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The Role of Ecological Risk Assessment
in Environmental Decision Making
ALAN W. MAK]
Exxon Company, USA
MICHAEL W. SLIMAK
U.S. Environmental Protection Agency
PREDICTIVE ASSESSMENT OF ECOLOGICAL RISKS
Potential impacts and effects of pollutants on ecosystems are often
complex and far-reaching. The simplest counter to a chemical use that
produces immediate and obviously deleterious environmental effects is to
impose a ban on its use before the effects become irreversible. However,
many of the less obvious and subtle environmental effects of pollutants
are not readily recognized and therefore are considerably more difficult
to handle. Thus, the effect of pollutants on ecosystems is an issue which
requires the development and enhancement of methodology to predict the
fate and effects of substances in the environment prior to their manufacture,
use, or distribution.
Procedures for ecosystem risk assessment are currently evolving. An
ecosystem nsk assessment is defined as a set of procedures for measuring
risk to the environment associated with the use of substances through an
objective and probabilistic exercise based on empirical data and scientific
judgment. The results of such a risk assessment can then be used to provide
a consistent means of estimating the limiting concentrations of substances
that will produce no unacceptably negative effects on ecosystems which are
potentially exposed to the substance.
Thus, ecological risk assessments serve as the scientific basis for decid-
ing whether the risks are acceptable or unacceptable for the environment,
i.e., a risk management decision. Basically, the risk assessment process
consists of two parallel lines of investigation and relates observed biological
effects to expected exposure concentrations. Figure 1 represents the two
77
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78
ECOLOGICAL RISKS
c
-
In
.
~ ~c. ~
Highest test concentration
/ producing no biological
effects.
-
-
<°ofj~e
`~/s
'~ Flighest expected environmental
concentration .
1
5 6
Sequential Tests of Hazard Assessment
Procedure
FIGURE 1 Diagrammatic representation of a sequential hazard assessment procedure
demonstrating increasingly narrow confidence limits for estimates of no biological effect
concentration and actual expected environmental concentration.
concentrations as parallel lines and demonstrates that increasingly more ac-
curate and statistically reliable estimates of these concentrations will result
from a sequential series of tests completed along the x axis of the graph.
Using the risk assessment process, increasingly more accurate estimates of
fate and effects can be made to the point where it becomes possible to
state with a high degree of confidence that environmental concentrations
and biological effects will likely result in negative environmental conse-
quences. It is a matter of judgment to determine just how far into the
hazard-evaluation process investigation must proceed to establish accept-
able confidence regarding fate and effect concentration predictions (Cairns
et al., 1978~.
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ENVIRONMENTAL AL4NAGEMENT CONCEPTS
DETERMINE THE
CHEMICAL AND
PHYSICAL
PROPERTIES
EST1~1ATE
ENVIQON~tENTAL
CONC£N TRATIONS
79
PREDICT USAGE
PATTERNS AND
QUANTlilES
1
. ~
TEST FOR TEST FOR
ENVIRONMENTAL ~ ENVIRONMENTAL
FATE EFFECTS
~ - .
DECISIONS
DECISIONS
ESTIMAtE
HUI~AN
EXPOSURES
_ _
TEST FOR
HEALtH
EFFECTS
my'
0691SE RESTRICTIONS
TO DIMINISH EXPOSURES
\
MONITOR |
DO NOr
USE
FIGURE 2 Flow chart for the 10 phases of the safeW evaluation program.
The process of making and reviewing an environmental risk assessment
can be broken down into ten stages (Beck et al., 1981~. These stages and
how they are related to each other are shown in Figure 2. The sequence
of stages splits into two paths, one for environmental safety and one for
human safety, which come together again at the point of decision making.
Each stage is described briefly below:
1. The evaluation starts with a consideration of the properties of
the substance (e.g., chemicals, materials) ascertained from the literature
or determined in the laboratory, if necessary. Estimates may suffice in
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80
ECOLOGICAL RISKS
the early stages, but more precise determinations will generally be needed
later. This is the time for initial development of the analytical methodology
that will be required to measure the substance in the environment and in
biological tissues.
2. Use of the substance, and quantities involved must be considered,
..
since usage patterns (along with such related matters as manufacturing,
shipping, and disposal) influence the routes and amounts of environmental
exposure.
