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Field observations and experimental measurements of the partitioning coefficient (Kd) of7Be in fresh water show that it varies inversely with the solids concentration at typical environmental values (up to 30 mg/1). This behavior is similar to that of many other metals and organic pollutants, which means that 7Be may be useful as a tracer of the movement of these substances in the water column. However, the wide range in the percentage of 7Be adsorbed by solids over this range of concentrations (over 50%) means that in order to use 7Be either to measure total sedimentation rates or to trace lateral sediment movement it will be necessary to monitor changes in sediment concentration over the area and time period of interest. The wide scatter in our data at both high and low solids concentrations suggests that other factors also affect Kd. Until these factors are identified, application of our results to other systems will be risky. At high (greater than 100 mg/1) solids concentrations over 90% of 7Be is associated with the solid phase, so it may be a useful tracer of reworking rates in bottom sediments. 7Be has a slightly greater affinity for the solid phase in fresh water than in seawater.