Some substances cannot be broken down in nature. What are they called?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about substances that cannot be broken down in nature. This means we are looking for a specific term that describes these substances.

2. **Identifying the Type of Substances**: There are two categories of substances based on their ability to decompose: biodegradable and non-biodegradable. Biodegradable substances can be broken down by natural organisms, while non-biodegradable substances cannot.

3. **Defining Non-Biodegradable Substances**: Non-biodegradable substances are those that cannot be decomposed by natural organisms such as fungi and bacteria. These substances remain in the environment for a long time and contribute to pollution.

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