United States
Environmental Protection
Agency
Assessment and
Management of
Toxics in the Watershed
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EPA/600/R-03/032
March 2003
Assessment and Management of
Toxics in the Watershed
by
Teri L Richardson
Land Remediation and Pollution Control Division
National Risk Management Research Laboratory
Cincinnati, Ohio 45268
Johnny Springer, Jr.
Sustainable Technology Division
National Risk Management Research Laboratory
Cincinnati, Ohio 45268
Nationai Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
/TV Recycled/Recyclable
Printed with vegetable-based ink on
paper that contains a minimum of
50% post-consumer fiber content
processed chlorine free.
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Notice
This document is a technical study that was prepared to aid research planning. It has been
reviewed in accordance with U.S. Environmental Agency (USEPA) policy and approved for publica-
tion Its contents do not necessarily reflect the views and policies of the EPA or of any other organi-
zation mentioned in this document. Mention of trade names or commercial products does not consti-
tute endorsement or recommendation for use.
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Foreword
The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation's
land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to
formulate and implement actions leading to a compatible balance between human activities and the
ability of natural systems to support and nurture life.To meet this mandate, EPA's research program is
providing data and technical support for solving environmental problems today and building a science
knowledge base necessary to manage our ecological resources wisely, understand how pollutants
affect our health, and prevent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for investigation of
technological and management approaches for preventing and reducing risks from pollution that threatens
human health and the environment. The focus of the Laboratory's research program is on methods and
their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface
resources; protection of water quality in .public water systems; remediation of contaminated sites,
sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosys-
tems. NRMRL collaborates with both public and private sector partners to foster technologies that
reduce the cost of compliance and to anticipate emerging problems. NRMRL's research provides
-solutions to environmental problems by: developing and promoting technologies that protect and im-
prove the environment; advancing scientific and engineering information to support regulatory and
policy decisions; and providing the technical support and information transfer to ensure implementa-
tion of environmental regulations and strategies at the national, state, and community levels.
This publication has been produced as part of the Laboratory's strategic long-term research plan.
It is published and made available by EPA's Office of Research and Development to assist the user
community and to link researchers with their clients.
Hugh W. McKinnon, Director
National Risk Management Research Laboratory
m
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Abstract
The demand for water is beginning to outstrip the available supply of water. The truly insidious
insult to freshwater supplies comes from anthropogenic impacts that pollute freshwater supplies and
the surrounding watersheds, making even less water available for use.
Watersheds are impacted by a variety of toxic substances. Some of these toxic pollutants enter
the watershed through direct introduction but by far the most serious problems of toxics found in the
nation's water supplies are created through indirect means. Many toxics are introduced into the water
supply through their movement through the biosphere. The more ubiquitous of these toxic substances
are mercury and pesticides. Challenges to managing the numerous risks posed by mercury in the
environment include: alternative treatment options for mercury contaminated wastes; in situ treat-
ment of mercury in sediments; identification and control of diffusive sources of mercury; and the fate
and transport of mercury in the watershed environment. Challenges to managing the numerous risks
posed by pesticides in the environment include: pesticide degradate and mixture characterization and
behavior; pesticide application and transport data; and reliability and effectiveness of pesticide occur-
rence modeling and pesticide management practices.
This paper summarizes the current state of knowledge on the toxic sources, their impact on
ecosystem and human health, discusses challenges to the successful management of. toxics, and
presents an outline of suggested management-related research for watersheds.
IV
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Contents
Notice ii
Foreword iii
Abstract ....iv
Acknowledgment vi
I, Introduction 1
II. Mercury 2
Background 2
Aquatic Ecosystem Effects 2
Atmospheric Transport and Fate 3
TerrestrialTransport and Fate 3
Management 4
Research Needs 4
NRMRL Research Objectives 5
III. Pesticides 7
Background 7
Atmospheric Transport 7
TerrestrialTransport 8
Fate 8
Environmental Impacts 9
Human Health Impacts 10
Management 10
Research Needs 10
IV. Bibliography 12
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Acknowledgments
The authors express their appreciation to the following persons who provided peer reviews of the
document:
Mr. Richard Brenner, Office of Research and Development, National Risk Management Research
Laboratory, Land Remediation and Pollution Control Division, Cincinnati, Ohio
Mr. Dennis Timberlake, Office of Research and Development, National Risk Management Re-
search Laboratory, Land Remediation and Pollution Control Division, Cincinnati, Ohio
VI
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I. Introduction
As part of EPA's mission to protect human health and the
environment, the National Risk Management Research
Laboratory's Watershed Management Team embarked upon
the development of information on key issues impacting the
health and viability of the nation's watersheds. As a result of
examining environmental impacts at the watershed level,
the watershed management team amassed a daunting list
of impacts to watersheds. It was determined that the list of
impacts could be categorized under five major issues: flow,
nutrients, toxics, sediments, and pathogens. Each of these
issues has been addressed by an individual document that
examines the human health and ecological impacts, man-
agement and control activities, and research needs regard-
ing the issue at the watershed level.
One of the major issues impacting watersheds is the sub-
ject of toxic substances or "toxics". Watersheds are impacted
by a variety of toxic substances. Some of these toxic pollut-
ants enter the watershed through direct introduction but by
far the most serious problems of toxics found in the Nation's
water supplies are created through indirect means. Many
toxics are introduced into the water supply through its move-
ment through the biosphere. Some of the main contributors
of contamination to watersheds are:
• Contaminated sediments
• Pathogens
• Mercury
* Disinfection By-Products
• Pesticides
• MTBE
• Metals
• Endocrine Disrupting Chemicals
• Synthetic Organic Chemicals
• Perchlorates
• Nitrates/Nitrites
Coverage of all of these toxic substances under one docu-
ment would be cumbersome. Also, EPA has well developed
research programs on many of these substances and the
Watershed Management Team is addressing contaminated
sediments, nutrients, and pathogens under separate papers,
As a result of these factors, this paper has been narrowed in
scope to cover the toxic substances mercury and pesticides.
Each toxic substance is examined according to the impact
that the pollutant has on aquatic and terrestrial systems and
the source of the pollutant. The human health effects of the
pollutant are also summarized. Following the discussion of
the sources and impacts of the pollutant, the management
controls that have been or can be deployed to remediate
and control the impact of the pollutant are described. Finally,
future research needs of the pollutant are addressed.
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II. Mercury
Mercury: Background
There is general agreement among researchers that the
amount of mercury being released into the atmospheric has
increased steadily since the dawn of the industrial era (U.S.
