/
L
to
a
concentration
less
than
0.04
mg/
L
(
the
concentration
required
to
protect
listed
aquatic
species)
ranges
from
approximately
8
days
to
7.5
hours,
with
dilutions
ranging
from
10:
1
to
50:
1.
The
time
required
for
xylene
to
dissipate
from
1
mg/
L
to
less
than
0.04
ranges
from
approximately
5
days
to
5
hours.
Increasing
the
flow
rate
(
with
same
application
rate)
increases
the
time
or
distance
necessary
to
lower
the
concentration
to
a
level
that
is
protective
of
listed
aquatic
species
(
assuming
that
degradation
remains
constant).

Although
terrestrial
species
are
exposed
to
xylenes
from
the
use
and
accidental
release
of
petroleum­
based
products,
aromatic
petroleum
solvents
are
not
used
to
control
terrestrial
weed
growth.
Therefore,
the
potential
for
direct
exposure
to
terrestrial
organisms
is
very
low.
The
most
likely
exposure
pathways
for
terrestrial
animals
are
through
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.
Exposure
estimates
for
ingestion
of
contaminated
water
for
birds
and
mammals
were
based
on
the
allowable
concentration
range
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
178
mg/
L,
and
the
calculated
amount
of
water
that
birds
and
mammals
are
expected
to
consume
in
one
day.

To
assess
risks
associated
with
inhalation
exposure
to
mammals,
a
xylene
concentration
in
air
was
estimated
using
the
nondimensional
Henry's
Law
constant,
which
relates
the
concentration
of
a
compound
in
the
gas
phase
to
its
concentration
in
the
solution
phase.
The
solution
concentration
was
assumed
to
be
the
maximum
solubility
of
xylene
(
178
ppm),
with
no
emulsifiers.
The
inhalation
exposure
is
equal
to
the
concentration
of
xylene
in
air,
assuming
the
dimensions
of
the
breathing
zone
for
a
potential
receptor.
The
breathing
zone
was
assumed
to
be
several
cm
above
the
ground
to
reflect
the
area
where
small
mammals
breath.
This
zone
was
assumed
to
have
a
uniform
xylene
concentration,
although
in
reality
concentration
probably
decreases
with
height.
The
EEC
for
air
is
considered
to
be
representative
of
a
4­
hour
time
period,
which
corresponds
to
the
reported
exposure
duration
for
the
available
mammalian
inhalation
toxicity
study.
For
this
risk
assessment,
the
maximum
estimated
exposure
concentration
for
volatilized
xylenes
in
air
was
estimated
to
be
38.5
ppm,
assuming
that
no
losses
from
wind
or
degradation.

D.
Conclusions
­
Effects
Characterization
No
registrant­
submitted
toxicity
studies
in
which
xylene
mixtures
or
xylene
isomers
were
the
sole
active
ingredient
were
identified.
Therefore,
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
from
the
published
open
literature.
Since
chronic
exposure
of
aquatic
and
terrestrial
ecosystems
is
not
anticipated
due
to
rapid
volatilization,
chronic
exposure
studies
were
not
reviewed
for
this
assessment.

In
general,
results
of
acute
toxicity
studies
indicate
that
mixed
xylenes
and
xylene
isomers
are
moderately
to
highly
toxic
to
aquatic
species.
The
acute
toxicity
values
used
to
estimate
risks
to
6
aquatic
organisms
are
as
follows:

°
freshwater
fish:
96­
hour
LC
50
value
of
2.6
mg/
L
for
p­
xylene
in
rainbow
trout
(
Salmo
gairdneri);

°
freshwater
invertebrates:
24­
hour
LC
50
value
of
1.0
mg/
L
for
m­
xylene
in
water
flea
(
Daphnia
magna);

°
estuarine/
marine
invertebrates:
96­
hour
LC
50
value
of
7.4
mg/
L
for
mixed
xylenes
in
grass
shrimp
(
Palaemonetes
pugio);

°
algae:
72­
hour
LC
50
value
of
3.2
mg/
L
for
p­
xylene
in
green
algae
(
Selenastrum
capricornutum).

Although
limited
information
is
available
regarding
sublethal
effects
of
mixed
xylenes
or
xylene
isomers
in
aquatic
animals,
results
of
a
study
in
rainbow
trout
show
a
dose­
dependent
loss
of
equilibrium
in
fish
that
were
exposed
to
xylene
for
approximately
1.4
hours,
with
NOAEC
and
LOAEC
values
of
0.65
mg/
L
and
3.2
mg/
L,
respectively.
It
is
important
to
note
that
due
to
their
high
volatility,
xylene
isomers
disappear
rapidly
from
solution.
Therefore,
interpretation
of
aquatic
toxicity
data
may
be
confounded
by
the
rapid
loss
of
xylenes
from
solution.

For
terrestrial
species,
the
types
of
toxicity
studies
pertinent
to
this
risk
assessment
were
acute
oral
exposure
and
acute
inhalation
exposure.
For
birds,
no
single
oral
exposure
studies
were
available;
results
of
an
acute
dietary
study
on
Japanese
quail
suggest
that
mixed
xylenes
are
practically
nontoxic
on
an
acute
dietary
basis
(
LC
50
>
20,000
mg
a.
i./
kg
diet).
No
acute
inhalation
studies
in
avian
species
were
identified
from
the
available
literature.
For
mammals,
the
lowest
toxicity
values
reported
for
mixed
xylenes
were
a
subacute
oral
LD
50
value
of
1608
mg/
kg
body
weight
in
rats
and
an
acute
inhalation
LC
50
value
of
6700
ppm
in
rats.

E.
Uncertainties
and
Data
Gaps
Uncertainties
and
data
gaps
pertaining
to
surface
water
modeling
and
inhalation
exposure
have
been
identified
as
follows:

°
The
aquatic
exposure
estimates
contain
considerable
uncertainty
due
to
limited
label
language
and
limited
information
concerning
the
use
of
xylene.
The
xylene
containing
product
is
applied
to
irrigation
canals
and
ditches,
or
drainage
ditches
at
a
rate
of
11
gallons
product
per
1
cubic
foot
per
second
(
1
cfs)
of
water
flow
velocity
for
20
or
30
minutes,
which
yields
an
initial
level
of
740
ppm.
This
level
exceeds
the
solubility
limits
of
xylenes;
however,
xylenes
are
applied
with
an
emulsifier
which
can
increase
the
apparent
solubility
of
the
product.
Therefore,
there
is
a
degree
of
uncertainty
regarding
the
actual
maximum
exposure
level
for
aquatic
organisms
in
irrigation
canals
and
ditches
as
well
as
receiving
waters.
7
Considerable
uncertainties
are
also
associated
with
10
ppm
exposure
value
from
the
return
flow.
The
return
flow
may
be
lower
due
to
volatilization
and
dilution
before
being
leased
into
receiving
water
bodies.
The
actual
concentration
of
xylene
in
the
return
flow
and
potential
receiving
water
bodies
will
be
a
function
of
the
initial
concentration
and
dissipation
processes
including
volatilization,
dilution,
and
degradation.
The
size
of
the
water
bodies
receiving
treated
irrigation
water
is
unknown;
therefore,
there
is
uncertainty
associated
with
the
modeled
dilution
factors
of
1:
1,
10:
1,
20:
1,
and
50:
1
and
no
dilution.

°
The
concentration
of
xylene
in
the
return
flow
will
depend
upon
the
concentration
in
the
irrigation
water
(
applied
to
crop)
and
the
dissipation
(
degradation,
volatilization,
and
sorption)
that
occurs
from
point
of
application
in
the
field
to
the
point
where
water
draining
from
the
field
reaches
the
receiving
body
of
water.
The
higher
the
concentration
in
the
irrigation
water,
the
greater
the
need
for
dissipation
to
occur
before
the
return
flow
enters
the
receiving
water.
The
xylene
dissipation
from
the
return
flow
to
the
receiving
water
body
depends
on
the
amount,
rate,
and
length
of
irrigation,
length
of
time
it
takes
for
the
water
to
reach
the
receiving
body,
amount
and
rate
of
xylene
and
volume
of
water
entering
the
receiving
body,
and
rate
of
flow
and
volume
of
the
receiving
water
body.

°
The
environmental
parameters
for
xylenes
used
in
this
assessment
represent
values
obtained
from
open
literature
for
the
various
xylene
isomers
and
do
not
consider
the
influence
of
the
emulsifiers
(
excluding
the
use
of
emulsifiers
to
increase
the
"
solubility").
The
estimates
of
the
volatilization
of
the
xylenes
from
water
is
influenced
by
the
solubility
(
considered
in
Henry's
Law),
which
is
uncertain
due
to
the
influence
of
emulsifiers.

°
Given
the
uncertainties
associated
with
the
presence
of
the
emulsifier
in
the
end
use
product
and
its
potential
effect
on
the
solubility
and
volatility
of
xylene
in
irrigation
ditches
and
canals,
further
information
on
the
comparative
volatility
of
xylene
with
and
without
the
emulsifier
is
needed
to
characterize
the
dissipation
of
the
herbicide
under
field
conditions.

°
The
geometries
and
flow
rate
of
the
irrigation
canals
and
ditches
where
xylene
is
applied
are
not
known;
therefore,
there
is
uncertainty
associated
with
estimated
exposure
concentrations.
The
geometry
and
environmental
parameters
of
the
ditch
used
in
this
assessment
is
intended
to
be
representative
of
a
small
segment
of
a
ditch
or
canal
to
which
xylenes
may
be
released.
It
is
understood
that
the
physical
properties
of
any
drainage
ditch
or
canal
may
vary
significantly
from
location
to
location;
therefore,
the
assumed
model
drainage
ditch
used
in
this
assessment
represents
a
source
of
uncertainty
in
the
assessment.

°
Inhalation
exposure
was
estimated
using
a
nondimensional
Henry's
law
constant
to
8
estimate
a
"
maximum
air
concentration"
from
a
concentration
in
solution
assuming
ideal
gas
and
steady
state
conditions.
The
transfer
process
of
xylene
from
water
to
the
atmosphere
is
dependant
upon
the
chemical
and
physical
properties
of
xylene
and
the
physical
properties
(
e.
g.,
flow
velocity,
depth,
and
turbulence)
of
the
water
body.
Factors
that
control
volatilization
of
xylene
are
solubility,
molecular
weight,
and
vapor
pressure
of
xylene
and
the
nature
of
the
air­
water
interface
through
which
it
must
pass.
The
volatilization
rates
from
water
are
highly
variable.
The
air
concentration
would
not
be
expected
to
exceed
the
value
estimated
from
the
Henry's
constant
and
solubility
values.

The
actual
flux
rate
of
xylenes
from
a
model
drainage
ditch
will
vary
over
a
4­
hour
exposure
period;
therefore,
the
actual
duration
of
inhalation
exposure
is
uncertain.
The
loss
of
xylenes
out
of
the
air
compartment
is
highly
uncertain
since
it
is
dependent
upon
several
environmental
parameters
(
e.
g.
wind
velocity)
which
will
vary
based
upon
location
and
time
of
year.
The
influence
of
the
emulsifiers
on
the
volatilization
of
xylene
is
not
known
(
except
to
increase
solubility).
Solubility
is
assumed
to
be
the
178
ppm
(
without
emulsifiers).
In
practice,
this
flux
can
be
expected
to
vary
with
changes
in
the
water
concentration,
such
that
the
flux
peaks
shortly
after
the
initial
application
to
water
and
decreases
as
the
concentration
in
water
decreases
due
to
transport
and
degradation.

The
ecological
effects
database
for
mixed
xylenes
is
incomplete.
Data
gaps
and
uncertainties
for
ecological
effects
have
been
identified
as
follows:

°
No
registrant­
submitted
toxicity
studies
in
which
xylene
mixtures
or
xylene
isomers
were
the
sole
active
ingredient
were
identified;
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
obtained
from
the
published
open
literature.
Although
some
of
the
acute
aquatic
studies
were
conducted
in
accordance
with
OECD
guidelines,
no
consistent
experimental
protocols
were
followed
for
estuarine/
marine
invertebrates.
Therefore,
there
is
a
high
degree
of
uncertainty
to
the
toxicity
data
for
this
taxonomic
group.

°
Toxicity
data
are
not
available
for
estuarine/
marine
fish;
therefore,
risks
for
this
taxonomic
group
are
assumed
based
on
xylene's
known
toxicity
to
freshwater
fish.

°
Toxicity
data
are
not
available
for
vascular
aquatic
macrophytes;
therefore,
risks
for
this
taxonomic
group
are
assumed
based
on
xylene's
mode
of
action
as
an
aquatic
herbicide
and
available
information
on
the
toxicity
of
xylene
to
non­
vascular
aquatic
plants.

°
There
is
uncertainty
associated
with
the
acute
dietary
toxicity
study
for
birds,
given
xylene's
high
volatility.
Therefore,
the
registrant
should
provide
information
on
a
avian
LD
50
value
for
xylene
or
submit
an
acute
avian
oral
toxicity
study
(
LD
50
),
9
using
either
a
bobwhite
quail
or
mallard
duck,
to
satisfy
the
§
71­
1
guideline
requirements.

°
Acute
inhalation
toxicity
data
are
not
available
for
birds;
therefore,
avian
risk
from
inhalation
exposure
cannot
be
assessed.
10
II.
Problem
Formulation
A.
Stressor
Source
and
Distribution
1.
Source
and
Intensity
Aromatic
petroleum
products
that
are
used
for
aquatic
weed
killers
are
mixed
xylene
isomers
(
m­,
o­,
and
p­
isomers
of
xylene)
that
may
contain
minor
amounts
of
other
compounds
such
as
ethylbenzene.
Depending
upon
the
manufacturing
process,
xylene
may
also
initially
contain
benzene,
toluene,
trimethylbenzene,
phenol,
thiophene,
and
pyridine;
however,
the
combined
volume
of
these
non­
xylene
hydrocarbons
is
only
a
fraction
of
a
percentage
of
the
composition
of
mixed
xylene
(
ATSDR
1995).
The
composition
of
a
mixed
xylene
depends
on
the
manufacturing
method
used.
Currently,
most
mixed
xylene
is
produced
as
a
catalytic
reformate
of
petroleum
and
consists
of
approximately
44%
m­
xylene,
20%
o­
xylene,
20%
p­
xylene,
and
15%
ethylbenzene
(
ATSDR,
1995).
Mixed
xylene
may
also
be
manufactured
from
coal
tar,
yielding
a
mixture
of
approximately
45 
70%
m­
xylene,
23%
p­
xylene,
10 
15%
o­
xylene,
and
6 
10%
ethylbenzene
(
ATSDR
1995).
Other
production
processes
include
gasoline
pyrolysis
and
disproportionation
of
toluene,
both
of
which
produce
a
mixture
of
xylenes
that
are
virtually
free
of
ethylbenzene
(
ATSDR
1995).
According
to
the
aquatic
weed
killer
product
labels
(
Sim­
Chem
Aquatic
Weed
Killer,
EPA
Reg.
No.
11682­
8;
T­
Chem
Aquatic
Weed
Killer,
EPA
Reg.
No.
9768­
18),
most
formulations
applied
to
drainage
ditches
to
control
unwanted
vegetation
are
98­
99%
mixed
xylenes
(
isomeric
ratios
unspecified)
and
about
1%
ethylbenzene.

Formulations
of
mixed
xylenes
are
used
to
control
unwanted
aquatic
vegetation
drainage
and
irrigation
ditches
by
application
below
the
surface
of
the
water.
To
apply
these
products
to
a
drainage
ditch,
a
boom
section
from
an
ordinary
sprayer
is
connected
to
the
pump
by
a
hose
and
then
lowered
to
the
bottom
of
the
channel
so
that
the
nozzle
flows
directly
into
the
water
without
hitting
the
bottom,
weeds
or
other
obstacles.
One
application
method
is
to
apply
at
several
locations,
each
typically
two
to
four
miles
apart.
At
each
location,
11
gallons
of
the
product
are
added
for
each
cubic
foot
per
second
(
cfs)
of
canal
flow,
over
an
application
period
of
20
to
30
minutes.
The
second
application
method
is
to
apply
six
gallons
of
product
per
cfs
flow,
over
a
20
to
30
minute
time
period,
at
successive
stations
one
mile
apart
down
channel.
An
application
is
typically
considered
to
be
an
effective
dose
if
it
results
in
a
treatment
concentration
of
740
mg/
L.
It
is
noted
that
this
concentration
exceeds
the
solubility
limits
of
xylenes
(
solubility
of
the
xylene
isomers
in
water
is
approximately
160­
180
ppm);
however,
xylenes
used
to
treat
drainage
ditches
are
usually
applied
with
an
emulsifier,
which
may
result
in
reduced
volatility
and
a
greater
apparent
solubility
(
and
thus
higher
exposure
levels)
than
the
actual
solubility
limits
in
water.

Aromatic
petroleum
solvents
are
used
to
control
submerged
weeds
and
pond
scum
in
drainage
ditches
or
canals,
and
cannot
be
used
in
rivers,
lakes,
or
streams.
As
specified
on
the
label,
any
water
from
a
treated
ditch
flowing
into
receiving
waters
should
contain
less
than
10
ppm
xylene
and
treated
water
should
not
be
used
for
domestic
or
livestock
purposes.
11
2.
Physical/
Chemical/
Fate
and
Transport
Properties
The
most
important
dissipation
pathway
for
xylenes
applied
to
a
drainage
ditch
is
volatilization.
Xylenes
are
also
susceptible
to
biodegradation
under
aerobic
conditions,
but
the
rate
of
volatilization
(
half­
life
of
about
2
days
in
a
shallow
water
body;
1.2
days
in
typical
river
and
6.0
days
in
a
pond
(
http://
www.
epa.
gov/
OGWDW/
dwh/
t­
voc/
xylenes.
html)
is
significantly
greater
than
the
rate
of
degradation
(
half­
life
on
the
order
of
20
days)
(
API
1994).
Abiotic
degradation
mechanisms,
such
as
hydrolysis
and
photolysis,
are
not
important
for
aromatic
petroleum
solvents.
Xylenes
have
a
high
to
moderate
mobility
in
soils,
thus
when
volatilization
does
not
readily
occur
xylenes
could
leach
to
groundwater.
For
example,
when
applied
directly
to
water,
leaching
of
xylene
to
the
soil
from
the
canal
or
ditch
is
possible;
however,
groundwater
below
the
ditch
is
not
likely
to
be
a
source
of
drinking
water.
The
chemical
and
physical
properties
of
the
three
isomers
of
xylene
are
provided
in
Table
1.
Other
than
increasing
the
"
solubility",
the
influence
of
the
emulsifiers
used
during
the
addition
of
xylene
to
the
irrigation
water
is
not
known.

Table
1.
Physical
and
Chemical
Properties
of
Xylene
Isomers.

Property
m­
Xylene
a,
b
o­
Xylene
a,
b
p­
Xylene
a,
b
Molecular
Weight
106.16
106.16
106.16
Melting
point
(
oC)
­
47.8
­
25.2
13.2
Boiling
point
(
oC)
139.1
144.5
138.3
Density
(
g/
cm3)
0.864
0.88
0.861
Water
solubility
(
mg/
L)
161
178
162
log
Kow
3.2
3.12
3.15
Vapor
pressure
(
mm
Hg)
8.29
6.61
8.84
Henry's
law
constant
(
atmm3
mol)
0.00718
0.00518
0.00690
Aerobic
soil
metabolism
half­
life
5.8
days
5
days
c
7
days
c
Aerobic
aquatic
metabolism
halflife
14­
23
days
d
9­
20
days
d
14­
25
days
d
Anaerobic
aquatic
metabolism
half­
life
>
400
days
d
>
400
days
d
>
400
days
d
Koc
(
adsorption)
39­
365
e
39­
365
e
39­
365
e
Table
1.
Physical
and
Chemical
Properties
of
Xylene
Isomers.

Property
m­
Xylene
a,
b
o­
Xylene
a,
b
p­
Xylene
a,
b
12
a
ATSDR
1995
b
HSDB
2005
c
Tsao
et
al.
1998
d
API
1994
e
Pavlostathis
and
Mathavan
1992
3.
Pesticide
Type,
Class,
and
Mode
of
Action
Xylenes
are
considered
a
contact
herbicide,
and
are
phytotoxic
to
most
vegetation.
Contact
herbicides
act
quickly
by
destroying
plant
cells;
however,
they
do
not
kill
the
roots
and
reapplication
several
weeks
or
months
following
the
initial
application
may
be
required.
Aquatic
weeds
have
limited
cuticle
to
protect
cell
membranes.
Xylene
solubilize
the
hydrophobic
tail
of
the
phospholipid
bilayer
that
makes
up
the
cell
membrane,
causing
the
membrane
to
leak
and
allowing
internal
fluids
to
escape.
When
the
effect
is
severe,
weeds
are
killed.

The
mechanisms
by
which
xylene
produces
toxic
effects
in
animals
is
not
established.
However,
several
theories
exist,
including
alterations
of
lipid
cell
membrane
fluidity,
alteration
of
cell
membrane
protein
conformation,
changes
in
central
nervous
system
neurotransmitters,
and
inhibition
of
microsomal
enzymes
(
ATSDR
1995).

4.
Overview
of
Pesticide
Usage
Chem
Aquatic
Weed
Killer
(
EPA
Reg.
No.
9768­
18),
the
only
registered
pesticide
product
containing
aromatic
emulsifiable
petroleum
solvents,
is
used
to
control
submerged
weeds
in
irrigation
and
drainage
canals.
Targeted
weeds
include
a
variety
of
aquatic
nuisances
such
as
surface
pond
scum
(
filamentous
algae),
American
pondweed
(
Potamogeton
nodosus
Poir),
horned
pondweed
(
Zannichellia
palustris),
leafy
pondweed
(
Potamogeton
foliosus
Raf
),
Richardson's
pondweed
(
Potamogeton
richardsonii),
curly
leaf
pondweed
(
Potamogeton
crispus),
coon
tail
water
weed
(
Ceratophyllum
demers)
and
water
star
grass
(
Heteranthera
dubia).
Usage
data
for
aromatic
emulsifiable
petroleum
solvents
is
non­
existent.
No
pesticide
usage
data
are
available
in
publicly
available
databases
including
the
National
Center
for
Agricultural
and
Food
Policy
(
NCFAP
2005),
National
Agricultural
Statistics
Service
Chemical
Usage
Database
(
NASS
2005),
and
the
California
Department
of
Pesticide
Regulation
Pesticide
Use
Reporting
system
(
CDPR
2005).
The
Washington
State
Department
of
Ecology
reported
that
over
750,000
gallons
of
xylene
were
used
to
treat
drainage
ditches
in
Oregon,
Washington
and
Idaho
in
1967
(
WSDE
2002).
Data
from
1969
(
USDI­
BR,
1969)
reports
similar
use
levels
(
800,000
gallons
per
season)
including
more
than
10,000
applications
to
40,000
miles
(
equivalent
to
1
application
every
4
miles)
of
canals,
laterals,
and
drains
throughout
the
Pacific
Northwest.

Based
on
information
on
the
label,
Chem
Aquatic
Weed
Killer
may
be
used
only
in
states
specified
13
in
the
Bureau
of
Reclamation,
Reclamation
Act/
Newlands
Act
of
1902.
States
included
in
the
Reclamation
Act
include
Arizona,
California,
Colorado,
Idaho,
Kansas,
Montana,
Nebraska,
Nevada,
New
Mexico,
North
Dakota,
Oklahoma,
Oregon,
South
Dakota,
Utah,
Washington,
and
Wyoming.

B.
Receptors
Each
assessment
endpoint
requires
one
or
more
measures
of
ecological
effect,
which
are
defined
as
changes
in
the
attributes
of
an
assessment
endpoint
itself
or
changes
in
a
surrogate
entity
or
attribute
in
response
to
exposure
to
a
pesticide.
For
mixed
xylenes,
ecological
measurement
endpoints
for
the
screening
level
risk
assessment
are
based
on
a
selection
of
toxicity
studies
performed
on
a
limited
number
of
organisms
in
broad
groupings.
Within
each
of
these
very
broad
taxonomic
groups,
the
most
sensitive
acute
endpoint
is
selected
from
the
available
test
data.
A
complete
discussion
of
the
toxicity
data
selected
for
this
risk
assessment
for
each
taxonomic
group
is
provided
in
Appendix
E.

The
chemical
of
interest
for
this
risk
assessment
is
mixed
xylenes,
which
is
a
mixture
of
the
three
isomeric
xylene
compounds
(
ortho­
,
meta­,
and
para­
xylene).
To
assess
risk
to
aquatic
and
terrestrial
receptors,
data
obtained
from
toxicity
studies
using
mixed
xylenes
and
the
xylene
isomers
were
considered.
The
lowest
toxicity
value
from
data
on
mixed
xylenes
and
the
individual
xylene
isomers
was
used
to
estimate
risk.

1.
Aquatic
Effects
Acute
toxicity
data
from
the
open
literature
was
used
to
evaluate
potential
effects
for
aquatic
receptors.
Data
sufficient
for
use
in
a
quantitative
risk
assessment
for
mixed
xylenes
and/
or
xylene
isomers
are
available
for
freshwater
fish,
freshwater
invertebrates,
estuarine/
marine
invertebrates,
and
algae.
Although
no
studies
suitable
for
quantitative
risk
assessment
were
identified
for
estuarine/
marine
fish
and
vascular
aquatic
plants,
risks
for
these
taxonomic
groups
were
qualitatively
evaluated.
Since
mixed
xylenes
are
highly
volatile,
surface
water
concentrations
are
expected
to
decrease
rapidly;
thus,
chronic
exposure
to
aquatic
plants
and
animals
is
not
anticipated.

2.
Terrestrial
Effects
The
anticipated
exposure
pathways
for
terrestrial
animals
are
oral
exposure
via
drinking
of
contaminated
water,
and
inhalation
exposure
of
volatilized
xylene.
Based
on
these
exposure
scenarios,
open
literature
data
sources
were
queried
for
acute
and
subacute
oral
and
acute
inhalation
toxicity
studies
in
birds
and
mammals.
Acceptable
subacute
oral
toxicity
studies
were
identified
for
mammals,
an
acute
dietary
study
was
identified
for
birds,
and
acute
inhalation
toxicity
studies
were
identified
for
mammals;
the
lack
of
acute
inhalation
data
in
birds
was
treated
as
a
data
gap
in
this
assessment.
Due
to
rapid
volatilization,
chronic
exposure
of
terrestrial
receptors
is
not
14
anticipated.
In
addition,
given
that
mixed
xylenes
are
applied
directly
below
the
surface
of
water,
exposure
of
terrestrial
plants
is
not
anticipated.
Although
terrestrial
plants
may
potentially
be
exposed
via
treated
ditch
or
canal
water
used
as
irrigation
water,
exposures
are
expected
to
be
minimal
given
xylene's
high
rate
of
volatilization.

3.
Ecosystems
at
Risk
Aquatic
ecosystems
potentially
at
risk
include
the
irrigation
and
drainage
canals
where
xylene
is
applied
to
control
aquatic
weeds,
as
well
as
return
flows
of
treated
irrigation
waters
into
receiving
rivers,
streams,
or
lakes.
For
use
in
coastal
areas,
aquatic
habitat
also
includes
marine
ecosystems
including
estuaries.
Given
that
the
drainage
canals
are
used
as
a
source
of
irrigation
water,
it
is
assumed
that
these
systems
are
primarily
freshwater,
whereas
receiving
water
bodies
may
be
either
freshwater
or
estuarine/
marine,
depending
on
proximity
to
coastal
areas.
In
addition,
it
should
be
noted
that
irrigation
canals
and
drainage
ditches
contain
water
only
during
the
growing
season
when
they
are
delivering
water
to
crops.
As
such,
they
can
be
dry
from
3
to
6
months
out
of
the
year,
depending
on
the
area
and
crops
being
irrigated.
Although
these
canals
and
ditches
are
likely
to
be
intermittent,
these
aquatic
systems
provide
viable
habitat
for
such
organisms
as
larval
amphibians,
aquatic
reptiles,
benthic
aquatic
invertebrates
(
including
a
number
of
emergent
insects),
and
diapausal
pelagic
(
i.
e.,
living
in
the
open
water)
invertebrates
and
fish;
spawning
habitat
for
fishes;
and
feeding
habitat
for
piscivorous
and
insectivorous
wildlife.

Given
the
method
of
application,
exposure
of
terrestrial
ecosystems
to
xylene
is
expected
to
be
minimal;
however,
terrestrial
mammals
and
birds
may
be
exposed
via
drinking
water
and
inhalation
pathways.
In
addition,
terrestrial
ecosystems
may
be
potentially
exposed
to
treated
irrigation
water
used
for
furrow
or
flood
irrigation,
although
exposures
are
expected
to
be
minimal
given
xylene's
high
rate
of
volatilization.

Ecosystems
potentially
at
risk
are
expressed
in
terms
of
the
selected
assessment
measures
of
effect.
The
typical
assessment
measures
of
effect
for
screening­
level
pesticide
ecological
risk
assessments
are
reduced
survival,
and
reproductive
and
growth
impairment
for
both
aquatic
and
terrestrial
animal
species.
Aquatic
species
of
potential
concern
include
freshwater
fish
and
invertebrates,
estuarine/
marine
fish
and
invertebrates,
amphibians,
algae,
and
aquatic
macrophytes.
Terrestrial
species
of
potential
concern
include
birds
and
mammals.
For
both
aquatic
and
terrestrial
animals,
direct
acute
exposures
are
considered.
Due
to
the
rapid
volatilization
of
mixed
xylenes,
chronic
exposures
are
not
considered
in
this
assessment.
Since
mixed
xylenes
are
applied
under
the
surface
of
the
water,
exposures
of
terrestrial
plants
and
topical
exposure
of
beneficial
insects
are
not
considered
in
this
assessment.
The
types
of
toxicity
studies
available
for
mixed
xylenes
and
isomers
of
xylene
are
summarized
in
Table
2.

In
order
to
protect
threatened
and
endangered
(
listed)
species,
all
assessment
endpoints
are
measured
at
the
individual
level.
Although
all
endpoints
are
measured
at
the
individual
level,
they
provide
insight
about
risks
at
higher
levels
of
biological
organization
(
e.
g.
populations
and
communities).
For
example,
pesticide
effects
on
individual
survival
have
important
implications
for
15
both
population
rates
of
increase
and
habitat
carrying
capacity.

The
ecological
relevance
of
selecting
the
above­
mentioned
assessment
measures
of
effect
is
as
follows:
1)
complete
exposure
pathways
exist
for
these
receptors;
2)
the
receptors
may
be
potentially
sensitive
to
pesticides
in
affected
media;
and
3)
the
receptors
could
potentially
inhabit
areas
where
pesticides
are
applied.

Table
2.
Summary
of
Assessment
Endpoints
and
Measures
of
Effect
for
Xylene
Mixtures
and
Xylene
Isomers.

Assessment
Endpoint
Measure
of
Effect
1.
Abundance
(
i.
e.,
survival,
reproduction,
and
growth)
of
individuals
and
populations
of
birds.
1a.
Japanese
quail
5­
day
oral
LC50
(
non­
guidelinerecommended
species).
1b.
Acute
inhalation
LC50:
No
data.

2.
Abundance
(
i.
e.,
survival,
reproduction,
and
growth)
of
individuals
and
populations
of
mammals.
2a.
Laboratory
rat
subacute
oral
LD50.
2b.
Laboratory
rat
acute
inhalation
LC50.

3.
Survival
and
reproduction
of
individuals
and
communities
of
freshwater
fish
and
invertebrates.
3a.
Rainbow
trout
and
bluegill
sunfish
acute
LC50
(
guideline­
recommended
species).
Acute
LC50
in
fathead
minnow,
guppy,
goldfish,
and
white
sucker
fish
(
non­
guideline­
recommended
species).
3b.
Water
flea
acute
LC50
(
guideline­
recommended
species).
Snail
acute
LC50
(
non­
guidelinerecommended
species).

4.
Survival
and
reproduction
of
individuals
and
communities
of
estuarine/
marine
fish
and
invertebrates.
4a.
No
data
for
estuarine/
marine
fish.
4a.
Acute
LC50
in
grass
shrimp,
brine
shrimp,
and
sea
urchin
eggs
(
non­
guideline­
recommended
species).

6.
Survival
and
reproduction
of
individuals
and
communities
of
non­
vascular
and
vascular
aquatic
plants.
6a.
Acute
EC50
in
algae
Selenastrum
capricornutum
and
Skeletonema
costarum
((
guideline­
recommended
species).
6b.
No
data
for
vascular
aquatic
plants.

LD50
=
Lethal
dose
to
50%
of
the
test
population.
LC50
(
EC50)
=
Lethal
(
effective)
concentration
to
50%
of
the
test
population.
NOAEC
=
No­
observed­
adverse­
effect
concentration.
LOAEC
=
Lowest­
observed­
adverse­
effect
concentration.

C.
Assessment
Endpoints
Assessment
endpoints
are
defined
as
"
explicit
expressions
of
the
actual
environmental
value
that
is
to
be
protected."
Defining
an
assessment
endpoint
involves
two
steps:
1)
identifying
the
valued
attributes
of
the
environment
that
are
considered
to
be
at
risk;
and
2)
operationally
defining
the
assessment
endpoint
in
terms
of
an
ecological
entity
(
i.
e.,
a
community
of
fish
and
aquatic
invertebrates)
and
its
attributes
(
i.
e.,
survival
and
reproduction).
Therefore,
selection
of
the
16
assessment
endpoints
is
based
on
valued
entities
(
i.
e.,
ecological
receptors),
the
ecosystems
potentially
at
risk,
the
migration
pathways
of
pesticides,
and
the
routes
by
which
ecological
receptors
are
exposed
to
pesticide­
related
contamination.
The
selection
of
clearly
defined
assessment
endpoints
is
important
because
they
provide
direction
and
boundaries
in
the
risk
assessment
for
addressing
risk
management
issues
of
concern.

A
summary
of
the
assessment
endpoints
and
measures
of
effects
selected
to
characterize
potential
ecological
risks
associated
with
exposure
to
mixed
xylenes
and
isomers
is
provided
in
Table
2.

This
ecological
risk
assessment
considers
exposures
for
the
label­
recommended
range
of
surface
water
concentrations
for
mixed
xylenes
applied
directly
below
the
water
surface
to
control
aquatic
weeds.
Mixed
xylenes
are
applied
to
achieve
an
initial
concentration
of
approximately
740
ppm,
with
the
concentration
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
rivers
and
streams)
not
to
exceed
10
ppm.
However,
since
the
maximum
allowable
concentration
of
740
ppm
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
o­
xylene
of
178
ppm
(
the
highest
solubility
limit
reported
for
the
three
xylene
isomers).
This
exposure
estimate
was
chosen
to
provide
consistency
with
the
chemical­
physical
properties
of
xylenes
applied
without
the
addition
of
emulsifiers.
This
assessment
is
not
intended
to
represent
a
site­
or
time­
specific
analysis.
Instead,
this
assessment
is
intended
to
represent
highend
exposures
at
a
national
level.
Likewise,
the
most
sensitive
toxicity
measures
of
effect
are
used
from
surrogate
test
species
to
estimate
treatment­
related
direct
effects
on
acute
mortality.
Toxicity
tests
are
intended
to
determine
effects
of
mixed
xylenes
exposure
on
birds,
mammals,
fish,
aquatic
invertebrates,
and
aquatic
plants.
These
short­
term
acute
studies
are
typically
arranged
in
a
hierarchical
or
tiered
system
that
progresses
from
basic
laboratory
tests
to
applied
field
studies.
The
toxicity
studies
are
used
to
evaluate
the
potential
of
mixed
xylenes
and/
or
xylene
isomers
to
cause
adverse
effects,
to
determine
whether
further
testing
is
required,
and
to
determine
the
need
for
precautionary
label
statements
to
minimize
the
potential
adverse
effects
to
non­
target
animals
and
plants
(
CFR
40
§
158.202,
2002).

D.
Conceptual
Model
A
conceptual
model
provides
a
written
description
and
visual
representation
of
the
predicted
relationships
between
the
stressor,
potential
routes
of
exposure,
and
the
predicted
effects
for
the
assessment
endpoint.
The
conceptual
model
consists
of
two
major
components:
the
risk
hypotheses
and
a
diagram.

1.
Risk
Hypotheses
Risk
hypotheses
are
specific
assumptions
about
potential
adverse
effects
(
i.
e.,
changes
in
assessment
endpoints)
and
may
be
based
on
theory
and
logic,
empirical
data,
mathematical
models,
or
probability
models
(
US
EPA
2004).
For
this
assessment,
the
risk
is
stressor­
initiated,
where
the
stressor
is
the
release
of
mixed
xylenes
to
the
environment.
The
following
risk
hypothesis
is
presumed
for
this
screening
level
assessment:
17
Non­
target
aquatic
animals
and
plants
and
terrestrial
animals
may
be
exposed
to
mixed
xylenes
that
are
applied
underwater
according
to
the
label
to
control
aquatic
weeds
in
drainage
and
irrigation
ditches.
Based
on
available
information
regarding
volatilization,
persistence,
and
direct
and
indirect
toxicity,
mixed
xylenes
have
the
potential
to
compromise
survival
and
cause
sublethal
effects
in
non­
target
aquatic
animals
and
plants,
and
terrestrial
mammals
and
birds.

