Partition coefficients for dissolved and particulate organic material (K dom and Κ pom , respectively) and five organic chemicals were meas ured in surface waters and leachates from soils and sediments. Kdom was measured by using changes in Daphnia magna dry-weight bioconcentration factors, and Kpom was measured by centrifugation. The results showed that sorption by dissolved organic matter can dominate the distribution of organic chemicals in the water column and affects calculation of Kpom. The linear relationship of log Kdom and log Kpom values to log Kow (octanol-water partition coefficient) was similar to the relationship found by Kenaga and Goring for soils and sediments. This resemblance indicates that organic materials in the water column, soils, and sedimentary material sorb chemicals by a similar mechanism. SORPTION OF HYDROPHOBIC ORGANIC CHEMICALS by naturally occurring organic matter in soils and aquatic systems is an important factor in determining their distribution in the environment. Incorporation of sorption by the organic matter in soils and sedimentary material into fate and transport1Current address: BCM Engineers