Various CBRNE (Chemical, Biological, Radiological, Nuclear, and Explosive) weapons can be used for area denial, as long as the agent is long-lasting. Fallout from nuclear weapons might be used in such a role. While never actually employed in this form, its use had been suggested by Douglas MacArthur during the Korean War, who proposed spreading radioactive waste across transportation corridors to inhibit the movement of Chinese and North Korean forces. 
Anthrax spores can contaminate the ground for long periods of time, thus providing a form of area denial. However, the short-term (tactical) effects are likely to be low - the psychological effects on an opponent would likely be more significant.
The massive use of defoliants such as Agent Orange can be used as an interdiction measure because they leave areas empty of any form of vegetation cover. In the desert-like terrain that ensues, it is impossible for the enemy to travel without being seen, and there is little cover in case of an attack, especially from the air.
Many chemical weapons also produce toxic effects on any personnel in an affected area. However, this usually has no tactical value, as the effects of indirect exposure do not develop fast or substantially enough - though again, the psychological effect upon an enemy aware of the chemical usage may be considerable. There are however some chemical agents that are by design non-degrading, such as the nerve agent VX. Sulfur mustard (mustard gas) was extensively used by both German and allied forces on the west front in World War I as an effective area-denial weapon, usually through contaminating large land stripes by extensive shelling with HD/Gelbkreuz ordnance. Since sulfur mustard is very persistent, involatile, hard-to-decontaminate and highly effective in inflicting debilitating casualties at even low doses, this tactic proved to be very effective.