Sciencemadness Discussion Board

Oxalic Acid Danger

Murexide - 27-12-2018 at 21:30

Oxalic acid is quite frequently used to standardise potassium permanganate solutions. However, it is corrosive and toxic (kidney stones from calcium oxalate build up). Initially I assumed that oxalic acid, with latex gloves and care, would be relatively safe to work with (similar to KMnO4 in danger). However, further research shows that oxalic acid is rated at least a 3/4 and sometimes a 4/4 on health risk (!!!) as "extreme" (see http://www.chemicalstore.com/MSDS/MSDS_Oxalic_Acid.pdf). This is rather unsettling, especially for such a common chemical. Note that a 4/4 health rating is normally reserved for extremely toxic chemicals e.g HF or dimethyl mercury

P.S Once the standard solution (0.1M) is made the health risk is obviously non existent. So, this obviously is relevant only for the powder and concentrated solutions


[Edited on 28-12-2018 by Murexide]

j_sum1 - 27-12-2018 at 22:14

Not sure what your health ratings are based on. There is no question that HCN is more toxic than oxalic Acid.

I think you are referring to the so:called fire diamond. The reality is that thos gives very little information. It was never intended to. It is for quick assessment of potential hazards for containment purposes.

If you swallow enough OA, you will die. If you handle without gloves it will irritate skin. But follow routine handling procedures and there is minimal risk.

Fulmen - 27-12-2018 at 23:01

I've also seen OA listed as "extremely toxic", but Wikipedia has the following to say:
"In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg. It has been reported that the lethal oral dose is 15 to 30 grams"

That's about 5x the values for table salt, so I wouldn't worry.

fusso - 27-12-2018 at 23:33

Quote: Originally posted by Fulmen  
I've also seen OA listed as "extremely toxic", but Wikipedia has the following to say:
"In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg. It has been reported that the lethal oral dose is 15 to 30 grams"

That's about 5x the values for table salt, so I wouldn't worry.
Wiki: 3 g/kg (oral, rats)[6]

Sulaiman - 28-12-2018 at 03:39

Here in UK Oxalic acid is restricted to 10% w/w (EPP)
I believe that the restriction is due to its potential for deliberate long term slow poisoning,
causing renal falure over a period of time, that would not be seen as 'unnatural' by a coroner.
- 'inheritance powder' for the patient poisoner.

[Edited on 28-12-2018 by Sulaiman]

morganbw - 28-12-2018 at 04:32

We used Oxalic acid by the pallets where I retired from.
There were no real concerns about it.

I am not saying that it is completely benign just that we used no special care dealing with it.

Fulmen - 28-12-2018 at 05:52

Also, spinach contain appr 1% OA.

XeonTheMGPony - 28-12-2018 at 08:40

Rhubarb leaf has nice high concentrations as well

https://en.wikipedia.org/wiki/Rhubarb

Fulmen - 28-12-2018 at 08:44

True, but you don't usually eat the leaves. The stalks have only 0.25% or so, although plants damaged by cold can apparently have higher levels.

Murexide - 28-12-2018 at 14:34

I had a look at the UK restrictions for possession just then and they look rather surprisingly high. Especially 15% sulfuric acid and 3% nitric acid, without your mineral acids it’s rather hard to do much Chemistry! Although oxalic acid could easily be concentrated by boiling and nitric acid by distillation.

As for oxalic acid danger, it is looking more like it only causes renal failure and kidney stones and such after ingestion. It isn’t too corrosive and doesn’t absorb through skin too well so as long as it isn’t eaten it should be fine I assume.

Vomaturge - 28-12-2018 at 19:18

I don't know how they come up with those (NFPA 704 fire diamond) ratings. I know that they're meant more for estimating immediate temporary hazards than safe long term usage of chemicals, but some don't even make sense. According to Wikipedia, lead II acetate is just a "2 of 4." But it's hard to think of an exposure scenario where a gram of oxalic acid would be more dangerous than the same amount of lead acetate. Maybe if the oxalic was suspended as a fine dust, and caused a pulmonary burn?

I know which I'd prefer to have a gram of in my salad:
Quote: Originally posted by Fulmen  
Also, spinach contain appr 1% OA.


I love spinach!

Murexide - 28-12-2018 at 19:42

Rather surprisingly lead nitrate is a 3/4, somehow more toxic than lead acetate. And sodium Oxalate is a 1/4, presenting only a slight health hazard, but oxalic Acid presents extreme toxicity hazards???