Environmental Toxicology: A Brief Introduction

The scientific study of toxins, compounds that can harm living things, and the health consequences of exposure to them is known as environmental toxicology. Substances that are discharged into the environment that have the potential to be harmful to the health of humans, animals, and plants are known as environmental toxicants.

The understanding that both man-made and naturally occurring chemicals can have detrimental effects on living things and ecological processes, as well as that human survival depends on the health of other species in addition to the availability of clean air, water, and food, is what drives the study of environmental toxicology. Therefore, the study of environmental toxicology focuses on how environmental toxicants interact with other species to affect the health and welfare of people, animals, and plants. In addition to controlling these pollutants, the field deals with safeguarding ecosystems and people from harm.

Overview of Some Common Contaminants

Arsenic

• Arsenic is a naturally occurring element that can be found in food, soil, water, dust, and the air in our surroundings.
• Arsenic levels can differ geographically as a result of natural geological processes, farming, and industry.
• As a long-term source of exposure, arsenic from farming and smelting tends to bind well to the soil and is predicted to stay close to the surface of the land for hundreds of years.
• Chromoluminized copper arsenate (CCA)-treated wood is frequently seen in outdoor playground equipment, decks, and railings of existing homes. Certain subterranean aquifers are found in soil or rock that naturally contains a lot of arsenic.
• The majority of arsenic enters the body through food or drink. Many nations around the world, including Bangladesh, Chile, China, Vietnam, Taiwan, India, and the United States, have issues with arsenic in their drinking water.
• Because it is absorbed from soil and water, arsenic can also be found in food, such as rice and some seafood.
• Additionally, inhaling arsenic-containing dust can allow it to enter the body. It’s been discovered by researchers that arsenic can affect the body’s endocrine system even at low concentrations.
• Another recognized human carcinogen linked to skin, lung, bladder, kidney, and liver cancer is arsenic.

Mercury

• Mercury is a metal that occurs naturally, a valuable ingredient in some goods, and a possible health hazard.
• There are other forms of mercury, but the two to which humans are most commonly exposed are methylmercury and elemental mercury.
• At room temperature, elemental mercury is a silver-white, glossy liquid that has the potential to evaporate into a dangerous, odorless vapor.
• The chemical molecule methylmercury can accumulate in the bodies of long-lived, carnivorous fish. It’s crucial to dispose of products containing mercury at a hazardous waste site to prevent mercury from getting into our food and air. Today’s common products that have trace levels of mercury in them include button-cell batteries and fluorescent lamps.
• Despite the many nutritional advantages of fish and shellfish, eating a lot of fish raises one’s risk of mercury exposure. Frequent consumption of fish high in mercury by pregnant women increases the chance of lasting harm to their developing fetuses. These women may give birth to children who struggle with motor skills, sensory issues, and cognitive deficiencies.

Bisphenol A (BPA)

• Bisphenol A (BPA) is a chemical produced on a large scale, mainly utilized in the manufacturing of polycarbonate plastics and epoxy resins.
• Polycarbonate plastics have diverse applications, including food and beverage packaging such as water and baby bottles, compact discs, impact-resistant safety gear, and medical devices.
• Epoxy resins serve as coatings for metal items like food cans, bottle caps, and water pipes.
• BPA exposure can also occur through some dental sealants and composites.
• The primary route of BPA exposure for most individuals is dietary, as it can migrate into food from epoxy resin coatings in canned foods and various consumer products like polycarbonate tableware, food containers, water bottles, and baby bottles.
• The leaching of BPA from polycarbonate bottles into liquids may be influenced more by the liquid or bottle temperature than the container’s age. Additionally, BPA has been detected in breast milk.

Phthalates

• Phthalates constitute a group of artificial compounds employed to impart flexibility and softness to plastic and vinyl products.
• The addition of phthalates is a common practice to render polyvinyl chloride more pliable.
• These versatile chemicals are utilized in numerous consumer items, spanning cosmetics and personal care products like perfume, hair spray, soap, shampoo, nail polish, and skin moisturizers.
• They are also integral to the composition of various consumer goods such as flexible plastic and vinyl toys, shower curtains, wallpaper, vinyl miniblinds, food packaging, and plastic wrap.
• Exposure to phthalates at low levels can occur through the consumption of food packaged in plastic containing phthalates, as well as inhaling dust in environments with vinyl miniblinds, wallpaper, or recently installed flooring containing these compounds.
• Drinking water contaminated with phthalates is another potential source of exposure. Phthalates are under suspicion for their potential role as endocrine disruptors.