EPA, 1997). According to one estimate, approximately two-
thirds of the total world's yield of Hg has been produced
during the twentieth century, and anthropogenic inputs of Hg
to the environment have increased about 3-fold since 1900
(Fitzgerald, 1991),
The sources of the mercury emissions are broadly cat-
egorized as natural mercury emissions and anthropogenic
mercury emissions (U.S. EPA, 1997).The emissions of mer-
cury that are not specifically from current human activity nor
from truly natural sources are referred to as "recycled," or
"re-emitted," anthropogenic emissions.
Current theory suggests that a large part of the current
atmospheric mercury burden is in the form of a worldwide
background concentration composed almost entirely of el-
emental mercury (HgO) in gaseous form. Deposition from
the atmosphere to the earth's surface, however, involves
oxidized mercury. Natural and recycled anthropogenic emis-
sions are thought to be mostly in the form of HgO (Bullock,
1999). Anthropogenically emitted mercury is deposited (to
the oceans) as Hg(ll) and then reduced to volatile HgO and
re-emitted (U.S. EPA, 1997).
The primary sources of natural mercury emissions are
volcanic eruptions and volatilization or solubilization of mer-
cury from rocks, soils, and sediments; anthropogenic mer-
cury releases are thought to be dominated by industrial pro-
cesses such as chlorine alkali processing and metal pro-
cessing, and combustion sources that release mercury into
the atmosphere, including coal-fired power plants and mu-
nicipal and medical waste incinerators.The Expert Panel on
Mercury Atmospheric Processes (1994) estimated that the
anthropogenic emissions may account for 50-75 percent of
the total annual input to the global atmosphere (Expert Panel
on Mercury Atmospheric Processes, 1994). The estimates
of the panel are corroborated by Lindqvist et al., (1991), and
Porcella (1994) (U.S. EPA, 1997).
The re-emission of deposited mercury results most sig-
nificantly from the evasion of elemental mercury from the
oceans. This process could account for approximately 30%
of total mercury flux to the atmosphere (U.S. EPA, 1997).
Mercury also can contaminate land and water when it is
directly released in industrial waste waters, or when waste
containing batteries and other sources of mercury are dis-
posed of (U.S. EPA, 1997).
Given the present understanding of the mercury cycle,
the flux of mercury from the atmosphere to land or water at
any one location is comprised of contributions from the natu-
ral global cycle, the global cycle perturbed by human activi-
ties, regional sources, and local sources (U.S. EPA, 1997);
however, the knowledge of where mercury settles in the en-
vironment is incomplete; its source attribution and the de-
posited mercury's origin have proven difficult to quantify
(Hanisch, 1998). Ultimately, mercury ends up in the sedi-
ments, fish and wildlife, or evades back to the atmosphere
by volatilization (U.S. Geological Survey, 1995).
The effective risk management of mercury in watersheds
requires extensive knowledge about deposition and source
attribution within and among watersheds, atmospheric and
ground transport mechanisms, and the influence of the en-
vironment on chemical transformations. As one of several
research arms of the United States Environmental Protec-
tion Agency's (U.S. ERA) Office of Research and Develop-
ment (ORD), the National Risk Management Research Labo-
ratory (NRMRL) strives to conduct and direct research that
will further the understanding of mercury contamination and
management and provide to regulators and watershed man-
agers the information that can be used to make informed
risk reduction and management decisions.
Mercury: Aquatic Ecosystem Effects
The greatest concern with mercury pollution is methylm-
ercury (CH3Hg*), an organic form of mercury produced by
sutfate-reducing bacteria from inorganic mercury in both sedi-
ments and waters. The formation of methylmercury is the
most significant transformation because methylmercury is
far more toxic and bioavailable than any other form of mer-
cury. Methylmercury accumulates in the food chain and
reaches humans, other mammals, and birds through meth-
ylmercury-tainted fish (Rouhi, 2001), the consumption of
which is known to be the dominant pathway for exposure.
(U.S. EPA, 2001).The biological effects of exposure to mer-
cury at levels realistically found in ecosystems remain un-
certain; however, the pattern of mercury deposition nation-
wide influences which eco-regions and eco-systems will be
more highly exposed.
Methylmercury contamination now accounts for 78 per-
cent of the fish-consumption advisories in the United States.
Forty-one states had advisories attributed to mercury as of
1999, and the number of statewide fish-consumption advi-
sories issued for lakes, rivers, and coastal waters has in-
creased substantially in the last decade. Many waters with
contemporary fish-consumption advisories can be charac-
terized as lightly contaminated systems, and seemingly small
inventories or inputs of mercury can cause significant con-
tamination of fish (Wiener, 2001).
The factors that contribute to methylmercury
bioaccumulation in fish have been the topic of extensive
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research. Previously, it was suggested that a low pH and
relatively large amounts of dissolved organic carbon in the
water would increase the buildup in fish. More recently, this
suggestion has been challenged. Research conducted by
the Electric Power Research Institute (EPRI) found that al-
though there is some correlation between the concentration
of dissolved methylmercury in the water and increased lev-
els in the fish, it was not possible to explain the differences
in bioaccumulation solely on the basis of pH and dissolved
organic carbon. Other factors, such as the presence of chlo-
rophyll, sulfate, chloride, and calcium also appear to be at
least partly responsible for the differences in bioaccumulation
(Douglas, 1994). Also, the disturbance of wetland sediments
could facilitate mercury transport by changing oxidation
states, lowering pH, and resuspending sediment-bound mer-
cury complexes in the water column.
Mercury: Atmospheric Transport and Fate
The atmospheric pathway of the global mercury cycle is
known to be the key source of mercury contamination to
most threaten aquatic systems (Bullock, 1999), and although
much uncertainty still exists, several studies indicate that
the relative contribution of mercury loadings to land and water
from atmospheric deposition can be substantial.
Numerous studies of elevated mercury levels in remote
locations, where atmospheric transport and deposition ap-
pears to be the principal mechanism for contamination, pro-
vide further evidence of the importance of the atmospheric
pathway. It is also thought that any contributions from soils
also originate from the atmosphere (Sorensen et al., 1990).
The air transport and deposition patterns in the United
States for mercury emissions depend on various factors,
including the form of mercury emitted, the location of the
emissions sou rce, the stack height of the source, the topog-
raphy near the source, and the prevailing air circulation pat-
terns.
An understanding of the transport and oxidation of mer-
cury in the atmosphere is essential for predicting the impact
of emissions on deposition (Douglas, 1994), but despite de-
cades of research, the transformations of mercury in the
environment or when mercury is released directly to land or
water bodies are not fully understood (Rouhi, 2001; U.S. EPA,
2000). A significant barrier to this understanding is the diffi-
culty of separating current mercury concentrations by origin
because of the continuous cycling of the element in the en-
vironment. For example, anthropogenic releases of elemen-
tal mercury may be oxidized and deposit as divalent mer-
cury far from the source; the deposited mercury may be
reduced and re-emitted as elemental mercury only to be
deposited again continents away.
