Document ID: EPA-HQ-OPP-2003-0072-0013
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-02-13T05:00Z

XVI
­
1
Appendix
XV.
Differences
Between
Deterministic
and
Probabilistic
Risk
Assessments
Deterministic
Risk
Assessments
The
standard
method
used
in
the
OPP
to
characterize
ecological
risk
is
the
ratio
or
quotient
method.
"
Typically,
the
ratio
(
or
quotient)
is
expressed
as
an
exposure
concentration
divided
by
an
effects
concentration"
(
U.
S.
EPA
1998,
Part
A,
Section
5.1.3).
A
risk
quotient
(
RQ)
is
the
ratio
of
the
estimated
environmental
concentration
of
a
chemical
to
a
toxicity
test
effect
level
for
a
given
species.
It
is
calculated
by
dividing
an
appropriate
exposure
estimate
(
e.
g.
EEC
or
estimated
environmental
concentration)
by
an
appropriate
toxicity
test
effect
level
(
e.
g.
LC50).
Thus,
the
RQ
is
an
index
(
an
indicator
or
measure
of
a
condition)
of
the
potential
adverse
effects.
As
an
index,
the
risk
quotient
needs
some
reference
point
or
bearing
to
have
meaning.
Thus,
the
Agency
has
established
Levels
of
Concern
(
LOCs)
in
order
to
identify
when
the
potential
adverse
effects
are
of
concern
to
the
Agency
(
see
Table
1).
LOCs
are
criteria
used
to
indicate
potential
risk
to
non­
target
organisms
and
the
need
to
consider
regulatory
action.
The
criteria
indicate
that
a
pesticide,
when
used
as
directed,
has
the
potential
to
cause
adverse
effects
on
nontarget
organisms.
Typically,
an
RQ
is
compared
to
an
LOC
to
determine
if
the
OPP
should
consider
taking
some
regulatory
action
to
reduce
or
eliminate
the
potential
risk,
or
to
further
refine
the
risk
assessment.

OPP
first
presented
this
risk
index
method
in
the
Standard
Evaluation
Procedure
for
Ecological
Risk
Assessment
in
1986
(
U.
S.
EPA.
1986).
Since
the
issuance
of
the
1992
policy
by
the
Assistant
Administrator
(
U.
S.
EPA.
1992),
OPP
has
generally
pursued
ecological
risk
mitigation
whenever
RQs
exceed
the
LOCs.
Currently
these
RQs
and
LOCs
are
used
in
screening
level
risk
assessments
to
express
potential
acute
and
chronic
risk
to
birds,
wild
mammals,
fish,
aquatic
invertebrates,
and
plants.

The
current
ecological
risk
characterization
process,
which
is
based
on
RQs
and
LOCs,
is
useful
and
can
provide
the
risk
managers
with
a
screening
method
to
facilitate
the
rapid
identification
of
pesticides
that
are
not
likely
to
pose
an
ecological
risk
or
those
that
may
pose
a
risk.
As
noted
in
the
EPA
Ecological
Risk
Assessment
Guidelines,
"
The
principal
advantages
of
the
quotient
method
are
that
it
is
simple
and
quick
to
use
and
risk
assessors
and
managers
are
familiar
with
its
application.
It
provides
an
efficient,
inexpensive
means
of
identifying
high­
or
low­
risk
situations
that
can
allow
risk
management
decisions
to
be
made
without
the
need
for
further
information"
(
U.
S.
EPA
1998,
Part
A,
Section
5.1.3).
It
also
provides
a
"
crude
index
of
magnitude
of
effects
and
therefore
can
be
used
for
comparisons
among
alternative
compounds
where
comparable
data
are
available"
(
Ecological
Committee
on
FIFRA
Risk
Assessment
Methods,
1999b,
Section
5.3,
page
5­
11).
Thus,
RQs
and
LOCs
are
useful
as
part
of
an
initial
or
screening
level
characterization
of
the
ecological
risk.
In
addition,
there
are
a
number
of
reasons
to
continue
to
include
RQs
and
LOCs
in
OPP
ecological
risk
assessment,
including:
"
Quotients
may
serve
as
an
interim
measure
that
provides
a
bridge
for
risk
assessors
and
risk
managers
between
current
and
new
probabilistic
risk
assessment
methods;
Quotients
remain
a
primary
method
...
may
continue
to
be
used
by
EPA
risk
managers;
[
lacking
good
case
studies
using
other
methods
including
probability]...
it
is
premature
to
eliminate
deterministic
quotients;
Quotients
may
play
a
role
in
1Much
of
the
discussion
of
probabilistic
risk
assessment
methods
was
based
on
the
following
document:
U.
S.
EPA.
1999.
Risk
Assessment
Guidance
for
Superfund
(
RAGS):
Volume
3,
Part
A,
Process
for
conducting
Probabilistic
Risk
Assessments.
Draft.

