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Date:

October 21, 2000

Subject:

EPA ADVISORS ASSESS RISKS, BENEFITS OF BT CROPS

 

EPA ADVISORS ASSESS RISKS, BENEFITS OF BT CROPS
Agency reaffirms findings of no unreasonable adverse effects in report to
their Scientific Advisory Panel
from : cast@cast-science.org

INTRODUCTION: Several insect-protected crops (corn, cotton and potato),
which contain a protein-producing gene from the soil bacterium Bacillus
thuringiensis (Bt), have been registered by the U.S. Environmental
Protection Agency (EPA). The Bt cotton and Bt corn registrations are to be
reviewed for renewal in the fall of 2001. In anticipation of that review,
EPA has prepared a detailed summary of data about risks and benefits of
the products. A 36-member Scientific Advisory Panel (SAP) will review the
summary and hear public comment and then provide their comments to the
Agency prior to the Agency's final decision on re-registration
eligibility. (p. IIC1) Titled "Bt Biopesticides Registration Action
Document," the EPA's review contains 283 pages and can be viewed in its
entirety at www.epa.gov/scipoly/sap. The EPA review discusses studies that
were submitted by registrants in order to obtain initial registration as
well as new studies that have been conducted by registrants, universities
and other independent researchers during the five-year period that Bt
crops have been sold. (p. I1-I13) Additionally, EPA has evaluated the
benefits, both financial and environmental, of the Bt crops. The EPA
review and discussions at the October 18 to 20, 2000 SAP meeting include
the following crystalline proteins of Bt: Cry1Ab (corn), Cry1Ac (cotton),
Cry3A (potato) and Cry9C (corn). (p. I4). NOTE: In an October 12, 2000
statement to the press, EPA announced that the Cry9C registration had been
withdrawn voluntarily by the registrant. (Johnson, 2000)

Key sections of the EPA review focus on a human health assessment, an
ecological assessment, insect resistance management, and benefits of the
technology. The summary contains a detailed discussion about Bt corn and
the possible impact its pollen might have on Monarch butterflies.
Significant statements from the EPA review follow:

HUMAN HEALTH ASSESSMENT: Information generated for this assessment "is
intended to show that the Bt protein behaves as would be expected of a
dietary protein, is not structurally related to any known food allergen or
protein toxin, and does not display any oral toxicity when administered at
high doses." (p. IIB1)

"All the Bt plant-pesticides are proteins. Proteins are commonly found in
the diet and, except for a few well-described phenomena, present little
risk as a mammalian hazard. In addition, for the majority of (Bt) proteins
currently registered, the source bacterium has been a registered microbial
pesticide which has been approved on food crops without specific
restrictions…A long history of safe use is associated with many Bt
products." (p. IIB1) (NOTE: Bt sprays are widely used in agriculture and
forestry, including use by organic farmers. Cry9C does not have a history
of usage in microbial pesticides.) "Despite decades of widespread use of
Bt as a pesticide (it has been registered since 1961), there have been no
confirmed reports of immediate or delayed allergic reactions to the
delta-endotoxin itself despite significant oral, dermal and inhalation
exposure to the microbial product."(p. IIB5)

The document explains various studies and assays used to determine the
safety of the introduced Bt protein. These include: * in vitro
digestibility assays to determine if the Bt protein is broken down in the
presence of typical digestive fluids, * studies to determine if the
protein can withstand heat and processing, * comparison of any structural
similarities to known allergens and * acute oral toxicity studies in which
a large amount of the protein is fed to laboratory mice. (p. IIB1) "None
of the products registered to date, which have a tolerance for food use,
show any characteristics of toxins or food allergens." (p. IIB3)

For the assessed proteins, Cry1Ab and Cry1A, EPA states, "There is a
reasonable certainty that no harm will result from aggregate exposure to
the U.S. population, including infants and children, to the (protein) and
the genetic material necessary for its production." (pp. IIB8, IIB15) For
Cry3A, EPA states that no mammalian toxicity or allergenicity is
anticipated from dietary exposure. p.IIB21-22) Cry9C was approved for
animal feed use only. (p. IIB21) Note that the registrations for all uses
of Cry9C were voluntarily cancelled by the registrant on October 12, 2000.
(Johnson, 2000)

EPA also assessed the genetic material necessary for the production of
the plant pesticide within the plant. These accompanying nucleic acids
(DNA) include coding material referred to as promoters, terminators and
enhancers, which control the expression of the proteins. "DNA is common to
all forms of plant and animal life, and the Agency knows of no instance
where these nucleic acids have been associated with toxic effects related
to their consumption as a component of food…No mammalian toxicity is
anticipated from dietary exposure (to them)." (p. IIB7)

ENVIRONMENTAL ASSESSMENT: Among key areas in this assessment were
outcrossing and potential for weeds to develop if pollen from Bt crops
were to fertilize other plants, effects on non-target species and the fate
of Bt proteins in the environment.

