TITLE:
Long-Term Fate of Agent Orange and Dioxin TCDD Contaminated Soils and Sediments in Vietnam Hotspots
AUTHORS:
Kenneth Ray Olson, Lois Wright Morton
KEYWORDS:
Soils of Vietnam, Agent Orange, Dioxin, TCDD, Herbicides, Soil Contaminant, Sediment Contaminant, Half-Life, Hotspots, Operation Ranch Hand, US Airbases in Vietnam, Vietnam War, Cu Chi Soil Tunnels, Guerilla Warfare, Incineration
JOURNAL NAME:
Open Journal of Soil Science,
Vol.9 No.1,
January
31,
2019
ABSTRACT: The soils, tropical climate, and network of canals and rivers of southern
Vietnam have created one of the most diverse tropical jungles and intensely
cultivated landscapes of Southeast Asia. This paradise has a long history of
numerous wars, foreign occupations, and most recently the Second Indochina
War (aka the Vietnam War 1965-1972) which defoliated rain forests and ancient
wetland mangroves and left behind contaminated soil and sediment
hotspots. During this war, the United States (US) military sprayed 80 million
liters of Agent Orange contaminated with the dioxin TCDD in a guerrilla war
against communist insurgents. Agent Orange was a synthetic plant growth
regulator comprised of equal amounts of two herbicides 2,4-dichloro phenoxyacetic
acid C8H6Cl2O3 (2,4-D) and 2,4,5-trichlorophenoxyacetic acid
C8H5Cl3O3 (2,4,5-T). TCDD, the dioxin, 2,3,7,8-tetrachlorodibenzodioxin
(C12H4Cl4O2) was an unintended byproduct of the accelerated combustion
process used in the manufacture of herbicides containing 2,4,5-T. Agent
Orange has frequently been blamed for soil and sediment contamination and
long-term human health problems; however, the true source of harm is the
dioxin TCDD. Agent Orange has a short half-life of days and weeks after application
to vegetation, and has not been found to persist, after 50 years, in
the water or soils of southern Vietnam. However, the half-life of dioxin
TCDD depends on where it is deposited and varies from 1 to 3 years on soil
surfaces that have been fully exposed to sunlight, to as long as 20 to 50 years
or more when buried in tropical subsoils, and more than 100 years in river
and sea sediments. Dioxin TCDD was heavily concentrated in the US Air
Force bases in Vietnam where the herbicides were stored, loaded on planes
and helicopters for aerial spraying, and used extensively around military base
perimeter fences as a security measure to prevent surprise attacks. Bien Hoa
Air Force base, 40 km northeast of Ho Chi Minh City, continues to be one of the mega-hotspots where after 48 years the dioxin TCDD levels in fish and
shrimp are still high and fishing is banned in ponds and lakes adjacent to the
airbase. Although expensive, one of the most effective remediation to dioxin
TCDD contaminated soils is incineration which is the recommended method
of dioxin TCDD disposal.