Def line (s) location

Ok, I changed my oil and filter last night and saw white chalky residue on my oil filter housing and in the immediate area. I've spilled def when I filled my tank a couple months ago so I do know it's white and sorta crystal looking. This kinda looked like that but after a while of crawling around under my truck I gave up. Do def lines (from the tank) run near the drivers side of the engine? Any ideas what else could have made the white mess on that side of the engine if it wasn't def? Thanks in advance for any assistance!