Environmental Fate of Organic Chemicals

Question 1

What are environmental sub compartments?

Answer 1

when theres soil/sediment and water in air, soil/sediment and air in water, and water and air in soil/sediment

Question 2

What drives partioning?

Answer 2

• molecular interactions: ion pair, dip-dip, H-bonding, induced dip/van der Waals, pi interactions (aromatic)
• structure of chemical drives the molecular interactions: EN, polarizability, dips, quadruples

Question 3

When is equilibrium patiotioning defines and is it driven by kinetics or thermodynamics?

Answer 3

• defined at steady state
• driven by thermodynamics

Question 4

Describe the two types of pi-interactoins

Answer 4

• pi-interactions: specific electrostatic interactions between patial negative charges above and below an aromatic ring and a positive charge species (e.g. small cations, H donors)
• pi-pi interactions: when a postive charge cromes from partial positive on a benzene ring – either edge-to-face or slip stack configuration

Question 5

Describe the relative strength of inter/intramolecular forces: list strongest to weakest

Answer 5

1. covalent bonds
2. ion pair
3. electrostatic: dip-dip > ion-dip > H-bonding > pi-interactions > van der waals (bigger molecules = greater overall strength of interactions)

Question 6

what is vapour pressure, what’s its relationship to volatility, what’s its relationship with intermolecular interactions

Answer 6

• vapour pressure = pressure a gas exerts on its surroundings when in equilibrium with its pure liquid or solid
• higher vapour pressure = higher volatitility
• if weak interactions in the solid or liquid phase –> higher vapour pressure

Question 7

What is the cavity model?

Answer 7

would a molecule interact with itself or break those interactions to interact with water (kinda like the hydrophobic effect)

Question 8

Why do we use octanol to represent the organic component of the environment? what is the organic component of the environment?

Answer 8

• octanol: model compound for lipids in biota
• “organic component” = lipids in biota, soil/sediment, oil

Question 9

How can we estimate logKow? state any assumptions

Answer 9

substituent substitution: assumes swapping an H for another functional group

Question 10

What are the different ways to report Kaw?

Answer 10

Kaw = Ca/Cw = HLC/RT, where HLC = Px/[X]

Question 11

How can we estimate Kaw?

Answer 11

bond contribution method: add up all bond contribution values, give logKaw

Question 12

What is bioconcentration vs bioaccumulation vs biomagnification?

Answer 12

• bioconcentration: from the surrounding environment (respiration, diffusion)
• bioaccumulation: build up of a chemical in an organism from all routes (includes diet)
• biomagnification: increasing chemical concentration in the predator relative to its prey, occurrs when BMF > 1

Question 13

Why do we need to consider the acidity/basicity of a molecule when it comes to partitioning?

Answer 13

if the molecule will have a charge at a specific pH, then it’ll more readily partition into water

Question 14

What is LogD? what does it assume, what is it based off of?

Answer 14

LogD = modified LogKow when considering that only the neutral portion will partition into the organic phase

fraction of acid is based on the pH of the solution and the pKa of the molecule

Question 15

what is adsorption?

Answer 15

organic compound partitions from air or water onto the surface of an environmental sample like soil particle, suspended sediment or aerosol

Question 16

what is Kd?

Answer 16

Kd = adsorption from water-soil, equilibrium partioning = Csolid/Cwater

Question 17

What is Koc?

Answer 17

Koc = Kd/foc

foc = fraction of organic content in particles

Question 18

What is the stolkholm convention?

Answer 18

lists all persistent organic pollutants (POPs) and names if they are being phased out, phased down, or are fine

Question 19

If a compound has a low vapour pressure, low Kaw, and high Koa, how can it be transported throught the air?

Answer 19

hitches a ride on particles

Question 20

how does the aromaticity of a molecule affect the absorption of light?

Answer 20

more cyclic aromatic rings –> absorbs greater wavelength light

Question 21

Describe how microbes can have very diverse living conditions. What are some microbially mediated reactions, which one is very important?

Answer 21

aerobic and anaerobic conditions, including extreme ranges of temperature, phosphorous, pH and nutrients

rxns: hydrolysis, oxidations, reductions, ring opening

reduction is important because we live in an oxidizing environment

Question 22

How are oil spill constituents degraded in biota, what about branched detergents?

Answer 22

B-oxidation cycle

branched detergents with a substituent of the beta carbon cannot undergo B-oxidaiton –> persistant

Question 23

Why is DDT important whats the significance about its metabolites?

Answer 23

DDT = insecticide, important for controlling malaria

DDD = fine
DDE = thinning of eggshells and reducing populaitons of bald eageles and other birds of prey in the US

Question 24

What is a xenobiotic, what is the main goal when metabolizing a xenobiotic?

Answer 24

xenobiotic = substance that is very foreign in the body

goal = increase polarity (via oxidation) to enable excretion

Question 25

describe phase I and II metabolism in humans, what enzymes mediate phase I metabolism?

Answer 25

phase l

• functionalization to increase polarity
• addition of polar functional groups of alteration of exisiting polar functional groups
• mediated by CYP450 enzymes

phase ll

• conjugation to further increase polarity

Question 26

Describe an instance when metabolism can be deterimental

Answer 26

• aflatoxin B1 metabolite is the strongest known carcinogen
• food toxin made from molds that grow on cereals, oil seeds, spices, tree nuts
• genetic target = p53

Question 27

What green chemistry principle aligns with trying to reduce persistance and toxicity, respectively?

Answer 27

persistence = design for degradation

toxicity = designing safer chemicals

Question 28

What parameters can we use to predict long range transport?

Answer 28

• persistence + voltitlity or water soubility
• if stable, can be transported far

Question 29

What is the P-sufficient approach for predicting persistance?

Answer 29

if persistant can…

• undergo LRT
• build up in the environment and biota
• reamin the in the environment for a long time, be harder to remediate
• if persistence, and later find out toxic, big problems

Question 30

How does the P-sufficient approach define persistence?

Answer 30

half life > 6 mo = very persistent