Transcript What is environmental toxicology ?

What is environmental toxicology ?
– ‘ecotoxicology’
– Definition: ‘study of impacts of pollutants on the
structure and function of ecosystems’
– manmade poisonous chemicals and their effect on the
environment
– does not include the study of naturally occurring toxins, for
example cholera toxin, or brevitoxin
– Environmental toxicology is a new discipline that grew out of
studies on the environmental fate and transport of pesticides in
the 1940s and 1950s
– The discipline ‘toxicology’ is as old as medicine – many toxic
plant chemicals are used as therapeutic agents in medicine.
– The term ‘ecotoxicology’ appeared in the literature in 1969
– Field was pioneered by Rachel Carson
Environmental toxicology is highly interdisciplinary field
• Rachel Carson
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1907-1964
Marine Biologist from Pennsylvania
MA from Johns Hopkins U.
Author of ‘Silent Spring’
Received much attention, because she wrote
and presented scientific facts well
She was disturbed by the widespread and indiscriminate use of
pesticides
Many of these pesticides were known to affect wildlife e.g. kill birds
She lobbied very hard to control and ban certain highly toxic
chemicals
Testified before congress in 1963 and called for new policies with
respect to human health and the environment
Environmental toxicology is driven by legislation
• National Environmental Policy Act
• Clean Air Act
• Federal Environmental Pesticide Control Act
• Federal Water Pollution Control Act
• Safe Drinking Water Act
• Toxic Substances Control Act
• Resource Conservation and Recovery Act
• Comprehensive Environmental Response, Compensation and Liabilities Act
• Clean Water Act
• First piece of environmental legislation was the National
Environmental Policy Act
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1970
Created the EPA
Initially 5000 employees (1970)
Budget of 1.3 B
In 1995 there were >18,000 employees, budget of 7.2 B
USA is divided into 10 management regions
• Clean Air Act
– Also in 1970
– Required the EPA to set standards
– EPA in charge of controlling mobile and stationary emissions
sources
– EPA controls hazardous pollutants
– Amended in 1977 to set compliance standards
– Amended again in 1990 to regulate acid rain and CFC emissions
• Federal Environmental Pesticide Control Act
– 1972
– amended to FIFRA – Federal Insecticide, Fungicide, and
Rodendicide Act
– Required manufactures to provide PMNs (Pre Manufacture
Notice) with toxicological information to register a pesticide
– Sets up system of tiered toxicity testing – mechanism, mesocosm
experiment, field test
• Federal Water Pollution and Control Act
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1972
Provided sewage treatment plant grants for many municipalities
Set effluent limits based on technology standards
Toxicity testing is used to set maximum allowable concentrations
of toxicants in discharges and receiving waters
– Goal was to have all water fishable and swimable by 1983
– Established goal to eliminate pollution discharges by 1985
• Safe Drinking Water Act
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1974
Set mandatory drinking water standards
Controlled underground injection of wastes (aquifer protection)
Amended in 1984 to set a schedule for establishing drinking
water standards for 80 chemicals (provides notice to consumers)
• Toxic Substances Control Act
– 1976
– Regulated the use of chemicals in manufacturing and production
– Goal was to characterize the human health and environmental
impact of EVERY chemical manufactured in the USA
– EPA has only 90 days to review the PMN to evaluate data
– Because there are thousands of chemicals produced in the USA
every year, QSAR models or rapid throughput assays are usually
used
• Resource Conservation and Recovery Act
– 1976
– Controlled the disposal of solid waste
– Set new hazardous waste regulations
• Comprehensive Environmental Response, Compensation
and Liabilities Act
– Also known as SUPERFUND
– 1980
– Provided funding mechanisms to clean up abandoned waste
sites
– Amended in 1984 to ban ‘land disposal of hazardous waste
– Amended in 1986 to include requirements for community
emergency plans and publication of corporate Toxic Release
Inventories
– Established the SBRP program to develop innovative approaches
for cleanup and assessment of hazards
• Clean Water Act
– 1987
– sets national water quality standards
• Toxicological (animal) testing of ‘xenobiotics’ is federally
mandated by
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Federal Insecticide, Fungicide, and Rodendicide Act (FIFRA)
Federal Environmental Pesticide Control Act
Federal Water Pollution Control Act
Safe Drinking water act
Toxic Substances control Act
• Definition : XENOBIOTIC
– a chemical that is foreign to the biosphere i.e. is not produced by a
natural biological or abiotic source
– Also called anthropogenic, man-made, synthetic, pollutant,
contaminant, recalcitrant, persistent, and toxicant
– Distinguishes between quantity and scale – Gordon Gribble e.g.
studied the natural occurrence of organohallogens (chlorbenzoates
in fungi) – this is different from large scale chemical processes for
the production of PCBs
– BTEX is an acronym for benzene, toluene, ethylbenzene, and
xzylene – natural ??