XVI
­
2
future
evaluations
by
providing
a
benchmark
to
which
new
methods
could
be
compared;
Further
evaluation
of
risk
characterization
methods
...
may
demonstrate
that
quotients
serve
a
useful
purpose
in
determining
the
applicability
of
the
risk
assessment
and
identification
of
scenarios
of
concern
(
e.
g.,
during
the
Problem
Formulation
stage)"
(
ibid,
Section
6.2,
pages
6­
3
and
6­
4).

While
the
objective
of
EFED
is
to
advance
toward
probabilistic
risk
assessment
methods,
current
deterministic
methods
such
as
the
quotient
have
not
been
dismissed.
Rather,
they
remain
an
integral
component
of
the
current
risk
assessment
for
the
registration
and
reregistration
of
pesticides.
This
is
consistent
with
current
Agency
guidance
for
Ecological
Risk
Assessment.
However,
many
risk
assessors
and
risk
managers
who
use
RQs
recognize
that
they
contain
an
unknown
degree
of
conservatism
and
they
tend
to
obscure
uncertainties
and
variability.
Thus,
while
an
RQ
can
be
useful
in
determining
whether
risk
is
likely
to
be
high
or
low,
it
may
not
be
helpful
to
a
risk
manager
who
needs
to
make
a
decision
requiring
an
incremental
quantification
of
risk
(
U.
S.
EPA
1998
p.
97).
Likewise,
an
RQ
does
not
provide
the
risk
manager
with
an
indication
of
uncertainty
surrounding
the
risk
estimation
(
ibid).
Further,
RQs
cannot
address
some
questions
raised
by
risk
managers
which
can
be
pivotal
to
major
regulatory
decision­
making
on
the
basis
of
ecological
risk
concerns:
°
What
is
the
magnitude
of
defined
risk
­­
How
big
is
it?
°
What
is
the
probability
of
the
risk
­­
How
likely
is
it
to
occur?
°
How
certain
are
you
that
an
adverse
effect
will
occur
­­
How
sure
are
you?

As
noted
in
the
US
EPA
Ecological
Risk
Assessment
Guidelines
(
U.
S.
EPA
1998,
p.
92),
"
If
the
risks
are
not
sufficiently
defined
to
support
a
management
decision,
risk
managers
may
elect
to
proceed
with
another
iteration
of
one
or
more
phases
of
the
risk
assessment
process."

Refined
Risk
Assessment
Methods1
Ecological
risk
assessments
may
be
refined
in
many
ways,
including
deterministic
and
probabilistic
methods.
The
newest
method,
and
the
one
receiving
widespread
attention
at
the
present
time,
is
the
probabilistic
risk
assessment.
Probabilistic
risk
assessment
is
a
general
term
for
a
risk
assessment
that
uses
probability
distributions
to
characterize
variability
and/
or
uncertainty
in
risk
estimates.
In
these
risk
assessments,
one
or
more
(
random)
variables
in
the
risk
equation
are
defined
mathematically
by
probability
distributions.
Similarly,
the
output
of
a
probabilistic
risk
assessment
is
a
range
or
distribution
of
risks
experienced
by
the
various
members
of
the
exposed
population
of
non­
target
organisms
of
concern.
A
risk
assessment
performed
using
probabilistic
methods
relies
on
the
same
fundamental
concepts
and
equations
as
the
traditional
point
estimate
approaches.

In
ecological
risk
assessments,
risk
distributions
may
reflect
variability
or
uncertainty
in
exposure
or
toxicity.
Following
a
deterministic
screening
level
assessment
that
indicated
XVI
­
3
potential
high
acute
risk,
a
risk
manager
may
request
an
answer
to
the
following
question:
"
What
is
the
magnitude
and
likelihood
(
i.
e.,
probability)
of
acute
risks
to
an
exposed
individual
from
the
use
of
Pesticide
X?"
After
determining
that
the
time,
resources
and
expertise
required
to
perform
a
probabilistic
risk
assessment
was
justified,
the
results
of
such
an
assessment
could
provide
the
following
conclusion:
Based
on
the
best
available
information
regarding
exposure
and
toxicity,
mortality
is
expected
to
be
10%
or
greater
in
the
majority
(
50%
of
more)
of
the
scenarios,
with
a
probability
of
95%.
The
above
example
is
based
on
a
situation
where
the
available
data
permitted
the
development
of
distributions
for
both
the
toxicity
and
exposure
variables.
Other
probabilistic
results
are
possible
when
only
one
of
the
variables
can
be
represented
by
a
distribution.

