Title: Ecotoxicology Ecotoxicological study is a multi-step
1Ecotoxicology
- Ecotoxicological study is a multi-step process,
involving - The entry, distribution and fate of pollutants
within the environment - The entry and fate of pollutants in living
(biota) organisms within an ecosystem and - The harmful effects of the chemical pollutants on
the constituents (biotic abiotic) of ecosystems
(which include man).
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7Beyond our toxin trailIs the grave deeper than
we thought?
Metabolized and/or stored
Reaches an organ
molecular mechanism
Adverse health effect
Physiological chain of events
8- Ecotoxicology
- Bioaccumulation
- Bioconcentration (in water)
- Biomagnification
- Never single effects
- Movement between media (air, water)
- Toxicology
- Host defense mechanisms
- Individual susceptibility states
- Single effects
- Cumulative exposure
9Ecological bases of Ecotoxicology
- The basis for determining the effects of
contaminants on ecosystem is at organism level - At organism level, response can be
- Acute toxicity causing mortality
- Chronically accumulating damage ultimately
causing death - Sublethal impairment of various aspects of
physiology and morphology - Sublethal behavioral effects
- Measurable biochemical changes
10- At population level, response can be
- Size and dynamics (based on birth rates, death
rates, gains, from immigration and losses from
emigration) - Cause a reduction or an increase in the natural
flowchart of numbers, in the biomass, sex ratio,
etc. - At community level, response can be
- species diversity
- predator prey relationship, etc
- Change in ecosystem
- nutrient cycling rates, patterns of nutrient
flow, - physical-chemical conditions etc.
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12 Assessment of Structural Changes
changes in species / population structure
- appearance/disappearance of
an indicator species -
number of individuals of a species
- biomass of a species
- presence or absence of a
species Biomass-a quantitative estimate of the
total mass of living plant or animal materials
13 changes in community/ecosystem structure
- biomass
- abundance
- biotic indices (e.g.
trophic types) -
species richness / diversity
- dominance - food
chain length/complexity
14Chemicals of ecotoxicological interest
- They are toxic and in many cases their
metabolites are also harmful e.g. DDT DDE
(metabolite of DDT) - They are very stable both chemically and
environmentally - Their stability has lead to their persistence and
ubiquitous nature in the environment - Almost all chemicals of ecotoxicologigal interest
are bioavailable and in most cases undergo
bioaccumluation and biomagnification (food chain)
15Bioavailabiltiy The fraction of a chemical that
is in an available form to an organism e.g. fish
food, absorption from water
Bioconcentration - where the chemical
concentration in an organism exceeds the
concentration in the surrounding media (i.e.
aquatic environment) as a result of exposure
through the respiratory surfaces (i.e.
gills/dermal surfaces) - not food! Bioconcentrati
on Factor conc. in organism conc. in
ambient medium (usually water)
16- Bioaccumulation - where the chemical
concentration in an organism achieves a level
that exceeds that in the water/media as a result
of chemical uptake through all routes of
exposure. - Bioaccumulation factor Conc. in organism
- Conc. in
food - (or
ingested water) - Bio-accumulation of Cd is higher than most metals
as it is assimilated rapidly and excreted slowly - depends on the rate of excretion
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18 Biomagnification - where the chemical
concentration in an organism achieves a level
that exceeds that in the organisms diet due to
dietary absorption. i.e. higher trophic levels
accumulate more chemical
Biomagnification Factor Conc. in
predator Conc. in
prey Factors that influence bioaccumulation -Envir
onmental persistence -Lipophilicity -Biotransforma
tion
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20Toxic Effects
- The biochemical (molecular in nature) or
physiological (observed at organ and whole
organism levels) changes which adversely affect
individual organisms birth, growth or mortality
rates. - Both biochemical and physiological changes could
lead to behavioral (whole organism level) changes.
21- Toxicant binding
- Reversible vs. Irreversible binding
- Irreversible binding (covalent) causes harmful
effects. - Types of bonding
- Covalent gt ionic gt Hydrogen binding gt Vanderwaals
gt hydrophilic - Biochemical responses
- Biochemical response could be protective or
non-protective (may or may not cause harmful
effect). - Non-protective biochemical responses have
carcinogenic, mutagenic, teratogenic and
neurotoxic potentials.
