Toxicity

Toxicity refers to the potential of a substance to cause harm to the living body. Toxic substances, or toxicants, can be naturally occurring (such as lead), synthetic (like phthalates), or produced by a living organism (like mold). Those produced by a living organism fall into a subclassification of toxicants called toxins.

Toxicology is the study of how toxicants can cause harm to living organisms.¹ A substance’s toxicity depends on several factors: its potency, the means of exposure, dosage and length of exposure, as well as individual characteristics of the person exposed. Factors such as an individual’s health and nutritional status, age, metabolism, allergies, pregnancy, and possible interactions with other chemicals, can affect a toxicant’s impact on the body.²

A person can be exposed to toxic substances through inhalation, ingestion, direct contact, or intravenously.³ The toxic effect of a substance depends on its route of exposure – a substance that is toxic when ingested is not necessarily toxic when it comes into contact with the skin. Inhalation of a gas, vapor, airborne powder, dust, or aerosolized liquid may cause irritation of the nose, eye, air passages, and lungs. Once reaching the lungs, a substance can be absorbed directly into the bloodstream and circulate throughout the body.⁴ In the workplace, inhalation is typically the entry route of greatest concern.⁶ Ingestion, or swallowing, of toxicants usually occurs by consuming contaminated foods or drinks, or using utensils or hands that have come into contact with chemicals. When ingested, chemicals enter the bloodstream and can be carried throughout the body. Children are at particular risk of ingestion because they tend to put their hands and other objects in their mouths. Substances can also be absorbed through direct contact with skin or eyes. This kind of exposure can cause local irritation or enter the bloodstream and travel through the body. Injured, cracked, or cut skin can accelerate the process of entering the bloodstream, although systemic effects through skin exposure are typically not as immediate as those seen through inhalation.⁷ Toxicants can also enter the body intravenously when the skin is punctured with a contaminated needle or other sharp object.⁸ Exposure to toxicants can induce a local or systemic effect. While some substances are harmful on direct contact, others can enter the bloodstream and move throughout the body, or they can target certain bodily systems or organs.⁹

A dose refers to the total amount of a substance that a person is exposed to, which depends on both the concentration of the substance and the duration of exposure.¹⁰ A substance causes toxicity when it reaches a certain concentration in the body. Its strength, or potency, determines the amount of a chemical necessary to cause harm; the more toxic the chemical, the smaller the dosage needed to cause harm.¹¹ Similarly, the greater the dosage, the more likely there will be adverse effects. Any chemical has the potential for toxicity in certain conditions – even over the counter medicines like aspirin, taken beyond recommended doses, can be dangerous. Body weight is an important factor in calculating dosage. Any given amount of a toxic substance is likely to affect a child more than an adult.¹²

Another factor that affects dose is the duration of exposure. Exposure can be chronic, experienced regularly over a period of time, or acute, meaning that contact occurs as a single event. Some substances, like ammonia, can be harmful in the short-term but cause little long-term harm. Other materials, like asbestos, become harmful through chronic exposure.¹³ Typically, acute health effects are caused by high levels of exposure, while long-term effects are the result of sustained low exposure. Depending on the toxicant, exposure over a long period of time can exacerbate its effects on the body. For example, momentary exposure to a skin irritant may be less harmful than the inhalation of toxic chemicals over a period of months or years.¹⁴ Chronic exposure can happen in the workplace or at home, through chemicals in furniture, carpeting, or cleaning products. Toxic chemicals may also enter the groundwater from landfills or industrial sites and contaminate nearby air and drinking water. Regardless of whether the exposure was acute or chronic, effects may not appear for months or years. This delay between exposure and the manifestation of health effects is called the latency period. For example, some kinds of cancer can be caused by sustained exposure to toxic chemicals, but symptoms may not appear until five to forty years after exposure.

1. Parsons School of Design’s Healthier Materials & Sustainable Building Certificate Program
2. US National Library of Medicine: Factors Influencing Toxicity
3. University of Toronto: Health Effects of Toxic Chemicals
4. New York State Department of Health: What You Know Can Help You – An Introduction to Toxic Substances
5. University of Toronto: Health Effects of Toxic Chemicals
6. US Department of Health and Human Services: Key Principles of Toxicology and Exposure
7. University of Toronto: Health Effects of Toxic Chemicals
8. New York State Department of Health: What You Know Can Help You – An Introduction to Toxic Substances
9. US Department of Health and Human Services: Key Principles of Toxicology and Exposure
10. University of Toronto: Health Effects of Toxic Chemicals
11. New York State Department of Health: What You Know Can Help You – An Introduction to Toxic Substances
12. University of Toronto: Health Effects of Toxic Chemicals
13. US Department of Health and Human Services: Key Principles of Toxicology and Exposure
14. New York State Department of Health: What You Know Can Help You – An Introduction to Toxic Substances