Arsenic is everywhere – but new detection methods could help save lives
- Written by Magdalena Wajrak, Senior Lecturer in Chemistry, Edith Cowan University
Arsenic is a nasty poison that once reigned as the ultimate weapon of deception. In the 18th century, it was the poison of choice for those wanting to kill their enemies and spouses, favoured for its undetectable nature and the way its symptoms mimicked common gastrointestinal issues like stomach pain, diarrhoea and vomiting.
One of the most famous deaths believed to be due to arsenic poisoning was that of French general Napoleon Bonaparte in 1821. While there’s still considerable controversy over the definite cause of Napoleon’s death, there is enough evidence that arsenic did at least contribute.
Analysis of Napoleon’s hair in 1961 found it contained more than ten times the normal concentrations of arsenic. The most likely source of exposure was from an arsenic compound used as a pigment in wallpapers in the 18th century.
Centuries later, arsenic is still widespread in the world, and causing major health problems. But thankfully scientists – including myself – are developing more effective ways of measuring arsenic to reduce the harm it causes to people.
A tasteless poison
Arsenic in its elemental state is a grey, brittle solid. Its nucleus has 33 protons and 42 neutrons, giving it similar chemical properties to phosphorus.
The elemental form of arsenic is actually non-toxic; it is the compounds of arsenic that are poisonous. Pure elements have a tendency to bond to other elements and form compounds, because this provides elements with more stability.
When arsenic combines with oxygen, it forms an extremely toxic compound called arsenic trioxide. Only 70mg of this odourless and tasteless compound is needed to kill an adult human.
When arsenic enters our bodies, it can have major impacts on DNA. Phosphorous is an essential component of the backbone of DNA, but arsenic can replace it. This can lead to genome instability and a higher risk of genetic mutations, which can ultimately increase the risk of developing cancer.
Arsenic also inhibits the enzymes necessary for bodily functions.
When arsenic is inhaled or ingested, it is rapidly distributed around the body. It initially remains in the liver before being stored in the kidneys, then the spleen and lungs. Our bodies are very clever, however, and have a process capable of removing very small amounts of arsenic through urine.
But that process takes time. So if you are exposed to high levels of arsenic, your body will not be able to eliminate it fast enough and damage will occur.
Arsenic is everywhere
The main environmental sources of arsenic are volcanoes and the erosion of mineral deposits. This can contaminate groundwater sources, as happened in Bangladesh where the building of tube wells for irrigation and drinking water from the mid 20th century onwards accidentally caused the “world’s worst mass poisoning”.
Human sources of arsenic in the environment are predominantly from smelters of copper, gold and iron ores. These smelters often use arsenic compounds such as copper arsenate to treat and preserve wood. They also use pesticides and antiparasitic chemicals, some of which contain arsenic.
We also find very small amounts of arsenic compounds in LED lights and in bronze.
The most common sources of exposure to arsenic are from cigarettes and food products. Foods grown in arsenic-contaminated soil or exposed to contaminated water will absorb arsenic.
For example, rice is very susceptible to absorbing elements from soil and water, so can contain high levels of arsenic if grown in contaminated areas. However, rice is generally safe to eat and rinsing it removes most of the arsenic it might have absorbed.
Detecting arsenic
Being able to detect and monitor arsenic concentrations in our environment and in our bodies is important for our health.
However, common analytical techniques for arsenic detection are laboratory-based and require complicated infrastructure – such as constant access to argon gas to produce a plasma – and a specifically trained chemist or lab technician.
Thankfully scientists are developing new techniques. These are not only reliable and accurate, but highly portable and simple enough to be used outside laboratories to test for arsenic in environmental, biological and industrial samples.
One of these is an electrochemical technique, known as “anodic stripping voltammetry”.
This technique can detect trace amounts of arsenic. It works by measuring the minute electric current produced by the poison. The amount of current produced is directly proportional to the concentration of arsenic in the sample.
Being able to quickly, simply and accurately detect arsenic in, say, drinking water, could reduce people’s exposure to it. In turn, this would help reduce the likelihood of future health problems, such as skin cancers.
It is impossible to eliminate arsenic from our environment. So constant monitoring of arsenic levels in the environment and food products is the best way to reduce our exposure to this notorious poison.
Authors: Magdalena Wajrak, Senior Lecturer in Chemistry, Edith Cowan University