Aquatic
receptors
that
may
be
exposed
to
mixed
xylenes
include
aquatic
animals
(
i.
e.,
freshwater
and
estuarine/
marine
fish
and
invertebrates,
and
aquatic­
phase
amphibians)
and
plants.
Terrestrial
receptors
that
may
be
exposed
to
mixed
xylenes
include
terrestrial
and
semi­
aquatic
wildlife
(
i.
e.,
mammals,
birds,
reptiles,
and
terrestrial­
phase
amphibians).
Since
mixed
xylenes
are
applied
underwater,
exposure
of
terrestrial
plants
and
topical
exposure
of
insects
is
not
anticipated.
Furthermore,
given
the
high
volatility
of
mixed
xylenes,
chronic
exposure
of
aquatic
and
terrestrial
receptors
is
not
anticipated.
The
open
literature
was
reviewed
to
provide
data
for
identifying
potential
endpoints,
stressors,
and
ecological
effects
associated
with
uses
of
mixed
xylenes
and
xylene
isomers.

Based
on
the
available
acute
toxicity
data
from
the
open
literature,
measures
of
effect
suitable
for
a
quantitative
assessment
of
xylene
mixtures
have
been
identified.
Aquatic
toxicity
data
can
be
used
to
quantify
potential
adverse
effects
associated
with
reduction
of
aquatic
invertebrates
and
fish,
indirect
effects
on
aquatic
communities
due
to
loss
of
species
that
are
sensitive
to
mixed
xylenes,
and
changes
in
structure
and
functional
characteristics
of
the
affected
communities.
For
the
aquatic
ecosystem,
acute
toxicity
data
are
available
for
freshwater
fish
and
invertebrates,
estuarine/
marine
invertebrates,
and
aquatic
algae.
For
the
terrestrial
ecosystem,
acute
toxicity
data
were
identified
to
quantify
mammalian
and
avian
risks
associated
with
exposure
to
mixed
xylenes
via
consumption
of
contaminated
water.
In
addition,
inhalation
toxicity
data
is
available
to
characterize
risks
associated
with
inhalation
of
contaminated
air
by
mammals.

2.
Diagram
The
conceptual
model
used
to
depict
the
potential
ecological
risk
associated
with
mixed
xylenes
is
fairly
generic
and
assumes
that
as
a
pesticide,
mixed
xylenes
are
capable
of
affecting
aquatic
organisms
at
the
anticipated
environmental
concentrations
resulting
from
proposed
label
uses.
All
potential
routes
of
exposure
are
considered
and
presented
in
the
conceptual
model
(
Figure
1).
The
conceptual
model
generically
depicts
the
potential
source
of
mixed
xylenes,
release
mechanisms,
abiotic
receiving
media,
biological
receptor
types,
and
effects
endpoints
of
potential
concern.

In
order
for
a
chemical
to
pose
an
ecological
risk,
it
must
reach
ecological
receptors
in
biologically
significant
concentrations.
An
exposure
pathway
is
the
means
by
which
a
contaminant
moves
in
the
environment
from
a
source
to
an
ecological
receptor.
For
an
ecological
exposure
pathway
to
be
complete,
it
must
have
a
source,
a
release
mechanism,
an
environmental
transport
medium,
a
18
point
of
exposure
for
ecological
receptors,
and
a
feasible
route
of
exposure.
The
assessment
of
ecological
exposure
pathways,
therefore,
includes
an
examination
of
the
source
and
potential
migration
pathways
for
constituents,
and
the
determination
of
potential
exposure
routes
(
e.
g.,
ingestion,
inhalation,
dermal
contact).

Exposure
to
aquatic
organisms
and
plants
is
expected
from
surface
waters
contaminated
with
mixed
xylenes
through
direct
application
and
from
treated
irrigation
water
that
flows
into
receiving
rivers,
streams,
or
lakes.
Due
to
the
high
volatility
of
mixed
xylenes,
chronic
exposure
of
aquatic
and
terrestrial
ecosystems
is
not
expected
to
occur.
Since
mixed
xylenes
are
applied
underwater,
exposure
of
terrestrial
plants
via
direct
application
or
spray
drift
or
contamination
of
plants
and
insect
forage
sources
for
terrestrial
animals
are
not
anticipated
exposure
pathways.
Based
on
the
use
pattern
for
xylenes,
the
main
exposure
pathways
for
terrestrial
animals
are
exposure
via
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.
19
Application
of
Mixed
Xylenes
to
Irrigation
and
Drainage
Canals
Direct
Subsurface
Application
Surface
Water
Ingestion
of
Contaminated
Water
Mammals
Birds
Reduced
Survival
Sublethal
Effects
Receptors
Attribute
Changes
Exposure
Point
Source/
Exposure
Media
Source/
Transport
Pathways
Surface
Water
Gill/
Integument
Uptake
Aquatic
Invertebrates
Aquatic
Vertebrates
Amphibians
Algae
and
Aquatic
Plants
Reduced
Survival
Sublethal
Effects
Surface
Water
Inhalation
(
Xylenes
Volatilized
from
Water)

Mammals
Birds
Reduced
Survival
Sublethal
Effects
Treated
Irrigation
Water
&

Return
Flow
Direct
Contact
Water
Ingestion
Inhalation
Aquatic
Invertebrates
Aquatic
Vertebrates
Amphibians
Aquatic
Plants
Mammals
Birds
Figure
1.
Ecological
Conceptual
Exposure
Model
for
Screening­
Level
Risk
Assessment
of
Mixed
Xylenes
Applied
to
Irrigation
Canals
and
Drainage
Ditches
20
E.
Analysis
Plan
The
Agency's
reregistration
eligibility
science
chapter
for
mixed
xylenes
consists
of
a
deterministic
screening
level
risk
quotient
analysis.
This
document
characterizes
the
environmental
fate
and
effects
of
mixed
xylenes
to
aquatic
and
terrestrial
environments.
Since
mixed
xylenes
are
highly
volatile,
chronic
exposure
of
aquatic
and
terrestrial
ecosystems
is
not
anticipated;
thus,
this
analysis
plan
focuses
on
acute
exposure
only.

For
aquatic
animals,
the
pathway
of
mixed
xylenes
exposure
is
by
direct
application
to
water.
Risks
to
aquatic
species
are
based
on
the
maximum
allowable
concentrations
in
water
in
irrigation
canals
and
receiving
water;
that
is,
an
initial
concentration
of
740
ppm,
with
the
concentration
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
rivers
and
streams)
not
to
exceed
10
ppm.
Since
the
maximum
allowable
concentration
of
740
ppm
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
o­
xylene
of
178
ppm.
This
exposure
estimate
was
chosen
to
provide
consistency
with
the
chemical/
physical
properties
of
xylenes
applied
without
the
addition
of
emulsifiers.

Since
mixed
xylenes
are
applied
directly
below
the
water
surface,
terrestrial
exposure
pathways
and
receptors
typically
considered
in
EFED
science
chapters,
i.
e.,
exposure
of
terrestrial
animal
food
sources
and
plants
via
direct
application
or
spray
drift,
are
not
considered.
Any
potential
exposure
to
terrestrial
ecosystems
via
treated
irrigation
water
is
expected
to
be
minimal.
Based
on
the
use
pattern
for
xylenes,
the
main
exposure
pathways
for
terrestrial
animals
are
exposure
via
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.
To
assess
exposure
of
terrestrial
animals
via
ingestion
of
contaminated
water,
the
maximum
allowable
concentrations
in
irrigations
canals
and
receiving
water
(
740
and
10
ppm,
respectively),
and
the
maximum
solubility
limit
for
o­
xylene
(
178
ppm)
were
used.
To
determine
the
average
amount
of
drinking
water
that
birds
and
mammals
may
consume,
allometric
equations
or
empirical
values
given
in
the
Wildlife
Exposure
Factors
Handbook
were
used.
Xylene
concentrations
in
air
were
estimated
using
Henry's
Law
constant,
which
relates
the
concentration
of
a
compound
in
the
gas
phase
to
its
concentration
in
the
liquid
phase.
Assumptions
include
steady­
state
conditions
and
two
phases
(
air
and
water)
which
are
partitioned
by
the
non­
dimensional
Henry's
law
constant.
Insufficient
toxicity
data
are
available
to
assess
risk
of
acute
inhalation
exposure
of
avian
species.
To
assess
the
risk
to
mammals
from
a
combination
of
exposure
via
drinking
water
and
inhalation,
a
"
composite"
risk
quotient
(
RQ)
was
derived.
The
composite
RQ
was
defined
as
the
sum
of
oral
(
drinking
water)
and
inhalation
RQs.

No
registrant­
submitted
studies
in
which
mixed
xylenes
or
xylene
isomers
were
the
sole
active
ingredient
were
identified.
Thus,
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
obtained
from
the
published
open
literature.
Four
sources
were
used
to
identify
appropriate
open
literature
publications:
EPA's
Ecotoxicology
database
ECOTOX,
the
Agency
for
Toxic
Substances
and
Disease
Registry
(
ATSDR)
Toxicological
Profile
for
Xylene
(
ATSDR
1995),
the
World
Health
Organization
(
WHO)
Environmental
Health
Criteria
Document
for
Xylenes
(
WHO
1997),
and
the
National
Toxicology
Program
(
NTP)
Technical
Report
on
Xylene
(
NTP,
1986).
21
Risks
were
estimated
based
on
a
deterministic
approach,
where
a
single
point
estimate
of
toxicity
is
divided
by
an
upper
and
lower
bound
exposure
estimate
to
calculate
a
risk
quotient
(
RQ).
The
acute
RQ
values
for
each
taxonomic
group
identified
as
an
assessment
endpoint
were
compared
to
the
Agency's
Levels
of
Concern
(
LOCs).
LOCs
serve
as
criteria
for
categorizing
potential
risk
to
non­
target
organisms.
RQ
values
were
calculated
in
the
risk
estimation
section
for
each
endpoint,
and
characterization
and
interpretation
of
risk
is
described
in
the
risk
description.
Risks
for
each
taxonomic
group
were
described
based
on
available
lines
of
evidence
from
open
literature
data
on
mixed
xylenes
and
the
three
xylene
isomers.
In
addition,
a
preliminary
assessment
of
listed
species
of
concern
was
also
completed.

1.
Preliminary
Identification
of
Data
Gaps
and
Methods
The
adequacy
of
the
submitted
data
was
evaluated
relative
to
Agency
guidelines.
The
following
identified
data
gaps
for
ecological
fate
and
effects
measures
of
effect
result
in
a
degree
of
uncertainty
in
evaluating
the
ecological
risks
of
xylenes.

°
There
is
uncertainty
regarding
the
maximum
exposure
concentrations
for
aquatic
organisms
in
both
the
irrigation
canals
and
receiving
waters.
The
solubility
limits
for
xylene
isomers
are
approximately
160­
180
mg/
L;
however,
they
are
applied
with
an
emulsifier
which
may
result
in
a
greater
apparent
solubility,
possibly
approaching
the
initial
740
ppm
concentration
level.
There
is
also
uncertainty
in
assuming
the
concentration
in
receiving
water
bodies
and
water
ways.
The
label
permits
concentrations
of
xylene
of
up
to
10
ppm
to
be
released
in
receiving
waters;
however,
it
is
unlikely
that
large
volumes
of
irrigation
water
would
be
released
to
receiving
water
bodies
(
given
its
high
value
in
western
states),
and
concentrations
in
receiving
water
are
likely
to
be
less
than
10
ppm
due
to
dissipation
and
dilution.

°
No
registrant­
submitted
toxicity
studies
in
which
mixed
xylenes
or
xylene
isomers
were
the
sole
active
ingredient
were
identified;
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
identified
from
published
open
literature.
Although
some
of
the
acute
aquatic
studies
were
conducted
in
accordance
with
OECD
guidelines,
no
consistent
experimental
protocols
were
followed
for
estuarine/
marine
invertebrates.
Therefore,
there
is
a
high
degree
of
uncertainty
to
the
toxicity
data
for
this
taxonomic
group.

°
Toxicity
data
on
estuarine/
marine
fish
and
vascular
aquatic
plants
suitable
for
quantitative
used
in
risk
assessment
was
not
identified
from
the
available
literature.
Given
xylene's
acute
toxicity
to
freshwater
fish,
it
is
assumed
that
similar
adverse
effects
are
likely
for
estuarine/
marine
fish.
In
addition,
because
mixed
xylenes
are
used
to
control
aquatic
vegetation,
it
is
anticipated
that
exposure
will
produce
adverse
effects
in
vascular
aquatic
plants,
including
macrophytes.

°
Acute
inhalation
data
on
avian
species
were
not
identified
from
the
available
22
literature;
therefore,
risks
associated
with
avian
inhalation
of
xylene
that
has
volatilized
from
xylene­
treated
waters
is
not
possible.

°
There
is
uncertainty
associated
with
the
acute
dietary
toxicity
study
for
birds,
given
xylene's
high
volatility.
Therefore,
the
registrant
should
provide
information
on
a
avian
LD
50
value
or
submit
an
acute
avian
oral
toxicity
study
(
LD
50
),
using
either
a
bobwhite
quail
or
mallard
duck,
to
satisfy
the
§
71­
1
guideline
requirements.

2.
Measures
to
Evaluate
Risk
Hypotheses
and
Conceptual
Model
a.
Measures
of
Exposure
Water
Exposure
Water
in
canals
and
ditches
treated
with
xylene
is
expected
to
have
xylene
concentrations
ranging
from
740
ppm
(
the
initial
maximum
concentration
in
the
treated
canal
or
ditch
based
on
11
gallons
of
product
applied
over
a
20­
30
minute
period
to
water
flowing
at
1
cfs)
at
the
point
of
application
to
10
ppm
(
current
maximum
allowable
concentration
in
return
flow).
When
concentrations
fall
below
100
or
200
ppm,
additional
xylene
may
be
applied
as
a
"
booster
application"
(
Walsh
et
al.
1977),
suggesting
that
xylene
concentrations
must
be
greater
than
100
ppm
to
be
effective
in
controlling
aquatic
weeds.
The
xylene
concentrations
at
the
release
points
for
return
flow
should
not
exceed
10
ppm,
but
may
be
less
based
on
limited
monitoring
data.

The
change
in
concentration
of
a
chemical
being
released
into
a
flowing
water
channel
depends
upon
its
concentration
in
the
water
entering
the
channel
(
return
flow
concentration
­
Co),
the
rate
the
solution
water
is
entering
the
channel
(
return
flow
rate
­
Q),
the
initial
concentration
in
the
channel
(
receiving
water
­
assumed
to
be
0
for
xylene),
and
the
amount
of
water
in
the
channel
(
volume
­
Vol).
Concentration
reductions
were
approximated
by
a
simple
steady­
state
plug
flow
model.

Several
receiving
water
body
geometries
were
considered:
equal
volumes
of
return
flow
and
receiving
water,
and
10,
20,
and
50
times
the
return
flow
volumes.
Larger
volumes
such
as
in
a
lake
or
a
river
could
result
in
an
even
larger
dilution.
Since
it
is
assumed
that
the
flow
rates
are
the
same
for
the
released
water
and
the
receiving
water,
the
dilution
would
reflect
increases
in
the
area
(
width
times
depth)
of
the
water
channel.
A
"
no
dilution"
scenario
was
also
presented
to
represent
xylene­
treated
flowing
water
in
a
dry
channel
and
to
provide
an
upper
bound
of
the
time
necessary
to
hold
the
water
before
being
released.
23
Inhalation
Exposure
The
rapid
volatilization
of
xylene
from
water
suggests
that
mammalian
and
avian
species
may
be
exposed
to
levels
of
volatilized
xylene
over
short
time
durations.
Inhalation
exposure
is
related
to
the
flux
rate
(
i.
e.,
mass
per
unit
time
transported
to
air),
the
exposure
duration
associated
with
toxicity,
and
the
dimensions
of
the
breathing
zone
for
a
potential
receptor.
For
this
assessment,
the
xylene
concentration
in
the
air
following
application
to
a
drainage
ditch
was
estimated
using
Henry's
Law,
which
relates
the
concentration
of
a
compound
in
air
to
its
concentration
in
water.

Xylene
concentrations
are
assumed
to
be
uniform
through
the
"
breathing
zone"
To
estimate
an
inhalation
exposure
concentration,
the
averaging
time
of
4­
hours
was
used
to
correspond
with
the
exposure
duration
used
in
the
available
mammalian
toxicity
studies.

b.
Measures
of
Effect
No
registrant­
submitted
studies
in
which
mixed
xylenes
or
xylene
isomers
were
the
sole
active
ingredient
were
identified.
Thus,
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
obtained
from
the
published
literature.
Four
sources
were
used
to
identify
appropriate
open
literature
publications:
EPA's
Ecotoxicology
database
ECOTOX,
the
ATSDR
Toxicological
Profile
for
Xylene
(
ATSDR
1995),
the
WHO
Environmental
Health
Criteria
Document
for
Xylenes
(
WHO
1997),
and
the
National
Toxicology
Program
(
NTP)
Technical
Report
on
Xylene
(
NTP,
1986).
There
is
an
extensive
body
of
literature
on
the
ecological
effects
of
mixed
xylenes
and
xylene
isomers.
However,
a
full
review
of
all
open
literature
is
beyond
the
scope
of
this
risk
assessment.
Therefore,
the
review
of
the
available
open
literature
data
was
focused
on
publications
identified
in
the
ECOTOX
database.
Additional
publications
including
ATSDR,
WHO,
and
NTP
were
also
consulted
in
order
to
provide
a
comprehensive
review
of
available
toxicity
information.

The
chemical
of
interest
for
this
risk
assessment
is
mixed
xylenes,
which
is
a
mixture
of
the
three
isomeric
xylene
compounds
(
ortho­
,
meta­,
and
para­
xylene).
To
assess
risk
to
aquatic
and
terrestrial
receptors,
data
obtained
from
toxicity
studies
using
mixed
xylenes
and
xylene
isomers
were
considered.
The
most
sensitive
endpoint
from
either
the
mixed
xylene
or
individual
isomer
data
was
used
to
estimate
risk.

A
complete
summary
of
the
measures
of
effect
based
on
toxicity
studies
for
different
ecological
receptors
and
measures
of
effect
for
mixed
xylenes
and
isomers
is
provided
in
Table
1,
with
study
details
provided
in
Appendix
E.
Given
the
rapid
volatilization
of
xylenes,
chronic
toxicity
tests
are
not
required;
however,
the
Agency
reserves
the
right
to
request
additional
data
if
label
usage
changes.

c.
Measures
of
Ecosystem
and
Receptor
Characteristics
The
terrestrial
and
aquatic
ecosystems
considered
in
this
assessment
are
intended
to
be
generally
representative
of
any
aquatic
or
terrestrial
ecosystem
associated
with
areas
where
mixed
xylenes
are
used.
The
receptors
addressed
by
the
aquatic
and
terrestrial
risk
assessments
are
summarized
in
24
Table
1.
For
aquatic
assessments,
freshwater
fish
and
invertebrates,
estuarine/
marine
fish
and
invertebrates,
and
algae
are
represented.
For
terrestrial
assessments,
birds
and
mammals
are
represented
by
three
different
weight
categories.
Detailed
information
regarding
the
data
available
for
these
various
classes
of
aquatic
and
terrestrial
receptors
is
provided
in
Appendix
E.

III.
Analysis
A.
Use
Characterization
Chem
Aquatic
Weed
Killer,
the
only
registered
pesticide
product
(
EPA
Reg.
No.
9768­
18)
containing
aromatic
emulsifiable
petroleum
solvents,
is
used
to
control
submerged
weeds
in
irrigation
and
drainage
canals.
The
product
is
used
by
the
Bureau
of
Reclamation,
the
U.
S.
Dept.
of
Interior,
and
cooperating
state
water
use
organizations
to
control
a
variety
of
aquatic
nuisances
such
as
surface
pond
scum
(
filamentous
algae),
American
pondweed,
horned
pondweed
,
leafy
pondweed,
Richardson's
pondweed,
curly
leaf
pondweed,
coon
tail
water
weed,
and
water
star
grass.
Applications
depend
on
the
individual
water
body,
but
in
general
the
product
is
applied
to
drainage
ditches
as
a
liquid
when
weed
growth
begins
to
impede
water
flow.
The
formulated
product
is
highly
toxic
to
fish
and
other
aquatic
organisms,
and
consists
of
98%
mixed
xylene
isomers
and
small
quantities
of
ethylbenzene
and
emulsifiers
to
aid
in
the
dispersal
of
the
xylenes
throughout
the
channel.
The
influence
of
the
emulsifiers
on
the
fate
and
toxicity
test
values
is
not
known;
however,
for
the
purposes
of
this
assessment,
their
influence
will
not
alter
the
conclusions
significantly
since
the
toxic
thresholds
for
aquatic
organisms
is
significantly
lower
than
the
solubility
of
xylene.

Current
usage
data
for
aromatic
emulsifiable
petroleum
solvents
is
non­
existent.
No
pesticide
usage
data
are
available
in
publicly
available
databases
including
the
National
Center
for
Agricultural
and
Food
Policy
(
NCFAP
2005),
National
Agricultural
Statistics
Service
Chemical
Usage
Database
(
NASS
2005),
and
the
California
Department
of
Pesticide
Regulation
Pesticide
Use
Reporting
system
(
CDPR
2005).
No
current
estimates
of
usage
are
available
at
the
state
level
and
historical
estimates
are
sporadic.
One
reference
from
the
Washington
State
Department
of
Ecology
indicates
that
in
1967
over
750,000
gallons
of
xylene
were
used
to
treat
drainage
ditches
in
Oregon,
Washington
and
Idaho
(
WSDE
2002).
Data
from
1969
(
USDI­
BR,
1969)
reports
similar
use
levels
(
800,000
gallons
per
season)
including
more
than
10,000
applications
to
40,000
miles
(
equivalent
to
1
application
every
4
miles)
of
canals,
laterals,
and
drains
throughout
the
Pacific
Northwest.

Based
on
information
on
the
label,
Chem
Aquatic
Weed
Killer
may
be
used
only
in
states
included
in
the
Bureau
of
Reclamation,
Reclamation
Act/
Newlands
Act
of
1902.
These
states
include
Arizona,
California,
Colorado,
Idaho,
Kansas,
Montana,
Nebraska,
Nevada,
New
Mexico,
North
Dakota,
Oklahoma,
Oregon,
South
Dakota,
Utah,
Washington,
and
Wyoming.
While
these
are
the
states
where
it
is
theoretically
used,
actual
use
is
probably
in
far
fewer
states.
25
B.
Exposure
Characterization
1.
Environmental
Fate
and
Transport
Characterization
a.
Summary
of
Empirical
Data
Following
application
to
a
drainage
ditch,
xylenes
is
expected
to
volatilize
rapidly.
Xylene
has
a
sweet
smell
and
an
odor
threshold
of
about
1
ppm.
Photolysis
and
hydrolysis
are
not
important
environmental
fate
pathways
since
these
compounds
do
not
absorb
photons
of
light
with
a
wavelength
greater
than
290
nm,
nor
do
they
possess
functional
groups
that
are
susceptible
to
hydrolysis
under
environmental
conditions.
In
aquatic
systems,
xylenes
undergo
biodegradation
under
aerobic
conditions
relatively
quickly,
with
half­
lives
on
the
order
of
20
days,
but
degradation
under
anaerobic
conditions
proceeds
very
slowly.
Other
than
increasing
the
"
solubility,
the
influence
of
the
emulsifiers
on
the
fate
the
xylenes
are
not
known.
The
Agency
assumes
that
the
emulsifiers
will
also
lower
"
volatility."

b.
Degradation
and
Metabolism
The
degradation
rate
of
xylene
under
aerobic
and
anaerobic
conditions
have
been
summarized
in
peer
reviewed
papers
from
the
open
literature
and
several
review
articles
and
databases
(
ATSDR
1995;
HSDB
2005).
Although
much
of
the
published
literature
seeks
to
determine
the
environmental
fate
of
xylene
when
released
from
petroleum
storage
tanks,
spills,
etc.,
these
data
may
still
be
useful
when
assessing
the
fate
of
xylenes
applied
to
control
aquatic
vegetation
in
a
drainage
ditch.
In
general,
under
aerobic
conditions,
the
half­
lives
of
the
isomers
of
xylene
in
soil
range
from
several
days
to
a
few
weeks,
although
at
very
high
concentrations
(
as
might
be
encountered
at
a
petroleum
spill),
these
compounds
can
be
toxic
to
microorganisms,
resulting
in
long
lag
periods
and
a
slow
rate
of
degradation.
Since
aromatic
petroleum
solvents
used
as
aquatic
weed
killers
are
not
applied
to
soil
surfaces
or
terrestrial
vegetation,
aerobic
and
anaerobic
biodegradation
in
soils
will
not
be
an
important
fate
process
for
these
products.

In
aquatic
systems,
xylenes
were
shown
to
degrade
readily
under
aerobic
conditions,
but
were
generally
not
degraded
under
anaerobic
conditions.
Using
PS­
6
gasoline
as
a
substrate,
and
microcosms
constructed
of
3
g
of
sandy
soil
and
20
mL
of
groundwater,
the
individual
xylene
isomers
maintained
under
aerobic
environments
had
biodegradation
half­
lives
of
approximately
9­
25
days
depending
upon
the
initial
starting
conditions
(
API
1994).
Under
anaerobic
conditions,
very
little
degradation
was
observed
over
a
400
day
incubation
period.

c.
Transport
and
Mobility
The
large
vapor
pressure
(
approximately
6.6
to
9.6
mm
Hg)
and
Henry's
law
constants
(
approximately
0.005
to
0.008
atm­
m3/
mol)
for
the
isomers
of
xylene
suggest
that
volatilization
from
water
surfaces
will
be
an
important
route
of
dissipation
for
these
compounds
(
ATSDR
1995).
An
experiment
which
measured
the
rate
of
evaporation
of
xylenes
from
a
1:
1000
jet
fuel:
water
mixture
found
that
this
rate
averaged
approximately
0.6
times
the
oxygen
re­
aeration
rate
(
Smith
26
and
Harper
1980).
Combining
this
ratio
with
oxygen
reaeration
rates,
the
half­
life
for
evaporation
of
xylenes
from
a
typical
river
or
pond
is
estimated
as
29
and
144
hours,
respectively.
While
volatilization
from
water
is
a
significant
route
of
dissipation,
volatilization
from
water
is
controlled
by
the
water
phase
rather
than
the
vapor
phase.

Xylenes
have
moderate
to
high
mobility
in
soils
based
upon
K
oc
values
in
the
range
of
39­
365
(
Lindhardt
et
al.
1994;
Pavlostathis
and
Mathavan1992;
Vowles
and
Mantoura
1987).
Since
aromatic
petroleum
solvents
are
used
for
aquatic
weed
control,
they
are
not
directly
applied
to
terrestrial
vegetation
(
sites);
however,
irrigation
water
containing
xylene
flows
onto
terrestrial
sites
Therefore,
irrigation
of
fields
with
xylene­
treated
water
may
result
in
runoff
and/
or
return
flow
of
xylene­
treated
water
in
receiving
water
bodies.
Since,
the
xylene
is
applied
to
a
flowing
water
body
(
canal
or
ditch),
leaching
out
(
or
leakage)
of
the
canal
is
possible.
Because
many
of
these
canals
or
ditches
only
contain
water
part
of
the
year,
it
is
unlikely
that
any
groundwater
present
around
these
ditches
would
be
used
for
drinking
water.
When
water
is
present
in
the
canals
or
ditches,
water
would
tend
to
move
away
from
the
channel,
when
the
channel
is
dry,
water
would
tend
to
move
back
toward
the
channel.

d.
Field
Studies
Terrestrial
and
groundwater­
contaminated
field
studies
have
been
conducted
to
predict
the
environmental
fate
of
xylene
in
the
case
of
an
accidental
spill
or
leaking
underground
petroleum
tank.
These
studies
are
not
highly
relevant
to
the
environmental
fate
of
aromatic
petroleum
solvents
applied
to
a
drainage
ditch
to
control
unwanted
surface
vegetation.

Six
irrigation
canals
located
in
Wyoming,
Colorado,
and
Washington
were
treated
with
aquatic
weed
killer
containing
emulsified
xylenes
(
Walsh
et
al.
1977).
This
product
was
released
at
a
rate
of
10
gallons
per
cfs
of
water
flow
within
a
30
minute
emission
period,
corresponding
to
an
initial
theoretical
xylene
level
of
740
ppm
(
Walsh
et
al.
1977).
In
one
of
the
canals,
xylene
levels
dissipated
from
~
555
ppm
to
<
10
ppm
one
mile
downstream
from
its
release
point.
In
the
other
canals
with
greater
water
velocity,
xylene
levels
remained
at
100
ppm
or
greater
for
at
least
4
miles
downstream.
In
general,
the
xylene
levels
declined
to
100­
200
ppm
or
less
after
travelling
5­
10
miles
downstream.
However,
monitoring
of
xylene
residues
in
return
flow
in
the
same
study
showed
a
decrease
in
concentration
from
500
ppm
in
the
water
removed
from
lateral
ditches
used
for
irrigation
to
less
than
0.2
ppm
(
200
ppb)
(
study
detection
limit)
in
return
flow
after
flowing
through
irrigation
fields
(
length
of
irrigation
rills
750
to
1320
feet).
No
half­
life
was
reported
nor
was
any
attempt
made
to
discern
the
most
important
dissipation
pathway,
although
it
was
assumed
volatilization
was
responsible
for
dissipation
in
the
canals.

Recently
the
Agency
obtained
limited
monitoring
from
the
Washington
State
Department
of
Ecology
(
WDE,
2005).
The
samples
were
collected,
from
one
to
several
sampling
stations
and
from
one
to
several
times,
during
2002
to
2004
from
four
irrigation
districts.
These
data
reported
xylene
concentrations
in
irrigation
waste
water
(
prior
to
release)
to
range
between
0.004
and
10.9
ppm.
There
were
67
detections
out
of
108
samples.
The
mean
value
was
0.862
ppm.
About
25
percent
of
the
detections
had
concentration
less
than
0.04
ppm
and
about
80
percent
of
the
27
detections
were
less
than
1.0
ppm.

Additional
data
on
the
affect
emulsifiers
on
the
properties
of
xylene
in
water
would
be
useful
to
quantify
the
rates
of
dissipation
associated
with
different
irrigation
methods,
furrow
lengths,
field
conditions,
channel
geometries,
and
flow
rates
and
how
these
factors
influence
the
concentration
of
xylene
in
return
flows.
These
data
have
moderate
value
and
would
be
useful
in
further
refining
exposure
to
nontarget
and
listed
species.

e.
Bioaccumulation
Bioconcentration
factors
(
BCF)
ranging
from
14
to
24
have
been
reported
for
fish
exposed
to
xylene
isomers(
Ogata
and
Miyaka
1978;
Ogata
et
al.
1984).
These
BCF
values
suggest
that
bioconcentration
and
bioaccumulation
in
aquatic
organisms
is
low.

2.
Measures
of
Aquatic
Exposure
a.
Aquatic
Exposure
Modeling
Water
in
canals
and
ditches
treated
with
xylene
are
expected
to
have
xylene
concentrations
ranging
from
740
ppm
(
the
initial
maximum
concentration
in
the
treated
canal
or
ditch)
at
the
point
of
application
to
10
ppm
(
current
maximum
allowable
concentration
in
return
flow
).
When
concentrations
fall
below
100
ppm
(
effective
concentration),
an
additional
xylene
application
may
be
required
downstream
from
initial
point
of
application
(
Walsh
et
al.,
1977).
The
xylene
concentrations
of
the
return
flow
at
the
release
points
to
receiving
water
bodies
should
not
exceed
10
ppm,
but
may
be
less.

The
xylene
concentration
in
the
treated
irrigation
and
drainage
canals
and
channels
depend
upon
the
flow
rates
of
the
water,
the
geometry
of
the
ditch
or
canal,
and
the
dissipation
rates
of
xylene
in
the
treated
canal.
The
concentration
in
the
receiving
water
body
depends
upon
the
concentration
in
the
return
flow,
the
individual
flow
rates
of
the
return
flow
and
receiving
water
body,
the
geometry
of
the
receiving
water
body,
and
the
degradation
rates
of
xylene
in
the
receiving
water
body.

A
simple
steady­
state
plug
flow
model
was
used
to
estimate
the
exposure
concentrations
in
the
receiving
waters
(
Appendix
B).
The
change
in
concentration
of
a
chemical
being
released
into
a
flowing
water
channel
depends
upon
its
concentration
in
the
water
entering
the
channel
(
return
flow
concentration
­
Co),
the
rate
the
solution
water
is
entering
the
channel
(
return
flow
rate
­
Q),
the
initial
concentration
in
the
channel
(
receiving
water
­
assumed
to
be
0
for
xylene)
and
the
amount
of
water
in
the
channel
(
volume
­
Vol).
The
model
assumes
that
mixing
is
ideal
(
constantly
stirred),
Q
is
constant,
and
the
same
amount
of
water
enters
the
channel
as
leaves
the
channel
(
with
no
leaching
or
evaporation).
Assuming
steady­
state
flow
system,
the
mass
balance
describing
the
time
variation
of
the
concentration
in
a
flowing
channel
can
be
estimated
by
the
following
equation:

C(
t)
=
C
o
*
exp((
TVol/
Q)*­
R)
28
where:

C(
t)
=
Concentration
in
mixed
water
body
(
mass/
volume)
at
time
t
C
o
=
initial
concentration
in
return
flow
(
mass/
volume),
assumed
=
10
ppm
R
=
first­
order
degradation
rate
constant
for
volatilization
(
1/
time);
median
of
literature
values
for
flowing
water.

Q
=
Flux
density
(
length3/
time)

TVol
=
Volume
of
return
flow
+
volume
of
receiving
water
(
i.
e.,
dilution)
(
length3)

and
where
TVol
=
Cross­
sectional
area
of
receiving
water
+
cross­
sectional
area
of
return
flow
(
length2)
*
flow
rate
(
length/
time).
When
there
is
no
receiving
water
volume,
the
volume
of
receiving
water
is
0
and
the
Tvol
is
equal
to
the
volume
of
return
flow.

Several
receiving
water
body
geometries
were
considered:
a
dry
ditch
containing
no
water
(
dilution
0),
equal
volumes
of
return
flow
and
receiving
water
(
dilution
1:
1),
and
10,
20,
and
50
times
the
return
flow
volumes
(
Tables
3).
Larger
volumes
such
as
those
in
a
lake
or
a
river
could
result
in
an
even
larger
dilution.

Table
3.
Relationship
Between
Return
Flow
Volume
and
Receiving
Water
Volumes
Used
in
the
Plug
Flow
Model.

Dilution
Q
Discharged
Return
Flow
Receiving
water
Total
Flux
(
ft3/
s)
Velocity
(
ft/
s)
Area
(
ft2)
vol
(
ft3)
Velocity
(
ft/
s)
Area
(
ft2)
vol
(
ft3)
TVol
(
ft3)

no
dilution­
dry
channel
1
1
1
1
0
0
0
1
1:
1
1
1
1
1
1
1
1
2
10:
1
1
1
1
1
1
10
10
11
20:
1
1
1
1
1
1
20
20
21
50:
1
1
1
1
1
1
50
50
51
The
model
was
used
to
provide
an
estimate
of
the
time
or
travel
distance
downstream
needed
to
reduce
the
xylene
concentration
in
the
return
flow
(
assumed
10
ppm)
to
a
concentration
less
than
the
0.04
ppm
(
mg/
L).
The
0.04
mg/
L
level
represents
a
concentration
of
xylene
in
water
that
is
29
expected
to
protective
of
listed
aquatic
species
(
see
the
Risk
Description
to
Aquatic
Organisms,
Section
IV.
B.
1).
When
the
receiving
water
flow
rate
is
equal
to
return
flow
rates,
almost
8
days
are
required
for
the
concentration
to
drop
below
0.04
ppm,
10
to
1
ratio
(
volume
receiving
to
volume
return
flow)
about
1.5
days
are
required,
20:
1
ratio
about
0.76
days,
and
30
to
1
about
0.55
days.
Additional
discussion
can
be
found
in
Appendix
B.
Table
4
also
shows
that
almost
16
days
would
be
required
for
xylene
concentrations
to
dissipate
to
0.04
mg/
L
if
the
return
water
flows
into
a
dry
ditch.

Figure
2
shows
the
decline
in
xylene
concentrations
as
calculated
from
the
plug
flow
model
with
different
dilution
ratios.
Estimated
dilution
factors
are
derived
from
the
assumed
geometry
(
shape)
of
the
receiving
water
body
(
width
and
depth).
The
wider
and/
or
deeper
the
channel,
the
greater
the
volume
available
for
dilution.
Figure
2
shows
the
length
of
time
it
takes
for
xylene
to
decline
to
a
concentration
that
is
protective
of
listed
aquatic
species
with
no
dilution(
degradation­
volatilization
only)
at,
1
to
1
equal
volumes,
10
to
1,
20
to
1,
and
50
to
1
volume
of
receiving
water
to
volume
of
return
flows
(
assume
=
flow
rate).

Figure
2.
Conce
ntration
of
Xylene
in
Receiving
Water
Versus
Dilution
and
Time.
(
Dilutions
are
none,
10:
1,
20:
1,
and
50:
1).

b.
Aquatic
Exposure
Monitoring
and
Field
Data
30
Data
from
a
paper
published
by
Walsh
predicts
xylene
concentrations
of
<
0.2
ppm
in
return
flows
from
treated
fields.