Lead

• Lead is a naturally occurring metal found in the earth’s crust within rocks and soil. Additionally, it is generated through the combustion of fossil fuels like coal, oil, gasoline, and natural gas, as well as various industrial processes such as mining and manufacturing.
• Lacking distinct taste or odor, elemental lead is denoted by the chemical symbol Pb.
• Its versatile applications include the production of batteries, pipes, roofing materials, scientific electronic equipment, military tracking systems, medical devices, and items designed for X-ray and nuclear radiation shielding. Lead is also utilized in ceramic glazes and crystal glassware.
• Categorized as “reasonably anticipated to be a human carcinogen,” lead and its compounds can adversely affect nearly every organ and system in the body.
• Exposure, whether through inhalation or ingestion, poses significant risks, particularly to the central nervous system, with children being more susceptible to lead poisoning than adults.
• Extensive lead ingestion by a child can lead to brain damage, resulting in convulsions and mortality, as well as complications such as blood anemia, kidney damage, colic, and muscle weakness.
• Repeated low-level exposure may impede a child’s normal mental and physical growth, leading to learning or behavioral issues.
• High lead exposure during pregnancy can contribute to miscarriage, premature births, and smaller babies.
• Chronic exposure may cause lead to accumulate in the body, leading to lead poisoning.

Formaldehyde

• Formaldehyde is a combustible, colorless gas or liquid with an overpowering smell.
• It is an organic substance that readily turns into a vapor or gas, known as a volatile organic compound.
• Additionally, the human body naturally produces it in trace levels. Breathing air containing formaldehyde is the main way that humans might be exposed to it. Industries using or producing formaldehyde, wood products (such as particle board, plywood, and furniture), car exhaust, cigarette smoke, paints and varnishes, carpets, and permanent press fabrics are among the sources of formaldehyde releases into the atmosphere. Formaldehyde is released by nail polish and professionally applied floor finishes.
• Because many consumer goods, construction materials, and textiles produce formaldehyde, interior surroundings generally have higher concentrations than outside environments. The range of formaldehyde concentrations seen in indoor air is 0.02–4 parts per million (ppm). Urban regions have outdoor air levels of formaldehyde ranging from 0.001 to 0.02 ppm.

Radiation

• Atoms emit radiation, which is what surrounds us. Daily radiation exposure occurs from the sun, rocks, and soil, among other natural sources.
• In addition, radiation from artificial sources like smoke detectors and medical X-rays exposes us to radiation.
• Even watching television, some building materials, and cross-country trips expose us to low doses of radiation. Radiation cannot be tasted, smelled, or seen. Certain kinds of radioactive materials provide a greater risk than others.
• Therefore, it’s critical to manage radiation and radioactive materials carefully to safeguard public health and the environment.

Radon

• Colorless and odorless, radon is a naturally occurring radioactive gas.
• It originates from uranium or thorium which naturally decays and is present in almost all soils. It usually enters a house through foundation, wall, and floor fissures and travels upward through the ground.
• Additionally, well water and building materials may emit it. Radon decays rapidly and releases radioactive particles. Lung cancer may result from prolonged exposure to these particles. The U.S. Environmental Protection Agency states that radon is the second most common cause of lung cancer after smoking among nonsmokers.

Route of exposure to chemicals

To be harmful to your health, chemicals need to go inside your body. Certain substances can enter your bloodstream after they have entered your body and make their way to internal organs like the kidneys, liver, lungs, or nervous system. There are three primary pathways through which a chemical can enter your body and cause exposure:

• Inhalation: The first method involves inhaling chemical gasses, mists, or dusts that are present in the air. Since the lungs’ air sacs are structures for gas exchange and are made of only one thin layer of cells, chemicals inhaled can quickly go from the air sacs into capillaries and the bloodstream. Toxins inhaled can also harm the mouth, respiratory tract, and lungs locally.
• Ingestion: The second method is ingestion, which is the eating of chemicals that have leaked or collected on hands, beards, cigarettes, food, or drinks. After causing localized harm to the digestive system, toxins have the potential to enter the bloodstream through the intestines, where they are most frequently absorbed.
• Skin or eye contact: Touching the skin or eyes is the third route. Chemicals can cause localized damage or enter the bloodstream through the skin when they come into contact with the skin or get in the eyes. In contrast to ingestion and inhalation, it is more difficult for toxins to enter the body through the skin since it is made up of numerous cell layers that are fortified by defensive substances. On the other hand, certain substances can be absorbed through undamaged skin, while toxins can readily penetrate through damaged skin. Toxins can easily enter the bloodstream through eye contact since the eyes have a high blood supply.

What Forms Do Chemicals Take?

