PPP-35

PURDUEURDUE PESTICIDEESTICIDE PROGRAMSROGRAMS
Purdue University Cooperative Extension Service

PESTICIDES AND WATER QUALITY
PRINCIPLES, POLICIES, AND PROGRAMSFred Whitford, Coordinator, Purdue Pesticide Programs
Jeffrey Wolt, Technical Leader, Environmental Chemistry Laboratory, DowElanco
Henry Nelson, Surface Water Branch, U.S. Environmental Protection Agency
Michael Barrett, Ground Water Section, U.S. Environmental Protection Agency
Sarah Brichford, Extension Water Quality Specialist, Purdue University
Ronald Turco, Associate Director, Indiana Water Resources Research Center, Purdue University
Edited byArlene Blessing, Purdue Pesticide Programs

TABLE OF CONTENTS

PAGE

Introduction ....................................................................................................................................

3

The Earth’s Water Cycle: Nature’s Oldest Recycling Program ......................................................

5

The Fate of Pesticides in the Environment ....................................................................................

10

The Pesticide Testing Process ......................................................................................................

18

Regulatory Evaluation of Environmental Fate Data for Water Quality Concerns ..........................

28

Risk Assessment of Pesticides for Water Quality Concerns .........................................................

40

The Pesticide Label .......................................................................................................................

44

Public Policy, Pesticides, and Water Quality .................................................................................

49

Special Initiatives ...........................................................................................................................

51

Conclusions ...................................................................................................................................

55

Acknowledgments ..........................................................................................................................

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PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, IN 47907

INTRODUCTION

Today we face challenges concerning water resources, both in our own communities and nationwide.
Proponents of economic development and supportersof environmental conservation debate the use of water.
As the turn of the century approached, there was nodebate over water as a renewable and limited resource; rather, its availability was generally assumed to
be unlimited. Rivers and streams were viewed ascheap, dependable sources of water in support of thenational surge in manufacturing, construction, andemployment; and they often served as prime avenues
for the disposal of waste materials.
By the turn of the century, the oppression of surface
water was evident; and the dumping of sewage effluent
and by-products of manufacturing and agriculture had
become associated with the terms contamination andpollution. Rivers and streams once considered pristine
were tainted from the repeated introduction of waste.
Several contamination incidents received significant
media attention, sparking public concern for water
quality. Some evoked such emotional outrage thatpublic coalitions demanded legislative attention. The
resulting multitude of new laws—both state andfederal— specified policies and goals for establishingwater quality, placing the responsibility for compliancesquarely on the cities and industries (including agriculture) releasing pollutants into water.
Protecting water quality is a top environmental
priority as we approach the twenty-first century. However, the pendulum of public debate has shifted fromgovernment regulation to one of cooperation amonggroups with divergent viewpoints. This shift evolved asfactions began to view a community’s prosperity as afunction of its development of water policies that blend
both economic goals and environmental incentives.
While cooperation is now common, major differences
still exist among public, industrial, regulatory, andenvironmental groups. Ideas presented and solutions
offered may differ, but there is universal agreement thatwater resources must be pollution-free and abundant if
the nation is to prosper economically.

Pesticides and Water Quality
Using pesticides effectively while maintaining water
quality presents an important challenge. As citizens, wemust recognize the significant role of pesticides inmaintaining a high quality of life. We must acknowledge
that the effective production of food and fiber relies on
pesticides to control weeds, insects, and plant diseases

3that interfere with the growth, harvest, and marketabilityof crops. As pest control operators and homeowners—
rural as well as urban—we must acknowledge theimportance of pesticides in controlling pests in ourhomes, restaurants, hospitals, parks, ornamental
plantings, golf courses, etc. But at the same time wemust be aware that pesticide applications can affectwater quality. Human and environmental health may bethreatened when excessive concentrations of pesticides enter surface or ground water.
‘Pesticides and water quality’ is a complex subject,both technically and politically; but if current and future
expectations for community life, agriculture, industry,
wildlife, and natural habitats are to be met, input froman educated public is essential. A basic knowledge ofthe subject is important to allow informed participationin the ongoing debate. This publication presents
information on water science, environmental fate, andpublic policy to assist the reader in developing an
understanding of the issues surrounding pesticide use
and water quality.

4THE EARTH’S WATER CYCLE:
NATURE’S OLDEST RECYCLINGPROGRAM

Oceans contain 97 percent of the world’s watersupply. The remaining three percent is fresh water, of
which approximately 70 percent is stored as ice inglaciers. Nearly all of the unfrozen fresh water on theplanet occurs in aquifers below ground; only one
percent is stored in lakes, streams, and rivers.
Water drawn from rivers and tapped from deep
within the earth’s aquifers is not ‘new’. It has been
continuously recycled between land and atmosphere
for thousands of years through intricate processes of
evaporation, transpiration, precipitation, overland
runoff, and infiltration. Together these processes arelinked as the hydrologic (water) cycle.
The sun energizes the hydrologic cycle. Solarenergy converts surface water to atmospheric water
vapor through the process we know as evaporation.
Plants absorb water from the soil and can release it5into the atmosphere by transpiring (giving off) water
vapor from leaves. Water vapor rises, then condenses
in the cooler atmosphere to form clouds; water stored
in clouds is eventually returned as precipitation in theform or rain, hail, sleet, and snow which can fall directly
into rivers, streams, lakes, ponds, and wetlands. Water
also can move into these bodies by overland runoff orpercolation below ground. Water entering the soil can
infiltrate deeper to reach ground water which, in turn,can discharge to surface water or arrive back at thesurface through wells, marshes, and springs. Once on
the surface, water is again energized by the sun torepeat the evaporation and transpiration processes thatprovide water vapor for cloud formation and continuation of the hydrologic cycle.

Ground Water: The Hidden Resource
Ground water is a widely distributed natural resource found beneath the earth’s surface. Many people
have the mistaken impression that ground water occurs
as underground rivers and reservoirs. However, mostground water occurs in tiny voids (spaces) between
grains of sand and gravel, between silt and clay, or incracks and fractures in bedrock.

Geology of Ground Water
The geology of a particular location dictates thedepth and volume of ground water. Usable groundwater available to supply wells and springs comes fromgeologic formations called aquifers, which may be
shallow (near the earth’s surface) or very deep (hundreds of feet below the surface). As a general rule,
fresh water aquifers tend to lie 60–300 feet below
ground.
Aquifers are composed of various materials such as
rock, sand, and gravel that reflect local geology. Someconsist of unconsolidated (loose) deposits of sand,clay, silt, or gravel containing water in the voids between particles and rock fragments. Other aquifers
occur as cracks in bedrock or consolidated (solid)materials such as igneous rock (granite, basalt),
sedimentary rock (limestone, siltstone, sandstone), or
metamorphic rock (slate).
Aquifers are characterized as either confined or
unconfined. Confined aquifers lie below a layer of lesspermeable clay or rock—a confining layer—which
greatly slows the vertical movement of water. The
water in confined aquifers can be recharged from waterthat moves into the water-bearing zone from distantareas where there are no confining layers.
Unconfined aquifers do not have a confining layer
and are ‘open’ to water moving down from surfaces

6directly above. The water surface of unconfined
aquifers—the water table—fluctuates with changes inatmospheric pressure, rainfall, and other factors.
Unconfined, unconsolidated aquifers are particularly
vulnerable to contamination because, typically, they arequite shallow and surface water can infiltrate quickly
down to the water table (ground water) in certain soils.

Downward Movement of Water
Between top soil and water-saturated soils, voids ofunconsolidated materials fill with water and air, forming
the vadose (unsaturated) zone. The portion of thevadose zone near the soil surface is where plants root,
vegetation decays, and animals burrow; it is in this areathat most terrestrial plants and soil organisms reside.
The lower portion of the vadose zone hosts lessbiological activity.
Precipitation either runs off sloping land or infiltrates
only the upper few inches of soil, then percolates
downward and permeates the upper vadose zone. As
water enters soil voids, a variety of physical processes
pull it into the vadose zone, replacing air. The watertable is defined as the area that separates the vadoseand saturated zones. Water below the water table isground water.
All soils can store water in voids. A soil’s ability tostore and transfer water downward in saturated or
unsaturated conditions is a function of numerous
interrelated processes and features. For example, thenature of soil particulates and the way they aggregate
influence features such as porosity and how water is
attracted to soils. Soils with small voids can store morewater than those with larger voids. Under saturated
flow, porosity and the pull of gravity greatly influencewater movement. Under unsaturated conditions,attraction of water to soil surfaces (matrix potential),
movement along a maze-like flow path, and very small
pores (capillaries) influence water movement.
Natural ground water movement is often (but notalways) in the direction defined by local topography.
Horizontal flow of ground water generally is slow and ismeasured in inches per day or feet per year, dependingon the porosity and the permeability of the materials
making up the aquifer.

Surface Water: The Visible Water
Resource
Surface water is water stored or flowing at theearth’s surface: natural bodies of water such as rivers,
lakes, and wetlands, as well as constructed (artificial)water reservoirs such as canals, man-made lakes, anddrainage ditches. The quantity and quality of surface
water is important for many activities: consumption,

7

recreation, transportation, waste assimilation, agricultural production, and industrial use.

Movement of Surface Water
Surface water is linked to both ground water andatmospheric water through the hydrologic cycle.
Surface water moves into ground water by infiltrating
the soil and percolating downward; it also enters theatmosphere through evaporation and transpiration.
Likewise, water from the atmosphere and ground watercan recharge surface waters. Atmospheric water falls
as precipitation: rain, sleet, hail, and snow. Groundwater that moves to the earth’s surface contributes tothe base flow of streams, lakes, wetlands, and otherwaterways.
Rainfall and melting snow initially infiltrate the top
layers of the soil at a rate commensurate with the soil’s
porosity and initial water content, as well as the intensity and duration of precipitation. Continuing precipitation may saturate the upper few inches of the soil,
temporarily exceeding its capacity to hold water; water
begins to accumulate on the land surface and perhaps
flow overland to lower elevations. This movement,termed overland flow or surface runoff, may occur
across a small or large area, depending on the amountand intensity of precipitation and on the local terrain.
Soil type, land slope, and vegetative cover are contributing factors. A gentle rain lasting all day may result in
only moderate runoff; but an intense summer thunderstorm producing a large amount of rainfall in a shorttime may yield significant runoff. The amount of runoff
produced by a storm also is influenced by the moisturelevel of the soil prior to the storm, and by local topography. Runoff also can result from miscalculated timing,
intensity, and duration of irrigation.
Runoff flows down slope until it reaches a storage
area (e.g., a stream, pond, or low spot); and when thestorage/infiltration capacities of that area are exceeded,runoff will flow even farther down slope. Flooding
occurs when precipitation exceeds the storage capacityof surface depressions and bodies of water for a given
area. Large amounts of runoff for an extended timeraise stream levels, spilling water onto adjacent land—
the flood plain.