Xylenes
are
ubiquitous
in
the
environment
due
to
fugitive
emissions
from
industrial
sources,
automobiles,
and
accidental
spills
of
petroleum
solvents.
Typical
xylene
levels
usually
range
from
about
4
to
130
:
g/
m3
in
outdoor
air
(
ATSDR
1995).
According
to
groundwater
surveys
conducted
in
the
United
States,
xylenes
are
generally
detected
in
less
than
5%
of
groundwater
samples.
However,
xylene
concentrations
in
contaminated
groundwater
have
been
reported
as
high
as
10,000
ppb
(
ATSDR
19955).
Less
than
6%
of
drinking
water
samples
collected
during
U.
S.
drinking
water
surveys
contained
xylenes,
and
mean
concentrations
in
positive
samples
were
typically
less
than
2
ppb.
Since
xylenes
volatilize
rapidly
from
surface
water,
little
data
exists
regarding
background
levels
in
streams,
lakes,
etc.
Limited
data
were
located
in
EPA's
STORET
database
(
US
EPA
2005)
regarding
the
levels
of
total
xylenes
(
m­
xylene,
p­
xylene,
and
o­
xylene)
in
treated
drainage
canals.
STORET
contained
samples
collected
by
Dade
Environmental
Resource
Management
(
Florida)
for
25
drainage
canals
with
concentrations
of
1.2
:
g/
L
or
less,
however
there
is
little
indication
as
to
the
source
of
the
xylene.
STORET
also
reports
that
the
Alaska
Department
of
Environmental
Conservation
detected
xylene
concentrations
as
high
as
75,000
:
g/
L
in
a
ground
water
monitoring
well
contaminated
by
a
former
gasoline
service
station
(
site
102.26.003MW004).
It
is
important
to
note
that
these
concentrations
are
the
result
of
groundwater
contamination
by
leaking
underground
storage
tanks,
and
not
pesticide
usage.
These
concentrations
are
not
expected
to
result
from
pesticide
application,
but
do
provide
an
illustration
of
the
ubiquitousness
and
magnitude
of
xylenes
introduced
into
the
environment
from
non­
pesticide
sources.

The
m­,
o­,
and
p­
isomers
of
xylene
have
been
detected
in
both
surface
water
and
ground
water
in
the
USGS
NAQWA
monitoring
program
(
drinking
water).
In
surface
water,
the
m­
xylene
isomer
was
detected
in
13.5
percent
of
the
samples,
and
the
o­
and
p­
xylene
isomers
were
detected
in
18.9
percent
(
n=
56)
of
the
samples.
In
ground
water,
m­
xylene
was
detected
in
5.3
percent
and
p­
and
oxylene
were
detected
in
10.8
percent
of
the
samples
(
n
=
78).
The
maximum
detected
concentrations
of
o­
xylene
in
surface
water
and
groundwater
was
1.16
:
g/
L
and
0.93
:
g/
L,
respectively.

3.
Measures
of
Terrestrial
Exposure
a.
Terrestrial
Exposure
Modeling
The
anticipated
exposure
pathways
for
terrestrial
animals
are
oral
exposure
via
consumption
of
contaminated
water
and
inhalation
exposure
of
volatilized
xylene.
Exposure
estimates
for
these
pathways
were
derived
as
described
in
the
following
sections.
31
(
1).
Estimates
for
Exposure
Via
Consumption
of
Contaminated
Water
To
determine
the
exposure
of
mammals
and
birds
to
xylenes
via
consumption
of
contaminated
water,
a
single
daily
dose
of
xylenes
was
estimated
using
the
calculated
volume
of
water
that
birds
and
mammals
are
expected
to
consume
per
day
and
the
concentration
of
xylenes
in
water
as
follows:

Daily
Exposure
(
mg/
kg
BW)
=
Daily
Water
Consumption
(
L)
×
Water
Concentration
(
mg/
L)
Body
Weight
(
kg)

For
this
risk
assessment,
water
concentrations
were
taken
as
the
maximum
allowable
concentration
range
for
mixed
xylenes
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
178
mg/
L.
Mixed
xylenes
are
applied
to
achieve
an
initial
concentration
of
approximately
740
ppm,
with
the
concentration
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
rivers
and
streams)
not
to
exceed
10
ppm.
However,
since
the
maximum
allowable
concentration
of
740
ppm
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
oxylene
of
178
ppm
(
the
highest
solubility
limit
reported
for
the
three
xylene
isomers).
This
exposure
estimate
was
chosen
to
provide
consistency
with
the
chemical
physical
properties
of
xylenes
applied
without
the
addition
of
emulsifiers.

To
estimate
the
volume
of
water
that
mammals
and
birds
are
expected
to
consume
per
day,
allometric
equations
from
the
EPA
Wildlife
Exposure
Factors
Handbook
(
US
EPA
1993)
were
used.
For
birds,
the
daily
water
consumption
(
L)
was
calculated
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.059
and
$
=
0.67
(
US
EPA
1993,
Equation
3­
15,
p.
3­
8,
for
all
birds).
For
mammals,
the
daily
water
consumption
(
L)
was
calculated
as
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.099
and
$
=
0.9
(
US
EPA
1993,
Equation
3­
7,
p.
3­
10,
for
all
mammals).
As
summarized
in
Table
4,
a
single
daily
exposure
via
drinking
water
containing
10
and
740
mg/
L
xylenes
was
calculated
for
three
weight
classes
of
birds
(
20,
100,
and
1000g)
and
mammals
(
15,
35,
and
1000g).
32
Table
4.
Exposure
Estimates
for
Birds
and
Mammals
via
Consumption
of
Contaminated
Water.

Species
Body
Weight
(
g)
Daily
Water
Consumption
(
L)
a
Estimates
for
Exposure
from
Contaminated
Water
b
Minimum
Exposure
(
mg/
kg
BW)
Based
on
a
Water
Concentration
of
10
mg/
L
Maximum
Exposure
(
mg/
kg
BW)
Based
on
a
Water
Concentration
of
740
mg/
L
Exposure
(
mg/
kg
BW)
Based
on
a
Water
Concentration
of
178
mg/
L
c
Birds
20
0.0043
2.15
160
38.5
100
0.013
1.30
96
23
1000
0.059
0.59
43.7
10.5
Mammals
15
0.0023
1.53
113
27.3
35
0.0048
1.37
103
24.3
1000
0.099
0.99
73.3
17.6
a
For
birds,
the
daily
water
consumption
(
L)
was
calculated
using
the
following
equation:
"
(
body
weight)
$,
where
"
=
0.059
and
$
=
0.67
(
US
EPA
1993,
Equation
3­
15,
p.
3­
8,
for
all
birds).
For
mammals,
the
daily
water
consumption
(
L)
was
calculated
as
using
the
following
equation:
"
(
body
weight)
$,
where
"
=
0.099
and
$
=
0.9
(
US
EPA
1993,
Equation
3­
7,
p.
3­
10,
for
all
mammals).
b
Exposure
estimates
based
were
calculated
as
follows:
Daily
exposure
(
mg/
kg
BW)
=
(
Daily
water
consumption
(
L)
×
Water
concentration
(
mg/
L))/
BW
(
kg).
b
Concentration
based
on
the
solubility
limit
for
o­
xylene.

(
2).
Estimates
for
Exposure
via
Inhalation
of
Volatilized
Xylenes
The
rapid
volatilization
of
xylene
from
water
suggests
that
mammalian
and
avian
species
may
be
exposed
to
high
levels
of
volatilized
xylene
over
short
time
durations.
Although
volatilization
from
water
is
rapid,
it
is
more
rapid
in
air.
Thus,
the
water
phase
controls
the
volatilization
of
xylene
from
water.
The
non­
dimensional
Henry's
law
constant
was
used
to
calculate
a
xylene
exposure
concentration
in
air;
the
constant
relates
the
concentration
of
a
compound
in
the
gas
phase
(
air)
to
its
concentration
in
water.
This
relationship
is
presented
in
the
following
equation:

H
nl
=
c
g
/
c
l
where:
H
nl
=
Henrys'
constant
(
nondimesional)

c
g
=
concentration
in
the
gas
phase
(
mass/
volume,
mg/
m3)
33
c
l
=
concentration
in
the
water
phase
(
mass/
volume,
mg/
m3)

This
relationship
provides
an
upper
limit
of
the
xylene
concentration
in
air
resulting
from
water
vaporization
of
xylene.
Thomas
(
1990)
suggests
that
for
compounds
with
Henry's
Law
constants
>
than
10­
3
atm­
mol­
3/
mol,
the
liquid
phase
will
control
the
transfer
from
the
liquid
phase
to
gas
phase.

A
conservative
inhalation
exposure
value
can
be
estimated
from
the
maximum
air
concentration,
the
exposure
duration
associated
with
toxicity,
and
the
dimensions
of
the
breathing
zone
for
a
potential
receptor.
The
volume
of
air
within
the
breathing
zone
of
a
receptor
is
based
on
the
effective
surface
area
of
the
receiving
water,
and
a
height
above
the
water
body
that
is
considered
relevant
to
ecological
receptors.
The
surface
area
of
the
channel
is
assumed
to
be
the
same
as
the
area
of
the
breathing
zone;
therefore,
the
area
can
be
simply
represented
by
a
unit
area
(
m2),
and
the
height
of
the
breathing
zone
for
terrestrial
receptors
(
i.
e.,
small
mammals
and
waterfowl)
is
assumed
to
be
0.1
m.
A
breathing
zone
height
of
0.1
m
was
chosen
to
represent
a
uniform
concentration
of
xylene.
The
average
breathing
zone
concentration
of
4­
hours
is
used
to
correspond
to
the
4­
hour
exposure
duration
used
in
the
available
mammalian
inhalation
toxicity
studies.
The
xylene
concentration
in
the
air
above
the
stream,
for
this
assessment
is
assumed
to
remain
constant
(
a
conservative
estimate).

The
maximum
estimated
exposure
concentration
for
volatilized
xylenes
is
summarized
in
Table
5.
To
convert
estimated
air
concentrations
of
xylene
expressed
in
terms
of
mg/
m3
to
ppm,
the
following
relationship
was
used:
1
mg/
m3
=
0.23
ppm
(
ATSDR
1995).
The
maximum
exposure
value
does
not
take
into
account
the
potential
loss
of
xylenes
in
the
breathing
zone
due
to
wind
and
degradation.
The
EEC
for
air
was
calculated
for
a
4­
hour
time
period
(
assuming
constant
exposure
during
this
period)
to
correspond
to
the
exposure
period
reported
for
the
inhalation
mammalian
toxicity
study
used
to
derive
acute
inhalation
risk
quotients
(
4­
hour
LC
50
value
of
6700
ppm
in
rats
for
mixed
xylenes;
Carpenter
1975).

Table
5.
Maximum
Estimated
Exposure
for
Volatilized
Xylenes.

Exposure
Scenario
EEC
(
mg/
m3)
EEC
a
(
ppm)

Maximum
Exposure
167.4
38.5
a
To
convert
the
EEC
in
expressed
terms
of
ppm
to
mg/
m3,
the
following
relationship
was
used:
1
mg/
m3
=
0.23
ppm
(
ATSDR
1995).
The
EEC
expressed
in
terms
of
ppm
was
used
to
derive
acute
inhalation
risk
quotients
for
mammals.
34
b.
Residue
Studies
Mixed
xylenes
are
applied
under
water
for
use
in
the
control
of
aquatic
weeds
in
drainage
and
irrigation
ditches.
Thus,
exposure
of
terrestrial
ecosystems
is
not
associated
with
the
use
of
this
chemical,
and
residue
studies
for
terrestrial
systems
were
not
considered.

C.
Ecological
Effects
Characterization
In
screening­
level
ecological
risk
assessments,
effects
characterization
describes
the
types
of
effects
a
pesticide
can
have
on
aquatic
or
terrestrial
organisms.
No
registrant­
submitted
studies
in
which
mixed
xylenes
or
xylene
isomers
were
the
sole
active
ingredient
were
identified.
Thus,
all
ecological
effects
data
reviewed
for
this
risk
assessment
were
obtained
from
the
published
open
literature.
Four
sources
were
used
to
identify
appropriate
open
literature
publications:
EPA's
Ecotoxicology
database
ECOTOX,
the
ATSDR
Toxicological
Profile
for
Xylene
(
ATSDR
1995),
and
the
WHO
Environmental
Health
Criteria
Document
for
Xylenes
(
WHO
1997),
and
the
National
Toxicology
Program
(
NTP)
Technical
Report
on
Xylene
(
NTP,
1986).
There
is
an
extensive
body
of
literature
on
the
ecological
effects
of
mixed
xylenes
and
xylene
isomers.
However,
a
full
review
of
all
open
literature
is
beyond
the
scope
of
this
risk
assessment.
Therefore,
the
review
of
the
available
open
literature
data
was
focused
on
publications
identified
in
the
ECOTOX
database.
Additional
publications
including
ATSDR,
WHO,
and
NTP
were
also
consulted
in
order
to
provide
a
comprehensive
review
of
available
toxicity
information.

Appendix
E
summarizes
the
results
of
the
open
literature
studies
used
to
characterize
effects
for
this
risk
assessment.
Toxicity
testing
reported
in
this
section
does
not
represent
all
species
of
birds,
mammals,
or
aquatic
organisms.
Only
a
few
surrogate
species
for
both
freshwater
fish
and
birds
are
used
to
represent
all
freshwater
fish
(
2000+)
and
bird
(
680+)
species
in
the
United
States.
For
mammals,
acute
studies
are
usually
limited
to
the
Norway
rat
or
the
house
mouse.
Estuarine/
marine
testing
is
usually
limited
to
a
crustacean,
a
mollusk,
and
a
fish.
Also,
testing
for
reptiles
and
amphibians
are
not
required.
The
risk
assessment
assumes
that
reptiles
are
not
more
sensitive
than
birds.
The
same
assumption
is
used
for
fish
and
amphibians
(
i.
e.,
amphibians
are
not
more
sensitive
than
fish).

1.
Aquatic
Effects
Characterization
The
acute
toxicity
reference
values
used
to
assess
risks
to
aquatic
organisms
are
summarized
in
Table
6.
A
more
detailed
summary
of
the
aquatic
toxicity
data
available
to
characterize
risks
associated
with
mixed
xylenes
and
xylene
isomers
is
given
in
Appendix
E,
Tables
E­
1
through
E­
5.
In
general,
results
of
acute
toxicity
studies
indicate
that
xylenes
are
moderately
to
highly
toxic
to
aquatic
animals.
It
is
important
to
note
that
due
to
their
high
volatility,
xylene
isomers
disappear
rapidly
from
solution.
In
a
study
evaluating
the
acute
toxicity
effects
of
xylenes
in
several
aquatic
species
using
an
open
system,
significant
losses
of
xylenes
were
observed
over
a
96­
hour
monitoring
period
(
19
to
99%
loss
from
24
to
96
hours)
(
Benville
and
Korn
1977).
Given
these
levels
of
loss,
exposure
concentrations
can
be
difficult
to
determine.
Therefore,
unless
toxicity
tests
were
35
conducted
under
closed
conditions,
interpretation
of
toxicity
data
in
aquatic
animals
may
be
confounded
by
the
rapid
loss
of
xylenes
from
solution.

The
chemical
of
interest
for
this
risk
assessment
is
mixed
xylenes,
a
combination
of
the
three
isomeric
xylene
compounds
(
ortho­
,
meta­,
and
para­
xylene).
To
assess
acute
risk
to
aquatic
organisms,
toxicity
data
was
obtained
from
studies
using
mixed
xylenes
and
the
three
isomeric
xylene
compounds.
Comparison
of
available
acute
toxicity
values
from
the
open
literature
shows
that
the
three
xylene
isomers
and
mixed
xylene
have
similar
potencies
in
aquatic
animals
(
Table
7).
It
should
be
noted,
however,
that
aquatic
toxicity
data
on
the
end
use
product
(
mixed
xylene
plus
the
emulsifier)
is
not
available;
therefore,
it
is
not
possible
to
determine
the
potential
effect
of
the
emulsifier
on
the
toxicity
of
aquatic
animals
and
plants.
36
Table
6.
Xylene
Toxicity
Reference
Values
(
TRVs)
for
Aquatic
Organisms.

Exposure
Scenario
Species
Exposure
Duration
Toxicity
Reference
Value
(
Test
Substance)
Reference
(
Classification)

Freshwater
Fish
Acute
rainbow
trout
96
hours
LC50
=
2.6
mg/
L
d
(
p­
xylene)
Galassi
et
al.,
1988
(
Supplemental)

Chronic
No
Data
(
not
required)

Freshwater
Invertebrates
Acute
Daphnia
magna
24
hours
IC50
=
1.0
mg/
L
a,
d
(
o­
xylene)
Galassi
et
al.,
1988
(
Supplemental)

Chronic
No
Data
(
not
required)

Estuarine/
Marine
Fish
Acute
No
Data
Chronic
No
Data
(
not
required)

Estuarine/
Marine
Invertebrates
Acute
sea
urchin
96
hours
EC50
=
4.1
mg/
L
d
(
o­
xylene)
Falk­
Petersen
et
al.
1985
(
Supplemental)

Chronic
No
Data
(
not
required)

Aquatic
Plants
Non­
vascular
plants
Selenastrum
capricornutum
72
hours
EC50
=
3.2
mg/
L
b,
c,
d
(
p­
xylene)
Galassi
et
al
1988
(
Supplemental)

Vascular
plants
No
Data
a
IC50
is
the
concentration
resulting
in
immobility
in
50%
of
the
test
organisms.
Immobility
is
used
as
a
surrogate
value
for
lethality.
b
EC50
is
the
concentration
resulting
in
growth
inhibition
in
50%
of
test
organisms.
c
Purity
of
test
material
was
not
specified;
therefore,
data
are
not
expressed
in
terms
of
the
concentration
of
a.
i.
d
Test
conducted
under
closed
conditions
to
minimize
loss
due
to
volatilization.
e
Test
conducted
under
open
conditions;
loss
due
to
volatilization
was
not
controlled.
37
Table
7.
Comparison
of
the
Range
of
Acute
Toxicity
Values
for
Mixed
Xylenes
and
Xylene
Isomers
in
Aquatic
Animals.

Species
Category
LC50
Value
(
Exposure
Time
in
Hours)

Mixed
Xylenes
o­
Xylene
m­
Xylene
p­
Xylene
Freshwater
Fish
Lowest
Value
no
data
7.6
mg/
L
(
96)
b
8.4
mg/
L
(
96)
b
2.6
mg/
L
(
96)
b
Highest
Value
no
data
16.1mg/
L
(
48)
c
12.9
mg/
L
(
96)
d
10
mg/
L
(
96)
a
Freshwater
Invertebrates
Lowest
Value
no
data
1.0
mg/
L
(
24)
e
4.7
mg/
L
(
24)
e
3.6
mg/
L
(
24)
e
Highest
Value
no
data
>
22.4
mg/
L
(
48)
f
9.6
mg/
L
(
48)
g
8.5
mg/
L
(
48)
g
Estuarine/
Marine
Fish:
no
data
Estuarine/
Marine
Invertebrates
Lowest
Value
7.4
mg/
L
(
96)
h
4.1
mg/
L
(
96)
i
19.3
mg/
L
(
48)
j
24.5
mg/
L
(
48)
j
Highest
Value
14.0
mg/
L
(
24)
h
24.7
mg/
l
(
48)
j
19.3
mg/
L
(
48)
j
24.5
mg/
L
(
48)
j
a
Species:
rainbow
trout
(
Folmar
et
al.
1976)
b
Species:
rainbow
trout
(
Galassi
et
al.
1988)
c
Species:
fathead
minnow,
bluegill
sunfish,
goldfish,
white
sucker
fish
(
Holcombe
et
al.
1987)
d
Species:
guppy
(
Galassi
et
al.
1988)
e
Species:
Daphnia
magna
(
Galassi
et
al.
1988)
f
Species:
snail
(
Holcombe
et
al.
1987)
g
Species:
Daphnia
magna
(
Abernethy
et
al.
1986)
h
Species:
grass
shrimp
(
Tatem
et
al.
1978)
i
Species:
sea
urchin
(
Falk­
Peterson
et
al.
1985)
j
Species:
brine
shrimp
(
Abernethy
et
al.
1986)

a.
Aquatic
Animals
(
1).
Acute
Effects
Freshwater
Fish
No
acute
toxicity
studies
on
mixed
xylenes
in
freshwater
fish
were
identified
from
the
available
literature.
The
acute
toxicity
of
xylene
isomers
has
been
evaluated
in
freshwater
fish;
study
details
38
are
provided
in
Appendix
E,
Table
E­
1.
The
acute
freshwater
fish
toxicity
data
show
similar
levels
of
toxicity
for
each
of
the
three
isomers
with
the
lowest
LC
50
values
ranging
from
2.6
to
7.6
mg
a.
i./
L.

For
o­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
7.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al,
1988)
to
the
96­
hour
LC
50
value
of
16.1
mg/
L
in
bluegill
sunfish,
fathead
minnow,
goldfish,
and
white
sucker
fish
(
Holcombe
et
al.
1978).
Results
of
these
studies
indicate
that
o­
xylene
is
slightly
to
moderately
toxic
to
freshwater
fish
on
an
acute
basis.
For
m­
xylene,
acute
toxicity
values
range
from
the
96­
hour
LC
50
value
of
8.4
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
to
the
96­
hour
LC
50
value
of
12.9
mg
a.
i./
L
in
guppy
(
Galassi
et
al.
1988),
suggesting
that
mxylene
is
moderately
toxic
to
freshwater
fish.
Acute
toxicity
values
for
p­
xylene
range
from
the
96­
hour
LC
50
value
of
2.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
to
the
96­
hour
LC
50
value
of
10
mg
a.
i./
L
in
rainbow
trout
(
Folmar
1976),
indicating
that
p­
xylene
is
moderately
toxic
to
freshwater
fish
on
an
acute
basis.
The
lowest
acute
toxicity
value
obtained
for
the
p­
xylene
isomer
(
96­
hour
LC
50
value
of
2.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
freshwater
fish.
The
study
by
Galassi
et
al.
(
1988)
was
conducted
in
accordance
with
OECD
standardized
method
No.
203,
modified
for
testing
volatile
compounds.
Closed
conditions
were
used
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.

The
acute
toxicity
of
xylene
(
type
not
specified)
and
xylene
plus
emulsifier
(
2%
AD­
410)
were
compared
in
a
single
artificial
stream
study
using
rainbow
trout
(
Walsh
et
al.
1977).
Results
of
this
study
show
that
the
addition
of
emulsifier
does
not
appear
to
alter
the
acute
toxicity
of
xylene.
The
24­
hour
LC
50
values
for
xylene
alone
and
xylene
plus
emulsifier
were
13
mg/
L
and
17.3
mg/
L,
respectively.
It
should
be
noted
that
these
acute
toxicity
values
are
not
true
24­
hour
LC
50
values;
fish
were
exposed
for
a
2­
hour
time
period
and
lethality
was
recorded
24
hours
after
the
start
of
exposure.

Freshwater
Invertebrates
No
acute
toxicity
studies
on
mixed
xylenes
in
freshwater
invertebrates
were
identified
from
the
available
literature.
The
acute
toxicity
of
xylene
isomers
has
been
evaluated
in
freshwater
invertebrates;
study
details
are
provided
in
Appendix
E,
Table
E­
2.
Results
indicate
that
the
three
xylene
isomers
have
similar
toxicities
to
freshwater
invertebrates.
For
o­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
1.0
mg
a.
i./
L
in
Daphnia
magna
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
>
22.4
mg/
L
in
the
snail
(
Holcombe
et
al.
1987),
indicating
that
the
toxicity
of
xylene
isomers
ranges
from
slightly
to
highly
toxic
in
freshwater
invertebrates.
For
m­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
4.7
mg
a.
i./
L
in
Daphnia
magna
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
9.6
mg
a.
i./
L
in
Daphnia
magna
(
Abernethy
et
al.
1986),
indicating
that
m­
xylene
is
moderately
toxic
to
freshwater
invertebrates.
Acute
toxicity
values
in
Daphnia
magna
for
p­
xylene
range
from
the
24­
hour
LC
50
value
of
3.6
mg
a.
i./
L
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
8.5
mg
a.
i./
L
(
Abernethy
et
al.
1986),
indicating
that
p­
xylene
is
moderately
toxic
to
freshwater
invertebrates
on
an
acute
basis.
The
lowest
acute
toxicity
value
obtained
for
the
o­
xylene
isomer,
the
24­
hour
LC
50
value
of
1.0
mg
a.
i./
L
in
Daphnia
magna
(
Galassi
et
al.
1988)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
freshwater
invertebrates.
As
39
previously
noted,
the
study
by
Galassi
et
al.
(
1988)
was
conducted
under
closed
conditions
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.
The
study
was
conducted
in
accordance
with
OECD
standardized
method
No.
202,
with
modifications
for
testing
volatile
compounds.
The
24­
hour
toxicity
value
of
1.0
mg
a.
i./
L
was
chosen
as
the
representative
acute
endpoint
for
freshwater
invertebrates
over
48­
hour
studies,
given
the
rapid
volatilization
of
xylene,
and
because
the
study
was
conducted
in
accordance
with
OECD
guidelines.

Estuarine/
Marine
Fish
No
acceptable
acute
toxicity
studies
on
mixed
xylenes
or
xylene
isomers
in
estuarine/
marine
fish
were
identified
from
the
available
literature.

Estuarine/
Marine
Invertebrates
The
acute
toxicity
of
mixed
xylenes
has
been
evaluated
in
grass
shrimp
(
Tatem
et
al.
1978);
study
details
are
provided
in
Appendix
E,
Table
E­
4.
Results
of
the
study
reports
an
acute
96­
hour
LC
50
value
of
7.4
mg/
L
in
grass
shrimp,
indicating
that
mixed
xylenes
are
moderately
toxic
to
estuarine/
marine
invertebrates.

Additional
information
on
the
acute
toxicity
of
xylene
in
estuarine/
marine
invertebrates
was
obtained
in
studies
using
xylene
isomers.
Study
details
are
summarized
in
Appendix
E,
Table
E­
4.
Results
indicate
that
the
xylene
isomers
have
a
similar
degree
of
toxicity
as
mixed
xylenes
to
estuarine/
marine
invertebrates.
For
o­
xylene,
acute
toxicity
values
range
from
the
96­
hour
embryo
lethality
EC
50
value
of
4.1
mg/
L
in
sea
urchin
eggs
(
Falk­
Petersen
et
al.
1985)
to
the
48­
hour
LC
50
value
of
24.7
mg/
L
in
brine
shrimp
(
Abernathy
et
al.
1986).
Results
of
these
studies
indicate
that
oxylene
is
slightly
to
moderately
toxic
to
estuarine/
marine
invertebrates
on
an
acute
basis.
For
mxylene
and
p­
xylene,
the
respective
48­
hour
LC
50
values
are
19.3
and
24.5
mg/
L
in
brine
shrimp
(
Abernathy
et
al.
1986),
suggesting
that
the
m­
xylene
and
p­
xylene
isomers
are
slightly
toxic
to
estuarine/
marine
invertebrates
on
an
acute
basis.

The
lowest
acute
toxicity
value
obtained
for
o­
xylene
(
the
96­
hour
EC
50
of
4.1
mg/
L
in
sea
urchin
eggs
(
Falk­
Petersen
et
al.
1985)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
estuarine/
marine
invertebrates.
It
should
be
noted
that
there
is
uncertainty
associated
with
this
study
because
it
was
conducted
under
open
conditions,
and
the
authors
report
a
significant
decrease
in
xylene
concentration
over
the
course
of
the
exposure
period.
However,
it
appears
that
the
results
were
expressed
in
terms
of
measured
concentrations.
Despite
the
uncertainties
associated
with
this
study,
the
results
suggest
that
reproductive
effects
in
sea
urchins
may
result
from
short­
term
exposures
to
o­
xylene.

(
2).
Chronic
Effects
Due
to
the
rapid
volatilization
of
mixed
xylenes
in
receiving
waters,
chronic
exposure
of
aquatic
organisms
is
not
expected
to
occur;
thus,
chronic
toxicity
studies
in
aquatic
animals
are
not
required.
In
irrigation
ditches,
relatively
high
concentrations
are
maintained
for
long
periods
of
time
which
will
result
in
mortality
to
aquatic
animals
occurring
there;
therefore
chronic
effects
would
not
have
time
40
to
occur,
so
chronic
data
are
not
required
for
this
exposure
either.

(
3).
Sublethal
Effects
Limited
information
is
available
regarding
sublethal
effects
of
mixed
xylenes
or
xylene
isomers
in
aquatic
animals.
A
study
in
rainbow
trout
reports
that
fish
exposed
to
xylene
(
type
not
specified)
concentrations
of
3.2
mg/
L
and
higher
for
two
hours
resulted
in
the
development
of
sublethal
effects
(
loss
of
equilibrium),
with
an
NOAEC
value
of
0.65
mg/
L
(
Walsh
et
al.
1977).
The
severity
of
the
effect
was
dose­
dependent
and
the
onset
of
effects
was
approximately
1.4
hours
after
the
initiation
of
exposure.
Effects
in
survivors
were
reversible,
with
fish
recovering
after
a
"
short
time"
in
untreated
water.
In
rainbow
trout
exposed
to
0.001,
0.01,
and
0.1
mg/
L
p­
xylene
for
1
hour,
fish
exhibited
attractant
behavior
at
a
concentration
of
0.01
mg/
L,
but
avoidance
behavior
at
a
concentration
of
0.1
mg/
L
(
Folmar
1976).

(
4).
Field
Studies
Field
studies
on
the
effects
of
mixed
xylenes
or
xylene
isomers
in
aquatic
animals
are
not
available.

b.
Aquatic
Plants
No
studies
on
the
acute
effects
of
mixed
xylenes
in
algae
were
identified
from
the
available
literature.
The
acute
toxicity
of
xylene
isomers
was
evaluated
in
two
studies
using
Selenastrum
capricornutum,
a
green
algae
(
Galassi
et
al.
1988;
Herman
et
al.
1990).
Galassi
et
al.
(
1988)
report
72­
hour
EC
50
values
for
growth
inhibition
ranging
from
3.2
mg
a.
i./
L
for
p­
xylene
to
4.9
mg
a.
i/
L
for
m­
xylene.
Herman
et
al.
(
1990)
report
8­
day
EC
50
values
for
growth
inhibition
ranging
from
3.9
mg/
L
for
mxylene
to
4.4
mg/
L
for
p­
xylene.
Study
details
are
provided
in
Appendix
E,
Table
E­
5.
The
lowest
acute
toxicity
value
obtained
for
the
p­
xylene
isomer,
the
72­
hour
EC
50
value
of
3.2
mg
a.
i./
L
in
Selenastrum
capricornutum
(
Galassi
et
al.
1988),
is
used
to
assess
acute
risk
of
mixed
xylenes
to
algae.
It
should
be
noted
that
NOEAC
data
for
non­
vascular
plants
is
not
available.
The
study
by
Galassi
et
al.
(
1988),
which
was
performed
in
accordance
with
OECD
standardized
method
No.
201,
was
conducted
under
closed
conditions
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.

Limited
information
is
available
regarding
the
toxicity
of
mixed
xylenes
or
xylene
isomers
to
aquatic
macrophytes
and
other
vascular
plants.
Results
of
a
single
laboratory
study
on
the
efficacy
of
xylene
(
xylene
type
not
reported)
on
target
aquatic
macrophytes
shows
that
xylene
damaged
target
plants
under
standing
and
moving
water
conditions
(
Frank
et
al.
1961);
study
details
are
provided
in
Appendix
E,
Table
E­
5.
The
plant
species
used
in
this
study
were
water
weed
(
Elodea
canadensis),
American
pondweed
(
Potamogeton
nodosus),
sago
pondweed
(
P.
pectinatus).
Under
static
conditions,
extensive
damage
was
observed
to
all
three
plant
species
tested
at
a
concentration
of
100
ppm,
but
no
damage
was
observed
at
a
concentration
of
5
ppm.
Under
moving
water
conditions,
extensive
damage
was
observed
to
all
three
species
at
test
concentrations
of
300
and
600
ppm.
Since
EC/
LC
50
values
or
NOAEC
values
were
not
determined,
data
are
not
suitable
for
quantitative
41
use.
Given
that
mixed
xylenes
are
used
to
control
aquatic
vegetation,
toxicity
of
xylenes
to
aquatic
plants
is
presumed.

2.
Terrestrial
Effects
Characterization
The
toxicity
endpoints
used
to
characterize
risks
of
acute
mixed
xylenes
exposure
to
birds
and
mammals
are
summarized
in
Table
8.
Results
of
all
studies
in
terrestrial
organisms
are
summarized
in
Appendix
E,
Tables
E­
6
and
E­
7.
As
discussed
in
Section
II,
the
anticipated
exposure
pathways
for
terrestrial
animals
are
by
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes
in
air.
Therefore,
the
types
of
toxicity
studies
pertinent
to
this
risk
assessment
are
acute
oral
exposure,
acute
dietary
exposure,
and
acute
inhalation
exposure.

Table
8.
Toxicity
Reference
Values
(
TRVs)
for
Mixed
Xylenes
in
Terrestrial
Organisms.

Exposure
Scenario
Species
Exposure
Duration
Toxicity
Reference
Value
Reference
(
Classification)

Mammals
Subacute
Dose­
based
rat
14
days
LD50
=
1608
mg/
kg
BW
NTP,
1986
(
Supplemental)

Acute
Inhalation
rat
4
hours
LC50
=
6700
ppm
Carpenter
et
al.
1975
(
Supplemental)

Chronic
No
Data
Available
 
not
required
Birds
Acute
Dose­
based
No
Data
Available
Acute
Dietary­
based
Japanese
quail
5­
day
dietary
LC50
>
20,000
mg
a.
i./
kg
diet
Hill
and
Carmardese
1986
(
Supplemental)

Acute
Inhalation
No
Data
Available
Chronic
No
Data
Available
 
not
required
Plants
No
Data
Available
 
not
required
a.
Terrestrial
Animals
(
1).
Acute
Effects
Birds
No
acute
oral
or
acute
inhalation
toxicity
studies
in
birds
with
mixed
xylenes
or
xylene
isomers
were
identified
from
the
available
literature.
A
single
acute
dietary
study
in
Japanese
quail
was
identified
from
the
available
literature
(
Hill
and
Camardese
1986);
study
details
are
provided
in
Appendix
E,
42
Table
E­
6.
This
study
failed
to
establish
an
acute
lethality
value
in
birds,
with
the
acute
dietary
LC
50
value
reported
as
>
20,000
mg
a.
i./
kg
diet.
The
LC
50
value
of
>
20,000
mg
a.
i./
kg
diet
in
Japanese
quail
is
used
to
characterize
acute
risk
to
birds
from
ingestion
of
mixed
xylenes
in
contaminated
water.

Exposure
estimates
for
birds
via
drinking
contaminated
water
were
expressed
in
terms
of
a
single
daily
dose
(
mg/
kg
BW)
for
three
different
body
weight
classes
of
birds
(
20,
100,
and
1000
g)
(
Table
4).
Therefore,
to
calculate
acute
RQs
for
birds,
the
acute
dietary
LC
50
was
converted
to
a
daily
dose
for
exposure
via
drinking
water
(
expressed
in
terms
of
mg/
kg
BW
xylenes)
for
each
of
the
three
body
weight
classes
as
follows:
the
avian
acute
dietary
LC
50
value
expressed
in
terms
of
mg/
kg
diet
was
first
converted
to
an
equivalent
LD
50
value
expressed
in
terms
of
mg/
kg
body
weight,
using
the
following
equation:

LD50
(
mg/
kg
body
weight)
=
LC50
in
food
(
mg/
kg
diet)
×
daily
food
consumption
(
kg
diet)
body
weight
(
kg)

where
the
average
daily
food
consumption
per
bird
reported
in
the
Hill
and
Camardese
(
1986)
study
was
0.0126
kg.
The
body
weights
of
Japanese
quail
was
not
reported
in
the
Hill
and
Camaradese
(
1986)
study;
therefore,
for
this
calculation,
the
average
body
weight
for
a
14­
day
Japanese
quail
was
taken
as
approximately
0.043
kg
(
Woodard
et
al.
1973).

Thus,
the
acute
oral
LD
50
for
Japanese
quail
was
derived
as
>
5,860
mg/
kg
body
weight
[>
20,000
mg/
kg
diet
×
0.0126
kg
diet/
0.043
kg
body
weight
=
>
5,860
mg/
kg
body
weight].
To
obtain
the
adjusted
LD
50
value,
the
acute
oral
LD
50
value
for
the
Japanese
quail
(>
5,860
mg/
kg
body
weight)
was
adjusted
for
the
size
of
the
animal
tested
compared
with
the
size
of
the
animal
being
assessed
(
e.
g.,
20
g
bird).
Exposure
estimates
from
contaminated
water
and
toxicity
values
are
relative
to
the
animal's
body
weight
(
mg
residue/
kg
BW)
because
consumption
of
the
same
mass
of
pesticide
residue
results
in
a
higher
body
burden
in
smaller
animals
as
compared
with
larger
animals.
The
following
equation
was
used
for
the
LD
50
adjustment
for
birds:

Adjusted
LD
50
=
LD
50
(
AW/
TW)(
x­
1)

where:

Adjusted
LD
50
=
Adjusted
LD
50
(
mg/
kg
BW)
calculated
by
the
equation;
LD
50
=
>
5,860
mg/
kg
BW
(
acute
oral
LD
50
value
for
the
Japanese
quail);
AW
=
Body
weight
of
assessed
bird
(
20
g,
100
g,
and
1000
g);
TW
=
Body
weight
of
tested
animal
(
43
g
for
14­
day
Japanese
quail);
and
x
=
Mineau
scaling
factor
for
birds;
EFED
default
is
1.15.