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• Environmental toxicology depends on
– Lab work
• Effects of toxicants on biochemistry and physiology
– Field work
• Field observations of reproduction and survival in polluted vs.
non-polluted sites
– Modeling of fate and transport of toxicants in the
environment i.e. exposure and risk assessment
• Static models
• Strategic models
• Testable models
: short term modeling of ecosystems
: model of a specific aspect of a
system
: model makes predictions that can
be tested in the field or laboratory
• Purpose/function of environmental toxicology is to
– Identify the mode / site of action of a xenobiotic
– FATE and TRANSPORT / interaction of a xenobiotic with the
biosphere (including specific organisms) after it is released /
pollution occurs
– identify the effect the xenoboitic has on an ecosystems / higher
level organisation e.g. loss of fertility of Alligators in Lake Apopca
site of
action
physiology
behavior
Introduction of
xenobiotic
biotransformation
community
parameters
Ecosystem
effect
biochemistry
population
dynamics
Parameters of xenobiotic interaction with the ecosystem
DNA
RNA
Receptors
Key enzymes
Biochemical integrity
Physiology, Behavior
Chromosome damage
Lesions, Necrosis
Tumors
Teratogenic effects
Behavior, Mortality
Community structure
Diversity
Energy transfer
Stability
Succession
Chemical parameters
Introduction of
xenobiotic
Stress proteins
Population density
enzyme induction
Metabolic indicators
Productivity
Glutathione S Transferase
Acetylcholinesterase inhibition
Mating success
Mixed Functional Oxidases
Adenyl energy charge
Fecundity
Hydrolases
Metallothionen production
Genetic alterations
DNA repair mechanisms
Immuno suppression
Competitive alterations
Ecosystem
effect
How do we measure these effect ?
• Physio-chemical characteristics:
– QSAR (quantitative structure activity relationship)
O
N
CH2
CH
COOH
CH
CH3
S
NH
CH3
O
COOH
CH2
O
N
COOH
CH3
N
HC
CH
O
CH
CH3
S
S
CH3
CH3
HN
– Estimate the contribution of portions of the molecule to physiochemical characteristics
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Ionic interactions
Hydrophobic interactions
Van der Vaals forces
Hydrogen bonding
• Abiotic environmental fate
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Partitioning
Adsorption
Transport/advection
PCB vs. Benzene …
• Biotic environmental fate
– The interaction of a xenobiotic at the site of action in an organism is often
‘molecular happenstance’ i.e. xenobiotic mimic compounds which are naturally
found in species that they affect – hormone mimics
– Bioaccumulation
• The storage of a compound in fatty tissue of an animal
• Result of food chain / trophic levels
– Biotransformation
• Metabolic processes, mainly by environmental bacteria, that alter the
structure and toxicity of a compound
– Biodegradation
• Breakdown of a xenobiotic to CO2 and water
• Biotic mode of action (Receptors)
– Chemicals that interfere with biochemical receptor sites
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Signaling
proteins in membranes
Replication
Protein synthesis
– Chemicals that damage biochemical or molecular targets
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DNA damage
Strange breakage
Chromosome abnormalities
Cancer
Non-genotoxic effects such as immunosuppression
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Physiological and behavioral effects
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Standard tool for assessing toxicological effects on populations
Tissue lesions
Tumors
Reproductive success
• Population success
– Population age structure – xenobiotics often exert a stronger
effect on juveniles => a shift in age structure might indicate that a
population is not doing well, because it is affected by a
xenobiotic
– Shift in bacterial communities – contamination reduces bacterial
diversity; bacterial numbers often increase because the
contaminant is food for some while it is toxic for others
• Community effects
– Species diversity
– Abundance
– Distribution
• Ecosystem effects
– Productivity
– Trophic level structure
– Stability