Overview of environmental health

INTRODUCTION — 

Environmental health is concerned with the health effects of air, climate, water, sanitation, use of chemicals, radiation exposure, agricultural practices, and aspects of cities and built environments [1]. An overview of environmental health is presented here. Adult lead poisoning, arsenic toxicity, female reproductive toxicity, occupational health, climate emergencies, and chemical and biologic terrorism are discussed separately.

●(See "Overview of occupational health".)

●(See "Occupational asthma: Definitions, epidemiology, causes, and risk factors".)

●(See "Lead exposure, toxicity, and poisoning in adults: Clinical manifestations and diagnosis".)

●(See "Arsenic exposure and chronic poisoning".)

●(See "Acute arsenic and arsine gas poisoning".)

●(See "Overview of occupational and environmental risks to reproduction in females".)

●(See "Chemical terrorism: Rapid recognition and initial medical management".)

●(See "Identifying and managing casualties of biological terrorism".)

●(See "Climate emergencies".)

ROLE OF THE CLINICIAN — 

Environmental issues present diagnostic challenges, as well as opportunities for preventive care and treatment in primary care practice, emergency medicine, pediatrics, and various medical specialties. Practitioners should be knowledgeable about environmental health risks [2,3].

History

General approach — The first step in the environmental history is noting whether or not the person has any concerns about specific exposures or hazards at home or at work, and whether they have concerns about any environmental threats to their health, including climate change-related risks. This basic information sets the stage both for preventive guidance, as well as for determining if environmental factors could be contributing to a patient's symptoms. For specific symptoms, the next step is paying attention to clues suggesting a relationship to the patient's environment (algorithm 1) [4-6]. Finding a clear temporal relationship between symptoms and exposure is useful, but some exposures cause immediate or subacute symptoms (such as allergic reactions and acute chemical toxicity), while others lead to more delayed effects (such as cancer or pneumoconiosis) (table 1 and table 2).

Environmental exposures can occur inside or outside the home. Household exposures may result from the use of household chemicals or products, consumption of drinking water or food, performance of certain hobbies, home remodeling, or bringing home contaminated work clothing (table 3 and table 4). (See "Household nonpharmaceutical product ingestions".)

Depending upon the patient's complaints, inquiry about home insulation, heating and cooling systems, home cleaning agents, pesticide use, water supply, water leaks, recent renovations, air pollution, hobbies, hazardous waste contamination, spills, floods, diet, cosmetics, or other relevant exposures may be warranted. Some exposures are related to specific events (wildfires, storms, floods/home water intrusion, heat emergencies), many of which may be related to climate change.

Pediatric environmental health — A child's physiology and behavior put them at an increased risk for adverse effects from many toxicants [7]. Most attention concerning environmental exposures to children previously centered on lead and secondhand tobacco smoke. There has been increasing awareness about the potential health effects of other exposures, including chemical allergens and irritants (eg, formaldehyde resins), indoor and outdoor air pollutants, pesticides, other toxicants, and climate change [8-12]. The pediatric history involves asking screening questions at the initial visit and follow-up visits that are relevant to the child's developmental stage. Questions are directed toward describing the home or other environments frequented by the child, as well as household members' jobs [8]. (See "Secondhand smoke exposure: Effects in children" and "Childhood lead exposures: Exposure and prevention" and "Childhood lead poisoning: Management".)

Recognizing Industrial disasters and chemical exposures — Concerns about potential chemical or biologic terrorism, as well as the occurrence of industrial disasters, have made it imperative that clinicians recognize patterns associated with exposures to key chemical agents (such as cyanide and nerve agents) and biologic agents (such as anthrax) [13,14] (table 5). Hospitals and health centers should have sufficient background to respond to exposures from accidental contaminations of drinking water or air. (See "Chemical terrorism: Rapid recognition and initial medical management" and "Identifying and managing casualties of biological terrorism" and "Climate emergencies" and "Common occupational chemical exposures: General approach and management of selected exposures".)

