Introduction to Toxicity and LD50

Based on How Toxic is Toxic?ChemMatters, Dec. 2014

Chemical Hazard Awareness ModuleSupplement

Sponsored by WA State Department of Ecology (http://www.ecy.wa.gov/greenchemistry/)

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

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

400 mg/kg exposureLD50

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

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

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

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