Comment on How do I verbally say 2.1 ng/kg
andrewta@lemmy.world 4 months agoSo are they saying nanograms of the stuff per kilograms of the human?
In other words are they saying it’s a ratio compared to the weight of the person?
Yeah, personally I would say that it’s per kg bodyweight.
But I would also do my darndest to try write it, since “ng/kg” is kind of just nonsense. It makes it look like you could divide the grams out of that to get a fixed ratio, which is not correct at all.
But it is a fixed ratio.
If it was in pounds, metric tons, moles or atomic mass units… It doesn’t change the ratio, the actual number.
Would it be acceptable to drop the unit all together?
“Lethal dose is 0.000000012 : 1 (substance : bodyweight)” (I made up the number).
I’m not sure if there is a better way of writing the ratio.
Could a fraction be more applicable?
“lethal dose is 1/600000 of bodyweight”
I’m sure it’s written as ng/kg to show the base units are the same, and the rest is just “fiddling” scientific notation
moles
would not work, as they are no mass unit. 1 mol of Botox does not have the same weight as 1 mole of human (If that is defined at all, as organisms are no pure substances).
Ah, yes good point
Well, what I meant with that, is that it’s semantically important that it’s ng of the substance per kg bodyweight.
If it was ng of the substance per kg of the substance, then in proper mathematical physics, the unit would disappear completely.
So, for example:
42000000000 ng of the substance / kg of the substance
Is equivalent to:
42000000000 * 0.000000001 * kg of the substance / kg of the substance
Which means in the end, you just have: 42
As my physics teacher would often say: Is that 42 potatoes or sausages or what is it?
A number without a unit is just devoid of meaning…
Thank you
Yeah - the dose is the poison (if you drink enough water it becomes toxic), so if you are talking precisely you need to describe the concentration of a substance in which it is likely lethal to a person, and that’s typically expressed as mass of a substance per mass of bodyweight. A lot of the time you will also see this expressed as an “LD50” value; the dose at which you’d expect 50% of people to die. This accounts for the fact that people’s metabolisms vary quite widely.
~1ng/kg ~= 0.08ug for a typical (~80kg) person, which is a very tiny amount - whatever you are talking about is incredibly toxic.
A quick Google of the numbers says OP is likely talking about botulism so I guess they perhaps have been reading about Botox
Close was talking about Clostridium botulinum
LD50 is per kg of rat by weight
ZapBeebz_@lemmy.world 4 months ago
That is correct. The ratio is nanograms of substance to kilograms of bodyweight
andrewta@lemmy.world 4 months ago
Thank you