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Toxic Substances & Environmental Health

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.

Toxins

Toxic substances or toxins are those chemicals that cause adverse effects on organisms. These are also known as toxicants.

Toxicology

Toxicology is the study of the effects of toxicants.

Types of toxicity

Toxic effects are mainly divided into two types:

Acute toxicity

  • 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 toxicity

  • 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:

  1. By regulating the enzymatic activity
  2. By binding directly to cell
  3. 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
effects
Environmental effects
A. Pesticides
Aldrin/dieldrin  Chemically
manufactured
Insecticides (termites,
grasshopper)
Tremors, convulsions,
damage to kidney, suspected
carcinogenic, mutagen
Reproductive failure of birds and fish. Persistant
organic pollutants
DDT
(Dichlorodiphe
nyltrichloroethane)
Tremors,
Degradation of
central nervous
systems (CNS)
Reproductive failure of
fish, eggshell thinning in birds
Parathion (cotton, rice,
fruit trees)
Acute toxicity Kills wild life
2,4-D (2, 4-
Dichloropheno
xyacetic acid)
Herbicides(Broad-leaved
weeds)
Forms
nitrosamines in
intestinal tract
Kills wild life
B. Industrial chemicals
Asbestos Mining,
milling
Brake lining,
fire proofing,
insulation
Lung damage, lung
cancer, stomach
cancer
Environmental toxicity,
pollution
Benzene Petroleum
refining
Gas additive,
insecticides,
detergents, fibre
Anemia, bone
marrow damage,
leukemia
Environmental toxicity,
pollution
Vinyl
chloride
Chemically
manufactured
Plastic,
polyvinyl
chloride (PVC)
Toys, packages
etc.
Liver damage, birth
anomalies, liver,
respiratory brain
cancer, bone
damage
Liver damage in
mammals, kidney
damage, eggshell thinning
in birds, suspected
reproductive failure in
birds
Most toxic plastic (WHO)
C. Metals
Arsenic Mining,
smelting,
Underground
water
Glass, pesticides,
hardening agent for
copper, lead and
alloy
Vomiting, poisoning,
degeneration of liver and
kidney, lung and causes
cancer
Persists in soils,
toxic to crops
Lead Mining,
leaching
Batteries, piping in
drainage system,
coloring agent
Anemia, Kidney damage
CNS damage
Poisoning in
domestic animals,
birds and fish
Mercury Mining,
leaching,
volcanic ashes
Chlorine production,
scientific and
industrial
instruments,
batteries, pesticides
Irritability, nervousness,
depression, hallucination,
Kidney damage
Reproductive
failure, death of
fish

Structures of some chemicals

DDT (DichloroDiphenylTrichloroethane) 2,4-D (2, 4-Dichlorophenoxyacetic acid)
Source: DDT Wikipedia
Parathion (Parathion-ethyl organophosphates compound)

Vinyl Chloride

 
Source here.

 

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.
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About Abulais Shomrat

Abulais Shomrat
Currently in 4th year (Hons) in the Department of Botany, University of Dhaka. Planning to have multiple careers one by one but promised to be with 'Plantlet' as long as it's primary stage remains unfinished.

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