Quantitative equilibrium calculations

Fundamentals
Problems
      Fraction of atrazine
           Help
           Answer
     Retardation factor
           Answer
     Raining out
           Answer
     Carpet
           Help
           Answer
     Sorption kinetics
           Help
           Answer
     Organic pollutants in water
           Answer
     Fish toxicity test
           Answer
     Ethylacetate
           Answer
     Tetrachlorobenzene
           Answer
     Hexachlorobenzene
           Answer
     Chlorobenzene
           Answer
     Toxicity test
           Answer
     Toxicity test - improving...
     3 phases problem
           Answer
     Sorption experiment
           Answer
     HCH
Excercises for an improved intuitive understanding
Questions for recapitulation
Good to know
Minesweeper-problems

Toxicity test - improving experimental conditions

One can make use of the sorption effect discussed in the previous question in order to improve the experimental conditions in a toxicity test. In many cases one faces the problem that uptake and/or metabolism of the compound do affect the aqueous concentration throughout the run of the experiment. Without a constant aqueous concentration the whole toxicity experiment is not well defined and might not be reproducible or applicable to natural systems. If, however, the experimental system contains a sorbent with a quick partition kinetic and with a capacity much higher than that of the fish and the water, then this sorbent would act as a buffer and replace most of the compound that has been taken up (and metabolised) by the fish.

How would you do this for the following situation: You want to conduct a tox test with hexachlorobenzene (HCB). Your goal is that the HCB concentration must not drop below 90 % of the starting concentration when 1 kg fish are put into the tank and start taking up the HCB. The average fat content of the fish is about 5 %  (i.e. 0.05 kg lipid per kg wet weight). There is no sediment or any other sorbing phase in the system.

How much of a sorbent (pre-equilibrated with HCB at the starting concentration) would you have to add as a buffer to the aquarium before the start of the experiment in order to achieve this goal?


Use the following partition constants:

log Klipid/water= 5.8 (Lwater/Llipid)

log Ksorbent/water = 5.0 (Lwater/Lsorbent)

 

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