The Grel'lix wanted Redjuice, an iodine derivative. They are not originally part of the Treaty.
In exchange, they gave the humans of Earth-Be Antimony, which they need for various technological processes.
Negotiations took place on their moon, which has lower, more Earth-like gravity than the planet's surface.
Enough materials were traded to cover the nations for the next 3 years while trade procedures are established.
The Antimony has been shown to carry unknown contaminants that emit Phi-Radiation.
A small amount of Phi-Rad exposure is expected, as this poorly-understood wave which impacts both space and time at once is the key to interstellar travel.
This emitter, however, releases unorthodox levels.
Left unchecked, Phi-Radiation via this transmission causes horrific mutations.