3. From anticipated usage patterns, the concentrations that can be
expected in various environmental compartments are predicted. These
estimates can be helpful in projecting exposures, but their chief value is in
suggesting how extensively the material should be tested for environmental
properties, e.g., the rate of chemical and biological degradation. Then,
from the results of the environmental fate tests, more refined predictions of
environmental concentrations can be made. These estimates are necessary
both for predicting exposures- and for interpreting the results of tests to
evaluate environmental effects.
4. Tests for environmental fate suggest what may happen to the sub-
stance after it is released into the environment. The nature of both the
substance and the potentially affected ecosystem is important in determin-
ing fate. This kind of information is necessary for making the refined
estimates of environmental concentration referred to above, and this is one
of the factors influencing the estimate of exposure.
5. Estimates of exposure can be made from information about man-
ufacturing, transport, and usage patterns and from the estimates of envi-
ronmental concentration. A number of estimates are needed to cover such
diverse situations as direct exposure to pesticides or indirect exposures from
a contaminated food source. Exposure may be by oral, respiratory, ocular,
or dermal routes. These estimates of exposure are of value in determining
which effects tests should be conducted, and are essential in evaluating the
results of those tests.
6. Tests for hazard are concerned with the possible effects of the
material on non-target health, but most of the tests are conducted with
laboratory animals. From information about the kinds of effects produced
in these animals, and the concentrations of chemicals necessary to produce
them, it is possible to determine the exposure of chemicals that would be
acceptably low risk to non-target organisms.
7. Tests for environmental effects indicates whether the concentra-
tions expected may cause harm to the environment, particularly to the
living organisms in it, the kinds of injury that may occur, and the species
or processes most likely to be affected. Further discussion of ecological
responses to stress can be found in subsequent chapters by Howell et al.
and Breymeyer (Chapters 7 and 8, this volume).
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ENVIRONMENTAL MANAGEMENT CONCEPTS
81
8. Decision making occurs repeatedly throughout the process. If
the decision is to use the material, field monitoring may be needed to
determine whether the resulting environmental concentrations correspond
to those that were predicted from laboratory testing and modelling.
9. The first step in decision making is to compare the concentra-
tions of a chemical that are predicted to cause unacceptable harm to the
environment with the concentrations that will likely result from using the
chemical. From this comparison, it is possible to assess the risk of causing
adverse effects. Finally, the decision is made whether the risks are soci-
etally acceptable or not. It is not necessary to do all the tests that are listed
before making this decision; there are provisions at many points in the
process for deciding that no further testmg is necessary and that regulation
is or is not required.
10. If any of the risks associated with using the chemical as originally
planned are judged unacceptable, it may be possible to devise restrictions on
the use of the chemical that would diminish the anticipated exposure and
therefore lower the risk. The restrictions might be of many sorts, ranging
from warning labels to the construction of containment dikes around storage
tanks. Once such restrictions have been devised, it will then be necessary
to go through parts of the decision-making process again to see whether
the risk becomes acceptable.
ECOTOXICOLOGY: THE PRACTICE OF RISK ASSESSMENTS
Ecotoxicology can be defined as the study of the fate and effects of
toxic agents in ecosystems. Ecotoxicology is the study of toxic effects on
biota particularly on populations and communities—and their interactions
with processes controlling the functioning of defined ecosystems.
The U.S. Environmental Protection Agency (EPA) has primary re-
sponsibility for determining the ecological risks associated with the use of
pesticides and industrial chemicals (xenobiotics) in the United States. This
responsibility comes from two major pieces of legislation: the Toxic Sub-
stances Control Act DISCO) and the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA).
In practice, both programs assess risks to ecological resources using
an ecotoxicological approach: laboratory toxicity bioassays to determine
hazard; determination of exposure either from monitoring data or predicted
from models; and a comparison of exposure to hazard using the quotient
method. In the quotient method, the exposure value is directly compared
with a toxicity endpoint (e.g., concentration in water to an LC50 value; 10
ppm/100 ppm). The closer the quotient is to 1 (or greater), the higher the
probability that an adverse effect will occur. Interpreting this adverse effect
(i.e., the likelihood that what is observed in the lab will actually occur in
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ECOLOGICAL RISKS
the field) is one of the biggest uncertainties in both programs. Although
each program derives it differently, the final result is the application of
either a safety factor or an assessment factor to account for uncertainty.