Outcrossing. Opponents of biotechnology raise the possibility of
"superweeds," which they imply could be created as pollen from biotech
crops crosses with other plants in the environment. The EPA summary
thoroughly discusses this issue and concludes: "There is no significant
risk of gene capture and expression of any Bt Cry protein by wild or weedy
relatives of corn, cotton or potato in the U.S." The explanation for that
statement is clear – there are no wild plants in regions where Bt crops
are grown that are biologically capable of accepting pollen from the
crops. "Feral species related to these crops, as found within the United
States, cannot be pollinated by these crops due to differences in
chromosome number, phenology (periodicity or time of events within an
organism’s life cycle as related to climate, e.g. flowering time) and
habitat." Note that there is one exception – wild relatives of cotton in
southern Florida and Hawaii, but "EPA has prohibited or restricted the
sale or distribution of Bt cotton in these areas." (p. IIC1)

Non-target species. The summary includes a discussion of ecological
effects, specifically the potential for the protein in Bt crops to harm
non-target species of wildlife. "(Data) provide a weight of evidence
assessment indicating no unreasonable adverse effects of Bt Cry proteins
expressed in plants to non-target wildlife or beneficial invertebrates,
whether they are earthworms, springtails, parasites, predators,
pollinators or soil microbial and invertebrate flora." (p. IIC72) The
summary details that no adverse effects were seen in species-specific
acute oral feeding studies conducted with mice, birds, fish, honey bees
and other beneficial insects, earthworms and springtails, and aquatic
invertebrates. "EPA believes that cultivation of (Bt plants) may result in
fewer adverse impacts to non-target organisms than result from the use of
chemical pesticides. Under normal circumstances, Bt crops require
substantially fewer applications of chemical pesticides. This should
result in fewer adverse impacts to non-target organisms."(p. IIC72)

Endangered butterfly species. "Examination of an overlay map showing the
county level distribution of endangered lepidopteran species [i.e.,
butterflies and moths] relative to corn production…shows that as a rule,
endangered lepidopteran species do not occur in agricultural areas where
corn is grown, nor is corn considered a host plant for these species. The
map clearly indicates that any potential concern regarding range overlap
with corn production is restricted to the Karner blue butterfly…The Karner
blue requires wild lupine (for egg laying)…Wild lupine does not occur in
corn fields…Moreover, it is important to note that Karner blue larvae are
not likely to be feeding during or following the time of corn pollen
shed…The risk of Bt corn pollen affecting Karner blue larvae is not likely
to exist." (pp. IIC49-50)

Green lacewings. The summary reviews laboratory studies by Hilbeck et
al., which showed an adverse effect on green lacewing larvae fed a diet of
corn borer larvae, that had previously consumed the Bt protein. "Their
data show that lacewing mortality and developmental effects more likely
are related to the study diet, not to any potential Bt endotoxin effects.
Moreover, even if the reported results are taken at face value, the
adverse effects are so slight as to suggest no significant impact on
beneficial insects in the field….The lacewing was not given a choice in
diet. In nature, the lacewing does not rely on a single food source
(lacewing prefers insect eggs and aphids)…The dead or dying prey (corn
borers fed to lacewings) may have been septicemic (and therefore
indirectly toxic), of limited nutritional value, or unpalatable to the
lacewing…In addition, all available Agency in-house and published field
data do not show significant detrimental effects due to Bt endotoxin on
the lacewing." (p. IIC42)

Fate in soils and indirect effects on soil organisms. "Limited data do
not indicate that Cry proteins have any measurable effect on microbial
populations in the soil…Bt soils show no effect on total biomass,
bacteria, actinomyces, fungi, protozoa, nematodes, springtails or
earthworms." The assessment discusses several laboratory studies by
Stotzky et al., which indicate that Bt proteins may bind to clay in soil
and degrade slowly in soils with low pH (below 5.0). EPA points out that
corn, cotton and potatoes do not grow well in soils with pH below 5.0 so
farmers typically choose higher pH soils or alter the soil accordingly.
Further work by Stotzky conducted in 2000 indicates that Cry proteins are
unlikely to have adverse impacts on soil organisms, micro-organisms or
soil enzymes. "It was also reported that the same degree of Bt protein
persistence takes place in soils that have been exposed to repeat Bt spray
applications compared to soil exposed to growing Bt crops. Live Bt cells
were also recovered from the soils after spray applications for up to
eight months of testing." "EPA does not believe there are any valid data
demonstrating specific adverse impacts of (Bt plants) on beneficial soil
invertebrates. To the contrary, EPA believes…cultivation of Bt crops has a
positive effect on soil flora, when compared to the mostly likely
alternative, use of non-selective synthetic chemical pesticides." (p.
IIC46)
MONARCH BUTTERFLIES:

Two significant statements are made in this section: 1) Several field
studies have failed to detect pollen from Bt corn products due for
re-registration at levels that are toxic to butterflies – even inside a
corn field, and 2) there is very little overlap of butterfly breeding and
pollen shed. (p. IIC54) Given that toxic levels are not found on milkweeds
(the main food of monarch larvae) in and near the field and larval
exposure to pollen is very limited, one could only conclude that there is
little risk to butterfly populations. "Milkweeds in cornfields to within 1
meter of cornfields are unlikely to be dusted with toxic levels of Bt
pollen…The Agency concludes that the published preliminary monarch
toxicity information is not sufficient to cause undue concern of
widespread risk to monarch butterflies at this time."(p. IIC58)

Extensive discussion was given to the potential for the Bt protein in corn
to harm the larvae of non-target butterflies. EPA states that in initially
registering Bt corn, the Agency accepted that the protein could be harmful
to Lepidoptera and based its risk assessment solely on potential exposure.
"Long-term effects from the use of Bt sprays to control gypsy moths have
been studied in U.S. Forest Service sponsored research. Since the exposure
to butterflies and moths from the agricultural uses of Bt was not expected
to be as high as in forest spraying (where no widespread/recurring or
irreversible harm to lepidopteran insects was observed), Bt corn likewise
was not expected to cause widespread or irreversible harm to non-target
lepidopteran insects." (pp. IIC70-71) When a much-publicized laboratory
study (Losey et al., 1999) demonstrated that Bt pollen could harm monarch
butterflies, EPA called for more data to address exposure. (p. IIC50)
"Reports of toxicity of high doses of Bt to monarchs in the laboratory do
not necessarily translate into exposure at toxic levels in the field." (p.
IIC48)

Data call-in. EPA required that registrants provide additional data,
including public sources, in five specific areas: Toxicity of corn pollen
to lepidopterans; distribution of monarchs, milkweeds and corn; corn
pollen release and movement; monarch egg-laying and feeding behavior; and
monarch population monitoring. Some, but not all of the additional data
have been reviewed. (p. IIC51)

Bt corn pollen toxicity. Based on results of several studies, EPA
estimated that there would be no observable adverse effect on monarch
butterflies at a concentration (NOEC) up to 150 pollen grains per square
centimeter of milkweed leaf surface for the two most widely used Bt corn
products (Bt 11 and MON 810). "Pollen from these events (is) unlikely to
be found in densities that may affect non-target lepidopterans, even on
milkweeds within a corn field." Reports from several field studies show
concentrations much lower than that even within the cornfield. "In
Maryland, the highest level of pollen deposition was inside and at the
edge of the corn field, where pollen was found at about 50 grains per
square centimeter. In the Nebraska study, pollen deposition ranged from
6.0 grains at the field edge to less than 1 grain beyond 10 meters.
Samples collected from fields in Ontario immediately following the period
of peak pollen shed showed pollen concentrations averaged 78 grains at the
field edge. Bt corn pollen was typically below (and only rarely exceeded)
the NOEC (within three meters of the corn field) at all locations
evaluated." (p. IIC55) (NOTE: Two much publicized studies (Losey et al,
1999; Hansen and Obrycki, 2000), which demonstrated toxicity in a
laboratory, used corn pollen that contained Bt Event 176, which is much
more toxic via pollen than Bt 11, CBH 351 and MON 810. Event 176, which
never accounted for more than 2 percent of Bt corn sales in the U.S., is
being voluntarily cancelled by its developers in the U.S. (p. I3) and was
not assessed in the EPA re-registration eligibility summary.)

