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Midterm

Environmental Toxicology midterm.docx


Department
Toxicology
Course Code
TOX 2000
Professor
Aaron Witham
Study Guide
Midterm

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Environmental Toxicology:
Persistent organic pollutants (POPs)- organic compounds resistant to environmental
degradation through chemical, biological or photolytic processes
United Nations banned 16 chemicals: aldrin/dieldrin, endrin, DDT/DDE, HCH/lindane,
chlordane, heptachlor, toxaphene, By-products- PCDDs, PCDFs, HCB, PCBs
Regulation- protocols easy to achieve when there is no political agenda interfering, most of the
dirty dozen have been banned by most countries, far more difficult to reach international
consensus when national agendas are at stake focus on issues in the economy
Environmental toxicology- multidisciplinary field in which effects of chemical, biological and
physical agents on living organisms is studied
Ecotoxicology- focuses on effects of chemical on populations and communities
Assessment endpoints (AEs)- explicit expressions of actual value to be protected, the ultimate
focus in risk characterization and act as a link to risk management process and to policy goals;
ecologically relevant, susceptible (responsive) to the stressor, societal value, unambiguous
(specificity/minimal uncertainty)
Keystone species- species that has a disproportionately large effect on its environment relative
to its abundance, functions can’t be replaced, function of community or ecosystem would be
significantly changed in their absence ex. Elephants, sea otter; could be detrimental if lost; have
ecological relevance
Societal relevance- paragon falcon- not a keystone species, ecosystem wouldn’t be affected if
they were removed but society likes them
Wetlands- critical for bird migrations, buffers for toxins, very valuable- need more societal
relevance
Basis for assessment endpoint- functional and structural responses, structural response can
depend on if organism is keystone or food source
Structure- who is present in the system (what we see in the system) eg. Abundance, diversity
Function- interaction of population with other populations or abiotic environment including
energy and nutrient flow, biomass production, consumption of biomass, controlling abundance of
other species, providing food for predators, processing organic detritus
Measures of effect- a measurable characteristic (test endpoint) ex. Mortality, growth,
reproduction, that is related quantitatively or qualitatively to AEs; should consider both direct

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and indirect effects, integrate sensitivity and response time, have high diagnostic capacity,
consider practicality issues
Ecosystems- temporal changes (seasonal changes), spatial changes (stream vs. river segments)
States- present state (normal function and structure) disturbance regime (pollutants)
transient state recovery (resilience)
Regime shift (dramatic) changes to new state
Bistable ecosystem- 2 possible endpoints (resilient)
Multistable ecosystem- several endpoints at different levels of complexity (resilient)
Impact vs. time/[ ]- organism: physiological adaptation, Population- avoidance/emigration,
toxicity, local extinction, loss of diversity, loss of function; loss of ecosystem ex. Increased
nitrogen in water increased nutrient levels which increased plant growth and caused green water
Restoration and recovery- ecosystem- relocalization; population/community- habitat
conditioning, opportunists, succession; organism- immigration
Toxicity involves 3 components- exposure ([ ]/dose), exposure duration (time), response
- Extrinsic property that is dependent on number of molecules present
LC50- concentration at which is lethal to 50% of the population
(per unit volume) QUANTAL (dead or alive)
EC50- effective concentration- amount of substance per unit
volume that affects 50% of the test population (for continuous
non-quantal responses)
NOAEC- no observed adverse effect concentration
LOAEC- lowest observed adverse effect concentration
MATC- maximum allowable toxic concentration- geometric mean of LOEC and NOEC
Increase [ ] + increase time => increased % mortality
Direct reciprocity- LC50 on a day 2 is ½ that of day one
Incipient lethal level- threshold level of exposure to toxic substance beyond which 50% of
population or of organisms can’t survive
Non-quantal responses- response measures
are continuous (can take on fractional values)
toxicity may be judged by use of severity
scales assigned when difficult to determine

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if organisms have been affected (growth, yield, biomass production)
Hormesis- low dose does good, high dose does bad
Duration of effect- effect declines rapidly after exposure effects are seen after exposure due to
storage and release of substance (bioaccumulative), effect declines after slowly after exposure
(persistent), adaptation occurs before end of exposure (effect essentially stops but still has
exposure)
Testing for effects: in sediment, soil, water, in surrogates ie. test animals for extrapolation to
other species
Bioassays- assess potency of a substance by measuring effects on living organisms; protocols:
exposure conditions, flow through vs. renewal vs. static, measured [ ], multiple observations over
time, appropriate experimental (statistical design)
Exposure: Fish- toxicant brought from water site of action in gills, excreted and not taken up or
metabolized and excreted, concentration decreases in water and increases in fish
Accumulation occurs via: Bioconcentration- accumulation of pollutants through chemical
partitioning from aqueous to organic phase; bioaccumulation- accumulation of pollutants
through chemical partitioning from all sources into organic phase; biomagnification- increase in
tissue [ ] of substance as it moves up the food chain
Receptor mediated- specific, less compound for effect
Narcotic- not specific, more compound for effect
Environmental effects: riskpersistence x mobility x toxicity x volume
Persistence- how long chemical lasts for; Mobility- how quickly and how far does the chemical
move (binds with ligins) toxicity- how potent is the chemical (what are the effects), volume of
use- how much is released into the environment (add enough to saturate binding ligands; found
in water column becomes biologically available
Anthropogenic effects- dams (mills), pollution
caused by wool, pulp and paper mills, reduced
access to upper reaches of rivers and streams for
spawning , O2 depletion, toxic effects of pollutants
in water
Solutions- fish ladders, efforts to reduce pollution
(sewage treatment, agricultural management
practices, riparian buffers
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