Every human activity impacts the environment, and one 1️⃣ of the most major of those impacts is pollution. In APES, we can define pollution as anything that is present or introduced to the environment with harmful effects.
In this section, we will begin by classifying pollutants into two main categories, Point Source and Nonpoint Source. When you look at the images below, your first thought might be that they are the same when in fact they are very different. Can you identify which one is a Point Source and which is a Nonpoint Source?
Point Source Pollution
Pollutants that are emitted from a single, identifiable source are known as point source pollutants. Examples of point source pollution include smoke from a smokestack of a factory, untreated sewage coming out of a pipe into a river 💩, and vehicle exhaust coming out of a car tailpipe. Point sources of pollution are easy to identify and much easier to regulate pollution coming from these sources.
A major characteristic of point source pollution is a plume which is where the pollutant is most concentrated. Here’s an example:
Legislation Connection - Clean Water Act
This act makes it unlawful for anyone to discharge any point source pollution without permits.
- The act requires that we use “Best Practicable Technology” (BPT) to clean point sources and “Best Available Technology” (BAT) be used to clean up toxins
- This act funds construction of several important facilities such as sewage treatment plants and includes provisions for protecting wetlands
- The main goal of this act is to get to the point where all water is “fishable and swimmable”
Nonpoint Source Pollution
Nonpoint source pollutants come from a non-identifiable location, and are often spread out over a large area. Nonpoint source pollution transported by moving water, or going into water, is commonly referred to as "runoff"
Graphic displaying the non-point sources of pollution in a watershed
Be careful using this graphic to define nonpoint sources of pollution! While everything on the image is true, be aware that sometimes you can identify sources of pollution from Industry, like in the pipe shown in the image above.
Examples of nonpoint source pollution can include excess fertilizer washing off all the lawns in a neighborhood during a rain storm and into a local creek, as well as smoke from a wildfire. Since nonpoint source pollution is diffuse in its location, it is very difficult to regulate and thus is usually the largest source of surface water pollution.
Check Your Understanding
Go back to the image of the smokestack and water runoff. Although they both look similar in that they are a pipe emitting pollution, the smokestack is a point source because it is coming from one identifiable factory, and, if needed, it would be ‘simple’ to create regulations to prevent that factory from polluting. The water runoff, however, is a collection of alllll the potential pollutants found on the street. If something toxic was found in that water it would be very difficult to track down and regulate the original source.
Environmental Hazards
| Hazard Type | Definition | Examples |
|---|---|---|
| Physical Hazards | Arise from processes that occur naturally in our environment and pose risks to human health | Fires, Floods, Blizzards |
| Chemical Hazards | Synthetic Chemicals that our society manufactures | Hydrocarbons, Lead, Asbestos |
| Biological Hazards | Ecological interactions when hosts become sick after a virus or bacteria invades. | Viral infection, bacterial infection, parasite |
| Cultural Hazards | Hazards that result from our place of residence, our socioeconomic status, and our behavior. | Smoking cigarettes, Noise Pollution |
Practice MCQ (Multiple Choice Question) Time
Which of the following in the chart correctly gives examples of Point and Non-Point Source Pollution?
| Answer | Point Source | Nonpoint Source |
|---|---|---|
| A | Someone throws a cigarette butt out of their car window. | Smoke is emitted from a factory and can be seen from miles away. |
| B | Sewage draining from a pipe into a nearby river. | After a large rainstorm, multiple different pollutants are found in a nearby river. |
| C | A large rainstorm comes and carries away fertilizer from many farms. | Sewage draining from a pipe into a nearby river. |
| D | After a large rainstorm, multiple different pollutants are found in a nearby river. | Someone throws a cigarette butt out of their car window. |
✅ Correct Answer Choice
B! Remember that with point source pollution, you can point to a direct source. With nonpoint source, you will have a combination of pollutants from different sources.
Need more practice with Source of Pollution? Check out a trivia game
Frequently Asked Questions
What is the difference between point source and nonpoint source pollution?
