Chapter 20
Enhanced Biodegradation of Pesticides in the Environment Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 07/09/18. For personal use only.
Implications of Enhanced Biodegradation for the Use and Study of Pesticides in the Soil Environment Kenneth D. Racke Environmental Chemistry Laboratory, DowElanco, 9001 Building, Midland, MI 48641-1706
Microbial adaptation for biodegradation is a common microevolutionary phenomenon that occurs wherever biodegradable pesticides or other xenobiotics contact microbial populations. The accelerated biodegradation of pesticides in agricultural systems has certainly had a substantial impact on pesticide users, researchers, and the agrochemicals industry. Major advances in our understanding of the theoretical and practical aspects of enhanced biodegradation have come about as a result of the recent flurry of research activity generated by contemporary occurrences associated with pest control failure. Future challenges and opportunities that remain relate to the development of conceptual predictive models, the design of biodegradable yet adaptation-resistant pesticides, clarification of the soil microbial ecology of biodegradation, and the application of adapted microbial strains for environmental decontamination and hazardous waste detoxification.
Enhanced
pesticide
interest
and concern.
outlined
the
involved,
biodégradation
tion,
In the
of
have
detailed
occurs to
way
the
the
place the need
enhanced recent that to
its
true
the
coping
of
been
and
chemical
with
enhanced
The purpose
pesticide
impact
have
be
of
this
biodégradation
enhanced
made,
and
in
biodégradathe
future
addressed.
Biodégradation impact
of
enhanced
i n a g r i c u l t u r a l systems been
of
much
systematically
microbiological means
i n agroecosystems.
advances that
Enhanced
problem has
regarding
generated
by d i s c u s s i n g
frustrating
pesticides
recently chapters
and d i s c u s s e d
is
challenges
Impact a
it
major r e s e a r c h
research The
as
chapter
perspective
has
The p r e c e e d i n g
phenomenon,
interactions concluding
biodégradation
is
difference
significance.
of
very
biodégradation hard
opinion
F o r example,
to
quantify.
that an
0097-6156/90/0426-0269$06.00/0 © 1990 American Chemical Society
has
of Part
of
existed
industry
spokesman
270
ENHANCED BIODEGRADATION O F PESTICIDES IN T H E ENVIRONMENT
was
quoted
as
interesting problem.
saying:
I n what (I).
private
and p u b l i c
Despite
enhanced
(2,3,4).
From a
we're
a l l . . . " of
"From a
problem.
seeing, type
of
sectors
have
felt
biodégradation
degradation:
"The c a s e
this
phenomenon
practices
in
enhanced
certain
Pesticide
Users. been
have
by
the
degradation, as
Actual
are
within
the
number
used
in
no
1985
have
Asia,
are
rare
of
of
enhanced
enhanced show
that
affected
by
that of
rootworm
years,
the
greatest
(0-18%)
indicates
1983
and
that
they
perceived
378
gave
1984
Analyses
60% o f
were of
significant herbicides weed o r
correlation detected
(9).
because
directly
the
marauding
insects
there
certainly
of
the
products.
failures
both
of
highly
a
taken
This
new
of
is
by s u r p r i s e
Pesticide
Manufacturers.
Pesticide
adversely
affected
occurrence
products.
One o f
products
or
by the
sales
the most due
to
direct real
a of
weed
these control impact
always caused
reality,
reliable pest (e.g.,
due
estimate.
not
often
isofenphos)
in
by and the
and
control carbofuran)
often
have,
(10).
manufacturers of
enhanced
adverse or
corn.
among g r o w e r s
supply
pesticides
(e.g.,
in
found
to
in
indicated
economic
is
p a r t i a l l y because
reliable
pesticides
everyone
confidence to
weeds
competition is
Nebraska
users
difficult
or
control
Central
and poor
perception
industry
A similar
weed
actual
of
be
degradation
reduction
damage
But
loss
long-used,
touted
seemingly,
crop yield
of
very
by
behavior may
fields
enhanced
are
observed
agrochemicals
efficacious
of
1984,
failures
failures
butylate
control
insecticide growers
For
(8).