Erosion and Sedimentation
Surface water flows in defined channels such as
streams and rivers. The amount and rate of flow vary
primarily with precipitation, channel substrate andgeometry, and gradient.
Flowing water can carry dissolved pollutants andothers adsorbed to suspended sediment. Suspended

8

sediment comes from eroded soil, which is carried inrunoff, and from the channel’s sides and bottom. The
distance it travels varies, depending on the size andsurface characteristics of the materials and the waterflow rate. When flowing water meets stored water, suchas when a stream enters a pond, the flow rate is greatly
decreased and much of the coarser, larger, heavier
sediment settles to the bottom; finer, smaller, lightweight materials such as clays may stay in suspension
for longer periods of time. Generally, sediment isdeposited, resuspended, and redeposited by flowing
water. Conversely, storage waters tend to host pollutants for longer periods of time although, because ofdilution, concentrations may be lower than in a stream.

The Surface Water System
A surface water system is characterized by its
watershed or drainage basin. A watershed is the areaof land draining to a specific river; the watershedboundary is defined by a region’s topography. Watersheds vary in size and can be nested within otherwatersheds of increasing size, similar to a family
genealogy or the branching of a tree. For example, theentire Mississippi River watershed draining into theGulf of Mexico is a large area encompassing most of
the central United States; it consists of thousands of9smaller subwatersheds, each contributing to the total
water volume flowing into the Gulf.
The watershed concept is important because it links
land area to bodies of surface water along a sequenceof increasing scale. Land use within a watershedlargely determines the quality of the local surface
water. The quality of water leaving a watershed can, inturn, affect the cumulative quality of water far downstream. For example, pesticides detected in a city’s
drinking water supply could come from lawn and otherurban uses or from an upstream watershed where
agriculture is predominant. The potential exists forcompounds to move off site and travel downstream
through the surface water system; however, many
biological, physical, and chemical processes affect thefate of pesticides in the environment.
Within a watershed, surface water occurs in a
network of storage and flow areas; e.g., soil constitutes
a large internal catchment (storage body) for water
within a watershed. Catchments can cycle their water;in other words, a ‘new’ volume of water can replace the‘old’ volume. The storage time of water—also known ashydrological residence time— depends on the hydrologic characteristics of the catchment. The meanhydrological residence time, stated as a ratio of theaverage volume to the average flow, represents how
long it takes to replace an ‘old’ volume of water with a‘new’ volume.

THE FATE OF PESTICIDES IN THE
ENVIRONMENT

The interaction of pesticides with soils, surface
water, and ground water is complex. Pesticide fate iscontrolled by numerous simultaneous biological,
physical, and chemical reactions. Comprehending thefate of pesticides requires an understanding of certain
processes: transformation; transfer; and transport.
Transformation refers to biological and chemical
processes that change the structure of a pesticide orcompletely degrade it. Transfer refers to the way inwhich a pesticide is distributed between solids andliquids (e.g., between soil and soil water), or between
solids and gases (as between soil and the air it contains). Transport is the movement from one environmental compartment to another, such as the leachingof pesticides through soil to ground water; volatilization
into the air; or runoff to surface water.

10

When a pesticide is applied to a field, certain
reactions follow. Foliar-applied pesticides stick toleaves, where they are absorbed. But rainfall inevitably
washes some of the chemical off the leaf surface onto
the soil below; and some may be transformed bysunlight. Soil-applied pesticides generally interact firstwith moisture around and between soil particles,
influencing how the chemical ultimately will react in theenvironment. Thus, a ‘soil solution’ can be viewed as achemical staging area for most reactions controlling
environmental fate. For instance, sorption processes(transfer), degradation by microbial and chemical
reactions (transformation), volatilization to the atmosphere, leaching into deeper soil profiles, and overland
flow (transport) all occur predominantly from soil
solution.

Sorption
Sorption is a transfer process by which pesticides
are dispersed between solid matter and water, in soil; it
is important in regulating the concentration of pesticides in soil water. One important environmental sink(retention or storage site) for many pesticides isorganic matter. The transfer—called ‘partitioning’—of apesticide into organic matter in soil is a somewhat
nonspecific mechanism.
Much organic matter (humus) is made up of a seriesof organic polymers (long chains or mats of molecules)

11and generally consists of two systems: a hydrophilic(water-loving) surface; and a hydrophobic (waterhating) interior. The convention of ‘like dissolves like’
holds for pesticide interactions with organic matter insoil. Nonionic (noncharged or neutral) pesticides
escape from soil solution into the hydrophobic interior
and, as a result, a pesticide equilibrium is set up
between organic matter and soil solution. Pesticides
move between organic matter and water in soil. Also,
pesticides may undergo an aging process, over time,
whereby the chemical moves deeper into organic
matter and becomes unavailable to move back into soil
solution. Pesticides that are water soluble tend toremain at the surface of soil organic matter, while thosethat are insoluble will penetrate to the hydrophobic
interior.
The amount of pesticide sorbed is largely a functionof the total amount of organic matter (sorption regions)in the soil. Sorption to clay mineral particles also occurs
but usually is less significant than sorption to organic
matter in determining environmental fate, unless thesoil has very low organic matter content.
Many pesticides develop a charge as the result ofsoil solution pH (a measure of acidity); i.e., neutral
pesticide molecules can become ionic (charged) andmore reactive. If the pH-induced charge is positive, thepesticide can bind to negatively charged soil. If theinduced charge is negative, the pesticide may actually
be repelled from the negatively charged surfaces of soil
solids.
Sorption to soil particles is also dependent on soil
water content because water is necessary for chemical
movement; and water molecules will compete withpesticide molecules for attachment sites on clay andorganic matter. Therefore, pesticide sorption tends tobe greater in dry soils than in wet soils. Decreased soil
water content forces the pesticide to interact with soil
surfaces; however, the amount of sorption also depends on the type of clay and organic matter content.
The bond between a pesticide molecule and a soil
particle determines, to a large degree, the environmental fate of the pesticide. For instance, pesticides thatare tightly sorbed to soil particles have decreased
mobility and are less likely to contaminate groundwater. The bond may decrease the rate at which thepesticide is degraded by soil microbes, leading tolonger environmental persistence. Pesticides strongly
sorbed to soil particles may travel primarily with erodedsoil and enter surface water, while weakly sorbed
pesticides that are more water soluble may be released
into soil water solution and enter surface water as
runoff.

12

Microbial Degradation
Communities of soil microorganisms are very
diverse. For example, researchers have estimated thatbetween 5,000 and 7,000 different bacterial species
may exist in a single gram of fertile soil. Populations ofbacteria can often exceed one hundred million individuals in one gram of soil, and populations of fungal
colonies can exceed ten thousand.
Microbial degradation is a transformation processthat results when soil microorganisms (bacteria andfungi) either partially or completely metabolize (breakdown) a pesticide. Microorganisms can cause changes
in a pesticide when this activity occurs; in the presenceof oxygen it is termed aerobic metabolism, and in theabsence of oxygen, anaerobic metabolism. Most
microorganisms inhabiting the soil profile where oxygenis plentiful degrade pesticides via aerobic metabolism.
As a pesticide undergoes aerobic metabolism, it isnormally transformed into carbon dioxide and water.
Under anaerobic metabolic conditions, microorganism
degradation may produce additional end products suchas methane. Those microorganisms using anaerobic
metabolism for breaking down pesticides are typical ofthe microbes inhabiting waterlogged soils in terrestrial
systems or living in the bottom sediments of ponds,
lakes, and rivers. These organisms are also present inground water and, to some extent, in the soil profile.

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Pesticides, along with many other naturally occurring organic molecules, may serve as a source of foodor energy for soil microbes. Because they occur at very
low environmental concentrations, however, it isunlikely that their capacity to serve as a food source isadequate to sustain high numbers of microbes. Pesticides are more apt to serve as incidental food sources
for microbes also drawing from other food sources.
Most soil microbes are associated in colonies on thesoil surface, not free in soil solution. A pesticide in soil
solution has to move to these microbial colonies andcross the microbial cell membrane into the cell tometabolize. Some microbes produce enzymes which
are exported from the cell to predigest pesticides thatare poorly transported. Once inside an organism, apesticide can metabolize via internal enzyme systems.
Any energy derived from the breakdown of the chemical can be used for growth and reproduction; any
portion not fully degraded to carbon dioxide or incorporated into cells is released back into soil solution asintermediate chemical metabolites.
Recent studies have revealed that multiple organisms often are involved in the degradation phenomenon. Previous notions that single species are solely
responsible for microbial degradation of a pesticide
probably are not correct. Different species havedifferent capabilities, and together they can form a ‘poolof talent’ resulting in degradation of the pesticide. The
likelihood that the chemical will be completely degraded is decreased if any of the microbes are missing
from the pool. The ability of microbes to degrade apesticide is related to their metabolic capacity and thecomplexity of the molecule, and to environmental
factors that regulate microbial activity (water content,
temperature, aeration, nutrients).

Abiotic Degradation
Abiotic (chemical) degradation is the breakdown ofpesticides by nonbiological reactions (i.e., without the
involvement of living organisms) occurring in soil
solution and on the soil surface. Factors which affectabiotic degradation include the chemical nature of thepesticide as well as its temperature, water content, andpH. Hydrolysis (reaction with water) is important for the
degradation of many pesticides, as is photodegradation(reaction with sunlight); these two processes generally
are the most important abiotic mechanisms involved.
Abiotic degradation results in less transformation of amolecule than does biological degradation.
Hydrolysis is a common chemical reaction—aprocess by which a pesticide reacts with a watermolecule. Hydrolysis reactions generally substitute anhydroxyl (OH) group from water (HOH or H20 is the14chemical structure of water) into the structure of thepesticide, displacing another group. Reaction withwater breaks apart the molecule, and the extent ofbreakdown is pH dependent.
Photodegradation (photolysis) involves the breakdown of organic pesticides by direct or indirect energy
from sunlight. Light energy can be absorbed by thepesticide or by secondary materials (e.g., organic
matter) which become ‘activated’ and, in turn, transfer
energy to the pesticide. In either case, pesticides
absorb energy from sunlight, become unstable orreactive, and degrade. Photolysis can occur in water, inair, or on surfaces such as soil or a plant leaf. Photolytic reactions occur near the surface of the ground(in the top few hundredths of an inch) or near water
surfaces, where light can penetrate.

Volatilization
Volatilization is the process whereby a solid or liquid
evaporates into the atmosphere as a gas. The processprovides a significant pathway of transfer for somepesticides. In principle, volatilization is an escapemechanism. Compounds with high vapor pressure andlow water solubility have a tendency to volatilize. The
tendency of a pesticide to volatilize from water isapproximated by the ratio of its vapor pressure to its
aqueous solubility. The same is partially true for soils,
but the tendency for a pesticide to volatilize from soil
also can be inversely proportional to its potential tobind to soil.
Specific environmental factors that tend to increase
volatilization include high temperature, low relative
humidity, and air movement. A pesticide that is tightly
sorbed to soil will have a lower solution concentration
and be less likely to volatilize. That is, less volatilization
occurs from drier soils because the lack of water allows
the pesticide to sorb onto soil particles. Volatile pesticides usually are incorporated (plowed into the soil)
after application to reduce loss into the atmosphere.
However, it has also been shown that pesticide volatilization from soil is complex and highly dependent on
the movement of water to and from the soil surface.
Once a pesticide enters the atmosphere as a gas, it
can become ‘diluted’ in water droplets and, as a result,highly susceptible to long-range transport from theapplication site. Within the atmosphere, the pesticide
may undergo reactions with light (photolysis) and water(hydrolysis) and sorb to suspended materials such as
dust particles. Pesticides in a gaseous state may
dissolve in atmospheric water and be transferred backto the soil surface during rainfall.

