It’s not often that I come across a method to kill a character in a novel with delightful efficiency and flair, but thallium is one of those chemicals.

Thallium is a bluish-white metal that, in pure form, is odorless and tasteless. When combined with chorine, it turns colorless and dissolves well in water. That means it’s not easily detected in food or drink. To me, thallium seems like a perfect substance to kill a fictional character.

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 due to safety concerns. It’s highly toxic and readily absorbed through the pores of skin.

Thallium’s extreme toxicity is due in part to its chemical similarity to potassium. It uses the body’s potassium uptake pathways to be absorbed, although it bypasses the natural self-limiting mechanism that we have for potassium ingestion. Thallium also binds with sulfur, an element essential for nutrient absorption and utilization, and it disrupts necessary cellular processes. That’s primarily why it’s such a good rat poison.

One of its more distinctive side effects of thallium 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, nausea, and sensations similar to walking slowly over hot coals—in short, it’s a dramatic way to kill off a character you no longer need.

Thallium was very popular in the past as a murder weapon. In fact, it was often 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 more recent mystery novels, but the substance continues to take center stage in thrillers and stories of international intrigue.

But be warned! There are now diagnostic tools to detect and quantify thallium poisoning in blood and urine to aid medical and legal investigators looking into suspicious deaths. Normal body concentrations are minimal (usually less than 1mcg/L), but a poisoned victim could have a thousand to ten thousand times this normal level (1-10mg/L). But without body fluid analysis, symptoms easily could be attributed to some other illness. It’s reasonable to assume that proper diagnosis might not be made before death occurs.

Depending on the thallium dose and the duration of exposure, a patient might recover with an antidote (Prussian blue, for example) and other life support treatments. More likely, however, the victim will be beyond hope and die a painful death within days of exposure.

Fortunately, thallium is more regulated now than it was in the past. Presently, it’s used mainly for manufacturing electronic devices and semiconductor parts. However, I’m sure a creative villain can find a reliable source when the need arises.

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