Classification of environmental toxicants causing harm to life

Poisonous substances produced inside the body of a living organism is called a toxin. The synthetic or non-natural products produced as a result of human activity like waste products of the industry are called toxicants. It is a measure of the degree to which a substance can harm the body of an organism.

Factors affecting toxicity

Following factors can influence the toxicity of a substance;

• The passageway of entrance in the body is either absorbed through the skin or inhaled.
• Contact time with the toxicant.

Terms used for toxicant exposure

Acute exposure

Acute exposure means sole exposure and as a result, disturbs the metabolism of the body.

Chronic exposure      

Long-term exposure to a chemical substance causes damage to the body.

Classification

Toxicants are classified based on different factors include;

Based on toxicant source

Toxicants derived from plants 

Curare these are extracts of a plant used in the poisoning of the arrow. Curare stops the Nicotinic Acetylcholine Receptors. It causes death by asphyxiation and also causes muscle problems like skeletal muscle problems.

Strychnine is very toxic and has no color, control the population of the vertebrate pest. It causes death due to asphyxia and  originated from tree seeds named Strychnos nux-vomica

Animal toxicants (zoo-toxins)

These are a mixture of long chains of peptides and damage the body cells. Venom is a combination of polypeptides, enzymes, and many other substances. All these combine to damage the cells or disturb nerve impulse transmission. 

Toxicants derived from minerals 

Lead is a very lethal metal and shows its effects on all body parts. Mostly lead is absorbed in the blood. It binds with the sulfhydryl group on enzymes or replaces cofactors their metals(cofactor) include calcium, and iron, and zinc. When ion and calcium level increases it prevent poisoning and when level decreases chances increases. 

Copper

Copper toxicity can not be chronic in the case of humans due to the transport system that is continuously regulating the rate of excretion and rate of absorption. This system does not work properly when a mutation occurs in autosomal recessive alleles and result in Wilson’s Disease due to an increase of copper in the body and if two defective genes are transferred in the next-generation it leads to the destruction of liver enzymes.

Selenium

This mineral is present in the soil, water, and various foods too. It is required in little quantity but plays a very important role in body metabolism.

 Iron

Iron causes poisoning when a very large amount of iron accumulates in the body. Its amount varies according to body size or weight. More than 20mg/kg show symptoms according to the weight of the child.

Man-made toxicants

Organophosphate poisoning occurs due to (OPs). Organophosphates are used to kill insects. These signs appear due to the poisoning of organophosphate; spitting and nausea, puzzlement, etc. These symptoms can appear in few minutes to an hour and sometimes appear after several weeks. 

Aluminum phosphide toxic effects appear when phosphine gas is released and due to hypoxia oxidative phosphorylation stops and results in failure of circulation. There are no medicines for ALP toxicity that’s why the death rate increases about 37 percent to 100 percent(37-100%).

Based on toxicant physical

Gas toxicants

Hydrogen cyanide(HCN), it is also called prussic acid, abbreviated as HCN, has no color, lethal, and catch fire rapidly, and has a boiling point of 25.6°C.

Carbon monoxide, abbreviated as CO has no color and smell.CO gas is produced due to the burning of fuel in engines of vehicles. Its presence show symptoms like pain in the head, stomach problems, nausea, pain in the chest, and nervousness. Those people who have drunk or sleeping died without showing any kind of symptoms. Carbon monoxide affects equally all age groups

Sulfur dioxide is a gas that has a smell like a burnt match stick and is produced during a volcanic eruption, during the copper extraction process, and when fossil fuels are burnt having sulfur-containing compounds.

Liquor toxicants

Sulfuric acid also called oil of vitriol, is a combination of H₂, O_2, and S that have no color, smell, and usually thick and can easily dissolve in water and produced during an exothermic reaction. 

Nicotine is a hazardous and very addictive compound. It increases the blood pressure, heartbeat rate, blood Nicotine also hardens the walls of arteries which result in myocardial infarction.

Solid toxicants: e.g. strychnine, opium.

Opium this toxicant is derived from Papaver somniferum. Seeds capsules of opium poppy are the main source of opium and about twelve percent of opium is derived from pain-relieving alkaloid morphine which is further used to form heroin and other medicines.