15

Leaching
Leaching is the term for the transport process ofdownward movement (infiltration) of pesticides inwater. Two kinds of phenomena are associated withleaching: preferential flow, and matrix flow.
Preferential flow allows pesticide molecules to move
rapidly through a section of the soil profile, with reduced likelihood that the molecules will be retained bysoil particles or degraded by microbes. Preferential flow
is characterized by water that flows rapidly throughworm holes, root channels, cracks, and large structural
voids in soil.
Matrix flow results in a slower migration of waterand chemical through the soil structure; the pesticide
moves slowly with water into small pores in soil andhas more time to contact soil particles.
The potential for volatilization and photolysis
diminishes considerably as the pesticide infiltrates thefirst few hundredths of an inch of soil. As the pesticide
moves lower into the root zone, there is generally lessorganic matter, more compaction, and lower biotic
activity. Once the pesticide leaches past the root zone,
abiotic degradation reactions frequently become more
important than biotic reactions because microbial

16

populations generally are smaller below the root zone.
In fact, microbes in deeper soils operate under ‘starvation’ and are less energetic due to a lack of carbon andnitrogen. In addition, pesticides rarely reach deep into
the soil profile; so microbes, therefore, are not adapted
to degrade them quickly.
The most important factors in determining whether apesticide will leach are its degradation (persistence)capabilities, its sorption characteristics, and its inclination to release rapidly into soil solution once it issorbed. Pesticides that are weakly sorbed by soil andresist degradation are more likely to leach to groundwater than are those that remain bound to soil. Factors
such as soil type, topography, and rainfall also may
impact the leaching potential of a pesticide; and factors
such as application rate, frequency, and type (foliar,
pre- and post-emergence) need to be considered.
The fate of pesticides in aquifers is unclear. Studies
have shown that degradation will occur in the capillaryfringe (the region above the aquifer) and in groundwater. Subsurface rates of degradation tend to belower than those in surface soils, perhaps reflecting
smaller microbial populations, limitations in essential
secondary nutrients, or lack of adaption (of microbial
populations) to use the compound.

Runoff and Erosion
Runoff—movement of water across the soil surface—occurs when water collects (due to rainfall,
irrigation, or melting snow) at a rate faster than it can
infiltrate the soil. As rain falls, small soil particles
become dislodged and are carried laterally by water ina process known as erosion. Because pesticides areapplied directly to the soil, large amounts eventually
end up there; and as water runs off and soils erode,dissolved and sorbed pesticides go along. Runoff anderosion have the potential to move more pesticide offsite than leaching, due to the fact that runoff is asurface phenomenon. Surface runoff and erosion move
pesticides and other pollutants laterally from points ofhigher elevations to collection points (streams, rivers,
ponds, lakes) at lower elevations. Climatic factors suchas rainfall timing, duration, and intensity, and surface
features such as slope length and grade, soil permeability, and surface cover greatly influence the degree
to which pesticides are mobilized by runoff and erosion.
Similarly, pesticide management factors may significantly affect runoff; for example, a soil-incorporated
pesticide is less likely to run off site than the same
compound applied to the soil surface.

17THE PESTICIDE TESTING PROCESSThe goal of modern pesticide chemistry is to
produce pesticides that are effective in smaller quantities, more target-specific, and less persistent in theenvironment. Pesticide structures are developed to
mimic—and therefore substitute for—specific molecules in targeted biological reactions; i.e., the pesticide mode of action is unique to the targeted pest.
Such specificity is achievable with complex chemical
structures which disrupt target-specific biologicalprocesses to effect the desired control and yield lesspersistence in the environment.
Pesticide products new to the marketplace began
the registration journey seven to nine years earlier in a
research laboratory. After development, two years of
exploratory research are needed by the manufacturer
to define the chemical’s biological and environmental
characteristics and to make comparisons with existingproducts. Pesticides identified as commercially viable
are studied for an additional three to five years to18

ensure that they meet the health and environmental
criteria established by company philosophy and policy,
and government regulations. During this additional
testing period, an average of 120 studies are completed to satisfy testing mandates as specified by theFederal Insecticide, Fungicide, and Rodenticide Act(FIFRA) administered by the U.S. Environmental
Protection Agency (EPA). Typically, the development
and registration of a new pesticide costs between $40
million and $50 million; and upon completion, the entire
research package is submitted to EPA for review.
The EPA review process takes two or more years,
followed by assignment of an EPA registration number(a legal requirement that must be met before the new
product can be sold to the public). Under FIFRA, a
product may be granted a registration number only if
supporting data indicate that its potential benefits tosociety outweigh the probability of risk to people,
wildlife, and the environment when used as directed in
its labeling. Recouping development costs from yearsof research and subsequently generating profits for thecompany to reinvest in new pesticide research hingeon the ability of the product to compete successfully
with others in the marketplace.
Because of the time lag between discovery andproduct registration, manufacturers must foresee any
effects which imminent environmental regulations might
have on current research data. Failure to anticipatechanges in environmental regulations could lead to
additional years of research prior to registration.

Development of Environmental Fate
Data
Discovery of ‘environmentally acceptable’ pesticides requires researchers to unravel the complexities
of chemical behavior in the environment. Experiments
designed to do so are time-consuming and costly andrequire expertise from numerous scientific disciplines.

Discovery Phase
Most manufacturers employ a screening process to
identify promising compounds for further study andunfavorable ones to be discarded. Primary screens areused to pinpoint chemicals with pesticidal properties.
Their impact on growth, development, behavior, andmortality of pest insects, weeds, and diseases iscarefully observed and recorded. It is important that theprocess uncover novel modes of action rather than
generating copycats of those already in the marketplace. From a marketing standpoint, chemicals lacking
distinct advantages in terms of efficacy and selectivity
are unlikely to generate revenues sufficient to support

19the significant costs associated with development,
registration, and field support.
Pesticides entering the screening trials may besynthesized with specific targets in mind or producedby microorganisms inhabiting the soil. Others may bediscovered by examining structural activity relationships coupled with molecular modeling. New pesticides
originate from industrial manufacturing waste streams
and from by-products of other industries; these sources
provide about 30,000 chemicals annually for inclusionin pesticide screening programs.
Fewer than 200 of the 30,000 chemicals per year
display the kind of activity on pests that warrants
further evaluation. Most compounds are excluded fromadditional testing because they are not sufficiently
selective, the cost to the manufacturer is unacceptable,
the potential market is too small, or they demonstrateunacceptable hazards. In order to be economically
viable, the pesticide must be used commercially for one
or more major crops (corn, soybeans, wheat, or
cotton).
Secondary screening (on compounds which havesurvived primary screening) involves the use of proven,reliable predictors of biological and environmental
properties to identify negative chemical attributes.
Biological, environmental, and economic questions
pertinent to the commercial potential of these chemicals are listed below.
• What is the water solubility of the material?
• How mobile is the compound in soil?
• How persistent is the compound in the environment?
• What are the short-term effects on laboratory test
animals such as rats?
• How toxic is the compound to man, birds, aquaticorganisms, insects, and nontarget plants?
• Will the chemical be toxic to desirable nontarget
plants?
• Does the material bioaccumulate (that is, does itbuild up in the environment)?
• What prototype formulation will be tested?
• Can the material be produced in sufficient quantity
to continue testing?
• What kinds of manufacturing processes may beneeded?
• Is there a market, and does it meet other commercial objectives?
• Can it be produced at a cost that will provide a
product at a price that the users will pay?
• What are the strengths and weaknesses of current
and expected competing products?

20

Research and economic development teams
evaluate the relative strengths and weaknesses ofeach chemical and, in turn, their analyses are consolidated into product profiles. Many products are shelved
because their profiles indicate undesirable health orenvironmental attributes, manufacturing problems, or
sales potential insufficient to capture an adequate
share of the market. Decisions to eliminate certain
products carry an expensive price tag: two years of
research costing a million dollars for each chemical in
the secondary screen.

Predevelopment Phase
Chemicals which survive the secondary screening
process are tested extensively to produce a databasethat supports EPA registration of the product. Manufacturers must conduct and analyze research and present
their findings according to protocol outlined by EPA. Alldata submitted in support of pesticide registration must
result from research conducted under Good Laboratory
Practices (GLPs). GLPs are regulations issued by EPA
that prescribe the procedures for extensive documentation and verification of every step of the testing process. This assures that the data were developed byappropriately trained scientists and verifies the authenticity of the data used to achieve the results. The
auditing of data and reports to assure GLP complianceis a very expensive component of the product development process.

Summary of Environmental Fate Studies
Required by EPA
Three basic questions on environmental fate must
be answered in the data supporting EPA registration:(1) How fast and via what pathways does the pesticidedegrade? (2) What are the breakdown products? (3)How much of the pesticide or its metabolites will
migrate, and where will they accumulate in the environment? Environmental fate data generated from laboratory and field experiments are then used to assess thepotential for negative impact on the environment. Risk
assessment involves comparing effects data fromvarious toxicological studies with fate and exposure
data to predict potential health and environmental
impacts—and to protect natural resources in general.
A tiered approach to testing is used to simplify theprocess of investigating environmental fate data forpesticide registration. The first tier of environmental
fate studies addresses hydrolysis; photodegradation inwater and soil; aerobic soil and anaerobic aquatic
metabolism; mobility; and terrestrial field dissipation.
The second tier consists of field soil studies andadditional laboratory research triggered by results offirst tier work.

21

Finally, a third tier addresses key transport mechanisms indicated (by preliminary studies) as significant
in assessing the ultimate environmental impact of the
product—for example, small scale ground water
monitoring studies or surface water runoff evaluations.
If a product’s margin of safety is low in any environmental compartment, large scale surface and groundwater monitoring programs and ecosystem investigations may be conducted under ‘conditional’ registration
for the purpose of demonstrating in-use safety.

Abiotic Degradation Studies
The reactions of a pesticide with water (hydrolysis)
and light (photolysis) are important in predicting achemical’s ultimate environmental fate. When a pesticide reacts with water or absorbs solar energy, either
directly or indirectly, the chemical bonds holding theparent molecule together are broken. Degradation
studies are conducted to document the formation anddecline of the parent compound, as well as transformation products.

