Environmental impacts and social responses to genetically
engineered crops
L. LaReesa WolfenbargerUniversity of Nebraska at Omaha
Potential benefits of transgenic organisms: environmental, health, social
Why so much potential?
• Genetic engineering provides a greater range of possibilities for transferring desired traits into organisms.
The potential is biological novelty
• Genetic engineering provides a greater range of possibilities for transferring desired traits into organisms.– A greater diversity of organisms may be
modified– The quantity and quality of traits are limited
by the identification of useful genes and are not constrained by existing variation among interbreeding relatives
Are they good or bad for the environment?
Yes, according to the plant biotechnology industry
No, according to environmental activist groups
Answer
• Environmental impacts vary on a case by case basis
• Environmental tradeoffs most likely • Values and not science determine
whether outcome is good or bad
Level of disturbance to environment
Effe
ct o
n en
viro
nmen
tThe role of science:
what are the environmental consequences?
x x
Level of disturbance to environment
Effe
ct o
n en
viro
nmen
tSocial responses:
what consequences are acceptable?
x x
One point of agreement
• Case-by-case environmental impacts
Overview
• Possible environmental consequences• Environmental impacts of Bt corn and
Round up Ready soybean• Social responses to these impacts• Predicting environmental impacts of
future GE crops
What are the possible environmental consequences of
GE crops?
No changeFurther
degradation Improvement
Using past experience to think of possible effects
• Past experience with introductions of chemicals – Vary in toxicity, persistence– Lethal, Sublethal, No effect
• Past introductions of species: intentional and unintentional– Unwanted spread of an organism or its
genes
Chemicals and rat mortality
Chemical Substance Oral LD50 (mg/kg)Sucrose 30,000Sodium chloride 3,750Malathion 2,000DDT 200Nicotine 50TCDD 0.01
Persistence of chemicals varies
ChemicalDose
(kg/ha/yr)Half-life
(Yrs)95% Loss
(Yrs)Aldrin 1.1-3.4 0.3 3Chlordane 1.1-2.2 1.0 3.5Lindane 1.1-2.8 1.2 6.5Endrin 1.1-3.4 2.2 7Dieldrin 1.1-3.4 2.5 8DDT 1.1-2.8 2.8 10
Using past experience to think of possible effects
• Past experience with introductions of chemicals
• Past introductions of species: intentional and unintentional
Past biological introductions
Intentional• Landscaping• Restoration/
reintroductions• Agricultural crops• Biological control
Unintentional• Hitchhikers
Survival or Death
Reproduction or not
Self-sustaining population
Spread and persistence
Possible outcomes of biological introductionsIntroduction
of plants
Population dies out
Never really spreads
Kudzu spread and persists beyond its intended purpose
Can ecologists predict how species will spread
• Can identify plants characteristics in common
BUT• Lag times can occur.• Repeated introductions have different
results.• Biological organisms can evolve.
Survival or Death
Reproduction
Self-sustaining population
Spread and persistence
Pollen flows to wild relative Hybrid formation
or not
Hybrid survival or death
Hybrid reproduction or not
Self-sustaining hybrids
Possible outcomes of biological introductions
Introductionof plant
Gene flow from crops to wild relatives is implicated in enhanced weediness in wild relatives of 7 of the world’s 13 most important crops.
(Ellstrand, 1999)
Are current GE crops likely to spread?
Self-sustainingpopulations
Outside of cultivation
HT Corn
Bt and GNA Potato
HT Oilseed rape
HT Sugar beet
Unlikely
Unlikely
Unlikely
Unlikely
Crop
Crawley et al. 2001. Nature 409: 682-683.
Summary of possible environmental impacts
• Improvements if less toxic and does not spread outside of cultivation
• Degradation if more toxic or spreads uncontrollably
Less toxic to what?Spread where?
The environment: Biodiversity and interactions
Plants
Herbivores
PredatorsBigger predators
Ecological functions
Plants: primary producers
Decomposers
HerbivoresPollinators
PredatorsBigger predators
Impacts on the environment occur through alterations of…
• what species are present• how many individuals of each species• the ecological function(s) of a species in
an ecosystem• the biological interactions affecting a
species’ function in the environment
Humans are part of the environment
• herbivores• predators• environmental engineers
Environments are a continuum
Grassland environment
Agricultural environment
Forest environment
What general factors define the context?
