Environmental health addresses the physical, chemical, and biological factors outside a person that affect health — air, water, food, housing, waste, noise, radiation, and climate — and the ways communities can control them. Many major public health gains (safe water, sanitation, lead removal from gasoline and paint) came from environmental action, not from individual treatment.
Exposure assessment asks five questions:
- Source — where the hazard comes from (factory, old paint, well water)
- Route — inhalation, ingestion, or dermal (skin) absorption
- Dose — how much reaches the body
- Duration and frequency — acute or chronic
- Susceptible groups — fetuses, infants and children (more intake per kg, hand-to-mouth behavior, developing organs), pregnant women, older adults, and people with chronic heart or lung disease
Key terms
| Term | Meaning |
|---|
| Primary air pollutant | Emitted directly (carbon monoxide, sulfur dioxide, nitrogen oxides, primary particles) |
| Secondary air pollutant | Formed in the air by chemical reactions — ground-level ozone forms when nitrogen oxides and volatile organic compounds react in sunlight |
| PM2.5 | Fine particles 2.5 micrometers or smaller; reach the alveoli and can enter the bloodstream, so they harm the heart as well as the lungs — more dangerous than larger PM10 |
| Endocrine disruptors | Chemicals (for example, some plastics additives and pesticides) that mimic or block hormones at very low doses; fetuses and young children are most vulnerable |
| Precautionary principle | When an activity threatens serious or irreversible harm, take preventive action even if scientific proof is incomplete |
| Urban heat island | Cities are hotter than surrounding areas because of pavement, buildings, waste heat, and little green space |
| Environmental justice | Fair treatment and meaningful involvement of all people; low-income and minority communities often bear more pollution |
Climate change and health: more frequent and intense heat waves, wildfire smoke, floods, and storms; worse ozone and allergens; and shifts in the range and season of vector-borne diseases (for example, Lyme disease and West Nile virus) and waterborne illness.
US environmental laws and agencies
| Law or agency | Role |
|---|
| Environmental Protection Agency (EPA) | Sets and enforces national standards for air, water, waste, pesticides, and chemicals |
| Clean Air Act | National ambient air quality standards; EPA's Air Quality Index (AQI): 0–50 good, 51–100 moderate, 101–150 unhealthy for sensitive groups, 151–200 unhealthy, 201–300 very unhealthy, 301 and above hazardous |
| Safe Drinking Water Act | Standards for public water systems; utilities test, treat, and notify the public (boil-water advisories). Private wells are not regulated — owners must test them |
| Clean Water Act | Protects surface water from pollution discharges |
| Resource Conservation and Recovery Act and Superfund (CERCLA) | Hazardous waste handling; cleanup of contaminated sites |
| FDA and USDA | Food safety; FDA also regulates bottled water |
| OSHA | Workplace exposures, including noise and chemicals |
| CDC and ATSDR | Surveillance, lead poisoning prevention, health effects of toxic substances |
| State and local health departments | Restaurant inspection, outbreak investigation, well-water and septic programs, lead case management |
Levels of prevention in environmental health
- Primary: remove or reduce the hazard — emission regulations, clean water treatment, lead paint abatement, smoke-free laws. Regulation that reduces exposure at the source is the strongest primary prevention.
- Secondary: screening for exposure — blood lead testing, radon testing, surveillance.
- Tertiary: treating and limiting harm in people already affected.
Waste management hierarchy: Reduce, Reuse, Recycle (the 3Rs) come first; energy recovery next; landfill is the last option and is not one of the 3Rs.
Environmental epidemiology uses the same designs as other epidemiology. An ecological study compares groups (for example, respiratory illness rates in neighborhoods near and far from a factory) when individual exposure data are not available; its weakness is the ecological fallacy (group associations may not hold for individuals).
Air
- Outdoor air on bad days (AQI unhealthy, wildfire smoke): stay indoors with windows and doors closed, use a high-efficiency air cleaner or HVAC filter, reduce outdoor exertion, keep rescue inhalers ready, and follow asthma or COPD action plans. A well-fitted N95 respirator gives more protection than a cloth or surgical mask when outdoors is unavoidable.