22- Protective biochemical responses
- Monoxygenase (OCs and PAHs)
- Induction and binding to metalothionein (Cu, Cd,
Zn and Hg) - Binding to blood plasma, bones and hair (Metals
and xenobiotics) - Dissolving in fat (organics- e.g. OCs)
- Mineralization ( e.g. MeHg to Hg 2)
- Demineralization (As to MeAs)
23Protective biochemical response
- Heavy metals for example can be stored and
detoxified by organisms either by binding to
specific proteins e.g. metallothioneins (-SH
proteins) - In some cases it is mineralized to inorganic
form, which is less toxic e.g. Hg bound to Se is
a mineralized Hg (detoxified Hg MeHg to Hg). On
the other hand, the inorganic form, which is more
toxic can be methylated to a less toxic form e.g.
As.
24Protective biochemical response
- PHASE 1 REACTION.
- Organic pollutants could also be metabolized and
detoxified by Cytochrome P450 enzymes (Microsomal
Monoxygenase MMO). -
- PHASE 2 REACTION
- The metabolites undergo conjugation with
endogenous molecules e.g. GSH. - For some chemicals the metabolites/conjugated
form are more toxic than the parent compound and
can lead to cancer formation.
25Non-protective response
- Binding to DNA (DNA adduct)
- DNA structural damage (strands break) induced by
genotoxic compounds - Binding to SH-Protein (Protein adduct) enzymes
and proteins - Neurotoxicity prolongation of K and Na flow and
inhibition of AChE activity in the brain
26Non-protective response
- Mitochondrial Poison (lost of proton gradient)
- Inhibition of vitamin K cycle (competition with
vit K binding site) - Inhibition of Thyroxine (competition with
thyrosine binding site) - Inhibition of ATPase (enzymes for transport of
ions e.g. K, Na, Ca)
27Non-protective response
- Environmental estrogens (eg DDT) and androgens
(tributhyl Tin) - Endocrine disrupters (binding to endocrine
receptors) - Photosystems of Plants (interruption of electron
flow) - Plant growth regulation
28Physiological changes
- Non-protective biochemical responses lead to
Physiological changes which could be observed at
organ and organism levels - Organ level
- accumulation of Cd in kidney, which could cause
cell death (cytotoxicity), resulting in
dysfunction of the kidney - PAHs and Lung cancer
- Organism level
- decrease in production (growth and reproduction)
- changes in gene frequency
- decrease in resources acquisition and uptake
29Behavioral Changes
- Either or both physiological and biochemical
effects could lead to behavioral effects at
organism level- - migration,
- intraspecific attraction,
- aggregation,
- aggression,
- predation,
- vulnerability,
- mating
- caring for young ones and avoidance of predator.
- .
30Population Changes
- Changes in population may come about as a result
of direct changes in numbers of individual
organism and gene frequency - By indirect means (decrease in population of
predators due to toxic chemicals could lead to
increase in numbers of its prey).
31Diclofenac residues as the cause of vulture
population decline in Pakistan.Nature. 2004 Feb
12427(6975)630-3.
- Diclofenac causes kidney damage, increased serum
uric acid concentrations, visceral gout, and
death.
32- Changes in community structure
- change in pyhtoplankton assemblage due to
eutrophication - acid rain affecting microorganisms in the soil,
- aquatic life
- Changes in Ecosystem level (earth as an
ecosystem) - carbon dioxide increase
- ozone depletion
33What is an Endocrine Disruptor ?
An exogenous agent that interferes with the
synthesis, secretion, transport, binding, action,
or elimination of natural hormones in the body
that are responsible for the maintenance of
homeostasis, reproduction, development and/or
behavior.
