01 / 20

Pollution and
Human Health

How air, water, and soil pollutants enter the human body, cause disease, and create environmental justice challenges.

AP Environmental Science

What Is Pollution?

Pollution is the introduction of harmful substances or energy into the environment at rates that exceed the environment's capacity to disperse, dilute, decompose, recycle, or store them in a harmless form.

Point Source
A single, identifiable origin: a factory smokestack or a sewage outfall pipe.
Nonpoint Source
Diffuse origins that are hard to trace: agricultural runoff, urban stormwater.

Major Categories of Pollutants

Air
Particulate matter (PM), ground-level ozone (\(O_3\)), CO, \(SO_2\), \(NO_x\), lead
Water
Pathogens, heavy metals (Hg, Pb), nitrates, pharmaceuticals, thermal pollution
Soil
Pesticides, heavy metals, industrial solvents, PFAS ("forever chemicals")

Exposure Pathways

Source Air Water Soil / Food Inhalation Ingestion Skin Contact Human

Explain exposure differences through location, activity and susceptibility.

Use this illustration to explore the concept described in its caption.

A neighborhood with an industrial source and plume, with hypothetical nearer location A and farther location B. A is associated with a longer duration and B with a shorter duration; exposure depends on concentration and time.
Equal emissions can lead to different exposure because people occupy different places for different durations. Concentration depends on local conditions; susceptibility affects health impact separately. Marked locations are hypothetical and do not establish measured exposures.

Transport pathways determine where pollutants reach receptors

A field,road and river above a soil and groundwater cutaway showing several transport contexts.Dissolved pollutants can move with groundwater, while adsorbed pollutants may travel with sediment. Chemical form affects transport and exposure; intake, absorbed dose and tissue concentration are different quantities.

Dissolved and sediment-bound differ

Dissolved and sediment-bound differ. Dissolved pollutants can move with groundwater, while adsorbed pollutants may travel with sediment. Chemical form affects transport and exposure; intake, absorbed dose and tissue concentration are different quantities.Dissolved pollutants can move with groundwater, while adsorbed pollutants may travel with sediment. Chemical form affects transport and exposure; intake, absorbed dose and tissue concentration are different quantities.

The Dose-Response Relationship

Toxicology's central principle: "The dose makes the poison." The severity of a health effect depends on the amount of substance an organism is exposed to over a given time.

Dose (mg/kg) Response (%) 0 25 50 75 100 LD50 Threshold

Bioaccumulation vs. Biomagnification

Bioaccumulation
A single organism absorbs a toxin faster than it can excrete it, so the concentration builds over its lifetime.
Biomagnification
Toxin concentration increases at each trophic level of a food chain: predators accumulate more than their prey.
Producers (algae) Primary Consumers (fish) Secondary Consumers Top Predator 1x 10x 100x 1000x [Toxin]

Acute vs. Chronic Effects

Acute Exposure Chronic Exposure
Duration Single or short-term event (hours to days) Repeated low-level exposure over months or years
Onset Symptoms appear quickly Symptoms develop gradually
Example Chemical spill causing respiratory distress Lead in drinking water causing neurological damage
Measurement \(\text{LD}_{50}\) Chronic daily intake (CDI)

Pollutants and Health Effects

Pollutant Primary Source Health Effect
Lead (Pb) Old pipes, paint Neurological damage, reduced IQ in children
Mercury (Hg) Coal plants, fish Minamata disease, CNS damage
Asbestos Building insulation Mesothelioma (lung cancer)
\(\text{PM}_{2.5}\) Combustion, vehicles Cardiovascular and respiratory disease
Ground-level \(O_3\) NOx + VOCs + sunlight Asthma exacerbation, lung inflammation

How to Analyze a Pollution Problem

1
Identify the pollutant. Is it a criteria air pollutant, heavy metal, pathogen, or organic compound?
2
Determine the source. Point source (factory, pipe) or nonpoint source (runoff, atmosphere)?
3
Trace the pathway. Through which medium does it travel: air, water, or soil? How does it reach humans?
4
Assess the dose and duration. Acute or chronic? Use \(\text{LD}_{50}\) data or threshold values.
5
Evaluate vulnerable populations. Children, elderly, low-income communities, and outdoor workers face disproportionate risk.

