7. Source & Fate Flashcards
How do pollutants enter the ecosystem? (4)
- Unintended release from human activities (e.g. nuclear accidents, mining operations, shipwrecks, fires)
- Disposal of wastes (e.g. sewage, industrial effluents)
- Deliberate application of biocides (e.g. pest and vector controls, pharmaceuticals)
- Natural processes (e.g. weathering of rocks, volcanoes, forest fires)
Natural sources of PAHs (Polycyclic Aromatic Hydrocarbons) (4)
- Oil seeps
- Forest/grass fires
- Volcanoes
- Wood and animal decay
Anthropogenic sources of PAHs (3)
- Oil spills, leaks
- Burning of fossil fuels (car exhaust)
- Cigarettes
Overall source of PAHs (1)
Incomplete combustion of organic matter
Pyrogenic source of PAHs
- Originate from high temperature combustion
- Mostly unsubstituted → do not have any groups attached to the benzene rings
- High molecular weight
Petrogenic source of PAHs
- Originate from petroleum: crude oil, fuels, lubricants, and their derivatives
- Higher percentage of alkylated PAHs
- Tend to be alkylated (here has a methyl group)
- Alkyl = carbon group e.g. methyl
Are the sources of PCBs (a HAH) natural or anthropogenic
Anthropogenic → they are manufactured compounds
Source of PCBs (what specifically)
Dielectric fluids in transformers and capacitors, coolant, lubricant, etc.
Are PCBs PBTs?
Yes
What does PBT stand for
Persistent
Bioaccumulative
and Toxic substance
PCBs were banned. These legacy contaminants’ concentration decrease as years go by. But why are there still background levels today (if they are manufactured only and banned)?
- Because there are still hotspots, or places where there were leaks, so its like a secondary source
- We cannot get completely rid of them, bc there are small point sources here and there that leak into the environment, even though they are not perpetually persistent
What is the OG source of mercury?
Mercury is a naturally occuring element
Why has the concentration of mercury increase in the environment?
Human activities
What is chemical fate?
It is what happens to a chemical once it enters the environment
What are the 4 major compartments that contaminants are distributed to?
- Air (atmosphere)
- Surface waters (hydrosphere)
- Land surface (soil/sediment)
- Living organisms (biosphere)
What determines the fraction of each chemical that will be found in each compartment?
Physical-chemical properties are a major determinant of the fraction of each chemical that will be found in each compartment
What properties of chemicals can influence their fate? (4)
- polarity and water solubility
- partition coefficients
- vapour pressure
- molecular stability (has to do with persistence)
What environmental conditions can influence the fate of a chemical? (2)
- temperature
- flows of water, air, solid matter
What patterns of use of the chemicals can influence their chemical fate? (3)
- which compartment the chemical is introduced into
- if the introduction of the chemical is episodic or continuous
- if the introduction is in conjuction with other chemicals (e.g. pesticides + additives, oil + dispersants)
What is an example of an episodic introduction of a contaminant?
A pesticide you only put out a few times per season
What is an example of an continuous introduction of a contaminant?
Coal burning
Key physical-chemical properties (3)
- Solubility in water
- Partition between environmental compartments, and Octanol-water partition coefficient
- Susceptibility to degradation/transformation
* solibility: more polar molecules are more water soluble
hydrophobic
chemicals that are relatively insoluble and tend to move out of the aqueous phase
hydrophillic
chemicals that are quite soluble in water
