5. Organics Flashcards
What are organic contaminants?
Chemicals that contain carbon and more than one C-H covalent bond
What is the “origin” of organic contaminants
Absent from the Earth’s crust; number without limit and increasing
Background concentration approaches 0.
What is a hydrocarbon?
A molecule consisting of hydrogen and carbon.
What is an aromatic hydrocarbon?
Includes an aromatic group (ring structure)
What are PAHs?
Polycyclic Aromatic Hydrocarbons
Characteristics of PAHs (5)
- Two or more fused benzene rings
- Exists as complex mixtures
○ 100s of congeners
○ Additive, synergistic, antagonistic effects - Persistent (years to decades to break down)
- Natural and anthropogenic sources
○ Natural: burning of organic matter (forest fire, volcanoes)
○ Anthropogenic: oil spills, charring your meat on the BBQ - Environmentally significant PAHs range from 2 rings (naphthalene) to 7 rings (coronene)
What are congeners
Different forms within a class
(dioxins, furans, PAHs, PCBs, all have each some congeners)
Characteristics of low molecular weight (LMW) PAHs? (3)
- water soluble
- not likely to bioaccumualte
- can be acutely toxic
Characteristics of high molecular weight (HMW) PAHs? (5)
- Hydrophobic
- More resistant to oxidation, reduction, and vaporization
- Can accumulate in sediments and organisms
○ Particularly in invertebrates (lack of metabolizing enzymes) - Carcinogens
- More harmful to birds because they bioaccumulate (hazard less, exposure higher, so risk higher)
What are HAHs?
Halogenated Aromatic Hydrocarbons
Characteristics of HAHs (2)
- Many congeners, all occur as complex mixtures
○ Always these → number of rings - Very potent and very persistent
○ Very potent → only need a little bit to have an effect
○ Longer half life (more than PAHs)
Effects of PAHs (4)
- Development Abnormalities
- Carcinogenic
- Endocrine disruption
- Immune effects
Examples of HAHs (4)
- dioxins
- furans
- PCBs
- some pesticides e.g. DDT
What is the structure of dioxins
2 halogenated benzene rings linked together by 2 oxygens
What is the structure of furans?
2 halogenated bezene rings linked together with 1 oxygen
What is the source of dioxins and furans
Not manufactured: they are products of high temperature incineration (e.g. volcanoes, forest fires, municipal garbage incineration)
* Never produced on purpose, sometimes made by accident when you’re doing things at high temperature
* For instance, agent orange was contaminated with dioxin
What is the structure of PCBs
2 halogenated benzene rings linked together only by carbon (like its only a line connecting the two rings)
What are dioxin like compounds (DLCs)? (4 characteristics)
- Compounds that act like dioxins
- They form a subset of HAHs
- All exert toxicity through binding to the AHR
- Very potent toxicants
Examples of DLCs
- dioxins
- furans
- some PCBs
3 steps of the AHR pathway
- Contaminant binds to AHR
- Induce expression of metabolic enzymes (CYP1A)
- CYP1A metabolizes contaminant
Issue with DLCs and the AHR pathway
- DLCs turn on the pathway
- They are not well matabolized by CYP1A
- So the AHR pathway stays active
- This is toxic to the cell (the continuous expression of CYP1A)
How do PAHs exert toxicity through the AHR pathway?
- PAHs bind to AHR
- They are well metabolized by CYP1A
- They are not considered DLCs because their toxicity occurs through a different metabolism
- It is the product of the metabolism of PAHs by CYP1A that is carcinogenic
Characteristics of organic pesticides (3 points)
- A chemical designed and used to kill ‘pests’
○ e.g. herbicide, pesticide, rodenticide, fungicide - Diverse structures and modes of actions
- Concerns about the safety of non-target species
Categories of pesticides (3)
- organochlorines
- organophophates
- neonicitinoids
Characteristics of organochlorines (3)
- Persistent, biomagnify
- Most banned in North America
- Affective to combat malaria
Examples of organochlorines (2)
- DDT
- chlordane
Characteristics of organophosphates (4)
- Less persistent than organochlorines
- Inhibit acetylcholinesterase (neurotransmitter)
- Similar receptors in insects, birds and mammals,
○ So problematic because if you are targeting insects you might also hurt birds and mammals due to this - Extremely toxic to birds at low doses
Examples of organophosphates (2)
- monocrotophos
- chlorpyrifos
Characteristics of neonicitinoids (6)
- Neuroactive insecticides
- Selective: ‘safe’ for mammals and birds
- Because they target a receptor that is specific to insects
- Toxic for insects
- Honey bee collapse disorder
- More recent evidence suggests that they are toxic to birds
Example of neoicitinods (1)
imidacloprid
Example: Monocrotophos event and issues (5 points)
- Withdrawn form the US market in the 1980s
- This left a gap in the record and data
- Still available in other countries (it was the scecond most used organophophate insectisde in the 1990s worldwide)
- Sprayed on firelds to control grasshoppers in Argentina
- Resulted in death of approximately 20,000 Swainson’s Hawks
Example: Neonicitinoids insectiside event and issues
- Systemic insecticide available since 1992
○ Applied to seed coat (not sprayed) - Linked to honey bee collapse disorder
○ Behavioral effects
○ Controversial, because you don’t know how much is being exposed to bees in real life - Toxic to birds?
○ Toxicity or diminished food supply
○ Because it targets the specific insect receptor
Endocrine disruption def
exogenous substance or mixtures that alters function(s) of the endocrine system and consequently causes adverse health effects
What is the endocrine system?
A system of glands and hormones that regulates distant organs through chemical signalling
Estrogen signalling
- Hypothalamus releases hormone to pituitary
- Pit releases to ovaries
- When estradiol (female sex hormone) is released, it travels throughout the body
- The response to estrogen is analogous to the response of dioxin
- Estrogen or an estrogen mimic comes into the cell, binds to the receptor, causes transcription changes,
*Makes vitellogenin (?) - Problem is when there is a mimic of estrogen and binds to it not properly, for example in a male
What is vitellogin?
- Vitellogenin is a biomarker for exposure to estrogenic compounds
- Vitellogenin (VTG) is an egg yolk precursor protein
- Normally only produced in females during oocyte maturation
○ Very low background levels in males - Effective biomarker for estrogenic chemicals
Another endocrine disruptor definiton (reading)
“An [ED] needs sufficient molecular similarity, specificity (affinity), and efficacy to achieve a potency that would interfere with the endocrine system by either: (1) mimicking a hormone produced in the body or by (2) interfering with normal binding of the hormone to its receptor and through effects on transport, synthesis, breakdown, or excretion.”
* If it really mimics your body, you are disrupting messaging system in your body that is fundamental to your growth
* That one little tweak sends out crazy signals
