I'm addicted to you, don't you know that you're toxic?!

I'm addicted to you, don't you know that you're toxic?!

It is one of the lines on the song of Britney Spears toxic. Being addicted to something is not good, because you’re being dependent to it and sometimes you think you can’t complete your day without it. The degree of the harm that a chemical can cause to someone will depend on the dose that a person takes in or the degree of the exposure as well on the other factors.

What is Toxicology?

Toxicology is the study of adverse effect or interaction of chemicals to a living organism.  It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people. 

Toxic substances may be organic or inorganic in composition

Chemical hazards in the workplace and in the environment
People may be exposed to a range of toxic chemicals at work or in the general environment. Here are some examples:

Category	Examples
Metals, and metalloids	arsenic, cadmium, lead, mercury, nickel, tin, etc
Inorganics (other)	asbestos, carbon monoxide, hydrogen sulphide
Hydrocarbons - aliphatic	propane, butane, pentane, hexane
Aliphatic alcohols, ketones, ethers, aldehydes and acids	ethyl alcohol (ethanol), acetone, diethyl ether, formaldehyde, acetic acid
Hydrocarbons - aromatic	benzene, toluene, xylene, naphthalene
Phenols	phenol, pentachlorophenol
Chlorinated volatile organic compounds	perchlorethylene (tetrachloroethene), trichloroethylene (trichloroethene), vinyl chloride
Chlorinated non volatile organic compounds	chlorinated dioxins and dibenzofurans, polychlorinated biphenyls, pesticides such as chlordane and DDT
Miscellaneous organic compounds	acrylonitrile, benzidine, aniline, di-isocyanates, organophosphates

Toxicokinetics

 - or how the body handles poisons 

Absorption into the body

• As a general rule, fat soluble liquids are readily absorbed through the skin and fat soluble vapours are readily absorbed through the lungs. Notably these routes apply to organic solvents such as hexane, toluene, trichlorethylene and many others. 

Distribution within the body

• Many factors affect the delivery of a toxic material but water or fat solubility is very important. Thus for example water soluble compounds of lead are found (amongst other places) in the red blood cells, while fat soluble ones concentrate in the central nervous system (CNS).
• The distribution of a toxic substance determines its concentration at a particular tissue and therefore the number and type of cells exposed to high concentrations of it. 

Routes of elimination of toxic substances / or their metabolites

• Kidneys - especially water soluble substances
• Lungs - especially fat soluble vapours e.g. - alcohols, or gases such as carbon monoxide

Toxicodynamics

-         or what poisons may do to the body

A note on terminology: 

• Acute effects refer to the short term consequences of  exposure
• Chronic effects relate to a much longer time scale, while  sub-acute are in between acute and chronic)
• Some effects may be dose related - the higher the exposure the worse it gets e.g. irritant effects on the skin, asthma, asbestosis etc
• Other effects are 'all or none' and for a given exposure there is an element of chance (stochastic) as to whether or not the disease develops e.g.the development of cancer (carcinogenesis) or some forms of developmental damage to the foetus (teratogenesis)

Other effects  on specific organs:

You may wish to refer to another resource on specific organ damage, but here are some other points: 

• 'Heavy' metals e.g. Pb (lead) Cd (Cadmium) and Hg (mercury) have a propensity to bind sulphur and indeed in nature in the earth's crust are often found as sulphides. they tend to bind to sulphydryl groups -SH in enzymes and other proteins and cause damage in various parts of the body
• The lungs are often the subject of damage e.g paraquat poisoning
• Cardiovascular effects include arrhythmias e.g. caused by trichloroethane or by carbon disulphide
• A very specific effect of exposure to some poisons such as the organophosphate insecticides (e.g. malathion, parathion) relates to their anticholinesterase effect. Synaptic transmission from a nerve cell to another cell such as a muscle cell in many situations relies on acetyl choline. The enzyme  acetylcholinesterase in nerve endings catalyses the hydrolysis of acetylcholine to choline and acetylCoA, thus determining a very short action of acetylcholine. Organophosphate and carbamate pesticides inhibit acetylcholinesterase and lead to accumulation of acetylcholine at sites of  neuromuscular transmission causing weakness of muscles, and paralysis including of respiration.
• Endocrine mimicking agents can act as endocrine disrupters

Prevention and treatment

Preventing exposure: 

Through the practice of good occupational hygiene

Treatment: 

• Decontamination e.g. eye washes, showers, etc 
• Antidotes e.g. methylene blue for treating methaemoglobinaemisa caused by aniline
• Other treatment e.g. oxygen for asphyxia

Note:

For a more detailed account of occupational and environmental toxicology, another resource comes strongly recommended.

References:

• http://www.agius.com/hew/resource/toxicol.htm
• http://www.eoearth.org/article/Toxicology

Photo Credit:

• http://www.niehs.nih.gov/research/atniehs/labs/assets/images/i_k/laboratory_of_reproductive_developmental_toxicology.jpg
• http://www.google.com.ph/imgres?q=cartooned+cigarettes,alcohols,+drugs&start=99&um=1&hl=fil&noj=1&gbv=2&tbm=isch&tbnid=esYpso_a-6EmDM:&imgrefurl=http://www.cartoonstock.com/directory/m/marijuana.asp&docid=i-fOKE9Hi0aAzM&imgurl=http://www.cartoonstock.com/newscartoons/cartoonists/tzu/lowres/tzun1672l.jpg&w=354&h=400&ei=WWcCUN-oHdCdiAfujICvDQ&zoom=1&iact=hc&vpx=510&vpy=304&dur=4724&hovh=239&hovw=211&tx=109&ty=138&sig=106511949639111273421&page=5&tbnh=143&tbnw=127&ndsp=24&ved=1t:429,r:8,s:99,i:31&biw=1237&bih=653
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