TOXICITIES OF SUBSTANCES¹
in order of increasing toxicity and
TOXICITY EXERCISES

¹  Most LD₅₀ values were extracted from https://chem.nlm.nih.gov/chemidplus/chemidlite.jsp.  For tables of LD₅₀ values, please visit:  https://en.wikipedia.org/wiki/Median_lethal_dose  and/or https://ntp.niehs.nih.gov/iccvam/docs/acutetox_docs/guidance0801/appa.pdf .  Toxicity exericises were derived from:  http://murov.info/EM-TOC.htm  and  http://www.cengage.com/c/experiments-in-general-chemistry-6e-murov/9781285458540 .
² The LD₅₀ (Oral-rat) values represent the number of mg/kg of body weight that will kill half of the rats that orally consume the amount given. One source used was: https://chem.nlm.nih.gov/chemidplus/chemidlite.jsp 
³ The applications of these values to a 70 kg human is subject to question and can result in misleading and inaccurate conclusions. However, this toxicity data is the most widely and generally available information.
⁴ Densities are included to demonstrate that most of the substances have densities near 1 g/cm3. Reference to the image of 1 gm of sugar should yield a very rough idea of the toxic amount of the substance.
⁵ 0.2 g of methanol can cause blindness.
⁶ Typical tablets of Tylenol, ibuprofen and aspirin contain a few hundred milligrams of substance, substantially below the LD₅₀ values of 133 to 14 grams.
⁷ A typical cup of coffee contains about 0.1 g of caffeine and a glass of cola about 0.05 g

The availability of the Internet has made it relatively quick and easy to obtain toxicological information about chemicals. When working with chemicals, it is helpful to have some idea of the relative toxicities of the chemicals. In the case of high toxicity, special precautions may be necessary. Because it is generally not possible to obtain toxicological data for humans (except as a result of terrible accidents), most existing toxicological data has been obtained from the study of rodents. The LD₅₀ (Oral-rat) values represent the number of milligrams per kilogram of body weight that will kill half of the rats that orally consume the amount given. The applications of these values to humans is certainly arguable and undoubtedly sometimes leads to incorrect conclusions. The LD₅₀ (Oral-rat) values are often included in MSDS (Material Safety Data Sheet) and there are many sites on the Internet that can locate MSDS. Listings of MSDS sites can be found at:  http://murov.info/orgsolvents.htm .  If you are using an MSDS listing, scroll down to the toxicological heading (usually #11, the second one after physical properties which is another very useful section of the MSDS) which is about 3/4 of the way through the MSDS and look for LD₅₀ (Oral-rat) values.

Other options are to type in the name of the chemical followed by msds in the Google search box or the name of the chemical followed by LD₅₀ at http://www.wolframalpha.com/ .  Probably the quickest way to locate the desired information is to use the Chemidplus site https://chem.nlm.nih.gov/chemidplus/chemidlite.jsp .

TOXICITY EXERCISES

For more organic chemistry exercises, please see:  http://murov.info/orglab/exercises.htm

1. a. The average cup of coffee contains about 100 mg of caffeine. How many cups of coffee could potentially be lethal to half of the drinkers? (Note:  The LD₅₀ value for rats is the same as the LD_LO for humans. Unexpected and unusual coincidences should be viewed with suspicion and it is possible that one of the values was incorrectly recorded. There are many errors in LD₅₀ tabulations presumably because lists have been compiled by non-chemists and differences in labels and chemical names have not been adequately noticed.)

b. Recognizing that the answer to #1a depends on many assumptions and has a large margin of error, is the very sad and unfortunate story reported at the site below surprising?

http://the-tech.mit.edu/V118/N56/shorts.56n.html
http://www.solarnavigator.net/solar_cola/caffeine.htm

2. Assume that a typical glass of beer contains 6% ethyl alcohol and 350 mL. How many beers could potentially be lethal to half of the drinkers?

  3. The average cigarette contains about 20 mg of nicotine and the smoking of one cigarette results in the absorption of about 1 mg of nicotine in the bloodstream. To a 70 kg human, how many cigarettes could be lethal if consumed and how many if smoked?

4. During nuclear accidents, people exposed to radiation are sometimes advised to take potassium iodide to dilute the radioactive iodide that has been released and can be incorporated into the thyroid gland.

a. Does this sound like a wise procedure?

b. During these episodes, the media often describes the use of "iodine" as therapy. Explain the problem with this announcement.

c. The iodine LD_LO value for a human is 28 mg/kg but the LD₅₀ value for rats is listed as 14 g/kg.  Halogens are considered to be very toxic but the LD₅₀ value for rats seems to indicate a low toxicity. Critically evaluate the values.

5. Would you consider vanillin to be a safe food additive? Explain your answer.

6. Hetch Hetchy reservoir in the Sierra Nevada Mountains near Yosemite was formed when the O'Shaughnessy Dam was completed in 1923 on the Tuolomne River to provide a water source and storage for San Francisco. The reservoir holds 360,000 acre feet of water. An acre ft. = 1.23x106 L. Terrorist threats are in the news today on a daily basis and one of the many concerns is that our water supplies could be contaminated with a very toxic substance.

a. To determine whether this is feasible, calculate the amount of potassium cyanide that would have to be dumped into Hetch Hetchy to kill half of the people who drink 230 grams (about 8 oz.) of the water. Assume the density of the reservoir contents is 1.0 g/mL.

b. Do you think it would be possible to dump the amount calculated above into the reservoir without being detected? Explain your answer.

c. Answer the previous question assuming that dioxin is used instead of potassium cyanide. Explain your answer.

7.  a. The venom of black widows has a rat subcutaneous LD₅₀ of approximately 0.2 mg/kg. Assuming a density of 1 g/mL, what volume of venom do black widows have to inject to have a 50% chance of killing a human? What are the many assumptions that go into this calculation? Does the amount intuitively seem like a reasonable amount for a spider bite?  (Note that oral values are not available but it is claimed that unless a person has an ulcer or similar, the oral toxicity of spider and snake venoms is low.  (See: http://members.tripod.com/~c_kianwee/rpotent.htm and http://members.tripod.com/~c_kianwee/venom3.htm.  For snake values, see: http://snakedatabase.org/pages/LD50.php , http://www.seanthomas.net/oldsite/ld50tot.html ).

8. Warfarin (also called coumadin) is a commonly used prescription drug used to thin blood. A person on coumadin, must have frequent blood tests to monitor the coumadin concentration. Does the LD₅₀ of coumadin explain the need for the frequent testing. Explain your answer.

9. Dioxin is a byproduct in some organic syntheses and is produced in small quantities during some of the processes used to bleach paper. Does LD50 justify concern about the use of this chemical. Perform an Internet search on dioxin to determine if there have been any environmental problems caused by dioxin.

10. Strychnine is used as a rat poison. Should it be used carefully? Explain your answer.

11. Acetaminophen is the active ingredient in “non-aspirin” pain relievers. Extra strength tablets contain 500 mg of acetaminophen. How many tablets would be toxic to half the population of 70 kg humans (assuming the rat LD50 values apply to humans)?