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Many aplogies for posting 3 emails in a row with gobbledygook and many thanks to those who have advised me on how to get over these peoblems.  I always find it a bit strange that Jiscmail does not send you your own message so you can't understand why people can't read your message!  Fingers crossed this one works.

I came up with this method (not that it is anything novel) for deriving a GAC for assessing acute exposure from easily liberatable cyanide in a risk assessment I did.  Would be interested to hear what people think:

 

Where,   GACacute = TDacute_oral x BW / Sing

            GACacute = GAC for acute exposure (mg.kg-1)

            TDacute_oral = tolerable dose for acute oral exposure (mg.kg(bw)-1)

            BW = body weight (kg)

            Sing = mass of soil ingested in one day/event (kg)

·        Tolerable dose for acute oral exposure.  The existing TOX report for cyanide states that the lowest reported fatal oral dose of cyanide for humans is 0.56 mg.kg(bw)-1.  As there is the possibility of death at this dose it can be assumed that a tolerable dose will be significantly below this value.  The US Agency for Toxic Substances and Disease Registry, in its toxicological review of cyanide (ATSDR, 2006), did not derive a minimum risk level (MRL) for acute exposure but did derive an MRL for intermediate exposure of 0.05 mg.kg(bw)-1.d-1.  This is based on a no observed adverse effect level (NOAEL) of 4.5 mg.kg(bw)-1.d-1 derived from a 13 week study on rats exposed to sodium cyanide in drinking water divided by an uncertainty factor of 100 (10 for extrapolation from animals to humans and 10 for human variability).  Given that this MRL is intended for intermediate duration exposure (i.e. repeated exposure for weeks to months) it can be assumed that a one off exposure of this amount would not result in harm to human health and would be tolerable.  Thus I assumed that a one off dose of 0.05 mg.kg(bw)-1 as the tolerable dose for acute oral exposure to easily liberatable cyanide.


Body weight - say 13.3 kg? - average BW of 0-6 yr old female


Mass of soil ingested in one day/event - who knows? - has to be higher than the assumed average of 100 mg/d - could be loads higher of soil pica behaviour occurs - but the SGVs are not currently protective of such receptors.  This is obviously a sensitive and highly uncertain parameter.  If we choose a value of 1000 mg/d we get a GAC of 665 mg/kg - if we choose 10,000 mg/d (i.e. 100 times average + equivalent to a couple of teaspoons) then we get 66.5 mg/d.  I guess it comes down to how protective you want to be - do you want to make soil safe to eat as a healthy snack or protective of  typical soil eating behaviour?  Given that easily liberatable cyanide is not often found in such high concs -perhaps its as well to be particuarly protective in this case and go with the lower GAC?


In terms of complex cyanide, I derived a tolerable dose for  acute exposure thus:

The toxicity of complex cyanide is lower due to its lower relative bioavailability compared to free cyanide (RIVM, 2001).  RIVM (2001) derive a tolerable daily intake (TDI) for chronic exposure to complex cyanide by multiplying the TDI for free cyanide by the ratio of the relative bioavailability of free cyanide (50%) to the relative bioavailability of complex cyanide (3%).  A tolerable dose for acute oral exposure for complex cyanide of 0.83 mg.kg(bw)-1 has been derived using this approach (0.05 mg.kg(bw)-1 x 50% / 3%).  I then used the same approach as above to get a GAC 16 times higher than that for easily lib cyanide.


Cheers


Simon






On 03/09/2010 10:15, John Allison wrote:
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Nicola,

I used to work in a factory as a chemist where cyanide was used as a raw material to make thiocyanate. Detailed specialist training was provided before even qualified people were allowed anywhere near cyanide. I am therefore able to offer a bit information from industry where there is occupational exposure. There can’t be much doubt that acute risks of cyanide far outweigh the long term risks, in fact major operators in the chemical industry -  with some justification in my opinion - regard the long term risks of cyanide in occupational exposure as more or less negligible especially when compared to other chemicals, e.g mixed hydrocarbons. The human body quite happily metabolises small quantities of cyanide which are naturally present in some foods, but of course the same could be said about metabolising alcohol, this does not mean it is not having long term effects, but on the whole at the time I took the course which is going back a few years there was no evidence of long term issues with cyanide based on one large company’s own data over many decades whereas the same could not be said of other chemicals.

So for acute risks, it was considered that 50mg/kg free cyanide in a commercial setting provided no risk in product in terms of handling etc., and bear in mind some products were drug intermediates. In terms of complex cyanides we had no concerns as the antidote for suspected cyanide poisoning is swallow stuff to complex it in your stomach.

Since then I have seen figures in the region of 30-50mg/kg free cyanide used for soil which perhaps in the context of the above do not sound unreasonable. I think there was a way to work out a level in one of the old CLR documents but can’t remember the detail, perhaps someone else can help?

Regards

John

John Allison BSc(Hons) CSci CChem MRSC SiLC
Principal Land Quality Consultant


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From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Nicola Brookfield
Sent: 02 September 2010 16:01
To: [log in to unmask]
Subject: Re: Cyanide and Free Cyanide

 

 

Thanks Chris.  Tox 5 is current but is not very useful for assessing the more concerning acute risks from CN other than to say it needs to be considered! 

 

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Nicola Brookfield

Associate Director - RPS Planning & Development

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-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Dainton
Sent: 02 September 2010 15:47
To: [log in to unmask]
Subject: Re: Cyanide and Free Cyanide

 

Tox 5 for inorganic cyanide is still 'current' and provides plenty of useful information.

 

 

Chris Dainton

Peak Environmental Solutions

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