Although the two programs are similar in their approach to assessing
ecological risk, the quantity of data used to make assessments is strik-
ingly different: TSCA assessments tend to be data-poor while FIFING
assessments are usually data-rich. This difference is due to what is being
regulated. TSCA regulates new and existing industrial chemicals, many
of which are site-limited intermediates, are produced in low volumes with
limited potential for environmental release, and are not manufactured pri-
marily for their toxicological (biological) properties. Pesticides, on the
other hand, are generally very active biologically, are designed to kill pests
and other organisms, and are broadly released into the environment on a
regional scale.
The Toxic Substances Control Act
The Office of Toxic Substances (OTS) at EPA is responsible for im-
plementing provisions of TSCN TSCA was enacted in 1976 to protect
humans and the environment from unreasonable risks caused by industrial
chemicals and mixtures. Section 4 of TSCA is primarily concerned with
existing chemicals which were in production before the law was passed.
Because of the thousands of chemicals on the inventory, a prioritization
scheme had to be established to effectively assess potential risks. Thus, an
Inter-Agengy Testing Committee recommends to EPA chemicals it believes
should be given priority testing for hazard determination. EPA evaluates
these recommendations and can either refute them or proceed with hazard
testing. Chloroparaffins are an example of a group of chemicals for which
ecological testing has been required pursuant to this section of TSCN
OTS used and refined existing ecosystem-level models to address the risks
to natural populations posed by indirect and direct toxic effects of these
chemicals. The use of these higher level models was necessary since the
quotient method of assessment indicated a likelihood of adverse effects.
Section 5 of TSCA covers chemicals which are new, i.e., those which
were produced since the law was passed. Industrial chemicals regulated
in this section are referred to as Pre-Manufacturing Notice chemicals or
"PMNs." This section of the law requires a manufacturer to submit a pre-
manufacture notice to EPA before it manufactures a particular chemical.
EPA then has 90 days (or, with good cause, 180 days) to review the
notice for potential risks to the environment. There were over 2,000 PMNs
submitted to EPA in 1988. Generally, however, ecotoxicological data is not
submitted by the manufacturer and the potential hazard must therefore be
determined using predictive toxicological techniques (e.g., structure/activi~
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ENF7RONMENTAL MANAGEMENT CONCEPTS
1
83
relationships) techniques. If an unacceptable risk is judged to be a high
probability (risk = hazard + exposure), then the manufacturer may be asked
to conduct suitable tests.
Because of the large numbers of industrial chemicals that must be
assessed in this program, a method was devised to insure uniformity and
consistency in identifying chemicals for testing to determine ecological haz-
ard. Assessment factors are used in conjunction with the hazard assessment
to derive concentrations of concern in aquatic media which, if equaled or
exceeded, provide a basis for further testing. Assessment factors are num-
bers which are used to adjust standard toxicological measurements (e.g.,
LC50, EC50, etc.) to derive a "concern level." An environmental concen-
tration of concern is that concentration at which populations of organisms
are adversely affected as found in a field study conducted under simulated
or actual conditions of production, use, and disposal. Assessment factors
take into account the uncertainties due to such variables as test species
sensitivity to acute and chronic exposures, laboratory test conditions, and
age-group susceptibility. There are four assessment factors currently being
used: 1, 10, 100, and 1000.
Able 1, taken from EPA (1984), summarizes the application of assess-
ment factors. OTS does not consider assessment factors to be equivalent
to safety factors. Safety factors are usually interpreted as being a margin
of safety applied to a no-observed-effect level to produce a value below
which exposures are presumed to be safe. Assessment factors are used
with acute or chronic toxicity values to arrive at a concentration which if
equaled or exceeded could cause adverse effects. Assessment factors have
been developed solely for the PMN process to identify those chemicals
which require ecological testing to fully assess ecological risks.
In assessing risks to PMN chemicals, OTS uses the quotient or ratio
method. The specific equation used is:
Environmental Concentration/Concern Level = Risk
If the quotient is equal to or greater than 1, the conclusion is that ad-
verse effects are likely to occur to the population of organisms represented
by the toxicity data. The quotient method is only used, however, to de-
termine if actual testing is necessary. If actual hazard data is obtained,
the quotient method is still used; however, more analysis is conducted
using dose/response curves in conjunction with the measured or predicted
environmental concentration. In addition, consideration is given to un-
derstanding the acute to chronic ratios, and inter- and intra-taxa dose
relationships. In some instances, simulation models, such as the Standard
Water Column Model (SWACOM) developed by Bartell et al. (1988), have
been employed where the chemical impact on one trophic level is analyzed
relative to the other trophic levels.
