Toxicology Reflections


Trihalomethanes in Drinking Water

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About Trihalomethanes

Trihalomethanes are compounds consisting of a carbon atom bound to a hydrogen atom and three halogen atoms (i.e. like methane, but with three of the hydrogen atoms replaced with halogens such as fluorine, chlorine, and/or bromine).  The halogen atoms can be of the same type or in different combinations.  Chloroform is a well-known example of a trihalomethane that has many industrial and chemical applications; these compounds are not unique to drinking water and exposure to trihalomethanes can occur due to environmental contamination as well as through drinking water.

Trihalomethanes in Drinking Water

Chlorination and filtration of water supplies if often cited as one of the greatest public health achievements of the 20th century, greatly reducing the incidence of diseases such as cholera, dysentery, and typhoid (Calderon, 2000) where implemented.  However, it was discovered in the 1970s that chlorine could react with naturally-occurring organic matter in the water to form trihalomethanes (THMs), especially chloroform.

THMs are sometimes also referred to as disinfection by-products, or DBPs.  While THMs appear to be the first DBPs recognized, we are now aware of over 600 compounds that appear in drinking water as a result of a variety of disinfection processes (Richardson, 2012).  However, only a few DBPs are regulated, and this discussion will be limited primarily to THMs formed as a result of chlorination.

There are four trihalomethanes that have historically been of concern in drinking water, which are sometimes grouped under the heading total trihalomethanes or TTHMs:

  • Chloroform (CHCl3)
  • Bromodichloromethane (CHCl2Br)
  • Dibromochloromethane ( CHClBr2)
  • Bromoform – (CHBr3)

Of these, it is chloroform that forms the basis for the minimum acceptable concentration of THMs in Canada (with respect to drinking water standards), because it the compound for which the most data on toxicological effects is available.  The drinking water standard is based on the cumulative dose of all four THMs.  Canada also has a separate standard for bromodichloromethane (even though it is also included within the trihalomethane guideline).  The guidelines are primarily based on evidence from animal studies that identify chloroform as a potential carcinogen.  Human studies have also suggested links to cancer, and at high levels reproductive effects.  It has been suggested that trihalomethanes that contain bromine are more toxic than chloroform, and bromodichloromethane has been identified as a carcinogen in rodent studies (it is thought to be the most potent carcinogen of the four trihalomethanes being considered, at least in rodents)(Health Canada, 2006).  Other guidelines are in effect elsewhere, as will be discussed in future reflections along with the rationale for these guidelines.

Other topics for reflection will included balancing the concern over trihalomethanes against the benefits of disinfecting water supplies, the importance of exposure routes, considering the risk of trihalomethanes relative to the risks of byproducts from alternate disinfection methods and relative to the hundereds of other disinfection by products.


References cited:

Calderon, R. L. (2000). The epidemiology of chemical contaminants of drinking water. Food and Chemical Toxicology38, Supplement 1(0), S13–S20.

Government of Canada, H. C. (2006, May 2). Guidelines for Canadian Drinking Water Quality: Guideline Technical Document: Trihalomethanes – Health Canada. publication. Retrieved September 10, 2013, from

Richardson, S. D., & Postigo, C. (2012). Drinking water disinfection by-products. In Emerging Organic Contaminants and Human Health (pp. 93–137). Springer. Retrieved from




Importance of Soil Background Concentrations

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Decisions on the remediation of metal contaminated soils are based on risk estimates derived from soil guideline values. Soil guideline values for metals are most commonly based on toxicological reference values. However guideline values are not only a reflection of scientific understanding but also reflect political decisions and legislative requirements, implemented by the regulator.

The United Kingdom is one such example of how changes to legislation of influenced the need to understand background soil concentrations. Part 2A of the contaminated land stator Guidance was issued by Department of Environment, Food and Rural Affairs in April 2012 (Defra, 2011). This guidance outlined changes to how contaminated land would be considered in the United Kingdom. Under this new guideline the term “normal” was introduced to the regulatory system with the requirements to remediate soils to normal levels.

Normal background concentration of soil contaminants not only includes geological and natural variation in soil element concentration but that of historical contamination and “normal” concentration of different elements found in soils of different environments (urban vs. rural). This series of post will be considering the important of determining soil background concentration and the different approaches which can be used to derive background concentration of soil contaminates in the environment.

Defra, 2011. Draft Contaminated Land Statutory Guidance


The Controversy of Caffeine

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There is a lot of debate around whether caffeine is “safe” or not.  There are old wives’ tales regarding coffee stunting children’s growth and leeching calcium from bones.  But does it?  Caffeine is often used as a stimulant to help users stay mentally and physically alert.  What sorts of benefits does it really give?  Nearly all of us have felt our hearts race after an energy drink or an extra strong cup of coffee.  Could caffeine be to blame for heart disease and high blood pressure?  Does it cause cancer?  Is it addictive and can you experience withdrawal?  Some tout it as a cure for hyper activity and/or ADHD.  Since it crosses the blood-brain barrier how much is “safe” for adults?  Could it be a leading cause of infertility? What are its effects after crossing the placental barrier?  Is it “safe” for children? Is caffeine really “good” or “bad”?  For such a ubiquitous substance I feel I have a severe lack of knowledge on the subject.  With the following posts I hope to educate myself and readers on one of my favourite substances.  By discussing findings in the literature hopefully some of the questions asked above can be answered.

So where does dietary caffeine come from?  Caffeine (1,3,7-trimethylxanthine) is a nitrogenous organic compound produced by plants.  It is found in the seeds, fruit and leaves of plants such as coffee (beans), cocoa (beans), tea (leaves), and kola (nut).  When these plants are ingested we inevitably intake some caffeine.  Caffeine compounds are also added to consumables such as soft drinks, chocolate, energy drinks, and medications (cold, headache and pain remedies, over the counter stimulants and other drug products)1,2.  According to Health Canada Canadian adults get approximately 60%, 30% and 10% of their caffeine from coffee, tea and cola beverages/chocolate/medicines respectively.  Children (1-5yrs) get approximately 55%, 30% and 14% from cola drinks, tea and chocolate respectively.

Health Canada1 recommends healthy adults keep caffeine intake to 400 mg/d (about 3 8oz cups of brewed coffee), 300 mg/d for women of childbearing age and 2.5mg/kg for children.  That is approximately 45mg for children 4-6 years old, 62.5mg for children 7-9 and 85 mg for children 10-12.  These ranges encompass about 1-2 12oz cans of cola per day (considering the health effects of caffeine only).  To accurately calculate your daily caffeine intake visit Health Canada’s website where they provide a detailed guide on amounts of caffeine found in various foods.

For some additional information on caffeine consumption visit these websites (accessed September 2013).

Graphs on international coffee consumption

Interesting graphs on Canadian beverage consumption – soft drink industry website

Nawrot P, Jordan S, Eastwood J, Rotstein J, Hugenholtz A & Feeley M (2003) Effects of caffeine on human health.  Toxicological Evaluation Section, Chemical Health Hazard Assessment Division, Bureau of Chemical Safety, Food Directorate, Health Canada.  Food Additive and Contaminants 20,1-30.

Health Canada (2013)  Caffeine: It’s your health. (accessed September 2013).