8.13 Dose Response Curve

Introduction

Dose-response studies are a type of research that assesses the relationship between the dose of a chemical or drug, and the response of an organism or population. These studies are used to determine the safe and effective use of a chemical or drug by identifying the minimum and maximum doses that produce the desired effect, while minimizing the risk of harm.

One common method of measuring the effects of a chemical on an organism is by determining the Lethal Dose 50% (LD50). 

LD50, which stands for "median lethal dose," is a measure of the toxicity of a substance, typically expressed as the amount of the substance per unit of body weight that is required to kill 50% of a test population. In real-life locations, LD50 values are often used in industrial settings or in scientific research to determine the safety and potential hazards of chemicals and other substances.

Here are some examples of LD50 values for different substances:

• Sodium chloride (table salt): 3,000 mg/kg (oral, rat)
• Nicotine: 50-60 mg/kg (oral, rat)
• Lead: 100-200 mg/kg (oral, rat)
• Methanol: 790 mg/kg (oral, rat)
• Botulinum toxin (botox): 0.003-0.007 ng/kg (oral, rat)

It's important to note that LD50 values can vary depending on the species, the route of exposure, and the duration of exposure. Additionally, LD50 is not the only indicator of toxicity, and other factors such as carcinogenicity, reproductive toxicity, or chronic effects should also be considered.

Dose-response studies are typically conducted on animals, and the data collected is used to create a dose-response curve. This curve shows the relationship between the dose of a chemical and the response of the organism or population. The curve typically follows an S-shape, with a small increase in the dose leading to a small increase in the response, and then a steep increase in the response as the dose increases further.

Dose-response studies are an important tool for scientists and regulators as they help to understand the toxic effects of chemicals, and to establish safe levels of exposure. These studies help to identify the concentrations of a chemical that are harmful and set limits to exposure, which in turn helps to protect human and animal health.

Overview of Common Contaminants

A contaminant is a substance or organism that is present in an environment where it is not naturally or normally found, and which can have negative impacts on the health of humans or other living organisms, or on the environment. Examples of contaminants include pollutants in air or water, pesticides, heavy metals, and bacteria or viruses in food or water.

There are many different types of contaminants that can be found in various environments. Here is an overview of some common contaminants:

• Air pollutants: These include chemicals and particles that are released into the air, such as carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter, and volatile organic compounds. These pollutants can have negative impacts on human health, as well as on the environment.
• Water pollutants: These include chemicals and organisms that are present in water, such as bacteria, viruses, pesticides, heavy metals, and nutrients such as nitrogen and phosphorus. These pollutants can have negative impacts on human health and on the health of aquatic organisms.
• Soil pollutants: These include chemicals and other substances that are present in soil, such as pesticides, heavy metals, and toxic industrial chemicals. These pollutants can have negative impacts on human health, as well as on the health of plants and other organisms that live in the soil.
• Food contaminants: These include chemicals and organisms that are present in food, such as bacteria, viruses, pesticides, and heavy metals. These contaminants can have negative impacts on human health, and can also cause food spoilage.
• Radiological contaminants: These include substances that emit radiation, such as radioactive isotopes. They can have negative impacts on human health, as well as on the environment.

Arsenic

Arsenic is a naturally occurring element found in the environment in various forms such as water, soil, dust, air and food. Exposure to arsenic can occur through various ways such as through drinking water, food, breathing dust containing arsenic and wood treated with chromated copper arsenate. It is a known human carcinogen and has been linked to various types of cancer including skin, lung, bladder, kidney and liver cancer. It can also interfere with the body's endocrine system and is a global concern, with high levels found in countries such as Bangladesh, Chile, China, Vietnam, Taiwan, India, and the United States.

Mercury

Mercury is a naturally occurring metal that can exist in several forms, including methylmercury and elemental mercury. Elemental mercury is a liquid at room temperature and can produce a harmful vapor, while methylmercury is an organic compound that can build up in the bodies of long-living predatory fish. People can be exposed to mercury through products such as fluorescent lights and button-cell batteries, as well as by consuming fish and shellfish that contain high levels of mercury. Pregnant women who regularly eat fish high in mercury risk permanently damaging their developing fetuses, and children born to these mothers may exhibit motor difficulties, sensory problems, and cognitive deficits. To reduce exposure to mercury, it is important to dispose of mercury-containing products properly and to be aware of the typical levels of mercury in commonly consumed commercial and sport-caught fish.