The
calculated
toxicity
value
for
a
daily
dose
for
each
weight
class
of
birds
are
summarized
in
Table
9.
The
derived
daily
dose
values
were
used
to
calculate
acute
RQs
for
birds
for
exposure
via
consumption
of
contaminated
water.
43
Table
9.
Adjusted
Acute
Toxicity
Values
for
Birds,
Expressed
in
Terms
of
a
Single
Xylene
Dose
(
mg/
kg
BW).

Species
Body
Weight
(
g)
Adjusted
LD50
a
(
mg/
kg
body
weight)

Birds
20
>
5224
100
>
6651
1000
>
9396
a
Adjusted
LD50
=
LD50
(
AW/
TW)(
x­
1)
where
LD50
=
>
5860
mg/
kg
BW
(>
20,000
mg/
kg
diet
for
the
Japanese
quail;
Hill
and
Camardese);
AW
=
0.02,
0.1,
and
1.0
kg;
TW
=
0.043
kg
for
the
14­
day
Japanese
quail,
and
x
=
Mineau
scaling
factor
for
birds
=
EFED
default
value
of
1.15.

Mammals
Results
of
the
acute
oral
toxicity
studies
on
mixed
xylenes
are
summarized
in
Table
E­
7.
Acceptable
subacute
oral
toxicity
data
for
mammals
was
located
in
the
NTP
(
1986)
study,
where
male
and
female
rats
were
exposed
to
doses
of
mixed
xylene
ranging
from
125
to
2000
mg/
kg
BW
over
a
duration
of
14
days.
Three
of
five
male
and
five
of
five
female
rats
that
received
2000
mg/
kg
BW
died
before
the
end
of
the
study.
Two
other
deaths
at
lower
doses
(
1
male
death
at
125
mg/
kg
BW
and
1
female
death
at
250
mg/
kg
BW)
were
attributed
to
gavage
trauma.
It
should
be
noted
that
all
of
the
mortalities
were
observed
within
the
first
2
to
4
days
of
the
study.
Based
on
the
results
of
this
study,
the
subacute
oral
LD
50
value
is
1608
mg/
kg
BW.
The
lowest
LD
50
value
of
1608
mg/
kg
body
weight
(
NTP
1986)
is
used
to
assess
acute
toxic
risk
for
oral
exposure
of
mammals
to
mixed
xylenes.

Exposure
estimates
for
mammals
via
drinking
contaminated
water
were
expressed
in
terms
of
a
single
daily
dose
(
mg/
kg
BW)
for
three
different
body
weight
classes
(
15,
25,
and
1000
g)
(
Table
4).
Therefore,
to
obtain
the
adjusted
mammalian
LD
50
value,
the
subacute
mammalian
LD
50
value
for
the
rat
(
1608
mg/
kg
body
weight)
is
adjusted
for
the
size
of
the
animal
tested
compared
with
the
size
of
the
animal
being
assessed
(
e.
g.,
15
g
mammal).
The
following
equation
is
used
for
the
LD
50
adjustment
for
mammals:

Adjusted
LD
50
=
LD
50
(
TW/
AW)(
0.25)

where:

Adjusted
LD
50
=
Adjusted
LD
50
(
mg/
kg
BW)
calculated
by
the
equation;
LD
50
=
1608
mg/
kg
BW
(
subacute
oral
LD
50
value
for
the
rat);
TW
=
Body
weight
of
tested
animal
(
350
g
rat);
and
AW
=
Body
weight
of
assessed
mammal
(
15
g,
35
g,
and
1000
g);

The
calculated
toxicity
values
for
a
daily
dose
for
each
weight
class
of
mammals
are
summarized
in
44
Table
10.
The
derived
daily
dose
values
were
used
to
calculate
acute
RQs
for
mammals
for
exposure
via
consumption
of
contaminated
water.

Table
10.
Adjusted
Acute
Toxicity
Values
for
Mammals,
Expressed
in
Terms
of
a
Single
Xylene
Dose
(
mg/
kg
BW).

Species
Body
Weight
(
g)
Adjusted
LD50
a
(
mg/
kg
body
weight)

Mammals
15
3534
35
2859
1000
1237
a
Adjusted
LD50
=
LD50
(
TW/
AW)(
0.25)
where:
LD50
=
1608
mg/
kg
BW
(
Carpenter
et
al.
1975);
AW
=
0.015,
0.035,
and
1.0
kg;
and
TW
=
0.35
kg
for
rat.

Since
mixed
xylenes
are
highly
volatile,
acute
inhalation
exposure
is
an
anticipated
exposure
route
for
mammals
near
the
application
site,
and
acute
inhalation
toxicity
studies
were
reviewed
for
this
risk
assessment.
The
4­
hour
LC
50
value
for
rats
for
mixed
xylenes
is
6700
ppm
(
Carpenter
et
al.
1975);
this
value
is
used
to
assess
acute
toxic
risk
of
acute
inhalation
exposure
of
mammals
to
mixed
xylenes.
It
should
be
noted
that
there
are
uncertainties
related
to
the
dosing
method
for
the
inhalation
mammalian
toxicity
test
because
the
study
author
does
not
specifically
discuss
the
methodology,
but
rather
refers
to
another
paper.

(
2).
Chronic
Effects
Due
to
the
rapid
volatilization
of
mixed
xylenes,
and
low
potential
to
accumulate,
chronic
exposure
of
terrestrial
animals
is
not
expected
to
occur;
thus,
chronic
toxicity
studies
in
terrestrial
animals
are
not
required.

(
3).
Sublethal
Effects
Birds
No
information
regarding
sublethal
effects
of
acute
exposure
to
mixed
xylenes
or
xylene
isomers
in
birds
was
identified
from
the
available
literature.
The
acute
dietary
exposure
study
in
Japanese
quail
reports
that
no
adverse
effects
were
observed
at
a
dietary
concentration
of
5,000
mg/
kg
diet,
the
lowest
concentration
tested
(
Hill
and
Camardese
1986).
This
statement
implies
that
adverse
effects
were
observed
at
dietary
concentrations
greater
than
5000
mg/
kg
diet;
however,
no
information
regarding
adverse
effects
of
acute
dietary
exposure
to
xylenes
was
reported
in
this
study.
45
Mammals
Exposure
of
rats
to
mixed
xylene
over
a
period
of
14
days
resulted
in
decreased
body
weight.
The
change
in
mean
body
weight
relative
to
controls
was
23
to
29%
lower
for
males
that
received
250,
500,
and
1000
mg/
kg
BW
and
17%
and
26%
lower
for
females
that
received
125
and
1000
mg/
kg
BW
after
14
days.
Shallow,
labored
breathing
and
prostration
were
observed
immediately
after
dosing
for
male
and
female
rats
that
received
2000
mg/
kg
BW.
No
compound­
related
effects
were
observed
at
necropsy.

Clinical
signs
of
neurotoxicity
were
reported
in
an
acute
inhalation
exposure
study
in
rats
(
Carpenter
et
al.
1975).
At
a
concentration
of
1300
ppm,
rats
exhibited
poor
coordination
after
two
hours
of
exposure,
but
fully
recovered
following
exposure.
At
concentrations
of
2800
ppm,
rats
became
prostrate,
but
recovered
within
an
hour
although
coordination
remained
poor.
The
NOAEC
for
signs
of
toxicity
was
reported
as
580
ppm.

(
4).
Field
Studies
Field
studies
on
the
effects
of
mixed
xylenes
or
xylene
isomers
in
terrestrial
animals
are
not
available.

Terrestrial
Invertebrates
No
information
on
the
acute
toxicity
of
xylenes
exposure
to
terrestrial
invertebrates
was
identified
from
the
available
literature.
The
method
of
application
should
preclude
exposure
to
honey
bees,
so
honey
bee
testing
is
not
required.

b.
Terrestrial
Plants
Under
the
conditions
of
recommended
use,
chronic
exposure
of
terrestrial
plants
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
terrestrial
plants
are
not
required.

IV.
Risk
Characterization
Risk
characterization
is
the
integration
of
exposure
and
effects
characterizations
to
determine
the
ecological
risk
from
the
use
of
mixed
xylenes
and
the
effects
on
aquatic
life
and
wildlife
based
on
recommended
use
scenarios.
The
risk
characterization
provides
an
estimation
and
a
description
of
the
risk;
articulates
risk
assessment
assumptions,
limitations,
and
uncertainties;
synthesizes
an
overall
conclusion;
and
provides
the
risk
managers
with
information
to
make
regulatory
decisions.

A.
Risk
Estimation
­
Integration
of
Exposure
and
Effects
Data
Results
of
the
exposure
and
toxicity
effects
data
are
used
to
evaluate
the
likelihood
of
adverse
ecological
effects
on
non­
target
species.
For
the
assessment
of
mixed
xylenes
risks,
the
risk
quotient
(
RQ)
method
is
used
to
compare
exposure
and
measured
toxicity
values
(
see
Appendix
F).
Estimated
environmental
concentrations
(
EECs)
are
divided
by
acute
toxicity
values.
The
resulting
RQs
are
then
compared
to
the
Agency's
levels
of
concern
(
LOCs).
These
LOCs,
summarized
in
46
Appendix
F,
are
the
Agency's
interpretive
policy
used
to
analyze
potential
risk
to
non­
target
organisms
and
the
need
to
consider
regulatory
action.
Details
of
all
RQs
derived
for
this
assessment
are
provided
in
Appendix
G.

For
exposures
of
non­
target
aquatic
species,
three
EECs
were
used
to
assess
acute
risk:
10
mg/
L
(
maximum
allowable
concentration
in
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Mixed
xylenes
are
applied
to
achieve
an
initial
concentration
of
approximately
740
mg/
L,
with
the
concentration
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
rivers
and
streams)
not
to
exceed
10
mg/
L.
However,
since
the
maximum
allowable
concentration
of
740
mg/
L
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
o­
xylene
of
178
mg/
L
(
the
highest
solubility
limit
reported
for
the
three
xylene
isomers).
The
value
of
178
mg/
L
was
chosen
to
provide
consistency
with
the
chemical­
physical
properties
of
xylenes
applied
without
the
addition
of
emulsifiers.
Since
mixed
xylenes
are
highly
volatile,
chronic
exposure
of
aquatic
ecosystems
is
not
anticipated;
thus,
only
acute
risk
from
xylenes
exposure
was
assessed.
Toxicity
reference
values
for
aquatic
exposure
to
mixed
xylenes
and
xylene
isomers
are
summarized
in
Table
6.

Mixed
xylenes
are
applied
underwater;
therefore,
exposure
of
terrestrial
organisms
via
direct
application
and
spray
drift
are
not
considered
as
potential
exposure
pathways
for
terrestrial
organisms.
Risks
to
terrestrial
plants
via
irrigation
water
and
exposure
of
mammals
and
birds
via
ingestion
of
contaminated
forage
items
was
not
considered
for
this
assessment
because
exposures
for
these
pathways
are
expected
to
minimal.
The
most
likely
exposure
pathways
for
terrestrial
animals
are
through
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.
Exposure
estimates
for
ingestion
of
contaminated
water
by
birds
and
mammals
were
based
on
the
allowable
concentration
range
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
178
mg/
L,
and
the
amount
of
water
birds
and
mammals
are
expected
to
consume
in
one
day
(
Table
4).
To
assess
risks
due
to
inhalation
exposure,
the
non­
dimensional
Henry's
law
constant
was
used
to
estimate
xylene
air
concentrations
in
a
breathing
zone
above
the
water
based
upon
the
concentration
of
xylene
in
water
(
solubility
limit
­
178
mg/
L).
The
maximum
exposure
concentration
of
xylene
in
air
(
38.5
ppm)
assumes
no
loss
of
xylene
from
the
breathing
zone
due
to
wind
or
degradation
(
Table
5).
Since
mixed
xylenes
are
highly
volatile,
chronic
exposure
of
terrestrial
ecosystems
is
not
anticipated;
thus,
only
acute
risk
from
xylenes
exposure
was
assessed.
Toxicity
reference
values
for
terrestrial
organisms
exposed
to
mixed
xylenes
are
summarized
in
Table
7.

1.
Non­
Target
Aquatic
Animals
and
Plants
To
assess
risks
of
mixed
xylenes
to
non­
target
aquatic
animals
(
i.
e.,
fish,
invertebrates)
and
plants
(
i.
e.,
algae),
three
EECs
were
used
to
assess
acute
risk:
10
mg/
L
(
maximum
allowable
concentration
in
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Toxicity
data
are
available
to
assess
acute
risk
to
freshwater
fish,
freshwater
invertebrates,
estuarine/
marine
fish,
estuarine/
marine
invertebrates,
and
non­
vascular
aquatic
plants.
No
toxicity
data
are
available
to
evaluate
acute
risks
to
vascular
aquatic
plants.
47
Acute
RQs
for
aquatic
species
are
summarized
in
Table
11.
The
LOCs
for
acute
risk
(
LOC
0.5),
are
exceeded
for
the
three
water
concentrations
considered
for
this
assessment.
RQs
for
the
lowest
allowable
exposure
level
of
10
mg/
L
range
from
3
for
non­
vascular
aquatic
plants
(
i.
e.,
algae)
to
10
for
freshwater
invertebrates.
For
the
maximum
exposure
level
of
740
mg/
L,
acute
RQs
range
from
231
for
non­
vascular
aquatic
plants
to
740
for
freshwater
invertebrates.
All
RQs
based
on
the
solubility
limit
for
o­
xylene
exceed
all
acute
LOCs,
ranging
from
56
for
non­
vascular
aquatic
plants
to
178
for
freshwater
invertebrates.
Although
acute
toxicity
data
is
not
available
for
estuarine/
marine
fish,
LOC
exceedances
for
this
taxonomic
group
are
assumed
based
on
xylene's
known
toxicity
to
freshwater
fish.
Thus,
results
of
this
analysis
show
that
at
all
exposure
concentrations
considered
in
this
assessment,
including
the
maximum
allowable
concentration
in
return
flows
of
treated
irrigation,
all
aquatic
animals
and
plants
assessed
are
at
acute
risk
from
exposure
to
xylenes.

Table
11.
Acute
RQs
for
Freshwater
Fish,
Freshwater
Invertebrates,
Estuarine/
Marine
Fish,
Estuarine/
Marine
Invertebrates,
and
Algae
Exposed
to
Mixed
Xylenes
or
Xylene
Isomers.

Species
Toxicity
Value
(
mg/
L)
Acute
RQ
for
Receiving
Water
Exposure
a
Acute
RQ
for
Irrigation
Canal
Exposure
b
Acute
RQ
Based
on
the
Solubility
Limit
for
o­
Xylene
c
Freshwater
Fish
2.6
mg/
L
d
3.8
h
284
h
68
h
Freshwater
Invertebrates
1.0
mg/
L
e
10
h
740
h
178
h
Estuarine/
Marine
Fish
No
data
NA
NA
NA
Estuarine/
Marine
Invertebrates
4.1
mg/
L
f
2.4
h
180
h
43
h
Non­
vascular
Aquatic
Plants
3.2
mg/
L
h
3
h
231
h
56
h
a
EEC/
LC50,
where
the
EEC
is
the
maximum
allowable
exposure
of
10
mg/
L
in
receiving
waters.
b
EEC/
LC50,
where
the
EEC
is
the
maximum
exposure
of
740
mg/
L
in
irrigation
canals.
c
EEC/
LC50,
where
the
EEC
is
the
solubility
limit
for
o­
xylene
of
178
mg/
L.
d
96­
hour
LC50
value
in
rainbow
trout
for
p­
xylene
(
Galassi
et
al.
1988).
Study
conducted
under
closed
conditions.
e
24­
hour
LC50
value
in
Daphnia
magna
for
o­
xylene
(
Galassi
et
al.
1988).
Study
conducted
under
closed
conditions.
f
96­
hour
EC50
value
in
sea
urchin
eggs
for
o­
xylene
(
Falk­
Petersen
et
al.
1985).
Study
conducted
under
open
conditions.
g
72­
hour
EC50
value
(
for
growth
inhibition)
in
Selenastrum
capricornutum
for
p­
xylene
(
Galassi
et
al.
1988).
Study
conducted
under
closed
conditions.
No
NOAEC
value
is
available
to
characterize
risks
to
listed
non­
vascular
plant
species.
h
RQ
exceeds
the
acute
LOCs
for
acute
risk
(
0.5),
acute
restricted
use
(
LOC
0.1)
and
acute
endangered
species
(
LOC
0.05).
48
2.
Non­
Target
Terrestrial
Animals
The
most
likely
exposure
pathways
for
terrestrial
animals
are
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.
Based
on
these
potential
exposure
pathways,
the
following
scenarios
were
assessed
for
terrestrial
animals:
acute
risks
to
mammals
and
birds
from
ingestion
of
contaminated
water;
acute
risks
to
mammals
via
inhalation
of
volatilized
xylenes;
and
acute
risks
to
mammals
from
combined
exposure
via
contaminated
water
and
inhalation.
Due
to
lack
of
inhalation
toxicity
data
in
birds,
acute
risks
of
exposure
to
birds
via
inhalation
of
volatilized
xylenes
and
combined
exposure
via
contaminated
water
and
inhalation
could
not
be
assessed.

a.
Acute
Risk
to
Mammals
and
Birds
from
Ingestion
of
Contaminated
Water
To
assess
acute
risks
to
terrestrial
animals
from
ingestion
of
contaminated
water,
three
EECs
were
used:
10
mg/
L
(
maximum
allowable
concentration
in
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Acute
RQs
for
birds
and
mammals
exposed
to
xylenes
via
consumption
of
contaminated
water
were
calculated
using
the
derived
daily
exposure
value
for
xylenes
(
expressed
in
terms
of
mg/
kg
BW)
(
Table
4)
and
the
adjusted
LD
50
toxicity
value
for
a
daily
dose
of
xylenes
(
expressed
in
terms
of
mg/
kg
BW)
for
birds
(
Table
9)
and
mammals
(
Table
10).
Three
weight
classes
of
birds
and
mammals
were
evaluated.
Additional
details
regarding
these
derived
exposure
and
toxicity
values
are
provided
in
Section
III.
B.
3.
a
and
Section
III.
C.
2.
a.(
1)
of
this
report,
respectively.

Acute
RQs
for
birds
and
mammals
exposed
to
xylenes
via
consumption
of
contaminated
water
are
summarized
in
Table
12.
All
acute
RQs
for
mammals
and
birds
for
exposure
from
drinking
contaminated
water
are
below
acute
endangered
species
LOCs
(
LOC
=
0.1).
For
birds,
acute
RQs
range
from
<
0.01
(
for
all
three
weight
classes
for
water
concentrations
of
10
and
178
mg/
L)
to
<
0.031
(
20
g
birds
for
a
water
concentration
of
740
mg/
L).
Due
to
the
failure
of
acute
dietary
toxicity
studies
in
birds
to
establish
a
definitive
acute
LC
50
value
(
LC
50
>
20,000
mg
a.
i./
kg
diet),
acute
avian
RQs
are
reported
as
"
less
than"
values.
For
mammals,
acute
RQs
range
from
0.004
(
15
g
mammals
for
a
water
concentration
of
10
mg/
L)
to
0.059
(
1000
g
mammals
consuming
water
at
a
concentration
of
740
mg/
L).
Based
on
this
assessment,
mammals
and
birds
do
not
appear
at
acute
risk
from
exposure
via
consumption
of
contaminated
water.
49
Table
12.
Acute
RQs
for
Birds
and
Mammals
Exposed
to
Mixed
Xylenes
via
Consumption
of
Contaminated
Water.

Species
Body
Weight
(
g)
Acute
RQ
Based
on
a
Water
Concentration
of
10
mg/
L
a,
b
Acute
RQ
Based
on
a
Water
Concentration
of
740
mg/
L
a,
b
Acute
RQ
Based
on
the
Solubility
Limit
for
o­
xylene
of
178
mg/
L
a,
b
Birds
c
20
<
0.01
<
0.031
<
0.01
100
<
0.01
<
0.014
<
0.01
1000
<
0.01
<
0.01
<
0.01
Mammals
15
0.0004
0.032
0.008
35
0.0005
0.036
0.008
1000
0.0008
0.059
0.014
a
Acute
RQs
were
calculated
using
the
exposure
values
(
mg/
kg
BW)
derived
in
Table
G­
2
and
the
adjusted
LD50
values
(
mg/
kg
BW)
shown
in
Table
G­
3,
as
follows:
EEC/
Adjusted
LD50
value.
b
RQs
are
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).
c
RQs
for
birds
are
based
on
the
LC50
value
>
20,000
mg/
kg
diet
(
adjusted
LD50
values
for
20
g,
100
g,
and
1000
g
birds
are
>
5224,
>
6651,
and
>
9396
mg/
kg
BW,
respectively.
Therefore,
acute
avian
RQs
are
reported
as
"
less
than"
values.

b.
Acute
Risk
to
Mammals
Via
Inhalation
Exposure
This
assessment
only
considers
the
inhalation
exposure
of
mammals
to
those
vapors
which
are
derived
from
the
treated
canal
or
ditch.
The
non­
dimensional
Henry's
law
constant
was
used
to
estimate
air
concentrations
in
a
breathing
zone
above
the
water
based
upon
the
concentration
in
water
(
solubility
limit
­
178
mg/
L).
The
maximum
exposure
concentration
of
38.5
ppm
assumes
no
loss
of
xylene
from
the
breathing
zone
due
to
wind
or
degradation
(
Table
5).
The
lowest
4­
hour
LC
50
value
for
rats
exposed
to
mixed
xylenes
via
inhalation
(
6700
ppm;
Carpenter
et
al.
1975)
was
used
as
the
toxicity
value
to
calculate
acute
inhalation
RQs.

The
acute
RQ
for
mammals
exposed
to
xylenes
via
inhalation
is
below
the
acute
endangered
species
LOC
(
LOC
=
0.1)
(
Table
13).
The
acute
inhalation
RQ
based
on
the
maximum
inhalation
EEC
is
0.006.
Based
on
this
analysis,
mammals
exposed
to
volatilized
xylenes
do
not
appear
to
be
at
acute
risk.
50
Table
13
Acute
RQs
for
Mammals
Exposed
to
Volatilized
Mixed
Xylenes
Via
Inhalation.

Inhalation
Toxicity
Value
a
(
ppm)
Acute
Inhalation
RQ
Based
on
Maximum
Estimated
Exposure
Maximum
EEC
in
Air
(
ppm)
b
Maximum
Acute
Inhalation
RQ
c
(
EEC/
Toxicity
Value)

6700
38.5
0.006
a
4­
hour
LC50
value
in
rats
for
mixed
xylenes
(
Carpenter
et
al.
1975).
b
EECs
generated
with
the
non­
dimensional
Henry's
law
constant
which
estimates
the
concentration
of
a
compound
in
the
gas
phase
in
relationship
to
its
concentration
in
liquid
phase
Cg
=
Cl
*
Henry
C.
c
RQ
is
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).

c.
Acute
Risk
to
Mammals
from
Combined
Exposure
via
Inhalation
and
Contaminated
Water
To
determine
if
a
combination
of
exposures
by
consumption
of
contaminated
water
and
inhalation
of
volatilized
xylenes
poses
a
risk
to
mammals,
a
composite
acute
RQ
was
derived.
The
composite
acute
RQ
is
defined
as
the
sum
of
the
acute
drinking
water
RQ
and
the
acute
inhalation
RQ.
Composite
acute
RQs
were
calculated
using
the
maximum
acute
drinking
water
RQs
for
the
three
mammalian
weight
classes
based
on
the
maximum
concentration
in
water
of
740
mg/
L
(
Table
12
and
the
acute
inhalation
RQ
for
the
maximum
estimated
exposure
for
volatilized
xylenes
in
air
(
Table
13)
Since
the
minimum
acute
drinking
water
RQs
and
the
minimum
acute
inhalation
RQ
for
mammals
are
several
orders
of
magnitude
below
the
acute
LOCs,
composite
RQs
using
the
minimum
acute
inhalation
RQs
were
not
derived.

Composite
acute
RQs
for
mammals
range
from
0.038
(
15
g
mammals)
to
0.065
(
1000
g
mammals)
(
Table
14.)
Based
on
this
assessment,
mammals
do
not
appear
to
be
at
risk
from
the
combination
of
exposure
by
ingestion
of
contaminated
water
and
exposure
by
inhalation
of
volatilized
xylenes.
51
Table
14
Composite
Acute
RQs
for
Mammals
Exposed
to
Mixed
Xylenes
by
Consumption
of
Contaminated
Water
and
Inhalation.

Mammalian
Body
Weight
(
g)
Maximum
Acute
RQ
for
Consumption
of
Water
Containing
740
mg/
L
Xylenes
a
Maximum
Acute
Inhalation
RQ
b
Maximum
Acute
Composite
RQ
c,
d
15
0.032
0.006
0.038
35
0.036
0.006
0.042
1000
0.059
0.006
0.065
a
Details
of
RQ
calculation
are
provided
in
Table
G­
4.
b
Details
of
RQ
calculation
are
provided
in
Table
G­
5.
c
RQ
is
calculated
as
the
sum
of
the
acute
RQ
for
consumption
of
contaminated
water
and
the
acute
inhalation
RQ.
d
RQs
are
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).

B.
Risk
Description
The
focus
of
this
screening­
level
assessment
is
to
evaluate
risks
associated
with
exposure
to
mixed
xylenes
applied
underwater
for
use
in
the
control
of
aquatic
weeds
in
two
different
types
of
habitat
including:
1)
canals
and
ditches
which
contain
xylene­
treated
irrigation
water,
and
2)
water
bodies
(
i.
e.,
streams,
rivers,
and/
or
lakes)
which
receive
return
flow
from
xylene­
treated
irrigation
water.
In
evaluating
the
possible
risks
of
mixed
xylenes
to
aquatic
and
terrestrial
receptors
in
and
around
treated
ditches,
the
range
of
potential
water
concentrations
include
the
recommended
application
concentration
of
approximately
740
mg/
L,
and
lower
concentrations
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
water
bodies).
Given
this
use
pattern,
potential
exposure
pathways
for
aquatic
and
terrestrial
ecosystems
are
from
direct
exposure
to
contaminated
water
(
aquatic
organisms)
and
from
ingesting
treated
water
and
inhalation
exposure
of
xylenes
that
volatilize
from
contaminated
water
(
terrestrial
animals).
The
focus
of
the
assessment
was
on
acute
effects
because
no
useful
chronic
data
were
found.
Chronic
testing
is
not
recommended
because
chronic
exposure
of
aquatic
and
terrestrial
ecosystems
outside
of
the
treated
ditches
is
not
expected
to
significantly
contribute
to
impact,
due
to
the
rapid
volatilization
of
xylenes
from
water
(
half­
life
of
approximately
1­
6
days
in
various
water
bodies
(
Smith
and
Harper
1980).
Since
mixed
xylenes
are
applied
directly
below
the
surface
of
the
water,
terrestrial
exposure
pathways
such
as
exposure
of
terrestrial
animal
food
sources
and
plants
via
direct
application
or
spray
drift,
were
not
considered
likely.

The
results
of
this
screening­
level
risk
assessment
suggest
the
potential
for
direct
adverse
acute
effects
to
fish
and
aquatic
invertebrates
and
aquatic
plants
in
the
irrigation
canals
and
ditches
(
where
concentrations
of
xylene
may
be
as
high
as
740
mg/
L).
Although
terrestrial
mammals
and
birds
may
be
exposed
to
xylene
via
drinking
water
and
inhalation
pathways,
these
routes
of
exposure
are
unlikely
to
result
in
acute
adverse
effects.
The
potential
for
effects
in
receiving
waters
is
less
certain.
52
The
current
label
permits
release
of
up
to
10
ppm,
and
at
this
rate
of
release,
significant
potential
for
downstream
effects
exist.
However,
if
this
level
is
reduced
to
~
1
ppm
or
lower,
the
potential
for
effects
to
aquatic
animals
in
the
receiving
waters
(
where
the
maximum
allowable
concentration
would
not
exceed
1
ppm),
would
drop
considerably
both
in
magnitude,
duration
and
distance
downstream.

1.
Risks
to
Aquatic
Organisms
As
previously
mentioned,
the
focus
of
the
aquatic
assessment
was
to
evaluate
risks
in
two
habitat
types
including
the
irrigation
canals
and
ditches
were
xylene
is
applied
and
the
receiving
water
bodies
which
receive
return
flow
of
xylene­
treated
irrigation
water.
Given
the
high
exposure
levels
associated
with
the
recommended
initial
concentration
of
mixed
xylenes
in
irrigation
canals
and
ditches,
acute
risks
are
predicted
for
all
freshwater
aquatic
animals
and
plants
inhabiting
the
canals
and
ditches.
However,
it
is
unlikely
that
estuarine/
marine
animals
and
plants
would
be
exposed
to
xylene­
treated
water
in
the
irrigation
canals
because
these
systems
are
assumed
to
be
freshwater;
therefore,
risks
to
estuarine/
marine
species
are
not
anticipated
in
irrigation
canals.

Acute
risks
to
freshwater
and
estuarine/
marine
animals
and
plants
species
in
receiving
water
bodies
were
assessed
using
two
exposure
scenarios.
First
assuming
return
flows
of
treated
irrigation
into
receiving
rivers
and
streams
at
the
maximum
allowable
concentration
of
10
mg/
L.
Then,
an
assumption
of
a
maximum
return
flow
concentration
of
1
mg/
L
was
assessed.
If
return
flows
of
treated
water
are
to
large,
rapidly
moving
water
bodies,
the
concentration
of
xylene
would
be
expected
to
decrease
rapidly,
minimizing
acute
risks
to
non­
target
aquatic
organisms.
However,
if
return
flows
of
treated
water
are
to
small,
slow
moving
or
stagnant
water
bodies,
only
minimal
dilution
of
xylene
may
occur.

To
determine
the
concentrations
at
which
listed
aquatic
organisms
in
receiving
waters
would
not
be
at
acute
risk
from
xylene
in
return
flows,
a
concentration
at
which
no
acute
LOCs
are
exceeded
for
aquatic
organisms
was
calculated,
as
summarized
in
Table
18.
The
maximum
water
concentrations
that
yield
acute
RQs
below
the
lowest
acute
LOC
(
acute
endangered
risk
LOC
for
aquatic
animals
=
0.05;
aquatic
endangered
risk
LOC
for
aquatic
plants
=
1.0)
were
calculated
for
each
aquatic
species
category
using
the
following
relationship:

EEC/
LC
50
=
acute
RQ
that
is
less
than
the
acute
endangered
LOC
(
0.05
or
1.0).

Concentrations
that
are
protective
of
listed
aquatic
species
were
calculated
using
the
lowest
LC
50
/
EC
50
values
reported
for
aquatic
organisms
and
target
RQs
of
0.04
for
aquatic
animals
and
0.90
for
aquatic
plants.
In
order
to
ensure
that
listed
aquatic
organisms
in
receiving
waters
are
not
at
acute
risk
from
xylene
in
return
flows,
xylene
concentrations
in
return
flows
should
not
exceed
0.04
mg/
L
for
freshwater
environments
and
0.16
for
estuarine/
marine
environments.
Calculated
concentrations
that
are
protective
of
listed
aquatic
species
in
return
flows
are
approximately
250­
and
63­
fold
lower
than
the
current
allowable
concentration
of
10
mg/
L
for
freshwater
and
estuarine/
marine
environments,
respectively.
53
Table
15.
Calculated
Xylene
Concentrations
at
which
Acute
RQs
Are
Less
Than
Acute
LOCs
for
Aquatic
Organisms
.

Species
Toxicity
Value
(
mg/
L)
Target
Acute
RQ
EEC
Protective
of
Listed
Aquatic
Species
(
mg/
L)
a
Freshwater
Fish
b
2.6
mg/
L
0.04
0.10
Freshwater
Invertebrates
c
1.0
mg/
L
0.04
0.04
Estuarine/
Marine
Invertebrates
d
4.1
mg/
L
0.04
0.16
Algae
e
3.2
mg/
L
0.90
2.88
a
EEC
=
Target
Acute
RQ
×
Toxicity
Value.
b
96­
hour
LC50
value
in
rainbow
trout
for
p­
xylene
(
Galassi
et
al.
1988).
c
24­
hour
LC50
value
in
Daphnia
magna
for
o­
xylene
(
Galassi
et
al.
1988).
d
96­
hour
LC50
value
in
sea
urchin
eggs
for
o­
xylene
(
Peterson­
Falk
et
al.
1985).
e
72­
hour
EC50
value
(
for
growth
inhibition)
in
Selenastrum
capricornutum
for
p­
xylene
(
Galassi
et
al.
1988).

A
simple
steady­
state
plug
flow
dilution
model
(
see
Appendix
B)
was
used
to
estimate
the
amount
of
dissipation
that
would
be
required
to
achieve
a
xylene
concentration
of
0.04
mg/
L
that
is
protective
of
listed
aquatic
species
in
receiving
water.
Specifically,
the
model
was
used
to
predict
the
length
of
time
and/
or
dissipation
distance
required
for
xylene­
treated
water
to
decrease
from
a
concentration
of
10
mg/
L
(
as
specified
in
the
current
label),
as
well
as
an
alternative
concentration
of
1
mg/
L,
to
a
concentration
of
0.04
mg/
L
required
to
be
protective
of
listed
aquatic
species.
Given
the
uncertainties
associated
with
the
actual
size
of
the
receiving
water
body,
the
model
was
run
assuming
a
range
of
dilution
factors.
In
addition,
the
water
flow
rate
was
assumed
to
be
1
cfs
and
the
volatilization
half­
life
was
assumed
to
be
2
days.
The
results
of
the
model,
which
are
summarized
in
Table
19,
show
that
the
time
and
distance
required
for
xylene
to
dissipate
to
a
concentration
of
0.04
mg/
L
in
receiving
water
decreases
with
increasing
dilution.
The
distance
required
to
dissipate
to
0.04
mg/
L
is
dependant
on
the
geometries
of
the
both
the
receiving
water
and
the
return
flow
systems.
The
point
to
stress
is
that
the
reduction
in
xylene
concentration
occurs
over
both
time
and
distance.
Generally,
the
larger
the
volume
of
the
receiving
water,
the
shorter
the
downstream
return
flow
component
in
the
irrigation
canal
or
drainage
ditch
necessary
to
obtain
the
desired
decrease
in
xylene
concentrations.
Note
that
the
duration
of
exposure
to
a
given
organisms
is
not
determined
by
the
time
frames
reported;
these
only
represent
how
long
a
slug
of
water
containing
xylene
takes
to
dissipate.
The
duration
of
exposure
to
specific
organisms
or
communities
is
a
function
of
the
duration
of
release
of
ditch
water.
As
long
as
the
ditch
water
is
being
released
exposure
will
continue
downstream
from
the
release
point.

In
as
much
as
the
risk
management
goal
for
xylene
is
to
reduce
the
concentration
of
the
release
water
to
1
mg/
L,
the
remaining
discussion
will
focus
on
that
scenario.

Assuming
a
one­
to­
one
dilution,
it
would
take
approximately
4.5
days
(
or
a
length
of
76
miles)
for
54
xylene­
treated
water
to
dissipate
from
1
mg/
L
to
a
protective
concentration
of
0.04
mg/
L.
As
previously
mentioned,
the
amount
of
dilution
in
a
particular
body
of
water
is
dependant
on
the
size
and
environmental
conditions
of
the
receiving
water
body.
Increasing
the
dilution
factor
by
10,
20,
and
50
decreases
the
amount
of
time
and
distance
(
required
for
xylene­
treated
water
to
dissipate
from
1
mg/
L
to
0.04
mg/
L)
by
the
same
factor,
resulting
in
dissipation
times/
distances
of
approximately
20
hours/
13.8
miles,
10.5
hours/
7.2
miles,
and
4.8
hours/
3
miles,
respectively.

Table
16.
Time,
Distance,
and
Dilution
for
Xylene
Concentrations
to
Decrease
from
10ppm
and
1ppm
to
<
0.04
ppm
Based
on
a
Steady­
State
Plug
Flow
Dilution
Model
Condition
Reduction
from
1
ppm
to
0.04
ppm
1:
1
dilution
10:
1
dilution
20:
1
dilution
50:
1
dilution
Time
(
days)
4.64
0.84
0.44
0.2
Distance
(
miles)
76
13.8
7.2
3.0
The
important
point
to
consider
is
that
at
a
1.0
mg/
L,
only
a
1:
25
dilution
would
be
needed
to
reach
a
concentration
of
0.04
mg/
L.
At
a
1.0
mg/
L
concentration,
the
amount
of
xylene
in
the
receiving
water
body
will
continue
to
dissipate
due
to
volatilization
and
mixing.
Therefore,
this
supports
reducing
from
10
mg/
L
to
1
mg/
L
or
some
other
lower
value.
In
addition,
it
is
recommended
that
the
revised
label
language
include
a
statement
that
treated
irrigation
water
be
used
to
irrigate
fields.
Since
xylene
is
highly
volatile,
this
common
agricultural
practice
will
greatly
reduce
the
amount
of
xylene
in
the
canal
outflows
that
ultimately
reach
natural
water
bodies.
If
treating
the
fields
is
not
feasible,
the
treated
water
should
be
held
until
measurable
xylene
concentrations
are
1
mg/
L
or
less.

