Environmental Toxicology: Definition & Historical Background
Toxicology is traditionally known as “the science of poisons”.
A simple definition is “toxicology is the study of the adverse effects of chemical, biological, or physical agents on living organisms.” (Radenkova, 2008).
Environmental Toxicology, also known as entox, is defined by Britannica as the “ field of study in the environmental sciences that is concerned with the assessment of toxic substances in the environment.”
Another definition of Environmental toxicology is, “A multidisciplinary field of science concerned with the study of harmful effects of various chemical, biological, and physical agents on living organisms.”
It is a fundamental field in environmental health that studies the adverse effects of toxicants at the population and ecosystem levels. The subject is primarily concerned with the environmental toxicants’ effects on health and the environment.
The term “health” refers to human health as well as the health of other living things, plants, and animals.
Agents that pose adverse effects on health and the environment when released in the general environment are called environmental toxicants.
The subject of toxicology has a rich history, with poisons used for various purposes, such as weapons, anti-venoms, and medicines.
For example, in 400 A.D., the Romans used poisons for executions.
Over centuries, the study of poisons evolved into the modern subject of toxicology that intersects with other disciplines, including biology, chemistry, and epidemiology.
However, environmental Toxicology is a relatively new field. Its origin is quipped in the mid-20th century.
Environmental toxicology’s importance stems from the fact that;
- Human survival depends on other species’ well-being and ecosystem services. The availability of clean water, air, and food are fundamental requirements.
- Chemicals released into the general environment, either from anthropogenic processes or from naturally occurring processes, can have detrimental effects on all kinds of living organisms and the environment they’re living in.
American biologist Rachel Carson made a distinct field within toxicology with her book “Silent Spring (1962)”. She is thus considered the mother of environmental Toxicology. Her book extensively covered the environmental side effects of uncontrolled use of pesticides such as DDT.
The term ecotoxicology was coined by René Truhart in 1969 “to describe the study of the toxic effects of pollutants on the biological components of ecosystems.”
In the 1970s, scientists focused on harmful agents of biological warfare, industrial pollution, and mine waste.
In the 1980s, the Bhopal disaster killed 15,000-20,000 people with toxic gas and the Chornobyl nuclear accident spread radiation, causing deaths and land contamination for years to come.
By the late 20th century, environmental toxicology expanded to cover oil spills, medical and nuclear waste, pollution, and synthetic chemicals in the environment.
Addressing these issues requires global collaboration, stricter policies, and continued research on safer alternatives.
In Environmental Toxicology, we use different perspectives and terms like forensic toxicology, analytical toxicology, clinical toxicology, occupational toxicology, and economic toxicology.
Analytical Toxicology is concerned with the identification of toxicants through analysis of gut contents and body fluids.
Economic Toxicology deals with the use of food additives in food processing and preservation, synthetic fertilizers, and pesticides in agriculture and the risks associated with these applications.
Occupational toxicology studies the acute and chronic effects of toxicants on workers.
Forensic toxicology deals with the harmful effects of toxic chemicals on humans in medico-legal aspects. Narcotics, doping, suicide, murder, etc, come into the forensic study.
The Interdisciplinary Approach of Environmental Toxicology
A discipline of Environmental Science, Environmental Toxicology is an interdisciplinary field of science that encompasses multiple disciplines. These disciplines include chemistry, pharmacology, molecular biology, biochemistry, ecology, limnology, among others.
Environmental Toxicology studies how environmental toxicants, through their interaction, influence the health and well-being of humans, animals, and plants.
Toxicology can be defined in both traditional and modern terms.
The traditional definition refers to toxicology as the science of poisons. And modern definition defines it as the study of the adverse effects of chemicals on living organisms.
Toxicology also applies to wildlife, plants, and other species.
It is an interdisciplinary field. The sub-specializations include descriptive toxicology (which tests toxic chemicals), forensic toxicology (which investigates toxic substances in crime scenes), and environmental toxicology (which studies the effects of toxic chemicals on environmental health).
The components of environmental Toxicology also include:
- Analytical Chemistry
- Biometrics
- Ecology
- Chemistry
- Biochemistry
- Chemical Engineering
- Meteorology
- Physiology
- Marine Biology
- Oceanography
- Microbiology
- Population biology
- Evolutionary biology
- Molecular Genetics
- Risk Assessment and Risk Management
- Population biology
- Limnology
- Cell Biology
- Development biology
The National Toxicology Program (NTP) in the USA evaluates the impact of toxic chemicals on human health.
