Risk is defined as the possibility of something bad happening or the chance of loss or injury. It involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environment), often focusing on negative, undesirable consequences^{1, 2, 3, 4}. ¹ Risk - Wikipedia. https://en.wikipedia.org/wiki/Risk. ²Risk Definition & Meaning | Britannica Dictionary. https://www.britannica.com/dictionary/risk. ³ Risk Definition & Meaning - Merriam-Webster. https://www.merriam-webster.com/dictionary/risk. ⁴What is a Risk? 10 definitions from different industries and standards. https://www.stakeholdermap.com/risk/risk-definition.html. The United States Environmental Protection Agency (USEPA) considers "**risk** to be the chance of harmful effects to human health or to ecological systems resulting from exposure to an environmental stressor. A stressor is any physical, chemical, or biological entity that can induce an adverse effect in humans or ecosystems. Stressors may adversely affect specific natural resources or entire ecosystems, including plants and animals, as well as the environment with which they interact.⁵" In general terms, risk depends on the following three factors⁶: 1. **How much of a stressor is present** in an environmental medium (e.g., soil, water, air) over what geographic area, 2. **How much contact (exposure)** a person or ecological receptor has with the contaminated environmental medium, and 3. **How it affects** the health of humans (e.g., **toxicity**) or ecological receptors (e.g., **fish killed by lack of oxygen**). ⁵ [[Resources/Human Health Risk Assessment]] ⁶ [About Risk Assessment | US EPA](https://www.epa.gov/risk/about-risk-assessment#whatisrisk) *** 2023 cloudedknowledge.net