Understanding effects of climate change — Climate change causes record heat, increased likelihood of wildfires, greater risk of severe weather events (eg, heat waves, floods, severe hurricanes, droughts), poorer air quality, and sea level rise [15,16]. These climate effects have major health consequences and increased health risks, including injuries, heat-related illness and death, exacerbations of respiratory and cardiovascular disease, infectious diseases (eg, changes in vector-related diseases and venomous snake habitats) [17,18], and physical and mental health effects related to forced migration (figure 1) [15,19,20]. Children, older adults, and pregnant individuals are among the most vulnerable groups affected by climate change [21,22]. (See "Climate emergencies" and "Overview of health effects of climate change".)

Education and prevention — The clinician can provide education and ensure that patients are aware of potential effects of climate change and have plans on how to mitigate those risks (see "Climate emergencies"). Clinicians also have an opportunity for patient education and preventive care related to specific environmental exposures. A patient's reported exposures and living conditions may prompt important interventions to prevent future illnesses or injuries by addressing potential health risks [2,21,23,24]. It is important to consider whether others have been exposed and need to be evaluated and treated once the diagnosis of an environment-related illness has been made. The practitioner may find it useful to contact the local state Department of Environmental Protection or city departments of public health for environmental problems.

POTENTIAL ENVIRONMENTAL EXPOSURES

Air pollution

Sources — Burning fossil fuels generates a variety of pollutants, including ground-level ozone, particulate matter (particularly fine particulate matter, PM_2.5, PM ₁₀), carbon monoxide (CO), and sulfur dioxide, as well as greenhouse gases. Wildfire smoke can lead to the emission of high levels of natural and building material-related air pollutants [25]. This is discussed separately. (See "Climate emergencies", section on 'Wildfire health impact'.)

Clinical impact — Air pollution has been linked to increased morbidity and mortality. In addition, exposure to wildfire smoke has been associated with both short- and long-term adverse health effects, including pulmonary, cardiovascular, cerebrovascular, and psychological [16,25-27]. (See "Climate emergencies", section on 'Wildfire health impact'.)

●Morbidity – Higher air pollution levels, particularly to fine particulate matter, are associated with increased cardiovascular disease, cerebrovascular disease, respiratory disease, and other conditions including cancer [28-33]. (See "Overview of possible risk factors for cardiovascular disease", section on 'Air pollution'.)

●Mortality – According to the World Health Organization (WHO), outdoor air pollution caused an excess of 4.2 million deaths globally in 2019 [34]. Studies have consistently shown an association between elevated ambient levels of fine PM with aerodynamic diameters ≤2.5 microns (PM_2.5) and increased mortality [35-41]. As an example, in a longitudinal study of the population of six United States cities followed for 14 to 16 years (mid-1970s through 1990), increased air pollution was associated with increased mortality; this increased mortality was most closely associated with the increase in fine particulate pollution [42]. Furthermore, a dose response was observed, with an increased mortality rate of 13 percent for every 10 mcg/m³ rise in PM_2.5 (1.16, 95% CI 1.07-1.26) [42]. With extended follow-up in the same cities, there were improvements in air quality with a decrease in PM_2.5; this decrease was associated with improvements in mortality risk [43].

In addition, even a short-term increase in levels of pollution (including particulate pollution and ozone) can be associated with a rise in daily all-cause mortality [40,44]. In a time-series study including over 650 cities in 24 countries, increases of 10 mcg/m³ in the two-day average levels of PM_2.5 and PM with aerodynamic diameters ≤10 microns (PM₁₀) were associated with an increase in daily all-cause mortality (0.68, 95% CI 0.59-0.77 and 0.44, 95% CI 0.39-0.50, respectively) [40]. In regions with better overall air quality, the observed dose-response effect was greater with no threshold for effects, thus implying that even countries with relatively good air quality could still see public health benefits from further reduction in PM [45]. Based upon these and other studies, in 2024 the United States Environmental Protection Agency lowered the annual National Ambient Air Quality standard for PM_2.5 from 12 mcg/cubic meter (established in 2012) to 9 mcg/cubic meter [46].

●Effect on pediatric patients – Air pollution is also associated with adverse health effects in children, including infant brain development, lung development and function (including asthma), and mortality rates [47-49]. The United Nations International Children's Emergency Fund has estimated that approximately 300 million children live in regions where air pollution exceeds standards by at least sixfold, and it is the major contributor to the deaths of 600,000 children under the age of five annually [50]. Improved air quality can benefit the health of all children, not only those with lung disease. As an example, in a cohort study evaluating the pulmonary function of children ages 11 to 15 years with and without asthma, better air quality (decreased levels of nitrogen dioxide and PM) was associated with improvements in both forced expiratory volume in one second and forced vital capacity [51].