• The transgenic organism• Where it is introduced
– environment• Baseline for comparison and evaluation
– What GE crop will replace: regional agricultural practices
How a GE plant will interact with the environment
• Presence of transgenic crop or its transgene – plant above ground – roots – decomposing tissue – pollen drift – gene flow to wild relatives in
natural ecosystem
Other ways introducing a GE crop will affect the environment
• Changes in agricultural practices associated with adoption of a transgenic crop – Pesticide use patterns– Amount of agricultural land– Tillage practices– Crop diversity/rotation
Phytoremediation
• Remove and sequester toxic heavy metals
• Transform pollutants into less toxic forms
What do we know about environmental impacts of
current GE crops?
0102030405060708090
100
1996199719981999200020012002200320042005Year
% transgenic acreage
SoybeanCottonCorn
Source: Biotechnology Industry Organization and USDA
Adoption of GE crops in U.S.
Bt crops protect plants against specific insect pests
The story of Monarchs and Bt corn
0
25
50
75
100
DaysSurvival of monarch
larvae (%)
no pollennon-Bt pollenBt pollen
We saw the findings as an illustration of how superficial risk assessment [for genetically modified foods] was...The question still remains, would this science have been done if the monarch wasn’t such a beautiful butterfly?”
We saw an embargoed copy of a Cornell press release where we thought the risk seemed exaggerated,”
Components of risk assessment for monarch butterflies
Bt corn•Production and Distribution•Pollen characterization
•Bt expression•Pollen shed (timing, duration, quantity)•Deposition and dispersal
Milkweed•Occurrence and Distribution
•(Regional, landscape, habitat, abundance in corn)
MonarchOccurrence and DistributionBehavior (oviposition preferences,phenology)
Environmental exposure Risk
Monarch•Toxic effect (lethal/sublethal)
Adapted from Sears et al. 2001.PNAS 98: 11937-11942.
Monarch survival: 9 days after onset of pollen deposition
0
20
40
60
80
100
Bt Non-Bt Non-Bt(T)
3 m outside
3 m inside
• No differences among Bt and Non-Bt sweet corn treatments
• Survival significantly decreased in presence of insecticide treatment
From Stanley-Horn et al. 2001. PNAS 98: 11931-11936
Per
cent
sur
viva
l
Studies with Bt corn underscore importance of context
• Susceptibility of butterfly and moth species varies
• Exposure varies geographically and locally
• Susceptibility of lacewings (predatory insect) varies with prey species
Results of formal risk assessment
• The six studies published in PNAS showed there was little risk to monarch larvae from the two most commonly grown types of Bt corn because the pollen isn’t toxic in the concentrations that monarch larvae would encounter in the fields.
Components of risk assessment for monarch butterflies
Bt corn•Production and Distribution•Pollen characterization
•Bt expression•Pollen shed (timing, duration, quantity)•Deposition and dispersal
Milkweed•Occurrence and Distribution
•(Regional, landscape, habitat, abundance in corn)
MonarchOccurrence and DistributionBehavior (oviposition preferences,phenology)
Environmental exposure Risk
Monarch•Toxic effect (lethal/sublethal)
Adapted from Sears et al. 2001.PNAS 98: 11937-11942.
Responses to EPA’s decision
“I felt that the conclusions made from a one year study that excluded anthers were premature,” Obrycki says. “That’s why we requested that EPA shorten the reauthorization period until we had data from subsequent studies.”
• the studies do not rule out very small effects, long-term or sublethal effects
Epilogue
• Concern about ingestion of other plant parts
• Longer term studies occurring
• Registration will expire in 2006
My response and questions
• subtle effects seem likely• Should this change the registration?
– no, minimize impacts on monarchs• What if a broader number of butterfly
species are affected?
Reduced impacts from pesticides
Insecticide use in cotton
0
0.5
1
1.5
2
2.5
3
3.5
1993 1994 1995 1996 1997 1998 1999 2000
CautionWarningDanger
Num
ber o
f tre
atm
ent/a
cres
Roundup ready soybeans are the best for weed management
0102030405060708090
100
1990 1995 2000 2005
Lbs. AI (x106)
ACRES SOY
Glyphosate
TOTAL HERBICIDES(Millions of Lbs AI)Pendimethalin
Imazethapyr
Trifluralin
Fomesafen
Compiled from USDA Agriculture Chemical Usage reports 1991-2002http://usda.mannlib.cornell.edu/reports/nassr/other/pcu-bb/
Herbicide use in U.S. soybean production
Benefits from changing agricultural practices with soy
No till and conservation tillage
• Reduce erosion
• Decrease water loss
• Increase soil organic matter
Increase in No Till acreage
0
10
20
30
40
1989 1991 1993 1995 1997 2000Year
% acres in US with no
tillage
Roundup Ready soy introduced
How do we predict future impacts?
• Use past experience• Expect tradeoffs• Evaluate on a case-
by-case basis• Remember that
genetic engineering is a tool