biosolids are very low because of the natural attenuation of pathogens due to environmental factors such as dessication and ultraviolet light.

Endotoxin, also known as lipopolysaccharide, is ubiquitous throughout the environment and may be one of the most important human allergens (Sharif et al., 2004). Endotoxin—derived from the cell wall of gram negative bacteria—is continually released during both active cell growth and cell decay (Brooks, 2004). In soils, bacterial concentrations routinely exceed 10⁸ per gram, and soil particles containing sorbed microbes can be aerosolized and act as a source of endotoxin. Farming operations (e.g., driving a tractor across a field) have been shown to cause exposure to high levels of endotoxin. When inhaled, endotoxin can cause a wide variety of health effects, including fever, asthma, and shock (Methel, 2003).

Mycotoxins are secondary metabolites produced by fungal molds. Fungi, such as species of Aspergillus, Alternaria, Fusarium, and Penicillium, are common soilborne fungi capable of producing mycotoxins. Aflatoxin, produced by Aspergillus flavus, is one of the most potent carcinogens known and is linked to a variety of health problems (Williams et al., 2004).

Allergic diseases are the sixth leading cause of chronic illness in the United States, affecting roughly 17% of the population. Approximately 40 million Americans suffer from allergic rhinitis (hay fever), largely in response to common aeroallergens, and asthma prevalence and deaths in this country rose substantially from 1984 to the late 1990s (AAAAI, 2000; CDC, 2002, 2004; Mannino et al., 1998; IOM, 2000). Aeroallergens may also contribute to chronic obstructive pulmonary disease and cardiovascular disease (Brunekreef et al., 2000).

The biouptake and coupled interactions of airborne materials—both particulate matter and gaseous components—have important negative impacts on human well-being. In an era when our ability to apply multispectral and hyperspectral satellite data to better understand the nature and characteristics of airborne pollutants continues to increase, our understanding of the sources of airborne pollutants emanating from the surface of the earth, and transported by earth processes, remains inadequate. Even the basic framework for describing the nation’s surface—a detailed and comprehensive map of the geochemical and textural characteristics