The use of chemical weapons is nothing new. Already in ancient times, the Persians ignited bitumen and sulfur crystals to produce gases to poison Roman soldiers. During the First World War, the use of chlorine gas was widespread, marking the start of the modern era of warfare involving weapons of mass destruction. Altogether, around 124,000 metric tons (137,000 tons) of chemical weapons were utilized during World War I, killing 90,000 people and affecting the health of one million others. German chemist and Nobel Prize-winner Fritz Haber was the key figure in the development of poisonous gases for usage in warfare.

Chemical weapons have been controversial from the start. Already in 1925, the Geneva Protocol prohibited their use. Despite this, they continued to be employed in World War II, the Vietnam War and the Gulf War. Their destructive force was particularly evident during an attack on the Iraqi city of Halabja on March 16, 1988, in which around 5,000 people were killed.

Efforts to ban chemical warfare continued, however, achieving success in April 1997 with the Chemical Weapons Convention, which has to this day been signed by 188 states. Not party to the agreement are Angola, Egypt, Israel, Myanmar, North Korea, Somalia, South Sudan and Syria. The convention obliges members to destroy existing chemical weapons. The organization behind the agreement, the Organization for the Prohibition of Chemical Weapons (OPCW), sits in The Hague and oversees the implementation of the guidelines.

Different types of damage

Chemical weapons are typically lethal chemicals housed in munitions such as mines, hand grenades, bombs, spray tanks and rockets. They either suffocate, paralyze, or poison the victim. Initially, they consisted of poisonous gases, such as chlorine, or hydrogen cyanide; however, these proved to be too volatile.

The industry then began producing liquid poisons, which not only affected the lungs but could enter the body through the skin and spread quickly. Particularly potent is mustard gas, which was first produced by a Belgian chemist in 1822 and used to maim and kill thousands of people during World War I.

Sarin, whose use has been suspected in the current Syrian conflict, is classified as a nerve agent. Developed during World War II, it is fatal even in small doses. It can be inhaled, or can enter the body through skin contact.

"A person cannot protect themselves against sarin unless they are wearing a full-body suit," said Gunnar Jeremias, Head of Research for Bio-Weapons Control at the Center for Science and Peace Research at the University of Hamburg. "It disrupts the contact between nerve cells and through this causes respiratory failure."

Long-lasting consequences

Although not always lethal, exposure to chemical weapons often has devastating health consequences, such as blindness, skin damage and birth defects. Some chemical weapons cause long-lasting environmental contamination. One of these is Agent Orange, a defoliant used by the US military during the Vietnam War. An estimated two to four million people are suffering its after-effects today in the Southeast Asian country.

"It's not classified as a chemical weapon under international law because its intended effect is not killing or injuring people, but the defoliation of forested areas," explained Jeremias. "But, of course, you can see that many people have died or suffered illness as a result."

Easy to make and resilient

The production of chemical weapons is relatively simple. More difficult is the acquisition of the necessary ingredients. The Chemical Weapons Convention also applies to the production and sale of substances which might be converted into chemical weapons. Experts believe that such substances are traded on the international black market.

In addition to everything else, chemical weapons tend to be highly durable. This is why chemical munitions from the First World War that are still sometimes found today in the German-French border region need to be disposed of with great care. Meanwhile, both the US and Russia are believed to still possess large stockpiles - going against the international convention.