Strychnine is very toxic and has no color. This is used to control the population of the vertebrate pest. It causes death due to asphyxia and originated from tree seeds named Strychnos nux-vomica.

Dirt toxicants

It includes all types of dust like silicon and metallic dust.

Based on the materialistic characteristics

Inflammable & Non-inflammable

      Flammable toxicants are:

• 1,3-Butadiene
• Carbon monoxide
• Dimethylamine

Explosive / Non-explosive

A volatile (or explosive material) is a chemical substance that has very high potential energy and results in the blast when suddenly released and also produce heat, sound, and light

Based on physical effects

Irritant / Non-irritant

Those substances harm or injured the body organs even when the person is exposed to toxicants only once. Early symptoms are very light and sometimes invisible in case of a weak irritant. But if weak irritants come in contact again and again then they cause complexity. In the case of strong irritants, serious symptoms like breathing problems appear.

 The best examples are:

• Washing powder and washing soaps
• acids
• solvents

Corrosive / Non-corrosive

A Corrosive substance is a very reactive substance and harms the tissues of the body. Corrosive substances do not affect directly body parts or indirectly by swelling of the targeted area.

• He
• Kr
• Ne

Based on target site

Toxicants not only affect a single site they also affect many other neighboring sites so it is not easy to classify toxicants based on their target site  and here we classify the toxicants based on their primary action site; 

• Hepatotoxins (Damage the liver) e.g. CCl₄, *aflatoxins, *Phenol.
• Neurotoxins (Damage to nerve tissue) includes1- organophosphorus insecticides 2-pyrethroids, anesthetics, 3-nicotine.
• Nephrotoxins (Damage to the kidney)includes pb, cd
• Pulmonic—Toxicants (Damage to the respiratory system) include 1-alpha-naphthylthiourea (ANTU), 2-H₂S, 3-ammonia gas.
• Haematotoxins (Damage to red blood cells) 1-warfarin, 2-CN, 3-phenothiazine, 4-snake venom (pit viper venom).
• Dermatotoxicants (Damage to the skin)1- compounds of tar coal,pb, and cd.

 On basis of the nature of toxicant

Inorganic toxins: Based on the chemical nature of toxicant can be acid and base, metallic or nonmetallic.

• Metals, include *lead, Cu, *mercury, *antimony.
• Non-metals includes PO₄, S, Cl, NO₂.
• Acids, salts.   

Raw toxins: Toxicants having C containing elements and not oxides of carbon are called organic toxicants.

• Hydrocarbons includes -cyclopropane, C₆H₆ , -paraffin, -naphthalene.
• Derivatives of halogen hydrocarbons eg CCl₄.
• Alcohols and phenols include CH₃OH, C₂H₅OH,

On basis of diagnostic behavior

Based on diagnostic or analytical behavior toxicant are classified in these categories;

• Explosive—toxicants
• Acid extractable toxicants 1-organic acids, 2-nitro compounds.
• Alkaline extracted toxicants. alkaloids
• Metals and metalloids include Cu, Hg, Zn

On basis of toxicant effect

A single toxicant affects one site at a time and it is not easy to classify them.

• Cancer-causing toxicant includes thiouracil, vinyl chloride, nickel.
• The mutation causing toxicant includes UltraViolet light.
• Birth defect causing toxicant
• Clastogens includes ultraviolet light.

On basis of toxicant principle use

• Insect killing chemicals include* pyrethroids.
• Fungi killing chemicals include *captan.
• Herb destroying chemicals include *triazine,
• Rodent killing chemicals.
• Foodstuff

Based on health and environmental hazards

• Air pollutants: Air pollutants cause air pollution. This pollutant includes dust particles, factories emission, plant pollens, and gases. Ozone gas is the source of air pollution called smog.
• Water pollutants: Water bodies pollute by garbage, pesticides, explosive substances, dung, acid rain, etc. Diseases caused by drinking contaminated water are typhoid, diarrhea, amebiasis, etc.
• Radiation hazards: Radiation sources are atomic plants and power plants. It can cause diseases like skin problems and sometimes heart problems and cancer.

Reviewed by:
Dr. Muhammad Adnan Asghar (Ph.D.)
Chinese Academy of Sciences Fuzhou, Fujian