It is also difficult to make a direct connection between
emissions of any pollutant at one location and deposition at
another. Emissions from a particular source may spread over
a wide area and deposit in several watersheds. Several stud-
ies suggest links between atmospheric deposition and envi-
ronmental impacts; however, it is difficult to actually trace
most atmospheric pollutants into the food web because pol-
lutants that have been deposited through air deposition are
difficult to distinguish from those that entered the food chain
through other pathways. Modeling is typically used to make
these links (U.S. EPA, 2001).
These uncertainties have caused controversy over how
to control mercury emissions. Although the U.S. EPA ac-
cepts a plausible relationship between emissions from in-
dustrial sources and deposition, there is still a need for more
quantitative certainty about the amounts of mercury that are
locally deposited rather than globally dispersed (Hanisch,
1998). There is also a lack of reliable data about the specia-
tion of mercury, which contributes further to assessment.
Mercury: Terrestrial Transport and Fate
The atmospheric input of mercury to soil is thought to
exceed greatly the amount leached from soil, and the amount
of mercury partitioning to runoff is considered to be a small
fraction of the amount of mercury stored in soil. The affinity
of mercury species for soil results in soil acting as a large
reservoir for anthropogenic mercury emissions. Even if an-
thropogenic emissions were to stop entirely, leaching of
mercury from soil would not be expected to diminish for many
years (U.S. EPA, 1997), and according to a modeled sce-
nario that was constructed as part of a research effort on
northern Wisconsin lakes, it would take eight years before
any change in fish concentrations would be observed, and
the decrease would be small (U.S. Geological Survey, 1995).
An accurate assessment of the fate and transport of mer-
cury after it has been deposited on the land's surface is
inherently a complex task, owing to a vast number of inter-
action possibilities that can occur. Watersheds character-
ized by various land uses and soil types make it difficult to
delineate individual transport processes.
Once deposited, the Hg(JI) species are subject to a wide
array of chemical and biological reactions. Soil conditions
(e.g., pH, temperature and soil humic content) are typically
favorable for the formation of inorganic Hg(ll) compounds
such as HgCI2, Hg(OH)2 and inorganic Hg(ll) compounds
complexed with organic anions. Although inorganic Hg(ll)
compounds are quite soluble (and, thus, theoretically mo-
bile) they form complexes with soil organic matter (mainly
fulvic and humic acids) and mineral colloids; the former is
the dominating process. This complexing behavior greatly
limits the mobility of mercury in soil.
Much of the mercury in soil is bound to bulk organic mat-
ter and is susceptible to elution in runoff only by being at-
tached to suspended soil or humus. Some Hg(ll), however,
will be adsorbed onto dissolvable prganic ligands and other
forms of dissolved organic carbon and may then partition to
runoff in the dissolved phase (U.S.EPA, 1997).
Sediments also serve as a major repository for persistent
and toxic chemical pollutants, including mercury, released
into the environment. In the aquatic environment, chemical
waste products of anthropogenic origin that do not easily
degrade can eventually accumulate in sediments (Salomons
et. al., 1987). In most aquatic systems, the rapid and effi-
cient processes of sorption and settling scavenge hydro-
phobic organic contaminants from the water column, with
the result that the largest fraction of persistent trace con-
taminant inventories presently reside in sediments (Eadie)
The concentration of the contaminant in the sediments will
be highly site specific and dependent on the physical, chemi-
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cal, and biological factors affecting sediment-water exchange
(Medine,1989).
operative mercury efforts (U.S. EPA, 2000). Examples in-
clude:
Mercury: Management
The development of a variety of tools has led to better
understanding of mercury in the environment (Porcella, 2001).
For instance, models can be used to answer questions about
deposition rates and source attribution of mercury. And, al-
though models can be useful tools, the information derived
from them is reliant on the quality of the data and reason-
ableness of the assumptions that go into making them.There-
fore, the limitations and sensitivity of a model must be clearly
understood, and the model must be based on reasonable
data with known error margins and reasonable assumptions.
Other mercury management strategies have been imple-
mented as a result of regulations that have been enacted.
These strategies have stemmed the release of mercury from
primary sources during the past decade. It is estimated that
the eventual outcome of the regulations will reduce mercury
emissions from anthropogenic sources by more than 50%,
as compared to 1990 levels.
Actions for which impacts have been, or should be, real-
ized include:
EPA issued emission standards for medical waste incin-
erators
• EPA issued emission standards for hazardous waste
combustors, including incinerators, cement kilns, and
light weight aggregate kilns
• EPA Draft Action Plan which prescribes actions to re-
spond to the public's right to know about sources of
mercury emissions, integrate EPA's actions under its
various programs to address mercury, emphasize pollu-
tion prevention and efficient use of resources to control
mercury emissions, and foster communication and co-
operation among all stakeholders in developing strate-
gies to control mercury.
Actions to control air emissions of other pollutants will
also reduce mercury emissions. The implementation of the
National Ambient Air Quality Standards for fine particulate
matter and ozone, and the second phase of the acid rain
program could result in a reduction of mercury emissions
from utility boilers. Similarly, actions to reduce emissions of
the greenhouse gases could also reduce mercury emissions
from utilities and other industrial boilers, whereas the Land
Disposal Restrictions for Mercury-bearing Hazardous Wastes
will re-evaluate land disposal restrictions on mercury to con-
sider alternatives to mercury recovery and incineration (U.S.
EPA, 1997; U.S. EPA, 2000).
Although these actions affect mercury emissions from the
major sources, the scope of the impact will be limited in that
they apply only to facilities that operate within the continen-
tal United States.To stem the release of mercury nationwide
will require a focused and concerted effort among the af-
fected nations.
A number of bilateral and multilateral programs offer the
United States an opportunity to promote and engage in co-
• The Great Lakes Binational Toxics Strategy, signed by
the United States and Canada seeks a 50 percent re-
duction in the deliberate use of mercury and a 50 per-
cent reduction in the release of mercury caused by hu-
man activity by 2006.
• The United Nations Economic Commission for Europe
negotiated a leally binding protocol on mercury and other
metals, which includes obligations to control mercury
emissions from stationary sources and to establish, up-
date, and report mercury emission inventories.
• The Arctic Environmental Protection Strategy, which is
implemented through five working groups, is responsible
for monitoring the levels and assessing the effects of
selected anthropogenic pollutants in all compartments
of the Arctic.
Mercury: Research Needs
Mercury-related research, as it applies to watersheds, can
be broadly grouped into the following categories: risk char-
acterization, fate and transport, management, and restora-
tion; as well as implementation of TMDLs.