Distribution of monarchs, milkweed and corn. EPA cited recent estimates
(MBRS, 1999; USDA, 2000) that only about 10.5 percent of the summer
monarch breeding area comprise corn fields. (This does not necessarily
mean that monarchs breed in the corn field, only that 10.5 percent of the
land area is made up of corn fields. Other habitats include fallow fields,
roadsides and pastures.) (p. IIC51) New research conducted in the summer
of 2000 showed that milkweeds grow well between corn rows and that monarch
larvae were seen on these plants. "This would indicate that monarch larva
exposure to Bt pollen would take place in Bt corn fields in geographical
locations where there is an overlap of pollen shed and monarch breeding."
However, EPA factors in other data about toxicity and timing of
pollination. "Here one needs to factor in the preliminary data showing
that there is no pollen shed and monarch breeding overlap in most of the
corn belt, except in the northern range. And in assessing hazard in the
northern corn belt, one needs to look at the findings that MON 810, CBH
351 and Bt 11 corn pollen at levels found in the fields show no
detrimental effect on monarch development." (p. IIC52, 54)

Pollen shed and movement. "Data on pollen movement…indicate that corn
pollen is only present at distances of up to 1 to 5 m outside of a corn
field in densities that could represent significant exposure to feeding
larvae. This edge area represents less that 0.25 percent of the total corn
acreage, and a correspondingly small percentage of non-corn milkweed
habitat. Monarch exposure to Bt corn pollen outside of the corn field,
therefore, appears to be minimal." Data also showed that milkweeds "retain
only approximately 30 percent of the pollen that impinges on leaves, and
that this pollen is readily dislodged (90%) by rain events and wind,
thereby limiting exposure to possibly harmful pollen levels within the
corn field system." Duration of pollen shed typically occurs over a 10 to
14 day period within a given field. "Under favorable environmental
conditions, the vast majority of pollen will be shed in a 1 to 2 day
period at the middle of this interval." Other studies show that corn
pollen grains remain viable for only a few hours after their release from
a plant. "These changes, in combination with the known tendency of Bt Cry
proteins to rapidly break down when exposed to ultraviolet light, heat or
biological activity, suggest that any insecticidal activity of Bt corn
pollen should degrade rapidly." (p. IIC52-53)

Monarch biology. The EPA review details several behavioral characteristics
that further reduce the likelihood of larval exposure to toxic levels of
pollen. "Data indicate that monarchs most frequently lay their eggs on the
underside of tender, young milkweed leaves, and the first instar larvae
[first stage of caterpillar development] begin feeding close to where the
eggs are laid. Leaves selected for oviposition are more frequently at the
tops of smaller milkweeds; these upper leaves retain less pollen than
lower leaves because of less surface area, and they are oriented more
vertically than lower leaves. Older larvae are quite mobile and very often
move from one milkweed plant to another. These behavioral and physical
considerations further reduce potential larval exposure to pollen." (NOTE:
It has been demonstrated in the laboratory (Hansen and Obrykci, 2000) that
larvae older than 12 hours had a much higher survival rate than did
neonate (first instar) larvae exposed to a high dose of pollen. Given that
larvae generally are hatched on underside surfaces that are free of
pollen, one should conclude that they would not likely have exposure to
pollen until they were older and more able to survive even high doses.
"Neonate larvae will begin feeding on the foliage immediately adjacent to
the egg before moving to other areas of the plant.") They may lay their
eggs on milkweed plants in cornfields when the milkweed plant is taller
than newly planted corn, but research shows that they avoid milkweeds
surrounded by tall corn. If they deposit eggs on small plants in
cornfields, larvae will be hatched and gone before surrounding corn plants
develop sufficiently to shed pollen. (p. IIC56-57)

Monarch conclusions.
"Overall, the available information indicates a very low probability of
risk to monarchs in areas beyond the near edge of cornfields. Inside
cornfields and at the near edge…there is low probability of monarch larvae
encountering a toxic level of pollen for the Bt corn products covered by
this risk assessment." (p. IIC57) "These products (Bt11, MON 810 and CBH
351) show relatively low toxicity to monarch larvae." (p. IIC57)
"Consideration of other factors, such as the reports that there is no
pollen shed and monarch breeding overlap in most of the corn belt, the
distribution of milkweed plants within corn fields (or the near edge)
compared to other milkweed habitats beyond the near edge of fields, the
egg laying and feeding activity of monarch larvae, and the low toxicity of
the Bt corn products covered by this assessment, indicates a low
probability for adverse effects of Bt corn on monarch larvae." (p. IIC57)

Bt CORN.

Grower benefits. Economic benefits of Bt corn vary each year, depending on
the level of European corn borer infestation and the price of corn. In
1997, a year of high corn borer pressure, average net benefit was
calculated at $18.43 per acre. "The average net benefit of $3.31 per acre
on 19.75 million acres of Bt corn planted in 1999 (a year of low corn
borer pressure) leads to the national estimate of $65.4 million." The net
benefit to sweet corn producers was calculated at $5.38 per acre in 1999.
(p. IIE7-10)

Environmental benefits. "Since Bt corn (was introduced) into the
marketplace, there is a reduction in use for those pesticides recommended
for European corn borer control from 6 million to slightly over 4 million
acre treatments in 1999, a reduction of about one-third." EPA calculated a
pesticide reduction of 4.3 treatments per acre on 30,000 acres of Bt
sweetcorn, for a reduction of 127,000 acre-treatments of chemical
pesticides. (p. IIE7-10)

Bt COTTON.

