United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA30613
Research and Development
EPA-600/S3-84-075 Aug. 1984
v>EPA Project Summary
Impact of High Chemical
Contaminant Concentrations on
Terrestrial and Aquatic
Ecosystems: A State-of-the-Art
Review
Louis J. Thibodeaux, Duane C. Wolf, and Martha Davis
The present state of knowledge con-
cerning high concentrations of
contaminants in terrestrial and aquatic
ecosystems was reviewed and gaps
that exist in information needed to
control potentially hazardous situations
were identified. The review included an
assessment of the state-of-the-art of
available methods for predicting
contaminant effects on ecosystem
properties, processes, functions,
cycles, and responses.
Chemical concentrations are
considered high if the contaminant is
present at a level of 5% or more, by
weight, in a soil or water sample and
causes major physical, chemical, or
biological changes in an ecosystem.
Environmental problems associated
with high chemical contaminant con-
centrations occur at landfills,
landfarms, (where waste is spread on
land), spill sites, and abandoned sites
where chemicals were produced, used,
stored, or discarded.
The review revealed considerable
information on the effects of pesticides,
polychlorinated biphenyls (PCBs), chlo-
rinated hydrocarbons, metal ions, and
other trace chemical contaminants in
the respective ecosystems. Predictive
techniques are becoming available to
describe the transport and transforma-
tion of such contaminants and, thus,
their fate and distribution in certain
components of the environment.
Present predictive methods and
models that track the transport and
transformation of chemical species are
based on "natural" soil and water
properties such as density, porosity,
infiltration, permeability, viscosity,
hydrophobicity, and diffusivity. When
the chemical contaminant is present in
high concentrations, the assumption of
"natural" soil and water properties is
very suspect. Among the important
research needs identified in the review,
the most significant was to provide an
assessment of microbial degradation
rates and microbial activity under stress
conditions in soil and water, such as the
high chemical contaminant concentra-
tions and limited oxygen, limited nutri-
ents, and limited microbial populations.
This Project Summary was developed
by EPA's Environmental Research Lab-
oratory, Athens, GA, to announce hey
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
As society's increasing demand for
chemical mixtures interacts with increas-
ing populations, encounters of the biota
with those mixtures will multiply dramat-
ically. The U.S. Environmental Protection
Agency regulates disposal of approxi-
mately 40 x 106 metric tons of hazardous
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waste per year of which some 80% is
disposed of on land. Knowledge of the
nature of these mixtures will enhance our
ability to reduce the risk of exposure to
toxic/hazardous substances by allowing
more accurate prediction of behavior in
the ecosystem and by supplying
information that will assist in the design
of storage and/or disposal facilities.
For this report, high chemical concen-
tration is taken to mean a level of single or
joint chemical content in air, water, or soil
that constitutes > 5% (wt), or > 50,000
ppm (wt) of the mixture. This is not an
arbitrary definition. At the 5% level, basic
properties of the air, water or soil begin to
be influenced significantly by the
presence of the foreign substance. For
example, transport coefficients cannot be
assumed to be constant and independent
of concentration at this level. High
chemical concentrations occur in "both
soil and water and lead to problems at
landfills, landfarms, and spill sites as well
as abandoned and active production, use,
storage and disposal sites.
The current problems involving high
concentrations of hazardous waste from
"chemical waste landfills" are not associ-
ated, generally, with the present gener-
ation of well-sited and well-constructed
facilities. The majority of problems
involve the past practices of codisposal of
chemical waste in municipal solid waste
landfills, the mixing of chemical waste
(including liquids) with garbage and fill
material to form a non-flowing landfill
"solid," the placement of sludges capable
of creating a hydraulic head in landfill
cells, and other expedient means of
disposing of chemical wastes. In the
latter category the most common is the
chemical dump in which solids and
liquids are placed on the ground, in
natural depressions, or in hastily dug pits
that are insufficient for containment of
the wastes. Abandoned dump or storage
sites also fall into the latter category.
