What is Carcinogenicity?
Carcinogen definition can be given as the substances, radionuclide, or the radiations, which are involved directly in the formation of cancer, are known as carcinogenic substances, otherwise, as a carcinogen, and this entire process is known to be carcinogenicity.
These carcinogenic substances can damage the genome or even disrupt the cells involved in the metabolism process. Various radioactive substances are considered carcinogenic, but these substances' carcinogenic behavior is caused by the radiation they emit. Alpha particles and Gamma rays are the carcinogens examples or examples of carcinogenic substances. Also, we have non-radioactive carcinogens such as certain dioxins, tobacco smoke, and the inhaled asbestos.
Note: Tobacco smoke produces harmful gases such as carbon monoxide, cancer-causing substances. Often, carcinogenic substances are thought of as synthetic chemicals or chemical carcinogens, but they can be synthetic and natural in reality. These substances need not be toxic immediately, as they are insidious.
Carcinogenic Substances
Cancer is a disease group that causes abnormal cell growth to spread to other parts of the human body. It is a disease where the body cells get damaged. In general, carcinogenic substances increase cancer risk because they damage the body's metabolic cells. Also, they damage the cell's DNA component, which is associated directly with various biological processes in the body, leading to tumors.
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Aflatoxin B1, which is produced by a fungus, grows on the surface of peanut butter, grains, and many nuts. It is also a microbial carcinogenic substance that occurs naturally. Also, the virus hepatitis B and human papilloma can cause cancer to the person infected by them.
Besides the virus, radiations, and fungus, there are various carcinogenic substances. The substances like polynuclear hydrocarbons and benzene, which have more than two benzene rings fused together, also contain carcinogenic effects. These polynuclear hydrocarbons form when incomplete combustion of organic material like coal, tobacco, and petroleum occurs. These substances undergo biochemical reactions by entering into the human body, which damages the DNA cells and causes cancer, further leading to death.
Toxicity is the degree to which a chemical can damage the body's human cells. We have seen the carcinogenicity effect and the substances associated with it. These are highly toxic substances in nature, and their use should be avoided to sustain a healthy body.
What is Toxicity?
Toxicity is the degree to which a chemical substance or a specific mixture of substances can lead to damage to an organism. It can refer to the whole organism's effect, such as an animal, plant, or bacterium, and the effect on the organism's substructure, such as an organ or cell (cytotoxicity) like the liver (hepatotoxicity).
As an extension, the word can be metaphorically used to describe the toxic effects on more complex groups, like the family unit or society. At times, the word is less or more synonymous with poisoning in daily usage.
The central concept of toxicology can be defined as the toxic effects are dose-dependent; even water can lead to intoxication when taken in higher doses. Even a very toxic substance like snake venom, there is a dose with no detectable toxic effect.
Recently, a novel Drug Toxicity Index (DTI) has been proposed considering the limitations of this dose-response concept. DTI involves the responsibilities like, recognizes hepatotoxic drugs, redefines the drug toxicity, predicts clinical outcomes, gives proper mechanistic insights, and has the potential as a screening tool. Toxicity is species-specific, making the cross-species analysis problematic.
On the other side, the newer metrics and paradigms are gradually developing to bypass animal testing while maintaining the concept or feature of toxicity endpoints.
Types of Toxicity
There are four types of toxic entities, as given below:
Chemical,
Biological,
Physical,
Radiation:
Chemical toxicants are inorganic substances including mercury, chlorine gas, hydrofluoric acid, and organic compounds like most medications, methyl alcohol, lead, and toxins.
The biological toxicity of pathogens is difficult to measure because the "threshold dose" can be a single organism. Theoretically, one virus, worm, or bacteria can reproduce to cause a serious infection.
Physical toxicants exist due to their interference and physical nature with biological processes. Examples can be given as asbestos fibers, coal dust, or finely divided silicon dioxide, which can ultimately be fatal if inhaled.
Radiation can hold a toxic effect on the organisms.
Classification of Toxicity
Let us look at the classification of Toxicity in detail.
For the substances to be handled and regulated appropriately, they must be classified and labeled properly. Approved calculations or testing measures determine the classification. It has determined the cut-off levels set by scientists and governments (threshold limit values, no-observed-adverse-effect levels, and tolerable daily intake levels).
The pesticides provide an example of well-established toxicity labels and class systems. While currently, most countries have various regulations concerning the test types, cut-off levels, numbers of tests, the Globally Harmonized System implementation has begun unifying these countries.
FAQs on Carcinogenicity and Toxicity
1. What is meant by the terms carcinogenicity and toxicity in chemistry?
Carcinogenicity is the potential of a substance, radiation, or radionuclide to cause cancer. The agent itself is called a carcinogen. Toxicity is a broader term referring to the degree to which a chemical substance can damage an organism. While all carcinogens are toxic, not all toxic substances are carcinogenic.
2. How does a chemical carcinogen lead to the formation of cancer at a cellular level?
A chemical carcinogen typically induces cancer through a process called carcinogenesis. When it enters the body, it can undergo metabolic changes that make it highly reactive. This reactive form can then attack and bind to cellular macromolecules like DNA, proteins, and RNA. The damage to DNA, if not repaired by the cell's natural mechanisms, can lead to mutations that disrupt the normal cell cycle, causing uncontrolled cell growth and the formation of a tumour.
3. Why are benzene and polynuclear hydrocarbons considered carcinogenic as per the Class 11 syllabus?
Benzene and certain polynuclear hydrocarbons (PNHs), which contain multiple fused benzene rings, are potent carcinogens. After entering the human body, they are metabolised into compounds like epoxide derivatives. These derivatives are electrophilic and can react with DNA, causing damage and mutations that may lead to cancer. These compounds are often produced from the incomplete combustion of organic materials like tobacco, coal, and petroleum.
4. What are some examples of different types of toxic entities?
Toxic entities can be classified based on their nature. The primary types are:
- Chemical toxicants: Includes inorganic substances like lead and mercury, and organic compounds like benzene and methyl alcohol.
- Biological toxicants: Pathogens such as certain viruses (e.g., Hepatitis B) or bacteria that can cause disease.
- Physical toxicants: Substances that cause harm due to their physical properties, such as asbestos fibres or coal dust which damage lung tissue.
- Radiation: Energy emitted as particles or waves, like gamma rays and alpha particles, which can damage cells and DNA.
5. Is a substance that is highly toxic always carcinogenic? Explain with an example.
No, a highly toxic substance is not necessarily carcinogenic. Toxicity refers to any harmful effect on the body, while carcinogenicity is the specific ability to cause cancer. For instance, hydrogen cyanide is extremely toxic and can be lethal in small doses by inhibiting cellular respiration, but it is not considered a carcinogen. Conversely, a substance like asbestos has low immediate toxicity but is a powerful carcinogen with long-term exposure.
6. What is the fundamental principle of toxicology regarding the dosage of a substance?
The central concept in toxicology is that the 'dose makes the poison'. This principle states that any substance, even one as essential as water, can be toxic if consumed in a high enough dose. Conversely, for even the most toxic substances like snake venom, there exists a dose so low that it produces no detectable toxic effect. This dose-response relationship is fundamental to determining safe exposure levels for chemicals.
7. How does a co-carcinogen differ from a carcinogen?
A carcinogen is a substance that can independently cause cancer. A co-carcinogen, however, is a chemical that does not cause cancer on its own but significantly enhances the carcinogenic effect of another substance. It works by promoting or accelerating the process of cancer formation initiated by a primary carcinogen.