Role of the clinician — Air pollution can be monitored by the air quality index (AQI). The AQI quantifies five air pollutants (ground-level ozone, PM, CO, sulfur dioxide, nitrogen dioxide) [52]. PM is categorized as PM₁₀ or PM_2.5. PM_2.5 and PM₁₀ are usually the major factors contributing to the AQI, and are sometimes also listed separately along with the AQI.

The AQI scale runs from 0 to 500, with a value of 100 or less corresponding to the national air quality standard (AQI of 0 to 50 is consistent with good air quality; AQI of 51 to 100 is consistent with moderate air quality). An AQI of greater than 100 is considered unhealthy for sensitive groups (ie, those with baseline lung disease), and a value greater than 300 signifies hazardous conditions. In the United States, real-time AQIs are available on smartphones at the following sites:

●AirNow.gov

●aqicn.org

Health care providers can educate patients about the AQI and how to consult these and other resources when advising at-risk patients, such as those with asthma, chronic lung disease, or cardiovascular disease on actions to take during "bad air" days [53].

Excess heat

Sources — Global warming has led to an increase in both average and extreme temperatures [54], and an increase in the frequency, duration, and intensity of heat waves [55,56].

Clinical impact — Excess heat events have adverse health effects. (See "Climate emergencies", section on 'Heat'.)

Role of the clinician — During warm months, providers should ask their patients if they have a way to stay cool when the weather is very hot, and also inquire whether they have a job that places them in a hot environment (such as indoors in kitchens, or outdoors, like roofers), or whether they exercise outside. Providers can identify patients at risk for heat-related illness [57], and provide education about early recognition and preventive actions (see resources here). Workers and anyone else can consult the Occupational Safety and Health Administration heat website and get the heat safety tool app downloaded to their smartphone. (See "Climate emergencies", section on 'Heat' and "Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis" and "Exertional heat illness in adolescents and adults: Management and prevention".)

Indoor air pollution

Sources — There are many sources of indoor air pollution, including fuel-burning appliances, building materials, household products, and heating and cooling systems. Cooking-related emissions are an important source of pollution and vary with the type of energy used, although both electric and gas cooking produce PM and ultrafine particles [58,59]. Wood-burning appliances also emit many pollutants, including PM2.5, ultrafine particles, CO, carbon dioxide, nitrogen oxide, methane, volatile organic compounds, and polyaromatic hydrocarbons [56]. Persons who cook with solid fuels such as wood, crop waste, charcoal, coal, dung, and/or kerosene are at higher risk of indoor air pollution [60]. Household products such as disinfectants, cleaning agents, and insulation materials can degrade indoor air quality. A household products database is available from the Consumer Product Information Database that provides potential health risk information on 26,000 consumer products.

Other components of poor indoor air quality, including CO, are discussed separately. (See "Building-related illness and building-related symptoms", section on 'Specific exposures' and "Building-related illness and building-related symptoms", section on 'Role of engineering and ventilation' and "Carbon monoxide poisoning".)

Clinical impact — Indoor pollution can lead to short-term effects (eg, irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue), or more long-term effects (eg, cardiovascular or respiratory disease, cancer) [61]. Environmental exposures at home appear to have contributed to the increased incidence and mortality of asthma in both adults and children [62,63]. In addition, concerns continue to be raised about potential health effects related to dampness and mold in indoor environments [64,65], including exacerbation of asthma [66]. (See "Allergen avoidance in the treatment of asthma and allergic rhinitis", section on 'Cockroaches' and "Trigger control to enhance asthma management", section on 'Indoor air pollution' and "Trigger control to enhance asthma management", section on 'Workplace irritants'.)

Role of the clinician — Clinicians can provide advice about reducing exposure to indoor pollutants, including improving ventilation, identifying and remediating areas of water intrusion, and/or using air purifiers. This is especially important for patients with lung diseases such as asthma. Patients should also be advised regarding the use of indoor air quality monitoring systems such as smoke detectors and carbon monoxide monitors.