- Nitrogen dioxide (from combustion, traffic, and gas stoves) irritates airways, reduces lung function, and increases respiratory infections and asthma attacks.
- Indoor air: no smoking indoors — air purifiers cannot remove all tobacco smoke toxins; ventilate after bringing in new furniture or finishes (volatile organic compounds); keep humidity moderate to limit mold and dust mites; vent gas appliances; install carbon monoxide alarms; never run generators or grills indoors or in garages.
- Radon: a colorless, odorless radioactive gas from soil and rock; the leading cause of lung cancer in people who do not smoke and the second leading cause overall. EPA recommends fixing homes at 4 pCi/L or higher and considering action between 2 and 4 pCi/L.
Water
- Waterborne outbreaks usually reflect failures in the public water system (source, treatment, or distribution), so the first community step is inspecting the system and testing the water, not supplying household filters.
- Boil-water advisory: bring water to a rolling boil for 1 minute (3 minutes above 6,500 feet), or use bottled water, for drinking, cooking, brushing teeth, and preparing formula.
- Private wells: test regularly for bacteria and nitrate; nitrate from fertilizer and manure is a nonpoint source pollutant and causes methemoglobinemia in infants.
- Legionella grows in warm, stagnant water (cooling towers, hot tubs, large building plumbing) and spreads by aerosol; prevention is a building water management program — flushing, cleaning, disinfection, and temperature control.
- Lead in water comes from lead service lines and plumbing. The 2024 Lead and Copper Rule Improvements require water systems to inventory lead service lines and replace them, generally within 10 years of the November 1, 2027 compliance date, and lower the lead action level to 10 ppb.
- Community water fluoridation at the US Public Health Service recommended level of 0.7 mg/L prevents tooth decay equitably across income groups. It is a state and local decision, not a federal mandate; in 2025 Utah and Florida became the first states to ban it statewide.
- Water softeners exchange calcium and magnesium for sodium; people on sodium restriction may need an unsoftened drinking tap. Softeners do not purify water.
Food
- Keep cold food at 40°F (4°C) or below; the "danger zone" is 40–140°F (4–60°C). Separate raw meat from ready-to-eat foods with separate cutting boards and knives to prevent cross-contamination; cook to safe internal temperatures; wash hands.
- Pregnancy: avoid raw or undercooked fish, meat, and eggs, unpasteurized dairy, and deli meats unless heated (Listeria, Toxoplasma, parasites); avoid fish high in mercury (shark, swordfish, king mackerel, tilefish, bigeye tuna, marlin, orange roughy).
- Norovirus spreads through infected food handlers and contaminated water; handwashing with soap and water and excluding ill workers are key.
- Coliform bacteria in food or water are an indicator of possible fecal contamination and poor sanitation, not proof of a specific pathogen.
- HACCP (Hazard Analysis and Critical Control Points) identifies hazards at each step from raw material to consumption and controls them at critical control points — a preventive system.
- Food allergies: read labels; US law requires labeling of the 9 major allergens (milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and sesame).
- Foodborne outbreak investigation: list everyone exposed (ate the same meal), interview ill and well people (primary data), collect food and stool samples, compare attack rates, and report to the health department.
Housing and physical environment
- Lead: homes built before 1978 may contain lead paint; dust from peeling paint and renovation is the main source for US children. There is no safe blood lead level; the CDC blood lead reference value is 3.5 µg/dL (0.17 µmol/L) — children at or above it need confirmatory testing, a search for the source, and follow-up.
- Falls: good lighting, handrails, grab bars, and removing clutter and loose rugs.
- Sunlight and ventilation improve comfort and help vitamin D synthesis; dampness promotes mold and asthma.
- Illegal dumping: assess first for disease vectors (rodents, mosquitoes breeding in standing water) and hazardous materials.
- Noise: causes hearing loss, sleep disturbance, stress, and higher blood pressure; people do not develop protective tolerance. OSHA requires a hearing conservation program at an 8-hour average of 85 dBA; the permissible exposure limit is 90 dBA.