1

Controlled hydrolysis studies are conducted according to federal regulations to identify how a pesticide
reacts with water. The chemical is added to watersterilized to kill pesticide-degrading microorganisms
and buffered to test hydrolysis under acidic, alkaline,
and neutral conditions. Pesticides containing taggedradioactive carbon-14 can be used to help scientists
track the environmental
fate of the chemical
through its degradedproducts. Placement indark incubators
prevents the pesticidefrom reacting with light.
Test samples arecollected periodicallyfor 30 days andanalyzed to determine
the amount of parent
molecule remaining
and the products
generated, and toaccount for all of theradioactive carbon-14.
Pesticide transformation also can occur via photolysis. Studies of photodegradation in water are conducted in a manner similar to hydrolysis experiments,
except that they are conducted in the presence of
simulated or actual sunlight. Photodegradation on soil
is studied by applying a radiolabeled pesticide to a thinlayer of sterile soil. The treated water or soil is irradiated with simulated or actual sunlight and degradation22

is charted. Samples
are collected over a
30-day period andanalyzed as in hydrolysis studies.
Aqueousphotodegradation
2
studies, compared tohydrolysis studies,show how sunlightaffects chemical
breakdown in water.
Soil photodegradation
studies show how soil
components (e.g., clay
and organic matter)
affect pesticide
breakdown. These data can be compared and pathways for the two systems established.

Metabolism Studies
In addition to plant metabolism and uptake studies,
the biological degradation of pesticides by microorganisms in soil is examined. The term metabolism is usedsince most pesticides are degraded primarily by
microorganisms in soil that metabolize all or part of thepesticide molecule.
Three kinds of environmental metabolism studies
are required under FIFRA: a one year aerobic soil
metabolism study using selected field soils; a 30-day
aerobic aquatic metabolism study using sediment and

4
3

23

natural water; and a one-year (maximum) anaerobic
aquatic metabolism study using sediment and natural
water. These studies seek to determine how fast parent
molecules are degraded by biological processes(mainly microorganisms) in different soils, aerobic
sediment and water, or anaerobic sediment and water,
and to determine what metabolites are formed. To bevalid, these studies also must account for the radioactive carbon-14 used as a tracer.
Field soils known to be previously unexposed topesticides are used in the various metabolism studies.
Oxygen is maintained for aerobic metabolism studies,while anaerobic studies require that the soils or sediments be purged of oxygen. A radiolabeled pesticide isapplied to the soil or sediment and, at specified intervals, researchers remove and analyze samples for theparent pesticide and any metabolites. If volatile materials and CO2 are released, they are trapped and analyzed.

Mobility Studies
Scientists estimate potential mobility of a pesticide
by first determining its sorption in soil. Soil and water
are made into a slurry which is then treated with arange of pesticide concentrations. After a period oftime, the slurry is centrifuged to separate the soil andwater, after which the chemical concentration in each isdetermined.
Pesticide retention is a sorption coefficient (Kd)expressed as a ratio of the concentration of chemicalsorbed to soil to the concentration of chemical remaining in water: Kd = sorption:solution.

5

The Kd is relevant to understanding
pesticide transport since chemicals
remaining in soil solution can leach or
become available in the water of apond or stream. Because pesticides insoil solution are subject to leaching,
the extent of sorption as measured by
the Kd serves as a predictor of mobility:
the higher the Kd, the lower thetendency to move in soil. For example,
if a Kd is lower than 2, the molecule istermed highly mobile; if it’s between 2
and 5, the molecule is consideredmobile; and if the Kd is greater than 5,
it’s deemed immobile with respect toleaching.
Frequently, the Kd is expressed asa Koc by dividing the Kd by the fractionof organic carbon present in the soil:
Koc = Kd ÷ fraction organic carbon.
This mathematical transformation24

allows the potential mobility of a chemical to be compared with that of other chemicals, regardless of soil
type. A Koc value greater than 500 is usually associatedwith immobile pesticides.

Field Dissipation Studies
Terrestrial field studies are conducted to verify the
integrated routes and rates of pesticide degradationand mobility demonstrated in the laboratory; the lengthof time required to complete the terrestrial studies is
estimated from data generated in the lab. Pesticides
which are persistent—those that have a soil metabolism half-life greater than 6 to 12 weeks under optimal
conditions for degradation—generally require at least
eighteen months per study. Field studies with lesspersistent pesticides often can be completed within a
year.
When a pesticide is proposed for use over large
areas and/or multiple crops, several field test locations
and cropping scenarios are required for field dissipation
studies. The test sites must be established and maintained according to best management practices for theintended crop or noncrop use. Preapplication sampling
and analysis of the soil to a depth of three feet are
performed to confirm that no pesticide is present. An
end-use product is applied with typical applicationequipment at the highest rate stated on the proposedlabel. At timed intervals, representative samples are
removed at prescribed depths and analyzed for thepresence of the parent product and environmentallysignificant metabolites. Since terrestrial dissipation
studies are most frequently conducted with unlabeledchemicals, precise method development to assure
sensitive analysis of soil residues is necessary. Pesticides that are active at low rates require sophisticatedand highly sensitive analytical methods for extraction
and analysis of the parent molecule and significant
metabolites; measurements in parts per billion arenecessary.
Dissipation studies also must be conducted todetermine the environmental fate of pesticides designated for aquatic crop and noncrop uses. Protocols for
conducting aquatic studies and the timetables involved
are similar to those of terrestrial field studies. Waterand sediment (and sometimes animal and plant)
samples are collected for analysis to detect the parent
molecule and significant metabolites.

Decisions to Move Toward Commercialization
Successful development of a product requires
teams of scientists working on various test components
and discussing their results at every level of the testing25

process. Discussion on the chemical’s fate and behavior, short- and long-term health effects, ecotoxicity,
environmental toxicity, and production and economic
information is ongoing. The benefits of the productversus its risk potential are under constant scrutiny.
The project may terminate at any time during thepredevelopment process if evidence suggests potential
biological, environmental, or marketing problems. Only
one or two chemicals out of 30,000 survive the rigors of
the seven- to nine-year research and evaluation
process, and those must assume the burden of recouping production costs for all.

Development/Registration Phase
Final internal review and discussion are conductedby the developer to ensure the validity, accuracy, andinterpretative summaries of all data. Each experimentmust be accompanied by complete descriptions of theprocedures used, by experimental designs, and bydetails that allow EPA data evaluators to reconstruct
the experiment. Environmental tests include qualitativeand quantitative descriptions of the active ingredientand metabolites; and besides the data, per se, asummary of data, data analysis, and sufficient description to verify statistical procedures are required. Oncethe internal company review is satisfactorily completed,the scientific data can be forwarded to EPA as part of
the registration package.
The registration package and the application forregistration are processed at EPA and assigned to a
Product Manager (PM) in the Registration Division
within the Office of Pesticide Programs (OPP). It is the
responsibility of the Registration Division to conclude
whether a new pesticide product satisfies the requirements of FIFRA and should be registered. The Registration Division is supported by others within OPP in
the review and evaluation of the supporting data
package. The PM tracks the current status of theregistration request and serves as liaison between EPA
and the registrant (i.e., pesticide manufacturer). EPA
has been mandated by the United States Congress toensure that the conduct of the investigations meets
scientific protocols.
Prior to the time a registration application is submitted to EPA, a company developing the product usually
requests permission (in the form of an experimental
use permit) to use the new pesticide under field conditions in numerous marketing areas. Prior to issuing anexperimental use permit, EPA must make the decisionthat use will not present unreasonable adverse effects
to man or the environment.

26

An experimental use permit is issued for finite
periods of time and allows the company to develop
data in support of registration that can be obtained only
under normal use conditions (as prescribed by the
proposed labeling). This work often is conducted byuniversities and consultants using farms or research
field stations. Experimental use permits are required
when field research is conducted on ten acres or more.
Once all of the required supporting data are developed,
the application for registration is submitted to EPA for
review and evaluation.
EPA may meet with company representatives todiscuss research methodologies or conclusions, or torequest the original data. The registrant may be asked
to repeat experiments, redesign research methods, or
conduct additional testing. Registration ultimately will
be granted only when EPA concludes that the benefitsof the product (increased production, lower food costs,etc.) outweigh any potential for harm to people, wildlife,or the environment. Since pesticide registration decisions, by law, are based on benefits as well as risk
assessment, all registrations are conditional; EPA may
require the registrant to conduct further studies,suggest and implement strategies to minimize risks tothe environment, or monitor for the presence of thepesticide and its metabolites in ground and surface
water. Product registration covers only the uses andcrops addressed in the studies submitted; additional
studies may be required to qualify the product for
expanded registration.

Product Stewardship Phase
The average cost of developing a single marketableproduct from among 30,000 chemicals screened isestimated at $35 million to $50 million; total expenditures might reach $150 million if the cost of manufacturing plants, etc., were factored into the equation.
Moreover, nearly half of the original 17-year patent lifeis spent on research, development, and registration
processes; and the pesticide that survives to earn an
EPA registration number is not guaranteed success inthe marketplace. Manufacturers must exercise goodstewardship in maintaining and supporting their pesticide product and ensuring that its use is consistent withthe label. They are required under FIFRA to report any
evidence of problems relative to the use of the productwhich are identified after registration; as a result,additional label restrictions, suspension, or cancellationof the product might be imposed—and the
manufacturer’s investment in the pesticide productmight be lost in the process!

27

REGULATORY EVALUATION OF
ENVIRONMENTAL FATE DATA FOR
WATER QUALITY CONCERNS

628

The environmental fate studies discussed previously provide the basis for screening pesticide registration candidates for effects on water quality. Evaluations
also may take place for previously registered pesticides
when their use has generated water quality concerns orwhen their data packages need to be upgraded tocurrent regulatory standards. The scope of the regulatory screening process focuses on two aspects ofpesticide behavior which affect leaching and runoff: 1)
persistence, or how long it takes for the pesticide to betransformed into an essentially harmless substance;and 2) mobility, or how easily the pesticide can betransported to ground or surface water.
As described previously, information on the persistence of the pesticide is obtained primarily from soil
metabolism, hydrolysis, photolysis, and field dissipation
studies. Information on the mobility of the pesticide is
obtained primarily from sorption experiments, leaching,
and field dissipation studies. A complete set of environmental fate studies generally is sufficient for identifying
pesticides that have the potential to leach into groundwater or to enter surface water as runoff.
The results of environmental fate studies are notalways sufficient to estimate concentrations of apesticide in aquifers or surface waters when thechemical is used in different geographical areas, or todefine specific areas where water contamination mightoccur. Therefore, presumptive decisions on use
restrictions or limitations must be made for pesticides
with the potential to affect water quality. These decisions might be madelong after registration,
as cumulative information warrants;
labels may be modified to be more or lessrestrictive, dependingon the results ofsurface and/or groundwater monitoringstudies.
Although there issome interaction
between surface andground water, theprimary mechanisms

of pesticide entry into the two usually are quite different. Therefore, EPA addresses concerns regarding
pesticide contamination of surface and ground water
independently.

