Today, people spend more time indoors than ever before. According to the US Environmental Protection Agency, on average we spend 90 percent of our lives indoors working, playing, sleeping, eating, learning, socializing, and exercising. This means that the quality of the indoor environment is critical to human health, especially because pollutant levels are often higher indoors than outdoors. Thousands of cancer deaths and hundreds of thousands of respiratory health problems each year are linked to indoor pollution. It is also tied to reproductive, developmental, cardiovascular, gastrointestinal, endocrine, kidney, neurological, skin, and liver diseases. The way buildings are constructed, operated, and maintained can make a huge difference in their health effects. This means that design and building professionals have a unique opportunity to choose innovative products, materials, and technologies that promote health and wellbeing. This article provides a brief behind-the-scenes look at how toxicologists and regulators determine what substances are dangerous, under which circumstances, and for whom. It will also explore the different pathways of exposure in indoor spaces, and some of the related health effects. The information below is part of an ongoing series of articles on toxicity and material health.
Risk Assessment Practices
Determining the toxicity of substance depends on several factors, including its potency, the means of exposure, dosage, length of exposure, and the individual characteristics of the person exposed. Toxicity occurs when the substance reaches a certain concentration in the body. Some chemicals are more potent than others, and so harm can be caused with smaller dosages—similarly, higher dosages are more likely to cause adverse effects. Government agencies and other regulators examine chemicals and other substances that might cause harm in a four-step process:
1. Hazard identification: The first step is to determine whether a chemical is toxic, and if so, what kind of toxicity (neurotoxicity, carcinogenicity, etc.). Toxicologists also measure the concentration of the substance in the environment and the conditions under which exposure might have health effects.
2. Dose-response assessment: The second step evaluates the health effects at given doses of toxic substances. Is there a threshold? What kinds of effects are manifested? This step may also look at variations in responses in different populations (for example, different age groups).
3. Exposure assessment: This step entails specifying which population is most likely to be exposed to the substance, identify routes of exposure, and estimating the magnitude, duration, and timing of possible exposure.
4. Risk characterization: The final step is the integration of the first three steps in order to estimate whether there is an actual risk to people who are exposed. This estimate might be qualitative or quantitative.
Routes of Exposure
Depending on the type of chemical and where it’s found, people are exposed in different ways. The most common routes of exposure are through inhalation, skin contact, or ingestion. The toxicity of a substance depends on how we’re exposed to it—something that’s toxic when ingested isn’t necessarily as harmful when it touches your skin. Harmful chemicals can be found in household products from paints, wood products, flooring, and carpets, to furniture, heating and cooling systems, and cleaning supplies. One of the most common routes of exposure is through dust. Particles that leach out of products may end up in dust, which can be either inhaled or ingested. Babies and small children are particularly susceptible to exposure through dust, since they tend to put their hands and other objects in their mouths. Humans can be exposed to some substances, like lead, through various routes. Lead paint can peel and make its way into dust, and it can also leach out of lead pipes and into drinking water.
Indoor air quality can also be compromised by volatile organic compounds (VOCs), gaseous chemical contaminants that can cause a range of effects, including respiratory issues, irritation of the eyes, nose, and throat, damage to the central nervous system, and cancer. VOCs can be released from building materials like paints and sealants; household products like carpeting and plastics; and furniture, like chairs and cushions. One of the diseases most studied in relation to indoor environment is asthma. More than 26 million people suffer from asthma in the US as of 2018, and there was an increase of 4.3 million between 2001 and 2009. A study by Perkins and Will found 374 household substances linked to asthma, including common ingredients found in many interior finishes, like floors, carpets, and paints. It is possible to improve prevention strategies for asthma and many other health effects caused by toxicity in indoor environments by reducing or eliminating these chemicals from building materials. You can also follow best practices outlined in healthy building certifications and rating systems. Find out more about toxicity in Knowledge Bank’s glossary of terms.