In South
measurements
and weeds. been
the
failure
actual to
efficacy
any
Iowa
during
variable
laboratory assay)
However, control
proportional
has
by
of
in
360
the
5 years.
from surveyed
between
of
rootworm
19% o f
carbamothioate
the
adapted
growers
many f a c t o r s
a n d 40% o f
with
taken
of
insecticides
results.
EPTC u s e r s
samples
insect
for
distinct
dissatisfied
soil (as
performance
more
that
rootworm c o n t r o l
Nebraska farmers
of
the
that
boundries!
percentage
but
diverse potatoes
observations
A survey
preceeding
enhanced
such
implies
with
an average
them
insect,
been
by
and
these
percentage
regarding experiences
compounds of
national
the
for
on
of
have
caused
avocados, East)
degradation
and r e l y
ravages
documented
degradation.
isofenphos,
performance
of
been
enhanced
failures
d i s t r i b u t i o n of
12% d u r i n g t h e
5
the
from the
onions,
23% f o r
ability
Who h a s
pesticides
The M i d d l e
respecters
performance
of
been
was
is
of
protection
agroecosystems
control
beets,
revealed
poor last
influencing
and
pest
sugar
estimates
an average
This
the
occurrence
clearly
crop
at
in
impact
reviewer
earlier
in
use
Many d i v e r s e of
Europe,
failures
experienced
survey
substantial one
(4).
great
impact
contemporary
affected
protection
The g e o g r a p h i c a l
growers
other
of
losers
actually
instances
experiencing
control and
pests.
rice,
America,
area
corn
adversely
significant
and
microorganisms one
had a
an
a
many r e s e a r c h e r s
the
presented
direct
who
effects
corn,
(3,4,5,6,7). (North
to
T h e most
and f u n g a l
touched crops
indeed
agroecosysterns."
growers
economically
weed,
that
is
not
major economic
hyperbole,
statement
histories has
no
this
it's
degradation?
game for
has
recent
standpoint,
standpoint,
there's
this
C o n s i d e r the
natural
theoretical practical
have
results
perceived
also
been
degradation
pest
involves control
of
the
their loss
failures.
20. RACKE The
Midwestern U.S.
supplies removed least
a
litany
from
(4,10). a
related
of
to
remedial
measures.
undergo
investigators in-house
at
effort
impossible
these
projects,
industrial of
as
Gray
well
as
and Joo of
a
that
screening
that
step
have the
efforts
have
for
that
efforts users
revolved
is
soil a
by
the
is
to
rapid companies for
developmental
ignore.
Considerable
means
coping
(17).
in
the
generally
pesticides
necessary of
For
with
example,
by S t a u f f e r
growers
and d e a l e r s ,
entitled
" C o r n Rootworm Management:
1985
contained
biodégradation extension
a
very
a
pesticide
including
a
pair
this
degradation
in
of
an
microbial
problems
have
been
hosted
by S t a u f f e r
effort
has
marketing
products
imply that
susceptible
to
insecticide
seems
all
microbial
one
of
two
known e n h a n c e d the
adaptation
(e.g.,
a
h a v i n g unknown e n h a n c e d
degradation
using
microbial
their
adaptation,
products
degradation
(e.g.,
a
grower
action".).
Unfortunately,
that
they
brochure: this
have need
"
of
grower 2.
The
no
resists
marketing a c t i v i t y
on
industry, seamier
enhanced 1.
types
are
of
Companies
problems
have
equally
brochure:
potential, have
and
by
Companies
sought
(21)
enhanced
conferences
These
products
problem.").
to
of
degradation
this
withresistance
immune t o
Experts"
sponsored use
For
booklet
researchers
strategies:
competitor's
area.
topic
a n d Dow.
involved
of
information
the
the
the
marketing purposes.
involved
with
from of
special
1985
usually
in
have
comely
digestable
informative
and p r i v a t e several
the
T h e more
facilitate
Insights
educational
sought
to
university
is
companies
supply
working
presentation
In a d d i t i o n ,
information for
have
to
d i s t r i b u t e d an
balanced
degradation
considered
and to
researchers
Carbide
by eight
personnel.
be
agrochemicals
around attempts
Union
growers
conducted
demonstrated It
costs of
industrial
exemplified
and r e s e a r c h e r s .
