7 hydrocarbons & halogenated hydrocarbons Flashcards
what are the major classes of hydrocarbons and halogenated hydrocarbons?
classified as POPs (persistent organic pollutants)
-polyaromatic hydrocarbons (PAHs)
-polychlorinated biphenyls (PCBs)/polybrominated biphenyls (PBBs)
-dibenzodioxins and dibenzofurans
what are PAHs?
-also called polycyclic aromatic hydrocarbons, polynuclear aromatic hydrocarbons
-hundreds of different forms
-not synthetic, they are natural organic compounds
what are PCBs and PBBs?
-209 different congeners
-structurally same but different number of chlorine and bromines
what are dibenzodioxins and dibenzofurans?
-polychlorinated dibenzodioxins (PCDDs)
-polychlorinated dibenzofurans (PCDFs)
-210 different dioxins and furans
what are priority PAHs?
classified as priority: most abundant in environment
-no sidechains= unsubstituted PAHs
-contain fused aromatic rings
-any organic compound that undergoes combustion creates PAHs (smoking, BBQ, burning wood)
what are the sources of PAHs?
-pyrogenic (fire related sources)
-petrogenic (crude oil and petroleum sources)
blue=anthropogenic sources
what are some aspects of PAHs?
-volatility=determine if remains in gaseous phase or not
-toxicity as per IARC=carcinogen level
-Log Koc=binding affinity for organic carbon (increased=more affinity)
-high molecular weight=less soluble (more lipophilic) which means more prone to accumulation
-lipophilic=remains in gaseous or solid state (doesn’t really stay in water)
-increased vapour pressure=more volatile
what are substituted PAHs?
have side chains
alkylated
-common in petrogenic PAHs
-low abundance in pyrogenic
-more persistent and toxic than unsubstituted
novel
-just found in environment in urban areas
-very persistent
what is the chemistry and kinetics of PAHs?
lipophilic environmental fate depends on its physic-chemistry
-highly bioaccumulative
rapidly metabolized and excreted by higher vertebrates
-crustaceans and some bivalves cannot metabolize PAHs, therefore they accumulate high levels
transported in the atmosphere, but more of a local problem due to easier chemical breakdown (except when alkylated/halogenated)
what are the major sources of PAHs in oceans?
study the impacts of deepwater horizon oil spill on marine wildlife:
oceans.si.edu/conservation/pollution/gulf-oil-spill
do oil sands contribute to PAHs?
-every year, PAH concentration goes up in the summer, down in the winter
-when volatile in summer, cold weather will make condense (liquid) onto snow, snow melts in the summer (why concentration its higher)
what are PCBs?
-209 congeners, 36 environmentally threatening
-coplanar vs non-coplanar
-coplanar- Aryl hydrocarbon receptor agonists
-coplanar are more toxic (not necessarily more lipophilic)
-AhR is an endogenous receptor which coplanar binds to (activates or deactivates)
-banned by the Stockholm Convention on Persistent Organic Pollutants in 2001 (not produced anymore but still found in environment)
what are the 12 coplanar PCBs?
coplanar because mono-ortho substituted PCBs
-either no Cl or one on ortho position (keeps then in perpendicular plane)
what are the sources of PCBs?
used as electrical insulators, coolants, lubricants, paint additives, and plasticizers (sealants and caulking materials)
-found in hard plastic materials
-by-product of many manufacturing processes
-PCB production and import are banned in Canada since 1977
what is some physical and chemical data for PCB congeners?
ones that you will find in gaseous state are low to moderate chlorination
what is the graph of biomagnification vs log Kow (degree of chlorination)?
high chlorination=more biomagnification
what are some structures of dioxins?
what is the metabolism of organic toxicants?
what are the enzymes that are involved in phase 1 of metabolism?
what are the enzymes involved in phase 2 of metabolism?
what is a problem with metabolism?
what is an example of xenobiotic activation?
epoxide formation
-benzo (a) pyrene
-epoxides bind covalently to DNA (DNA adducts)=leads to mutations which can lead to carcinogenicity
what is the second step of the activation of the xenobiotic?
all redox compounds (readily accept and donate electrons)
-can create ROS (causes oxidative stress)=will oxidative DNA, proteins and lipids
what can bind to AhR?
dioxin like compounds: Aryl Hydrocarbon Receptor (AhR) agonists (e.g. alkylated PAHs, co-planar PCBs, PCDDs and PCDFs)
-can all bind
-dioxins are lipophilic so they simply diffuse across membrane
-XRE=xenobiotic response element
-once binds, can activate or deactivate transcription of genes
what is the TEF and TEQ?
toxic equivalence factor (TEF): each compound is given a TEF based on its specific ability to elicit dioxin-like effects, with 2,3,7,8-TCDD being the most toxic and a TEF of 1
total toxic equivalent: the sum of the concentration of all individual dioxin-like-compounds multiplied by their specific TEFs
what is the example of calculating TEQ?
