Enhanced Biodegradation of Pesticides in the Environment

306 Pages·1990·5.45 MB·English

by  Kenneth D. Racke and Joel R. Coats (Eds.)

ACS SYMPOSIUM SERIES 426
Enhanced Biodegradation
of Pesticides in the Environment
Kenneth D. Racke, EDITOR
DowElanco
Joel R. Coats,
Iowa State University
Developed from a symposium sponsored
by the Division of Agrochemicals
at the 198th National Meeting
of the American Chemical Society,
Miami Beach, Florida
September 10-15, 1989
American Chemical Society, Washington, DC 1990
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Library of Congress Cataloging-in-Publication Data
Enhanced Biodegradation of Pesticides in the Environment
Kenneth D. Racke, editor Joel R. Coats, editor
p. cm.—(ACS Symposium Series, 0065-6156; 426).
"Developed from a symposium sponsored by the Division of
Agrochemicals at the 198th National Meeting of the American
Chemical Society, Miami Beach, Florida, September 10-15, 1989."
Includes bibliograpical references.
ISBN 0-8412-1784-X
1. Pesticides—Biodegradation—Congresses
metabolism—Congresses.
I. Racke, Kenneth D., 1959- . II. Coats, Joel R., 1948-
III. American Chemical Society. Division of Agrochemicals.
IV. American Chemical Society. Meeting (198th : 1989 : Miami
Beach, Fla.) V. Series
SB951.145.B54E54 1990
632'.95042—dc20 90-34194
CIP
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In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
ACS Symposium Series
M. Joan Comstock, Series Editor
1990 ACS Books Advisory Board
Paul S. Anderson Michael R. Ladisch
Merck Sharp & Dohme Research Purdue University
Laboratories
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Kraft General Foods
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Lehigh University U.S. Naval Research Laboratory
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In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that, in order to save time, the
papers are not typeset but are reproduced as they are submitted
by the authors in camera-ready form. Papers are reviewed under
the supervision of the Editors with the assistance of the Series
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lished papers are no
research are acceptable, because symposia may embrace both
types of presentation.
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Preface
MICROBIAL DEGRADATION HAS LONG BEEN RECOGNIZED as a primary
means of dissipating many pesticides in soil and water ecosystems, and
recognition of this has prompted the development of biodegradable her
bicides, insecticides, and fungicides. Because these biodegradable pesti
cides have predictable patterns of environmental persistence, they have
become key component f agricultural d industrial
systems. Early research
provided evidence that microbial adaptation could result in abnormally
accelerated rates of pesticide breakdown. However, because of the lack
of observable economic impact on pest control practices, the
phenomenon of enhanced microbial pesticide degradation languished as
an academic curiosity for many years. The contemporary occurrence of
enhanced degradation and associated pest control failures has spurred
reexamination of adapted microbial pesticide degradation as a critical
environmental process. The recent flurry of research into microbial
adaptation for pesticide degradation has spanned disciplines ranging
from applied agronomy to molecular biology.
This book is the first collection of research results to focus
exclusively on the adaptation of microorganisms for rapid pesticide
degradation. After an introductory chapter, the book is organized into
three sections, and it concludes with an appendix of key chemical struc
tures. The first section contains general field and laboratory observa
tions of enhanced herbicide, insecticide, and fungicide degradation. The
second section focuses more specifically on the microbiological and
biochemical aspects of adapted microbial pesticide metabolism in terres
trial and aquatic systems. Finally, the third section addresses manage
ment strategies and implications of enhanced pesticide degradation.
The editors thank the contributors to this volume, including authors,
coauthors, and reviewers, for their time and insight. We also express our
thanks to the Division of Agrochemicals, the sponsor of the symposium
on which this book is based, and to the ACS Books Department staff for
their hard work in presenting this volume.
ix
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Dedication
This book is dedicated to Dr. E. P. Lichtenstein of the University of
Wisconsin and Dr. R. L. Metcalf of the University of Illinois, who con
ducted pioneering work on the environmental chemistry of pesticides
and served as early mentors for the editors.
KENNETH D. RACKE
Environmental Chemistry Laboratory
DowElanco
Midland, MI 48841
JOEL R. COATS
Department of Entomology
Iowa State University
Ames, IA 50011-3140
January 19, 1990
x
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Chapter 1
Pesticides in the Soil Microbial Ecosystem
Kenneth D. Racke
Environmental Chemistry Laboratory, DowElanco, 9001 Building,
Midland, MI 48641-1706
The soil environment comprises a diverse ecosystem in
which the recyclin
link with global
contains populations of microorganisms that have
exceptional degradative capabilities and the ability
to adapt to utilize the variety of allochthonous organic
materials that enter the soil carbon cycle. As man has
come to rely upon the use of soil-applied pesticides in
many agroecosystems, he has learned that the residual
control provided by these compounds is modulated by
both abiotic and biotic degradative processes. The
ability of microorganisms to adapt for rapid catabolism
of some soil pesticides has in some cases resulted in
economically significant pest control failures. The
phenomenon of enhanced pesticide degradation has become
a significant concern requiring the development of
management strategies. Yet, this unwelcome occurrence
has led to valuable opportunities to investigate the
remarkable adaptability and complexity of the soil
microbial ecosystem.