Drinking water contamination

Sources — There are many sources of drinking water pollution, such as from chemicals such as fertilizers applied to the land near a water source, industrial meat farms, sewer overflows, stormwater, mining, manufacturing operations firefighting events [67]. Drinking water sources include surface water, city/municipality water, and individual wells. In the United States, most municipalities derive water from a protected watershed, with the water traveling via pipes to a water treatment facility and then via pipes to individual households. Municipalities test the water and are mandated to follow Environmental Protection Agency (EPA) regulations [68], and frequently release the water test results to the public. Water test results typically include measurement of coliforms, sodium, lead, copper, and various EPA-regulated chemicals. There is no mandated testing of individual wells, so any testing is at the discretion and cost of the owners.

Impact — Waterborne diseases include those caused by ingestion of water contaminated by human or animal feces which contains pathogenic organisms (cholera, typhoid, amoebic dysentery) or chemicals/metals (arsenic, nitrates from fertilizers, pesticides, lead) that have an adverse effect on human health. Lead poisoning is discussed separately. (See "Childhood lead poisoning: Clinical manifestations and diagnosis".)

The WHO estimates that in 2022, at least 1.7 billion people use a drinking water source that was contaminated with feces [69]. WHO has put out guidelines for drinking water quality, which include a broad range of chemicals that can affect drinking water quality [70].

Role of clinician — The role of the clinician may vary depending on the source of water. Knowing the source may be an important component of evaluating diarrheal and some infectious diseases. In high-resource countries, the clinician may be addressing patient questions related to water test results with high levels of contaminants, such as arsenic or per- and polyfluoroalkyl substances (PFAS) (see below). The clinician can also play an active preventive role by inquiring about the source of water, particularly if treating patients from areas where private wells are common, and suggesting testing if it has not already been done [71]. (See "Arsenic exposure and chronic poisoning".)

Contaminants from many sources — Some environmental contaminants are ubiquitous and can be found in the air, water, and other sources.

Per- and polyfluoroalkyl substances (PFAS) — PFAS, previously called perfluorochemicals, are man-made chemicals used in nonstick cookware, carpets, stain-resistant treatments for clothing, aqueous film-forming foam concentrate firefighting foam, nonstick packaging, and various industrial processes [72,73]. Population exposures are widespread and can occur through ingestion or inhalation through various pathways, such as drinking water, food, air, dust, food containers, cookware, and breast milk. The most common exposures occur through drinking water, which may have been contaminated through firefighting foam or other industrial processes. PFAS bind to tissue proteins and accumulate in blood along with lower levels in the liver, kidneys, and brain [74]. These chemicals stay in the body for varying lengths of time, including up to decades [75]. There are different PFAS, which may vary in the length of time they remain in the body and the potential adverse health effects. The most commonly studied ones are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). PFOA and PFOS have been phased out of production in the United States, although other countries may still manufacture and use them [76].

Clinical impacts — The NASEM consensus study on PFAS exposure, testing, and clinical follow-up found sufficient evidence of an association in humans between PFAS exposure and several adverse health outcomes including dyslipidemia, decreased infant and fetal growth, and increased risk of kidney cancer [76-78]. They found limited or suggestive evidence of increased risk of breast cancer and testicular cancer, liver enzyme alterations, pregnancy-induced hypertension, thyroid disease and dysfunction, and ulcerative colitis.

The impact of PFAS on reproduction and pregnancy is discussed separately. (See "Occupational and environmental risks to reproduction in females: Specific exposures and impact", section on 'Perfluoroalkyl substances (PFAS)'.)

Limited role for testing — The 2022 United States National Academies of Sciences, Engineering, and Medicine (NASEM) consensus study on PFAS suggests a role for blood testing for seven PFAS chemicals in certain situations for patients who are likely to have a history of elevated exposure [78]. This includes those with occupational exposure (eg, firefighters), those who live in communities where PFAS contamination has been documented (eg, drinking water exceeding regulatory limits), or those who live near PFAS-contaminated facilities. Patients should be aware that the costs of the PFAS blood tests may not be paid by health insurance, particularly in the absence of a relevant symptom or diagnosis.

