Agent Orange (Dioxin) was used from January 9, 1962 until May 7, 1975. 
In 1991 The United State Congress passed the Agent Orange Act. Section 2 of the Act contains one of the most important aspects of the legislation. It provides for a presumption of a service related connection between the diseases and the conditions identified in the Act and the spraying of Agent Orange.
Between 1991 and February 2002 Vietnam veteran who served on land, inland waterways, or off the coast of Vietnam were not required to present any sort of documentation as evidence for actually dioxin exposure.
In February 2002 the Department of Veterans Affairs changed their rules set forth in 1991 so that you needed to have “Boots on the Ground” in Vietnam or any of it’s offshore islands
In 2002 an Australian Study (EXAMINATION OF THE POTENTIAL EXPOSURE OF ROYAL AUSTRALIAN NAVY (RAN) PERSONNEL TO POLYCHLORINATED DIBENZODIOXINS AND POLYCHLORINATED DIBENZOFURANS VIA DRINKING WATER) found that the water distillation process would actually enhance the toxicity of any dioxin present in the original saltwater.
In August of 2001 Jonathan Haas, a veteran who served on the U.S.S. Katmai filed his claim for benefits based on the 1991 Agent Orange Act. His claim was denied and he appealed to the Veterans Court where the three-judge panel reversed the Veterans Board decision stating that the VA definition of service that required “foot on the ground” was too restrictive and was unreasonable.
In May 2008 in a 2-1 decision, the U.S. Court of Appeals for the Federal Circuit Courts reversed the Veterans Court and upheld the VA’s definition that “service in Vietnam” required “foot on the ground”. They admitted that they “ordinarily will not hear appeals from the Veterans Court in cases the Veterans Court remands to the Board of Veterans Appeals.
In 2012 and 2013, 40 years after the spraying of dioxin stopped, several areas within Vietnam still show high levels of dioxin.