In order to properly understand pesticides in the context of the soil
microbial ecosystem, it is important to consider the relevant
properties of the soil environment, the metabolic capabilities of the
soil microbial community, and the uses and dissipation routes of
soil-applied pesticides.
The Soil Environment
Soil has been defined as the "unconsolidated mineral material on the
immediate surface of the earth that serves as a natural medium for
the growth of land plants" (1). Although this sounds relatively
0097-6156/90/0426-0001S06.00/0
© 1990 American Chemical Society
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
2 ENHANCED BIODEGRADATION OF PESTICIDES IN THE ENVIRONMENT
simple, in reality soil is a complex ecosystem, not merely the "dirt"
of vernacular language. In a physical sense, soil is composed of
mineral material (clay, silt, sand, stones), air or water-filled pore
space, and organic matter. The soil organic matter is a very
important and active component. Roughly three fractions can be
delineated; a macroscopic component composed of particulate plant and
animal debris in early stages of breakdown , a chemically well-
defined assemblage of various simple organic compounds
(carbohydrates, amino acids, proteins), and a complex, dark-colored
component, largely aromatic and polymeric (i.e., "humus"), that is
relatively resistant to degradation (2). Turnover times for organic
debris, soluble compounds, and humus are on the order of 2-5 years,
5-25 years, and 250-2500 years, respectively (3). The physical
components of soil are integrated into a heterogeneous matrix that
forms the basis for the soil aggregate and particle. For example,
clays and humic materials are often intimately associated to form
organo-mineral complexe
The soil should be understoo
of microscopic (bacteria, fungi, protozoans, algae) and macroscopic
(annelids, arthropods) organisms forming complex food web
communities. The soil microflora play a key role in globally
significant nutrient cycles. Important examples of such
microbially-mediated processes are nitrification, denitrification,
and carbon mineralization. The soil ecosystem constitutes an
allochthonous one in an energetic sense, with plant and animal debris
entering the soil to begin the degradative process. In a practical
sense, the soil may be viewed as a vast recycling depot, continually
receiving reduced compounds of carbon and continually oxidizing them
to C02 and water (5). Of the soil organisms active in this recycling
effort, the soil fungi are particularly effective in initiating the
degradation of rather complex polymeric substrates (e.g., cellulose),
whereas the soil bacteria have in general specialized in the
degradation of simpler, soluble organics. Among the indigenous
populations are many bacterial species that are largely quiescent,
but flourish dramatically when readily available organic nutrients
are added (6). Thus, although the soil has often been viewed as a
rich, fertile ecosystem, in reality soil is considered to be an
oligotrophic environment (7). The fierce nature of competition for
the easily degradable organic compounds added to soil is exemplified
by antibiotic production by soil microorganisms, which probably
represents a form of chemical warfare over the defense of niches (6).
Pesticides Applied to the Soil Environment
Soil is the foundation of agriculture. It is the substrate in which
the agronomic crops of the earth find required nutrients, water,
microbial symbionts, and a physical anchor. Due to the presence in
soil of crop competitors and competitors for the use of this plant
biomass, pesticides have become indispensible tools in the management
of weeds, insects, and fungi of economic significance. At present
there are approximately 600 different pesticide active ingredients
registered for use in the U.S., and millions of pounds are globally
applied each year, with the world market estimated at greater than 20
billion dollars (8). Much of this use represents direct application
to soil, and a considerable portion of that which is foliarly applied
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
1. RACKE Pesticides in the Soil Microbial Ecosystem 3
may reach the soil as spray drift, runoff, or wash-off. One
consideration of the use of soil-applied pesticides is that they
should persist long enough in soil to control the target pest(s), but
not so long as to create environmental risks.
Herbicides which are applied directly to soil with the intent of
providing residual weed control may be applied prior to crop planting
(preplant) or after planting and prior to weed emergence
(preemergence). Classes of herbicides that are applied preplant or
preemergence include the triazines, substituted ureas, carbamates,
carbamothioates, sulfonyl ureas, chloracetarnides, and dinitroanilines
(9). Many important crops, such as corn and soybeans, rely upon
preplant or preemergence herbicides. A typical preemergent weed
control scenario is provided by the occurrence of wild proso millet
(Panicum miliaceum) in Midwestern U.S. corn. Wild proso millet is a
pernicious grass species, and often exhibits both early and late
season flushes (10). One of the herbicides that is effective against
this weed is EPTC, whic
(dichlormid) that allow
is applied preplant-incorporated at 2.2-6.7 kg/ha and must persist in
significant quantities for roughly 15-30 days for effective control
of early season flushes of wild proso millet (11.). Jt should be
noted that in many agroecosysterns, such as corn, herbicides or "tank
mixes" of multiple herbicides are applied to control complexes of
weed species.