Test results are challenging to interpret as there are different definitions of what constitutes elevated exposure, or PFAS contamination, given variations in state and national guidelines [78].

The NASEM report suggests the following approach based on the sum of serum or plasma concentrations of seven PFAS:

•For patients with PFAS blood concentrations below 2 nanograms/mL, no adverse effects would be expected.

•Patients with test results between 2 to 20 nanograms/mL may face potential adverse effects, especially in sensitive populations (such as pregnant persons). Clinicians should encourage reduction of PFAS exposure. "Following the usual standard of care, clinicians should also prioritize screening for dyslipidemia, hypertensive disorders of pregnancy, and breast cancer based on age and other risk factors" [79].

•Patients with test results above 20 nanograms/mL may face a higher risk of adverse effects. In addition to the above recommendations (for those between 2 and 20 nanograms/mL), clinicians should also conduct thyroid function testing and assess for signs of kidney and testicular cancer and ulcerative colitis at all wellness visits.

Role of the clinician — Patients may come to their clinician because they have concerns about PFAS exposure, particularly if they have received a report of high level of PFAS in their drinking water. In counseling patients, it is important to note that there is currently no way to remove or enhance excretion of the PFAS chemicals from the body. For those found to have elevated levels, we perform relevant screening for related potential health issues.

The most important guidance is to stop or reduce exposure:

●For those with known water contamination, use an alternative safe water for drinking and cooking, or install a filter certified to remove PFAS from a water system with high levels.

●Reduce, to the extent possible (particularly if pregnant), other potential sources such as contaminated food (from contaminated soil or water) or food in contact with materials containing PFAS (such as microwave popcorn bags, packaged fast foods, or processed foods).

●Reduce use of or replace nonstick pots and utensils and, if using, do not clean them in the dishwasher.

●Discard damaged stain-resistant carpeting and upholstery.

Additional educational resources specific to PFAS can be found at:

●PFAS and your health. Agency for Toxic Substances and Disease Registry (ATSDR).

●PFAS: Information for clinicians. ATSDR.

●PFAS. EPA.

Microplastics and nanoparticles — Microplastics (particles smaller than 5 mm) and nanoplastics (particles smaller than 1000 nanometers) enter the body through a variety of methods (ingestion, inhalation, skin exposure) and are believed to result in toxicologic effects [80,81]. Microplastics are created by the breakdown of plastic objects, car tires, clothing, paint coatings, and leakage of preproduction pellets and powders [81]. Consumers also have exposure to nanoparticles through their use in common products including clothing, sunscreens, and cosmetics, although the clinical effect of this exposure is not well quantified. The US Food and Drug Administration is formulating an approach to regulation [82,83]. (See "Selection of sunscreen and sun-protective measures", section on 'Safety'.)

SUMMARY AND RECOMMENDATIONS

●Roles of the clinician – All clinicians should assess the environmental risks to their patients.

•History – Clinicians need to know how to take a good environmental history and should have a reasonable understanding of common environmental-related illnesses and injuries as well as basics of exposure assessment. (algorithm 1). Some exposures cause immediate or subacute symptoms, while others lead to more delayed effects (table 1 and table 2). (See 'General approach' above.)

•Education and prevention – In addition, the clinical encounter is an opportunity for education and preventive care related to environmental and climate-related exposures. A patient's reported exposures may prompt important interventions to prevent illness or injuries for the patient and others. (See 'Education and prevention' above.)

•Understanding the effects of climate change – Climate change effects including heat, increased likelihood of wildfires, and greater risk of severe weather events have major health consequences and increased physical and mental health risks (figure 1). (See 'Understanding effects of climate change' above.)

●Potential exposures – Major sources of environmental health exposures include:

•Air pollution (see 'Air pollution' above)

•Excess heat (see 'Excess heat' above)

•Indoor air pollution (see 'Indoor air pollution' above)

•Drinking water contamination (see 'Drinking water contamination' above)

●Ubiquitous sources – Some contaminants are found in many sources within the environment. These include per- and polyfluoroalkyl substances (PFAS), and microplastics/nanoparticles. (See 'Per- and polyfluoroalkyl substances (PFAS)' above and 'Microplastics and nanoparticles' above.)