A point source is a single, identifiable origin of pollution—think a smokestack, a wastewater discharge pipe, or industrial discharge. It’s easy to trace, monitor, and regulate (EK STB-3.A.1). A nonpoint source is diffuse and harder to pinpoint—examples are agricultural runoff (pesticide/fertilizer runoff), urban/stormwater runoff, and septic leakage (EK STB-3.A.2). Nonpoint sources often cause nutrient loading that leads to eutrophication, and they’re harder to control because many small sources across a landscape contribute. For the AP exam you should be able to identify and give examples of each (Learning Objective STB-3.A)—that’s commonly tested on multiple-choice and free-response. For a quick review, see the Topic 8.1 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
How do I identify if a pollution source is point or nonpoint for the AP exam?
For the exam, ask: "Is the source single and traceable or broad and diffuse?" If you can point to one pipe, smokestack, waste-discharge outlet, or an identifiable facility → it’s a point source (CED EK STB-3.A: smokestack, wastewater discharge pipe, industrial discharge). If pollution comes from many places over a landscape—like agricultural runoff, pesticide spraying, stormwater/urban runoff, septic leakage, or atmospheric deposition → it’s nonpoint (CED EK STB-3.A.2: diffused sources; examples: nutrient loading from farms, stormwater). On multiple-choice/free-response, name the type and give a specific example and effect (e.g., "point: wastewater treatment plant effluent → easy to monitor/regulate; nonpoint: agricultural runoff → causes eutrophication and is harder to trace"). Review Topic 8.1 study guide for quick examples (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice more questions at the unit page (https://library.fiveable.me/ap-environmental-science/unit-8) or the practice bank (https://library.fiveable.me/practice/ap-environmental-science).
What are some examples of point source pollution that I should memorize?
Point source = a single, identifiable release of a pollutant (smokestack or a discharge pipe)—memorize that phrase + these concrete examples: - Smokestack emissions from a coal-fired power plant (air point source) - Wastewater discharge pipe from a factory or treatment plant (effluent) - Industrial discharge (chemical plants, metal refineries) - Municipal wastewater treatment plant effluent - Combined sewer overflow (CSO) pipes during storms - Acid mine drainage flowing from a mine tunnel or adit - Septic system leakage (a failed septic pipe/field) - Thermal discharge (cooling-water outflow from power plants causing thermal pollution) Why this matters for the AP exam: STB-3.A expects you to identify point vs nonpoint sources—these are classic point-source examples you can list on multiple-choice or FRQs. Review Topic 8.1 study guide for quick practice (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and try practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Why is nonpoint source pollution harder to control than point source pollution?
Point-source pollution comes from a single, identifiable discharge (like a smokestack or wastewater pipe), so you can monitor, regulate, and fix that one source. Nonpoint-source pollution is diffused across landscapes—agricultural runoff, pesticide spraying, stormwater/urban runoff—so it’s harder to trace back to one emitter, varies with rainfall and season, involves many landowners, and often enters waterways over large areas. That makes monitoring, enforcement, and targeted engineering fixes tough; solutions rely on broad prevention (best management practices, buffer strips, green infrastructure) and behavior/change across many users rather than a single permit or treatment system. For the AP exam, this difference maps to STB-3.A (identify point vs. nonpoint) and shows why policy and watershed-scale approaches matter. Review the Topic 8.1 study guide for examples and strategies (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice related questions at (https://library.fiveable.me/practice/ap-environmental-science).
I'm confused about urban runoff - is that point or nonpoint source pollution?
Urban runoff is usually a nonpoint source of pollution—it’s diffuse runoff from roads, rooftops, lawns and parking lots that’s hard to trace back to one single outlet (CED EK STB-3.A.2 lists urban/stormwater runoff as an example). For the AP exam, remember the rule: point = single identifiable source (like a discharge pipe or smokestack); nonpoint = spread-out sources (like pesticide spraying or urban runoff)—that’s what STB-3.A wants you to identify. One important caveat: if urban stormwater is collected and released through a single pipe (for example a combined sewer overflow or a distinct wastewater discharge), that specific discharge can be treated as a point source (wastewater discharge pipe → EK STB-3.A.1). For more review, check the Topic 8.1 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Can someone explain what makes a smokestack a point source in simple terms?
