New Caledonia's Vale nickel company has been fined just under $US2,000 for an acid spill in 2014.
The court found the company was negligent.
In May 2014, a few litres of acid was spilled in a storage area at the port in Prony.
At the time, the company said when the leak of hydrochloric acid was detected, specialist staff immediately found its source and contained it.
Vale may appeal against the conviction.
Civil cases brought against Vale by environmentalists are yet to be heard.
The plant in Goro in the very south of the territory has had several industrial accidents, with acid spilling into the lagoon which is a World Heritage site.