How to complete A Toxic Trail in Arc Raiders

Completing A Toxic Trail in Arc Raiders sees you returning to a location from a previous quest, namely where you had to find a toxic barrel dumped in a drain for the Source of Contamination quest. This time, you're revisiting the same location and the same barrel, but there are a few additional steps that might trip you up.

Considering the last thing you want to be doing is searching the swamp while there are other potentially loot-hungry Raiders on the prowl, here's what you need to do. I'd recommend foregoing a free loadout for this one, since a key you might need later drops at the end, and as we know with the Armored Transports quest, losing keys required for missions is a pain.

Return to the water intake below the Water Treatment Control building

The first step in this quest is pretty simple—you have to head back to the drain just outside and to the north of the Water Treatment Control building. Find the barrel, located on the map above by the drain to complete the first step.

You also came here previously for the Source of Contamination quest, though this time you don't actually have to examine the barrel. There are a few other steps instead.

Search the Swamp for traces of the barrel's origin

Instead of interacting with the barrel, you'll get the objective to find its origin in the swamp. This is the partly submerged truck carrying a load of barrels just to the northwest along the river, marked on the map above. Approach the vehicle and you'll get an objective to "take a photo of the barrel truck," which you do by interacting with any of the yellow marked icons around its side.

Once that's done, you have to "search the truck for clues about the saboteur's identity". Again, simply interact with the yellow icon by the door to the driver's compartment. This will drop a Spaceport Warehouse Key. Weirdly enough, you don't seem to have to pick up this key to complete the quest, but chances are you might have to use it later, so stow that in your safe pocket, or simply exfil at the Swamp elevator nearby straight away.