Chemical Warfare

During the Vietnam War, the U.S. military used large quantities of herbicides to deny their enemies agricultural food production and forest cover. Between 1961 and 1971, about 3.2 million acres (1.3 million ha) of forest and 247,000 acres (100,000 ha) of croplands were sprayed at least once. This is an area equivalent to about one-seventh of South Vietnam.

The most commonly used herbicide was called agent orange, a one-to-one blend of two phenoxy herbicides, Soldiers at Assaf Harofe Hospital washing "victims" in simulated chemical attack. Photograph by Jeffrey L. Rotman. Corbis. Reproduced by permission.

2,4-D and 2,4,5-T. Picloram and cacodylic acid were also used, but in much smaller amounts. In total, this military action used about 25,000 tons of 2,4-D; 21,000 tons of 2,4,5-T; and 1,500 tons of picloram. Agent orange was sprayed at a rate of about 22.3 lb/acre (25 kg/ha), equivalent to about ten times the rate at which those same chemicals were used for plant control in forestry. The spray rate was much more intense during warfare, because the intention was to destroy the ecosystems through ecocide, rather than to manage them towards a more positive purpose.

The ecological damages caused by the military use of herbicides in Vietnam were not studied in detail; however, cursory surveys were made by some visiting ecologists. These scientists observed that coastal mangrove forests were especially sensitive to herbicides. About 36% of the mangrove ecosystem of South Vietnam was subjected to herbicides, amounting to 272,000 acres (110,000 ha). Almost all of the plant species of mangrove forests proved to be highly vulnerable to herbicides, including the dominant species, the red mangrove. Consequently, mangrove forests were devastated over large areas, and extensive coastal barrens were created.

There were also severe ecological effects of herbicide spraying in the extremely biodiverse upland forests of Vietnam, especially rain forests. Mature tropical forests in this region have many species of hardwood trees. Because this forested ecosystem has such a dense and complexly layered canopy, a single spraying of herbicide killed only about 10% of the larger trees. Resprays of upland forests were often made, however, to achieve a greater and longer-lasting defoliation. To achieve this effect, about 34% of the area of Vietnam that was subjected to herbicides was treated more than once.

The effects on animals of the herbicide spraying in Vietnam were not well documented; however, there are many accounts of sparse populations of birds, mammals, reptiles, and other animals in the herbicide-treated mangrove forests and of large decreases in the yield of near-shore fisheries, for which an intact mangrove ecosystem provides important spawning and nursery habitat. More than a decade after the war, Vietnamese ecologists examined an inland valley that had been converted by herbicide spraying from a rich upland tropical forest into a degraded ecosystem dominated by grasses and shrubs. The secondary, degraded landscape only supported 24 species of birds and five species of mammals, compared with 145-170 birds and 30-55 mammals in nearby unsprayed forests.

The effects on wild animals were probably caused mostly by habitat changes resulting from herbicide spraying. There were also numerous reports of domesticated agricultural animals becoming ill or dying. Because of the constraints of warfare, the specific causes of these illnesses and deaths were never studied properly by veterinary scientists; however, these ailments were commonly attributed to toxic effects of exposure to herbicides, mostly ingested with their food.