An
essential
concept
in
PRA
is
the
distinction
between
"
variability"
and
"
uncertainty".
Variability
refers
to
true
heterogeneity
or
diversity.
For
example,
among
a
population
of
birds
that
feeds
in
a
field
treated
with
a
pesticide,
the
risks
from
consuming
contaminated
short
grass,
insects
and
seeds
may
vary.
This
may
be
due
to
differences
in
exposure
(
i.
e.,
different
birds
consuming
different
amounts
and
kinds
of
food
items,
having
different
body
weights,
different
exposure
frequencies,
and
different
exposure
durations)
as
well
as
differences
in
response
(
e.
g.,
genetic
differences
in
resistance
to
a
chemical
dose).
These
inherent
differences
are
referred
to
as
variability.
Differences
among
individuals
in
a
population
are
referred
to
as
inter­
species
variability,
while
differences
for
one
individual
over
time
is
referred
to
as
intra­
species
variability.

Uncertainty
occurs
because
of
a
lack
of
knowledge.
It
is
not
the
same
as
variability.
For
example,
a
risk
assessor
may
be
very
certain
that
different
birds
consume
different
amounts
of
contaminated
food,
but
may
be
uncertain
about
how
much
variability
there
is
in
food
consumption
within
the
population.
Uncertainty
can
often
be
reduced
by
collecting
more
and
better
data,
while
variability
is
an
inherent
property
of
the
population
being
evaluated.
Variability
can
be
better
characterized
with
more
data,
but
it
cannot
be
reduced
or
eliminated.
Efforts
to
clearly
distinguish
between
variability
and
uncertainty
are
important
for
both
risk
assessment
and
risk
communication.

The
primary
advantage
of
probabilistic
risk
assessment
for
assessing
ecological
risks
within
OPP
is
that
it
gives
a
quantitative
description
of
the
probability
or
likelihood
of
the
impact
as
well
as
the
magnitude
or
severity
of
the
effect.
The
quantitative
analysis
of
uncertainty
and
variability
provides
a
more
comprehensive
characterization
of
risk
than
is
possible
in
the
deterministic
RQ
or
point
estimate
method.
Another
significant
advantage
of
probabilistic
risk
assessment
is
the
additional
information
and
potential
flexibility
it
affords
the
risk
manager.
For
example,
the
risk
assessor
can
provide
a
range
of
percentile
exposures
(
e.
g.,
5th,
25th,
50th,
75th,
95th)
based
on
the
distribution
of
these
exposures,
and
the
manager
can
select
the
percentile
at
which
he/
she
is
comfortable
making
a
decision.
Probabilistic
risk
assessment
can
also
more
reliably
identify
the
variables
and
model
parameters
that
have
the
greatest
influence
on
the
risk
estimates
through
sensitivity
analyses.
Finally,
once
the
probabilistic
model
is
developed,
it
is
relatively
easy
to
modify
the
model
to
run
"
what­
if"
scenarios
to
determine
the
effect
of
mitigation
measures
on
the
risk
conclusions.
XVI
­
4
While
a
probabilistic
risk
assessment
can
provide
a
useful
tool
to
characterize
and
quantify
variability
and
uncertainty
in
risk
assessments,
it
is
not
appropriate
for
every
site.
It
generally
requires
more
time,
resources,
and
expertise
on
the
part
of
the
assessor,
reviewer,
and
risk
manager
than
a
point
estimate
risk
assessment.
In
addition,
communicating
the
results
of
a
probabilistic
risk
assessment
may
be
a
challenge.
If
the
additional
information
is
unlikely
to
affect
the
risk
management
decision,
then
it
may
not
be
prudent
to
proceed
with
a
probabilistic
risk
assessment.
However,
if
there
is
a
clear
value
added
from
performing
this
assessment,
then
the
use
of
probabilistic
risk
assessment
as
a
risk
assessment
tool
generally
should
be
considered
despite
the
additional
resources
that
may
be
needed.
The
decision
to
use
probabilistic
risk
assessment
methods
is
pesticide
and
use­
specific
and
is
based
on
the
complexity
of
the
problems
due
to
the
behavior
of
the
pesticide
and
the
quality
and
extent
of
site­
specific
data.
EFED
recommends
a
tiered
approach
to
risk
assessment
so
that
the
scope
of
the
assessment
matches
the
scope
of
the
pesticide
and
use­
specific
problems
being
assessed.

