Sodium benzoate

[tatuvaaj]

Randy,

An algae product I'm going to use contains Sodium benzoate (C7H5O2Na) as a preservative.

I have done some research on the subject and it seems that it is safe to use for human consumption and toxic levels in freshwater are somewhere in range 60-1291 mg/litre. The final concentration of Sodium benzoate in my case would be near 0.3 mg/l.

Here is a quote from "CONCISE INTERNATIONAL CHEMICAL ASSESSMENT DOCUMENT NO. 26" http://www.inchem.org/documents/cicads/cicads/cicad26.htm


From their physical/chemical properties, benzoic acid and sodium benzoate emitted to water and soil are not expected to volatilize to the atmosphere or to adsorb to sediment or soil particles. From the results of numerous removal experiments, the main elimination pathway for both chemicals should be biotic mineralization. Data from laboratory tests showed ready biodegradability for both substances under aerobic conditions. Several isolated microorganisms (bacteria, fungi) have been shown to utilize benzoic acid under aerobic or anaerobic conditions. From the experimental data on bioconcentration, a low to moderate potential for bioaccumulation is to be expected.


Do you have idea what would the end products and intermediate phases be from microorganism activity on sodium benzoate?

What is your opinion about the long term concentration of 0.3-0.6 mg/l of sodium benzoate in reef aquarium ?

TIA,

[Randy Holmes-Farley]

Tatu:

Tough questions! Let me see what I can find out.

[Gamera]

The answer to your question is actually in the article you provided a link to.

[Randy Holmes-Farley]

Thanks, Gamera.

Section 5.2 answers the questions about its breakdown. Table 1 shows breakdown in seawater to be fairly slow.

Tatu:

Are you talking about a one time use, or is this a food item that you would give the tank?


A later sections describes natural occurance:

"Owing to its occurrence in many organisms, benzoic acid is naturally present in foods (review in Sieber et al., 1989, 1990). Some typical examples specifying reported ranges of means in selected foods have been compiled from Sieber et al. (1989) as follows:"

If you had a reason to use this item, I'd probably go ahead, but pay attention to the potential for something unforseen to happen.

[tatuvaaj]

Sorry, the article is so full of rats and hamsters and cats that I somehow skipped that section.

But since I'm not so good at chemistry and my english isn't perfect, can you confirm that sodium benzoate is degraded to methane and CO2?

These escape from aquarium to air, right?

Could either of you show me the full reaction
C7H5O2Na -> CH4 + CO2

like I said, it is too long I've been in chemistry class. I hated it back then but now I find myself interested in seawater chemistry so I'm constantly learning :)

Randy, it is a phytoplankton product made for aquarium use so I would be using it constantly (maybe every other day). Every dosage would increase the amount of sodium benzoate around 0.3 mg/l

Thanks to both of you!

[Randy Holmes-Farley]

Tatu:

Both anerobic and aerobic degradation seem to take place. Here's another passage:

" Degradation assays using seawater as test medium ("natural water") or as inoculum (marine filter material given into a synthetic marine medium) according to an adapted Organisation for Economic Co-operation and Development (OECD) guideline (301B) resulted in a degradation of 85% and 97%, respectively (10 mg/litre; carbon dioxide measurement; 28 days) (Courtes et al., 1995)."

So, if it completely oxidizes aerobically to CO2, this is the reaction for benzoate (ignoring the sodium):

C6H5COO- + 7.5 O2 <-----> 7 CO2 + 2 H2O + OH-

If the reaction is anaerobic (as in sewage sludge) and results in some CO2 and some methane, it could be any of several possibilities. Methane would disappear to the air, yes. CO2 will get sucked into the carbonate buffer system, but not enough to be noticed.

Anaerobic degradation will use something else as an electron acceptor instead of oxygen. Nitrate, sulfate, etc. Without knowing what it was, it's hard to say what the reaction is exactly.