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ECOLOGICAL RISKS
TABLE 1 Application of assessment factors to evaluate need for testing.
-
DATA AVAILABLE
ASSESSMENT FACIOR
TO BE APPl IFD
Structure -Activity
Denved LCSo
Single LC50 Frown Gh~xnical Analog
Single Test LC'o for PMN
Two LC';os for Same Analog
(e.g., 1 Fish, 1 Algal test)
Two LC50s for PMN
(e.g., 1 Fish test, 1 Invertebrate)
Three Loos for Same Analog
(Fish, Algae, Invertebrate)
Five LC50s for Same Analog
(3 ~vertebrates, 2 Fish)
Five LC50s for the PMN
(e.g., 3 Algae, 2 Fish)
Maximum Acceptable Toxic
Concentration for Analog
Field Study
1000
1000
1000
1000
1000
100
100
100
10
SOURCE: U.S. EPA, 1984.
Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)
Under this law, EPA must determine whether a pesticide can be
registered for a particular use. FIFRA states that the EPA Administrator
shall register a pesticide if he determines that '~when used in accordance
with widespread and commonly recognized practice it will not generally
cause unreasonable adverse effects on the environment."
The term "unreasonable adverse effects on the environment" means
any unreasonable risk to humans or the environment, taking into account
the economic, social, and environmental costs and benefits of the use of
any pesticide. Under FIFRA, the process of determining whether or not
a risk is unreasonable (i.e., factoring in benefits along with risks) is a
risk management function. For this discussion, the important term used in
FIFRA is "risk to the environment." In order for the EPA Administrator to
determine if there will be an unreasonable risk to the environment from the
use of a pesticide, an ecological risk assessment from a pesticides perspec-
tive involves estimating the likelihood or probability that adverse effects
(e.g., mortality to single species of organisms; reductions in populations
of non-target organisms due to acute, chronic, and reproductive effects;
or disruption in community and ecosystem level functions) will occur, are
occurring, or have occurred.
Ecological risk is a function of toxicological hazard and environmental
exposure. Toxicological hazard is the intrinsic quality of a pesticide to cause
an adverse effect under a particular set of circumstances. Toxicological
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ENVIRONMENTAL MANAGEMENT CONCEPTS
TABLE 2 Regulator nskassessm~tcnmna for "sucides.
85
PRESUMPTION OF ~ K
PRESUMPTION THAT PLAY BE OBLIGATED PRESUMPTION OF
OF NO RUSK BY RESTRICTED USE UNACCEPTABLE RUSK
,
I. Acute Toxicity
1) Manuals
EEC* LC50
mg~day 1/5 LCso
2) B`r~
EEC <1/5 Leo 1/5 LCso~ EEC < LCso EEC 2 LC50
3) Aquatic Organisms
EEC <1/10 LCSo
EEC 2 1/10 LC
II. Chronic Toxicity
1110 LC50~ EEC EEC 21~ LCSo
~ 1/2 LCso
EEC < Chronic N/A EEC 2 Chronic Effect Levels
No Effect Level Including Reproductive Effects
*EEC = Expected Environmental Concentration. This is typically calculated using a series of
simple Homographs to complex exposure models.
SOURCE: Adapted from Urban and Cook, 1986.
hazard data includes, for example, laboratory fish, aquatic invertebrate,
or bird LC50 values, and effect levels for fish and avian reproduction
tests. Environmental exposure is a function of two data components. The
first is the estimated amount of the pesticide residue that will be in the
environment and available to non-target organisms. The second consists
of the numbers, types, distribution, abundance, dynamics, and natural
history of non-target organisms which will be used in contact with these
residues. Information on the proposed label use of the pesticide is essential
for such exposure estimates. Toxicological hazard is estimated first and
environmental exposure separately; then they are compared to each other.
In the EPA Pesticides Program, the comparison of exposure with effects
data is based on regulatory risk criteria. These criteria are summarized and
presented in Able 2. Within the table are risk criteria which contain specific
safety factors that were derived from a toxicological model developed by
the Program in 1975. The model was designed to provide a safety factor
that would allow for differential variability and sensitivity among fish and
wildlife species. A detailed explanation of the derivation of these safeW
factors is found in Urban and Cook (1986~.
