Thallium is a bluish-white metal that, in pure form, is odorless and tasteless.  When combined with other substances like chlorine or iodine, it turns colorless-to-white with maybe a slight yellow tinge.  It dissolves easily in water.  In other words, it’s not easily detected when mixed with food or drink.  Hmm!  Sounds like an interesting substance if you need a character killed off.

In years past, thallium was used as a rat poison and an ant killer, but since 1975 it’s been banned in the United States (and many other countries as well) due to safety concerns.  It’s highly toxic and readily absorbed through the pores as it comes into contact with skin.

Thallium’s extreme toxicity results in part from its chemical properties being similar to potassium.  It uses the body’s potassium uptake pathways to be absorbed but bypasses the natural self-limiting mechanism we have for potassium ingestion.  Thallium also binds easily with sulfur, an element essential for nutrient absorption and utilization.  It disrupts necessary cellular processes and that’s a primary reason it was such a good rat poison.

One of its more distinctive side effects is hair loss.  In fact, it was once used as a depilatory agent before its toxicity was fully appreciated.  Another distinctive sign of thallium poisoning is that it damages peripheral nerves, causing excruciating pain.  Victims are said to experience severe stomach cramps and nausea, and they experience sensations similar to walking slowly over hot coals.

Thallium was very popular in the past as a murder weapon.  In fact, thallium has often been referred to as “The Poisoner’s Poison” and “The Inheritance Powder”.  Investigations into suspicious deaths have discovered thallium in tea, sodas, soups and various foods.  Radioactive thallium poisoning was said to be a favorite of KGB assassins and documentation suggests that Saddam Hussein used it to poison dissidents.

Murders from thallium have fallen out of favor in mystery novels but the substance has taken center stage in thrillers and stories of international intrigue.  Primarily, that’s because of its antidote, Prussian blue.  Although Prussian blue has been around since the early 1700’s as a color pigment, more recently it has been designated as a counter-terrorism agent.  It’s not only recognized as a poison antidote but also as a decontamination treatment for radioactive poisonings: radioactive cesium and thallium in particular.  No good thriller can end without the hero saving the day, and having a treatment option available is a definite plus.

But be warned!  There are now diagnostic tools to detect and quantify thallium poisoning in blood and urine to aid medical and legal investigations into suspicious deaths.  Normal body concentrations are minimal, usually less than 1 mcg/L.  But a poison victim could have concentrations in both blood and urine of 1-10 mg/L (a thousand to ten thousand fold increase).  And without body fluid analysis, symptoms could be attributed to other illnesses and a proper diagnosis not made until it’s too late.

Depending on the thallium dosage and the duration of exposure, a patient may recover with the Prussian blue antidote and other life support treatments.  More likely, however, the victim will be beyond hope and die a painful death within days of exposure.

In my research I found many references to thallium being used as an effective poison in real life criminal situations and a multitude of references for its use as a poison in books, television episodes and movie plots.

Fortunately, thallium is more regulated now than in the past and used mostly in manufacturing electronic devices and semiconductor parts, but I’m sure a creative villain can find a source when the need arises.

Thoughts?  Comments?  I’d love to hear them!