in
products
by
manufactured by other
must
example,
efforts
considerable
been
EPTC c o n t a i n i n g
that
independent
of
who
is
and t e s t i n g
between
side
This
products
herbicide
industrial cost educational
toward p e s t i c i d e
information
soil
reports
work has
of
outside
these
developing
development
to
many
company c a n a f f o r d existing
gone
laboratories,
candidate
to
existing
development
f u n d i n g has
own c a r b a m o t h i o a t e s .
exchange
that
and
of
degradation
the
new
and f o r
(12).
projects
proprietary nature
Stauffer,
of
1985
numerous
of
herbicides
assay
exemplified
(18,19,20).
substantial directed
for
substantial
devoted
extensive
A final
these
no
been
formulation of
inhibitor
of
their
degradation of
consider altered
(16)
t h a n 8% b y
and p u b l i s h e d
that
enhanced
also
the
is
The magnitude
(13,14,15,16).
ongoing to
this
expended.
given
number o f of
potential
(Fisons), (Mobay)
c a r b o f u r a n plummeted
funded
and u n i v e r s i t y
presented
indicate
less
at
include
degradation
biodégradation
been
estimate
susceptibility
enhanced
also
but
to
Products
development
isofenphos
wherein
also
much o f
of
bendiocarb
and
enhanced
ill)
the
Whereas
several
recognized
efforts
of
laboratories
degradation
1977
stages
(Chevron),
i n d u s t r y has
government
to
to
( > 2 0 0 MM $ / y e a r )
products.
degradation
(Shell),
Iowa c o r n ,
enhanced
has
representatives work
in
late
enhanced
due
in
an assessment
to
in
bufencarb
sales
agrochemicals
products
of
market
and f a i l e d
halted
trimethacarb
20% m a r k e t s h a r e
The
or
(Chemagro), loss
insecticide
business
result
c a r b o f u r a n (FMC) use
from
is
a
(BASF),
The
lost
market
p a r t i a l l y as
cloethocarb
rootworm
of
this
fensulfothion
by
271
Implications for Use & Study of Pesticides in Soil
to
"No
marketing
or reassure
worry of
enhanced
microbial has
i n some
cases
272
ENHANCED BIODEGRADATION OF PESTICIDES IN T H E ENVIRONMENT
muddled t h e i s s u e w i t h growers r e g a r d i n g t h e a c t u a l s t a t u s o f enhanced d e g r a d a t i o n problems w i t h s p e c i f i c p e s t i c i d e p r o d u c t s . The R e s e a r c h / E x t e n s i o n Community. U n i v e r s i t y , s t a t e , and f e d e r a l r e s e a r c h e r s and e x t e n s i o n p e r s o n n e l have a l s o been a f f e c t e d by t h e contemporary o c c u r r e n c e o f enhanced d e g r a d a t i o n . The s t a t e e x t e n s i o n s e r v i c e s , which s e r v e as t h e c r i t i c a l l i n k between t h e heady s c i e n t i f i c u n i v e r s i t y r e s e a r c h and the p r a c t i c a l i n f o r m a t i o n a l needs o f growers, have o f t e n f o u n d themselves i n t h e most d i f f i c u l t p o s i t i o n i n r e g a r d t o enhanced d e g r a d a t i o n problems. They a r e t h e ones o f t e n c a l l e d upon t o d e a l w i t h p e s t c o n t r o l f a i l u r e problems and to make s p e c i f i c recommendations r e g a r d i n g ways t o a v o i d o r manage t h e s e problems. P a r t o f the agony o f e x t e n s i o n workers may be a t t r i b u t e d t o a l a c k o f p r o g r e s s on the r e s e a r c h l e v e l . For i n s t a n c e , the e a r l i e s t p u b l i s h e d r e p o r t s o f s t u d i e s e x a m i n i n g t h e p o s s i b i l i t y t h a t enhanced d e g r a d a t i o n was t h e c a u s e o f r e p o r t e d c a r b o f u r a n p e s t c o n t r o l f a i l u r e s i n Midwestern U.S. c o r n p r e s e n t e d c o n f l i c t i n g c o n c l u s i o n s , w i t h some n e g a t i v e (22,23) and some p o s i t i v e (24,25) f i n d i n g s . E x t e n s i o n recommendations o f t e n d i r e c t l y r e f l e c t the l e v e l o f r e s e a r c h u n d e r s t a n d i n g a v a i l a b l e . In t h e e a r l y 1980's t h e s e recommendations s t a r t e d t o a d d r e s s the problem o f enhanced degradation. F o r example, an A p r i l 1982 C o r n Rootworm Management b u l l e t i n from Iowa S t a t e U n i v e r s i t y (26) s t a t e d : " I t i s r e c o g n i z e d t h a t c o n t i n u e d carbamate i n s e c t i c i d e use enhanced t h e speed w i t h which c e r t a i n s o i l m i c r o o r g a n i s m break down Furadan, and t h a t t h i s i s t h e c a u s e o f poor c o n t r o l " . The recommendation t o a v o i d u s i n g c a r b o f u r a n i f i t performed p o o r l y f o l l o w e d . But r e f l e c t i n g t h e l a c k o f p r o o f t h a t organophosphorus i n s e c t i c i d e s c o u l d a l s o undergo enhanced d e g r a d a t i o n , t h i s statement a l s o appeared: " C u r r e n t l y a v a i l a b l e ISU r e s e a r c h d a t a do not i n d i c a t e t h a t c o n t i n u o u s use o f an organophosphate s o i l i n s e c t i c i d e s i g n i f i c a n t l y a f f e c t s t h e performance o f any i n s e c t i c i d e , . . . " . A f t e r the d i s c o v e r y o f enhanced i s o f e n p h o s d e g r a d a t i o n (10) e x t e n s i o n recommendations were m o d i f i e d and r e f l e c t e d the u n c e r t a i n t y r e g a r d i n g t h e a b i l i t y o f any s o i l i n s e c t i c i d e t o m a i n t a i n e f f i c a c y i f used c o n t i n u o u s l y (27,28). It was d u r i n g t h e mid 1980*s t h a t b o t h i n s e c t i c i d e and h e r b i c i d e recommendations s t a r t e d e m p h a s i z i n g t h e r o t a t i o n o r d i s u s e o f p e s t i c i d e s w i t h p r o v e n enhanced d e g r a d a t i o n p o t e n t i a l (27.28,29). R e s e a r c h e r s a t u n i v e r s i t y and government l a b o r a t o r i e s have responded t o enhanced d e g r a d a t i o n by f o c u s i n g c o n s i d e r a b l e r e s e a r c h e f f o r t s on u n r e s o l v e d i s s u e s . R e s e a r c h e r s i n many d i v e r s e d i s c i p l i n e s have become i n v o l v e d as f u n d i n g f o r enhanced d e g r a d a t i o n r e s e a r c h became a v a i l a b l e . One o f the l e a d i n g s p o n s o r s o f enhanced d e g r a d a t i o n r e s e a r c h i n t h e U.S. has been t h e P e s t i c i d e Impact Assessment Program (ΡΙΑΡ) o f the U.S. Department o f A g r i c u l t u r e . A f t e r s p o n s o r i n g a workshop on the problem i n S t . L o u i s i n 1984, t h e PIAP has a l l o c a t e d c o n s i d e r a b l e f u n d i n g t o enhanced d e g r a d a t i o n r e s e a r c h . F o r example, the N o r t h C e n t r a l Region PIAP a l l o c a t e d o v e r $300,000 f o r t h e s e p r o j e c t s between 1982 and 1989 (A.C. Waldron, p e r s o n a l communication). S t a t e f u n d i n g has a l s o been a v a i l a b l e f o r t h i s t y p e o f r e s e a r c h , as e x e m p l i f i e d by p r o j e c t s s u p p o r t e d by t h e N e b r a s k a C o r n Development Board (30), the Iowa C o r n P r o m o t i o n Board (31), and t h e O n t a r i o P e s t i c i d e s A d v i s o r y Committee (32). But t h i s s u p p o r t , a l t h o u g h s i g n i f i c a n t , has o f t e n p r o v e n i n a d e q u a t e f o r t h e t a s k , and f u n d i n g from the a g r o c h e m i c a l s i n d u s t r y has been used t o
20.