A smokestack is a point source because it’s a single, identifiable place where pollution comes out—one chimney you can point to, measure, and monitor. The CED even lists smokestack emissions as an example of a point source (EK STB-3.A.1). That’s different from nonpoint sources like pesticide spraying or urban runoff, which are diffuse and hard to trace to one spot (EK STB-3.A.2). For the AP exam, remember: point = single, traceable discharge (e.g., smokestack or wastewater pipe), nonpoint = many diffuse contributors (e.g., stormwater). If you want a quick refresher tied to Topic 8.1, check the Fiveable study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).
What's the difference between a waste discharge pipe and agricultural runoff in terms of pollution sources?
A waste discharge pipe is a point source: a single, identifiable outlet (e.g., a wastewater treatment plant effluent pipe or industrial discharge) that releases pollutants directly into water. Agricultural runoff is a nonpoint source: diffuse, coming from many fields and drains after rain or irrigation (fertilizers, manure, pesticides, sediment). Key differences: detectability and regulation—point sources are easier to monitor, trace, and permit under laws; nonpoint sources are harder to locate and control because they’re spread out and episodic. Pollution types overlap (both can add nutrients and pathogens), but ag runoff is a major cause of nutrient loading and eutrophication in lakes and coastal zones. For the AP exam, this maps to STB-3.A (identify point vs nonpoint). For a quick review, see the Topic 8.1 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and Unit 8 overview (https://library.fiveable.me/ap-environmental-science/unit-8).
How do pesticides count as nonpoint source pollution if farmers are spraying them in specific places?
Good question—spraying happens in specific spots, but pesticides are still often classified as nonpoint pollution because the pollutant’s pathway is diffuse and hard to trace to a single discharge point (CED EK STB-3.A.2). After spraying, pesticides can drift through air, run off fields during rain, leach into groundwater, or move in stormwater. Those multiple routes spread the chemical across landscapes and water bodies, so you can’t point to one pipe or smokestack as the single source. By contrast, a point source is one identifiable outlet like a discharge pipe (EK STB-3.A.1). For AP, remember “pesticide spraying” and “agricultural runoff” are listed examples of nonpoint sources. For a quick review, check the Topic 8.1 study guide on Fiveable (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).
Why do we need to distinguish between point and nonpoint sources of pollution?
You need to distinguish point vs. nonpoint sources because it changes how we identify, monitor, and fix pollution. Point sources are single, identifiable outlets (wastewater discharge pipes, smokestacks) so they’re easier to measure, permit, and regulate (think wastewater treatment plant effluent or an industrial discharge). Nonpoint sources are diffuse (agricultural runoff, pesticide spraying, urban/stormwater runoff), so they’re harder to trace, model, and control—they cause widespread problems like nutrient loading and eutrophication. On the APES CED this is STB-3.A: know the definitions and examples. For the exam and real policy, distinguishing source type determines sampling strategy, legal tools (permits for point sources vs. best-management practices for nonpoint), and remediation priorities. For a quick review, see the Topic 8.1 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and try practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Is a factory dumping chemicals into a river point source or nonpoint source pollution?
That’s a point source. The AP CED defines a point source as a single, identifiable origin of pollution—examples: a smokestack or a waste-discharge pipe. A factory dumping chemicals into a river fits that exactly (industrial discharge, wastewater discharge pipe). Point sources are easier to monitor and regulate than nonpoint sources (like urban runoff or pesticide spraying), which are diffuse and harder to trace. For AP exam wording, identify it as point source pollution and cite the single identifiable discharge (you can even mention potential consequences like nutrient loading or toxic contamination). For quick review, check the Topic 8.1 study guide on Fiveable (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and use Fiveable’s practice problems (https://library.fiveable.me/practice/ap-environmental-science) to drill similar CED-style questions.
I don't understand how something can be a "diffused" pollution source - what does that actually mean?
