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How do I verbally say 2.1 ng/kg (lemmy.world)
submitted 2 years ago by to c/nostupidquestions@lemmy.world
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I know the ng means nanogram

But I’m curious how would I say the above line of 2.1 ng/kg

For context I got it from this paragraph

a lethal dose of 1.3–2.1 ng/kg in humans

Would it be

2.1 nanogram per kilogram?

Also if I wanted to write that as a decimal number how would i write that?

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[–] [S] 12 points 2 years ago (3 children)

So 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?

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  • [–] 12 points 2 years ago (2 children)

    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.

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  • [–] 8 points 2 years ago (2 children)

    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

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  • [–] 1 point 2 years ago

    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...

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  • [–] 4 points 2 years ago (3 children)

    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.

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