Screening Pesticides for Potential to
Leach into Ground Water
In most cases, a period of a few months to several
years is required for a pesticide to leach considerable
distances through soil to reach ground water. Therefore, a pesticide generally needs to be both persistentand mobile to reach most aquifers.
The extent of pesticide movement through soil
depends on the degree of interaction between thepesticide and soil particles, soil microorganisms, andweather. The amount of pesticide that will reach low
soil depths varies dramatically with slight environmental
fluctuations, making estimation difficult. A judgment canbe made on the overall likelihood of ground watercontamination by comparing the mobility and persistence of a chemical to those of similar pesticides
previously detected in ground water at multiple use
sites. Many factors affecting the environmental fate of apesticide are not well understood. Site-specific behavior of pesticides in soils cannot be predicted unlessactual field data are available for comparison.

Assessment of Comparative Leaching
Potential
Several methods are used by federal and state
regulators to assess a pesticide’s leaching potential.
Most estimates rely heavily on soil half-life and Kd as
the most consequential parameters.
Modeling results should never be considered
equivalent to real data. All pesticide leaching models
are mathematical tools (with varying degrees of complexity and sophistication) that attempt to reduce what
happens in the ‘real world’ to formulas. However, noformula can cover every possible contingency in thenatural environment; there is still a great need tovalidate models by collecting pesticide residue andenvironmental condition data from the field. As more
validation work is done, models will come closer tosimulating the real world; but they probably never will
be sufficiently sophisticated to completely eliminate theneed for collection of field data.

Trigger Values
In this simplest of assessment methods, pesticides
are presumed to have ground water contamination
potential if environmental fate studies trigger multiple
criteria for both mobility and persistence. Trigger values

29are based strictly on laboratory data. Further refinements of ground water assessment of the pesticide
should consider additional field parameters such as
application rate, soil, and target crops. Trigger values
are determined from a group of reference pesticides
which have a history of use and extensive groundwater monitoring. The following values may be used byregulators as an initial step to identify pesticides most
likely to leach to ground water:

Trigger Values Related to Persistence
1. Aerobic soil metabolism half-life of greater than
two to three weeks;
2. Field dissipation half-life of greater than two to
three weeks;
3. Photolysis half-life greater than one week; or
4. Hydrolysis half-life greater than 60 days in sterilewater.

Trigger Values Related to Mobility
1. Koc usually less than 300;
2. The pesticide is a weak to moderate acid which
would not be attracted to most soil particles; or
3. Water solubility greater than 30 parts per million(ppm).

The Groundwater [sic] Ubiquity Score
The Groundwater [sic] Ubiquity Source (GUS) is
another estimator model which, like trigger values, isuseful for comparing the intrinsic leaching potential ofpesticides. The GUS model is more sophisticated thantrigger values because it uses a formula that combines
pesticide mobility and persistence parameters. To
calculate the GUS, average values for only two pesticide parameters are needed: the soil degradation halflife, and the soil Koc. Pesticides with a GUS greater than
2.8 are more likely to leach to ground water, while
those with GUS values between 1.8 and 2.8 aresomewhat less likely to leach. Pesticides with GUS
values less than 1.8 are unlikely to leach to groundwater.

The Pesticide Root Zone Model
The Pesticide Root Zone Model (PRZM) has beendeveloped by EPA and provides site-specific leaching
estimates. PRZM, like other pesticide soil fate andtransport models, incorporates soil characteristics andhydrology, weather, irrigation, and crop management
practices into complex mathematical formulas that
estimate leaching potential. EPA uses PRZM (andsimilar models) to make multiple site comparisons of
the leachability of a pesticide to older, reference
pesticides with histories of use and extensive groundwater monitoring. Models like PRZM also provide

30estimates of the concentration of a pesticide that willleach, but these estimates should be confirmed withactual field data.

The Pesticide Assessment Tool for Rating
Investigations of Transport
The Pesticide Assessment Tool for Rating Investigations of Transport (PATRIOT) is a site-specificscreening model. That is, PATRIOT provides a quick
estimation of the relative leaching potential of a pesticide at representative sites. The PATRIOT user firstmust select crops, geographical areas, and soil typesof interest. PATRIOT automatically simulates weather,using historical records from stations with soils thatclosely resemble those selected for modeling; and it
automatically incorporates appropriate irrigation
schemes. Pesticide characteristics needed for modeling are also provided by PATRIOT; however, for newer
pesticides the user must input personal estimates of
the required values. Finally, PATRIOT performs
simulations of pesticide leaching and provides estimates of pesticide leaching under varying conditions.
Therefore, the leaching potential of a pesticide indifferent cropping systems or in different soil types canbe evaluated with PATRIOT.

Special Studies to Evaluate Leaching
Potential
When analysis of environmental fate data indicatesa potential for ground water contamination, EPA may
require ground water monitoring studies (called second
tier studies) to determine if pesticide use limitations arenecessary. Ground water monitoring studies may berequired for a registered pesticide when new data(such as ground water detections at multiple sites)
indicate contamination not initially anticipated. Groundwater monitoring studies also may be required as acondition of registration when properties of a new
pesticide fall within an area where actual field data areneeded to better ascertain risks.
Before requiring a ground water study for pesticides
with established uses, EPA must determine that there
is a likelihood that ground water contamination at
multiple sites has occurred or may result from currently
registered uses. EPA also considers various environmental and toxicological effects that may be present.
Typically, field-scale studies are conducted in areasthat are relatively vulnerable to ground water contamination. These studies track the movement of an applied
pesticide and a tracer—a substance such as bromide
used to follow the subsurface movement of water
through the soil profile—into ground water. Tracer data

31

32

help analyze how readily a pesticide moves with water
through the soil profile.
Soil cores (soil-water sampling devices throughout
the subsoil) and the monitoring of wells which draw
ground water from the upper portion of the aquifer areused to track the movement of the pesticide and tracer.
Irrigation must be used as supplemental precipitation toensure that the site receives moisture equal to thatwhich would occur naturally in a wetter than averageyear.
Sampling in ground water monitoring studies is
continued until the degree of ground water contamination by the pesticide, if any, is well characterized.
Results from completed studies are used to evaluate
the magnitude of ground water contamination that may
occur over the proposed use area.
Pesticide leaching models such as PRZM may becompared to actual field study results at a given site todetermine their reliability in predicting leaching potential. If found sufficiently reliable, these models then canbe used to estimate the impact of a pesticide over anentire use area. The quality of data from ground water
monitoring studies influences estimates of predictedbehavior in the use area. Modeling based on real-world
data from ground water monitoring studies is useful inevaluating the potential for pesticide exposure. Additionally, modeling may be used to develop use restrictions to mitigate the potential for pesticides to reachground water.
Ground water monitoring data also are used by EPA
to evaluate the impact of pesticide use on ground water
quality in the public domain. One major effort in thisarea is the collection of data in the Pesticides in
Ground Water Database which is maintained by EPA's
Office of Pesticide Programs. The Pesticides in Ground
Water Database summarizes (by state and county)
monitoring data from various state entities, federal
agencies, and other sources. Validated data collectedfrom these sources according to rigorous, prescribed
processes may be used by EPA to support regulatory
decisions. In recent years, the U.S. Geological Survey(USGS) has greatly increased the number of pesticide
analyses included in their ground water monitoring
programs. USGS data often are of particular value toregulators because, traditionally, they have been
central to the USGS mission to collect a full complement of hydrogeologic data to facilitate interpretation ofwater resources monitoring data that they collect.
USDA’s Agriculture Research Service also is increasingly involved in collecting monitoring data.
Even under optimum conditions, not all questions
on the potential of a pesticide to impact ground water
can be answered from field scale monitoring studies

33

conducted in support of registration—or from outsidemonitoring studies.
Often there are some use situations where thelikelihood of a pesticide leaching to ground waterremains uncertain. Pesticide producers (registrants)
cooperate more and more with state regulatory,
agricultural, and environmental agencies to design
monitoring programs to ensure that unexpected andundesirable environmental effects do not surface after
a pesticide is registered. Should uncertainties remain
when a product is registered, pesticide registrants may
agree to conduct ongoing monitoring programs designed to provide information that can be used to headoff potential ground water contamination problems.

Screening Pesticides for Runoff Potential
The runoff potential of a pesticide is influenced bythree factors: type of soil; slope of terrain; and theintensity and timing (with respect to pesticide application) of rainfall. All three factors should be consideredwhen estimating runoff potential. A nonpersistentpesticide (i.e., one which does not sorb to soil particles
or organic matter) can be transported from its application site to major bodies of surface water in as little as afew minutes or hours when heavy rains occur shortly
after application. A pesticide exhibiting strong sorption
to soil usually will have a lower runoff potential than apesticide exhibiting weak sorption, but it can still reachsurface water if sorbed to soil particulates eroding withthe flow.
Data describing persistence and sorption are used
to categorize pesticides and their major degradation
products into one of nine categories. These nine
categories qualitatively separate pesticides according
to their relative potential to contaminate surface
water—in terms of both magnitude and duration of
occurrence expected. Pesticides also are distinguishedaccording to their relative propensity to occur in the
dissolving or sorption phase.
In evaluating surface runoff potential, pesticides are
assigned to the nine categories based on their halflives and sorptive Koc. The following criteria apply:• Sorptive Koc
1. Low sorption: Koc less than or equal to 1000
2. Intermediate sorption: Koc greater than 1000
and equal to or less than 10,000
3. High sorption: Koc greater than 10,00034• Persistence (Half-Life) in Soil
1. Short: half-life equal to or less than 2 weeks
2. Intermediate: half-life greater than 2 weeks
but less than or equal to 2 months
3. Long: half-life greater than 2 months
Thus, using the prescribed criteria, pesticides canbe grouped into nine categories representing eachpossible combination of low, intermediate, and highsorption relative to short-term, intermediate, and longterm persistence (e.g., low sorption/short persistence;or high sorption/intermediate persistence).
Persistence grouping helps predict how long a
pesticide will remain in the soil and, therefore, susceptible to runoff. Such considerations are important sincesome mitigation procedures effective in reducing soil
erosion are not necessarily effective in reducing runoff
volume, and vice versa. Sorption characteristics
influence how much of a pesticide dissolves in water
during runoff as opposed to how much is carried intorivers, streams, ponds, lakes, etc., where it remains
sorbed to sediment.

Assessment of Runoff Potential andSurface Water Contamination
The following methods may be used to assess thepotential of a pesticide to enter surface water as runoff.

Surface Water Monitoring Studies and Database
EPA uses data on surface water concentrations of
the widely used herbicides atrazine, cyanazine, simazine, alachlor, and metolochlor for risk assessments. For other pesticides, EPA must rely on partiallyvalidated computer modeling because data frommonitoring studies are limited. In cases where risk tonontarget organisms is known or predicted to be high,
EPA’s Office of Pesticide Programs requires runoff andsurface water studies to verify the effectiveness of
mitigation in reducing amounts of pesticides reachingsurface water through runoff.
EPA is developing a database for monitoring
pesticide residues in surface water. It will consist of
documented data which can be used in place of, or in
conjunction with, modeling predictions to perform
aquatic risk assessments. Data from the ongoing
USGS National Water Quality Assessment Program,the multi-agency Environmental Monitoring and Analysis Program, state agencies, water supply systems,
and pesticide registrants are used.