RACKE
Implications for Use & Study ofPesticides in Soil
273
f i l l t h i s gap. I n f o r m a t i o n on t h e magnitude o f i n d u s t r i a l s u p p o r t i s unavailable. However, some i d e a o f t h e e x t e n t o f t h i s s u p p o r t c a n be i n f e r r e d from p u b l i c a t i o n acknowledgements t h a t i n c l u d e mention o f BASF (6,33), Dow (34), FMC (23), Mobay (35), S t a u f f e r (36,37,38), and U n i o n C a r b i d e (39) as c o n t r i b u t i n g t o f i n a n c i a l s u p p o r t . The r e s e a r c h e f f o r t s t h a t have been s t i m u l a t e d by t h e phenomenon o f enhanced d e g r a d a t i o n have r e s u l t e d i n t h e c r e a t i o n o f a s u b s t a n t i a l knowledge base r e g a r d i n g m i c r o b i a l a d a p t a t i o n f o r p e s t i c i d e d e g r a d a t i o n and a s s o c i a t e d p e s t c o n t r o l f a i l u r e s . The body o f s c i e n t i f i c l i t e r a t u r e on t h e s u b j e c t has grown r a p i d l y and i s now substantial. Recent r e v i e w s o f enhanced d e g r a d a t i o n and m i c r o b i a l a d a p t a t i o n f o r p e s t i c i d e d e g r a d a t i o n by Kaufman (2) (59 r é f . ) , Kearney and K e l l o g g (40) (108 r é f . ) , Roeth (3) (167 r é f . ) , Sandmann et a l . (41) (161 r é f . ) , S u e t t and Walker (5) (37 r é f . ) , and F e l s o t (4) (117 r e f . ) a t t e s t t o the growth i n p u b l i s h e d i n f o r m a t i o n . In a d d i t i o n t o p u b l i s h e d communication o f r e s e a r c h r e s u l t s , a number o f c o n f e r e n c e s have f a c i l i t a t e d i n f o r m a t i o n exchange. In a d d i t i o n t o U.S. Department o f A g r i c u l t u r e and i n d u s t r y s p o n s o r e d meetings, t h e American Chemical S o c i e t y (1984, 1989), t h e Weed S c i e n c e S o c i e t y o f A m e r i c a (1986), and t h e E n t o m o l o g i c a l S o c i e t y o f A m e r i c a (1984) have s p o n s o r e d s p e c i a l symposia on enhanced d e g r a d a t i o n , and the S o i l S c i e n c e S o c i e t y o f A m e r i c a has been the forum f o r numerous p a p e r s on t h e t o p i c d u r i n g the 1980's. What advances i n our u n d e r s t a n d i n g o f enhanced p e s t i c i d e biodégradation have accompanied t h i s contemporary f l u r r y o f r e s e a r c h activity? Advances i n R e s e a r c h
Understanding
Major advances i n o u r s c i e n t i f i c u n d e r s t a n d i n g o f enhanced d e g r a d a t i o n may be r e l a t e d t o the f o l l o w i n g d e f i n i t i o n o f f e r e d f o r enhanced biodégradation o f a p e s t i c i d e ( o r o t h e r o r g a n i c ) : "Enhanced biodégradation i s the a c c e l e r a t e d r a t e o f p e s t i c i d e d e g r a d a t i o n , by adapted s o i l microorganisms, observed i n s o i l f o l l o w i n g previous a p p l i c a t i o n o f i t or a s i m i l a r p e s t i c i d e . Enhanced d e g r a d a t i o n may r e s u l t i n p e s t c o n t r o l f a i l u r e and c r o p y i e l d r e d u c t i o n . " A c c e l e r a t e d P e s t i c i d e D e g r a d a t i o n Rate. The a c c e l e r a t i o n i n d e g r a d a t i o n r a t e due t o m i c r o b i a l a d a p t a t i o n has been w e l l characterized. F o r p e s t i c i d e s t h a t a r e somewhat e n v i r o n m e n t a l l y u n s t a b l e (e.g., EPTC) the i n c r e a s e i n d e g r a d a t i o n r a t e a s s o c i a t e d w i t h enhanced d e g r a d a t i o n r e d u c e s an i n h e r e n t l y s h o r t s o i l h a l f - l i f e (13 d a y s ) t o an e x t r e m e l y s h o r t one (4 d a y s ) (42). For other p e s t i c i d e s (e.g., i s o f e n p h o s ) , enhanced d e g r a d a t i o n r e s u l t s i n more s p e c t a c u l a r d e c r e a s e s (12 weeks t o
