Toxicity to Various Agents

Exposure to harmful chemicals and toxic substances can occur every day through what we eat, breathe, touch, or swallow, affecting our health in ways that range from mild symptoms to life-threatening conditions.

Table of contents

• What Is Toxicity and How Toxic Substances Affect Health
• Types of Toxic Agents
• How Toxic Substances Enter the Body
• The Dose Makes the Poison
• Factors That Influence Toxic Effects
• Signs and Symptoms of Poisoning
• Treatment with Antidotes
• What to Do When Poisoning Occurs

What Is Toxicity and How Toxic Substances Affect Health

Toxicity refers to the degree to which a chemical substance or mixture of substances can damage a living organism^[1][2]. The term can describe effects on a whole organism, such as a person, animal, or plant, or on specific parts of the body, such as a cell (called cytotoxicity) or an organ like the liver (called hepatotoxicity)^[2].

A central idea in understanding toxicity is that the effects of a toxic substance depend on the dose. Even water can cause poisoning when consumed in very high amounts, while even highly toxic substances like snake venom have a dose below which no harmful effect occurs^[2]. This means that almost anything in our lives can be a poison if we are exposed to too much of it or in a way that was not intended^[4].

Toxic substances are substances that can be poisonous or cause health effects^[5]. These include everyday products such as household cleaners, prescription and over-the-counter drugs, gasoline, alcohol, pesticides, fuel oil, and cosmetics, as well as chemicals like polychlorinated biphenyls (PCBs) and dioxin that may be found at hazardous waste sites^[5].

Types of Toxic Agents

There are generally five types of toxicities: chemical, biological, physical, radioactive, and behavioral^[2]. Toxic chemicals can often be grouped into classes, where all the chemicals in a given class cause similar human health effects^[4].

Unspecified toxic chemicals are individual chemicals or mixtures of chemicals and their by-products that originate from human activities^[3]. These are toxic chemicals that may not yet have been identified but may be adversely affecting living organisms. They may be unknown because they have not been measured, or measurement is difficult due to episodic occurrence, unique chemistry, or low concentrations^[3].

Common sources of toxic chemicals include:

• Non-point sources from industrial, agricultural, mining, logging, urban, and residential activities
• Historical sources and landfills
• Spills and illegal dumping
• Point source discharges from industries, municipal treatment facilities, and animal husbandry operations^[3]

How Toxic Substances Enter the Body

A chemical’s physical state and the route of exposure influence its toxicity^[4]. The chemical’s state often determines the route of exposure, and for many chemicals, the toxic effects occur at the site where they are absorbed^[4].

Exposure to a substance can occur by inhalation, ingestion, or direct contact^[5]:

Inhalation (breathing) of gases, vapors, dusts, or mists is a common route of exposure. Chemicals can enter and irritate the nose, air passages, and lungs. They can become deposited in the airways or be absorbed by the lungs into the bloodstream, which can then carry these substances to the rest of the body^[5]. Gases, vapors, airborne powders, and aerosolized liquids are inhalation risks. Inhalation exposure allows some chemicals to enter the bloodstream rapidly, causing toxic effects distant from the entry route^[4].

Dermal exposure occurs when chemicals come in contact with the skin. Chemicals can cause local effects but may also enter the bloodstream and cause effects at distant sites from the entry route. Fat-soluble chemicals can rapidly penetrate the skin and enter the bloodstream. Skin exposure can delay the onset of systemic effects compared with the rapid entry through the lungs^[4].

Ingestion happens when toxic substances are swallowed. Since chemicals can be toxic when they enter or contact the body, drinking a toxic substance can cause burns, vomiting, diarrhea, and in very large amounts, drowsiness or death^[5].

The Dose Makes the Poison

Evaluating clinical effects based on the amount of exposure is a basic toxicology principle called dose-response^[4]. The dose is the total amount of chemical absorbed during an exposure. Dose depends on the concentration of the chemical and duration (contact time) of the exposure^[4].

Chemicals cause predictable toxic effects based on the dose. Incremental increases in the amount of a substance result in predictable increases in harmful effects, including altered consciousness, poor coordination, and eventually coma, respiratory depression, and death^[4].