34 Mechanisms of endocrine disrupting compounds 1)
Binding and activating the estrogen receptor 2)
Binding but not activating the estrogen receptor
(therefore acting as an anti-estrogen) 3) Binding
other receptors 4) Modifying the metabolism of
natural hormones 5) Modifying the number of
hormone receptors in a cell 6) Modifying the
production of natural hormones
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37Hormone regulation and feedback control Estrogen
levels depend on Estrodiol sulfate Estrodiol
serum-binding proteins ?-fetoprotein
(AFP) Testosterone-estradiol binding
globulin Xenoestrogens (ex. DES) 100-fold lower
affinity than E2 to these binding
protein Bioavailability increased
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39Non-genomic mechanisms of ED action
- Compounds of the azole type, such as ketoconazole
and the fungicide fenarimol, inhibit CYP isoforms
and consequently can also affect steroid
synthesis while the now-banned anti-fouling agent
tributyltin and its metabolites, which have
strong ED potential, are thought to act by the
same mechanism, probably by inhibition of
aromatase.
40Genomic mechanisms of ED action
- bind to oestrogen receptors and so act as
pseudoestrogens in vivo, giving feminizing
effects - tamoxifen and diethylstilbestrol and industrial
chemicals (e.g. octylphenol and bisphenol-A - fungicide vinclozolin binds competitively to the
androgen receptor, blocking the cellular actions
of testosterone on androgen-dependent tissue
growth and behaviour patterns - chlordecone, inhibit binding to the oestrogen and
progesterone receptors, whereas bisphenol-A can
block ligand binding to the thyroid receptor
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44Timing, duration, and amount of exposure.
Organization vs. activation Timing, duration, and
amount of exposure are each important
determinants of the outcome. There are windows of
vulnerability during fetal development in which
small exposures to endocrine disruptors may have
profound effects not observed in adults. Studies
of the intrauterine position of mice during fetal
development show that slight fluctuations of
steroid hormone levels influence genital
morphology, timing of puberty, sexual
attractiveness, sexual behavior, aggressiveness,
and activity level of offspring.
45Various Classes of EDCs
- Flame Retardants
- Fungicides
- Herbicides
- Insecticides
- Metals
- Pharmaceuticals
- Phenols
- Plasticizers
- Polyaromatic Hydrocarbons
- Soy Products
- Surfactants
Polybrominated diphenyl ether Vinclozolin Atrazine
Methoxychlor Tributyltin Ethynyl
Estradiol Bisphenol A Phthalates PCBs,
dioxins Genistein Alkylphenol Ethoxylates
46PBDEs(??????)
- Polybrominated diphenyl ethers (PBDEs) are a
class of recalcitrant and bioaccumulative
halogenated compounds that have emerged as a
major environmental pollutant. PBDEs are used as
a flame-retardant and are found in consumer goods
such as electrical equipment, construction
materials, coatings, textiles and polyurethane
foam (furniture padding).
47Bioavailability of PBDEs
- Found in animals
- Increase in fish
- Increase in whales
- Sewage sludge
- PCBs Found in Lake Washington Fish (PBDEs next?)
- Found in human (breast milk)
48PBDEs Breast Milk - Sweden
(Norén and Mieronyté, 1998)
49Health Effects of PBDEs
- Similar to PCBs (Polychlorinated biphenyls)
- Persistent Bioaccumulative Toxicant
- No human data
- Animals studies indicate
- Changes in thyroid hormone levels
- Neurobehavioral toxicity
- Development effects- alters Behavior
- Impairs memory and learning
- Delays sexual development
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51Vinclozolin
- Vinclozolin is a fungicide that has been shown to
cause Leydig cell tumors and atrophy of the
accessory sex glands in adult rodents. In
addition, exposure of rats during pregnancy
causes a pattern of malformations in the male
urogenital tract . - Androgen receptor antagonist
52Atrazine
- A chlorotriazine herbicide, is used to control
annual grasses and broadleaf weeds. - Suppression of the luteinizing hormone surge
during the estrus cycle by atrazine leads to the
maintenance of elevated blood levels of
17beta-estradiol (E2) and prolactin. - The mechanism for tumor development may include
one or more of the following the induction of
aromatase (CYP19) and/or other P450 oxygenases,
an antagonist action at the estrogen feedback
receptor in the hypothalamus, an agonist action
at the mammary gland estrogen receptor or an
effect on adrenergic neurons in the
hypothalamic-pituitary pathway.