Within the ORD, several laboratories are actively pursuing
mercury research, each with a different focus.The National
Exposure Research Laboratory (NERL) provides research
information on stressor sources; pollutant transport, trans-
formations and exposure; and source-to receptor predictive
exposure models applicable to the appropriate temporal
scales and to site, watershed/regional and global scales.
The National Center for Environmental Assessment (NCEA)
research activities are focused on developing and evaluat-
ing model-based methodologies and techniques to improve
the risk assessor's ability to synthesize, put into context
and use exposure and effects data in risk assessment.The
National Health and Environmental Effects Research Labo-
ratory (NHEERL) provides scientific research on the effects
of contaminants and environmental stressors on human
health and ecosystem integrity. The National Risk Manage-
ment Research Laboratory conducts research to reduce risks
from pollution that threaten human health and the environ-
ment.
To contribute to the further advancement of mercury re-
search and to improve the fundamental understanding of the
behavior of mercury in the watershed environment, future
research efforts should build upon the existing database of
knowledge, leverage resources where applicable, and be
conducted cooperatively when feasible.
The mercury transformations that occur in air, water, and
on land and methylmercury's accumulation in fish, wildlife,
and humans (based on the fish ingestion exposure pathway)
present a set of scientific and technical challenges for both
regulators and researchers. The priority mercury research
efforts, which will address some of the current challenges,
include developing methods that accurately characterize
mercury sources and the species of mercury released from
those sources; understanding mercury transport and the
transformations that occur in the air and water and on land;
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assessing mercury exposures to and effects on humans
and ecosystems; developing cost-effective ways to man-
age risks from mercury sources and sinks; and understand-
ing mercury cycling through air and water so that it is pos-
sible to predict how quickly changes in mercury sources
emissions can appear in receiving waters and fish (U.S. EPA,
2000; Shick, 2000).
In addition, it is important to establish whether or not a
reduction in mercury emissions directly corresponds to a
reduction of methylmercury in fish. As noted by the U.S.
EPA in its 1998 Report to Congress, the quantitative nature
of the relationship between power plant emissions and fish
methylmercury remains a. key uncertainty that must be re-
solved before the United States can adopt mercury man-
agement practices with predictable outcomes.
The prioritized research needs on the transport, transfor-
mation, and fate of mercury include enhanced monitoring of
atmospheric mercury deposition for model application, im-
proved understanding of the transport, transformation, and
fate of mercury in the aquatic and terrestrial media, and en-
hanced monitoring of mercury and methylmercury in the
aquatic and terrestrial media for improved risk management.
There is also a clear need for atmospheric models to be
used in the development of emissions limits to protect water
quality, human health, and ecological health (U.S. EPA, 2000).
Research activities are also needed that will bolster the
current mercury management strategies have been planned
and implemented by the U.S. EPA and other interested orga-
nizations. The scope of these research activities include 1)
evaluation of control technologies, 2) development of pre-
diction models to estimate stack-emitted mercury concen-
trations in the air, water, and soil, and 3) assessments to
examine the health and environmental effects of mercury
exposure (U.S. EPA, 1997).
Mercury: NRMRL Research Objectives
NRMRL has current research activities in various aspects
of the environmental impacts of mercury.
Whereas other research activities are more focused on
command and control or accounting, emphasis here is on
risk management related research that is within the scope
of the mission of NRMRL and part of the Laboratory=s re-
search plan for watershed management.
Based on the current needs and data gaps, priority re-
search areas for the NRMRL should include the evaluation
of alternative treatment options for mercury contaminated
wastes, in situ treatment of mercury in sediments, identifi-
cation and control of diffusive sources of mercury, and the
fate and transport of mercury in the watershed environment.
Critical areas of research involving mercury impaired waters
and watersheds yield research questions such as those out-
lined in this section.
* Can available models accurately predict the fate and
transport of mercury in a watershed? If riot, to what
extent do the models fail to predict the impacts of mer-
cury-contaminated sediments and mercury in mixed
land-use watersheds?
• To what extent can the existing watershed models be
modified to better serve the needs of water quality plan-
ners, specifically for the implementation of mercury-re-
lated total maximum daily loads (TMDL)?
As the U.S. EPA and state pollution control agencies have
increasingly emphasized watershed-based assessment and
integrated analysis of point and non-point sources, model-
ing has been used extensively to evaluate a wider range of
pollutant transport and environmental response issues.The
models are applied to answer a variety of questions, sup-
port watershed planning and analysis, and develop TMDLs.
One challenge faced by water quality managers is the lack
of integrated, scientifically sound approaches to identify prob-
lems in watersheds and to predict the results of potential
control actions on receiving water quality and aquatic habi-
tat. Developing a TMDL implies establishing a known cause-
and-effect relationship.The relationship between cause and
effect is often complex, and involves the interaction of point
and non-point sources, hydraulics, sediment transport, and
water quality. The mathematical models can provide a pre-
dictive capability which aids in determining TMDLs based
on establishing cause-and-effect relationships and address-
ing multiple stressors and interrelation within watersheds.
The focus of this research should be on the determination
of the state-of-science for watershed modeling as it pertains
to the assessment of mixed land-use watersheds, develop-
ment of modeling tools, improvement of modeling capabili-
ties, and to provide technical support and training.
The critical risk management areas for which there is cur-
rently no modeling capability should also be determined and
areas for which additional research would be beneficial should
be identified.
• What is the effectiveness and efficacy of the manage-
ment alternatives for the control of diffusive sources of
mercury?
• Can a plausible correlation between the reduction of
mercury through the alternative management options and
the reduction of methylmercury production?
Metals and mercury, in particular, are a major cause for
impairment of surface water bodies. The top four causes of
impairments include sediments, pathogens, nutrients, and
metals. These four sources of impairment result in half the
impairments nationwide, with metals comprising about a
fourth of these impairments. Mercury is the primary metal of
concern.
Three areas should be researched: an evaluation of exist-
ing best management practices, and, as necessary, the
modification of available models, landscape characteriza-
tion methods, or classifications schemes, and field evalua-
tions of mercury control techniques.
A comprehensive review of best management practices
(BMP) available for mercury reduction and/or control should
be conducted.These practices can include the evaluation of
waste disposal methods to riparian control techniques. Sub-
sequently, an evaluation of existing models, landscape char-
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acterization methods, and classification schemes for as-
sessment of mercury from diffuse sources. Afterwards,
modifications might be made to the models/methods to ad-
dress risk management approaches in controlling mercury.
• What is the effectiveness and efficacy of the manage-
ment alternatives for both the treatment of mercury-con-
taminated wastes and sediments?
The U.S. EPA Office of Solid Waste has deemed alterna-
tive technology research and demonstration as one of it's
priorities. Also of concern is the ultimate disposal of mer-
cury stockpiles and the approaches for the management of
mercury in sediments.