2.
Risks
to
Terrestrial
Organisms
Results
of
this
assessment
show
that
LOCs
for
birds
and
mammals
are
not
exceeded
when
exposed
via
ingestion
of
contaminated
water
(
Table
12).
Additionally,
mammals
do
not
appear
to
be
at
acute
risk
from
inhalation
exposure
(
Table
13)
or
from
the
combination
of
ingestion
of
contaminated
water
and
inhalation
exposure
(
Table
14).
However,
there
are
several
uncertainties
that
should
be
considered
in
interpreting
the
results
of
the
assessment
for
terrestrial
organisms.

To
estimate
acute
risks
to
birds
and
mammals
from
consumption
of
contaminated
water
for
the
maximum
exposure
concentration
of
740
mg/
L,
it
was
assumed
that
the
concentration
of
xylene
remained
constant
over
the
exposure
period
of
one
day.
Given
the
high
volatility
of
xylenes,
this
assumption
provides
a
very
conservative
exposure
estimate,
and
results
in
use
of
an
EEC
that
is
higher
than
that
which
can
be
reasonably
anticipated.
Thus,
acute
RQs
derived
using
the
maximum
exposure
concentration
of
740
mg/
L
are
likely
to
result
in
an
over­
estimation
of
risk.
However,
even
with
this
conservative
approach,
acute
RQs
for
birds
and
mammals
for
consumption
of
contaminated
55
water
are
below
all
acute
LOCs.

The
acute
avian
toxicity
values
used
to
assess
acute
risks
from
consumption
of
contaminated
water
were
reported
as
"
greater
than"
values;
thus,
avian
acute
RQs
are
likely
to
be
lower
than
those
reported.
However,
since
all
acute
avian
RQs
are
below
acute
LOCs,
uncertainties
associated
with
the
avian
toxicity
value
do
not
affect
the
conclusions
of
this
risk
assessment:
birds
do
not
appear
to
be
at
acute
risk
from
ingestion
of
contaminated
water,
even
at
the
highest
exposure
level.

Results
of
this
assessment
indicate
that
mammals
are
not
at
risk
from
exposure
via
inhalation
of
volatilized
xylenes.
Acute
inhalation
RQs
for
mammals
were
derived
using
the
4­
hour
LC
50
value
of
6700
ppm
for
mixed
xylenes
in
rats
(
Carpenter
et
al.
1975)
and
one
exposure
scenario,
which
represents
the
maximum
air
concentration
of
xylene
predicted
by
Henry's
Law,
and
assuming
a
solubility
of
178
mg/
L
(
Table
13).
It
is
likely
that
this
inhalation
exposure
concentration
is
overestimates
as
it
does
not
consider
degradation
and
dilution
due
to
wind.
Major
limitations
associated
with
the
estimated
inhalation
exposure
concentration
include
uncertainties
associated
with
the
potential
effect
of
the
emulsifier
on
volatilization
and
uncertainties
related
to
the
actual
height
at
which
exposures
occur.
Although
there
is
uncertainty
associated
with
the
inhalation
exposure
estimate,
use
of
the
most
conservative
exposure
estimate
results
in
RQs
that
are
below
acute
LOCs.

Avian
exposure
via
inhalation
of
volatilized
xylenes
was
not
characterized
due
to
a
lack
of
inhalation
toxicity
data
for
birds.
If
inhalation
toxicity
of
xylenes
to
birds
is
similar
to
that
of
mammals,
risks
associated
with
this
exposure
pathway
would
be
unlikely
for
avian
receptors.
In
order
for
there
to
be
LOC
exceedances
for
birds,
the
4­
hour
inhalation
toxicity
LC
50
value
for
birds
would
have
to
be
385
ppm
or
roughly
175
times
less
than
the
inhalation
toxicity
for
mammals.

The
composite
acute
RQ
derived
for
mammals
for
exposure
via
consumption
of
contaminated
water
and
inhalation
of
volatilized
xylenes
indicates
that
mammals
are
not
at
acute
risk
from
xylenes
applied
to
irrigation
ditches.
However,
this
assessment
does
not
consider
dermal
exposure
of
water
mammals,
such
as
beavers
or
otters,
that
may
spend
a
substantial
amount
of
time
in
contaminated
water.
It
is
anticipated
that
the
animals'
coats
would
act
as
a
barrier
to
xylenes,
thereby,
substantially
limiting
dermal
exposure.
However,
insufficient
information
is
available
to
assess
whether
the
dermal
absorption
represents
a
pathway
of
significant
exposure.

3.
Review
of
Incident
Data
Incident
reports
submitted
to
EPA
since
approximately
1994
have
been
tracked
by
assignment
of
EIIS
(
Environmental
Incident
Information
System)
in
an
Incident
Data
System
(
IDS).
There
are
no
incident
reports
for
xylenes
involving
aquatic
or
terrestrial
organisms.

4.
Endocrine
Effects
Results
of
a
study
on
sea
urchin
eggs
shows
that
exposure
to
xylenes
at
4.1
mg
a.
i./
L
results
in
embryo
death
to
50%
of
the
test
population
(
Falk­
Petersen
et
al.
1985).
The
results
of
this
study
indicate
that
reproductive
effects
in
sea
urchins
may
result
from
short­
term
exposures
to
o­
xylene.
56
Although
there
is
no
conclusive
evidence
that
exposure
to
xylenes
alters
developmental
effects
in
aquatic
species,
this
possibility
cannot
be
ruled
out.
Therefore,
EFED
must
consider
the
possibility
that
xylenes
may
have
detrimental
effects
on
the
endocrine
system.

Under
the
Federal
Food,
Drug
and
Cosmetic
Act
(
FFDCA),
as
amended
by
the
Food
Quality
Protection
Act
(
FQPA),
EPA
is
required
to
develop
a
screening
program
to
determine
whether
certain
substances
(
including
all
pesticide
active
and
other
ingredients)
"
may
have
an
effect
in
humans
that
is
similar
to
an
effect
produced
by
a
naturally­
occurring
estrogen,
or
other
such
endocrine
effects
as
the
Administrator
may
designate".
Following
the
recommendations
of
its
Endocrine
Disruptor
Screening
and
Testing
Advisory
Committee
(
EDSTAC),
EPA
determined
that
there
was
scientific
basis
for
including,
as
part
of
the
program,
the
androgen­
and
thyroid
hormone
systems,
in
addition
to
the
estrogen
hormone
system.
EPA
also
adopted
EDSTAC's
recommendation
that
the
Program
include
evaluations
of
potential
effects
in
wildlife.
For
pesticide
chemicals,
EPA
will
use
FIFRA
and,
to
the
extent
that
effects
in
wildlife
may
help
determine
whether
a
substance
may
have
an
effect
in
humans,
FFDCA
authority
to
require
the
wildlife
evaluations.
As
the
science
develops
and
resources
allow,
screening
of
additional
hormone
systems
may
be
added
to
the
Endocrine
Disruptor
Screening
Program
(
EDSP).
When
the
appropriate
screening
and
or
testing
protocols
being
considered
under
the
Agency's
Endocrine
Disruptor
Screening
Program
have
been
developed,
mixed
xylenes
may
be
subjected
to
additional
screening
and
or
testing
to
better
characterize
effects
related
to
endocrine
disruption.

5.
Federally
Threatened
and
Endangered
(
Listed)
Species
Concerns
a.
Action
Area
The
Endangered
Species
Act
defines
the
action
area
for
a
Federal
action
as
being
the
footprint
of
possible
direct
and
indirect
effects
stemming
from
the
action,
not
necessarily
limited
to
where
the
immediate
action
occurs.
The
screening­
level
risk
assessment
conservatively
assumes
that
listed
species
are
co­
located
with
the
pesticide
treatment
area.
For
example,
terrestrial
wildlife
potentially
occur
adjacent
to
the
irrigation
canals
and/
or
potential
receiving
waters,
and
aquatic
organisms
potentially
occur
downstream
of
where
xylene
is
initially
applied.
This
assessment
recognizes
the
potential
that
the
listed
species
are
located
within
an
assumed
area
which
has
the
relatively
highest
potential
exposure
to
xylene,
and
that
exposures
are
likely
to
decrease
with
distance
from
the
treated
area.

If
these
assumptions
result
in
RQs
that
are
below
the
listed
species
LOCs,
a
"
no
effect"
conclusion
is
made
with
respect
to
listed
species
in
that
taxa,
and
no
further
refinement
of
the
action
area
is
necessary.
Furthermore,
RQs
below
the
listed
species
LOCs
for
a
given
taxonomic
group
indicate
no
concern
for
indirect
effects
upon
listed
species
that
depend
upon
the
taxonomic
group
covered
by
the
RQ
as
a
resource.
However,
in
situations
where
the
screening
assumptions
lead
to
RQs
in
excess
of
the
listed
species
LOCs
for
a
give
taxonomic
group,
the
potential
for
a
"
may
affect"
conclusion
exists
and
may
be
associated
with
direct
effects
on
listed
species
that
depend
upon
that
taxonomic
group
or
may
extend
to
indirect
effects
upon
listed
species
that
depend
upon
that
taxonomic
group
as
a
resource.
In
such
cases,
additional
information
on
the
biology
of
listed
species,
the
locations
of
57
these
species,
and
the
locations
of
xylene
use
sites
would
be
considered
to
determine
the
extent
to
which
screening
assumptions
regarding
an
action
area
apply
to
a
particular
listed
organism.
These
subsequent
refinement
steps
would
consider
how
this
information
would
impact
the
action
area
for
a
particular
listed
organism
and
may
potentially
include
exposures
that
are
downstream
of
the
pesticide
use
site.

b.
Taxonomic
Groups
Potentially
at
Risk
(
1).
Discussion
of
Risk
Quotients
Should
estimated
exposure
levels
occur
in
proximity
to
listed
resources,
the
available
screening
level
information
suggests
a
potential
concern
for
direct
effects
on
listed
freshwater
fish
and
invertebrates
(
including
amphibians),
estuarine/
marine
invertebrates,
and
aquatic
plant
species
associated
with
the
use
of
xylene
in
irrigation
canals.
Direct
effects
are
possible
in
downstream
receiving
waters
at
the
estimated
exposure
levels.
Regarding
estuarine/
marine
fish
and
aquatic
plants,
LOC
exceedances
are
assumed
for
estuarine/
marine
fish
in
receiving
waters
and
vascular
plants
both
in
ditches
and
in
receiving
waters,
given
xylene's
known
toxicity
to
freshwater
fish
and
its
intended
use
to
kill
aquatic
weeds.
It
should
be
noted,
however,
that
although
LOCs
were
exceeded
for
non­
vascular
plants
(
i.
e.,
algae),
there
are
no
endangered
species
of
unicellular
(
non­
vascular)
plants.

(
2).
Probit
Dose
Response
Relationship
The
Agency
uses
the
probit
dose
response
relationship
as
a
tool
for
providing
additional
information
on
the
listed
animal
species
levels
of
concern.
The
acute
listed
species
LOC
of
0.05
is
used
for
aquatic
animals.
As
part
of
the
risk
characterization,
an
interpretation
of
acute
LOCs
for
listed
species
is
discussed.
This
interpretation
is
presented
in
terms
of
the
chance
of
an
individual
event
(
i.
e,
mortality
or
immobilization)
should
exposure
at
the
estimated
environmental
concentration
actually
occur
for
a
species
with
sensitivity
to
mixed
xylenes
on
par
with
the
acute
toxicity
endpoint
selected
for
RQ
calculation.
To
accomplish
this
interpretation,
the
Agency
uses
the
slope
of
the
dose
response
relationship
available
from
the
toxicity
study
used
to
establish
the
acute
toxicity
measures
of
effect
for
each
taxonomic
group.
The
individual
effects
probability
associated
with
the
LOCs
is
based
on
the
mean
estimate
of
the
slope
and
an
assumption
of
a
probit
dose
response
relationship.
In
addition
to
a
single
effects
probability
estimate
based
on
the
mean,
upper
and
lower
estimates
of
the
effects
probability
are
also
provided,
if
available,
to
account
for
variance
in
the
slope.
The
upper
and
lower
bounds
of
the
effects
probability
are
based
on
available
information
on
the
95%
confidence
interval
of
the
slope.
A
statement
regarding
the
confidence
in
the
estimated
event
probabilities
for
each
taxonomic
group
is
not
included
because
the
raw
data
was
not
presented
as
part
of
the
open
literature
toxicity
data.
Therefore,
it
was
not
possible
to
determine
if
the
data
exhibited
good
probit
fit
characteristics
or
to
derive
95%
confidence
intervals
for
the
reported
slope
values.

Individual
effect
probabilities
are
calculated
based
on
an
Excel
spreadsheet
tool
IEDV1.1
(
Individual
Effect
Chance
Model
Version
1.1)
developed
by
the
U.
S.
EPA,
OPP,
Environmental
Fate
and
Effects
Division
(
June
22,
2004).
The
model
allows
for
such
calculations
by
entering
the
mean
slope
estimate
(
and
the
95%
confidence
bounds
of
that
estimate,
if
available)
as
the
slope
parameter
for
58
that
spreadsheet.
In
addition,
the
LOC
(
0.05
for
aquatic
animals)
is
entered
as
the
desired
threshold.

(
3.)
Data
Related
to
Under­
represented
Taxa
Mixed
xylene
data
related
to
under­
represented
taxa,
such
as
amphibians,
are
not
available
from
the
open
literature.
(
4.)
Implications
of
Sublethal
Effects
Results
of
this
risk
analysis
indicate
that
at
the
exposure
levels
considered
in
this
assessment,
direct
effects
on
survival
of
aquatic
animals
and
growth
inhibition
of
aquatic
plants
are
likely.
However,
sublethal
effects
have
also
been
reported
in
freshwater
fish.
Although
limited
information
is
available
regarding
sublethal
effects
of
mixed
xylenes
or
xylene
isomers
in
aquatic
animals,
results
of
a
study
in
rainbow
trout
show
a
dose­
dependent
loss
of
equilibrium
in
fish
exposed
to
xylene
(
type
not
specified)
for
approximately
1.4
hours,
with
NOAEC
and
LOAEC
values
of
0.65
mg/
L
and
3.2
mg/
L,
respectively
(
Walsh
et
al.
1977).
Loss
of
equilibrium
is
likely
to
leave
fish
more
vulnerable
to
predation
pressure,
which
may
result
in
reduced
survival
of
aquatic
populations.
Sublethal
effects,
including
loss
of
equilibrium,
are
reported
to
occur
in
fish
at
exposure
levels
below
the
highest
level
currently
allowed
to
be
released
(
10
mg/
L).
If
the
maximum
release
level
is
reduced
to
1
mg/
L,
the
concentration
in
receiving
waterways
would
be
expected
to
relatively
quickly
decline
to
below
the
NOAEC
of
0.65
mg/
L.

There
is
evidence
to
suggest
that
fish
also
exhibit
avoidance
behavior
in
response
to
xylene.
In
rainbow
trout
exposed
to
0.001,
0.01,
and
0.1
mg
p­
xylene
for
1
hour,
fish
exhibited
attractant
behavior
at
a
concentration
of
0.01
mg/
L,
but
avoidance
behavior
at
a
concentration
of
0.1
mg/
L
(
Folmar
1976).
Avoidance
behavior
may
result
in
decreased
exposure
to
xylenes.
However,
depending
upon
the
conditions
of
the
waterways
where
mixed
xylenes
may
occur,
it
may
not
be
possible
for
fish
to
avoid
exposure
to
xylene
levels
associated
with
toxicity.

c.
Indirect
Effects
Analysis
The
Agency
acknowledges
that
pesticides
have
the
potential
to
exert
indirect
effects
upon
the
listed
organisms
by,
for
example,
perturbing
forage
or
prey
availability,
altering
the
extent
of
nesting
habitat,
etc.
In
conducting
a
screen
for
indirect
effects,
direct
effect
LOCs
for
each
taxonomic
group
are
used
to
make
inferences
concerning
the
potential
for
indirect
effects
upon
listed
species
that
rely
upon
non­
endangered
organisms
in
these
taxonomic
groups
as
resources
critical
to
their
life
cycle.
When
a
taxonomic
group
shows
an
RQ
higher
than
the
listed
species
LOC,
there
is
a
potential
concern
for
indirect
effects
to
any
listed
species
in
any
taxonomic
group
that
has
a
dependency
on
the
taxa
for
which
the
RQ
is
in
excess
of
the
LOC
and
which
is
co­
located
with
the
pesticide
use
site.

Because
screening­
level
acute
RQs
for
freshwater
fish
and
invertebrates
and
estuarine/
marine
invertebrates
exceed
the
listed
species
acute
LOCs,
the
Agency
uses
the
dose
response
relationship
from
the
toxicity
study
used
for
calculating
the
RQ
to
estimate
the
probability
of
acute
effects
associated
with
an
exposure
equivalent
to
the
EEC.
It
should
noted,
however,
that
data
on
the
dose
59
response
relationship
was
not
available
for
estuarine/
marine
invertebrates;
therefore,
a
default
slope
value
of
4.5
with
confidence
intervals
of
2
and
9
was
used.
The
uncertainty
associated
with
the
estimated
even
probabilities
for
estuarine/
marine
invertebrates
is
increased
by
the
large
default
confidence
intervals
associated
with
the
slope.

In
instances
where
information
on
the
dose
response
is
available,
it
serves
as
a
guide
to
establish
the
need
for
and
extent
of
additional
analysis
that
may
be
performed
using
Services­
provided
"
species
profiles"
as
well
as
evaluations
of
the
geographical
and
temporal
nature
of
the
exposure
to
ascertain
if
a
"
not
likely
to
adversely
affect"
determination
can
be
made.
The
degree
to
which
additional
analyses
are
performed
is
commensurate
with
the
predicted
probability
of
adverse
effects
from
the
comparison
of
dose
response
information
with
the
EECs.
The
greater
the
probability
that
exposures
will
produce
effects
on
a
taxa,
the
greater
the
concern
for
potential
indirect
effects
for
listed
species
dependant
upon
that
taxa,
and
therefore,
the
more
intensive
the
analysis
on
the
potential
listed
species
of
concern,
their
locations
relative
to
the
use
site,
and
information
regarding
the
use
scenario
(
e.
g.,
timing,
frequency,
and
geographical
extent
of
pesticide
application).

Indirect
effect
analyses
for
freshwater
and
estuarine/
marine
fish
and
invertebrates
and
aquatic
plants
are
described
in
further
detail
below.

Freshwater
Fish
Freshwater
fish
acute
endangered
species
LOCs
are
exceeded,
based
on
maximum
allowable
concentrations
of
xylene
in
receiving
waters
of
irrigation
canals.
Therefore,
there
are
potential
concerns
for
indirect
effects
on
listed
animals
that
eat
fish
or
amphibians
(
e.
g.,
fish,
mammals,
birds,
reptiles),
or
in
the
case
of
freshwater
mussels,
use
a
fish
as
a
necessary
host
in
the
life
cycle.

Because
raw
data
was
not
provided
as
part
of
the
acute
toxicity
study
for
the
rainbow
trout,
information
is
unavailable
to
derive
95%
confidence
intervals
for
the
reported
slope
value
of
1.1
(
Galassi
et
al.,
1988).
An
event
probability
was
calculated
for
the
listed
species
LOC
(
0.05)
based
on
the
reported
slope
value
of
1.1.
Based
on
an
assumption
of
a
probit
dose
response
relationship
with
a
slope
of
1.1,
the
corresponding
estimated
chance
of
individual
mortality
associated
with
the
listed
species
LOC
of
the
acute
toxic
endpoint
for
freshwater
fish
is
1
in
131
(~
0.76%).
The
uncertainty
in
estimated
event
probabilities
for
this
taxonomic
group
is
increased
by
the
lack
of
established
confidence
intervals
surrounding
the
mean
slope
value.

Freshwater
Invertebrates
Given
that
acute
LOCs
are
exceeded
for
freshwater
invertebrates,
indirect
effects
to
listed
species
(
e.
g.,
freshwater
fish,
mammals,
birds,
amphibians)
that
rely
on
freshwater
invertebrates
(
i.
e.,
daphnids)
as
a
primary
food
source
may
be
of
concern.

Raw
data
was
also
not
provided
as
part
of
the
acute
toxicity
study
for
D.
magna;
therefore,
it
was
not
possible
to
derive
95%
confidence
intervals
for
the
reported
slope
value
of
1.4
(
Galassi
et
al.,
1988).
Based
on
an
assumption
of
a
probit
dose
response
relationship
with
a
slope
of
1.4,
the
60
corresponding
estimated
chance
of
individual
mortality/
immobilization
associated
with
the
listed
species
LOC
of
the
acute
toxic
endpoint
for
freshwater
invertebrates
is
1
in
292
(~
0.34%).
Similar
to
freshwater
fish,
the
uncertainty
in
estimated
event
probabilities
for
freshwater
invertebrates
is
increased
by
the
lack
of
established
confidence
intervals
for
the
mean
slope
value.

Estuarine/
Marine
Fish
and
Invertebrates
Although
no
acute
toxicity
data
was
available
for
estuarine/
marine
fish,
risks
to
this
taxonomic
group
are
assumed
given
xylene's
known
toxicity
to
freshwater
fish.
Acute
endangered
species
LOCs
are
exceeded
for
estuarine/
marine
invertebrates
(
and
assumed
to
be
exceeded
for
estuarine/
marine
fish);
therefore,
there
are
potential
concerns
for
indirect
effects
on
listed
animals
that
eat
estuarine/
marine
fish
or
invertebrates
(
e.
g.,
fish,
mammals,
birds,
reptiles).

The
toxicity
endpoint
for
estuarine/
marine
invertebrates
was
obtained
from
a
study
on
sea
urchin
eggs
by
Falk­
Peterson
et
al.
(
1985).
Because
raw
data
was
not
provided
as
part
of
this
study,
information
was
not
available
to
estimate
a
slope
for
the
dose­
response
curve.
An
event
probability
was
calculated
for
the
listed
species
LOC
based
on
a
default
slope
assumption
of
4.5
(
Urban
and
Cook,
1986).
Based
on
an
assumption
of
a
probit
dose
response
relationship
with
a
default
slope
of
4.5,
the
corresponding
estimated
chance
of
individual
mortality
and/
or
reproductive
effect
associated
with
the
listed
species
LOC
(
0.05)
of
the
acute
toxic
endpoint
for
estuarine/
marine
invertebrates
is
1
in
4.17E+
08
(~
2.4E­
09%).
It
is
recognized
that
extrapolation
of
very
low
probability
events
is
associated
with
considerable
uncertainty
in
the
resulting
estimates.
In
order
to
explore
the
possible
bounds
to
such
estimates,
the
upper
and
lower
default
values
for
the
mean
default
slope
estimate
(
95%
C.
I.:
2
to
9,
Urban
and
Cook,
1986)
were
used
to
calculate
upper
and
lower
estimates
of
the
effects
probability
associated
with
the
listed
species
LOC.
The
respective
lower
and
upper
effects
probability
estimates
are
1
in
216
(~
0.46%)
and
1
in
1.0E+
16
(~
1.0E­
16%).
The
uncertainty
in
estimated
event
probabilities
for
estuarine/
marine
invertebrates
is
increased
by
the
large
confidence
intervals
associated
with
the
default
slope.

Aquatic
Plants
Although
aquatic
plant
data
suitable
for
use
in
risk
assessment
is
available
for
only
non­
vascular
aquatic
algae,
it
is
assumed
that
application
of
mixed
xylenes
to
irrigation
canals
at
the
recommended
label
rate
would
result
in
exceedances
of
non­
listed
and
listed
LOCs
vascular
and
non­
vascular
plants.
Therefore,
there
is
potential
concern
for
adverse
effects
to
those
listed
species
that
depend
on
plants
in
very
narrow
and
broad
ways
for
some
important
aspect
of
their
life
cycle.
Listed
species
of
concern
would
include
those
species
with
very
narrow
habitat,
feeding,
and/
or
larval
substrate
dependencies
(
termed
obligates)
as
well
as
those
with
more
general
herbivory
or
cover
type
dependencies.
There
is
concern
for
listed
species
that
rely
on
aquatic
plants
for
food
and/
or
habitat
and
shelter.
Species­
specific
concerns
for
mixed
xylenes
indirect
effects
to
listed
organisms
requires
a
determination
of
the
coincidence
of
pesticide
use
with
locations
of
listed
species
and
the
biologically
based
resources
upon
which
they
depend.

d.
Critical
Habitat
61
In
the
evaluation
of
pesticide
effects
on
designated
critical
habitat,
consideration
is
given
to
the
physical
and
biological
features
(
constituent
elements)
of
a
critical
habitat
identified
by
the
U.
S.
Fish
and
Wildlife
and
National
Marine
Fisheries
Services
as
essential
to
the
conservation
of
a
listed
species
and
which
may
require
special
management
considerations
or
protection.
The
evaluation
of
impacts
for
a
screening­
level
pesticide
risk
assessment
focuses
on
the
biological
features
that
are
constituent
elements
and
is
accomplished
using
the
screening­
level
taxonomic
analysis
(
RQs)
and
listed
species
LOCs
that
are
used
to
evaluate
direct
and
indirect
effects
to
listed
organisms.

The
screening­
level
risk
assessment
has
identified
potential
concerns
for
indirect
effects
on
listed
species
for
those
organisms
dependant
upon
freshwater
and
estuarine/
marine
fish
and
invertebrates
and
aquatic
plants.
In
light
of
the
potential
for
indirect
effects,
the
next
step
for
EPA
and
the
Service(
s)
is
to
identify
which
listed
species
and
critical
habitat
are
potentially
implicated.
Analytically,
the
identification
of
such
species
and
critical
habitat
can
occur
in
either
of
two
ways.
First,
the
agencies
could
determine
whether
the
action
area
overlaps
critical
habitat
or
the
occupied
range
of
any
listed
species.
If
so,
EPA
would
examine
whether
the
pesticide's
potential
impacts
on
non­
endangered
species
would
affect
the
listed
species
indirectly
or
directly
affect
a
constituent
element
of
the
critical
habitat.
Alternatively,
the
agencies
could
determine
which
listed
species
depend
on
biological
resources,
or
have
constituent
elements
that
fall
into,
the
taxa
that
may
be
directly
or
indirectly
impacted
by
mixed
xylenes.
EPA
would
then
determine
whether
mixed
xylenes
usage
overlaps
the
critical
habitat
or
the
occupied
range
of
those
listed
species.
At
present,
the
information
reviewed
by
EPA
does
not
permit
the
use
of
either
analytical
approach
to
make
a
definitive
identification
of
species
that
are
potentially
impacted
indirectly
or
of
critical
habitats
that
are
potentially
impacted
directly
by
the
use
of
mixed
xylenes
in
irrigation
canals.
EPA
and
the
Service(
s)
are
working
together
to
conduct
the
necessary
analysis.

This
screening­
level
risk
assessment
for
critical
habitat
provides
a
listing
of
potential
biological
features
that,
if
they
are
constituent
elements
of
one
or
more
critical
habitats,
would
be
of
concern.
These
correspond
to
the
taxa
identified
above
as
being
of
potential
concern
for
indirect
effects
and
include
the
following:
freshwater
and
estuarine/
marine
fish
and
invertebrates,
aquatic
plants,
birds,
and
mammals.
This
list
should
serve
as
an
initial
step
in
problem
formulation
for
further
assessment
of
critical
habitat
impacts
outlined
above,
should
additional
work
be
necessary.

e.
Co­
occurrence
Analysis
Given
the
usage
of
xylene
in
16
western
states,
a
large
number
of
listed
aquatic
species
are
likely
to
occur
in
counties
where
xylene
is
used
to
control
aquatic
weeds
in
irrigation
canals.
A
summary
of
the
number
of
listed
species
by
taxonomic
group
for
crops
where
irrigation
water
from
irrigation
canals
is
used
(
assumed
to
be
potential
xylene
use
areas)
is
provided
in
Table
17.
The
list
of
crops
likely
to
be
irrigated
with
water
from
irrigation
canals
was
obtained
from
the
USDA
National
Agricultural
Statistics
Service
(
NASS)
website
and
information
on
irrigated
crops
presented
in
a
paper
by
Walsh
et
al
(
1977).
A
total
of
487
listed
species
that
may
potentially
co­
occur
with
xylene
use
areas
were
identified.
Table
18
provides
a
summary
of
the
listed
species
by
State.
A
comprehensive
list
of
these
listed
species
is
provided
by
State
in
Appendix
J.
Given
the
large
number
of
listed
species,
EFED
recommends
restricting
xylene
use
to
a
smaller
number
of
states.
62
Restriction
of
xylene
usage
to
a
smaller
number
of
states
would
reduce
the
number
of
listed
species
that
may
be
potentially
affected.

The
registrant
must
provide
information
on
the
proximity
of
Federally
listed
endangered
species
to
mixed
xylenes
use
sites.
This
requirement
may
be
satisfied
in
one
of
three
ways:
1)
having
membership
in
the
FIFRA
Endangered
Species
Task
Force;
2)
citing
FIFRA
Endangered
Species
Task
Force
data;
or
3)
independently
producing
these
data,
provided
the
information
is
of
sufficient
quality
to
meet
FIFRA
requirements.
The
information
will
be
used
by
the
OPP
Endangered
Species
Protection
Program
to
develop
recommendations
to
avoid
adverse
effects
to
listed
species.
63
Birds
Mammals
Amphibians
Fish
Crustaceans
Reptile
Insects
Snails
Clams
Plants
Table
17.
Tabulation
by
Taxonomic
Group
and
Crop
of
Listed
Species
That
May
Occur
in
Mixed
Xylene
Use
Areas
Crop
Taxonomic
Group
Alfalfa
(
16
States)
26
42
9
71
9
8
23
10
3
246
Barley
(
16
States)
23
41
9
57
7
8
20
7
0
183
Carrots
(
16
States)
23
35
8
44
8
7
24
6
0
200
Citrus
(
AZ
and
CA)
18
29
7
25
8
8
18
2
0
171
Corn
for
grain
(
16
States)
22
37
8
42
8
8
13
10
3
166
Corn
for
silage
or
greenchop
(
16
States)
24
38
7
58
9
8
19
8
2
197
Cotton
(
AZ,
CA,
KA,
and
NM)
20
24
6
30
5
5
6
1
1
77
Dry
edible
beans,
excluding
limas
(
15
States
­
all
except
NV)
20
35
7
38
6
7
16
8
0
156
Forage
­
land
used
for
all
hay
and
haylage,
grass
silage,
and
greenchop
(
16
States)
26
42
9
71
9
9
27
10
3
259
Lima
beans
(
CA,
KA,
NM,
OK,
OR,
and
WA)
17
22
5
15
8
4
7
3
0
105
Lettuce
(
14
States
­
all
except
ND
and
WY)
23
37
8
48
7
9
26
3
0
219
Oats
for
grain
(
16
States)
23
40
8
66
8
9
21
8
3
223
Potatoes
(
16
States)
23
40
8
60
9
8
26
10
2
222
Rice
(
CA
and
OK)
9
9
1
10
3
3
6
0
1
30
Sorghum
for
grain
(
13
States
­
all
except
MO,
OR,
and
WA)
20
25
7
32
7
7
7
5
3
76
Soybeans
(
CO,
KA,
MO,
NE,
NM,
ND,
OK,
and
SD)
8
7
0
7
0
0
1
0
3
4
Sugarbeets
(
11
States
­
all
except
AR,
NV,
NM,
OK,
and
SD)
14
15
4
17
4
4
4
6
0
43
Tomatoes
(
16
States)
26
41
8
60
9
9
27
10
2
249
Wheat
for
grain
(
16
States)
25
36
8
57
9
8
22
9
3
202
Birds
Mammals
Amphibians
Fish
Crustaceans
Reptile
Insects
Snails
Clams
Plants
Crop
Taxonomic
Group
64
Birds
Mammals
Amphibians
Fish
Crustaceans
Reptile
Insects
Snails
Clams
Plants
Total
Unique
Species
26
42
9
71
9
9
27
10
3
259
Total
States
16
14
4
16
3
5
8
4
2
16
Total
Counties
731
289
48
362
39
39
74
9
5
203
Table
18.
Tabulation
by
Taxonomic
Group
and
State
of
Listed
Species
That
May
Occur
in
Mixed
Xylene
Use
Areas
State
Taxonomic
Group
Arizona
9
1
2
17
0
2
0
1
0
18
California
16
22
6
29
8
8
22
1
0
180
Colorado
3
2
0
6
0
0
2
0
0
13
Idaho
2
4
0
7
0
0
0
6
0
3
Kansas
4
2
0
4
0
0
1
0
0
2
Montana
4
3
0
4
0
0
0
0
0
2
Nebraska
4
1
0
2
0
0
0
0
1
3
Nevada
2
0
0
23
0
1
2
0
0
9
New
Mexico
7
5
1
12
2
1
0
5
0
0
North
Dakota
4
0
0
1
0
0
0
0
0
1
Oklahoma
7
3
0
4
0
0
1
0
2
2
Birds
Mammals
Amphibians
Fish
Crustaceans
Reptile
Insects
Snails
Clams
Plants
State
Taxonomic
Group
65
Oregon
5
1
0
24
1
0
2
0
0
13
South
Dakota
4
1
0
2
0
0
1
0
0
1
Utah
2
2
0
8
0
1
0
0
0
24
Washington
5
5
0
17
0
0
1
0
0
6
Wyoming
1
4
1
2
0
0
0
0
0
2
C.
Description
of
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
1.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
All
Taxa
There
are
a
number
of
areas
of
uncertainty
in
the
aquatic
and
terrestrial
risk
assessments.
The
toxicity
assessment
for
terrestrial
and
aquatic
animals
is
limited
by
the
number
of
species
tested
in
the
available
toxicity
studies.
Use
of
toxicity
data
on
representative
species
does
not
provide
information
on
the
potential
variability
in
susceptibility
to
acute
and
chronic
exposures.

Inhalation
exposure
to
mammals
and
birds
was
estimated
by
using
the
non­
dimensional
Henry's
law
constant,
which
relates
the
concentration
of
a
compound
in
the
gas
phase
to
its
concentration
in
the
liquid
phase.
This
approach
does
not
take
into
account
the
many
factors
which
influence
volatilization
from
water
such
as
channel
geometry,
flow
characteristics,
and
temperature.
Considerable
uncertainties
also
are
related
to
the
limits
of
the
breathing
zone
(
exposure
zone).
This
method
should
provide
a
conservative
estimate
of
the
possible
xylene
concentrations
in
air.

2.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
Aquatic
Species
For
exposures
of
non­
target
aquatic
species,
several
EECs
were
used
to
assess
acute
risk:
1
mg/
L
(
optional
reduced
concentration
in
outflow
waters)
10
mg/
L
(
maximum
allowable
concentration
in
66
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Mixed
xylenes
are
applied
to
achieve
an
initial
concentration
of
approximately
740
mg/
L,
with
the
concentration
in
return
flows
of
treated
irrigation
(
i.
e.,
flows
into
receiving
rivers
and
streams)
not
to
exceed
10
mg/
L.
However,
since
the
maximum
allowable
concentration
of
740
mg/
L
exceeds
the
solubility
limits
of
xylenes,
acute
risk
was
also
assessed
based
on
the
maximum
solubility
limit
for
o­
xylene
of
178
mg/
L
(
the
highest
solubility
limit
reported
for
the
three
xylene
isomers).
The
value
of
178
mg/
L
was
chosen
to
provide
consistency
with
the
chemicalphysical
properties
of
xylenes
applied
without
the
addition
of
emulsifiers.

Since
mixed
xylenes
are
highly
volatile,
xylene
concentrations
are
expected
to
rapidly
decrease.
However,
this
assessment
assumes
that
xylene
concentrations
remain
constant
over
the
exposure
period.

There
is
significant
uncertainty
in
estimating
concentrations
in
receiving
water
bodies
because,
while
the
label
permits
release
of
irrigation
water
with
up
to
10
ppm
xylene,
such
releases
are
thought
to
be
infrequent.
In
many
of
the
areas
were
xylene
treatment
occurs,
water
is
a
valuable
commodity
which
will
be
retained
and
used
to
the
maximum
extent
possible.
The
concentration
of
xylene
in
irrigation
water
will
rapidly
decline
to
below
1
ppm,
and
in
many
cases
to
below
the
concentration
that
results
in
risk
exceeding
the
listed
species
LOC.
Therefore,
10
ppm
is
considered
an
upper
bound
and
the
expected
concentrations
will
usually
be
lower.

The
major
limitations
associated
with
the
simple
plug­
flow
model
is
that
it
assumes
steady­
state
conditions
which
may
not
reflect
environmental
conditions.
The
geometry
and
flow
rates
and
degradate
rates
will
also
not
be
equal
or
constant.

The
limited
monitoring
was
not
collected
for
comparison
with
the
0.04
ppm
(
assumed
safe
level
for
endangered
species)
but
with
the
10
ppm
the
current
MCL
for
xylene.