53??A Bisphenol-A
BPA is used in the manufacture of polycarbonate
plastics and epoxy resins from which food and
beverage containers and dental materials are
made. Perinatal exposure to environmentally
relevant BPA doses results in morphological and
functional alterations of the male and female
genital tract and mammary glands that may
predispose the tissue to earlier onset of
disease, reduced fertility and mammary and
prostate cancer.
54????(PVC)????????????????????????????????????????
??????PVC??,?????????????(phthalates)?????????????
???????????????,????????????????????PE(???)???
??? alkylphenol(???) ???????????????(???????)??
??????????????????(polystyren)?????,???PS,????????
??????????,??????,????????????alkylphenol(???)????
??????????,?????????????????
55- ??????????
- ????????????????????????
- ??????(??????????)
- ?????(phthalates)
- ???(alkylphenol)
56Phthalates??????
- ??????????????????? ?
- ????????????????(???)?
- ????????????,???????PVC?PVDC???PVC?????
- male infertility
- Interfere with cholesterol uptake and androgen
biosynthesis
57Tributyltin (TBT) ?????????????,??????????,?????
????????,????????,????????????
58?????????????????,?????????????,??????????????????
,?????????????????
59TBT
60Yucheng (??) of Taiwan, 1979
- 2000 people exposed to PCB-contaminated rice oil
- with chloracne, fatigue, skin and nail
pigmentation, polyneuropathy, and abnormal liver
function - Long-term follow-up study was established for 1st
and 2nd generation (prenatal exposed)
61- Likely Kanechlor 500 (a Japanese PCB mixture)
62Semen Analysis40 Yucheng men (37-50 yr old)
compared with 28 controls
- Volume and count no difference
- Oligospermia 23 vs. 4
- Morphology 28 vs. 23 abnormal (18 increase)
- Motile sperm no difference
- Speed by CASA no difference
- Chinese hamster oocyte penetration after one
re-thaw cycle 16 vs. 32 (50 drop)
(Hsu et al., JAMA 2003)
63Children Prenatally Exposed
- More stillbirth (Yu et al., 2000)
- Called Yucheng children
- Born with darker skin, nail pigmentation and
deformity, and developmental delay (Rogan et al.,
1988) - Reduced neurocognitive functioning up to ages of
12 years (Chen et al., 1992) - Behavioral problems (Lai et al., 2002)
64Semen Analysis
- Young men prenatally exposed to PCBs/PCDFs as
well as their neighborhood-matched controls were
recruited for semen analysis - Volume, counts, morphology, motility, oocyte
penetration - Aged 16-21, consent obtained from young men and
their parents
65Penile length (cm) in Yucheng and Control Boys
by Age
Measured by Blinded physicians
66Hormones in prenatal PCB/PCDF-exposed boys and
unexposed controls after puberty
gt
lt
gt
lt
gt
lt
No difference luteinizing hormone
prolactin
(Hsu et al., JTEH 2005)
67(?)?????????????26?, (?)?????9?(?13)? (?)?????
9?(?13) (?)????????9?,(?13)????????????????????
(?)????????????????6?? (?)??????????????????????
3?,????????????????????????????????????? (?)??????
??2?,??????,????,??????,???????,?????? (?)???????
???????????????????????????????? (?)?????2?,????
????????????? (?)???????????,?????????????
68EDSTAC Tier 1 Assays Concerned with detecting
- Receptor binding assays (ER and AhR)
- Uterotrophic
- Hershberger
- Pubertal female
- Steroidogenesis
- Frog metamorphosis
- Fish reproductive screen
69EDSTAC Tier 2 dose-response relationship
- Mammal development and reproduction
- Bird development and reproduction
- Mysid shrimp life cycle
- Fish reproduction and development
- Amphibian development and reproduction
70 Species-dependent sex determination Mammal XY/XX
synthesis of testosterone/functional androgen
receptors estrogen receptor in the brain Birds
WZ/WW The ability to synthesize and recognize
17?-estradiol is necessary for female CNS and
gonadal sexual development to occur Reptile temper
ature-dependent sex determination (aromatase
related)
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73Temperature-dependent sex determination
thermosensitive period (TSP)
74Temperature determines their sex. A nest
temperature of 73.5 degrees would develop males.
If it heats up to 83.5, hormones would trigger
changes causing the embryonic cells to
differentiate as females.
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