35

Computer Modeling
Environmental fate data can be used in computermodels to predict pesticide contamination of surface
water in more locations, over longer periods of time,and under more diverse conditions than are feasible
from field use or monitoring studies. Runoff and surface
water monitoring studies are subject to unpredictable
weather factors, but computer modeling uses historical
weather data gathered over long time spans and wide
geographical areas.
Models currently used for predicting the potential for
pesticide runoff into surface water include PRZM and
Ground Water Loading Effects of Agricultural Management Systems (GLEAMS). The input to both models
includes pesticide fate properties, soil characteristics,
management practices, and daily weather. Output fromboth models includes estimated runoff volumes,
sediment yields, and associated pesticide concentrations at the edge of the field. Estimated pesticide runoff
concentrations from PRZM or GLEAMS and estimatedpesticide concentrations from spray drift are input to36

receiving surface watermodels such as the
Exposure Analysis
Modeling System
7(EXAMS) or the Water
Quality Analysis
Simulation Program(WASP). In addition topesticide concentrations from runoff andspray drift, input toboth EXAMS andWASP includes
pesticide fate properties and receiving
water characteristics.
Output—described asa function of time and location—from both EXAMS andWASP includes estimated peak and varied duration
average pesticide concentrations (1) present in water,(2) sorbed to suspended sediments, and (3) sorbed tobottom sediments.
Temporal and geographical distributions of pesticideconcentrations based on computer estimates (or on
adequate monitoring data) are used to predict where
and how frequently maximum, short-term average, or
long-term average concentrations will exceed acute or
chronic toxicity thresholds for humans and othernontarget organisms. The temporal and/or geographical distributions of computer-estimated or measured
concentrations generally are plotted as cumulative
frequency curves. Such curves are created by plotting
maximum, short-term average, or long-term average
pesticide concentrations against the percentage ofyears or sites where equal or higher concentrations
would be expected. Such approaches are useful
because they allow scientists and regulators to better
assess the likelihood of runoff and to predict when apesticide might exceed a level of health or environmental concern.
The primary disadvantage of computer modeling isa general lack of controlled field monitoring data tovalidate the results. Validation with the appropriate datais needed to ensure accurate model estimates. Due tothe conservative assumptions used and a knowledge ofexisting field and monitoring data, scientists at theEnvironmental Fate and Ground Water Branch of EPA
are reasonably confident their modeling estimates ofpesticide runoff and concentrations in surface water(using PRZM) are conservative—that is, higher thanactual and therefore protective. Although some validation has been performed, additional work is needed,
particularly with respect to pesticide fate modeling.

37

Studies to Evaluate Runoff to Surface
Water
Runoff studies are not routinely required under
FIFRA. When available, the results of field and small
scale runoff studies are used to assess the effectiveness of mitigation methods. Such results also are used
to verify and to better quantify preliminary and modeling estimates of the runoff potential of pesticides andtheir major products of degradation.
Both field and small scale studies provide data on
the amounts of water, soil, and pesticide transported inrunoff from agricultural fields during and following
rainfall. Small scale runoff studies are gradually gaining
favor over large scale field studies because they arelarge enough to consider the effects of formulation,
tillage, crop cover, soil type, and slope on the transportof water, soil, and pesticides from the field, yet smallenough to allow the use of weather-independent rainfall
simulators. Consequently, the problem of unpredictable
weather patterns in field studies is eliminated. Small38

scale studies also are much cheaper to conduct thanare field studies, so for the same cost more combinations of factors affecting runoff can be studied.
The major disadvantage of small scale studies isthat the amount of water, soil, and pesticide transported by runoff from each unit area often is substantially higher than from agricultural fields. Some of thisdifference apparently is due to site-specific hydrologicalfactors such as sediment deposition, ponding, andinfiltration. Experimental conditions such as the use ofhigh intensity artificial rainfall in small scale studies also
may account for much of the effect in variable output.

Surface Water Monitoring Studies
Surface water monitoring studies provide data on
the concentration of pesticides in streams, rivers, lakes,
and reservoirs. Pesticide concentrations in streams andrivers are highly seasonal, with peak concentrations
occurring during the first few runoff-producing storms
after application, followed by rapid decline. However,pesticide concentrations remain longer in lakes andreservoirs than in rivers and streams due to longerhydrological residence times.
Pesticide concentrations in samples collected
infrequently, or in samples collected at set samplingtimes not coincident with significant runoff, often do notaccurately reflect peak concentrations. Pesticideconcentrations in samples collected from a single
location can vary as much as tenfold from year to year.
Consequently, surface water samples taken on only a
few occasions, or over a short span of time, often do
not adequately represent the source. The multitude ofpesticide detection possibilities, the methods of differentiating between zero concentrations and parts per
billion, and the necessity of precise, timely, repetitive
sampling make surface water monitoring studies quite
costly.

Spray Drift Studies
Spray drift studies and modeling also are used toestimate drift and the correlated deposition of pesticides into adjacent bodies of surface water and onto
nontarget plants. The Spray Drift Task Force (SDTF), a
coalition of 32 pesticide registrants formed to develop acomprehensive database of off-target drift informationin support of pesticide registration requirements, hasconducted spray drift studies and evaluated spray drift
models. The results should afford EPA the ability to
predict pesticide spray drift deposition into surface
water based on distance from sites of application, andto predict the effectiveness of land buffers and application techniques in reducing pesticide spray drift tosurface waters.

39

RISK ASSESSMENT OF PESTICIDESFOR WATER QUALITY CONCERNS

Human Risk Assessment
The Safe Drinking Water Act was implemented in1974 to protect public water supplies from all types ofcontaminants. EPA’s Office of Drinking Water evaluates, describes, and communicates health risks fromcontaminants in drinking water through Health Advisory
Levels and Maximum Contaminant Levels.

Health Advisory Levels
A Health Advisory Level (HAL) is considered the
maximum level of a drinking water contaminant, inmilligrams per liter (parts per million, or ppm) or micrograms per liter (parts per billion, or ppb), that would not
be expected to cause noncarcinogenic health risks
over a given duration of exposure. This does not mean40

that levels above the HAL will necessarily pose healthrisks but, rather, that uncertainty warrants prevention of
exposure above the HAL. However, HALs are nonenforceable standards.
Understanding the toxicological properties of adrinking water contaminant is necessary when calculating a health advisory. Toxicological profiles for pesticides generally are derived from animal tests because
human testing is not possible. Data from humanepidemiological studies can be used, but such data
generally are unavailable. The Lowest Observed
Adverse Effect Level (LOAEL) or No Observed Adverse Effect Level (NOAEL) are two important toxicological endpoints determined from animal tests.
The NOAEL is the maximum daily dose (of thechemical tested) per unit of body weight shown to
produce no adverse health symptoms in test animals.
The LOAEL is the lowest daily dose per unit of bodyweight confirmed to affect test animals adversely. In
studies conducted for EPA, the NOAEL and LOAEL areobtained from experiments where test animals consume the pesticide through drinking water or as part oftheir dietary intake. The NOAEL and LOAEL represent
daily doses expressed as milligrams (or micrograms) of
a contaminant per kilogram of body weight: mg/kg (orµg/kg).
EPA standards for exposure differentiate between
adults and children on the basis of body weight: 10
kilograms (22 pounds) for children; 75 kilograms (155pounds) for adults. It is speculated that children might
consume one liter (about a quart) of water daily,
whereas an adult might drink two liters. Multiplication of
the representative body weights by the NOAEL and
LOAEL yields total daily doses on which to base thepotential for acute and chronic adverse effects.
Since the NOAEL and LOAEL values are derived
from animal testing, there is uncertainty as to whether
humans might be more sensitive than test animals to
the contaminant. To allow for that contingency, EPA
applies ‘uncertainty factors’ which further reduce theacceptable dose for drinking water. Typically, NOAEL
values for children and adults are divided by an uncertainty factor of 100 or more. If the Health Advisory is
calculated from the LOAEL, an uncertainty factor of1000 or more is used.
Thus, a HAL is based on toxicological evidence andconservative assumptions about the data. A HAL is
calculated as follows:

HAL (mg/L or µg/L) =(NOAEL or LOAEL) x body weight
uncertainty factors x water consumption

41Note that the HAL represents a concentration inwater, which is very different from the actual dose
consumed (i.e., the total mass of contaminant taken in
by a person).

Duration of Exposure
HALs are derived for the following exposure periods: one day; ten days; longer-term; and lifetime. The
one-day HAL is calculated for a child exposed to thedrinking water contaminant for one day. The ten-day
HAL provides information relative to a child drinking thecontaminant for one to two weeks. The longer-term
HAL is derived for both a child and an adult andassumes an exposure duration of seven years or ten
percent of an individual’s lifetime. A lifetime Health
Advisory is derived for an adult and assumes that theindividual will be exposed for a lifetime of 70 years.
Examples of Health Advisory Levels for a specificpesticide in drinking water are presented in the following table. The NOAEL and the LOAEL for this specificpesticide are 15 ppm and 150 ppm, respectively.

Exposure
Duration

Population
Segment

HAL(ppb)

Uncertainty
Factor1 day
10 days
7 years
7 years
70 years

child
child
child
adult
adult

100
100
50
200
3

100
100
100
100
1000

Maximum Contaminant Levels
The Safe Drinking Water Act (SDWA) directs EPA
to protect human health by establishing Maximum
Contaminant Levels (MCLs) for pesticides and otherpotential contaminants of drinking water. MCLs arelegally enforceable standards which may not be
exceeded. An MCL is the highest annual average
concentration of a contaminant allowed in public watersupplies. Like the lifetime HAL, the MCL is a calculated
value based on the assumption that the average
person weighs 70 kilograms, lives for 70 years, anddrinks two quarts of contaminated water daily. Calculation of the MCL trigger value, however, also includes
consideration of the costs, feasibility, and practicality ofcurrent technology to further reduce contaminantconcentrations. MCLs may change as new technolo-

42

gies evolve, making the reduction of contaminantconcentrations feasible.
MCLs for noncarcinogenic contaminants arecalculated much like health advisories. The MCL isestablished at a level 100–1000 times lower than thelowest dose known to affect the most sensitive test
animals; this ensures against the possibility thathumans might prove more sensitive to the contaminant
than are the animals tested.
For pesticides and other potential contaminants ofdrinking water that are carcinogenic, risk estimates are
rated on the basis that exposure, at some level, willcause one additional cancer per 100,000 or 1,000,000
people over a lifetime of 70 years (by extrapolation of
the results in animals studies where carcinogenicity
was observed). For pesticides or other chemicals which
are determined to be carcinogenic, MCLs must be set
at the lowest level feasible.
Currently, public water utilities are required by
SDWA to collect at least four samples per year fromthe finished water supply (tap water) for contamination
analysis. If the annual average residue of a pesticide(as determined from the samples) exceeds the maximum contaminant level, consumer notification isrequired. Water utilities may have to use an alternative
water supply, remove the contamination by filtration, or
blend the supply with water from an uncontaminatedsource.