“Diffused” means the pollution comes from many scattered, small sources rather than one obvious pipe or smokestack. In AP terms that’s a nonpoint source (contrast with a point source like a wastewater discharge pipe). Think agricultural fields where fertilizer washes off many acres during rain, or city streets where oil, pet waste, and lawn chemicals all mix into stormwater runoff—you can measure high nutrient or toxic levels downstream but you can’t point to one single emitter. That makes nonpoint sources harder to regulate and trace, and they often cause problems like nutrient loading and eutrophication. For exam answers: name specific examples (agricultural runoff, pesticide spraying, urban/stormwater runoff) and explain why identification/enforcement is difficult. For a quick review, check the Topic 8.1 study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice problems at (https://library.fiveable.me/practice/ap-environmental-science).
What are the main characteristics I should look for to identify nonpoint source pollution on the test?
Look for characteristics that match the CED definition of nonpoint source pollution: it’s diffuse (no single discharge pipe), hard to trace to one location, and results from widespread activities like agricultural runoff, pesticide spraying, stormwater/urban runoff, septic leakage, or acid mine drainage. On the test, key clues in the prompt: multiple potential sources across a landscape, events tied to precipitation or runoff, nutrient loading causing eutrophication, or seasonal/area-wide contamination rather than a single smokestack or outfall. If a question mentions “diffuse,” “widespread,” “after storms,” “agricultural fields,” or “urban streets,” pick nonpoint. Remember point-source contrasts (identifiable single source like a wastewater pipe or smokestack). This distinction is tested in both multiple choice and FRQs (identify/describe). Review the Topic 8.1 study guide for examples and practice (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and try practice questions (https://library.fiveable.me/practice/ap-environmental-science).
How does urban runoff become a pollution problem if it's just water flowing off streets?
Think of urban runoff as a delivery system for lots of pollutants—the water itself isn’t toxic, but as it flows over streets, parking lots, and lawns it picks up oil and gasoline, heavy metals (like lead, zinc), nutrients from fertilizers, sediment, trash, and pathogens. That’s why the CED calls urban runoff a nonpoint source: it’s diffuse and hard to trace (EK STB-3.A.2). Once those contaminants reach streams, lakes, or coastal zones they can cause eutrophication (nutrient loading → algal blooms → oxygen loss), contaminate drinking-water supplies, poison aquatic life, and trigger combined sewer overflows during storms. For the AP exam, you should be able to contrast this with point sources (smokestacks, discharge pipes) and give examples of effects and solutions (green infrastructure, permeable pavement, retention ponds). More on Topic 8.1 is in the Fiveable study guide (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Can a single farm be considered both a point source and nonpoint source of pollution?
Yes. A single farm can be both a point source and a nonpoint source of pollution depending on how the pollutant is leaving the site. If pollution is discharged from a single, identifiable outlet (for example, a wastewater pipe or an engineered drain that sends manure slurry or processing wastewater directly to a stream), that’s a point source (EK STB-3.A). But diffuse runoff from fields after rainfall—fertilizer, pesticides, or sediment washing off many parts of the property—counts as nonpoint source pollution because it’s spread out and hard to trace (EK STB-3.A.2). For AP exam framing: identify the difference (point = single identifiable discharge; nonpoint = diffuse runoff) and give examples like manure lagoon pipe vs. field runoff. For more review, see the Topic 8.1 study guide on Fiveable (https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).
Why is it harder to regulate nonpoint source pollution compared to point source pollution?
Point sources are easier to regulate because they're single, identifiable discharge points (like a smokestack or wastewater pipe) so you can monitor, permit, and enforce limits (think NPDES-style permits). Nonpoint sources are diffuse—agricultural runoff, pesticide spraying, urban/stormwater runoff, septic leakage—coming from many places across a landscape. That makes it hard to trace pollutants to a single responsible party, hard to monitor continuously, and highly variable with weather (rain events create big pulses). So regulation shifts from permits to broader land-use rules and best management practices (buffer strips, cover crops, stormwater management), which are harder to enforce and slower to show results. For AP exam focus: remember EK STB-3.A.1 vs EK STB-3.A.2—identifiable vs diffused sources (see the Topic 8.1 study guide on Fiveable for a quick review: https://library.fiveable.me/ap-environmental-science/unit-8/sources-pollution/study-guide/AAXMiQ1MNW3SoMgY3nBE). For extra practice, try problems at https://library.fiveable.me/practice/ap-environmental-science.