3.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Exposure
For
Terrestrial
Species
For
exposures
of
non­
target
terrestrial
species
via
drinking
contaminated
water,
the
maximum
solubility
(
178
mg/
L)
was
used
to
estimate
inhalation
exposure,
and
three
EECs
were
used
to
assess
acute
risk
from
wildlife
drinking
treated
water:
10
mg/
L
(
maximum
allowable
concentration
in
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
Since
mixed
xylenes
are
highly
volatile,
xylene
concentrations
are
expected
to
rapidly
decrease.
However,
this
assessment
assumes
that
xylene
concentrations
remain
constant
over
the
exposure
period.
67
4.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
Effects
Assessment
The
ecological
effects
database
to
support
the
aquatic
and
terrestrial
assessments
for
acute
exposures
is
not
complete.
Since
xylenes
are
highly
volatile,
chronic
exposure
is
not
considered
likely
for
aquatic
or
terrestrial
ecosystems.
Thus,
requirements
for
chronic
toxicity
studies
in
aquatic
and
terrestrial
receptors
are
not
required.

Data
gaps,
uncertainties,
and
limitations
for
the
acute
aquatic
and
terrestrial
assessments
are
summarized
as
follows:

°
No
registrant­
submitted
toxicity
studies
in
which
xylene
mixtures
or
xylene
isomers
were
the
sole
active
ingredient
were
identified;
all
ecological
effects
data
reviewed
in
this
risk
assessment
were
obtained
from
the
published
open
literature.
Although
some
of
the
acute
aquatic
studies
were
conducted
in
accordance
with
OECD
guidelines,
no
consistent
experimental
protocols
were
followed
for
estuarine/
marine
invertebrates.
Therefore,
there
is
a
high
degree
of
uncertainty
to
the
toxicity
data
for
this
taxonomic
group.

°
Toxicity
data
are
not
available
for
estuarine/
marine
fish;
therefore,
risks
for
this
taxonomic
group
are
assumed
based
on
xylene's
known
toxicity
to
freshwater
fish.

°
Acute
toxicity
data
are
not
available
for
vascular
aquatic
macrophytes,
therefore,
risks
for
this
taxonomic
group
are
assumed
based
on
xylene's
mode
of
action
as
an
aquatic
herbicide
and
available
information
on
the
toxicity
of
xylene
to
non­
vascular
aquatic
plants.

°
The
acute
dietary
toxicity
study
in
birds
failed
to
establish
an
acute
LC
50
value
(
the
LC
50
was
expressed
as
"
greater
than"
the
highest
dietary
concentration
tested);
thus,
significant
uncertainty
was
introduced
into
the
avian
RQ
calculations.

°
There
is
uncertainty
associated
with
the
acute
dietary
toxicity
study
for
birds,
given
xylene's
high
volatility.
Therefore,
the
registrant
should
provide
information
on
a
avian
LD
50
value
for
xylene
or
submit
an
acute
avian
oral
toxicity
study
(
LD
50
),
using
either
a
bobwhite
quail
or
mallard
duck,
to
satisfy
the
§
71­
1
guideline
requirements.

°
There
is
uncertainty
related
to
the
methodology
used
to
dose
the
rats
in
the
acute
inhalation
mammalian
study
used
to
derive
inhalation
RQs
(
Carpenter
et
al
1975)
because
the
study
authors
did
not
specifically
discuss
the
dosing
methodology,
but
rather
referred
to
an
approach
used
in
another
study
(
Carpenter
et
al
1975a).

°
Acute
inhalation
toxicity
data
are
not
available
for
birds;
therefore,
risk
from
inhalation
exposure
cannot
be
assessed.
68
Age
class
and
sensitivity
of
effects
thresholds
It
is
generally
recognized
that
test
organism
age
may
have
a
significant
impact
on
the
observed
sensitivity
to
a
toxicant.
The
screening
risk
assessment
acute
toxicity
data
for
fish
are
collected
on
juvenile
fish
weighing
between
0.1
and
5
grams.
Aquatic
invertebrate
acute
testing
is
performed
on
recommended
immature
age
classes
(
e.
g.,
first
instar
for
daphids,
second
instar
for
amphipods,
stoneflies
and
mayflies,
and
third
instar
for
midges).
Similarly,
acute
dietary
testing
with
birds
is
also
performed
on
juveniles,
with
mallard
being
5­
10
days
old
and
quail
10­
14
days
old.

Testing
of
juveniles
may
overestimate
toxicity
at
older
age
classes
for
pesticidal
active
ingredients,
such
as
mixed
xylenes,
that
act
directly
(
without
metabolic
transformation)
because
younger
age
classes
may
not
have
the
enzymatic
systems
associated
with
detoxifying
xenobiotics.
The
screening
risk
assessment
has
no
current
provisions
for
a
generally
applied
method
that
accounts
for
this
uncertainty.
In
so
far
as
the
available
toxicity
data
may
provide
ranges
of
sensitivity
information
with
respect
to
age
class,
the
risk
assessment
uses
the
most
sensitive
life­
stage
information
as
the
conservative
screening
endpoint.

Use
of
the
Most
Sensitive
Species
Tested
Although
the
screening
risk
assessment
relies
on
a
selected
toxicity
endpoint
from
the
most
sensitive
species
tested,
it
does
not
necessarily
mean
that
the
selected
toxicity
endpoints
reflect
sensitivity
of
the
most
sensitive
species
existing
in
a
given
environment.
The
relative
position
of
the
most
sensitive
species
tested
in
the
distribution
of
all
possible
species
is
a
function
of
the
overall
variability
among
species
to
a
particular
chemical.
In
the
case
of
listed
species,
there
is
uncertainty
regarding
the
relationship
of
the
listed
species'
sensitivity
and
the
most
sensitive
species
tested.

The
Agency
is
not
limited
to
a
base
set
of
surrogate
toxicity
information
in
establishing
risk
assessment
conclusions.
The
Agency
also
considers
toxicity
data
on
non­
standard
test
species
when
available.

5.
Assumptions,
Limitations,
Uncertainties,
Strengths
and
Data
Gaps
Related
to
the
Acute
and
Chronic
LOCs
The
risk
characterization
section
of
the
assessment
includes
an
evaluation
of
the
potential
for
individual
effects
at
an
exposure
level
equivalent
to
the
LOC.
This
evaluation
is
based
on
the
median
lethal
dose
estimate
and
dose/
response
relationship
established
for
the
effects
study
corresponding
to
each
taxonomic
group
for
which
the
LOCs
are
exceeded.

The
certainty
associated
with
the
confidence
in
estimated
event
probabilities
for
taxonomic
groups
including
estuarine/
marine
fish
and
invertebrates
is
low
because
no
information
was
available
to
estimate
a
slope
for
the
dose­
response
curve
for
these
taxonomic
groups.
Event
probabilities
for
listed
estuarine/
marine
fish
and
invertebrate
species
were
calculated
based
on
a
default
slope
assumption
of
4.5
with
upper
and
lower
confidence
intervals
of
2
and
9
(
Urban
and
Cook,
1986).
Given
the
large
uncertainty
associated
with
the
probability
estimates
it
is
not
possible
to
predict
the
chance
of
an
individual
mortality
event
for
listed
estuarine/
marine
fish
and
invertebrate
species.
69
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73
ACKNOWLEDGEMENTS
The
Environmental
Fate
and
Effects
Division
would
like
to
thank
Syracuse
Environmental
Research
Associates
Inc.
(
SERA)
(
Julie
Klotzbach
and
Mario
Citra)
for
their
assistance
in
developing
the
draft
screening­
level
risk
assessment
for
Xylene
Range
Aromatic
Solvents.
­
A­
1­
APPENDIX
A:
Environmental
Fate
Studies
Hydrolysis
161­
1
Xylenes
lack
functional
groups
that
are
susceptible
to
hydrolysis
under
environmental
conditions;
therefore,
hydrolysis
is
not
expected
to
be
an
important
environmental
fate
property
for
the
aromatic
solvents.

Photodegradation
in
water
161­
2;
Photodegradation
on
soil
161­
3
Xylenes
do
not
possess
functional
groups
that
absorb
photons
of
light
above
290
nm;
therefore,
photolysis
in
soil
and
water
systems
is
not
expected
to
be
an
important
environmental
fate
process
for
aromatic
solvents.

Aerobic
soil
metabolism
162­
1
p­
Xylene,
at
an
initial
concentration
of
45
ppm,
was
reported
to
be
completely
degraded
in
natural
potting
soil
microcosms
in
less
than
27
days
at
20
/

C,
but
was
not
degraded
at
6
/

C
(
ATSDR
1995).
Using
a
Nixon
sandy
loam
from
NJ,
14C
labeled
o­
and
p­
xylene
applied
at
a
concentration
of
3
µ
L/
g
soil,
degraded
with
half­
lives
of
approximately
5
and
7
days
respectively
(
Tsao
et
al.
1998).
A
3­
4
day
lag
period
was
observed
for
the
degradation
of
the
p­
isomer,
while
no
lag
period
or
acclimation
time
was
necessary
for
o­
xylene.
The
natural
pH
of
the
soil
(
5.5­
6.0)
was
raised
to
7.0
for
the
experiments
by
addition
of
CaCO
3
.
The
authors
noted
that
doubling
or
tripling
the
concentration
of
the
xylenes
resulted
in
inhibitory
effects
(
toxicity
to
the
microbial
population)
and
a
much
slower
rate
of
degradation.
The
main
degradation
products
observed
were
14CO
2
,
but
some
minor
degradation
products
such
as
3,6­
dimethylcatechol
were
also
observed
prior
to
complete
mineralization.

Under
aerobic
conditions,
xylenes
are
degraded
in
standard
biodegradability
tests
using
various
inocula
including
sewage
and
activated
sludge.
Employing
a
standard
biological
oxygen
demand
(
BOD)
dilution
technique
and
a
sewage
inoculum,
a
theoretical
BOD
of
52,
80
and
44%
was
achieved
over
a
5
day
incubation
period
for
o­,
m­,
and
p­
xylene
respectively
(
Bridie
et
al.
1979).
m­
Xylene
present
at
100
mg/
l,
reached
100%
of
its
theoretical
BOD
in
4
weeks
using
an
activated
sludge
inoculum
at
30
mg/
l
and
the
Japanese
MITI
test
(
CITI
1992).
These
data
suggest
that
under
aerobic
conditions,
xylenes
will
degrade
readily
in
the
environment.

Anaerobic
soil
metabolism
162­
2
Anaerobic
biodegradation
of
aromatic
compounds
in
soils
appear
to
occur
more
readily
under
nitrate
reducing
or
sulfate
reducing
conditions
as
compared
to
methanogenic
conditions
(
HSDB
2005).
Xylenes
were
shown
to
degrade
in
an
aquifer
microflora
laboratory
test
under
sulfate­
reducing
conditions,
but
not
under
methanogenic
conditions
(
ATSDR
1995).
m­
Xylene
was
completely
degraded
in
less
than
25
days
under
sulfate­
reducing
conditions
and
successive
metabolites
involved
in
the
anaerobic
degradation
of
xylenes
were
reported
to
be
methylbenzylsuccinic
acid,
toluic
acid,
­
A­
2­
phthalic
acid,
and
benzoic
acid
(
finally
degraded
to
carbon
dioxide)
(
ATSDR
1995).

Anaerobic
aquatic
metabolism
162­
3
Using
PS­
6
gasoline
as
substrate,
anaerobic
microcosms
constructed
of
3
g
of
sandy
soil
and
20
mL
of
groundwater
from
the
Borden
Canada
Forces
Base
in
Ontario,
were
employed
to
study
the
fate
of
BTEX
in
anaerobic
environments.
The
three
isomers
of
xylene
(
initial
concentrations
of
330­
800
µ
g/
L),
were
very
slowly
degraded
with
half­
lives
of
several
hundred
days
(
API
1994).
The
degradation
rates
in
these
anaerobic
microcosms
did
not
appear
to
follow
first­
order
kinetics;
however,
using
the
initial
concentration
and
final
concentrations
at
day
420,
estimated
half­
lives
were
432
days
(
p­
xylene),
235
days
(
m­
xylene),
and
676
days
(
o­
xylene).
Similar
results
were
obtained
using
PS­
6
gasoline
containing
the
oxygenates
MTBE
and
methanol.
At
lower
initial
starting
concentrations
the
rate
of
degradation
appears
to
increase.
Using
a
starting
concentration
of
250
µ
g/
L,
the
half­
lives
of
the
o­
and
m­
xylene
isomers
were
approximately
25
days
in
groundwater
from
Seal
Beach,
CA
(
Beller
et
al.
1995).
After
a
60
day
incubation
period,
over
95%
of
the
initially
applied
amount
of
xylene
isomers
had
been
degraded.
2­
Methylbenzyl
succinic
acid
and
2­
methylbenzyl
fumaric
acid
were
identified
as
metabolites
of
o­
xylene,
while
3­
methylbenzyl
succinic
acid
and
3­
methylbenzyl
fumaric
acid
were
identified
as
metabolites
of
m­
xylene.

Aerobic
aquatic
metabolism
162­
4
In
a
study
funded
by
the
American
Petroleum
Industry
(
API)
in
conjunction
with
Ontario
University,
benzene,
toluene,
ethylbenzene
and
xylenes,
(
BTEX)
degradation
rates
in
soil/
water
microcosms
were
studied
(
API
1994).
Using
PS­
6
gasoline
and
fully
aerobic
microcosms
constructed
of
3
g
of
sandy
soil
and
20
mL
of
groundwater
from
the
Borden
Canada
Forces
Base
in
Ontario,
the
3
isomers
of
xylene
were
shown
to
degrade
relatively
rapidly.
At
starting
concentrations
of
168,
216
and
85
µ
g/
L,
the
first­
order
degradation
rate
constants
for
o­,
m­,
and
p­
xylene
were
0.030,
0.038,
and
0.028
days­
1,
respectively;
corresponding
to
half­
lives
of
23,
20,
and
25
days.
Using
the
same
microcosms
and
PS­
6
gasoline
with
15%
MTBE
(
methyl
tertiary
butyl
ether)
the
rate
constants
were
0.047,
0.058
and
0.044
for
o­,
m­,
and
p­
xylene,
respectively;
corresponding
to
half­
lives
of
15,
12,
and
15
days.
For
microcosms
using
PS­
6
gasoline
with
15%
methanol
added,
the
rate
of
degradation
increased
with
half­
lives
of
14,
9
and
14
days
for
o­,
m­,
and
p­
xylene,
respectively.

Mobility/
Adsorption/
Desorption
163­
1
Adsorption
experiments
conducted
with
2
silty
clay
soils
and
a
course
sand
yielded
K
oc
values
for
xylenes
(
mixed
isomers)
ranging
from
39­
365
(
Pavlostathis
and
Mathavan
1992).
The
properties
of
the
soils
are
provided
in
table
A­
1.

Table
A­
1.
Adsorption
properties
of
xylenes
in
soils
Property
Soil
1
Soil
2
Soil
3
%
Sand
5
ND
40
­
A­
3­
%
Silt
70
ND
39
%
Clay
25
ND
21
%
Organic
carbon
0.17
1.4
0.09
pH
8.05
7.05
6.8
K
oc
365
39
311
K
d
0.62
0.54
0.28
These
K
oc
values
suggest
that
xylenes
will
have
high
to
moderate
mobility
in
soil,
depending
upon
the
characteristics
of
the
soil.
Sediment/
water
partition
coefficients
of
8.9
and
10.5
were
calculated
for
o­
xylene
and
p­
xylene,
respectively
(
Vowles
and
Mantoura
1987).
The
sediment
was
reported
to
contain
4%
organic
carbon;
therefore,
K
oc
values
of
222
and
262
were
derived
for
o­
xylene
and
pxylene
respectively.

The
adsorption
properties
of
o­
xylene
were
measured
in
2
course
sandy
soils
from
Denmark
under
saturated
and
unsaturated
moisture
conditions
(
Lindhardt
et
al.
1994).
In
general,
o­
xylene
was
expected
to
have
moderate
to
high
mobility
in
soils,
with
slightly
greater
adsorption
in
the
higher
organic
soil.
It
was
also
observed
that
the
mean
adsorption
coefficients
were
approximately
25­
35%
greater
under
unsaturated
conditions
as
compared
to
fully
saturated
moisture
conditions.
The
properties
of
the
two
soils
are
provided
in
table
A­
2.
­
A­
4­
Table
A­
2.
Adsorption
properties
of
o­
xylene
in
two
sandy
soils
Property
Soil
1
Soil
2
%
Course
Sand
(
0.2­
2
mm)
71.9
95.5
%
Fine
Sand
(
0.02­
0.2
mm)
17.3
1.8
%
Silt
3.8
0.5
%
Clay
4.8
2.1
%
Organic
carbon
1.1
0.11
pH
5.2
6.3
K
oc
(
saturated)
169
64
K
oc
(
saturated)
139
77
K
oc
(
2.5%
moisture
content)
207
103
K
oc
(
5%
moisture
content)
211
80
K
oc
(
average
value)
181
81
Field
volatility
163­
3
An
experiment
which
measured
the
rate
of
evaporation
of
xylenes
from
a
1:
1000
jet
fuel:
water
mixture
found
that
this
rate
averaged
approximately
0.6
times
the
oxygen
re­
aeration
rate
(
Smith
and
Harper
1980).
Combining
this
ratio
with
oxygen
reaeration
rates
for
typical
bodies
of
water,
one
estimates
that
the
half­
life
for
evaporation
of
xylenes
from
a
typical
river
or
pond
is
29
and
144
hours,
respectively.

A
field
monitoring
study
of
an
oil
spill
from
the
Trans­
Alaskan
Pipeline
which
leaked
into
the
Atigun
River
(
June
10,
1979)
indicated
xylenes
were
absent
from
the
40
km
long
river
in
the
contaminated
area
18
days
after
the
spill
indicating
that
the
majority
of
xylenes
volatilized
or
were
biodegraded.

Accumulation
in
Laboratory
Fish
165­
4
Eels
reared
in
seawater
containing
crude
oil
suspension
(
50
ppm
for
10
days),
had
BCF
values
of
23.6
and
21.4
for
m/
p­
xylene
and
o­
xylene,
respectively
(
Ogata
and
Miyaka
1978).
The
isomers
of
xylene
were
depurated
relatively
quickly
following
transfer
to
non
contaminated
water.
after
10
days
in
clean
sea
water,
BCF
values
were
approximately
5
for
m/
p­
xylene
and
3
for
o­
xylene.

Goldfish
reared
in
water
containing
1
mg/
L
o­,
m­,
and
p­
xylene
had
BCF
values
of
15
(
m­,
and
pxylene
and
14
(
o­
xylene)(
Ogata
et
al.
1984).
­
A­
5­
Terrestrial
field
dissipation
164­
1
In
order
to
simulate
the
dynamics
and
environmental
fate
of
xylenes
following
an
accidental
spill,
xylene
was
sub
surface
applied
(
depths
ranging
from
1.8
to
7.2
cm)
to
Westwood
silt
loam
soil
cores
at
levels
of
4.6­
19.0%
of
the
pore
volume,
and
continuously
flushed
with
water
to
simulate
rainfall
(
Aurelius
and
Brown
1987).
Following
application,
leachate
was
continuously
removed
at
33
kPa
tension.
The
majority
of
the
applied
xylenes
were
degraded
over
the
course
of
the
67
day
experiment,
with
smaller
amounts
volatilized
and
leached.
The
results
of
these
experiments
are
summarized
in
table
A­
3.

Table
A­
3.
Summation
of
the
fate
of
xylene
applied
to
soil
surfaces.

Soil
Core
Moisture
content
(
mg/
kg)
Application
depth
(
m)
Amount
volatilized
Amount
remaining
in
soila
Amount
leached
Amount
degraded
1
0.15
0.036
4.1%
11.9%
0.5%
83.5%

2
0.20
0.036
1.21%
11.3%
8.6%
78.9%

3
0.20
0.072
2.65%
6.7%
32.3%
57.8%

4
0.26
0.036
1.98%
12.8%
33.6%
50.9%

5
0.26
0.018
2.5%
11.4%
6.4%
76.6%

a.
67
days
post
application.

Aquatic
field
dissipation
164­
2
A
study
was
conducted
that
reviewed
the
impact
of
emulsified
xylenes
used
in
aquatic
weed
control
on
rainbow
trout
(
Walsh
et
al.
1977).
This
study
also
summarized
results
from
a
previous
investigation
that
reviewed
the
fate
of
xylenes
released
to
6
irrigation
canals
located
in
the
states
of
Wyoming,
Colorado,
and
Washington.
The
application
rate
was
10
gallons
of
xylene
per
ft3/
s
of
water
flow
within
a
30
minute
emission
period,
corresponding
to
a
level
of
740
ppm
(
Walsh
et
al.
1977).
The
rate
of
flow
in
these
6
irrigation
canals
ranged
from
11­
89
ft3/
s.
although
no
half­
lives
were
reported,
dissipation
curves
depicting
the
xylene
concentration
as
a
function
of
distance
from
the
release
point
were
provided.
The
concentration
of
xylenes
tended
to
vary
widely
near
the
release
point,
but
became
more
uniform
downstream.
In
one
of
the
canals,
xylene
levels
dissipated
from
~
555
ppm
to
<
10
ppm
one
mile
downstream
from
its
release
point.
In
the
other
canals
with
greater
water
velocity,
xylene
levels
remained
at
100
ppm
or
greater
for
at
least
4
miles
downstream.
In
general,
the
xylene
levels
declined
to
100­
200
ppm
or
less,
after
traveling
5­
10
miles
downstream.
The
monitoring
results
show
that
xylene
concentrations
in
the
treated
irrigation
canals
and
ditches
may
exceed
the
10
ppm
release
concentration.
However,
monitoring
of
xylene
residues
in
return
­
A­
6­
flow
in
the
same
study
showed
a
decrease
in
concentration
from
500
ppm
in
the
water
removed
from
lateral
ditches
for
irrigation
to
less
than
0.2
ppm
(
200
ppb)
(
study
detection
limit)
in
return
flow
after
flowing
through
irrigation
fields
(
length
of
irrigation
rills
750
to
1320
feet).
Similar
findings
were
summarized
in
a
Bulletin
publish
by
the
Bureau
of
Reclamation
(
USDI­
BR,
1969).
These
data
suggest
that
significant
dissipation
of
xylene
occurs
within
the
field
during
the
irrigation
process.
The
amount
of
water
coming
off
the
field
is
expected
to
vary
due
to
different
management
practices
and
type
of
irrigation.
­
A­
7­
References
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1995.
Toxicological
profile
for
xylenes.
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for
the
Agency
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Toxic
Substances
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1999­
00024.

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1994.
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methyl
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butyl
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MTBE)
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the
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MW,
Brown
KW
1987.
Fate
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spilled
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31.

Beller
HR,
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WH,
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situ
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Sci
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2864­
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AL,
Wolf
CJM,
Winter
M.
1979.
BOD
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627­
630.

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Chemical
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­
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89074­
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Lahvis
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RJ.
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the
water
table
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753­
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Lindhardt
B,
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TH,
Brun
A.
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o­
xylene
from
sandy
soil.
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29:
2965­
2937.

Lysyj,
I,
Perkins
G,
Farlow
JS
1980.
Trace
analysis
of
aromatic
hydrocarbons
in
natural
waters.
Environ
Int
4:
407­
16.

Ogata
M,
Miyaka
Y.
1978.
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of
aromatic
hydrocarbons
and
sulfur
compounds
from
fish
reared
in
crude
oil
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Water
Res
12:
1041­
1044.

Ogata
M,
Fujisawa
K,
Ogino
Y,
Mano
E.
1984.
Partition
coefficients
as
a
measure
of
bioconcentration
potential
of
crude
oil
components
in
fish
and
shellfish.
Bull.
Environ.
Contam.
Toxicol.
33:
561­
567.

Oregon
Department
of
Environmental
Quality
(
DEQ)
2002.
Summary
of
comments
and
response
to
comments
received
for
the
proposed
2002
Mutual
Agreement
and
Order
(
MAO)
for
the
application
of
acrolein,
xylene
and
copper
in
irrigation
systems.

Pavlostathis
SG,
Mathavan
GN.
1992.
Desorption
kinetics
of
selected
volatilie
organic
compounds
from
field
contaminated
soils.
Environ
Sci
Technol
26:
532­
538
(
1992).
­
A­
8­
Smith
JH,
Harper
JC
1980.
12th
Conference
on
Environ
Toxicol:
Behavior
of
Hydrocarbon
Fuels
in
Aquatic
Environment;
pp
336­
53.

Thomas,
R.
G.
1990.
Chapter
15.
Volatilization
from
Water.
In:
Handbook
of
Chemical
Property
Estimation
Methods.
Ed:
W.
J.
Lyman,
W.
F.
Reehl,
and
D.
H.
Rosenblatt.
American
Chemical
Society.
Washington,
D.
C.

Tsao
CW,
Song
HG,
Bartha
AR.
1998.
Metabolism
of
benzene,
toluene,
and
xylene
hydrocarbons
in
soil.
Appl
Environ
Microbiol
64:
4924­
4929.

United
States
Department
of
the
Interior,
Bureau
of
Reclamation.
1969.
Irrigation
Operation
and
Maintenance,
Bulletin
No.
69.
Division
of
Irrigation
Operations.
Office
of
Chief
Engineer,
Denver,
CO.

Walsh
DF,
Armstrong
JB,
Bartley
TR,
Salman
HA,
and
Frank
PA.
1977.
Residue
of
emulsified
xylene
in
aquatic
weed
control
and
their
impact
on
rainbow
trout
salmo
giardneri.
REC­
ERC­
76­
11.
NTIS
PB­
267270.
Bureau
Of
Reclamation
Denver,
CO.
­
B­
1­
APPENDIX
B:

Estimation
of
Concentration
in
Receiving
water
using
simple
plug
flow
model
The
change
in
concentration
of
a
chemical
being
released
into
a
flowing
water
channel
depends
upon
the
concentration
of
the
water
entering
the
channel
(
return
flow
concentration
­
Co),
the
rate
the
solution
water
is
entering
the
channel
(
return
flow
rate
­
Q),
the
initial
concentration
of
the
channel
(
receiving
water
­
assumed
to
be
0
for
xylene)
and
the
amount
of
water
in
the
channel
(
Vol).
Concentration
reductions
were
approximated
by
a
simple
steady­
state
plug
flow
model.

Assumptions
and
simplifications
are
the
mixing
is
ideal
(
constantly
stirred),
Q
is
constant,
same
amount
of
water
enters
the
channel
as
leaves
the
channel.

Assuming
a
steady­
state
flow
system,
the
mass
balance
describing
the
time
variation
of
an
average
concentration
in
a
flowing
channel
can
be
estimated.

C(
t)
=
Co
*
exp((
TVol/
Q)*­
R)

where:

C(
t)
=
Concentration
in
mixed
water
body
(
mass/
volume)
at
time
t
C
o
=
initial
concentration
in
return
flow
(
mass/
volume),
assumed
=
10
ppm
R
=
first­
order
degradation
rate
constant
for
volatilization
(
1/
time),
R
is
median
of
volatilization
half­
lives
report
in
literature.

Q
=
Flux
density
(
length3/
time)

TVol
=
Volume
of
return
flow
(
1
length3)
+
volume
(
dilution
x
1
length3)
of
receiving
water
(
i.
e.,
dilution)
(
length3)

and
where
TVol
=
Cross­
sectional
area
of
receiving
water
+
cross­
sectional
area
of
return
flow
(
length2)
*
flow
rate
(
length/
time).

The
following
table
shows
the
relationship
between
flow
properties
in
the
outflow
water
(
velocity,
area,
and
volume)
compared
to
the
receiving
water
and
receiving
water
(
velocity
return
flow,
receiving
area,
and
volume).
The
application
of
xylene
into
the
irrigation
canal
is
based
upon
flow
(
11
gallons
per
1
ft3/
sec
flow)
rate.
Thus,
if
the
flow
rate
is
double,
the
application
rate
also
doubles
with
the
concentrations
remaining
the
same.
­
B­
2­
The
dissipation
of
xylene
released
as
return
flow
into
a
receiving
body
of
water
will
correlated
with
the
flow
rate
and
cross­
sectional
area
and
degradation
rate
(
volatilization
and
biotic
metabolism).
If
the
flow
rates
are
equal,
the
cross­
section
area
(
essentially
a
dilution
factor)
has
the
greatest
influence
on
the
dissipation.

Table
B1.
Relationship
between
return
flow
and
receiving
water
in
plug
flow
model.

Q
Flow
Receiving
water
Total
Dilution
Flux
(
ft3/
s)
Velocity
(
ft/
s)
Area
(
ft2)
vol
(
ft3)
Velocity
(
ft/
s)
Area
(
ft2)
vol
(
ft3)
TVol
(
ft3)

no
dilution
1
1
1
1
0
0
0
1
1:
1
1
1
1
1
1
1
1
2
10:
1
1
1
1
1
1
10
10
11
20:
1
1
1
1
1
1
20
20
21
50:
1
1
1
1
1
1
50
50
51
Table
B2
shows
the
influence
of
return
flow
concentration
(
10
or
1
ppm)
with
different
dilutions.

Table
B2.
Time,
Distance,
and
Dilution
for
Xylene
Concentration
to
Decrease
from
10ppm
and
1ppm
to
<
0.04
ppm
Based
on
a
Steady­
State
Plug
Flow
Dilution
Model
Condition
Reduction
from
10
ppm
to
0.04
ppm
Reduction
from
1
ppm
to
0.04
ppm
1:
1
dilution
10:
1
dilution
20:
1
dilution
50:
1
dilution
1:
1
dilution
10:
1
dilution
20:
1
dilution
50:
1
dilution
Time
(
days)
7.96
1.45
0.76
0.31
4.64
0.84
0.44
0.2
Distance
(
miles)
130
23.7
12.4
5.1
76
13.8
7.2
3.0
Estimate
of
Xylene
Concentration
in
Air
The
concentration
of
xylene
in
air
was
estimated
by
the
following
equation:

C
g
=
C
l
*
H'

C
g
=
Concentration
in
gas
phase
(
mg/
L)
(
38.4925
mg/
L,
ppm)
­
B­
3­
C
l
=
Concentration
in
liquid
phase
(
178
mg/
L,
ppm)

H'
=
Nondimensional
Henry's
Law
constant
(
0.21625)
at
20
"

C
This
assume
ideal
conditions,
no
losses
of
xylene
through
degradation
or
wind.
The
uncertainty
of
these
conservative
assumptions
are
considered
acceptable
given
the
resulting
EECs
do
not
indicate
risk.
­
C­
1­
­
C­
1­
APPENDIX
C:
Data
Requirements
­
Environmental
Fate
Table
A1.
Status
of
environmental
fate
data
adequacy/
needs
for
xylenes.

Guideline
#
Data
Requirement
Adequate
for
Risk
Assessment
Citation
Study
Classification
161­
1
835.212
Hydrolysis
yes
HSDB
2005;
ATSDR
1995
open
lit.

161­
2
835.224
Photodegradatio
n
in
Water
yes
HSDB
2005;
ATSDR
1995
open
lit.

161­
3
835.241
Photodegradatio
n
on
Soil
yes
HSDB
2005;
ATSDR
1995
open
lit.

161­
4
835.237
Photodegradatio
n
in
Air
yes
HSDB
2005;
ATSDR
1995
open
lit.

162­
1
835.41
Aerobic
Soil
Metabolism
yes
Tsao
et
al.
1998
open
lit.

162­
2
835.42
Anaerobic
Soil
Metabolism
yes
HSDB
2005;
ATSDR
1995
open
lit.

162­
3
835.44
Anaerobic
Aquatic
Metabolism
yes
API
1994
open
lit.

162­
4
835.43
Aerobic
Aquatic
Metabolism
yes
API
1994
open
lit.

163­
1
835.1240
835.1230
Leaching­
Adsorption/
Deso
rption
yes
Pavlostathis
and
Mathavan
1992
Vowles
and
Mantoura
1987
Lindhardt
et
al.
1994
open
lit.

163­
2
835.141
Laboratory
Volatility
no
data
open
lit.

163­
3
835.81
Field
Volatility
yes
Smith
and
Harper
1980
open
lit.
Table
A1.
Status
of
environmental
fate
data
adequacy/
needs
for
xylenes.

Guideline
#
Data
Requirement
Adequate
for
Risk
Assessment
Citation
Study
Classification
­
C­
2­
164­
1
835.61
Terrestrial
Field
Dissipation
yes
Aurelius
and
Brown
1987
open
lit.

164­
2
835.62
Aquatic
Field
Dissipation
yes
Walsh
et
al.
1977
open
lit.

165­
4
850.173
Accumulation
in
Fish
yes
Ogata
and
Miyaka
1978
Ogata
et
al.
1984
open
lit.
­
D­
1­
APPENDIX
D:
Environmental
Fate
and
Monitoring
Bibliography
ATSDR
1995.
Toxicological
profile
for
xylenes.
Prepared
for
the
Agency
for
Toxic
Substances
and
Disease
Registry.
ATSDR
Contract
No.
205­
1999­
00024.

API.
1994.
A
study
to
characterize
air
concentrations
of
methyl
tertiary
butyl
ether
(
MTBE)
at
service
stations
in
the
Northeast.
American
Petroleum
Institute.

Aurelius
MW,
Brown
KW
1987.
Fate
of
spilled
xylene
influenced
by
moisture
content.
Wat.
Air
Soil
Pollut.
36:
23­
31.

Beller
HR,
Ding
WH,
Reinhard
M.
1995.
Byproducts
of
anaerobic
alkylbenzene
metabolism
useful
as
indicators
of
in
situ
bioremediation.
Environ
Sci
Technol
29:
2864­
2870.

Bridie
AL,
Wolf
CJM,
Winter
M.
1979.
BOD
and
COD
of
petroleum
chemicals.
Water
Res.
13:
627­
630.

California
Department
of
Pesticide
Regulation
(
CDPR)
Pesticide
Use
Reporting
(
PUR).
2005.
Pesticide
Usage
Database.
Available
on­
line
at
:
http://
www.
cdpr.
ca.
gov/
docs/
pur/
purmain.
htm.
Accessed
6
July
2005.

CITI.
1992.
Chemicals
Inspection
and
Testing
Institute.
Japan
Chemical
Industry
Ecology
­
Toxicology
and
Information
Center.
ISBN
4­
89074­
101­
1.

EXAMS.
2002.
Surface
Water
Model,
Version
2.98.04.
Environmental
Fate
and
Effects
Division,
Office
of
Pesticide
Programs,
U.
S.
Environmental
Protection
Agency,
Washington,
D.
C.

HSDB
2005
­
National
Library
of
Medicine
Hazardous
Substance
Databank.
Avaialable
at
:
http://
toxnet.
nlm.
nih.
gov/
cgi­
bin/
sis/
htmlgen.

Lahvis
MA,
Baehr
AL,
Baker
RJ.
1999.
Quantification
of
aerobic
biodegradation
and
volatilization
rates
of
gasoline
hydrocarbons
near
the
water
table
under
natural
attenuation
conditions.
Water
Resources
Research
35:
753­
765.

Lindhardt
B,
Christensen
TH,
Brun
A.
1994.
Volatilization
of
o­
xylene
from
sandy
soil.
Chemosphere
29:
2965­
2937.

Lysyj,
I,
Perkins
G,
Farlow
JS
1980.
Trace
analysis
of
aromatic
hydrocarbons
in
natural
waters.
Environ
Int
4:
407­
16.

National
Agricultural
Statistics
Service
(
NASS).
2005.
Agricultural
Chemical
Usage
Database.
Available
on­
line
at
http://
www.
pestmanagement.
info/
nass/
app_
usage.
cfm.
Accessed
6
July
2005.

National
Center
for
Food
and
Agricultural
Policy
(
NCFAP).
2005.
Pesticide
Usage
Database.
­
D­
2­
Available
on­
line
at
http://
pestdata.
ncsu.
edu/
ncfap/
search.
cfm.
Accessed
6
July
2005.

Ogata
M,
Miyaka
Y.
1978.
Disappearance
of
aromatic
hydrocarbons
and
sulfur
compounds
from
fish
reared
in
crude
oil
suspensions.
Water
Res
12:
1041­
1044.

Ogata
M,
Fujisawa
K,
Ogino
Y,
Mano
E.
1984.
Partition
coefficients
as
a
measure
of
bioconcentration
potential
of
crude
oil
components
in
fish
and
shellfish.
Bull.
Environ.
Contam.
Toxicol.
33:
561­
567.

Oregon
Department
of
Environmental
Quality
(
DEQ)
2002.
Summary
of
comments
and
response
to
comments
received
for
the
proposed
2002
Mutual
Agreement
and
Order
(
MAO)
for
the
application
of
acrolein,
xylene
and
copper
in
irrigation
systems.

Pavlostathis
SG,
Mathavan
GN.
1992.
Desorption
kinetics
of
selected
volatilie
organic
compounds
from
field
contaminated
soils.
Environ
Sci
Technol
26:
532­
538
(
1992).

Smith
JH,
Harper
JC
1980.
12th
Conf
on
Environ
Toxicol:
Behavior
of
Hydrocarbon
Fuels
in
Aquatic
Environment;
pp
336­
53.

Tsao
CW,
Song
HG,
Bartha
AR.
1998.
Metabolism
of
benzene,
toluene,
and
xylene
hydrocarbons
in
soil.
Appl
Environ
Microbiol
64:
4924­
4929.

USEPA.
2005.
USEPA
Storage
and
Retrieval
System
(
STORET).
Available
on­
line
at
http://
www.
epa.
gov/
storet/
dbtop.
html.
Accessed
6
July
2005.

Vowles
PD
and
Mantoura
RFC
1987.
Sediment­
water
partition
coefficients
and
hplc
retention
factors
of
aromatic
hydrocarbons.
Chemosphere
16:
109­
16.

