Where the
world gathers for metal finishing
Q&As since 1989


-----

Photoeffects of potassium dichromate

1999

Dear Sir,

in ecotoxicology many biotests like tests with waterfleas, algae or duckweed use potassium dichomate as reference toxicant, but knowledge about the toxic mechanism is rare. LemnaTec develops image analysis systems for this biotests and our own research suggests, that high light intensity enhances toxicity. We heard about but have no proof in experiment or literature that potassium dichromate becomes more reactive/changes its redox potential under light( 20-120 µE*m-÷*s-1, 040-700 nm, 6000-10000 lux).

We use potassium dicromate at a concentration of 0.1-50 mg/L in a nutrient solution (pH 6.5-8) with the following concentrations :
KNO3 350,00 mg/L
Ca(NO3)2*4H2O 295,00 mg/L
KH2PO4 90,00 mg/L
K2HPO4 12,60 mg/L
MgSO4*7H2O 100,00 mg/L
H3BO3 120,00 µg/L
ZnSO4*7H2O 180,00 µg/L
Na2MoO4*2H2O 44,00 µg/L
MnCl2*4H2O 180,00 µg/L
FeCl3*6H2O 760,00 µg/L
EDTA 150,00 µg/L

Could you please give me any hint, where I could find information about photochemistry or phototoxicity of potassium dichromate?

Thank you very much for your efforts.

Matthias Eberius
- Germany

---

1999

Matthias,

Photons can react with the inner electrons (kicks them into a higher energy state) of atoms and bonding pairs in compounds. The electrons will with time drop back and emit a photon in the process (fluorescence and phosfluorescence). A spectrograph can be used to measure the wavelength of the light (tight lines for atoms and wide bands for compounds)(and you should see the math to find the orbitals,wow!). You could try to measure the millivolts of the system before and after hitting it with light. So, the light might be energizing the dichromate. But, the light might so work by supplying some of the "energy of reaction" needed by bio-catalyzes or reaction sites, create free radials, increase metabolism, change the hormone levels (a few hours every day of strong light is use in the winter to bring people out of depression). Another area of interest for you might be the cancer drugs that are introduced into the blood stream and then activated by shining light into the body.

Hope this helps,

Fred Mueller, CEF
- Royersford, Pennsylvania