Grower benefits. Using U.S. Department of Agriculture/Economic Research
Service data, EPA calculated a national benefit of $47 million on 2.1
million acres of Bt cotton in 1997. (p. IIE21)

Environmental benefits. The reduction in pesticide usage in states with
high Bt cotton adoption "is estimated to be 1.2 million treatments per
acre. Based on 1.2 acre-treatment reduction for high user states, there is
a 7.5 million acre treatment reduction associated with Bt cotton"…or "a 21
percent reduction" over all cotton acres. (p. IIE18) "The estimated use
reduction…is evaluated with respect to human health and environmental
benefits including reducing the number of incidents to terrestrial and
aquatic wildlife caused by the top pesticide uses currently responsible
for the greatest morality to such wildlife. Three Bt cotton alternatives
(are) involved in aquatic incidents (p. IIE19)…Benefits to workers also
accrue…Those mixing/loading and applying pesticides have less exposure and
workers who scout for insects, move irrigation equipment, or perform other
activities that require them to be in the field will not be exposed to the
chemical insecticides replaced by Bt cotton." (p. IIE20)

Bt POTATO.

Grower benefits. EPA cites figures that show a financial benefit to potato
growers of $9.30 per acre. (p. IIE24)

Environmental benefits. EPA cited figures showing a national reduction of
89,000 acre-treatments of chemical pesticides. "Several of the (pesticide
alternatives to Bt have) potential or known adverse effects to non-target
organisms and workers." (p. IIE24)

INSECT RESISTANCE MANAGEMENT: The report states that "after five years of
commercialization, no reported insect resistance has occurred to the Bt
toxins expressed either in Bt potato, Bt corn or Bt cotton products." EPA
believes that current mandatory insect resistance management (IRM) plans
are adequate to protect against resistance in potato and corn but
indicates that the IRM plan for cotton may need to be strengthened. (p.
I3) (NOTE: The Bt cotton IRM plan was recently strengthened and approved
by EPA for the 2001 growing season.]

BENEFITS: "Bt seed has positive benefit to growers and consumers by
increasing yields and/or reducing input costs for chemical insecticides.
Direct benefit to growers for Bt corn, cotton and potatoes has likely
exceeded $100 million in 1999. Bt seed also has positive environmental
benefits, especially for aquatic wildlife as it replaces more toxic
organophosphate and pyrethroid insecticides, in cotton…The number of
incidents and mortalities to aquatic wildlife are likely to be lower
during the past four years as the use of pesticides toxic to aquatic
wildlife has been reduced." (p. IIE24)


REFERENCES:
Johnson, S. "Note to correspondents: STATEMENT BY STEPHEN JOHNSON EPA
DEPUTY ASSISTANT ADMINISTRATOR FOR PESTICIDES REGARDING STARLINK CORN."
Washington, DC. October 12, 2000.

U.S. Environmental Protection Agency, Office of Pesticide programs,
Biopesticides and Pollution Prevention Division. "Bt Biopesticides
Registration Action Document Preliminary Risks and Benefits Sections
Bacillus thuringiensis Plant-Pesticides" September 2000. Available on the
web at www.epa.gov/scipoly/sap in the section, October 18-20, 2000: Issues
pertaining to the Bt plant pesticides Risk and Benefit Assessments


This synopsis is based on EPA's comprehensive review of the Benefits and
Risks of Bt in plants, "Bt Biopesticides Registration Action Document,"
which can be viewed in its entirety at www.epa.gov/scipoly/sap. The
synopsis was prepared by Daniel Holman of Achieva for CAST and was
reviewed by Cindy Lynn Richard of Council for Agricultural Science and
Technology (CAST) and the members of the CAST leadership.

Should you need further assistance, please feel free to contact Cindy
Richard at 202-408-5383 or visit the CAST website at www.cast-science.org.

Council for Agricultural Science and Technology Biotechnology
Communications Main Office 900 Second Street, NE, Suite 205 4420 West
Lincoln Way Washington, DC 20002, USA. Ames, IA 50014-3447, USA. tel:(202)
408-5383, fax: (202) 408-5385 tel: (515) 292-2125, fax: (515) 292-4512
E-mail: crichard@cast-science.org E-mail: cast@cast-science.org Web:
www.cast-science.org