|Unlike dust, which is transferred by air movement, moisture plays a major role as the binder or vehicle for contamination by dirt. When moisture combines with solid particles, e.g. cargo residues, slimy, mushy or sticky substances are formed which are deposited on the surface of the cargo and, depending upon the porosity and thus absorbency of the surface, penetrate to a greater or lesser degree into the surface of the goods. The dirt mainly sticks on or may also mix with the goods. Goods in white linen cloth bags, e.g. flour, white sugar, salt, are extremely sensitive to dirt. Workers must not walk on the bags with dirty footwear during container packing.
Once dried, rain or sweat usually leave behind discolored areas, which then give rise to claims. Contamination by dust may turn into soiling on exposure to moisture.