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SELENIUM IN SELENIFEROUS ENVIRONMENTS 37 1971; Rahn & Lowenthal, 1985; Scheff et al., 1984). The EF for Se increased exponentially as particle size decreased. About 79~Io of the aerosol Se was associated with the <2.0 µm MMAD particles. The relative Se sorption to the particle is inversely related to particle size (Chiou & Manuel, 1986) and is likely a surface phenomena. A halving of the diameter of a sphere causes a doubling of the surface area for the same mass of particles. The particle distribution at Rolla, MO, may have been affected by the lead mines and smelters in the area. Most important is the fact that 70~7a of the particles collected by Chiou and Manuel (1986) were < 2.0 µm compared to the > 2.0 µm particles collected in other studies reported here. The computed EF values for select elements in the bulk Missouri aero- sol (particles of 0.01-7 µm MMAD) were: Tellurium 12 000 Selenium 2 200 Antimony 1900 Sulfur 780 Arsenic 320 Zinc 110 Chlorine 56 Manganese 5.6 Calcium 1.7 Aluminum 1.0 Small EF values indicate little redistribution of the element among various materials, whereas the large EF values indicate considerable redistribution. The EF for the Se in the 0.01 to 1.1 µm MMAD particles was about 50 000, which is much greater than the 2200 value calculated for the bulk aerosol. Upon combustion, coal-derived Se is preferentially partitioned to the submicron-sized particles, which are easily transported over long distances. This might account for the high enrichment factors of 18 000 reported for Se aerosols at the South Pole (Zoller et al., 1974) and the similar EF of 22 000 reported at Memphis, TN (Andren et al., 1975). Although these values are greater than the value of 2200 calculated for the Se in aerosols captured in Missouri (Chiou & Manuel, 1986), the two previous aerosols likely contained much smaller particles than those from Missouri. Using Se/S and Te/S ratios, Chiou and Manuel (1986) were able to show that coal combustion was the prime source of chalcogen elements (O, S, Se, and Te). They discounted the contribution of soil and volcanic ash to the Se found in the aerosols. Also, biological methylation of inorganic forms of Se in soil and sewage has been suggested as an important source of at- mospheric Se (Reamer &Zoller, 1980). However, the amounts generated by these mechanisms are not well quantified and are considered to be much less than those from the combustion of coal and refuse (Chiou & Manuel, 1986). Cutter & Church (1986) reported data on the concentration and oxida- tion state of Se in precipitation over coastal and midocean regions of the western Atlantic Ocean. The results indicate that fossil fuel combustion en-