The duration of exposure is one important factor affecting the dose. High concentrations over a long duration are more likely to produce adverse health effects than the same or lower concentration over a shorter exposure period^[4]. For example, an acid placed on the skin will cause more tissue destruction the longer it stays in contact with the tissues. If the acid is immediately washed off the skin, injury is limited^[4].

Factors That Influence Toxic Effects

To determine the risk of harmful health effects from a substance, it is important to understand how toxic the substance is, how much and by what means a person is exposed, and how sensitive that person is to the substance^[5].

Some substances are more toxic than others. The toxicity of a substance is described by the types of effects it causes and its potency (strength). A more potent chemical is more toxic^[5]. For example, sodium cyanide is more potent than table salt because swallowing a smaller amount of cyanide can poison you^[5].

The potency and toxicity of a chemical can be affected by its breakdown within the human body. When a substance is absorbed into the body, its chemical structure may be changed or metabolized to a substance that is more toxic or less toxic^[5].

Patients who have higher concentrations and longer durations of exposure receive greater doses and are more likely to have harmful effects. Those receiving larger doses need more urgent attention and possibly life-saving interventions than those receiving smaller doses, especially if they have no symptoms^[4].

Signs and Symptoms of Poisoning

Chemical classes of toxic substances can often be grouped together, whereby all the chemicals in a given class cause similar human health effects. These constellations of toxic effects or toxic syndromes comprise a set of clinical “fingerprints” for groups of toxins^[4].

During the early phases of a toxic chemical emergency, when the exact chemical is often unknown, identification of the toxic syndromes that are present can be a useful decision-making tool. Toxic syndromes are easily identified with only a few observations, such as vital signs, mental status, pupil size, mucous membrane irritation, lung examination for wheezes or rales, and skin for burns, moisture, and color^[4].

Symptoms of toxicity vary depending on the substance involved, its physical and chemical properties, the amount, route, and its mechanism of action, and whether or not it was combined with another substance^[12]. Common biological effects that can result from toxic exposure include:

• Abrupt increases in mortality
• Significant community changes, such as large reductions in species richness or abundance
• Abnormal behaviors
• Gross pathologies not typical of pathogens, such as tumors, deformities, or sloughing of tissues^[3]

Treatment with Antidotes

Antidotes are agents that negate the effect of a poison or toxin^[7]. An antidote is defined as a substance that neutralizes or counteracts the effects of poison^[12]. Antidotes mediate their effect either by preventing the absorption of the toxin, by binding and neutralizing the poison, antagonizing its end-organ effect, or by inhibition of conversion of the toxin to more toxic metabolites^[7].

Antidote administration may not only result in the reduction of free or active toxin level but also in the mitigation of end-organ effects of the toxin by mechanisms that include competitive inhibition, receptor blockade, or direct antagonism of the toxin^[7].

Antidotes are classified according to the mode of action. Some antidotes are very specific, working on only one type of poison, and others reverse the effects of many different types of poisons^[12]. Mechanisms by which antidotes act include:

• Reduction in free toxin level through specific and non-specific agents that bind to the toxin
• Competitive inhibition of enzymes
• Enhancement of enzyme function
• Competitive receptor blockade
• Reduction of the formation of toxic metabolites^[7]

When available, the appropriate and timely administration of a toxicity reversal agent can counteract the toxic action of the poison, enhance its elimination, and improve related illness and death rates. However, not every antidote is 100% effective and fatalities may still occur^[12].

What to Do When Poisoning Occurs

If you are concerned about possible poisoning, call Poison Help at 800-222-1222 in the United States or your regional poison control center^[10]. Poison control centers are excellent resources for poisoning information and, in many situations, may advise that in-home observation is all that is needed^[10].

Call 911 or your local emergency number immediately if the person is:

• Drowsy or unconscious
• Having difficulty breathing or has stopped breathing
• Uncontrollably restless or agitated
• Having seizures
• Known to have taken medicines or any other substance, intentionally or accidentally overdosed^[10]

Call Poison Help in the following situations:

• The person is stable and has no symptoms
• The person is going to be transported to the local emergency department^[10]

It is important to seek help as fast as possible. Poison control can walk you through whether you need to go to the emergency room. If the situation is serious enough, call 911 and emergency responders can bring you to the hospital^[12].