Ecological Risk Assessment
MCLs are designed to ensure that adverse humanhealth effects do not accrue from pesticide use, butthey do not address potential adverse effects on
nontarget plants and animals; however, pesticide
regulators are bound by legislative mandate to ensurethat pesticide use does not cause adverse environmental effects. Various (plant and animal)organisms undergo a series of toxicity tests
Contact the Purdue University
to determine what pesticide concentration
Cooperative Extension Service
levels might cause adverse effects. Somefor a copy of the publication
involve aquatic organisms such as fish or
Pesticides and Wildlife (PPP-30)
algae which might be exposed to pesticide
for additional information on
residues entering streams and lakes asecological considerations.
runoff from urban and/or rural sources.

Examples of Risk Assessments
Prevention of ground and surface water contamination is of primary concern where there is shown to be apotential for toxic effects on people, animals, andplants at concentrations which might realistically be
expected to occur. See examples (page 45) of exposure and toxicity profiles for two herbicides with very
different toxicological properties.

43

Both herbicide A and herbicide B (in the examples)
tend to be more toxic to plants than to other organisms.
Herbicide A is the more potent herbicide, affecting
terrestrial plants at concentrations of only a few hundredths of a part per billion in irrigation water. Herbicide
A residues might produce unforeseen ecosystemeffects in some surface waters; thus, its use nearendangered plants might be restricted.
Herbicide B is not as toxic as herbicide A but may
affect certain sensitive plants exposed (through irrigation) to concentrations in surface or ground water.
Herbicide B is somewhat more toxic than herbicide A tosome animal species, including mammals; based onlaboratory animal studies resulting in low MCLs, it ismore likely (than herbicide A) to receive a restricteduse classification. Unless new data are generated anda substantial increase in the MCL is realized, herbicide
B likely will receive a restricted-use classification— orcancellation—to prevent unacceptable levels in drinking water.

THE PESTICIDE LABEL
Each pesticide product is accompanied by a label
bearing directions for appropriate use. The label also
provides strict precautionary statements relative to theprotection of human health, wildlife and its habitat, andwater resources.
The intent of precautionary statements (normallyfound in the Environmental Hazards section of thepesticide label) is to protect ground and surface water
quality for aquatic organisms and wildlifethat use aquatic systems, and to prevent
Contact the Purdue University
contamination of ground water.
Cooperative Extension Service for
EPA-mandated instructions and precaua copy of the publication Pesticides
tionary statements are supported by theand the Label (PPP-24) whichbattery of toxicological and environmental
offers additional information on
tests required for pesticide registration.
pesticide labels.
Pesticides intended for outdoor uses (otherthan aquatic uses) will always containgeneral precautionary statements. Labels on pesticides
used to control weeds in aquatic environments—ponds,
reservoirs, and other impoundments—contain precautionary statements relative to the use of the treatedbody of water.

Protection of Surface Water
The Environmental Hazards section of the pesticide
label may contain information concerning the impact of
surface water contamination on wildlife. Example: ‘This
pesticide is toxic to aquatic organisms.’ Such statements are based on the cumulative evaluation of

44

}

}
45

Examples of General Statements'Do not apply directly to water or to areas where surface water is present, or tointertidal areas below the mean high water mark.''Do not contaminate water when disposing of equipment wash water or rinsate.'

Examples of Specific Statements‘Do not use fish from treated area for food or feed within 3 days of treatment.’‘Do not use water from treated area for watering livestock, for preparing agricultural
sprays for food crops, for irrigation, or for domestic purposes for (a length of time is given
based upon the rates applied).’‘Areas can be used for swimming twenty-four hours after treatment.’laboratory toxicity studies and are required when‘trigger levels’ have been exceeded. If the concentration in the environment is less than the level of concern, the statement is a reminder that use directions
are to be followed to avoid serious consequences. If
the environmental concentration exceeds the level ofconcern, specific label language may be mandated toprevent an even greater environmental risk.

Examples of Warning Statements Related to
Toxicity‘Runoff and drift from treatment areas may behazardous to aquatic organisms.’‘The pesticide is toxic to fish, aquatic invertebrates,
and wildlife.’‘Drift and runoff may be hazardous to aquaticorganisms in neighboring areas.’‘This pesticide is extremely toxic to fish and wildlife.’

Examples of Actions to Mitigate Entry into
Surface Water‘Avoid over-watering since excessive watering may
reduce performance and increase runoff.’‘Do not apply to turf sites that border lakes, ponds,
or streams.’‘Do not apply to fairways.’‘Do not apply when weather conditions are likely tocause drift from treated area.’‘This product may not be applied aerially or byground within 66 feet of the points where field surface
water runoff enters perennial or intermittent streams
and rivers.’‘If the product is applied to highly erodible land, the66-foot buffer or set-back from runoff points must be
planted to a crop or seeded with grass or other suitable
crop.’

46

‘Remove frompremises or tightly
cover fish tanks anddisconnect aerator
when applying indoors
where such containers
are present.’‘Keep out of lakes,
streams, ponds, tidal
marshes, and estuaries for waterfowl
protection; do not
apply immediately
before or during
irrigation or on fields inproximity to waterfowl
nesting areas.’‘Do not apply where fish, shrimp, crabs, and otheraquatic life are important resources.’

8

Protection of Ground Water
The Environmental Hazards section of the label
may contain specific directions to prevent the occurrence of the pesticide in ground water. A productalready on the market becomes subject to restrictions
and advisories when it is detected in ground water. The
restrictions are based on the chemical and physicalproperties of the compound (mobility, persistence,
environmental fate) and levels of concern for humanhealth, as well as plant and aquatic life. For instance, a
new registration for a pesticide must include specificprecautionary statements if the pesticide has been
identified as a potential leacher.

Examples of Warning Statements Related toEnvironmental Fate
If it has been found in ground water: ‘This chemical
is known to leach through soil into ground water undercertain conditions as a result of agricultural use. Use ofthis chemical in areas where soils are permeable,
particularly where the water table is shallow, may resultin ground water contamination.’
If it has not been found in ground water but hasleaching characteristics: ‘This chemical demonstrates
the properties and characteristics associated withchemicals detected in ground water. Use of thischemical in areas where soils are permeable, particularly where the water table is shallow, may result inground water contamination.’

Examples of Actions to Mitigate Entry into
Ground Water‘Care must be taken when using this product toprevent back-siphoning into wells, to prevent spills, and47

to dispose of excess pesticides, spray mixture, orrinsates appropriately.’‘Check valves or antisiphoning devices must be
used on all mixing and or irrigation equipment.’‘Users are advised not to apply this product to sandand loamy soils where the water table (ground water) isnear the surface and soils are permeable.’‘This product may not be mixed, loaded, or usedwithin 50 feet of all wells, including abandoned wells,
drainage wells, and sink holes.’910

Restricted-Use Pesticides
Pesticides are classified for restricted use if they
carry significant potential to harm people, wildlife, orthe environment. Classification is based on how close
estimated environmental concentrations are to levels ofconcern. When very near levels of concern, predictedenvironmental concentrations must be mitigated (as in
the previous examples). Pesticides may be assigned a48

restricted-use classification limiting their purchase anduse to certified and licensed pesticide applicators (orpersons working under the direct supervision of acertified and licensed applicator).
Nearly two decades have elapsed since commercial
pesticide applicators and farmers (private applicators)
were first required to meet proficiency standards. EPA
and state pesticide certification programs educate
commercial and private applicators in the judicial use ofpesticides, and applicators are continually updated onsafe handling procedures. More than a million commercial and private pesticide applicators are certified andlicensed, currently.
The pesticide certification process is enhanced bylegal requirements for retail dealers who sell restricteduse pesticides. Dealers must meet recordkeeping
requirements which include documentation of thepurchaser's name, address, and current pesticide
applicator license number; they also must record thename and amount of product sold. This recordkeeping
system allows regulatory agencies to monitor the saleand use of restricted-use pesticides.

PUBLIC POLICY, PESTICIDES, AND
WATER QUALITY

Changes in public expectations and new scientificknowledge mandate continual evaluation of pesticide
use by local, state, and federal agencies. As a result,public debate surrounding the use of pesticides has
driven frequent reassessment of their benefits tosociety versus risks attributable to their use. This shift
in public policy decision relies on a framework ofproposing, discussing, and drafting legislative mandates to ensure that pesticides' benefits to society
outweigh their potential risks to human and environmental health.
During the 1950s, pesticide production escalated ascompanies began to commercialize their discoveries.
The pesticide technology of the ’50s spurred federal
and state governments to pass amendments to existing
regulations to ensure adequate control of pesticides
used in the United States. Early policies required
USDA to register all pesticides and to establish standards for label content.
In the 1960s a number of issues developed, raising
alarming and bothersome questions relative to environmental risks associated with pesticides. The views
expressed in Rachel Carson’s Silent Spring in 196249

outraged, coalesced, and engaged the public. Government leaders subsequently made environmental issues
a priority when assessing a pesticide for registration.
The creation of the United States Environmental
Protection Agency in 1970 represented a dramaticchange in the federal regulation of pesticides. Emphasis during the registration process shifted from a
proposed product's benefits to the potential risks its
use might pose to human and environmental health.
Pesticide registration hinged on manufacturers' ability
to meet stringent guidelines via increasingly comprehensive testing procedures; i.e., research data insupport of specific health and environmental public
policy objectives became crucial to the registration
process. Pesticide labels became the conduit linking
research data to user instructions designed to reduce
the potential for adverse health and environmental
effects.
As Americans have increasingly distanced themselves from their agricultural roots, they have becomeless tolerant of traditional arguments favoring thebenefits of pesticides. Public concern has triggered
stringent testing requirements in pursuit of productregistration, and society's perception of the benefit-torisk scenario plays a major role in determining the fateof pesticides—that is, whether or not they'll remain on
the market. Legislators draft laws and regulations toreflect the desires of their constituents, and effective
communication will be the key in educating the public in
support of pesticide use.

Public Policy Establishes Water Quality
Legislation
Public policy strategies for dealing with pesticides
are decided by government. The process involves theprioritization of issues to be addressed, development ofa plan, and implementation; as a unit, these steps
comprise reaction. The speed with which government
reacts to a pesticide issue may be influenced by local
situations or by large-scale strategies orchestrated
within the executive or legislative branch of the federal
government. Changes may be instituted via legal
decisions and interpretations rendered by courts of law.
In essence, Congress passes laws (governing pesticides), and EPA establishes regulations and policies bywhich to enforce them. In turn, courts determine
whether or not EPA enforces the intent of Congress—
and the public drives the speed and direction of theoverall reaction.

50

Federal and State Regulatory
Responsibility
State and federal agencies are responsible for
implementing and managing• legislative statutes,• executive branch policy decisions, and• judicial interpretations
that deal with pesticides and their potential to impact
water resources. Legislation sets goals and provides
the framework which guides federal agencies in
executing prescribed programs.
State and federal regulations require pesticide
manufacturers, government agencies, and the generalpublic to take certain actions relative to the manufacture, transportation, storage, application, and disposalof pesticides in order to meet statutory goals. Regulations may• require that specific pesticides meet new registration standards,• stipulate mandatory pesticide use education, and• mandate environmental monitoring to determine
any adverse effects on water resources.