Data show that the solubility of mercury can increase un-
der certain landfill conditions. Currently, there is not an ac-
ceptable stabilization process that can permanently immo-
bilize mercury for disposal. The U.S. EPA is considering the
feasibility of requiring a macroencapsulation step in addition
to a stabilization process, prior to landfill. The performance
of macroencapsulation methods, including long term perfor-
mance, should be evaluated for selected mercury-bearing
wastes.
Thousands of tons of stockpiled excess mercury and
mercury-bearing wastes remain as a legacy of it's industrial
production. The long term management of these sources
remains a major challenge to environmental risk managers.
Also, the decommissioning of mercury cell chlor-alkali plants
remain a significant source of secondary mercury. NRMRL
will assess the alternatives for mercury storage and retire-
ment.
With regard to the management of mercury in sediments,
three approaches are available: capping, in-situ methods,
and dredging followed by confinement or treatment. NRMRL
has an established contaminated sediments research pro-
gram and many of its research findings for metals are appli-
cable to mercury. However, research is needed on in-place
management of mercury-contaminated sediments that fo-
cuses understanding and enhancement of processes that
sequester mercury from the food web.
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III. Pesticides
Pesticides: Background
A pesticide is any substance or mixture of substances
intended for preventing, destroying, repelling, or mitigating
any pest. Pests can be insects, mice and other animals,
unwanted plants (weeds), fungi, or microorganisms like bac-
teria and viruses. Though often misunderstood to refer only
to insecticides, the term pesticide also applies to herbicides,-
fungicides, and various other substances used to control
pests. Under United States law, a pesticide is also any sub-
stance or mixture of substances intended for use as a plant
regulator, defoliant, or desiccant.
By their very nature, most pesticides create some risk of
harm to humans, animals, or the environment because they
are designed to kill or otherwise adversely affect living or-
ganisms. At the same time, pesticides are useful to society
because of their ability to kill potential disease-causing or-
ganisms and control insects, weeds, and other pests. In the
United States, the Office of Pesticide Programs of the U.S.
EPA is chiefly responsible for regulating pesticides.
In the United States in a typical year, about 4.5 billion
pounds of chemicals are used as pesticides (measured on
the basis of active ingredient). For 1997, the quantities used
are estimated, by type of pesticide, as shown in Table 1.
Conventional pesticides and "other pesticide chemicals"
(e.g., sulfur, petroleum, etc.) account for about one-fourth of
the total pesticide active ingredient used in the United States
(1.23 billion pounds or 27 percent of the total). A majority of
these pesticides are used in agriculture to produce food and
fiber (77 percent or 944 million pounds of active ingredient in
Table 1. Estimated Pesticide Usage in the United States
Type
Conventional pesticides
Other pesticide chemicals (suKur,
petroleum, etc.)
Subtotal
Wood preservatives
Specialty biocides
Chlorine/hypochlorites
TOTAL
Ibs (billions)
.97
.26
1.23
.66
.27
2.46
4.62
%
21
6
27
14
6
53
100
1997), with the remainder used in industry/government ap-
plications and by homeowners. With usage of 1.23 billion
pounds (for conventional pesticides plus other pesticide
chemicals), the United States accounts for about one-fourth
of such usage world wide. Chlorine/hypochlorites are the lead-
ing type of pesticides in the United States, with half of the
United States total usage. Wood preservatives and specialty
biocides make up the remainder of the United States total of
4.63 billion pounds in 1997. The above quantities equal 4.6
pounds per capita in the United States for conventional pes-
ticides plus sulfur, etc., and 17.0 pounds per capita for the
total of all types. The most widely used pesticide in United
States agricultural crop production by volume is the herbi-
cide atrazine.The herbicide 2,4-D has the largest volume of
usage in the nonagricultural sectors. (U.S. EPA, 1999)
Urban/suburban pesticide sources may include mainte-
nance of residential yards, cemeteries, golf courses, con-
struction sites, schoolyards, and roadsides, as well as ex-
termination of cockroaches and termites. For example, atra-
zine and simazine have been used for controlling weeds
along roadways (Pitt et al., 1996) In particular, lawn applica-
tions by residential homeowners are a major concern. Us-
age of conventional pesticides by homeowners is estimated
at 76 million pounds for 1997 (U.S. EPA, 1999).
According to a U.S. EPA fact sheet (Wild Ones Hand-
book: Today's Lawns), the National Academy of Sciences
(NAS) believes that lawn use is "a significant component of
the total pesticide program." Although usage estimates from
the U.S. EPA Office of Pesticide Programs show that the
overwhelming majority of pesticide use is for agricultural pur-
poses, the NAS states that homeowners use "...10 times
more per acre than do farmers", suggesting a potential for
high pesticide impacts in streams drained by urban areas.
Pesticides: Atmospheric Transport
The atmosphere is an important part of the hydrologic
cycle that can transport pesticides from their point of appli-
cation and deposit them outside the area or basin of inter-
est. Nearly every pesticide that has been investigated has
been detected in air, rain, snow, or fog throughout the coun-
try at different times of year. Annual average concentrations
in air and rain are generally low, although elevated concen-
trations can occur during periods of high use, usually in spring
and summer months. Several instances have been recorded
in which concentrations in rain have exceeded drinking-wa-
ter standards foratrazine, alachlor, and 2,4-D. Atmospheric
contributions are most likely to affect stream quality during
periods when direct precipitation and surface runoff are the
major sources of streamflow.
-------
Finding agricultural herbicides like alachlor, atrazine and
cyanazine in urban stormwater may seem surprising since
these herbicides are not used in lawn and garden compounds.
However, U.S. Midwest studies suggest that concentrations
of atrazine in urban stormwater are consistent with concen-
trations found in rainfall. Both atrazine and alachlor easily
evaporate from treated farm fields and later end up in rainfall
or snow. Atrazine contamination of rainfall is more widespread
than alachlor contamination because atrazine is more widely
used and more persistent in the environment.
The detections in urban areas of alachlor (albeit at a con-
centration of less than 0.01 ug/L) and cyanazine, herbicides
with no known uses in nonagricultural settings, may have
been the result of historical use, atmospheric deposition, or
transport of the herbicides from nearby application areas,
either in the air (through spray drift) or in ground water. The
other three agricultural herbicides detected in the urban ar-
eas (atrazine, simazine, and metolachlor) may also have
entered the shallow ground water by atmospheric or subsur-
face transport from nearby agricultural applications. Indeed,
recent detections of alachlor, atrazine, cyanazine, and
metolachlor in rainfall and stormwater runoff in a small urban
watershed in Minneapolis, Minnesota, where none of these
compounds had been applied (Capel et. al, 1998), demon-
strate that agricultural pesticides may.be carried by atmo-
spheric transport from nearby application areas into a water-
shed where they have not been used. However, because
atrazine, simazine, and metolachlor are also used for nona-
gricultural purposes, the possibility that some of the detec-
tions of these compounds in the urban areas during the USGS
National Water Quality Association Land Use studies
(NAWQA LUS) could have resulted from their nonagricuf-
tural use near the sampled areas cannot be ruled out.