Heat
- Highest risk: older adults, infants and young children, people with chronic disease or obesity, outdoor workers, athletes, people taking diuretics, anticholinergics, or antipsychotics, people living alone or without air conditioning, and people experiencing homelessness.
- Teach water, rest, shade, cooling centers, and checking on neighbors. Workers with heat symptoms (dizziness, headache, nausea, weakness) must stop work immediately and cool down; confusion or collapse means possible heatstroke — call 911 and cool rapidly.
- Assess exposure with an environmental and occupational history (home age, water source, hobbies, jobs, "Do others at home or work have similar symptoms?").
- Educate families on indoor air, radon testing, lead-safe practices, safe water, food safety, and heat and air-quality action.
- Screen children for lead per state and Medicaid rules (Medicaid requires testing at 12 and 24 months).
- Investigate and report clusters and outbreaks with the health department; collect data carefully.
- Advocate for policies (smoke-free housing, lead abatement, clean air) and for environmental justice.
- Model practices in health care settings: waste reduction, safe chemical use.
- Report notifiable diseases (foodborne and waterborne outbreaks, elevated blood lead in many states) as state law requires.
- Protect client privacy while sharing necessary information with public health authorities.
- Environmental justice: advocate for communities that carry more pollution burden; involve residents in decisions.
- Precautionary principle supports action to protect vulnerable groups before proof is complete.
- Landlords must disclose known lead paint hazards in pre-1978 housing when renting or selling.
Case 1 — Diarrhea after heavy rain. After heavy rain, many residents served by one water system develop diarrhea. Correct first step: work with the health department and utility to inspect and test the water system and issue a boil-water advisory; teach boiling for 1 minute. Why: a common water source is the likely route.
Case 2 — Poor air day. The AQI forecast is "unhealthy." A client with COPD asks whether to air out his apartment. Correct advice: keep windows closed, use a filter or air cleaner, stay indoors, and follow his action plan. Why: opening windows brings polluted outdoor air inside.
Case 3 — Toddler in an old house. A 2-year-old living in a 1950s rental home under renovation has a capillary blood lead of 6 µg/dL. Correct action: arrange confirmatory venous testing, identify and control the lead source with the health department, and teach wet cleaning and handwashing. Why: the level is above the CDC reference value of 3.5 µg/dL.
Case 4 — Heat and outdoor work. A roofer feels dizzy and nauseated but wants to finish his shift. Correct action: stop work, move to shade, cool, and hydrate; seek emergency care if confusion develops. Why: continuing work risks heatstroke.
- Calling ozone a primary pollutant — it is secondary.
- Opening windows on high-pollution days.
- Recommending an air purifier instead of quitting smoking indoors.
- Treating coliform detection as proof of a specific pathogen — it is an indicator.
- Listing landfill or "recovery" as one of the 3Rs.
- Thinking private wells are covered by the Safe Drinking Water Act.
- Assuming a blood lead level below 10 µg/dL is safe — no level is safe; the reference value is 3.5 µg/dL.
- Believing people adapt to noise without harm.
- Exposure assessment: source, route (inhalation, ingestion, dermal), dose, duration, susceptible groups
- Ozone = secondary pollutant; PM2.5 reaches alveoli and blood
- AQI 101–150 = unhealthy for sensitive groups; on bad days, windows closed
- Radon: leading lung cancer cause in never-smokers; action at 4 pCi/L
- Boil water: rolling boil 1 minute (3 minutes above 6,500 ft)
- Legionella: warm stagnant water, aerosols → water management program
- Lead: pre-1978 paint; CDC reference value 3.5 µg/dL (0.17 µmol/L); no safe level
- Food: cold ≤ 40°F (4°C); separate cutting boards; pregnant women avoid raw fish
- HACCP = preventive control at critical control points
- 3Rs = reduce, reuse, recycle; landfill is last
- Precautionary principle: act before full proof when harm could be serious
- Strongest primary prevention = regulating the source