SPECIAL INITIATIVES

Ground Water Protection Strategy. EPA continually seeks national cancellation of pesticides that posea threat to water quality. Currently, EPA's efforts toprevent pesticides from reaching ground water include• Predicting (on the basis of research data submitted by the manufacturer) a pesticide's potential to leachinto ground water• Establishing national label restrictions addressing
concerns on leaching• Requiring a restricted-use classification, triggering
additional training requirements for users• Providing each state the opportunity to develop
and implement a State Management Plan for eachpesticide identified as a potential leacher• Cancelling pesticides known to contaminate
ground water despite aversion efforts

51

The cornerstone to EPA's ground water protection
policy is the State Management Plan (SMP), by whichstates can tailor their own strategies to prevent groundwater contamination. The basic components of the
SMP include philosophy and goals toward protecting
ground water:• Roles and responsibilities of state agencies• Legal authority• Resources• Basis for assessment and planning• Monitoring• Prevention actions• Response to detections of pesticides• Enforcement mechanisms• Public awareness and participation• Information dissemination• Records and reporting
Use of pesticides identified as risks to ground water
are tightly controlled by EPA-approved SMPs:• EPA determines the need for an SMP.
• EPA stipulates a time period for SMP development
and approval, during which use of the pesticide may
continue.
• Use of the pesticide is allowed only in accordancewith the approved SMP.

Pesticide Reregistration
More than 50,000 pesticide products have beenregistered in the United States since FIFRA wasenacted in 1947. Congress amended FIFRA in 1988
and mandated through legislative language that all
pesticides registered before November 1984 would be
subject to reregistration by EPA. The goal of the nineyear reregistration program was to ensure that all
chemicals on the market have been fully evaluated.
The amendment prescribed that each pesticide’s
chemistry, toxicology, and environmental effects bereexamined using current scientific, medical, andregulatory guidelines.
FIFRA amended 1988 made necessary the reevaluation of 1150 active ingredients in 45,000 formulated
products. The active ingredients were assigned to 612
chemical cases (groups) of related pesticide active
ingredients. The 612 chemical cases were subdivided
into lists A, B, C, and D based on the ranking of various
reference criteria such as the potential for adverse
effects to food; drinking water; human health; plants

52and animals. EPA
produces
Reregistration Eligibility
Documents (REDs)
once a substantiallycomplete set of data ona chemical case has
been reviewed and no
significant issues
remain concerning useof the pesticide.

• 1150 active ingredients (45,000 formulations)• 612 chemical cases (groups) subdivided into four lists(A,B,C,D) based on ranking of reference criteria:• potential for residues in/on food• potential for drinking water contamination• potential for adverse effects on human health• potential for adverse effects on animals and plants

EPA's Review After Pesticide
Registration
The responsibilities of EPA and pesticide manufacturers do not end at the point of registration. Productinformation is continually collected, assembled, reviewed, and analyzed in cases where scientific studies
and field use indicate a potential for adverse impacts
on human health (such as long-term health effects andworker poisoning), environmental pollution (such as
ground water contamination), and toxic effects on
nontarget organisms (such as fish poisonings resulting
from pesticide runoff).

Reporting Adverse Information After
Registration
EPA can obtain information on the adverse impactsof pesticides via two reporting mechanisms:• FIFRA section 6(a)(2) reporting• Incident reporting
FIFRA states in Section 6(a)(2) that "if at any timeafter the registration of a pesticide the registrant has
additional factual information regarding unreasonable
adverse effects on the environment of the pesticide, heshall submit such information to the Administrator." The
6(a)(2) reporting requirement is a legal obligation andapplies solely to the registrant. Reports to EPA canoriginate from scientific research conducted by the
manufacturer with the intention of supporting continued
registration; but more often they result from data (onadverse effects) collected in field use situations. The
pesticide manufacturer provides EPA information
clearly identified as a 6(a)(2) report; in addition, themanufacturer must identify the newly observed adverse
effect. Examples of incidents requiring 6(a)(2) reports:• When pesticides impact aquatic organisms at alower dose than previously shown• When evidence from additional toxicologicalstudies shows new types of potentially adverse effects

53

Incident reporting is used to measure the impact ofa pesticide in the marketplace. Incident data canoriginate from many sources: universities, poison
control centers, state and federal fish and gameagencies, state departments of agriculture, EPA
regional offices, or the news. Essentially, any adverse
impact is subject to incident reporting.
All section 6(a)(2) and incident reports submitted to
EPA are categorized and indexed on the Incident Data
System—part of the Pesticide Information Network
operated by EPA that is publicly available in the UnitedStates. Information concerning new, potentially adverse
effects is submitted to the proper division for review
and analysis to determine if an immediate EPA review
is warranted. For instance, the Environmental Fate andEffects Division would examine potential impacts on
wildlife, while human health concerns would be reviewed by the Health Effects Divisions within the Officeof Pesticide Programs.
An EPA work group meets weekly to discuss FIFRA
6(a)(2) and incident reports. Priority is given to thosepesticides with the most serious problem potential inorder to expedite review, response, and remedialaction. Those responsible for minimizing recurrent risk
from the use of the product in question are monitored
to ensure that appropriate measures are taken.

Special Review
The special review process allows EPA the regulatory flexibility to reevaluate the registration of a pesticide. A special review may be initiated when newevidence suggests that the legal use of a specificactive ingredient may pose unreasonable risk to humanhealth or the environment.
The process officially begins with an EPA letter of
notification (called the Grasley-Allen letter) to theregistrant, stating that the active ingredient is formallybeing placed under special review. The letter provides
a brief summary of the reasons why.
Information pertinent to the suspected risk associated with the active ingredient is scrutinized by EPA
reviewers who, in turn, prepare a 'risk review' forcomparison with its projected benefits. The availability
and efficacy of the pesticide, as well as the cost ofalternative controls, are appraised in a benefit-to-risk
analysis. Conclusions drawn from analysis are forwarded to the FIFRA Scientific Advisory Panel, to
USDA, and to the general public (through the Federal
Register) for comments on the scientific accuracy, datainterpretation, and rationale behind proposed risk
reduction measures. If after taking all comments underadvisement EPA concludes that risk reduction measures are needed, there are four avenues of pursuit:54

alteration of label language; classification of products
containing the active ingredient for restricted use;
elimination of specific uses; suspension or cancellationof the registration.

EPA’s Lower Risk Pesticide Policy
EPA has identified four areas for implementation ofa voluntary reduced-risk pesticide initiative for pesticide
manufacturers: developing criteria to identify lower-risk
pesticides; streamlining the overall registration process;
improving pesticide labels to effect well-informed
choices in the marketplace; and encouraging (viastatutory changes which would extend the period of
exclusive use of data, or patent protection) the development of reduced-risk pesticides.
Under this voluntary approach, manufacturers of
products containing a new active ingredient thought tobe worthy of reduced-risk classification must submit
substantiative data. Claims of reduced risk must be
supported by evidence of reduced toxicity to humans
and other nontarget organisms, and evidence of theenvironmental fate of the active ingredient must be
substantiated. Incorporation of the pesticide into an
integrated pest management program must be considered in comparison to alternative products. EPA will
determine the sequence of application review according to these elements, as described.
EPA's intent is to promote pesticides that pose
lower or reduced risks in comparison to alternative
pesticides. Applications documenting lower-risk characteristics will be granted priority consideration, thereby
gaining a distinct marketing advantage. In 1996, EPA
will strengthen the reduced-risk initiative further by
denying review of registration data for pesticides thatfail the agency’s reduced-risk screen.

CONCLUSIONS

Protection of ground and surface water quality is
critical to economic viability, as well as human healthand environmental quality. Although pesticides are
essential in the production of an adequate, economical
food supply, rural (agricultural) as well as urban uses
loom as possible sources of water contamination.
Detection of pesticides in water aroused public interestin the environmental impact of agricultural chemicals;
and the resulting heightened concern is reflected instrict legislation which impacts the pesticide industry
significantly.

55

In the interest of minimizing risks associated withpesticides, significant public resources have been
allocated for the development and implementation ofrational, pesticide use policies based on solid scientificevidence. Compliance involves extensive, detailed,expensive laboratory research and field studies todetermine the behavior and environmental fate ofpesticides—that is, in deriving the solid scientificevidence—and it follows that manufacturers must
commit significant financial resources to productdevelopment en route to the marketplace.
A pesticide's route and rate of entry into the environment, as well as its degradation characteristics, are key
to understanding and predicting its potential impact on
surface and ground water. Preregistration researchdata also play a significant role in determining use
pattern and hazard statement language for the pesticide label. Research findings also influence the stringency of post-registration monitoring programs.

56

Technological breakthroughs that allow for pesticide detections at very low concentrations, combinedwith increased scrutiny of water resources by researchers and regulators, have increased scientific understanding of the potential for pesticides to contaminate
water resources. The pesticide industry seeks todevelop pesticides and pesticide management practices with the lowest possible potential for adverse
environmental impact. The public interest is well served
by a cooperative effort among regulators, university
researchers, and industry to establish reasonable use
restrictions. These efforts should ensure that, whenused appropriately, pest control products will not posea threat to water quality.

ACKNOWLEDGMENTS

Special thanks to Marty Risch, U.S. Geological
Survey, for his constructive comments and ideas that
aided the development of this publication.
Thanks also to R. David Jones, U.S. EPA, for the
figure which appears on page 36; and to Ron Parker,
R. David Jones, and Siros Mostaghimi, U.S. EPA, forthe figure on page 38. Partial funding was provided by
U.S. EPA, Region 5.
All complementary illustrations are the work of artist
Stephen Adduci; his work is sincerely appreciated. The
following individuals are acknowledged for their invaluable, thorough reviews of this document.
K. Balu, Ciba Crop Protection
Aldos Barefoot, DuPont Agricultural Products
Elizabeth Behl, U.S. EPA
Don de Blasio, U.S. EPA, Region 5
Kevin Costello, U.S. EPA
Harry Craven, U.S. EPA
Allan Felsot, Washington State University
Dick Green, University of Hawaii at Manoa
Sidney Harper, Tennessee Valley Authority
Paul Hendley, Zeneca
Scott Jackson, BASF
Henry Jacoby, U.S. EPA
William Koskinen, USDA, ARS
Dennis Laskowski, DowElanco
Terry Lavy, University of Arkansas
Mark Lenz, Bayer, Inc.
Jim Lin, Bayer, Inc.
George Oliver, DowElanco
P.S.C. Rao, University of Florida

57

REVIEWED: 5/01
The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the Purdue University Cooperative Extension Service is implied.
It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to the programs and facilities without
regard to race, color, sex, religion, national origin, age, marital status, parental status, sexual orientation, or disability. Purdue University is an Affirmative Action employer.

60