Aquatic Organics

Question 1

What are PBTs

Answer 1

PBT = Persistent, Bioaccumulative, Toxic chemicals

Natural processes can mean that compounds increase in concentration in organism e.g. orcas were found to have high conc of PCBs which basically do NOT degrade at all

Sources: pesticides, herbicides, pharmaceuticals, personal care products, fire retardants

Question 2

What are environmental processes controlling organics?

Answer 2

• Inflow/outflow, dilution
• Deposition
• Sedimentation (and burial)/resuspension
• Volatilization: process by which organic chemicals transition from the liquid phase to the gas phase and enter the atmosphere. The rate of volatilization depends on factors such as the chemical’s vapor pressure, water temperature, and air-water interface area.
• Sorption: organic chemicals can adsorb onto solid particles present in water, such as sediment or suspended particles. This process can influence their concentration and distribution by reducing their mobility in the water column.
• Photolysis: degradation or transformation of organic chemicals due to exposure to sunlight. Some organic chemicals can undergo photodegradation when they absorb certain wavelengths of light. This process can impact their fate and concentration in water bodies, especially near the surface.

Question 3

Schweizerhalle fire – case study

Answer 3

1986, fire broke out in a warehouse and resulted in the release of a large amount of toxic substances into the nearby River Rhine. During the fire, the warehouse contained various chemicals, including pesticides, solvents, and dyes. As the fire raged, the intense heat caused the containers to rupture and spill their contents into the River Rhine, which served as a source of drinking water for several nearby towns and cities.
The pollutants caused widespread fish kills, resulting in the death of tens of thousands of fish. The contamination also affected the water supply, leading to disruptions in drinking water provision for many communities along the Rhine.
Pivotal role in shaping regulations and practices related to the storage, handling, and transport of hazardous chemicals to prevent similar incidents in the future.

Question 4

Persistent organic pollutants (POP)

Answer 4

Synthetic organic chemical which is persistent, long range transport possible, hydrophobic (bioaccumulate) -> all POPs are PBT

Global distribution: vapour pressure that allows them to be transported in the atmosphere in gas phase and deposited in cold areas

Stockholm dirty dozen: all contain chlorine -> every single chlorinated compound is dangerous

Question 5

Physical/chemical properties of organics

Answer 5

Aqueous solubility
- Sol ⇑ if T ⇑, salinity ⇓, DOM ⇑, Co-solvents ⇑ (pH can have both ways + neutral)
- PCB: solubility goes down for increase in number of chlorines

Vapor pressure = pressure in the gas phase when in thermodynamic equilibrium with its liquid form at a certain temperature.
- high vapour pressure at low T = volatile
- VP increases with temp

Henry’s law constant
- Vapor pressure / solubility in water
- K ⇑ if salinity ⇑, Co-solvents ⇓

Octanol water partition coefficient (KOW)
- Tendency of a chemical to dissolve/partition into hydrophobic organic matter
- Log KOW < 3: not so bioaccumulative, log KOW > 3: clearly bioaccumulative
- can be used to estimate solubility

Partition coefficient: describes partitioning between solid and liquid for one system, but is not transferable to another system
- Kd = sorption coefficient > describes equilibrium between sorbed and desorbed

Bioaccumulation factor/Bioconcentration factor
- Bioconcentration is the process by which a chemical substance is absorbed by an organism from the ambient environment only through its respiratory and dermal surfaces (diet not included).
- Bioaccumulation is the process in which a chemical substance is absorbed in an organism (bioconcentration + DIET)
- net result of chemical uptake - chemical elimination and dilution due to growth

note: as chemical gets bigger, more hydrophobic and solubility decreases

Question 6

Importance of low vapour pressure

Answer 6

Most of the organic compounds have low vapour pressure (PCB, alkenes, Benzene, …) but does not mean gas phase is unimportant -> low VP means higher susceptibility to long range atmospheric transport: they partition into particles or aerosol in atm so can be carried over long distances AND they are less susceptible to degradation if VP low