Introduction to Toxicity and LD50 Based on How Toxic is Toxic Introduction to Toxicity and LD50 Based on How Toxic is Toxic? ChemMatters, Dec. 2014 Chemical Hazard Awareness Module Supplement Sponsored by WA State Department of Ecology (http://www.ecy.wa.gov/greenchemistry/) Student reading: How Toxic is Toxic? By Brian Rohrig (ChemMatters, December 2014/January 2015) Slides and notes based on article and ChemMatters Dec 2014 Teacher’s Guide.

Toxicity Toxicity is a property of a chemical How toxic a substance is depends on: How it enters the body Mouth, skin, lungs, injection? How much is taken “The dose makes the poison.”

Measuring Toxicity LD50 – dose required to kill 50% of a test population “LD” = lethal dose Measures acute, or short-term, toxicity Units: mg of substance per kg body mass (mg/kg)

Example: Determining LD50 Starting population 100 mg/kg exposure 200 mg/kg exposure Measuring LD50 – test population (with same starting weight) all given toxic substance at the same time The dose that causes 50% of the population is considered the LD50 50% is chosen because some of the population may be more resistant to the toxic effects of a certain substance, so 50% represents somewhat of an average (ChemMatters, Dec 2014/Jan 2015 pg 6) *This slide may be broken up to reveal individual “experiments” slowly 300 mg/kg exposure 400 mg/kg exposure

Example: Determining LD50 Starting population 100 mg/kg exposure 200 mg/kg exposure 300 mg/kg exposure LD50 400 mg/kg exposure

LD50 and humans Lower LD50 means more toxic To know lethal dose for human Need weight in kg (1 kg = 2.2 lbs) If 1 g of substance kills 5 out 10 rats with weights of 1 kg, how much of the substance would have the same effect on a human weighing 45 kg (~100 lbs)?

LD50 and humans Lower LD50 means more toxic To know lethal dose for human Need weight in kg (1 kg = 2.2 lbs) If 1 g of substance kills 5 out 10 rats with weights of 1 kg, how much of the substance would have the same effect on a human weighing 45 kg (~100 lbs)? Answer: 45 g

Everyday Products Common everyday products can be toxic Even too much water can be toxic Knowing LD50 values of toxins of concern can help Examples: Vitamin D in milk Sodium fluoride in toothpaste Caffeine Fun link: http://www.caffeineinformer.com/death-by-caffeine Too much water can dilute sodium levels in blood to dangerous, potentially deadly, levels. Vitamin D is added to all milk by a government mandate to combat rickets, a disease that results in the weakening of bones. However, Vitamin D is technically classified as a poison because its LD50 value is lower than 50 mg/kg. Since the concentration in milk ends up being in the range of micrograms, it will not cause harm. Sodium fluoride in toothpaste is also classified as a poison, but, again, the concentrations swallowed as a result of teeth brushing are too small to cause harm. Caffeine has a low LD50 value in its pure form, causing cardiac arrhythmia if too much is taken. http://www.caffeineinformer.com/death-by-caffeine is a website that allows you to look at the lethal amount of different caffeinate beverages by weight.

Limitations of LD50 Only for acute toxicity Cannot provide information on chronic, or long-term, toxicity Example: Lead will build up in the body over time and result in poisoning when concentration becomes too high.

Where to Find LD50 Values SDS’s contain 16 sections that break down information about chemical properties; physical, health, and environmental hazards; and safety precautions for handling, storage and transport. Section 11 will list the LD50 information of the chemical, as well as results of short and long term exposure, symptoms, and if the substance is a known carcinogen. http://www.oshatraining.com/cmsimages/SDS_Binder.jpg

Toxic vs. Hazardous Toxicity is a property of a chemical that cannot be changed Hazards can vary and depend on Transportation Storage Use Lab safety rules are used to minimize hazards Possible student misconception – “all chemicals are hazardous” Chemicals are only a hazard when improperly handled. (ChemMatters Dec2014/Jan2015 Teacher background information)

Toxic vs. Poisonous Poisoning is a result of toxicity Poisonousness results from Type of exposure Dose Toxicity of substance Natural processes to remove chemical from body Natural differences between individuals

LD50 versus LC50 LD = Lethal Dose LC = Lethal Concentration Used in measuring aquatic toxicity Same concept as for humans, but applied to aquatic organisms Fish, crustacea, daphnia, algae

POSSIBLE QUESTION: If all substances are potentially toxic, why aren’t there warning labels on everything?” Many substances are catergorized as “practically non-toxic” or “relatively harmless” Putting warning labels on these types of substances would be a distraction and potentially cause unnecessary concern. (ChemMatters Dec2014/Jan2015 Teacher background information)