The treaty lists the agents and precursor chemicals that will be subject to control.

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The new plan goes further, aiming also at the supply of the precursor chemicals used to refine the drug and at money laundering.

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In 2011, the US director of national intelligence concluded that Syria remained "dependent on foreign sources for key elements" of its chemical weapons programme, including precursor chemicals, which are generally dual-use chemicals that can be combined to produce blister or nerve agents.

BBC: Syria's chemical weapons stockpile

There were precursor chemicals.

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One key element in searching for life on Mars is the presence of methane in the Martian atmosphere As a simple carbon compound, methane is often a precursor to the formation of the complex organic chemicals that make life possible.

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