Landfarming or landspreading is an
operation involving the placement of
sludges and aqueous waste on the soil
surface. Contaminated land involves high
levels of chemicals on or near the soil
surface. This soil contains substances
that, when present in sufficient
concentration, are likely to cause harm,
directly or indirectly, to humans. Much of
this land is on former industrial sites that
were developed and left in a contaminated
condition. The accidental spill of solids
and liquids during road or rail transport
also results in soil contaminated with
high chemical concentrations
High chemical concentrations also can
become associated with the aquatic
environment. Episodic spills of large
quantities of sinker chemicals (chemicals
with a density greater than water) in river
systems result in the bottom sediment
being highly contaminated such as
occurred in an incident involving chloro-
form spilled in the Mississippi River.
Long-term releases, such as kepone
contamination of the James River and
PCBs in the Hudson River, can result in
high concentrations in the sediment.
The research approach to the state-of-
the-art review entailed the following
activities.
1. A three-dimensional matrix was
developed to assure that all the
variables were considered. The
matrix included processes (e.g.,
mechanisms), soil and sediment
properties, and chemical properties.
2. Computer and manual literature
searches were conducted.
3. A scenario analysis of hypothetical
contaminant cases was performed.
Given that the chemical contami-
nant situation was known, the
purpose of the scenario analysis
was 19 assess the impact of the high
concentration waste on soil and
water properties and parameters,
on transformation reactions, and on
transport processes (both mass flow
and diffusion)." The result of this
exercise highlighted the extent to
which the present state of know-
ledge in microbiology, chemistry,
engineering, physics, and soil
science allows predictions involving
the above property/parameters of
affected soil and water.
4. Based on the results of the literature
search and scenario analysis,
information gapswere identified.
5. Based on the information gaps, a set
of priority recommendations for
needed field and laboratory
research was developed.
Literature Review and
Scenario Analysis
Information related to high chemical
concentration in aquatic environments
was sought for three chemical properties.
organic solubility, vapor pressure, and
partition coefficient between soil and
water.The variety of mixtures
encountered is extremely large, and, in
comparison, the set of reliable experi-
mental data on mutual solubilities in
aqueous and non-aqueous systems is
extremely small. Finding applicable
equilibrium solubility data for a particular
waste mixture is highly unlikely;
however, data on closely related systems
might be found, which, along with estab-
lished thermodynamic methods, might
provide useful information. An
abundance of data and methods is
available concerning vapor pressures of
chemicals in the pure state. Those that
exist in high concentrations in terrestrial
and aquatic ecosystems, however, are
typically in an impure state. Lack of data
and model testing is apparent for vapor
pressures with- high chemical
concentrations that result when water
residues are in contact with a
multicomponent liquid phase and soil
system. The effect of soil water at low
levels (e.g., 1 to 3%) upon the vapor
pressure of organics is not well
established. Information on vapor pres-
sure of volatiles above bio-sludges and
natural organic matter "solvents" was
not located. The partition coefficient
between soil and water will likely need to
be generalized to include high chemical
concentrations. It is unlikely that a simple
ratio will suffice for high chemical
concentrations and the presence of
solvents and mixtures.
Data on metal ion solubility product,
chelate and complex formation, and
biomethylation reactions were reviewed.
When a metal ion is introduced into an
environment such as a waste disposal
site, it can undergo numerous chemical
and biochemical reactions. The data on
solubility product represent aqueous
systems of the respective ions but do not
involve any mixed ionic or non-aqueous
systems that might be typical of
hazardous disposal sites. Soluble organo-
metallic chelates are important because
they increase the solubility and, thus, the
mobility and bioavailability of metal. In
disposal sites, a complex mixture of
organic compounds could beavailablefor
chelate formation, and subsequent
movement in a non-aqueous environ-
ment could be a potential problem.
Methylation of toxic metals by microor-
ganisms plays a significant role in metal
transport, and it may serve as a detoxifi-
cation mechanism for the microbial
population. Because of their solubility
and volatility, the methylated materials
are highly mobile in the environment.
The literature review also covered
occurrences of high chemical concentra-
tions in terrestrial ecosystems. The
factors considered included transport
processes in saturated soils, unsaturated
soils, and the air boundary layers.
