BINGO!!! A very common practice even though "Porta-Pottys" are mandated by OSHA here in the USA If you regularly take a dump wherever in your home country..., why walk a few thousand feet out of the field to a Porta-Potty and lose your production bonus???
I have always thought these immigrants were relieving themselves in the fields but WHY only romaine lettuce??? What about strawberries, blueberries, head lettuce, potatoes, radishes, ANY fruit or vegetables grown ON the ground!!!
Back in 1977, I worked in Durango, Mexico on a boiler installation in a paper mill. The interiors of boilers can be cavernous and have lots of dark corners in different parts of the equipment. It was the ONLY boiler in the world I worked on that have piles of human waste inside. I worked in power plants in about 12 countries, too.