Pesticides: Terrestrial Transport
Intensive pesticide use appears to be a necessary but not
a sufficient condition for encountering high frequencies of
pesticide detection in groundwater.The wider ranges in pes-
ticide detection frequencies observed at higher use are pre-
sumed to reflect the varying influence of other factors in
addition to use in governing pesticide detection rates among
different areas (e.g., soil properties, hydrogeology, and re-
charge rates) Soil permeability and intensive irrigation are
two factors known to facilitate the movement of pesticides
to groundwater. Pesticide application spray drift is another
method by which pesticides may contaminate surface wa-
ter.
The soil organic carbon partition coefficient (KJ, a mea-
sure of the tendency of a compound to partition into soil
organic carbon from aqueous solution, provides a quantita-
tive, inverse indication of its anticipated mobility in ground
water. Water solubility is often invoked as a measure of the
relative likelihood of pesticides to be detected in ground water.
Water solubility is less appropriate for this purpose than Koc,
however, because unlike the latter parameter, water solubil-
ity does not account for sorptive interactions between the
comppund and solid-phase organic matter in the subsurface
(Barbash and Resek, 1996). Henrys law constant quantifies
the relative degree of partitioning between gas and aqueous
phases in the unsaturated zone.
As is the case for other surface-derived contaminants,
the hydrogeologic factors that influence the movement of
pesticides to ground water are primarily those that control
the movement of water. Thus, pesticide detections in shal-
low ground water tend to be more common in areas with
permeable soils than in areas covered by glacial tills, clays,
and other low -permeability geologic materials. In addition,
higher levels of organic carbon in soils and other subsurface
materials may diminish the likelihood of pesticide contami-
nation of ground water by slowing pesticide migration (through
sorption) and, for compounds susceptible to bio- transfor-
mation, by enhancing microbial activity. Pesticide detections
generally are more common in unconsolidated and solution-
weathered (karst) aquifers than in relatively unweathered bed-
rock aquifers. Unconfined aquifers are more susceptible to
contamination than those that are confined. In general, pes-
ticide contamination tends to be more likely, and more tem-
porally variable, in shallow ground water than in deep ground
water (Barbash and Resek, 1996). Ground water in alluvial
aquifers associated with rivers carrying substantial pesti-
cide loads often contains detectable levels of pesticides par-
ticularly where the infiltration of the river water is enhanced
by the pumping of nearby wells.
Pesticides: Fate
Pesticide contamination of groundwater is an issue of na-
tional importance in the United States because groundwater
is used for drinking water by about 50% of the population
(Kolpin, et. al., 1998) Pesticides rank 12th on the list of top 16
causes of impairments to waterbodies based on the 1998
Clean Water Act 303(d) List.
The highest concentrations of pesticides in groundwater
are expected to be present at the water table. Pesticide con-
centrations may be undesirable because of (i) contamina-
tion of downstream public water supplies such as reservoirs;
(ii) the economic loss suffered by farmers who lose fertilizer
and pesticides to the stream; (iii) potential stresses on fish
communities; and (iv) eutrophication of downstream surface
waters. Tile drains and surface runoff have been shown to
be important pathways for migration of pesticides from agri-
cultural fields to surface waters. High concentrations of her-
bicides may occur in surface runoff during spring rains fol-
lowing herbicide application.
Physical and chemical properties of pesticides have been
used to examine their relations to the detection of these
compounds in groundwater. The four parameters that have
been used most frequently for this purpose are K which
describes the partitioning of organic compounds between
water and soil organic carbon; Henry's law constant, which
characterizes the partitioning between the aqueous and gas
phases; water solubility, which provides an estimate of the
maximum aqueous concentration likely to be encountered;
and soil dissipation half-life, which serves as a rough indica-
tor of persistence in situ.
All other factors being equal, the likelihood of detecting
one pesticide in ground water compared to another is' di-
rectly related to the degree of partitioning into the aqueous
-------
phase, relative to soil organic matter or soil gas (which, in
turn, affects relative mobility in the aqueous phase), and the
relative resistance to chemical transformation in soil, with or
without mediation by microorganisms.
Pesticides break down to other compounds over time in
the natural environment. Little is known about the occur-
rence of breakdown products, or their possible health and
environmental effects. Frequent detections of some break-
down products, however, indicate the need for their consid-
eration in the development of water-quality standards and
monitoring strategies.
The parameter used most commonly to quantify the envi-
ronmental persistence of pesticides in soil is the field dissi-
pation half-life, which represents the amount of time required
for the concentration of a compound measured in a field soil
to decrease to half of its initial value. Despite its widespread
use, however, this parameter is of only limited utility for un-
derstanding the rates and mechanisms of the underlying pro-
cesses responsible for dissipation in soil because it does
not distinguish between decreases in concentration caused
by the actual transformation of the parent compound and
those caused by its transport away from the site of mea-
surement in air, ground water, or surface water (Barbash and
Resek, 1996). Aerobic soil half-lives are measured in a labo-
ratory and, thus, are less representative of field conditions
than the field dissipation half-life. However, because aerobic
soil half-lives are measured under conditions that are con-
siderably more controlled and standardized and unaffected
by offsite transport comparisons among different compounds
and different studies are more reliable for aerobic soil half-
lives than for field dissipation half-lives, the time scales of
transformation of these herbicides in aerobic soil may vary
from weeks to years.
According to Gilliom et al. (1999), pesticides were com-
monly found in low-level mixtures. Stream water annual av-
erages seldom exceeded drinking water criteria (nor did
samples from wells). But the criteria only covers 43 com-
pounds and a limited range of effects. Most studies of pes-
ticides in surface water and groundwater have focused on
pesticide detection. But degradation products of pesticides
may be as toxic as the parent compound if not more so. A
study in Iowa (Kolpin et al., 1998) examined municipal wells
for agricultural pesticides and their degradates. If the
degradates were included in determining the pesticide con-
centrations, the authors found that the degradates can make
up a large (up to 90%) percentage of the total concentration.
Thus, the absence of a pesticide in the groundwater does
not guarantee that the compound is gone if the degradation
products have not been analyzed.
