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Lethal Dose 50% (LD50)

Grace Taylor

Grace Taylor

8 min read

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Study Guide Overview

This study guide covers LD50 and LC50, including their definitions, calculation, and application in risk assessment. It explains how to interpret these values, compare toxicity across substances, and understand the limitations of the data. The guide also discusses other toxicity measures like NOAEL, ED50, and the history and methods of LD50/LC50 testing, including ethical concerns. Finally, it provides practice questions and exam tips for the AP Environmental Science exam.

AP Environmental Science: Toxicity & LD50 - Your Ultimate Guide 🧪

Hey future AP Environmental Scientists! Let's break down the concept of LD50 and related toxicity measures. This guide is designed to be your go-to resource for acing the exam, especially the night before! We'll make sure everything clicks, and you feel super confident. Let's dive in!

Understanding Lethal Dose (LD50) and Lethal Concentration (LC50)

What are LD50 and LC50?

  • LD50 (Lethal Dose 50): The amount of a substance (usually in mg/kg of body weight) that kills 50% of a test population of animals. Think of it as the dose that's lethal to half the group. It's like a toxicity benchmark.
  • LC50 (Lethal Concentration 50): Similar to LD50, but it measures the concentration of a substance (in air or water) that kills 50% of a test population. It's used for substances in the environment (air, water) rather than direct doses.
Key Concept

LD50 and LC50 are acute toxicity measures, meaning they look at immediate effects, not long-term ones. They are also a measure of relative toxicity, not absolute safety.

Memory Aid

Quick Memory Aid: LD vs LC

Think of LD as Dose (direct amount given), and LC as Concentration (amount in the environment).

Examples of LD50 Values

SubstanceRouteLD50 (mg/kg in rats)Notes
NicotineOral~50Very toxic
CaffeineOral~190Moderately toxic
AspirinOral~200Moderately toxic
Ethanol (Alcohol)Oral~7,000Relatively low toxicity
Table SaltOral~3,000Relatively low toxicity

*Note: These values are for ...

Question 1 of 12

What does LD50 primarily measure? 🤔

The long-term effects of a substance

The dose that kills 50% of a test population

The concentration that causes a specific effect in 50% of the population

The highest dose with no adverse effects