Uptake, elimination, accumulation and QSAR

4 important questions on Uptake, elimination, accumulation and QSAR

How can toxins be uptaken and eliminated from a species?

Uptake:
- Water
- Food
- Skin

Elimination:
- Gills
- Urine & feces
- Biotransformation

Note: To simplify, this course sees all categories of uptake as one inflow and all categories of elimination as one outflow.

What is meant with bioconcentration factor and bioaccumulation factor?

Bioconcentration factor:
The concentration of a substance within organisms divided by the concentration of that substance in its surroundings (steady-state).

Bioaccumulation factor:
The concentration of a substance within organisms divided by the concentration of that substance in its prey (steady-state).

What is the difference between elimination and biodegradation and how does one calculate with biodegradation?

Elimination is when a pollutant leaves an organism but remains the pollutant itself. Degradation is when a pollutant is degraded by the body itself and does not exist anymore in the organism or outside an organism.

The formula of biodegradation is similar to the formula of elimination:
Ln(Ct / C0) = -kt * t
in which kt is the biodegradability constant.
kt is determined with help of the BOD5.
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How does the BOD5 formula, what does COD and THOD mean and how does one calculate the THOD?

BOD5 = BODu(1 - e^-kt * 5)
For good degradable substances BOD5 / BODu = 0.68 (which means that for good degradable compounds, after 5 days  68% is degraded.
For good degradable compounds BODu = COD. 
THOD is equal to COD.
THOD could be calculated with help of stoichiometric equations:
1. Make the reaction equation right
2. Calculate the amount of O2 required for degradation with stoichiometry.
3. BOD5 /THOD =  close to 0.68, then compounds is good degradable. (THOD = COD, and COD = BODu)

The question on the page originate from the summary of the following study material:

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