Many theoretical questions can be raised about the use of risk criteria
and safety factors in general. Currently, the Program does not use the
model to predict the probability of the pesticide causing significant acute
adverse effects to non-target organisms, since the model does not provide
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ECOLOGICAL RISKS
a mechanism for estimating model uncertainty. Thus, the risk criteria
with their safety factors are used as "rough" estimates of potential risk to
non-target organisms.
Specific information and testing data are necessary in order to conduct
an ecological risk assessment for a pesticide. Under FIFRA, EPA is not
responsible for producing the data needed to make an ecological risk
assessment. That burden is placed upon the applicants for registration.
The Office of Pesticides Programs has published regulations which specify
the data that are required for registration (40 CFR, Part 158 as cited
in Urban and Cook, 1986y, and guidelines which provide recommended
testing methods that are needed to produce the required data.
The EPA Pesticides Program follows four procedural steps-in assessing
ecological risk:
1. review and evaluation of hazard data to identify the nature of the
hazards;
2. identification and evaluation of the observed quantitative relation-
ship between dose and response;
3. identification of the conditions of exposure (e.g., intensity, fre-
quency, and duration of exposure); and
4. combination of dose/response and exposure information to derive
estimates of the probability that hazards associated with the use of the
chemical will be realized under conditions of exposure experienced by the
non-target populations) under consideration.
These steps result in the comparison of toxicological hazard data and
exposure data using regulatory risk criteria. Typically, toxicological hazard
data may consist of acute LD50 and LC50 values, or chronic no-effect levels
for the most sensitive indicator species. Exposure data normally consist of
model-based estimated environmental concentrations in important media
of concern (i.e., water, soil, and non-target organism food items). As the
ratio of these input data equals or exceeds the regulatory criteria, a risk is
inferred.
CONCLUSION
Both the toxic substances and pesticides programs at EPA recognize
that the ratio method for assessing risk has numerous weaknesses. For
example:
.
· it does not adequately account for effects of incremental dosages;
it does not compensate for differences between laboratory tests and
field populations;
· it cannot be used for estimating indirect effects of toxicants (e.g.,
food chain interactions);
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ENVIRONMENTAL MANAGEMENT CONCEPTS
87
· it has an unknown reliability;
· it does not quantify uncertainties; and
· it does not adequately account for other ecosystem effects (e.g.,
predator/prey relationships, community metabolism, structural shifts, etch.
Therefore, at the present time, the state-of-the-art does not provide a com-
plete characterization of the magnitude of risk or the degree of confidence
associated with the characterization.
The development of the field of ecotoxicity, like that of risk assessment,
has paralleled the increased awareness of the environment during the past
two decades. This awareness is especially evident now in Eastern Europe.
The science is complex and addresses a broad range of issues that are
frequently the focus of public concern and international policy. ~day,
many ecological risk assessment protocols are modifications of methods
used to characterize risk to public health. Unfortunately, these methods
often lack environmental validity and may not effectively measure ecosystem
integrity. New directions in this field reflect an increased emphasis on the
role of sediments, biomarkers, and ecosystem assessments in controlling
environmental contaminants. As these methods and protocols become
more refined and are practiced by a larger body of scientists, their role
and importance in environmental decision making will become much more
important.
REFERENCES
Bartell, S.M. 1988. Community and ecosystem models for ecological risk assessment. Oak
Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, Tennessee.
Beck, LOO., A.W. Maki, N.R. Artman, and E.R. Wilson. 1981. Outline and criteria for
evaluating the safety of new chemicals. Reg. Tax. and Pharmacology (1~:19-58.
Cairns, J. Jr., ILL" Dickson, and A W. Maki, eds. 1978. Estimating the hazard of chemical
substances to aquatic life. ASTM STP 667. American Society for Testing and Matenals,
Philadelphia, Pennsylvania.
Urban, DJ., and NJ. Cook. 1986. Hazard Evaluation Division, Standard Evaluation
Procedure, Ecological Risk Assessment 504/9-85 001; NTIS PD86-247457. U.S. Envi-
ronmental Protection Agency, Washington, D.C.
U.S. EPA. 1984. Estimating concern levels for concentrations of chemical substances in the
environment. U.S. Environmental Protection Agency, Washington, D.C.
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Representative terms from entire chapter:
risk criteria