Example: Lead in Flint, Michigan

In 2014, Flint switched its water source to the Flint River. The more corrosive water leached lead (Pb) from aging pipes. Blood lead levels in children doubled.

1
Pollutant: Lead (Pb): a heavy metal neurotoxin
2
Source: Point source: corroded municipal water pipes
3
Pathway: Ingestion of contaminated drinking water
4
Exposure: Chronic: low-level exposure over months and years
5
Vulnerable population: Low-income community, predominantly people of color: an environmental justice issue

Example: DDT and Biomagnification

DDT was widely used as a pesticide until Rachel Carson's Silent Spring (1962) documented its devastating ecological effects. DDT bioaccumulates in fatty tissue and biomagnifies up the food chain.

Plankton 0.04 ppm → Small Fish 0.5 ppm → Large Fish 2.0 ppm → Osprey 25 ppm DDT concentration increases ~625x from water to top predator

Example: Interpreting \(\text{LD}_{50}\) Data

Given the following \(\text{LD}_{50}\) values (mg/kg, oral, rat), rank these substances from most toxic to least toxic.

Substance \(\text{LD}_{50}\) (mg/kg)
Caffeine 192
Table salt (NaCl) 3,000
Nicotine 50
Botulinum toxin 0.001

Environmental Justice

Environmental justice is the fair treatment and meaningful involvement of all people regardless of race, income, or nationality with respect to environmental laws and policies. Pollution disproportionately affects marginalized communities.

Cancer Alley
An 85-mile stretch along the Mississippi River in Louisiana with over 150 petrochemical plants, primarily affecting Black communities.
Flint, MI
A majority-Black, low-income city where aging infrastructure exposed residents to lead-contaminated water for years.
E-Waste
Developed nations export electronic waste to developing countries, exposing workers (often children) to heavy metals and flame retardants.

Key Legislation

1
Clean Air Act (1970): Established NAAQS for six criteria pollutants; regulates stationary and mobile sources.
2
Clean Water Act (1972): Set standards for surface water quality; created the NPDES permit system for point-source discharges.
3
Safe Drinking Water Act (1974): Set maximum contaminant levels (MCLs) for public water systems.
4
CERCLA / Superfund (1980): Funds cleanup of hazardous waste sites; holds polluters liable.

Common Mistakes

✕ Confusing Bioaccumulation with Biomagnification
Bioaccumulation occurs within one organism. Biomagnification occurs across trophic levels. Use both terms precisely on the FRQ.
✕ Reversing LD50 Logic
A lower \(\text{LD}_{50}\) means more toxic, not less. Students often pick the higher number as "more dangerous."
✕ Mixing Up Acute and Chronic
Acute = short-term, high dose. Chronic = long-term, low dose. Don't assume "chronic" means "worse": both can be deadly.

Summary Table

Concept Definition AP Exam Tip
Point Source Single identifiable origin Give a specific example (factory, pipe)
Nonpoint Source Diffuse, widespread origin Agricultural runoff is the classic example
Bioaccumulation Toxin builds in one organism Within: fat-soluble compounds persist
Biomagnification Concentration rises per trophic level Across: DDT, mercury in food chains
\(\text{LD}_{50}\) Dose lethal to 50% of test organisms Lower = more toxic
Threshold Dose Below this, no observable effect Some substances have no safe threshold (e.g., lead)

Question 1 of 5

Which of the following best describes biomagnification?

Question 2 of 5

Substance X has an \(\text{LD}_{50}\) of 5 mg/kg. Substance Y has an \(\text{LD}_{50}\) of 500 mg/kg. Which statement is correct?

Question 3 of 5

A farmer applies pesticides to a crop field. Rain washes the pesticides into a nearby river. This is an example of:

Question 4 of 5

Which federal law specifically funds the cleanup of hazardous waste sites and holds polluters liable for contamination?

Question 5 of 5

Mercury contamination is found at high levels in tuna but not in the surrounding seawater. Which two processes best explain this observation?