The
FIFRA
Scientific
Advisory
Panel
(
SAP)
(
FIFRA
Scientific
Advisory
Panel,
1996a
and
1996b)
recognized
and
generally
reaffirmed
the
utility
of
the
current
assessment
process
and
methods
for
screening.
The
Panel
also
indicated
that
OPP's
methods
were
deterministic
for
assessing
the
effects
of
pesticides
to
non­
target
organisms
and
suggested
moving
to
probabilistic
assessments
for
the
chemicals
of
concern.
The
Panel
strongly
encouraged
OPP
to
develop
and
validate
tools
and
methodologies
to
conduct
probabilistic
assessments
of
ecological
risk,
as
the
Panel
believed
that
these
methods
were
necessary
in
order
to
achieve
an
appropriate
level
of
understanding
of
ecological
risk
to
support
major
regulatory
decision­
making.
In
1997
EFED
returned
to
the
SAP
and
provided
it
with
an
overview
of
EFED's
plans
to
move
forward
to
address
the
comments
made
during
the
May
1996
meeting.
The
SAP
was
extremely
supportive
of
EFED's
efforts
and
commended
the
Agency
for
its
"
proactive
response"
to
the
comments
made
during
the
May
1996
meeting
and
for
its
extensive
outreach
efforts
(
FIFRA
Scientific
Advisory
Panel,
1997).
In
June
1997,
OPP
began
an
initiative
to
develop
and
validate
tools
and
methodologies
for
conducting
probabilistic
assessments
that
address
terrestrial
and
aquatic
risk
within
the
context
of
the
FIFRA
regulatory
framework.
Subsequently,
EFED
formed
the
Ecological
Committee
on
FIFRA
Risk
Assessment
Methods
(
ECOFRAM),
which
was
divided
into
Aquatic
and
Terrestrial
Workgroups.
They
were
comprised
of
experts
drawn
from
government
agencies,
academia,
contract
laboratories,
environmental
advocacy
groups,
and
industry
and
were
tasked
with
identifying
and
developing
probabilistic
tools
and
methods
for
terrestrial
and
aquatic
assessments
under
the
FIFRA
regulatory
framework.
They
were
also
asked
to
identify
developmental
information
and
validation
needs
to
ensure
that
their
approaches
support
an
assessment
process
that
is
scientifically
defensible.

ECOFRAM's
conclusions
and
recommendations
were
summarized
in
the
Draft
Aquatic
Workgroup
Report
(
Ecological
Committee
on
FIFRA
Risk
Assessment
Methods,
1999a)
and
the
Draft
Terrestrial
Workgroup
Report
(
Ecological
Committee
on
FIFRA
Risk
Assessment
Methods,
1999b)
which
were
completed
in
April
1999.
In
these
reports,
ECOFRAM
provided
a
proposed
framework
for
risk
assessment
refinement.
This
was
based
on
a
tiered
approach
which
moves
from
simple
deterministic
assessments
through
probabilistic
methods,
to
an
issue­
specific
probabilistic
assessment
at
the
higher
tiers.
After
completion
of
the
ECOFRAM
draft
reports,
XVI
­
5
the
Agency
held
two
workshops
(
June
22
­
24,
1999)
to
provide
EPA
with
scientific
peer
review,
comment,
and
discussion
of
the
recommendations
contained
in
the
reports.
In
general,
the
workshop
participants
supported
the
basic
approach
described
by
ECOFRAM
and
concluded
it
was
scientifically
sound.
They
noted
some
general
issues,
such
as
the
need
for
validation
of
models,
describing
uncertainty
at
each
tier,
the
lack
of
addressing
multiple
stressors
or
multiple
chemicals,
and
the
need
for
case
studies.
They
also
provided
numerous
specific
comments
and
suggestions.

