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Just For Laughs The SOLE purpose of this forum is to put a smile on the face of a person reading the messages. Anything of a SERIOUS nature will either be deleted or moved out of here.

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Old 06-23-2003, 05:11 PM   #1
Seamus Haley
Website

It's hardly new but I was just reminded of it last night and I figured I'd share...

http://www.dhmo.org/

Is possibly the funniest satirical website online these days, funnier than petsorfood, funnier than bonzaikitten, funnier than jesushatessmut...

It rivals A Modest Proposal for sheer humor.

Take a look if you have a few minutes and spread the word about the dangers of dihydrogen monoxide.
 
Old 06-24-2003, 07:51 AM   #2
meretseger
And they laughed at me for doing the dishes in a lab coat.
Could you explain the LD50 on the MSDS for me briefly? Like what units it's in? I think I could make a lot of jokes comparing it to snake venom.

Erin B.
 
Old 06-24-2003, 09:52 AM   #3
Seamus Haley
The LD50 is a system that was intended to determine the toxicity of substances, seen a lot with herps when discussing snake venoms...

Essentially, largeish groups of test animals (Mice generally) are injected with the toxin in differing amounts (very slight differences, many test groups) until 50% of the test subjects die from the injected amount... you can work from a small injection up to a larger one, or the other way around...

Literally it's "Lethal Dose 50" and the number can vary, LD100s were done for quite a while as well, although are generally regarded as being slightly less accurate (it's easy to have all of something die).

LD tests have a number of huge problems though for determining actual toxicity... There are multiple injection methods (subcutaneous, intraveinous, intramuscular and so on), but the same method is used for a specific test group... Problem is, when it comes time to compare the results between species, not all of them inject venom in the same manner. Crotalids are a lot more likely to tag something and inject intramuscularly than an elapid is, it's a simple matter of fang length... Then there are toxins that have a greater effect on certain types of tissue or prey than others (hognoses aren't technically venomous, but the toxins in their saliva will melt a toad but have minimal effect on a mouse) and of course mice aren't identical to humans in the way they react to toxins.

Many people also use LD50s to try and label a snake "the most dangerous" or "the most venomous" which is an utter crock... LD50s don't take into account the venom yeild of the animal in question, the likelyhood of an envenomation, the likelyhood of encountering the snake, the ease with which medical attention can be obtained or any of the other factors contributing to danger...

'course... you already knew that, but someone else might not have and it's something I tend to get sidetracked by... since LD50s can be performed in different ways with different substances (not just venoms) on different test subjects (mice, rats, rabbits etc) the measurements used will vary depending on the specific test... some will use milliliters, some milligrams, some larger measurements and many older ones will use standard measurements rather than metric.

In the sheet for dihydrogen monoxide, they used grams/kilograms, this is the extrapolated amount required to hit that 50% death rate when the body weight of the test subjects and amount injected is multiplied out to hit a standard measurement... since every test animal will have a slightly different weight and the most common species used are pretty small, the results are often expressed as a proportional amount over body weight. So basically it takes X amount to produce a lethal effect in test animals that weigh Y amount, if a human weighs 80Y, then it becomes a concern when they are expoosed to 80X amount of the substance.

The abbreviations next to the two are indicative of the method of administration for the test animals, IPR is intraperitoneal if I remember correctly and IV is intraveinous.
 
Old 06-24-2003, 01:37 PM   #4
meretseger
Ok, I get it now. Off the top of my head it looks like you have to inject a mouse with quite a lot of water to kill it. (1/10 of its body weight IPR?).
Well, at any rate, I'm off to make a melted toad sandwich for lunch.

Erin B.
 
Old 06-25-2003, 07:26 AM   #5
meretseger
Oh, wait, milligrams per kilograms... this is why I do so bad in computer class, I'm bad with metrics and can't tell a megabyte from a kilobyte.

Erin B.
 
Old 06-25-2003, 07:41 AM   #6
Uffern
Thanks for the explanation on LD50. I was just professing my complete lack of understanding on it to a friend a few days ago.
 
Old 06-25-2003, 07:42 AM   #7
Seamus Haley
I'm pretty sure it was Grams to Kilograms, although with 190g/k, it would be about five and one fifth of the animal's body weight, give or take... and that's the amount required to produce a 50% death rate, not 100...

It sure is a lot of dihydrogen monoxide to have to inject in order to produce the result though.

And I think the computer terms aren't actually on a base 10 system the way metrics are... I was under the impression that there was some slight deviation when it was broken down into bytes due to the physical limitations of the materials used to make the hard drives... I may be way off though, I use my computer to wander around online and play tetris, anything else is beyond me.
 
Old 06-25-2003, 07:44 AM   #8
Seamus Haley
Ack! About one fifth... or going out two signifigant digits 1/5.26... sorry, just woke up, not writing clearly yet... I knew wqhat I meant anyway.
 
Old 06-25-2003, 08:25 AM   #9
Seamus Haley
Quote:
Thanks for the explanation on LD50. I was just professing my complete lack of understanding on it to a friend a few days ago.
The important thing to remember with LD50s is that they need to be looked at in the context which they were performed under and that the results have a limited meaning.

