The forest products industry can place a particularly heavy burden upon the environment. The chemicals and organic matter in the waste liquid from pulp mills are normally disposed of in adjacent water bodies (inorganic salts, mercury, and heat are all released); unpleasant odours and gases, some of which are toxic in concentrated forms, are produced; and sulphur dioxide, sulphides, and particulate matter are also released. Pollution - particularly noxious smoke and particulate contamination of the air - is also created by the mechanical woodworking industries such as sawmilling, and plywood, particle-board, and fibreboard manufacture. Timber preservatives may be toxic and some of the older creosote-based fungicides are carcinogenic.