Although the use of insecticides is not as heavily skewed toward
soil application as that for herbicides, there are several
significant crops such as corn, peanuts, and sugarbeets which rely
heavily on successful control of soil insect pests. A typical
example of soil insect pest control is provided by the corn rootworm
(Diabrotica spp.). This key pest of corn overwinters in the egg
stage in corn stubble, and after a variable hatching period the
larvae actively damage corn roots from early June to late July (12).
The most common method of corn rootworm control involves an
at-planting (April-May) application of a granular insecticide, such
as carbofuran, at 1 kg/ha. To provide effective rootworm control the
carbofuran applied must persist in toxic concentrations for
approximately 4-8 weeks after application (13). Insecticides of
several classes have been employed for soil insect control, including
organophosphorus, carbamate, and pyrethroid compounds.
Fungicides are applied to soil in a few specific instances for
control of soil-borne plant pathogens. Some crops for which
soil-applied fungicide applications are often necessary include
onions, peanuts, and avocado. An example of this would be the use of
iprodione for the control of white rot disease {Sclerotium cepivorum)
of onions in the United Kingdom (14). Soil-applied fungicides are
often systemic in nature, and may need to be taken up by plant roots
and translocated to stem and foliage for efficacious pathogen
control. Several commonly used soil fungicides are iprodione,
carbendazim, and thiabendazole.
Mechanisms of Pesticide Dissipation in Soil
Pesticides which are applied to soil become enmeshed in the transport
and degradation processes that affect all allochthonous organics
added to this dynamic ecosystem (15).
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
4 ENHANCED BIODEGRADATION OF PESTICIDES IN THE ENVIRONMENT
Transport Processes. There are several processes that are active in
transporting pesticide residues within or out of the soil ecosystem.
The first class of processes involves aerial transport of pesticides
from the soil into the atmosphere. Volatilization is an important
process by which pesticides in the vapor phase can move from the soil
surface into the atmosphere. Pesticides with vapor pressures greater
than approximately 10" mm Hg at 25°C are most greatly affected, and
losses from surface applications can approach greater than 50% in
less than 48 hours (16). In addition to the vapor pressure of a
pesticide, which increases with increasing temperature, several soil
properties such as moisture and organic matter content can greatly
modify the kinetics of volatilization. This is due to the fact that
pesticides in soil partition between at least three phases:
soil-sorbed, soil solution, and soil air (17). Although not
intensively investigated, movement of soil particles and attached
pesticides by wind may also play a role under some environmental
conditions.
The second class o
movement of dissolved or particulate-sorbed pesticides in water.
Leaching of pesticides has been recognized as a critical process, i f
not in the sense of the absolute percentage of applied pesticide
leached into the soil profile, then with respect to the contamination
of groundwater by trace quantities of pesticide. Several pathways of
dissolved pesticide movement with leaching water are recognized (18).
Convection and diffusion are often simultaneous processes that
involve pesticide transport in water moving gravitationally or with a
concentration gradient. Macropore flow involves pesticide transport
in water flowing through the irregular network of channels created by
earthworms, roots, insects, and burrowing animals. The extent of
leaching is governed by partitioning processes between sorbed and
solution phase pesticide, and often laboratory-determined sorption
coefficients (e.g. Freundlich Kd) are used to predict field leaching
potential (19). An understanding of the relationship between
observed partitioning behavior and actual field leaching measurement
is complicated by such factors as nonequi1ibrium partitioning
resulting from slow-desorption kinetics (20). Transport of
pesticides in water moving over the soil surface is also an important
process that can impact surface-water quality. Pesticides with water
solubilities greater than approximately 10 pg/g have been
hypothesized to move largely in the solution phase, while less
soluble pesticides are thought to move mainly sorbed to eroding soil
particles (21).
Abiotic Transformation Processes. Pesticides that reside within or
on the soil are subject to the abiotic and microbiological
transformation processes that operate in this great recycling
ecosystem. After numerous problems with the prolonged persistence of
some early soil pesticides (e.g. aldrin, chlordane), degradability is
viewed as a desirable attribute of modern soil-applied pesticides.
Degradation processes in soil may result in accumulation of
well-defined metabolites, incorporation of pesticide carbon or
nitrogen into the soil organic matter fraction, or complete
mineralization. Many of the abiotic degradation processes active in
soil result in partial degradation of the pesticide to products that
are further degraded microbially, accumulate in soil temporarily, or
In Enhanced Biodegradation of Pesticides in the Environment; Racke, K., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1990.