As per NTP data, over 80,000 chemicals have been registered for use in the United States.
Around 2,000 new chemicals are introduced annually. These new chemicals are found in products like food, personal care items, prescription drugs, and household cleaners.
Many of these chemicals’ effects remain unknown. These pose potential risks during manufacturing, distribution, use, and disposal.
Fortunately, only a small number of chemicals pose significant risks to human health.
The Relevance of Toxicology in Everyday Life
Toxic chemicals are prevalent in our daily lives.
At various stages of the life cycle, organisms are introduced to toxicants. However, the degree of toxicity of toxicants can vary depending on multiple factors.
Bioaccumulation of toxicants could occur when molecular compounds are stored in the fatty tissues of an organism. This could lead to biomagnification of certain toxicants through the food chain.
Chemicals may also be excreted back into the environment. They may be metabolized into other forms (bio-transformed) which may be more or less toxic than their original forms.
Biodegradation is an important process that releases by-products of Carbon dioxide and water. It could be limited in the presence of environmental toxicants.
It is important to study the adverse effects of chemicals and other man-made agents on environmental systems. Both humans and ecosystems are the receptors of such agents.
It’s of prime concern to anticipate the fate of these chemical agents and the risks associated with exposure.
Environmental Toxicology includes the study of pollutants that contaminate air, water, soil, and food. It also studies the impact of chemical substances on the structure and function of ecological services.
The subject also includes the decision-making processes by humans for environmental management and conservation and in regard to human health concerns.
For instance, in 2005, California considered placing warning labels on French fries. This was due to the concerns around the formation of Acrylamide when starchy food is heated at high temperatures.
Fish like swordfish or tuna, though considered healthy, may contain high levels of mercury. Mercury consumption could lead to health issues such as Alzheimer’s, Parkinson’s, and depression.
Lawn pesticides are used to kill insects. However, they can also be harmful, particularly to pets and children.
These examples show the importance of understanding toxicology. Chemicals affect our everyday lives.
However, it’s almost impossible and extremely expensive to go for an overall ecosystem assessment.
Studies are carried out on specific species or laboratory test-organisms to assess the degree of toxicity of substances, their adverse effects, and the risks posed to humans and other living organisms.
Objectives of Environmental Toxicology and The Role of Toxicologists
Toxicologists are scientists trained to investigate the adverse effects of chemicals on living organisms and assess the risks of exposure. They study the level of exposure at which chemicals become hazardous.
Environmental Toxicologist look for answers to these two questions mainly;
- What harmful effects are caused by released pollutants?
- How to prevent or minimize the risk of environmental toxicants to the biological and ecological system?
One important assumption in toxicology is that “the dose makes the poison.“
Essentially, any substance can be harmful at a high enough dose. For instance, even water, when consumed in excessive amounts, can lead to water intoxication.
Similarly, sodium chloride (table salt), in large quantities, can be toxic.
Certain substances like botulinum toxin (used in Botox, one of the most poisonous biological substances known) are highly toxic in small amounts but have medical uses in controlled doses.
The primary objectives of Environmental Toxicology are simplified into a 5-steps process that is useful for research, analysis, and decision-making.
- Release of pollutants into the environment
- Transport and fate of released environmental toxicants
- Exposure to biological and ecological system
- Understanding the responses and/or effects
- Designing remediation, minimization, conservation, and risk Assessment plans for the elimination, prevention, or prediction of environmental toxicants with adverse effects on health and the environment.
Toxicity and Toxins
Toxicity refers to the degree to which a substance is poisonous and harmful to humans and other living organisms. This depends on the chemical properties and nature of the substance.
Some chemicals, such as water and sodium chloride, have low toxicity. They must be consumed in large quantities to cause harm.
Highly toxic substances like dioxins and botulinum toxin can cause harm in tiny doses.
Natural toxins are poisonous substances produced by living organisms, including plants, animals, and microorganisms.
For example, certain species of mushrooms are highly toxic to humans.
In this regard, the Pollutant Release-Exposure-Dose-Response Paradigm plays a critical role.
Sources of Environmental Toxicity
Environmental Toxicity can come from several sources.
The release of toxicants from different sources leads to their disposal in our water, food, and air.
These sources include organic and inorganic pollutants, pesticides, and biological agents.
A toxic substance in the environment may exist in several different forms; dissolved, absorbed, suspended, deposited, accumulated, or incorporated.
