5 Environmental Health

What environmental health covers

Environmental health considers how surroundings and environmental conditions affect people. Its work includes identifying harmful exposures, reducing risks, and creating places where people can live, learn, work, and play safely. Clean air and water, safe food and housing, sanitation, and protection from harmful chemicals and radiation all support health.

Environmental exposures and pathways

An environmental exposure occurs when a person comes into contact with an environmental agent, or stressor. Stressors may be chemical, biological, or physical:

• Chemical: lead, pesticides, solvents, and air pollutants.

• Biological: bacteria, viruses, mold, and allergens.

• Physical: noise, heat, cold, radiation, and unsafe conditions that can cause injury.

Exposure may occur through inhalation (breathing), ingestion (swallowing), or dermal contact (skin contact). The presence of a contaminant alone does not establish that people are exposed or will become ill.

Tracing exposure

To assess a possible exposure pathway, investigators consider the source, how the agent moves through air, water, soil, or food, where contact occurs, the route into the body, and who may be exposed. They also consider exposure level, frequency, duration, and timing, along with characteristics such as age and health.

For example, a chemical released at an industrial site may move into groundwater. People in a nearby household that uses the groundwater could be exposed by drinking it, breathing vapors while showering, or skin contact. Testing the water and understanding how it is used help determine whether this pathway is occurring and what action is needed. A confirmed exposure pathway does not by itself mean illness will occur.

Built and natural environments

The built environment consists of human-made places and infrastructure, such as homes, schools, workplaces, roads, sidewalks, public transportation, and parks. Its design affects safety, physical activity, access to services, and exposure to traffic pollution, noise, heat, or hazardous materials. Connected sidewalks and accessible transit can make walking and daily travel easier, while poorly maintained housing can contribute to dampness, mold, or unsafe temperatures.

The natural environment includes air, water, soil, plants, animals, and ecosystems, as well as weather and climate conditions. It can support health through clean water, food, and opportunities for recreation, or threaten health through polluted air or water, extreme heat, floods, wildfires, and changing patterns of infectious disease. Climate-related effects can also occur indirectly when environmental disruptions affect food, water, housing, or livelihoods.

Interactions and unequal burdens

Built and natural environments interact. Paved surfaces and limited tree cover can make some neighborhoods hotter, while housing quality and access to cooling influence how strongly residents are affected. Environmental burdens and the resources available to avoid or recover from them are not always shared equally. Assessment should consider who is exposed, where people live or work, and whether some groups face greater exposure or vulnerability.

Assessing environmental risk

Risk is the likelihood and potential severity of harm under particular exposure conditions. A hazard is an agent’s ability to cause harm; risk also depends on whether people are exposed, how much exposure occurs, and how long it lasts.

Environmental health risk assessment commonly uses four connected steps:

1. Hazard identification: Determine what harmful effects an agent may cause.

2. Dose–response assessment: Examine how the likelihood or severity of effects relates to the amount of exposure.

3. Exposure assessment: Estimate who may be exposed, by which routes, and at what levels, frequency, and duration.

4. Risk characterization: Combine the evidence to describe estimated risk, important assumptions, and uncertainties.

For a contaminant in drinking water, investigators identify possible health effects, examine evidence about effects at different doses, measure or estimate concentrations and water use, and explain what the findings mean for residents. Risk assessment informs decisions; risk management is the choice and implementation of actions to reduce risk. Both should communicate uncertainties clearly and consider relevant populations and exposure pathways.

Preventing harm and protecting communities

Protection is most effective when it prevents or reduces exposure at its source. Measures include replacing hazardous materials, controlling emissions and discharges, treating water, safely managing waste, improving ventilation and housing, and designing safer streets and public spaces.

Monitoring air, water, soil, and workplaces can identify problems. Health surveillance, public alerts, and community communication can support a timely response. Involving affected communities helps ensure assessments reflect local conditions and protective actions are practical and accessible.

In the United States, environmental protections combine laws, regulations, monitoring, and enforcement. The Clean Air Act addresses air quality; the Clean Water Act regulates pollutant discharges and surface-water quality; and the Safe Drinking Water Act sets health-related standards for public water systems. Federal, state, Tribal, and local agencies have roles in implementing and enforcing environmental requirements.