Toxicity is the degree to which a substance can damage an organism. Toxicity can affect a whole organism, such as an animal, bacterium, or plant, as well as a cell (cytotoxicity) or an organ such as the liver (hepatotoxicity). Toxicity effects are dose-dependent; so, even water can lead to water intoxication when taken high dose, and even a very toxic substance such as snake venom there is a dose below which there is no detectable toxic effect.
Toxic substances or toxins are those chemicals that cause adverse effects on organisms. These are also known as toxicants.
Toxicology is the study of the effects of toxicants.
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Types of toxicity
Toxic effects are mainly divided into two types:
- Acute effects are manifested immediately after exposure.
- These are often short-lived and are generally caused by high levels of exposure.
- e.g. a headache while riding home in rush-hour traffic which may have been caused by CO from automobile exhaust.
- Chronic effects are delayed and long-lasting.
- These are generally the result of low-level exposure.
- e.g. changes in the normal anatomy and physiology of an organism.
- They may include cancer, mutation, birth effect and reproductive impairment.
- Toxicity due to arsenic consumption results into arsenicosis.
Mechanism of toxicity
Toxic substances work in 3 major ways:
- By regulating the enzymatic activity
- By binding directly to cell
- By releasing chemical substances
1. By regulating the enzymatic activity
- Enzymes regulate many important chemical reactions.
- Toxins can affect the functions of these enzymes.
- Therefore, the function of an organ or tissue may be altered seriously by the disturbance of enzymatic activity.
- For example, mercury (Hg) and lead (Pb) both bind to certain enzymes, blocking their activity.
- The activities of antioxidant and digestive enzymes superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT) are affected by Hg.
2. By binding directly to cell
- Toxins may bind directly to cells as molecules within the cell.
- As a result the chemical balance within the body is upset.
- For examples, CO binds to hemoglobin in blood, this interferes with the transport of O2 and can lead to death if levels are high enough.
3. By releasing chemical substances
- Toxin may cause the release of other naturally occurring substances that have an adverse effect.
- The toxin carbon tetrachloride (CCl4), used as fire extinguisher or cleaning agent, stimulates certain nerve cells to release large quantities of epinephrine (adrenaline) which is believed to cause liver damage.
Some toxic chemicals and their effects
|Category||Original source||Uses||Human health
damage to kidney, suspected
|Reproductive failure of birds and fish. Persistant
|Reproductive failure of
fish, eggshell thinning in birds
|Acute toxicity||Kills wild life|
|2,4-D (2, 4-
|Kills wild life|
|B. Industrial chemicals|
|Lung damage, lung
|Liver damage, birth
|Liver damage in
damage, eggshell thinning
in birds, suspected
reproductive failure in
Most toxic plastic (WHO)
hardening agent for
copper, lead and
degeneration of liver and
kidney, lung and causes
|Persists in soils,
toxic to crops
|Batteries, piping in
|Anemia, Kidney damage
birds and fish
failure, death of
Structures of some chemicals
|DDT (DichloroDiphenylTrichloroethane)||2,4-D (2, 4-Dichlorophenoxyacetic acid)|
|Parathion (Parathion-ethyl organophosphates compound)||
Good to know
- Asbestos: Six chemicals are defined as asbestos including-chrysotile, amosite, chrocidolite, tremolite, anthophyllite, and actinolite.
- Lead and mercury is a neurotoxin that accumulates in soft tissue of bone over time.