Milligrams per kilogram (mg/kg) is a dose unit that expresses how many milligrams of a chemical an organism receives for every kilogram of its body weight. In AP Enviro, it's the standard way to report LD50, the dose lethal to 50% of a test population.
Milligrams per kilogram (mg/kg) tells you how much of a substance an organism takes in relative to its size. One milligram per kilogram means one milligram of chemical for every kilogram the organism weighs. Because it scales to body weight, the same mg/kg dose is roughly fair to compare across a tiny mouse and a large human.
This is the unit you'll almost always see attached to LD50 (lethal dose 50%), the dose of a chemical that kills 50% of a test population of a species (8.12.A). When a toxicity study reports an LD50 of, say, 5 mg/kg versus 5,000 mg/kg, the lower number means the chemical is far more toxic because it takes a much smaller dose per kilogram of body weight to be lethal.
mg/kg lives in Unit 8 (Aquatic and Terrestrial Pollution), specifically in topic 8.12, where the learning objective AP Enviro 8.12.A asks you to define LD50. mg/kg is the unit that makes LD50 a real, comparable number. Without a dose-per-body-weight unit, you couldn't rank chemicals by how dangerous they are. On the exam, this connects to the bigger theme of pollution and human/ecosystem health: dose determines harm, and the unit is how you measure that dose.
Keep studying AP Environmental Science Unit 8
LD50 (Lethal Dose 50%) (Unit 8)
mg/kg is the unit LD50 is reported in. They travel together: LD50 is the value, mg/kg is the scale. A lower mg/kg LD50 means a more toxic chemical because less of it per kilogram of body weight kills half the population.
Parts per million (ppm) (Unit 8)
Both are concentration-style units, but they answer different questions. ppm measures how much of a substance is in an environment like water or air, while mg/kg (for dosing) measures how much enters a body relative to its weight.
Toxicity threshold (Unit 8)
A toxicity threshold is the dose where harmful effects begin to appear, often expressed in mg/kg. LD50 sits well above that threshold because it's the dose that kills half the population, not just where damage starts.
Expect mg/kg to show up as the unit on a dose-response graph or in an LD50 data table. The skill being tested is reading and comparing values: if Chemical A has an LD50 of 10 mg/kg and Chemical B has 800 mg/kg, you should be able to say A is more toxic because a smaller dose per kilogram of body weight is lethal. You may also need to scale a dose to body weight, multiplying the mg/kg value by an organism's mass in kilograms to get the total milligrams. Watch the direction of the logic. Lower mg/kg LD50 equals higher toxicity, which trips up a lot of people.
mg/kg as a dose is about how much chemical enters an organism per kilogram of its body weight. ppm is about how concentrated a substance is in a medium like water, soil, or air. One describes the dose hitting a body, the other describes the contamination level in the environment. Note that mg/kg and ppm can be numerically equal as mass ratios, but in AP Enviro you'll see mg/kg used for dosing and LD50.
Milligrams per kilogram (mg/kg) expresses a dose as milligrams of chemical per kilogram of body weight.
mg/kg is the standard unit for reporting LD50, the dose lethal to 50% of a test population (8.12.A).
A lower mg/kg LD50 means a more toxic chemical because less of it per kilogram is needed to kill.
Because mg/kg scales to body weight, it lets you compare toxicity fairly across species of different sizes.
To find a total dose, multiply the mg/kg value by the organism's body mass in kilograms.
It means milligrams of a chemical per kilogram of body weight, the unit used to express dose. In Unit 8 it's how LD50 values are reported so you can compare how toxic different chemicals are.
No, it's the opposite for LD50. A higher mg/kg LD50 means it takes a larger dose per kilogram of body weight to kill, so the chemical is less toxic. The lower the mg/kg, the more toxic it is.
mg/kg as a dose describes how much chemical enters a body relative to its weight, while ppm describes how concentrated a substance is in an environment like water or air. In AP Enviro, mg/kg goes with LD50 and dosing, ppm goes with environmental concentration.
Multiply the mg/kg value by the organism's body mass in kilograms. For example, a 5 mg/kg dose for a 70 kg person is 5 times 70, or 350 milligrams total.
No. LD50 is the value, the dose that's lethal to 50% of a population, and mg/kg is the unit that value is measured in. You'll usually see them together, like an LD50 of 25 mg/kg.