Vietnamese environment, and such chemical- and environment-specific parameter values as rates of TCDD degradation in Vietnamese coastal sediments. The committee found that, as is often the case for multimedia models and dioxins, input data and especially data with which to evaluate model performance were not available. Furthermore, large uncertainty would accompany any attempt to model overall TCDD fate by modeling emissions from individual spray paths on which data are available and scaling them up to hundreds of miles of coastline and coastal waters.

The committee explored the variability and uncertainty of several of the many parameters that could be used for assessing the fate and transport of TCDD in the environment, as described in the sections below. The goal of the exercise was a qualitative assessment of the fate of TCDD released during the Vietnam War. The discussion acknowledges the importance of location-specific factors that mediate chemical fate and transport, notably the tropical climate and the geography of Vietnam, which include episodic monsoons and the Mekong Delta, respectively. Most of the literature on the chemical fate of dioxins originates in temperate areas of the globe, such as Europe and North America, that differ substantially from the Vietnamese environment, and the committee was mindful of the differences as it developed its understanding of the fate of Agent Orange–associated TCDD in Vietnam.

THE VIETNAMESE ENVIRONMENT

The Republic of Vietnam is in the southern portion of the Indochina Peninsula in Southeast Asia. Its long, narrow shape extends nearly 1,100 km from north to south (about 8° to 17°N latitude) with a maximum width, in an east–west direction, of about 210 km and an area of nearly 170,000 km2. About 1,400 km of the nearly 1,660 km of Vietnam’s coastline is on the South China Sea, and the remaining (roughly 260 km) short stretch of coast on the southern end of the country faces the Gulf of Thailand. The inland portion of the northern two-thirds of southern Vietnam consists of high plateaus with coastal valleys and alluvial plains and streams that bring materials to the coastal zone. The coastline is irregular, with numerous headlands and bays.

The transport and fate of contaminants, such as TCDD, in the environment cannot be discussed without an understanding of the predominant hydrologic conditions of the area. The southern portion of



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