BPA

Bisphenol A (BPA) is a chemical commonly used in the production of polycarbonate plastics and epoxy resins. These materials are used in a wide range of products, including food and drink packaging, compact discs, safety equipment, and medical devices. Epoxy resins are also used as coatings for metal products such as food cans and bottle tops. Some dental sealants and composites may also contain BPA. The primary source of exposure to BPA for most people is through their diet, as it can leach into food from the internal coatings of canned foods and from consumer products such as water bottles, food storage containers and baby bottles. The leaching of BPA from polycarbonate bottles may depend more on the temperature of the liquid or bottle, rather than the age of the container. BPA can also be found in breast milk.

How can you prevent BPA exposure?

There are several ways to reduce exposure to BPA:

• Choose BPA-free products: Look for products labeled as BPA-free, particularly when purchasing food and drink containers, baby bottles, and other products that may come into contact with food or liquids.
• Avoid heating polycarbonate plastics: Avoid heating polycarbonate plastics, as high temperatures can cause the release of BPA into food or liquids.
• Use alternatives: Use glass, porcelain or stainless steel containers for hot foods and liquids instead of plastic containers.
• Reduce your consumption of canned foods: Canned foods may contain BPA in the lining of the can, so try to reduce your consumption of canned foods, or look for canned foods that are labeled as BPA-free.
• Support BPA-free legislation: Support legislation and regulations that aim to reduce or eliminate the use of BPA in consumer products.

It's also important to note that, although some steps can be taken to reduce exposure to BPA, it is a ubiquitous chemical, and it is impossible to completely eliminate exposure to it.

Phthalates

Phthalates are a group of chemicals used to soften and increase the flexibility of plastic and vinyl products. They are commonly found in hundreds of consumer products, such as cosmetics and personal care products like perfume, hair spray, soap, shampoo, nail polish, and skin moisturizers. They are also used in toys, shower curtains, wallpaper, vinyl mini-blinds, food packaging, and plastic wrap. People can be exposed to phthalates through ingestion of food packaged in plastic containing phthalates, breathing dust in rooms with vinyl mini-blinds, wallpaper, or recently installed flooring that contains phthalates, and drinking water that contains phthalates. Phthalates have been identified as a potential endocrine disruptor and are associated with various health risks, such as reproductive and developmental problems and cancer. To reduce exposure to phthalates, individuals can opt for phthalate-free products, properly wash their hands after handling products that contain phthalates, and avoid heating food in plastic containers.

Lead

Lead is a naturally occurring metal that can also be produced from human activities such as burning fossil fuels, mining, and manufacturing. It has no taste or smell, and has the chemical symbol Pb. Lead has been used in a variety of products, including batteries, pipes, roofing, electronic equipment, military tracking systems, medical devices, and radiation shielding. However, due to health concerns, lead and lead compounds have been banned from use in products such as house paint, solder used on water pipes, gasoline, food cans, and tin-coated foil on wine bottles. Additionally, the U.S. Food and Drug Administration has set limits on the amount of lead that can be used in ceramics.

Lead and lead compounds are listed as "reasonably anticipated to be a human carcinogen" and can have harmful effects on the body, whether inhaled or ingested. The central nervous system is particularly sensitive to lead exposure, and children are more vulnerable to lead poisoning than adults. High levels of lead exposure in children can lead to brain damage, convulsions, death, blood anemia, kidney damage, colic and muscle weakness. Low levels of exposure can also cause developmental and behavioral problems. Pregnant women exposed to high levels of lead may face risks such as miscarriage, premature births, and smaller babies. Chronic or repeated exposure can cause lead to build up in the body and lead to lead poisoning.

Formaldehyde

Formaldehyde is a colorless, flammable gas or liquid that has a strong, pungent odor. It is a volatile organic compound (VOC) which means it easily becomes a vapor or gas. It is naturally produced in small amounts in the human body, but can also be found in a variety of industrial and consumer products. The primary way of exposure to formaldehyde is through inhalation of air containing it. Formaldehyde can be released into the air from industries that use or manufacture it, wood products, automobile exhaust, cigarette smoke, paints, varnishes, carpets, and permanent press fabrics. It can also be found in consumer products such as nail polish and commercially applied floor finishes.