Following
ECOFRAM,
EFED
formed
the
Probabilistic
Risk
Assessment
Implementation
Team
within
EFED,
which
was
charged
with
developing
an
implementation
plan
for
OPP
that
incorporates
probabilistic
tools
and
methods
for
the
evaluation
of
potential
ecological
risk
from
pesticide
exposure.
The
reports
originating
out
of
the
ECOFRAM
initiative
served
as
the
basis
for
development
of
this
EFED
implementation
plan
for
conducting
probabilistic
ecological
risk
assessments.
The
implementation
plan,
presented
to
the
SAP
in
April
of
2000,
outlined
a
proposed
general
approach
for
assessing
pesticide
risks
to
birds
and
aquatic
organisms,
including
the
use
of
probabilistic
tools
in
a
tiered
manner
(
actually
four
Levels
of
Refinement).
During
the
following
months,
EFED
developed
pilot
aquatic
and
terrestrial
models
as
well
as
a
`
generic
case
study'
in
order
to
demonstrate
the
models.
The
models
and
the
case
study
were
reviewed
by
the
SAP
in
March
2001,
and
the
Panel
described
the
Agency's
efforts
as
being
at
the
forefront
of
conducting
an
ecological
probabilistic
risk
assessment.
The
EFED
Implementation
Team
is
currently
finalizing
the
models
which
will
be
used
for
Level
2
Probabilistic
Risk
Assessments.
[
Find
information
for
all
SAP
meetings
at
http://
www.
epa.
gov/
scipoly/
sap/
2001/
index.
htm
]

Bibliography
Ecological
Committee
on
FIFRA
Risk
Assessment
Methods
(
1999a)
ECOFRAM
Draft
Aquatic
Report
dated
May
4,
1999,
and
(
1999b)
ECOFRAM
Terrestrial
Draft
Report
dated
May
10,
1999.
http://
www.
epa.
gov/
oppefed1/
ecorisk/

FIFRA
Scientific
Advisory
Panel
(
1997)
A
Set
of
Scientific
Issues
Being
Considered
by
the
Agency
in
Connection
with
the
Progress
Report
on
developing
Probabilistic
Risk
Assessment
Methodologies
for
Aquatic
and
Terrestrial
Risk.
http://
www.
epa.
gov/
oppefed1/
ecorisk/

FIFRA
Scientific
Advisory
Panel
(
1996a)
A
Set
of
Scientific
Issues
Being
Considered
by
the
Agency
in
Connection
with
EPA's
Corn
Cluster
Ecological
Risk
Assessment.
http://
www.
epa.
gov/
oppefed1/
ecorisk/
sapreprt.
htm
FIFRA
Scientific
Advisory
Panel
(
1996b)
A
Set
of
Scientific
Issues
Being
Considered
by
the
Agency
in
Connection
with
EPA's
Ecological
Risk
Assessment
of
Carbofuran
Flowable
Products.
http://
www.
epa.
gov/
oppefed1/
ecorisk/
carbofur.
htm
XVI
­
6
U.
S.
EPA.
1998.
Guidelines
for
Ecological
Risk
Assessment.
Risk
Assessment
Forum.
U.
S.
Environmental
Protection
Agency,
Washington
DC.
EPA/
630/
R­
95/
002F.
April.
May
14,
1998
Federal
Register
63(
93):
26846­
26924.

U.
S.
EPA.
1992.
Memorandum
from
Linda
J.
Fisher,
Assistant
Administrator,
Office
of
Pesticides
and
Toxic
Substances,
to
Douglas
Campt,
Director,
Office
of
Pesticide
Programs,
October
29,
1992.
Decisions
on
the
Ecological,
Fate,
and
Effects
Task
Force.

U.
S.
EPA.
1986.
Hazard
Evaluation
Division,
Standard
Evaluation
Procedure
­
Ecological
Risk
Assessment.
EPA­
540/
9­
86­
167.

Table
1.

Risk
Presumptions
for
Terrestrial
Animals
Risk
Presumption
RQ
LOC
Birds
Acute
High
Risk
EEC1/
LC50
or
LD50/
sqft2
or
LD50/
day3
0.5
Acute
Restricted
Use
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOEC
1
Wild
Mammals
Acute
High
Risk
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.5
Acute
Restricted
Use
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOEC
1
1
abbreviation
for
Estimated
Environmental
Concentration
(
ppm)
on
avian/
mammalian
food
items
2
mg/
ft2
3
mg
of
toxicant
consumed/
day
LD50
*
wt.
of
bird
LD50
*
wt.
of
bird
Risk
Presumptions
for
Aquatic
Animals
Risk
Presumption
RQ
LOC
Acute
High
Risk
EEC1/
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/
MATC
or
NOEC
1
1
EEC
=
(
ppm
or
ppb)
in
water
XVI
­
7
Risk
Presumptions
for
Plants
Risk
Presumption
RQ
LOC
Terrestrial
and
Semi­
Aquatic
Plants
Acute
High
Risk
EEC1/
EC25
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
Aquatic
Plants
Acute
High
Risk
EEC2/
EC50
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
1
EEC
=
lbs
ai/
A
2
EEC
=
(
ppb/
ppm)
in
water