Walsh
DF,
Armstrong
JB,
Bartley
TR,
Salman
HA,
and
Frank
PA.
1977.
Residue
of
emulsified
xylene
in
aquatic
weed
control
and
their
impact
on
rainbow
trout
salmo
giardneri.
REC­
ERC­
76­
11.
NTIS
PB­
267270.
Bureau
Of
Reclamation
Denver,
CO.

WSDE
(
Washington
State
Department
of
Ecology)
2002.
Fact
sheet
for
aquatic
weed
control
in
irrigation
system.
General
NPDES
Permit.
April
17,
2002.
­
E­
1­
APPENDIX
E:
Ecological
Effects
The
primary
focus
of
this
risk
assessment
is
to
evaluate
the
potential
adverse
effects
of
mixed
xylenes
to
aquatic
and
terrestrial
ecosystems.
As
such,
toxicity
data
for
mixed
xylenes
and
the
three
xylene
isomers
(
m­,
o­,
and
p­
xylene)
were
considered
in
the
derivation
of
risk
quotients.

No
registrant­
submitted
toxicity
studies
in
which
xylene
(
mixed
xylenes
or
isomers)
is
the
sole
active
ingredient
were
identified;
thus,
all
toxicity
data
summarized
in
this
appendix
are
from
open
literatures
studies.
Three
sources
were
used
to
identify
open
literature
publications
on
xylenes:
EPA's
Ecotoxicology
database
ECOTOX,
the
ATSDR
Toxicological
Profile
for
Xylene
(
1995),
and
the
World
Health
Organization
Environmental
Health
Criteria
Document
for
Xylenes
(
1997).

I.
Categories
of
Acute
Toxicity
In
general,
categories
of
acute
toxicity
ranging
from
"
practically
nontoxic"
to
"
very
highly
toxic"
have
been
established
for
aquatic
organisms
(
based
on
LC
50
values),
terrestrial
organisms
(
based
on
LD
50
values),
and
avian
species
(
based
on
LC
50
values)
(
US
EPA
2001).

Categories
of
acute
toxicity
for
aquatic
organisms
can
be
classified
according
to
the
toxicity
reference
value
(
LC
50
)
given
by
a
study:

LC50
(
ppm)
Toxicity
Category
<
0.1
Very
highly
toxic
0.1 
1
Highly
toxic
>
1 
10
Moderately
toxic
>
10 
100
Slightly
toxic
>
100
Practically
non­
toxic
­
E­
2­
Categories
of
acute
toxicity
for
mammalian
species
can
be
classified
according
to
the
toxicity
reference
value
(
LD
50
)
given
by
a
study:

LD50
(
mg
a.
i./
kg)
Toxicity
Category
<
10
Very
highly
toxic
10 
50
Highly
toxic
51 
500
Moderately
toxic
501 
2000
Slightly
toxic
>
2000
Practically
non­
toxic
For
avian
species,
categories
of
acute
toxicity
for
can
be
classified
according
to
the
toxicity
reference
value
(
LC
50
)
given
by
a
study:

LC50
(
ppm)
Toxicity
Category
<
50
Very
highly
toxic
50 
500
Highly
toxic
501 
1000
Moderately
toxic
1001 
5000
Slightly
toxic
>
5000
Practically
nontoxic
II.
Toxicity
to
Freshwater
Aquatic
Animals
a.
Freshwater
Fish,
Acute
Two
freshwater
fish
toxicity
studies
are
required
to
establish
the
acute
toxicity
of
mixed
xylenes
to
fish.
The
preferred
test
species
are
bluegill
sunfish
(
a
warmwater
fish)
and
rainbow
trout
(
a
coldwater
fish).
No
acute
toxicity
studies
on
mixed
xylenes
in
freshwater
fish
were
identified
from
the
available
literature.

The
acute
toxicity
of
xylene
isomers
has
been
evaluated
in
several
species
of
freshwater
fish;
study
details
are
summarized
in
Table
E­
1.
For
o­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
7.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al,
1988)
to
the
96­
hour
LC
50
value
of
16.1
mg/
L
in
bluegill
sunfish,
fathead
minnow,
goldfish,
and
white
sucker
fish
(
Holcombe
et
al.
1978).
Results
of
­
E­
3­
these
studies
indicate
that
o­
xylene
is
slightly
to
moderately
toxic
to
freshwater
fish
on
an
acute
basis.
For
m­
xylene,
acute
toxicity
values
range
from
the
96­
hour
LC
50
value
of
8.4
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
to
the
96­
hour
LC
50
value
of
12.9
mg
a.
i./
L
in
guppy
(
Galassi
et
al.
1988),
suggesting
that
m­
xylene
is
moderately
toxic
to
freshwater
fish.
Acute
toxicity
values
for
p­
xylene
range
from
the
96­
hour
LC
50
value
of
2.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
to
the
96­
hour
LC
50
value
of
10
mg
a.
i./
L
in
rainbow
trout
(
Folmar
1976)
indicating
that
p­
xylene
is
moderately
toxic
to
freshwater
fish
on
a
acute
basis.
The
lowest
acute
toxicity
value
obtained
for
the
p­
xylene
isomer
(
24­
hour
LC50
value
of
2.6
mg
a.
i./
L
in
rainbow
trout
(
Galassi
et
al.
1988)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
freshwater
fish.
The
guideline
(
§
72­
1)
is
fulfilled
because
the
study
by
Galassi
et
al.
(
1988)
was
conducted
in
accordance
with
OECD
standardized
method
No.
203,
modified
for
testing
volatile
compounds.
Closed
conditions
were
used
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.

Information
on
sublethal
effects
was
reported
in
a
single
study
in
rainbow
trout
(
Walsh
et
al.
1977).
Dose­
dependent
signs
of
toxicity
(
loss
of
equilibrium
and
"
anesthetic"
effects)
were
observed
in
fish
exposed
to
xylene
concentrations
of
3.2
and
greater,
yielding
an
NOAEC
value
for
sublethal
effects
of
0.64
ppm.
In
addition,
Folmer
(
1976)
reported
that
rainbow
trout
actively
avoid
xylene
at
concentrations
as
low
as
0.1
ppm.

Table
E­
1.
Acute
Toxicity
of
Xylenes
to
Freshwater
Fish.

Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
rainbow
trout
(
Salmo
gairdneri)
p­
xylene
(
technical
grade)
Concentrations
tested:
0.001,
0.01.
and
0.1
mg/
L
(
nominal
concentrations)

96­
hour
LC50:
10
mg
a.
i./
L
(
nominal
concentration)

Trout
exhibited
attractant
behavior
at
a
concentration
of
0.01
mg/
L,
but
avoidance
behavior
at
a
concentration
of
0.1
mg/
L
after
1
hour
of
exposure.
moderately
toxic
Folmar
1976
Open
literature
(
Supplemental)
Table
E­
1.
Acute
Toxicity
of
Xylenes
to
Freshwater
Fish.

Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
4­
rainbow
trout
(
Salmo
gairdneri)
xylene
(
not
specified
if
mixed
or
isomer)
(
industrial
grade
material)

xylene
plus
2%
emulsifier
(
AD­
410)
Fish
exposed
to
averaged
(
measured
)
0.64,
3.6,
7.1,
16.1
and
25.6
ppm
for
2
hours.
Test
vessel
was
an
artificial
stream
approximately
750
feet
long
(
5
sections
of
150
feet).

At
the
16.1
and
25.6
ppm
concentrations,
all
fish
were
killed
within
24
hours
of
exposure.
No
fish
were
killed
at
lower
concentrations.
At
concentrations
of
3.6
and
7.2
ppm,
fish
exhibited
"
symptoms
similar
to
anesthesia",
including
loss
of
equilibrium,
after
1.4
hours
of
exposure.
Severity
of
effect
was
dosedependent
Fish
recovered
after
a
"
short
time"
in
untreated
water.

Values
for
xylene
only
(
NOTE:
values
based
on
deaths
at
24
and
96
hours.
Exposure
period
was
only
2
hours).
24­
hour
LC50
=
13.5
ppm
(
95%
CI:
9.5­
19.2)
96­
hour
LC50
=
13.5
ppm
(
95%
CI:
9.5­
19.2)
NOAEC
for
lethality:
7.1
ppm
NOAEC
for
sublethal
effects:
0.64
ppm
Acute
LC50
values
for
xylene
plus
emulsifier
:
24­
hour
LC50
=
17.3
ppm
(
95%
CI:
11.9­
19.2)
96­
hour
LC50
=
17.3
ppm
(
95%
CI:
11.9­
25.1)
NOAEC
values
not
reported.
slightly
toxic
Walsh
et
al.
1977
Open
literature
(
Supplemental)
Table
E­
1.
Acute
Toxicity
of
Xylenes
to
Freshwater
Fish.

Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
5­
rainbow
trout
(
Salmo
gairdneri)
o­
xylene
m­
xylene
p­
xylene
(
highest
purity)
Static
renewal
conditions.
Measured
concentrations.
Note:
all
tests
conducted
using
a
closed
system
to
minimize
loss
due
to
volatility.

96­
hour
LC50
values:
o­
xylene:
7.6
mg
a.
i./
L
m­
xylene:
8.4
mg
a.
i./
L
p­
xylene:
2.6
mg
a.
i./
L
Slope
functions:
o­
xylene:
1.11
m­
xylene:
1.11
p­
xylene:
1.10
moderately
toxic
Galassi
et
al.
1988
Open
literature
(
Supplemental
­
study
was
performed
in
accordance
with
OECD
Standard
Method
No.
203)

guppy
(
Peocilia
reticulata)
o­
xylene
m­
xylene
p­
xylene
(
highest
purity)
Static
renewal
conditions.
Measured
concentrations.
Note:
all
tests
conducted
using
a
closed
system
to
minimize
loss
due
to
volatility.

96­
hour
LC50
values:
o­
xylene:
12.0
mg
a.
i./
L
m­
xylene:
12.9
mg
a.
i./
L
p­
xylene:
8.8
mg
a.
i./
L
Slope
functions:
o­
xylene:
1.05
m­
xylene:
1.03
p­
xylene:
1.13
slightly
to
moderately
toxic
Galassi
et
al.
1988
Open
literature
(
Supplemental
­
study
was
performed
in
accordance
with
OECD
Standard
Method
No.
203)

fathead
minnow
(
Pimephales
promelas)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
16.1
mg/
L
95%
CI:
11.6­
22.4
slightly
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)
Table
E­
1.
Acute
Toxicity
of
Xylenes
to
Freshwater
Fish.

Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
6­
rainbow
trout
(
Salmo
gairdneri)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
8.05
mg/
L
95%
CI:
5.59­
22.6
moderately
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

bluegill
sunfish
(
Lepomis
machrochirus)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
16.1
mg/
L
95%
CI:
11.6­
22.4
moderately
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

goldfish
(
Carassius
auratus)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
16.1
mg/
L
95%
CI:
11.6­
22.4
moderately
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

white
sucker
(
Catostomus
commersoni)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
16.1
mg/
L
95%
CI:
11.6­
22.4
moderately
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

b.
Freshwater
Fish,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
freshwater
fish
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
freshwater
fish
are
not
required.
It
should
be
noted
that
no
chronic
freshwater
fish
toxicity
studies
for
mixed
xylenes
or
xylene
isomers
­
E­
7­
were
located
in
the
open
literature.

c.
Freshwater
Invertebrates,
Acute
A
freshwater
aquatic
invertebrate
toxicity
study
is
required
to
establish
the
toxicity
of
mixed
xylenes
to
freshwater
invertebrates.
The
preferred
test
species
is
the
water
flea
(
Daphnia
magna).
No
acute
toxicity
studies
on
mixed
xylenes
in
freshwater
invertebrates
were
identified
from
the
available
literature.

The
acute
toxicity
of
xylene
isomers
has
been
evaluated
in
freshwater
invertebrates;
study
details
are
summarized
in
Table
E­
2.
Results
indicate
that
the
three
xylene
isomers
have
similar
toxicities
to
freshwater
invertebrates.
For
o­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
1.0
mg
a.
i./
L
in
Daphnia
magna
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
>
22.4
mg/
L
in
the
snail
(
Holcombe
et
al.
1987),
indicating
that
xylene
isomers
are
slightly
to
highly
toxic
to
freshwater
invertebrates.
For
m­
xylene,
acute
toxicity
values
range
from
the
24­
hour
LC
50
value
of
4.7
mg
a.
i./
L
in
Daphnia
magna
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
9.6
mg
a.
i./
L
in
Daphnia
magna
(
Abernethy
et
al.
1986),
indicating
that
m­
xylene
is
moderately
toxic
to
freshwater
invertebrates.
Acute
toxicity
values
in
Daphnia
magna
for
p­
xylene
range
from
the
24­
hour
LC
50
value
of
3.6
mg
a.
i./
L
(
Galassi
et
al.
1988)
to
the
48­
hour
LC
50
value
of
8.5
mg
a.
i./
L
(
Abernethy
et
al.
1986),
indicating
that
p­
xylene
is
moderately
toxic
to
freshwater
invertebrates
on
an
acute
basis.
The
lowest
acute
toxicity
value
obtained
for
the
o­
xylene
isomer
(
24­
hour
LC50
value
of
1.0
mg
a.
i./
L
in
Daphnia
magna,
Galassi
et
al.
1988)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
freshwater
invertebrates.
The
guideline
(
§
72­
2)
is
fulfilled
because
the
Galassi
et
al.
(
1988)
study
was
conducted
in
accordance
with
OECD
standardized
method
No.
202,
with
modifications
for
testing
volatile
compounds.
As
previously
noted,
the
study
was
conducted
under
closed
conditions
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.
­
E­
8­
Table
E­
2.
Acute
Toxicity
of
Xylenes
to
Freshwater
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
Daphnia
magna
p­
xylene
m­
xylene
o­
xylene
all
test
substances
>
97%
a.
i.
Nominal
concentrations.
Static
conditions.

48­
hour
LC50
values
:
p­
xylene:
80
mmol/
m3
m­
xylene:
90
mmol/
m3
o­
xylene:
30
mmol/
m3
Based
on
Molecular
Weight
of
106.16
for
xylene,
the
above
LC50
values
are
calculated
in
terms
of
mg/
L,
where
1m3
=
1000
L
[
For
example:
20
mmole/
m3
×
1
m3/
1000
L
×
106.16
mg/
mmol
=
2.1
mg/
L]

p­
xylene:
8.5
mg
a.
i./
L
m­
xylene:
9.6
mg
a.
i./
L
o­
xylene:
3.2
mg
a.
i./
L
Note:
Airspace
exposure
was
eliminated
to
minimize
volatilization
loss.
all
values:
moderately
toxic
Abernethy
et
al.
1986
same
data
reported
in
Bobra
et
al.
1983
Open
literature
(
Supplemental)

Daphnia
magna
o­
xylene
m­
xylene
p­
xylene
(
highest
purity)
Static
renewal
conditions.
Measured
concentrations.
Note:
all
tests
conducted
using
a
closed
system
to
minimize
loss
due
to
volatility.

24­
hour
IC50
values
(
for
immobility)
o­
xylene:
1.0
mg
a.
i./
L
m­
xylene:
4.7
mg
a.
i./
L
p­
xylene:
3.6
mg
a.
i./
L
Slope
functions:
o­
xylene:
1.40
m­
xylene:
1.97
p­
xylene:
1.56
moderately
to
highly
toxic
Galassi
et
al.
1988
Open
literature
(
Supplemental
­
study
was
performed
in
accordance
with
OECD
Standard
Method
No.
202)
Table
E­
2.
Acute
Toxicity
of
Xylenes
to
Freshwater
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
9­
Daphnia
magna
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
3.82
mg/
L
95%
CI:
2.61­
5.59
moderately
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

snail
(
Aplexa
hypnorum)
o­
xylene
(
purity
not
reported)
Measured
concentrations.
Test
appears
to
be
conducted
under
static
renewal
conditions,
although
this
is
not
specifically
stated.

48­
hour
LC50:
>
22.4
mg/
L
slightly
toxic
Holcombe
et
al.
1987
Open
literature
(
Supplemental)

d.
Freshwater
Invertebrate,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
freshwater
invertebrates
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
freshwater
invertebrates
are
not
required.
No
chronic
toxicity
data
for
freshwater
invertebrates
were
located
in
the
open
literature.

III.
Toxicity
to
Estuarine
and
Marine
Animals
a.
Estuarine
and
Marine
Fish,
Acute
An
estuarine/
marine
fish
toxicity
study
is
required
to
establish
the
toxicity
of
mixed
xylenes
to
estuarine/
marine
fish.
The
preferred
test
species
is
the
sheepshead
minnow.
No
acute
toxicity
studies
on
mixed
xylenes
in
estuarine/
marine
fish
were
identified
from
the
available
open
literature.

Only
one
acute
xylene
isomer
toxicity
study
for
estuarine/
marine
fish
(
striped
bass)
was
located
in
the
open
literature
(
Benville
and
Korn
1977);
however,
the
study
is
classified
as
invalid
because
it
does
not
specifically
report
that
treatments
were
compared
to
an
acceptable
control
(
study
details
are
summarized
in
Table
E­
3).
Therefore,
the
guideline
(
§
72­
3)
is
not
fulfilled.
­
E­
10­
Table
E­
3.
Acute
Toxicity
of
Xylenes
to
Estuarine/
Marine
Fish
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
striped
bass
(
Morone
saxatilis)
m­
xylene
o­
xylene
p­
xylene
(>
99%
pure)
Conducted
under
static,
open
conditions.
Significant
loss
of
all
test
substances:
p­
xylene:
21­
99%
loss
from
24
to
96
hrs;
m­
xylene:
32­
99%
loss
from
24
to
96
hrs;
o­
xylene:
19­
99%
loss
from
24
to
96
hours.
Toxicity
values
expressed
in
terms
of
nominal
concentrations.
Water
concentrations
were
measured
at
24­
hour
intervals.

24­
hour
LC50:
m­
xylene:
9.2
ppm
(
95%
CL:
8.3­
10)
o­
xylene:
11
ppm
(
95%
CL:
9.4­
12)
p­
xylene:
2.0
(
95%
CL
not
reported)

96­
hourLC50:
m­
xylene:
9.2
ppm
(
95%
CL:
8.3­
10)
o­
xylene:
11
ppm
(
95%
CL:
9.4­
12)
p­
xylene:
2.0
ppm
(
95%
CL
not
reported)

Nearly
all
mortalities
occurred
during
the
first
6
hours
of
exposure.
based
on
96­
hour
values:

m­
xylene
(
moderately
toxic);
oxylene
(
slightly
toxic);
pxylene
(
moderately
toxic)
Benville
and
Korn
1977
Open
literature
(
Invalid:
No
control
data)

b.
Estuarine
and
Marine
Fish,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
estuarine/
marine
fish
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
estuarine/
marine
fish
are
not
required.
No
chronic
toxicity
data
for
estuarine/
marine
fish
were
located
in
the
open
literature.

c.
Estuarine
and
Marine
Aquatic
Invertebrates,
Acute
­
E­
11­
An
estuarine/
marine
invertebrate
toxicity
study
is
required
to
establish
the
toxicity
of
mixed
xylenes
to
estuarine/
marine
invertebrates.
The
preferred
test
species
is
the
mysid
shrimp.
The
acute
toxicity
of
mixed
xylenes
has
been
evaluated
in
bay
shrimp
(
Neff
et
al.
1976)
and
grass
shrimp
(
Tatem
et
al.
1978);
however,
the
results
of
the
Neff
et
al.
study
is
classified
as
invalid
because
it
does
not
specifically
report
that
treatments
were
compared
to
an
acceptable
control
(
details
of
both
studies
are
provided
in
Table
E­
4).
Results
of
the
Tatum
et
al.
(
1978)
study
reports
an
acute
96­
hour
LC
50
value
of
7.4
mg/
L
in
bay
shrimp,
indicating
that
mixed
xylenes
are
moderately
toxic
to
estuarine/
marine
invertebrates.

The
acute
toxicity
of
xylene
isomers
has
also
been
evaluated
in
several
species
of
estuarine/
marine
invertebrates
including
bay
shrimp
(
Benville
and
Korn
1977),
brine
shrimp
(
Abernathy
et
al.,
1986),
larval
stage
Dungeness
crab
(
Caldwell
et
al.
1977),
and
sea
urchin
eggs
(
Falk­
Peterson
et
al.
1985);
study
details
are
summarized
in
Table
E­
4.
Although
data
is
available
for
four
different
estuarine/
marine
invertebrate
species,
the
studies
using
bay
shrimp
(
Benville
and
Korn
1977)
and
Dungeness
crab
(
Caldwell
et
al.
1977)
are
classified
as
invalid
because
no
mention
of
control
data
was
included
as
part
of
the
study
methodology
or
results.
Available
data
for
the
brine
shrimp
(
Abernathy
et
al.
1986)
shows
that
xylene
isomers
are
slightly
toxic
to
estuarine/
marine
invertebrates
with
48­
hour
LC
50
values
of
19.3,
24.5,
and
24.7
mg/
L
for
m­
xylene,
p­
xylene,
and
o­
xylene,
respectively.

Results
of
a
sub­
acute
study
investigating
the
effect
of
o­
xylene
exposure
on
sea
urchin
eggs
show
that
embryo
lethality
was
observed
after
4
days
of
exposure,
with
a
96­
hour
EC50
value
of
4.1
mg/
L
(
Falk­
Peterson
et
al.
1985).
There
is
uncertainty
associated
with
this
study
because
it
was
conducted
under
open
conditions,
and
the
authors
report
a
significant
decrease
in
xylene
concentrations
over
the
course
of
the
exposure
period.
However,
although
not
specifically
stated,
it
appears
that
the
results
are
expressed
in
terms
of
measured
concentrations
The
lowest
acute
toxicity
value
obtained
for
o­
xylene
(
the
96­
hour
EC50
of
4.1
mg/
L
in
sea
urchin
eggs
(
Falk­
Peterson
et
al.
1985)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
estuarine/
marine
invertebrates.
The
guideline
(
§
72­
3)
is
fulfilled
based
on
the
available
information
obtained
from
the
open
literature.

Table
E­
4.
Acute
Toxicity
of
Xylenes
to
Estuarine/
Marine
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
bay
shrimp
(
Palaemonetes
pugio)
mixed
xylenes
(
purity
and
composition
of
test
material
not
reported)
96­
hour
LC50:
7.4
ppm
Not
reported
if
data
are
expressed
in
terms
of
nominal
or
measured
concentrations.
Conditions
of
exposure
(
static
or
flow­
through/
open
or
closed)
not
reported.
moderately
toxic
Neff
et
al.
1976
Open
literature
(
Invalid:
No
control
data)
Table
E­
4.
Acute
Toxicity
of
Xylenes
to
Estuarine/
Marine
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
12­
grass
shrimp
(
Palaemonetes
pugio)
xylenes
(
purity
and
composition
of
test
material
not
reported)
Static
conditions
conducted
under
"
covered"
conditions
to
minimize
volatilization
loss.
Report
does
not
specify
if
results
are
expressed
in
terms
of
nominal
or
measured
concentrations.

24­
hour
LC50:
14.0
ppm
48­
hour
LC50:
8.5
ppm
96­
hour
LC50:
7.4
ppm
slightly
to
moderately
toxic
Tatem
et
al.
1978
Open
literature
(
Supplemental)

bay
shrimp
(
Crago
francisocrum)
m­
xylene
o­
xylene
p­
xylene
(>
99%
pure)
Conducted
under
static,
open
conditions.
Significant
loss
of
all
test
substances:
p­
xylene:
21­
99%
loss
from
24
to
96
hrs;
m­
xylene:
32­
99%
loss
from
24
to
96
hrs;
o­
xylene:
19­
99%
loss
from
24
to
96
hours.
Toxicity
values
expressed
in
terms
of
nominal
concentrations.
Water
concentrations
were
measured
at
24­
hour
intervals.

24­
hour
LC50:
m­
xylene:
4.8
ppm
(
95%
CL:
3.6­
6.3)
o­
xylene:
5.3
ppm
(
95%
CL:
4.4­
6.5)
p­
xylene:
2.0
ppm
(
95%
LC
not
reported)

96­
hour
LC50:
m­
xylene:
3.7
ppm
95%
CL:
2.9­
4.7)
o­
xylene:
1.3
ppm
(
95%
CL:
1.1­
1.6)
p­
xylene:
2.0
ppm
(
95%
LC
not
reported)
moderately
toxic
to
highly
toxic
Benville
and
Korn
1977
Open
literature
(
Invalid:
No
control
data)
Table
E­
4.
Acute
Toxicity
of
Xylenes
to
Estuarine/
Marine
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
13­
brine
shrimp
(
Artemia
sp.)
p­
xylene
m­
xylene
o­
xylene
all
test
substances
<
97%
a.
i.
Nominal
concentrations.
Static
conditions.

48­
hour
LC50
values
p­
xylene:
232
mmol/
m3
m­
xylene:
182
mmol/
m3
o­
xylene:
223
mmol/
m3
Based
on
Molecular
Weight
of
106.16
for
xylene,
the
above
LC50
values
are
calculated
in
terms
of
mg/
L,
where
1m3
=
1000
L
[
For
example:
145
mmole/
m3
×
1
m3/
1000
L
×
106.16
mg/
mmol
=
mg/
L]

p­
xylene:
24.5
mg
a.
i./
L
m­
xylene:
19.3
mg
a.
i./
L
o­
xylene:
24.7
mg
a.
i./
L
Note:
Airspace
exposure
was
eliminated
to
minimize
volatilization
loss.
slightly
toxic
Abernethy
et
al.
1986
Open
literature
(
Supplemental)

Dungeness
crab
(
Canoer
magister
Dana)
­
larval
stage
m­
xylene
o­
xylene
(
purity
not
reported)
Static
conditions.
Report
does
not
indicate
if
toxicity
endpoints
are
expressed
in
terms
of
nominal
or
measured
values.

48­
hour
LC50
values:
m­
xylene:
33
mg/
L
o­
xylene:
38
mg/
L
96­
hour
LC50
values:
m­
xylene:
12
mg/
L
o­
xylene:
6.0
mg/
L
slightly
to
moderately
toxic
Caldwell
et
al.
1977
Open
literature
(
Invalid:
No
control
data)
Table
E­
4.
Acute
Toxicity
of
Xylenes
to
Estuarine/
Marine
Invertebrates
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
­
E­
14­
sea­
urchin
eggs
(
Strongylocentrotus
droebachiensis)
o­
xylene
(>
98%
a.
i.)
4­
day
exposure
period
under
static,
open
conditions.
Test
vessels
were
covered.
Significant
decrease
in
xylene
concentration
in
water
due
to
evaporative
loss.
Although
not
specifically
stated,
it
appears
that
results
are
expressed
in
terms
of
measured
concentrations.

Effect
measured:
embryo
death
96­
hour
EC50:
4.1
mg
a.
i./
L
moderately
toxic
Falk­
Petersen
et
al.
1985
Open
literature
(
Supplemental)

iv.
Estuarine
and
Marine
Invertebrate,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
estuarine/
marine
invertebrates
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
estuarine/
marine
invertebrates
are
not
required.
No
chronic
toxicity
data
for
estuarine/
marine
invertebrates
were
located
in
the
open
literature.

IV.
Toxicity
to
Aquatic
Plants
Acute
toxicity
studies
are
required
to
establish
the
toxicity
of
mixed
xylenes
to
aquatic
plants
(
both
algae
and
aquatic
macrophytes).
Details
of
all
studies
are
provided
in
Table
E­
5.
No
studies
on
the
acute
effects
of
mixed
xylenes
were
identified
from
the
available
literature.

The
acute
toxicity
of
xylene
isomers
has
been
evaluated
in
two
studies
in
Selenastrum
capricornutum,
a
green
algae
(
Galassi
et
al.
1988;
Herman
et
al.
1990).
Galassi
et
al.
(
1988)
report
72­
hour
EC
50
values
for
growth
inhibition
ranging
from
3.2
mg
a.
i./
L
for
p­
xylene
to
4.9
mg
a.
i/
L
for
m­
xylene.
Herman
et
al.
(
1990)
report
8­
day
EC
50
values
for
growth
inhibition
ranging
from
3.9
mg/
L
for
mxylene
to
4.4
mg/
L
for
p­
xylene.
Results
of
these
studies
show
that
the
xylene
isomers
have
very
similar
toxicities
to
algae.
The
lowest
acute
toxicity
value
obtained
for
the
p­
xylene
isomer
(
72­
hour
EC50
value
of
3.2
mg
a.
i./
L
in
Selenastrum
capricornutum
(
Galassi
et
al.
1988)
is
used
to
assess
acute
risk
of
mixed
xylenes
to
algae.
It
should
be
noted
that
NOEAC
data
for
non­
vascular
plants
is
not
available.
The
study
by
Galassi
et
al.
(
1988),
which
was
performed
in
accordance
with
OECD
standardized
method
No.
201,
was
conducted
under
closed
conditions
to
minimize
loss
of
xylenes
from
the
test
media,
and
toxicity
values
are
expressed
in
terms
of
measured
concentrations.
­
E­
15­
No
studies
suitable
for
use
in
a
quantitative
risk
assessment
on
the
effects
of
xylene
on
non­
target
vascular
aquatic
macrophytes
were
identified
from
the
available
literature.
Results
of
a
single
laboratory
study
on
the
efficacy
of
xylene
(
xylene
type
not
reported)
on
target
aquatic
macrophytes
shows
that
exposure
to
xylene
damaged
target
plants
under
both
standing
and
moving
water
conditions
(
Frank
et
al.,
1961).
Under
static
conditions,
extensive
damage
was
observed
to
the
three
plant
species
tested
at
a
concentration
of
100
ppm,
but
no
damage
was
observed
for
the
5
ppm
concentration.
Under
moving
water
conditions,
extensive
damage
was
observed
to
all
three
species
at
test
concentrations
of
300
and
600
ppm.
Since
EC/
LC
50
values
or
NOAEC
values
were
not
determined,
data
are
not
suitable
for
quantitative
use.
The
guideline
(
§
122­
2
and
123­
22)
requirements
for
aquatic
plant
toxicity
testing
are
not
fulfilled.

Table
E­
5.
Toxicity
of
Xylenes
to
Aquatic
Plants
Species
Test
Substance
LC50
Reference
Study
Classification
Selenastrum
capricornutum
(
green
algae)
p­
xylene
m­
xylene
o­
xylene
(
purity
not
reported)
Containers
were
air­
tight
and
sealed
to
minimize
volatilization
loss.
Measured
concentrations.

Effects
on
growth
8­
day
EC50
(
mg/
L)
p­
xylene:
4.4
m­
xylene:
3.9
o­
xylene:
4.2
Herman
et
al.
1990
Open
literature
(
Supplemental)

Selenastrum
capricornutum
(
green
algae)
o­
xylene
m­
xylene
p­
xylene
(
highest
purity)
Static
renewal
conditions.
Measured
concentrations.
Note:
all
tests
conducted
using
a
closed
system
to
minimize
loss
due
to
volatility.

72­
hour
EC50
values
(
for
growth
inhibition)
o­
xylene:
4.7
mg
a.
i/
L
m­
xylene:
4.9
mg
a.
i/
L
p­
xylene:
3.2
mg
a.
i/
L
Galassi
et
al.
1988
Open
literature
(
Supplemental
­
study
was
performed
in
accordance
with
OECD
Standard
Method
No.
201)
Table
E­
5.
Toxicity
of
Xylenes
to
Aquatic
Plants
Species
Test
Substance
LC50
Reference
Study
Classification
­
E­
16­
water
weed
(
Elodea
canadensis),
American
pondweed
(
Potamogeton
nodosus),
sago
pondweed
(
P.
pectinatus)
xylene
(
not
specified
if
mixture
or
isomer)

(
purity
not
reported)
Two
test
conditions
 
static
(
standing
water)
conditions
(
4­
week
exposure
to
5
or
100
ppm)
and
limited­
contact
(
30
minute
exposure
to
moving
water
at
concentrations
of
300
and
600
ppm).
Report
does
not
specify
nominal
or
measured
concentrations.

Results
of
static
test
show
that
a
concentation
of
5
ppm
did
not
damage
plants.
At
a
concentration
of
100
ppm,
significant
damage
was
observed
to
all
three
plant
species.

Results
of
limited­
contact
test
show
significant
damage
to
all
three
plant
species
at
both
exposure
concentrations.
Frank
et
al.
1961
Open
literature
(
Supplemental)

V.
Toxicity
to
Terrestrial
Animals
a.
Birds,
Acute
and
Subacute
An
acute
oral
toxicity
study
is
required
to
establish
the
toxicity
of
mixed
xylenes
to
birds.
The
preferred
test
species
is
either
mallard
duck
(
a
waterfowl)
or
bobwhite
quail
(
an
upland
gamebird).
No
acute
oral
toxicity
studies
in
birds
using
mixed
xylenes
or
xylene
isomers
were
identified
from
the
available
literature.
The
guideline
(
§
71­
1)
is
not
fulfilled
for
acute
oral
toxicity
to
birds.

Two
subacute
dietary
studies
are
required
to
establish
the
toxicity
of
mixed
xylenes
to
birds.
The
preferred
test
species
are
mallard
duck
and
bobwhite
quail.
A
single
acute
dietary
study
in
Japanese
quail
was
identified
from
the
available
open
literature
(
Hill
and
Camardese
1986);
study
details
are
provided
in
Table
E­
6.
Results
of
this
study
yield
an
acute
dietary
LC
50
value
of
>
20,000
mg
a.
i./
kg
diet.
Although
no
information
describing
the
types
of
sublethal
effects
or
signs
of
toxicity
were
provided
in
this
study
report,
the
authors
report
that
no
adverse
effects
were
observed
at
a
concentration
of
5,000
ppm
a.
i.,
the
lowest
concentration
tested.
The
LC50
value
of
>
20,000
mg
a.
i./
kg
diet
in
Japanese
quail
is
used
to
characterize
the
acute
risk
of
birds
to
mixed
xylenes.
The
guideline
(
§
71­
2)
is
fulfilled
for
acute
dietary
toxicity
to
birds.
­
E­
17­
Table
E­
6.
Acute
Dietary
Toxicity
of
Xylenes
to
Birds
Species
Test
Substance
LC50
Toxicity
Category
Reference
Study
Classification
Japanese
quail
mixed
xylenes
(
reagent
grade,
100
%
a.
i.)
5­
day
dietary
exposure
study.
Birds
were
14
days
old
at
the
start
of
the
5­
day
exposure
period.
Weight
of
animals
was
not
provided
in
the
study
report.

LC50
>
20,000
ppm
a.
i.

Study
does
not
report
if
any
deaths
occurred
at
the
highest
concentration
tested
(
20,000
ppm).
No
overt
signs
of
toxicity
at
5,000
ppm
a.
i.
Specific
signs
of
toxicity
at
higher
dietary
concentrations
were
not
reported.

Average
food
consumption
per
day:
Day
1:
12.2
g
food/
bird/
day
Day
2:
12.8
g
food/
bird/
day
Day
3:
12.9
g
food/
bird/
day
Day
4:
12.7
g
food/
bird/
day
Day
5:
12.2
g
food/
bird/
day
5­
day
average
food
consumption:
12.6
g
food/
bird/
day
(
equivalent
to
0.0126
kg)
practically
non­
toxic
Hill
and
Camardese
1986
Open
literature
(
Supplemental)

b.
Birds,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
birds
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
of
mixed
xylenes
in
birds
are
not
required.
No
chronic
toxicity
data
for
birds
were
located
in
the
open
literature.

c.
Mammals,
Acute
Oral
and
Inhalation
Results
of
the
acute
oral
toxicity
studies
on
mixed
xylenes
are
summarized
in
Table
E­
7.
Two
out
of
the
three
acute
studies
located
in
the
open
literature
(
NTP
1986
single
administration
gavage
study;
Hine
and
Zuidema
1970)
were
classified
as
invalid
because
control
data
were
not
included
as
part
of
the
study
results.
In
addition,
the
Hine
and
Zuidema
(
1970)
study
was
also
classified
as
invalid
because
the
route
of
xylene
exposure
was
by
intragastric
injection.
Acceptable
subacute
oral
toxicity
data
for
mammals
was
located
in
the
NTP
1986
study,
where
male
and
female
rats
were
exposed
to
doses
of
mixed
xylene
ranging
from
125
to
2000
mg/
kg
BW
over
a
duration
of
14
days.
Three
of
five
­
E­
18­
male
and
five
of
five
female
rats
that
received
2000
mg/
kg
BW
died
before
the
end
of
the
study.
Two
other
deaths
at
lower
doses
(
1
male
death
at
125
mg/
kg
BW
and
1
female
death
at
250
mg/
kg
BW)
were
attributed
to
gavage
trauma.
Based
on
the
results
of
this
study,
the
subacute
oral
LD
50
value
is
1608
mg/
kg
BW.
Therefore,
the
LD50
value
of
>
1608
mg/
kg
BW
is
used
to
assess
acute
toxic
risk
for
oral
exposure
of
mammals
to
mixed
xylenes.

Table
E­
7.
Acute
Oral
Toxicity
of
Xylenes
to
Mammals
Species
Test
Substance
Toxicity
Value
Reference
Study
Classification
rat
mixed
xylenes
(
60%
mxyleme
14%
p­
xylene,
9%
o­
xylene,
and
17%
ethylbenzene)
14­
day
oral
toxicity
test.
Doses
tested:
0,
125,
250,
500,
1,000,
and
2,000
mg/
kg
BW.