I got into an enormous argument with a few people in an online chat about this a few months back and am still a bit hot under the collar over it, so the rest of this is going to be something of a rant...

Different snakes have different venom compositions... both between species and between individuals. The venom types for species can often be generalized into broader catagories or even slightly more specific toxic compounds found within the venom, but the individual snakes have venom that will differ slightly in it's exact composition based on the reccent diet of the animal, the environmental conditions, the animal's age, the current hormonal levels, when it last envenomated a prey item or was milked... All very slight differences, but when looking at tests that use the venom from multiple milked individuals and venom that may or may not be "fresh" when it's applied (much like any other mostly organic substance, venom changes chemically as it ages) and when given in amounts that often vary by a milligram or two for each test group... It becomes a serious issue area of concern when looking at the results and the potential for uncontrolled factors in the experiment.

The different venom types (broad catagories) also react differently to different kinds of tissue... pretty much every venom will have an effect of some kind on whatever tissue it comes into contact with, but the effects can vary greatly when it hits fatty tissue vs. muscle vs. a vein vs. mildly subcutaneous injections... Further, the different venom types evolved right along with the snake on both their digestion (venom is a digestive aid first and foremost) and the physical injection method. Elapids have fixed fangs, these are shorter than the moveable fangs of vipers and crotalids (sea snakes and mole vipers were only reccently reclassified, the same rules apply for fang length, prey type and venom type, but I'm going to address the larger groups where trends are more easily seen) and as such they are capable of subcutaneous injection but very rarely would they penetrate intramuscularly... The venom has a greater effect when injected in the manner that the snake itself would when striking and a greater effect on animals that they are likely to consume as prey items. Since only mice, rats and rabbits are used for LD tests (maybe chickens, but I've never seen results from this if it's been done) and only one injection method per test, the results are going to be skewed.

As an added problem, I have yet to see an LD test that tested every known venomous species, freshly milked and using each injection method... most test around a hundred species or so for one published set of results, usually with packaged and frozen venom (really, it takes an enormous amount of venom to perform these tests, multiple control groups of test subjects numbering several hundred each, multiple test groups used until that 50% mark is reached, then several repeated attempts of the results which produced the 50% and those measuremnts of venom similar to it... so if 0.05 mg produces the 50% fatality rate, 0.055, 0.054, 0.056, 0.053 all need to be repeatedly tested to verify the results) and usually with a single injection method that isn't representative of realistic envenomations.

Then the part that really gets me uppity when someone tries it in a friendly debate... LD tests are in no way indicative of the danger inherent in any given snake. I dislike the use of the term "danger" to start, these animals have a capability that needs to be respected, approached correctly, there is no "danger" just "controlled risk" but... in terms of practical application for danger or such meaningless terms as "most venomous" (seen on croc hunter... Irwin angers me frequently, I break a lot of remotes by throwing them at his fat head) the LD50s are useless. They fail to take into account the likelyhood of encountering the species, the likelyhood of an envenomation, the venom yeild and the ease of getting medical attention.

As an example... using the LD50 for subcutaneous injection, the tiger rattlesnake (Crotalus tigris) is far more toxic than the eastern diamondback rattlesnake (Crotalus adamanteus) Searching online for this information, as an easy way to verify it, http://www.kingsnake.com/toxinology/LD50/ld50iv.html contains a list with both species on it. The tiger has 0.56mg/kg needed to produce that 50% mortality rate in mice, the EDB has 1.65mg/kg to produce the same... Looking at the numbers as represented, the tiger seems far more dangerous, far more toxic... Until one realizes that the tiger has an average venom yeild of around 7-10 mg and the EDB has an average of 550-600mg (The potential is slightly higher or lower than the averages I listed, some sources will have a broader range, some narrower). Further, the EDB is a lot more likely to strike and a lot more likely to envenomate if handled/harassed.

Looking at specific record holders... The EDB has the highest venom yeild (to the best of my knowledge anyway) of any snake. The highest number of human fatalities would be African Saw Scaled vipers. The most toxic is up in the air for the various injection methods but usually results in either the inland taipan, the australian brown or one of several sea snakes. The highest number of deaths when represented as a percentage of envenomations is the golden lancehead (because medical attention was impossible to obtain for years, they're found on what amounts to a good sized rock in the middle of the ocean). The species usually listed as making handlers and zookeepers apprehensive or regarded as dangerous because of the animal's physical capabilities coupled with unpredicatability is most often the mambas (I've usually seen black, but a few sources have listed greens)...

So... after all that, the only thing I really said was that LD50s are only valuable as LD50s... if you want to know which species has the most toxic venom when injected in a certain manner into mice... then the LDs are the way to go. Any additional conclusions drawn from that information may or may not be correct, however logical them seem in casual reflection.
 
Old 06-26-2003, 08:08 PM   #10
meretseger
Ok, thanks a bunch for making me remember something I learned in school this semester...
I think what the deal is is that there are 100 bytes in a megabyte but there are 800 bits in a megabyte because there are 8 bits in a byte. So the bytes are on a factor of
 

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