Risk Assessment of Atrazine
on Blue Crabs and
Chesapeake Bay Ecosystem
Caitlin Andrews
Russell Ford
David Lucero
Henrietta Oakley
Satish Serchan
Overview of the presentation
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Atrazine production and application
Controversy surrounding Atrazine
Chesapeake Bay and Blue Crab habitat
Studies of Atrazine on crustaceans,
Submerged Aquatic Vegetations (SAV)
• Alternatives to Atrazine
Purpose of this study
Amphibians
Atrazine
Blue Crab
Crustaceans
SAVs
Blue Crab Alert
• Blue crabs-the stock has undergone an
85% decline since 1990. (SERC)
– Complex migratory life cycle
– Salinity gradient
– SAVs and zooplanktons
Atrazine Use & Application
• Broad-leafed herbicide
– Inhibiting the photosynthesis
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1958
Syngenta Corporation
Corn
76 to 85 million pounds annually
Atrazine Cont’d
• regulated under water statutes
• Maximum Contaminant Level
– MCL of 3.0 ppb
• Surface and groundwater persistence
– Chesapeake Bay show that levels can exceed
100 μg/L (ppb) with at least 30 days of
persistence (EPA 2007)
Controversy (EPA Story)
• Low acute toxicity (EPA)
• Not likely to be human carcinogen
• Hormonal effects on lab animals resulted
from short term exposure
Dr. Tyrone Hayes Studies
• Scientific Advisory Panel hired by
Syngenta
• > 0.1 ppb of Atrazine in surface water
effectively turning males into
hermaphrodites
• Compare EPA’s MCL 3.0 ppb to 0.1 ppb
Hermaphroditic, demasculinized
frogs after exposure to the
herbicide atrazine at low
ecologically relevant doses
• Tyrone B. Hayes, et al.
• UC Berkeley Laboratory for Integrative
Studies in Amphibian Biology
Demasculinized frogs found near
Mid-western Farm Fields where
Atrazine in use
Blue Crabs: An Indicator Species
Indicator Species
Ecological Reasons
Socioeconomic Reasons
Distributes itself based on ecological
and anthropogenic changes
Blue Crab Life Cycle
Megalopae
• Responsible for selecting a secure habitat
which will influence their survival into
adulthood.
Smooth Cordgrass
Eel Grass
Prefer structural complexity
-3D grass habitats
Actively seeks prey
Atrazine’s Influence on the Food
Chain
Megalopae and juveniles live in estuaries
in and close to the mouth of the nine large
rivers and numerous other creeks that flow
into the Chesapeake Bay.
Atrazine in agriculturally dominated area
reach as high as 100 μ /L for periods as
long as 30 days.
Phytoplankton in Chesapeake Bay
354 species of phytoplankton
The bloom and bust cycles of these species of
phytoplankton are complicated with a few
species dominating the resources in different
sections of the estuary.
Green algae and Dinoflagellates – lowest
tolerance (<50μg/L)
Diatoms – higher tolerance (250μg/L)
SAV’s Submerged Aquatic
Vegetation
• How atrazine affects SAV’s
– Chloroplast function
– Oxygen production
– Habitat
• Hypoxia
• Habitat structure
• Predator/prey relationships and trophic cascades
Microbioreactor Study
• Studied effects of atrazine
on Elodea canadensis
• Found increased levels of
fluorescence inversely
associated with levels the
effective quantum yield of
photochemical conversion
• 50% inhibition in Oxygen
production when atrazine
concentrations were 50-75
ug/l
– Damage to Chloroplast
function
• No Oxygen production at
500 ug/l atrazine
Effects of Hypoxia
• Increases cannibalism by
adult Blue Crabs
– Chronic hypoxia causes
predator densities to
increase in shallower
habitats
– Juvenile Blue Crab
densities decrease
exponentially in response
– Periodic hypoxic up
swellings do not have the
same affect; adult Blue
Crabs migrate to suitable
waters
• Changes habitat structure
and function
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Hypoxia
• Alterations in predator/prey interactions
– Species have different responses and tolerances
– Crustaceans have relatively low hypoxia tolerance
– Blue Crabs migrate from hypoxic regions, as well as
use them to hunt impaired species
• Change in behavior
– Prey dumber by hypoxia – behavioral differences
observed
– Species interactions important in ecosystem structure
Crustaceans: the Blue Crab
• How the Blue Crab will be
affected by
– Loss of SAV production
• SAV’s are primary producers,
providing oxygen, nutrient
cycling, and serving as food
and shelter
– Hypoxia
• Chesapeake Bay experiences
periodic low oxygen stress,
especially in the summer
• Often has sublethal effects
• Alters habitat structure and
function
– Predator/prey interactions
Land Use and Crustacean
Abundances
• Negative correlation
with agricultural land
use and Blue Crab
abundances
• Hypoxia associated
with Ag land use
– Seasonal (summertime)
hypoxia coincides with
herbicide/pesticide/
fertilizer applications
– Atrazine part of this mix
• supports negative
feedback loop
• Increases hypoxia
Summary
• 85% stock Blue Crab Decline since 1990
• High levels of Atrazine in Chesapeake Bay
• Dr. Tyrone B. Hayes extensive research of
Demasculinized frogs
• Seen the affects of Atrazine on SAV
• So let’s just get rid of Atrazine?
Alternative
• University of Kentucky College of
Agriculture:
• Reduce the use of atrazine with postemergence herbicides
• Only use post-emergence herbicides
Pros
• The amount of herbicide needed will be
better judged
• Can be cheaper since extra herbicide will
not be used
• Can also be cheaper because postemergence herbicide can be cheaper than
pre-emergence
Cons
• May require re-application
• Requires more training and careful
management by the farmer
• Can cost more because re-application is
needed: more herbicide and energy
needed
• Injury to corn crop can occur
Alternatives/Whats next?
• More testing needed; more field data vs.
lab data
• Atrazine is one of many chemicals
entering the watershed and the specific
affects may be difficult to determine
• May have an additive quality, enforcing
negative feedback loops in the presence
of other pollutants