Average
body
weight
of
rats
at
dosing
=
161
g.

3/
5
males
and
5/
5
females
rats
that
received
2,000
mg/
kg
BW
died
before
the
end
of
the
study.
Two
other
deaths
(
1
male
at
the
125
mg/
kg
BW
treatment
and
1
female
at
the
250
mg/
kg
BW
treatment)
were
considered
due
to
gavage
trauma.
All
mortalities
occurred
with
the
first
2
to
4
days
of
the
study.
The
change
in
mean
body
weight
relative
to
controls
was
23
to
29%
lower
for
males
that
received
250,
500,
and
1000
mg/
kg
BW
and
17%
and
26%
lower
for
females
that
received
125
and
1000
mg/
kg
BW
after
14
days.
Shallow,
labored
breathing
and
prostration
were
observed
immediately
after
dosing
for
male
and
female
rats
that
received
2000
mg/
kg
BW.
No
compound­
related
effects
were
observed
at
necropsy.

Acute
oral
LD50
=
1,608
mg/
kg
BW
Slope
=
1.7
(
95%
C.
I.
=
­
2.43
­
5.83)
NTP
1986
Open
literature
(
Supplemental)
Table
E­
7.
Acute
Oral
Toxicity
of
Xylenes
to
Mammals
Species
Test
Substance
Toxicity
Value
Reference
Study
Classification
­
E­
19­
rat
mixed
xylenes
(
60%
mxyleme
14%
p­
xylene,
9%
o­
xylene,
and
17%
ethylbenzene)
Acute
oral
toxicity
test.
Doses
tested:
500,
1000,
2000,
4000,
and
6000
mg/
kg
BW
Average
body
weight
of
rats
at
dosing
=
158
g.

No
mortalities
or
serious
adverse
effects
noted
at
doses
up
to
2000
mg/
kg
body
wt.
In
the
2000
mg/
kg
body
wt
group,
rats
had
rough
coats.
At
doses
of
4000
and
6000
mg/
kg
body
wt,
lack
of
coordination,
prostration,
loss
of
hind
limb
movement
and
hunched
posture
were
detected
within
24
hours
of
exposure.
In
surviving
animals,
all
symptoms
resolved
within
1
week.

Mortality
(#
deaths/
group)
as
follows:
500
mg/
kg
body
wt
(
0/
10),
1000
mg/
kg
body
wt
(
1/
10),
2000
mg/
kg
body
wt
(
0/
10),
4000
mg/
kg
body
wt
(
3/
10),
and
6000
mg/
kg
body
wt
(
10/
10).

acute
oral
LD50
=
3523
mg/
kg
body
weight
NOAEC
for
signs
of
neurotoxicity:
2000
mg/
kg
body
wt.

NOAEC
for
signs
of
any
toxicity
(
rough
coats):
1000
mg/
kg
body
wt.
NTP
1986
Open
literature
(
Invalid:
No
control
data)
Table
E­
7.
Acute
Oral
Toxicity
of
Xylenes
to
Mammals
Species
Test
Substance
Toxicity
Value
Reference
Study
Classification
­
E­
20­
rat
(
males)
mixed
xylenes
(
purity
not
specified)
Acute
oral
LD50:
10.0
mL/
kg
body
weight
95%
CI:
7.5­
13.3
mL/
kg
body
weight
No
information
was
provided
regarding
the
time
from
dosing
to
death,
sublethal
effects,
or
signs
of
toxicity.
No
NOAEC
values
for
death
or
sublethal
effects
were
reported.

The
LD50
value
expressed
in
terms
of
mL/
kg
body
weight
is
converted
to
mg/
kg
body
wt
based
on
a
density
for
mixed
xylenes
of
0.864g/
mL
(
ATSDR
1995)
as
follows:
0.864
g/
mL
×
10.0
mL/
kg
body
weight
=
8.64
g/
kg
body
weight
=
8640
mg/
kg
body
weight.
Hine
and
Zuidema
1970
Open
literature
(
Invalid:
No
control
data;
exposure
via
intragastric
injection)

Since
mixed
xylenes
are
highly
volatile,
acute
inhalation
exposure
is
an
anticipated
exposure
route
for
mammals
near
the
application
site.
Thus,
acute
inhalation
toxicity
studies
have
been
reviewed
for
this
risk
assessment.
The
4­
hour
LC
50
values
for
rats
for
mixed
xylenes
range
from
6350
ppm
(
Hine
and
Zuidema
1970)
to
6700
ppm
(
Carpenter
et
al.
1975);
study
details
are
provided
in
Table
E­
8.
However,
the
study
by
Hine
and
Zuidema
(
1970)
is
classified
as
invalid
because
no
control
data
were
presented.
Dose­
response
information
is
available
in
the
study
by
Carpenter
et
al.
(
1975).
Surviving
rats
became
uncoordinated
and
prostrate
during
exposure.
The
NOAEC
value
of
1300
ppm
was
reported
for
sublethal
effects.
The
lowest
acceptable
LC50
value
of
6700
ppm
is
used
to
assess
acute
toxic
risk
of
acute
inhalation
exposure
of
mammals
to
mixed
xylenes.
It
should
be
noted
that
there
is
uncertainty
related
to
the
methodology
used
to
dose
the
rats
in
the
acute
inhalation
mammalian
study
used
to
derive
inhalation
RQs
(
Carpenter
et
al
1975)
because
the
study
authors
did
not
specifically
discuss
the
dosing
methodology,
but
rather
referred
to
an
approach
used
in
another
inhalation
toxicity
study
(
Carpenter
et
al
1975a).
­
E­
21­
Table
E­
8.
Acute
Inhalation
Toxicity
of
Xylenes
to
Mammals
Species
Test
Substance
Toxicity
Value
Reference
Study
Classification
rat
mixed
xylenes
(
purity
not
specified)
Acute
inhalation
toxicity
test.

4­
hour
LC50:
6350
ppm
95%
CI:
4670­
8640
ppm
All
deaths
occurred
during
the
4­
hour
exposure
period
(
time
not
specified);
survivors
were
comatose,
but
recovered
shortly
after
removal
of
animal
from
exposure
chamber.

No
information
was
provided
regarding
the
time
from
dosing
to
death,
sublethal
effects,
or
signs
of
toxicity.
No
NOAEC
values
for
death
or
sublethal
effects
were
reported.
Hine
and
Zuidema
1970
Open
literature
(
Invalid:
No
control
data)

rat
mixed
xylenes
Composition
of
test
substance:
p­
xylene
7.84%,
m­
xylene
65.01%,
oxylene
7.63%,
ethylbenzene
19.27%,
toluene
0.14%,
C9
+
aromatics
(
not
specified)
0.047,
and
nonaromatics
(
not
specified).
0.07%
Acute
inhalation
toxicity
test.
4­
hour
exposure
followed
by
14­
day
observation
period.
Measured
concentrations.

4­
hour
LC50:
29
mg/
L
(
equivalent
to
6700
ppm)

NOAEC
for
signs
of
toxicity:
2.5
mg/
L
(
580
ppm)

Fatalities
(#
deaths/
animals
per
group)
and
adverse
effects
as
follows
for
the
following
concentrations:
580
ppm,
0/
10
(
no
signs
of
toxicity);
1300
ppm,
0/
10
(
rats
had
poor
coordination
after
2
hours,
effects
resolved
after
exposure);
2800
ppm
(
all
rats
became
prostrate
between
2
and
3.5
hours),
0/
10;
6000
ppm,
4/
10
(
deaths
occurred
at
3.5
hours;
all
survivors
were
prostrate
in
30
minutes);
9000
ppm,
10/
10
(
deaths
occurred
at
2.25
hr.

NOAEC
for
lethality:
5.8
mg/
L
(
equivalent
to
1300
ppm)

For
fatalities,
findings
on
necropsy
included
atelectasis
(
collapsed
airways),
hemorrhage
and
interlobular
edema
of
the
lungs.

At
5.8
mg/
L
(
equivalent
to
1300
ppm),
rats
exhibited
poor
coordination
after
2
hours
of
exposure,
but
fully
recovered
after
exposure.
At
higher
concentrations,
rats
became
prostrate.
Carpenter
et
al.
1975
Open
literature
(
Supplemental)
­
E­
22­
d.
Mammals,
Chronic
Under
the
conditions
of
recommended
use,
chronic
exposure
of
mammals
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
mammals
are
not
required.
No
chronic
toxicity
data
for
mammals
were
located
in
the
open
literature.

e.
Terrestrial
Insects,
Acute
Contact
No
studies
on
the
effects
of
terrestrial
insects
were
identified
in
the
available
literature.
Under
the
conditions
of
recommended
use,
it
is
not
expected
that
terrestrial
insects
will
be
exposed
to
mixed
xylenes.
Thus,
guideline
requirements
for
terrestrial
insects
are
not
required.

V.
Toxicity
to
Terrestrial
Plants
Under
the
conditions
of
recommended
use,
chronic
exposure
of
terrestrial
plants
to
mixed
xylenes
is
not
anticipated.
Thus,
chronic
exposure
studies
on
mixed
xylenes
in
terrestrial
plants
are
not
required
by
EFED.

VI.
Literature
Cited
References
for
all
literature
cited
in
this
appendix
is
provided
in
the
Ecological
Effects
Bibliography,
Appendix
J.
­
F­
1­
APPENDIX
F.
The
Risk
Quotient
Method
and
Levels
of
Concern
The
risks
to
terrestrial
and
aquatic
organisms
are
determined
based
on
a
method
by
which
risk
quotients
(
RQs)
are
compared
with
levels
of
concern
(
LOCs).
This
method
provides
an
indication
of
a
chemical's
potential
to
cause
an
effect
in
the
field
from
effects
observed
in
laboratory
studies,
when
used
as
directed.
Risk
quotients
are
expressed
as
the
ratio
of
the
estimated
environmental
concentration
(
EEC)
to
the
species­
specific
toxicity
reference
value
(
TRV):

RQ
EEC
TRV
=

Units
for
EEC
and
TRV
should
be
the
same
(
e.
g.,
:
g/
L
or
ppb).
The
RQ
is
compared
to
the
LOC
as
part
of
a
risk
characterization.
Acute
and
chronic
LOCs
for
terrestrial
and
aquatic
organisms
are
given
in
recent
Agency
guidance
(
EPA,
2004)
and
summarized
in
Table
F­
1
below.

Table
F1.
Level
of
concern
(
LOC)
by
risk
presumption
category
(
US
EPA
2004).

Risk
Presumption
RQ
LOC
Mammals
and
Birds
Acute
Riska
EECb/
LC50
or
LD50/
sqftc
or
LD50/
dayd
0.5
Acute
Restricted
Usee
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Speciesf
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOEC
1
Aquatic
Animals
Acute
Risk
EEC/
LC50
or
EC50
0.5
Acute
Restricted
Use
EEC/
LC50
or
EC50
0.1
Acute
Endangered
Species
EEC/
LC50
or
EC50
0.05
Chronic
Risk
EEC/
NOEC
1
Terrestrial
Plants
and
Terrestrial
Plants
in
Semi­
Aquatic
Areas
Plants
Acute
Risk
EEC/
EC25
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
Table
F1.
Level
of
concern
(
LOC)
by
risk
presumption
category
(
US
EPA
2004).

Risk
Presumption
RQ
LOC
­
F­
2­
Aquatic
Plants
Acute
Risk
EEC/
EC50
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
aPotential
for
acute
toxicity
for
receptor
species
if
RQ
>
LOC
(
EPA,
2004).
bEstimated
environmental
concentration
(
ppm)
on
avian/
mammalian
food
items
cmg/
ft2
dmg
of
toxicant
consumed
per
day
ePotential
for
acute
toxicity
for
receptor
species,
even
considering
restricted
use
classification,
if
RQ
>
LOC
(
EPA,
2004).
fPotential
for
acute
toxicity
for
endangered
species
of
receptor
species
if
RQ
>
LOC
(
EPA,
2004).

For
acute
exposure
to
terrestrial
and
aquatic
plants,
an
LOC
of
1
is
used.
Currently
the
Agency
does
not
perform
assessments
for
chronic
risk
to
plants
or
acute/
chronic
risks
to
non­
target
insects.

For
this
risk
assessment,
chronic
exposure
or
exposure
of
terrestrial
plants
were
not
considered.

Three
exposure
estimate
were
used
to
assess
risks
of
mixed
xylenes
to
non­
target
aquatic
animals
(
i.
e.,
fish,
invertebrates)
and
plants
(
i.
e.,
algae):
10
mg/
L
(
maximum
allowable
concentration
in
receiving
waters),
740
mg/
L
(
maximum
allowable
concentration
in
irrigation
canals),
and
178
mg/
L
(
solubility
limit
for
o­
xylene).
The
most
likely
exposure
pathways
for
terrestrial
animals
are
through
ingestion
of
contaminated
water
and
inhalation
of
volatilized
xylenes.

Exposure
estimates
for
ingestion
of
contaminated
water
for
birds
was
based
on
the
allowable
concentration
range
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
178
mg/
L,
and
the
calculated
amount
of
water
birds
are
expected
to
consume
in
one
day.

Inhalation
exposure
was
estimated
by
using
nondimensional
Henry's
law
constant
to
estimate
a
"
maximum"
air
concentration
from
concentration
in
solution,
which
assumes
ideal
gas
conditions
and
steady
state
conditions.
The
solution
concentration
was
assumed
to
be
the
maximum
solubility
of
xylene
(
178
ppm),
with
no
emulsifiers.
The
transfer
process
of
xylene
from
water
to
the
atmosphere
is
dependant
upon
the
chemical
and
physical
properties
of
the
xylene
and
the
physical
properties
(
e.
g.,
flow
velocity,
depth,
and
turbulence)
of
the
water
body.
Factors
that
control
volatilization
of
xylene
are
solubility,
molecular
weight,
and
vapor
pressure
of
xylene
and
the
nature
of
the
air­
water
interface
through
which
it
must
pass.
The
volatilization
rates
from
water
vary
of
a
wide
range.
The
air
concentration
would
be
expected
not
to
exceed
the
value
estimated
from
the
Henry's
constant
and
solubility
values.
­
F­
3­
The
inhalation
exposure
is
related
to
the
air
concentration
and
the
dimensions
of
the
breathing
zone
(
area
and
height)
for
a
potential
receptor.
The
breathing
zone
was
assumed
to
have
a
uniform
xylene
concentration,
although
in
reality
concentration
probably
decreases
with
height.
The
EEC
for
air
is
considered
for
a
4­
hour
time
period
to
correspond
to
the
exposure
period
reported
for
the
available
inhalation
toxicity
study.
For
this
risk
assessment,
the
maximum
estimated
exposure
concentration
for
volatilized
xylenes
in
air
was
estimated
to
be
38.5
ppm,
assuming
that
no
loses
from
wind
or
degradation.

Literature
Cited
Thomas,
R.
G.
1990.
Chapter
15.
Volatilization
from
Water.
In:
Handbook
of
Chemical
Property
Estimation
Methods.
Ed:
W.
J.
Lyman,
W.
F.
Reehl,
and
D.
H.
Rosenblatt.
American
Chemical
Society.
Washington,
DC.

US
EPA
(
U.
S.
Environmental
Protection
Agency).
2004.
Overview
of
the
Ecological
Risk
Assessment
Process
in
the
Office
of
Pesticide
Programs,
U.
S.
Environmental
Protection
Agency:
Endangered
and
Threatened
Species
Effects
Determinations.
Office
of
Prevention,
Pesticide,
and
Toxic
Substances.
January
23.
­
G­
1­
APPENDIX
G:
Risk
Quotients
I.
Acute
Risk
Quotients
for
Aquatic
Species
For
this
risk
assessment,
the
allowable
concentration
range
for
mixed
xylenes
in
water
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
178
mg/
L
were
used
ro
assess
acute
risks
to
aquatic
organisms.
Acute
RQs
for
aquatic
species
are
summarized
in
Table
G­
1.

Table
G­
1.
Acute
RQs
for
Freshwater
Fish,
Freshwater
Invertebrates,
Estuarine/
Marine
Fish,
Estuarine/
Marine
Invertebrates,
and
Algae
Exposed
to
Mixed
Xylenes
or
Xylene
Isomers.

Species
Toxicity
Value
(
mg/
L)
Acute
RQ
for
Minimum
Exposure
a
Acute
RQ
for
Maximum
Exposure
b
Acute
RQ
Based
on
the
Solubility
Limit
for
o­
Xylene
c
Freshwater
Fish
2.6
mg/
L
d
3.8
h
284
h
68
h
Freshwater
Invertebrates
1.0
mg/
L
e
10
h
740
h
178
h
Estuarine/
Marine
Fish
No
data
NA
NA
NA
Estuarine/
Marine
Invertebrates
4.1
mg/
L
f
2.4
h
180
h
43
h
Non­
vascular
Aquatic
Plants
3.2
mg/
L
g
3
h
231
h
56
h
a
EEC/
LC50,
where
the
EEC
is
the
minimum
exposure
of
10
mg/
L.
b
EEC/
LC50,
where
the
EEC
is
the
maximum
exposure
of
740
mg/
L.
c
EEC/
LC50,
where
the
EEC
is
the
solubility
limit
for
o­
xylene
of
178
mg/
L.
d
96­
hour
LC50
value
in
rainbow
trout
for
p­
xylene
(
Galassi
et
al.
1988).
e
24­
hour
LC50
value
in
Daphnia
magna
for
o­
xylene
(
Galassi
et
al.
1988).
f
96­
hour
EC50
value
in
sea
urchin
eggs
for
o­
xylene
(
Falk­
Petersen
et
al.
1985).
g
72­
hour
EC50
value
(
for
growth
inhibition)
in
Selenastrum
capricornutum
for
p­
xylene
(
Galassi
et
al.
1988).
h
RQ
exceeds
the
acute
LOCs
for
acute
risk
(
0.5),
acute
restricted
use
(
LOC
0.1)
and
acute
endangered
species
(
LOC
0.05).
­
G­
2­
II.
Acute
Risk
Quotients
for
Terrestrial
Animals
A.
Acute
Risk
Quotients
for
Exposure
of
Mammals
and
Birds
Via
Drinking
of
Contaminated
Water
1.
Exposure
Values
for
Contaminated
Water
To
determine
the
exposure
of
mammals
and
birds
to
xylenes
via
consumption
of
contaminated
water,
a
single
daily
dose
of
xylenes
was
estimated
using
the
calculated
volume
of
water
that
birds
and
mammals
are
expected
to
consume
per
day
and
the
concentration
of
xylenes
in
water
as
follows:

Daily
Exposure
(
mg/
kg
BW)
=
Daily
Water
Consumption
(
L)
×
Water
Concentration
(
mg/
L)
Body
Weight
(
kg)

For
this
risk
assessment,
the
allowable
concentration
range
for
mixed
xylenes
of
10
to
740
mg/
L
and
the
solubility
limit
for
o­
xylene
of
1678
mg/
L
were
used
to
calculate
exposure
values.
To
estimate
the
volume
of
water
that
mammals
and
birds
are
expected
to
consume
per
day,
allometric
equations
from
the
EPA
Wildlife
Exposure
Factors
Handbook
(
US
EPA
1993)
were
used.
For
birds,
the
daily
water
consumption
(
L)
was
calculated
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.059
and
$
=
0.67
(
US
EPA
1993,
Equation
3­
15,
p.
3­
8,
for
all
birds).
For
mammals,
the
daily
water
consumption
(
L)
was
calculated
as
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.099
and
$
=
0.9
(
US
EPA
1993,
Equation
3­
7,
p.
3­
10,
for
all
mammals).
As
summarized
in
Table
G­
2,
a
single
daily
exposure
via
drinking
water
containing
10
and
740
mg/
L
xylenes
was
calculated
for
three
weight
classes
for
birds
(
20,
100,
and
1000g)
and
mammals
(
15,
35,
and
1000g).
­
G­
3­
Table
G­
2.
Exposure
Estimates
for
Birds
and
Mammals
via
Consumption
of
Contaminated
Water.

Species
Body
Weight
(
g)
Daily
Water
Consumption
(
L)
a
Exposure
Estimates
for
Exposure
from
Contaminated
Water
b
Minimum
Exposure
(
mg/
kg
BW)
Based
on
a
Water
Concentration
of
10
mg/
L
Maximum
Exposure
(
mg/
kg
BW)
Based
on
a
Water
Concentration
of
740
mg/
L
Exposure
(
mg/
kg
BW)
Based
on
the
Solubility
Limit
for
o­
xylene
of
178
mg/
L
Birds
20
0.0043
2.15
160
38.5
100
0.013
1.30
96
23
1000
0.059
0.59
43.7
10.5
Mammals
15
0.0023
1.53
113
27.3
35
0.0048
1.37
103
24.3
1000
0.099
0.99
73.3
17.6
a
For
birds,
the
daily
water
consumption
(
L)
was
calculated
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.059
and
$
=
0.67
(
US
EPA
1993,
Equation
3­
15,
p.
3­
8,
for
all
birds).
For
mammals,
the
daily
water
consumption
(
L)
was
calculated
using
the
following
equation:
"
(
body
weight
in
kg)
$,
where
"
=
0.099
and
$
=
0.9
(
US
EPA
1993,
Equation
3­
7,
p.
3­
10,
for
all
mammals).
b
Exposure
estimates
were
calculated
as
follows:
Daily
exposure
(
mg/
kg
BW)
=
(
Daily
water
consumption
(
L)
×
Water
concentration
(
mg/
L)
)
/
BW
(
kg).

2.
Acute
Toxicity
Values
for
Terrestrial
Animals
Birds
Exposure
estimates
for
terrestrial
animals
via
drinking
contaminated
water
were
expressed
in
terms
of
a
single
daily
dose
(
mg/
kg
BW)
for
three
different
body
weight
classes
for
birds
(
20,
100,
and
1000
g).
Therefore,
to
calculate
acute
RQs
for
birds,
the
acute
dietary
LC
50
was
converted
to
a
daily
dose
for
exposure
via
drinking
water
(
expressed
in
terms
of
mg/
kg
BW)
for
each
of
the
three
body
weight
classes
as
follows.
The
avian
acute
dietary
LC
50
value
expressed
in
terms
of
mg/
kg
diet
(>
20,000
mg/
kg
diet
in
14­
day
old
Japanese
quail;
Hill
and
Camardese
1986)
was
first
converted
to
an
equivalent
LD
50
value
expressed
in
terms
of
mg/
kg
body
weight,
using
the
following
equation:

LD50
(
mg/
kg
body
weight)
=
LC50
in
food
(
mg/
kg
diet)
×
daily
food
consumption
(
kg
diet)
body
weight
(
kg
body
weight)

The
average
daily
food
consumption
per
bird
reported
in
the
Hill
and
Camardese
(
1986)
study
was
0.0126
kg.
The
body
weights
of
Japanese
quail
were
not
reported
in
the
Hill
and
Camaradese
(
1986)
study;
therefore,
the
average
body
weight
for
a
14­
day
Japanese
quail
was
taken
as
approximately
­
G­
4­
0.043
kg
(
Woodard
et
al.
1973).
Thus,
the
acute
oral
LD
50
for
Japanese
quail
was
derived
as
>
5,860
mg/
kg
body
weight
[>
20,000
mg/
kg
diet
×
0.0126
kg
diet/
0.043
kg
body
weight
=
>
5,860
mg/
kg
body
weight].
To
obtain
the
adjusted
LD
50
value,
the
acute
oral
LD
50
value
for
the
Japanese
quail
(>
5,860
mg/
kg
body
weight)
is
adjusted
for
the
size
of
the
animal
tested
compared
with
the
size
of
the
animal
being
assessed
(
e.
g.,
20
g
bird).
Exposure
estimates
from
contaminated
water
and
toxicity
values
are
relative
to
the
animal's
body
weight
(
mg
residue/
kg
BW)
because
consumption
of
the
same
mass
of
pesticide
residue
results
in
a
higher
body
burden
in
smaller
animals
as
compared
with
larger
animals.
The
following
equation
is
used
for
the
LD
50
adjustment
for
birds:

Adjusted
LD
50
=
LD
50
(
AW/
TW)(
x­
1)

where:

Adjusted
LD
50
=
Adjusted
LD
50
(
mg/
kg
BW)
calculated
by
the
equation;
LD
50
=
>
5,860
mg/
kg
BW
(
acute
oral
LD
50
value
for
the
Japanese
quail);
AW
=
Body
weight
of
assessed
bird
(
20
g,
100
g,
and
1000
g);
TW
=
Body
weight
of
tested
animal
(
43
g
for
14­
day
Japanese
quail);
and
x
=
Mineau
scaling
factor
for
birds;
EFED
default
is
1.15.

The
calculated
adjusted
LD
50
values
for
three
different
weight
classes
of
birds
are
summarized
in
Table
G­
3.

Mammals
Exposure
estimates
for
terrestrial
animals
via
drinking
contaminated
water
were
expressed
in
terms
of
a
single
daily
dose
(
mg/
kg
BW)
for
three
different
body
weight
classes
for
mammals
(
15,
35,
and
1000
g).
To
obtain
the
adjusted
mammalian
LD
50
value,
the
subacute
mammalian
LD
50
value
for
the
rat
(
1,608
mg/
kg
body
weight)
is
adjusted
for
the
size
of
the
animal
tested
compared
with
the
size
of
the
animal
being
assessed
(
e.
g.,
15
g
mammal).
The
following
equation
is
used
for
the
LD
50
adjustment
for
mammals:

Adjusted
LD
50
=
LD
50
(
TW/
AW)(
0.25)

where:

Adjusted
LD
50
=
Adjusted
LD
50
(
mg/
kg
BW)
calculated
by
the
equation;
LD
50
=
1608
mg/
kg
BW
(
subacute
oral
LD
50
value
for
the
rat);
TW
=
Body
weight
of
tested
animal
(
350
g
rat);
and
AW
=
Body
weight
of
assessed
mammal
(
15
g,
35
g,
and
1000
g);

The
calculated
adjusted
LD
50
values
for
three
different
weight
classes
of
mammals
are
summarized
in
Table
G­
3.
­
G­
5­
Table
G­
3.
Adjusted
Acute
Toxicity
Values
for
Birds
and
Mammals,
Expressed
in
Terms
of
a
Single
Mixed
Xylenes
Dose
(
mg/
kg
BW).

Species
Body
Weight
(
g)
Adjusted
LD50
(
mg/
kg
body
weight)

Birds
20
>
5224a
100
>
6651a
1000
>
9396a
Mammals
15
3534b
35
2859b
1000
1237b
a
Adjusted
LD50
=
LD50
(
AW/
TW)(
x­
1)
where:
LD50
=
>
5860
mg/
kg
BW
(>
20,000
mg/
kg
diet)
for
the
Japanese
quail
(
Hill
and
Camardese
1986);
AW
=
0.02,
0.1,
and
1.0
kg;
TW
=
0.043
kg
for
14­
day
old
Japanese
quail,
and
x
=
Mineau
scaling
factor
for
birds
=
EFED
default
value
of
1.15.
b
Adjusted
LD50
=
LD50
(
TW/
AW)(
0.25)
where:
LD50
=
1608
mg/
kg
BW
(
Carpenter
et
al.
1975);
AW
=
0.015,
0.035,
and
1.0
kg;
and
TW
=
0.35
kg
for
rat.

3.
Acute
Risk
Quotients
for
Birds
and
Mammals
Exposed
to
Xylenes
Via
Consumption
of
Contaminated
Water
Acute
RQs
for
birds
mammals
exposed
to
xylenes
via
consumption
of
contaminated
water
were
calculated
using
the
daily
exposure
value
expressed
as
mg/
kg
BW
xylenes
(
Table
G­
2)
and
the
adjusted
toxicity
value
expressed
in
terms
of
mg/
kg
BW
xylenes
(
Table
G­
3),
as
summarized
in
Table
G­
4.

Table
G­
4.
Acute
RQs
for
Birds
and
Mammals
Exposed
to
Mixed
Xylenes
via
Consumption
of
Contaminated
Water.

Species
Body
Weight
(
g)
Acute
RQ
Based
on
a
Water
Concentration
of
10
mg/
L
a,
b,
c
Acute
RQ
Based
on
a
Water
Concentration
of
740
mg/
L
a,
b,
c
Acute
RQ
Based
on
the
Solubility
Limit
for
o­
xylene
of
178
mg/
L
a,
b,
c
Birds
c
20
<
0.01
<
0.031
<
0.01
100
<
0.01
<
0.014
<
0.01
1000
<
0.01
<
0.01
<
0.01
Mammals
20
0.0004
0.032
0.008
100
0.0005
0.036
0.008
1000
0.0008
0.059
0.014
Table
G­
4.
Acute
RQs
for
Birds
and
Mammals
Exposed
to
Mixed
Xylenes
via
Consumption
of
Contaminated
Water.

Species
Body
Weight
(
g)
Acute
RQ
Based
on
a
Water
Concentration
of
10
mg/
L
a,
b,
c
Acute
RQ
Based
on
a
Water
Concentration
of
740
mg/
L
a,
b,
c
Acute
RQ
Based
on
the
Solubility
Limit
for
o­
xylene
of
178
mg/
L
a,
b,
c
­
G­
6­
a
Acute
RQs
were
calculated
using
the
exposure
values
(
mg/
kg
BW)
derived
in
Table
G­
2
and
the
adjusted
LD50
values
(
mg/
kg
BW)
shown
in
Table
G­
3,
as
follows:
EEC/
Adjusted
LD50
value.
b
RQs
are
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).
c
RQs
for
birds
are
based
on
the
LC50
value
>
20,000
mg/
kg
diet
(
adjusted
LD50
values
for
20g,
100g,
and
1000g
birds
are
>
5224,
>
6651,
and
>
9396
mg/
kg
BW,
respectively).
Therefore,
acute
avian
RQs
are
reported
as
"
less
than"
values.

B.
Acute
Risk
Quotients
for
Mammals
Exposure
to
Volatilized
Xylenes
Via
Inhalation
All
details
pertaining
to
calculation
of
EECs
in
air
are
provided
in
Section
III.
B.
3.
a.(
2)
of
the
main
report.
For
this
risk
assessment,
the
maximum
estimated
exposure
for
volatilized
xylenes
in
air
is
38.5
ppm.

Table
G­
5.
Acute
RQs
for
Mammals
Exposed
to
Volatilized
Mixed
Xylenes
Via
Inhalation.

Inhalation
Toxicity
Value
a
(
ppm)
Acute
Inhalation
RQ
Based
on
Maximum
Estimated
Exposure
Maximum
EEC
in
Air
(
ppm)
b
Maximum
Acute
Inhalation
RQ
c
(
EEC/
Toxicity
Value)

6700
38.5
0.006
a
4­
hour
LC50
value
in
rats
for
mixed
xylenes
(
Carpenter
et
al.
1975).
b
EECs
generated
with
the
non­
dimensional
Henry's
law
constant
which
estimates
the
concentration
of
a
compound
in
the
gas
phase
in
relationship
to
its
concentration
in
liquid
phase
Cg
=
Cl
*
Henry
C.
c
RQ
is
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).

C.
Composite
Acute
Risk
Quotient
for
Mammals
Exposed
to
Xylenes
by
Consumption
of
Contaminated
Water
and
Inhalation
of
Volatilized
Xylenes
To
determine
if
a
combination
of
exposure
by
consumption
of
contaminated
water
and
inhalation
of
volatilized
xylenes
poses
a
risk
to
mammals,
a
composite
acute
RQ
was
derived.
The
composite
­
G­
7­
acute
RQ
is
defined
as
the
sum
of
the
acute
drinking
water
RQ
and
the
acute
inhalation
RQ.
Composite
acute
RQs
were
calculated
using
the
maximum
acute
drinking
water
RQs
for
the
three
mammalian
weight
classes
based
on
the
maximum
concentration
in
water
of
740
ppm
(
Table
G­
4)
and
the
acute
inhalation
RQ
for
the
maximum
estimated
exposure
for
volatilized
xylenes
in
air.
Since
the
minimum
acute
inhalation
RQs
and
minimum
acute
drinking
water
RQs
for
mammals
are
several
orders
of
magnitude
below
the
acute
LOCs,
composite
RQs
using
the
minimum
acute
inhalation
RQs
were
not
derived.
As
shown
in
Table
G­
6,
composite
acute
RQs
using
the
maximum
exposure
parameters
are
below
all
acute
LOCs.

Table
G­
6.
Composite
Acute
RQs
for
Mammals
Exposed
to
Mixed
Xylenes
by
Consumption
of
Contaminated
Water
and
Inhalation
Exposure.

Mammalian
Body
Weight
(
g)
Maximum
Acute
RQ
for
Consumption
of
Water
Containing
740
mg/
L
Xylenes
a
Maximum
Acute
Inhalation
RQ
b
Maximum
Acute
Composite
RQ
c,
d
15
0.032
0.006
0.038
35
0.036
0.006
0.042
1000
0.059
0.006
0.065
a
Details
of
RQ
calculation
are
provided
in
Table
G­
4.
b
Details
of
RQ
calculation
are
provided
in
Table
G­
5.
c
RQ
is
calculated
as
the
sum
of
the
acute
RQ
for
consumption
of
contaminated
water
and
the
acute
inhalation
RQ.
d
RQs
are
below
the
LOCs
for
acute
risk
(
LOC
0.5),
acute
restricted
use
(
LOC
0.2),
and
acute
endangered
species
(
LOC
0.1).
­
H­
1­
APPENDIX
H.
Data
Requirement
Tables
 
Ecological
Effects
Table
H­
1.
Ecological
Effects
Requirements
for
Xylene
Mixtures
and
Xylene
Isomers.

Guideline
Number
Data
Requirement
Test
Substance
Are
data
adequate
for
ecological
risk
assessment?
Citation
Study
Classification
71­
1
Avian
Oral
LD50
No
Data
Submitted
­
Data
Gap
71­
2
Avian
Dietary
LC50
mixtures
yes
Hill
and
Camardese
1986
Supplemental
71­
4
Avian
Reproduction
No
Data
Submitted
­
Not
Required
72­
1
Freshwater
Fish
LC50
mixtures
isomers
yes
Fomar
1976
Galassi
et
al.
1988
Holcombe
et
al.
1987
Supplemental
Supplemental
Supplemental
72­
2
Freshwater
Invertebrate
Acute
LC50
mixtures
isomers
yes
 

Abernathy
et
al.
1986
Galassi
et
al.
1988
Holcombe
et
al.
1987
 

Supplemental
Supplemental
Supplemental
72­
3(
a)
Estuarine/
Marine
Fish
LC50
mixtures
isomers
no
no
acceptable
data
­­

72­
3(
b)
Estuarine/
Marine
Mollusc
EC50
No
Data
Submitted
­
Data
Gap
72­
3(
c)
Estuairne/
Marine
Shrimp
LC50
mixtures
isomers
yes
Tatem
et
al.
1978
Abernathy
et
al.
1986
Supplemental
Supplemental
72­
4(
a)
Freshwater
Fish
Early
Life
Stage
No
Data
Submitted
­
Not
Required
72­
4(
b)
Aquatic
Invertebrate
Life­
Cycle
(
freshwater)
No
Data
Submitted
­
Not
Required
Table
H­
1.
Ecological
Effects
Requirements
for
Xylene
Mixtures
and
Xylene
Isomers.

Guideline
Number
Data
Requirement
Test
Substance
Are
data
adequate
for
ecological
risk
assessment?
Citation
Study
Classification
­
H­
2­
72­
4(
c)
Aquatic
Invertebrate
Life­
Cycle
(
Marine)
No
Data
Submitted
­
Not
Required
72­
5
Freshwater
Fish
Full
Life­
Cycle
No
Data
Submitted
­
Not
Required
122­
1(
a)
Seed
Germ./
Seedling
Emergence
(
Tier
I)
No
Data
Submitted
­
Not
Required
122­
1(
b)
Vegetative
Vigor
(
Tier
I)
No
Data
Submitted
­
Not
Required
122­
2
Aquatic
Plant
Growth
(
Tier
I*)
mixtures
isomers
no
 

Herman
et
al.
1990
Galassi
et
al
1988
 

Supplemental
Supplemental
123­
1(
a)
Seedling
Emergence
(
Tier
II)
No
Data
Submitted
­
Not
Required
123­
1(
b)
Vegetative
Vigor
(
Tier
II)
No
Data
Submitted
­
Not
Required
123­
2
Aquatic
Plant
Growth
(
Tier
II)
No
Data
Submitted
­
Data
Gap
141­
1
Honey
Bee
Acute
Contact
LD50
No
Data
Submitted
­
Not
Required
141­
2
Honey
Bee
Residue
on
Foliage
No
Data
Submitted
­
Not
Required
81­
1
Acute
Oral
Toxicity
to
Rat
mixtures
yes
NTP
1986
Supplemental
Acute
Inhalation
Toxicity
to
rat
mixtures
yes
Carpenter
et
al.
1975
Supplemental
83­
4
2­
Generation
Rat
Reproduction
No
Data
Submitted
­
Not
Required
­
I­
1­
APPENDIX
I.
ECOTOXICOLOGY
BIBLIOGRAPHY
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S,
Bobra
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WY,
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PG,
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D.
1986.
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PE,
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1983.
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Petersen,
I­
B,
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avoidance
reaction
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rainbow
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herbicides.
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I­
2­
Hill
EF
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MB.
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Hine
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Neff
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­
I­
3­
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pdf
­
I­
4­
Appendix
J
is
in
a
separate
electronic
file