It is reasonable to suppose that the more intensively a
pesticide is used in a given area, the more likely it is to be
detected in groundwater, but the evidence in support of this
hypothesis is remarkably sparse (for example, Barbash and
Resek, 1996; Kolpin et. al, 1998). This may, in part, be a
consequence of the limitations in the spatial and temporal
resolution of the data currently available on pesticide use in
the U.S. At present, the finest scale at which pesticide use
information can be obtained across the Nation is on a
countywide basis, and only for their applications within agri-
cultural settings. Data on nonagricultural pesticide use are
considerably more limited and are available only at a na-
tional scale.
The predominance of atrazine relative to prometon in shal-
low ground water beneath agricultural areas is consistent
with the primarily agricultural use of atrazine, whereas the
predominance of prometon relative to atrazine in the urban
areas reflects the primarily nonagricultural use of prometon.
The relatively common occurrence of prometon in agricul-
tural settings, however, suggests that pesticide applications
for nonagricultural purposes such as for treating pavement,
fence rows, rights-of-way, and other commercial and resi-
dential areas may still be relatively extensive in agricultural
areas. The similarity in simazine detection frequencies be-
tween the agricultural and urban areas is consistent with
the fact that the nationwide use of this herbicide in nonagri-
cultural settings is nearly as high as in agricultural locations.
Atrazine residues were detected more frequently than any
other pesticide compounds. The widespread detections of
atrazine residues in groundwater were likely to have been
the combined result of the comparatively slow rate of atra-
zine transformation under environmental conditions and the
extensive long term use of the herbicide in both agricultural
and nonagricultural settings in this country. Indeed, atrazine
has been the pesticide used most extensively in the United
States since the early 1970s (Kolpin, et al, 1998).
Prometon is used primarily for nonagricultural purposes;
such as domestic and commercial applications to driveways,
fence lines, lawns, and gardens and as an asphalt additive
(Kolpin, et al, 1998). Prometon was the pesticide most fre-
quently detected in urban settings and third most detected
parent compound overall. Research has documented a di-
rect relationship between urban-residential land use and
prometon detections in groundwater as well as in surface
water(Kolpin, etal, 1998).
Pesticide results from 41 land use studies conducted dur-
ing 1993-1995 indicate that pesticides were commonly de-
tected in shallow groundwater, having been found in 54.4%
of the 1034 sites sampled in agricultural and urban settings
across the United States. Pesticide concentrations were gen-
erally low with over 95% of the detections at concentrations
less than 1 ug/l. The compounds detected most frequently
were atrazine (38.2%), deethylatrazine (34.2%), simazine
(18.0%), metolachlor (14.6%), and prometon (13.9%).
Pesticides were commonly detected in both agricultural
and urban settings. Urban and suburban pesticide use sig-
nificantly contribute to pesticide occurrence in shallow ground-
water.
Pesticides: Environmental Impacts
Common lawn and garden insecticides such as diazinon
and malathion may not be persistent in the environment, but
they are toxic to bees, fish, aquatic insects, and other wild-
life. Diazinon is especially toxic to birds. It has been banned
from golf courses because there are documented cases of
waterfowl dying while feeding on areas treated with diazinon.
There is a continuum in the movement of water, solids,
and solutes (e.g., atrazine) from a terrestrial environment,
such as an agricultural field, through a surface water sys-
tem and eventually to the marine environment. In 1996,2,193
-------
fish consumption advisories were issued in 48 states. Mer-
cury, PCBs, chlordane, dioxin, and DDT were responsible
for almost all fish consumption advisories in 1996 (U.S. EPA,
1998).
Evidence has accumulated to demonstrate that pesticides
are routinely present in streamwater and groundwater asso-
ciated with urban/suburban settings. A synthesis of National
Water-Quality Association (NAWQA) results from across the
United States (Gilliom et al., 1999) details pesticide find-
ings. The authors report the unsettling results that pesti-
cides were found in almost every stream sampled, and in
50% of wells sampled; the study sites included urban land-
use areas. It found that herbicide concentrations are highest
in agricultural areas and insecticides are highest in urban
areas.The common herbicides in urban areas are simazine,
prometon, 2,4-D, diuron, and tebuthiuron.The most common
insecticides in urban locales are diazinon, chlorpyrifos, car-
baryl, and malathion.
Maximum Contaminant Levels (MCLs) established by the
U.S. EPA do not cover pesticide degradates, and at present
do not take into account additive or synergistic effects of
combinations of pesticide compounds or potential effects
on nearby aquatic ecosystems.
Pesticides: Human Health Impacts
Laboratory studies show that pesticides can cause health
problems, such as birth defects, nerve damage, cancer, and
other effects that might occur over a long period of time.
However, these effects depend on how toxic the pesticide is
and how much of it is consumed. Some pesticides also pose
unique health risks to children.
For these reasons, the Federal Government, in coopera-
tion with the States, carefully regulates pesticides to ensure
that their use does not pose unreasonable risks to human
health or the environment. In particular, the Federal pesti-
cide program is designed to ensure that these products can
be used with a reasonable certainty that they will pose no
harm to infants, children, and adults (U.S. EPA, 2000).
Pesticides: Management
Prevention
For many pests, alternatives to the use of traditional chemi-
cal products are available that are equally effective and are
cost-competitive with chemical control methods. Integrated
Pest Management programs have been put in place in some
cases, using natural biological predators to keep pests un-
der control without using pesticides. The need for chemical
pesticides can be reduced through careful selection of pest
resistant vegetation, plant and hardware selection to mini-
mize requirements for irrigation, best mowing practices, and
planned elimination of pest habitats (e.g., standing water
that may attract mosquitoes, cracks and crevices in struc-
tures that will admit and harbor cockroaches). Best manage-
ment practices have been developed to utilize less toxic
pesticide alternatives wherever possible. Facility design and
operational procedures are developed to accommodate pest
management practices that are less susceptible to offsite
transport of chemicals, such as pesticides and fertilizers,
thereby reducing the potential for groundwater contamina-
tion. Less persistent pesticides are used in concert with spot
application techniques and minimum application levels. Bio-
logically-based pesticides, such as pheromones and micro-
bial pesticides, are becoming increasingly popular and often
are safer than traditional chemical pesticides.
Control
The storage, handling, and use of pesticides can lead to
environmental degradation through the interaction of incom-
patible chemicals due to improper storage, expiration of
materials (which subsequently become wastes), spills and
other uncontrolled releases, employee exposure to toxic
chemicals, and pesticide runoff into environmentally sensi-
tive areas. Pesticide inventory and control practices have
been implemented to avoid the need to handle pesticides as
waste and to limit uncontrolled releases of pesticides. Safe
mixing techniques include ensuring that pesticides are mixed
in clear and open areas that can be easily cleaned and avoid-
ing mixing upstream from waterbodies (including drains lead-
ing to surface water bodies and groundwater aquifers). Other
techniques include mixing the least amount of pesticide pos-
sible and using closed mixing systems that reduce the po-
tential for release and exposure. Facilities are advised to
have a pesticide spill prevention and control plan. Employee
education and awareness programs are being developed to
ensure employees understand the optimal situations for pes-
ticide use.