Chemicals can exist in many different forms. They may manifest as threads, mists, fumes, vapors, gasses, solids, liquids, or dusts. The way a drug enters your body and the potential harm it can cause depends greatly on its shape. Moreover, a chemical can shift forms. For instance, liquid solvents have the ability to evaporate and release fumes that are breathable. Sometimes chemicals exist in forms that are invisible to the human eye or sense of smell, making detection difficult.

Health Effects of chemicals/toxins

Numerous factors influence how a toxin acts.

• First of all, different people may react differently to the same poison at the same concentration based on a variety of characteristics such as age, general health, gender, and heredity. For example, heavy metals and bisphenol A (BPA) can be particularly harmful to young children.
• Elderly people are also more vulnerable to some toxins because the liver processes a lot of toxins and liver function declines with age. In a similar vein, someone in generally good health is probably more resilient to toxic exposure than someone with other health issues.
• Genetically speaking, certain people may possess gene variants that increase their susceptibility to or resistance to particular poisons.
• Apart from the individual characteristics, toxicity is also affected by the duration of exposure, the presence of other toxins, and the concentration (dosage).

Acute vs. Chronic Effects of Chemical

• A toxin’s acute effect happens quickly following extensive exposure to that chemical.
• Small doses of a pollutant over an extended length of time can have a chronic effect on a person. In this scenario, the impact might not be immediately apparent.
• Chronic impacts can take years to manifest, making measurement challenging.
• It is believed that moderate alcohol consumption, low-level radiation exposure, and prolonged cigarette smoking can all have long-term impacts.

Toxicological Interactions

Various effects, or chemical interactions, can arise from simultaneous exposure to numerous substances. These can be applied to any chemical that has an impact on the body, such as medications and toxins (toxicological interactions refer to the latter). An additive chemical interaction occurs when the combined effect of two compounds is equal to the total of their individual effects.

• Assume that the effects of drugs A and B on the body are identical (e.g., both raise heart rate by five beats per minute). If taking both medications at the same time caused the heart rate to rise by ten beats per minute, this would have an additive impact.
• Conversely, if taking medications A and B concurrently caused a rise in heart rate of less than 10 bpm (less than the sum of both increases), this would be seen as an antagonistic effect, meaning that the drugs interfere with one another.
• Drugs A and B would interact synergistically if they raised heart rate by more than 10 beats per minute, meaning that their combined effect outweighed the sum of their separate effects.

Dose-dependent effects of chemicals/toxins

Scientists have known for ages that almost every drug can be harmful in large enough doses. For instance, while living things need trace amounts of selenium to function properly, excessive concentrations can lead to cancer.

• The dosage (quantity) of a drug determines how it affects a specific person.
• Many drugs’ lethal doses for humans have been established using data compiled from animal experiments, accidental poisonings, and murder case files.
• The term “lethal dose-50%,” or LD-50, refers to a dosage that is fatal to 50% of test animal subjects. To provide a measure of the toxicity of new synthetic compounds, the LD-50 must be determined.
• Effective dosage 50%, or ED-50, is the dose at which 50% of a population shows any discernible response (such as hair loss or stunted development). Certain poisons have a threshold concentration below which the exposed population shows no discernible effects.

Precautionary Principle

• Using a dose-response curve, one may determine a safe amount by applying the precautionary principle, which is essentially the idea that “it’s better safe than sorry.”
• Precautionary measures give room for safety if a toxin or medication is later shown to have harmful effects at a lower dosage than initially discovered. Usually, 1% or even 0.1% of the NOAEL is the safe amount.
• The precautionary principle is occasionally extended to various aspects of environmental toxicology. In the European Union (EU), manufacturers are obligated to establish the safety of their products before their sale.
• While a similar requirement exists in the United States for novel chemicals, there is no parallel regulation for existing products. In the U.S., the burden lies with the Environmental Protection Agency (EPA) to demonstrate the unsafe nature of products already in circulation before imposing a ban.
• To sum up, both the EU and the U.S. employ the precautionary principle in overseeing potential toxins in products, yet the EU adopts a broader application. The EU leans towards caution, potentially prohibiting substances that may be innocuous until proven safe, whereas the U.S. assumes the risk of exposure to potential toxins until their safety is conclusively determined.

Video on Environmental Toxicology

References

• https://bio.libretexts.org/Bookshelves/Ecology/Environmental_Science_(Ha_and_Schleiger)/04%3A_Humans_and_the_Environment/4.04%3A_Environmental_Health/4.4.04%3A_Environmental_Toxicology
• https://byjus.com/chemistry/environmental-toxicology/
• https://openoregon.pressbooks.pub/envirobiology/chapter/6-3-environmental-toxicology/
• https://www.longdom.org/open-access/causes-of-environmental-toxicology-and-its-impacts-97292.html