Key toxic substances of concern include Polychlorinated biphenyls (PCBs), heavy metals, pesticides like DDT, and chemicals such as sulfuryl fluoride.
| Concern | Description |
|---|---|
| Chemical Pollution | Persistent Organic Pollutants (POPs): “Human exposure — for some compounds and scenarios, even to low levels of POPs — can lead to many health effects including increased cancer risk, reproductive disorders, alteration of the immune system, neurobehavioral impairment, endocrine disruption, genotoxicity, and increased birth defects.” (World Health Organization) Heavy Metals: Metals like lead and mercury damage the nervous system, and organs, and hinder development, even in small amounts. |
| Pesticides | “Studies have linked pesticides to risk for Parkinson’s disease, thyroid disease, diabetes, kidney diseases, rheumatoid arthritis, and shingles (herpes zoster), among other health issues.” (National Institute of Environmental Health Sciences) |
| Air Pollution | Pollutants like particulate matter (PM), nitrogen oxides, and sulfur dioxide lead to respiratory diseases, and heart problems. |
| Water Contamination | Heavy Metals and Chemicals: Pollutants such as arsenic and lead in water cause cancer, organ damage, and neurological disorders. Microplastics: Tiny plastic particles harm marine life and could pose long-term risks to human health. |
| Food Contamination | Food contamination poses serious public health risks due to harmful substances like pesticides, heavy metals, and pathogens |
| Pharmaceuticals and Personal Care Products (PPCPs) | Drugs and chemicals from personal care products enter water supplies, contributing to antibiotic resistance and other health risks. |
| Plastic Pollution | Plastic waste impacts marine life. It enters the food chain affecting human health. |
| Occupational Exposure | Workers in industries such as mining or manufacturing are exposed to toxic chemicals. |
| Nanotechnology | Tiny particles in electronics or cosmetics may penetrate human tissues, posing potential but poorly understood health risks. |
| Climate Change and Toxicology | Climate change worsens toxicological concerns by spreading pollutants and triggering natural disasters that release toxins. |
Dose-Response Relationship
The dose-response relationship is a key concept in toxicology.
It demonstrates how different levels of exposure to a chemical relate to health outcomes.
The term “dose” refers to the amount of a substance taken at one time.
For example, in a 2007 incident in Sacramento, California, a woman died of acute water intoxication.
"Jennifer Strange, a 28-year-old Rancho Cordova, Calif. mother of three, died of acute water intoxication in January, 2007 after the challenge to see which contestant could drink the most water without using the restroom. A Nintendo Wii video game was the prize for winning the "Hold Your Wee for a Wii" contest." (source: CBS News)
This tragic event underscores how even water, at excessive levels, can become toxic.
Dose-response relationships can be studied at both the individual and population levels.
Factors Determining Toxicity
Several factors influence the toxicity of chemicals, including:
Route and Site of Entry:
Chemicals can enter the body via ingestion, inhalation, injection, or skin contact. The speed and strength of their effect depend on the route of entry. Injections directly into the bloodstream have the fastest effect.
Duration of Exposure:
Exposure can be acute (short-term, often less than a day) or chronic (long-term, occurring over months or years).
Acute exposure often results in immediate effects. Chronic exposure can lead to cumulative damage.
Chemical Mixtures:
Toxicologists study the combined effects of chemical mixtures. It can sometimes have additives (equal to the sum of their parts). Also Synergistic (greater than the sum), or antagonistic (less than the sum) effects.
For example, the combination of asbestos exposure and smoking significantly increases the risk of lung cancer—a synergistic effect.
Individual Susceptibility:
Age, sex, genetic background, and health status all influence how individuals respond to toxic substances.
Children are more vulnerable to certain exposures due to their smaller body size and developing systems. The elderly are sensitive to toxicant exposure due to weakened immune systems.
Conclusion
Toxicology is a crucial field that helps us understand the risks associated with chemicals in our environment and everyday lives.
Environmental Toxicology is the scientific study of environmental toxicants. It includes their chemical nature, source and status, environmental fate, adverse effects on living organisms, and ecological services.
Toxic substances are present in all components of the biosphere.
The young and interdisciplinary field of environmental Toxicology uses basic and applied scientific knowledge to understand the source, transport, risk, impact, dose-response, and the fate of environmental toxicants.
Global toxicology concerns focus on the harmful effects of chemicals, pollutants, and toxins on human health and the environment. These risks have increased with industrialization, urbanization, and agricultural practices.
The field of Environmental Toxicology borrows from various disciplines, including environmental chemistry, analytical chemistry, pharmacy, soil science, ecology, marine biology, physiology, wildlife biology, etc.