Concerning saturated soil, it was found
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that solute (contaminant) transport
models are in an early stage of
development compared to flow models;
consequently, the use of transport
models is more limited. For the
movement of many wastes, the cause-
effect relationships, especially those
involving physical-chemical behavior, are
only partially understood. The presence
of chemical waste on or near soil surfaces
creates situations involving complex
transport mechanisms. The present
generation of models neglects soil-water
gradients, thermal gradients and
capillary force-induced gradients. Few
direct measurements of the flux of vadose
water have ever been attempted at
depths of a few meters, and uncertainty
exists on how retardation factors yet to be
measured for unsaturated flow
conditions will compare with those
reported for saturated flow
Transport processes and transforma-
tion (biotic and abiotic) processes for the
aquatic ecosystems that include the
sediment zone of rivers and lakes were
also reviewed.
A scenario analysis of two hypothetical
contaminant cases was undertaken. One
involved a binary solvent system
(aqueous and non-polar organic) and the
other a tertiary solvent system. Each of
these solvent systems was applied to a
terrestrial and an aquatic high chemical
concentration contamination scenario,
respectively. The terrestrial ecosystem
contamination scenario provides the
framework for considering the fate of
chemicals moving upward to the
atmosphere, downward to the ground
water, and in the lateral direction The
hypothetical binary was water and 1,2-
dichloroethane, and the tertiary was
water, benzene, and phenol. The aquatic
ecosystem contamination scenario
provides the framework for considering
the movement of chemicals from a
streambed up the water column and then
to the atmosphere, and also downward to
the ground water. The binary solvent
system was water and naphthalene, and
the tertiary was water, naphthalene, and
pentachlorophenol.
The scenario analysis exercise
amplified and reflected the findings of the
literature review By considering a series
of specific cases, the investigators could
realistically consider the case of high
chemical concentrations and what is
known or what can be reasonably
predicted, in general, only gross features
of mobility based upon density, solubility,
vapor pressure, etc. could be delineated.
The crude state of the science of fate
predictability for high chemical concen-
trations was made vividly apparent
through the scenario analysis.
Research Needs
In priority order, research is needed to
provide information on:
1. Microbial degradation rates and
microbial activity under stress
conditions in soil and water (eg.,
high chemical contaminant
concentrations and limited oxygen,
limited nutrients, and/or limited
microbial populations).
2. Abiotic transformations of
chemicals at high concentrations
and the effect of altered
environmental conditions on these
abiotic processes
3. Equilibrium sorption on soil and
bottom sediment of single organic
species, both polar and nonpolar, in
the high chemical concentration
range or at the solubility limit of the
chemical. The appropriateness of
various isotherm model formula-
tions needs to be evaluated.
4. Equilibrium sorption on soil of multi-
component organic mixtures with
the combined concentration of all
species at high concentrations in
the presence and absence of organ-
ic matter.
5. Formation, transformation, and
transport of organometallic che-
lates and complexes in soil and
sediment. The studies should also
include equilibrium sorption of high
concentrations of metals
6. Laboratory simulation of leachate
migration processes (e.g., density
stratification and two-phase flow)
for high chemical concentrations.
Model reformulation based on the
observed mechanisms to account
for density stratification and the
presence of two phases.
7. Vapor equilibrium sorption on "air-
dry" soils, including polar and
nonpolar species in single, binary,
and tertiary mixtures.
8. Vapor equilibrium sorption on moist
soils concerning the behavior of
equilibrium isotherms for water
contents between "air-dry" and ca.
10% water (5 bars).
9. Transport processes in unsaturated
soils including effective gas and
liquid phase diffusivities,
convection processes due to water
and gas movement, processes
driven by capillary forces, andtemp-
erature gradients.
10. The deposition and re-entrainment
of particles containing hazardous
chemical constituents in the
presence of fluid flow to cover both
air and water regions above earthen
surfaces.
11. Solubility for aqueous-organic
liquids characteristic of high chemi-
cal concentrations appropriate to
chemical waste landfill leachate.
Existing solution models should be
validated.
12. Vapor pressure for chemical waste
and organic sludge (e.g., cellulose,
biological, petroleum-petrochem)
mixtures of high chemical
concentration. Existing mixture
models should be validated
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L. J. Thibodeaux, D. C. Wolf, and M. Davis are with the University ol Arkansas,
Fayetteville, AR 72701.
G. W. Bailey is the EPA Project Officer (see below).
The complete report, entitled "Impact of High Chemical Contaminant Concen-
trations on Terrestrial and Aquatic Ecosystems: A State-of-the-Art Review,"
(Order No. PB 84-220 292; Cost: $13.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Athens, GA 30613
U S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7771
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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