There are technologies in place that minimize the amount
of pesticide applied by using proper orifice spray nozzles at
the correct pressure to minimize the amount of pesticide
needed to treat a given area. The technologies also control
pesticide droplet size and deposition. Pesticide runoff can
be reduced by using row banding application techniques to
limit the amount of pesticides applied, using contact pesti-
cides that do not have to be incorporated into the sod, and
not spraying in potentially sensitive areas.
The residuals resulting from the use of pesticides, such
as wastewater and empty pesticide containers, must be prop-
erly managed to ensure that the environment is not nega-
tively affected. Options to reduce the volume of this waste
stream include purchasing products in bulk, refutable or re-
turnable containers, and products with water soluble pack-
aging. Federal regulations require rinsing empty pesticide
containers at least three times before disposal. Pesticide
containers must not be buried or burned, even after triple-
rinsing. Rinsed containers can be disposed of at a sanitary
landfill or often may be returned to the supplier for reuse.
Reusable containers reduce the need for rinsing and dis-
posal. Pesticide-contaminated rinse waters can be used in
future pesticide mixing and application as an alternative to
disposal, or can be applied in onsite landscape applications.
Pesticides: Research Needs
Significant advances in pesticide-related research have
been made. The research, which has been conducted by the
U.S. EPA Office of Pesticide Programs, ORD, universities,
the private sector, and other federal organizations, has cov-
ered a variety of topics.
10
-------
Within ORD, several laboratories are currently involved in
pesticide research. NCEA is currently researching a spatial
approach to non-point sources of pesticides in surface wa-
ters as part of its pesticide research efforts. NERL is focus-
ing on pesticide exposure assessment, surface water hy-
drology, and constituent transport. NHEERL is conducting
research investigating the impact of pesticide exposure on
children and the laboratory is also investigating the ecosys-
tem effects of pesticide contamination. NRMRL is involved
in collaborative pesticide research efforts with the other labo-
ratories and also is investigating the improvement of pesti-
cide spray application technology to reduce spray drift of
pesticides during application.
To contribute to the further advancement of pesticides re-
search and to improve the fundamental understanding of the
behavior of pesticides in the watershed environment, future
research efforts should build upon the existing database of
knowledge, leverage resources where applicable, and be con-
ducted cooperatively when feasible.
As a result of a review of current research activities in the
area of pesticide impacts on watersheds, it was discovered
that the pesticides of most concern in the contamination of
watersheds are atrazine, simazine, cyanazine, metalochlor,
alachlor, 2,4 D (2,4 Dichlorophenoxy Acetic Acid), diazinon,
chlorpyrifos, prometon. Research focused on these pesti-
cides would address the impacts they have on both surface
and groundwater.They would also address the impacts of
pesticides on agricultural watersheds and urban/suburban
watersheds.
For pesticide degradate and mixture characterization and
behavior, not enough is known about additive or synergistic
effects when more than one pesticide is present. Also, not
much is known about low-level long-term exposure with
pulses. Pesticide degradation products present an additional
concern.The National Research Council (NRC) echoes this
sentiment in it's 1998 book Identifying Future Drinking Water
Contaminants by concluding that "polar degradates of herbi-
cides are increasingly important." Research questions in-
clude:
• What are the degradation products of pesticides?
• What are the effects of low-level long term exposure to
pesticides?
• What are the synergistic effects when more than one
pesticide is present in water?
Research in this area would improve our understanding of
the impacts of mixtures of pesticides on human health and
the environment by generating sound scientific data on health
and environmental effects of degradation products of pesti-
cides. This data should seek to delineate the transformation
process that results in the creation of degradates. The data
should also provide information on the toxicity of degradates
and various pesticide mixtures to ecosystems and human
health.
Mixtures of contaminants also require special consider-
ation in assessing possible health and environmental effects,
and thus in developing and improving water-quality standards.
More than one-half of all stream samples contained five or
more pesticides, and nearly one-quarter of groundwater
samples contained two or more.These mixtures of pesticide
parent compounds also occur with breakdown products and
other contaminants, such as nitrate. Continued research is
needed to help reduce the current uncertainty in estimating
risks from commonly occurring mixtures. As improved infor-
mation is accumulated, the occurrence of contaminant mix-
tures should be considered when developing water-quality
standards and monitoring requirements.
For pesticide application and transport data, improved data
is needed on the amounts of pesticides applied and areas
treated particularly in the case of pesticides used in urban/
nonagricultural settings. Understanding the mechanisms of
pesticide and N transport is crucial to understanding the
occurrence, distribution, and concentrations of agrichemicals
in the water resources. Research in this area should collect
data to better understand the air deposition of pesticides
within watersheds. Also, more comprehensive monitoring is
needed of pesticides during hydrologic events. Without moni-
toring information during major hydrologic events, a full ac-
counting of nutrients and pesticides transported by streams
is incomplete, and a full understanding of the effects of these
contaminants on the health and living resources of receiving
waters is restricted.
NRMRL research should focus in three areas:
• Control of Pesticides in watersheds as an alternative to
drinking water treatment
• Pesticide Application/Transport Data
• Reliability and Effectiveness of Pesticide Occurrence
Modeling and Pesticide Management Practices
For reliability and effectiveness of pesticide occurrence
modeling and pesticide management practices, quantifying
nonpoint pollutant sources is challenging because they are
diffuse, transient, and highly variable site to site, within a
runoff event and among different events.Therefore, there is
a need to rely on estimation techniques and models to quan-
tify these pesticide sources. Improvement in the science on
the mechanisms of degradation, fate, andjransport of pes-
ticides into surface waters and groundwater and their im-
pacts on the watershed and its and the ecosystems should
provide supportive data for the development of improved
watershed models. The U.S. EPA, for example, is using
NAWQA pesticide data to test the reliability of models now
being used to predict possible pesticide occurrence in
streams and reservoirs. Water-quality models have been in
use for many years, but their utility depends on their reliabil-
ity for representing actual conditions. Without demonstrated
reliability based on comparisons to measured conditions,
confidence in a model is difficult to attain, and the useful-
ness of the model in decision making, especially in contro-
versial situations, is limited.
Development of data on the impact and effectiveness of
pesticide best management practices such as pollution pre-
vention and treatment alternatives for contaminated drink-
ing water and sediments along with quantifying sources of
pesticide and their impacts on water quality improve models
for movement of pesticides through the watershed.
11
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