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Tributyltin (TBT) has been measured in water in 12 of 15 harbors studied during US Navy baseline surveys. The highest concentrations of TBT (some exceeding laboratory toxicity limits) have been found in yacht harbors and near vessel repair facilities. Many sites (75%) in harbors and estuaries had no detectable ( < 5 ng dm-3) TBT. TBT monitoring studies with increased detection limits (< 1 ng dm-3) have documented a high degree of TBT variability associated with tide, season and intermittent point source discharges. Although yacht harbors were shown to be the principal TBT source in most regions, dry-docks can be significant sources. Tributyltin degradation studies were conducted using unfiltered seawater from four geographic regions and incubated under natural conditions. Degradation half-lives were always in the range of 4-19 days, providing evidence that TBT is not highly persistent in the water column at environmental concentrations. Preliminary degradation experiments suggest that TBT has a longer residence time in sediment with a half-life of several months. Tributyltin is primarily in the dissolved form in unfiltered seawater, although the association with particulate fractions may increase in samples collected near yacht repair facilities. Partition coefficients for particulate TBT versus bulk water are frequently near 3000 and vary with the particulate concentration, salinity and presence of natural organics.

In an earlier publication 1 the problem of the equilibrium between the two phases in a phaseseparated liquid He 3 -He 4 mixture near 0°K has been discussed on the basis of the theory of impurities in liquid helium put forward by Landau and Pomeranchuk. 2 ' 3 The theory gives the way in which the excitation spectrum of the liquid is modified by the presence of the impurity; e.g., a small concentration X of He 3 modifies the Landau (phonon + roton) excitation spectrum of liquid-helium II by adding a branch of Fermi particles, equal in number to the number of He 3 atoms, and with energy-momentum relation e = -E 3 (X) +p 2 /2m 3 *. The effective mass ra 3 * has been determined from second sound measurements 4 to be 2.5 times the real mass of He 3 at the saturated vapor pressure. The binding energy E s is found 5 from vapor-pressure data to be rather close to L 3°, the latent heat of vaporization per atom of pure liquid He 3 at 0°K, although it actually depends slightly on X. In a similar way the Fermi quasiparticle spectrum of pure liquid He 3 is modified by the addition of a Bose branch when He 4 is dissolved in it. 8 The thermodynamic properties of dilute He s -He 4 mixtures can thus be calculated in a straightforward way using standard formulas of statistical mechanics. In particular, in a mixture in which phase separation has occurred, one can equate the chemical potentials of each isotope in the two phases to obtain the concentration in each phase as a function of T. It was found earlier 1 that the upper He 3 -rich phase is almost pure He 3 for T^ 0.2°K and this has been confirmed by experiment. 7 The theory also shows that it is possible, in principle, for He 3 to remain dissolved in He 4 up to a certain concentration, even at C^K. 1 This is true for any solution in which He 3 is more strongly bound than it is in pure liquid He 3 . The maximum solubility at 0°K, X 0 , is then determined by equating the latent heat of vaporization of He 3 from the solution to that from the pure liquid:-W + *W = -L 3-where kTj? is the Fermi energy of He 3 in solution (calculated for a gas of the same number density and with mass m 3 *). Determinations of E 3 (X) from vapor-pressure data are not at present sufficiently precise to demonstrate that this possibility is realized in nature.A more sensitive method of determining E 3 (X) than from vapor pressures is from measurements of the phase-separation temperatures T$ of dilute solutions of known X. This has been done in the present work by measuring the heat capacity of the solutions under their saturated vapor pressure down to temperatures of about 0.1 °K or less. The solutions were contained in a nylon calorimeter packed with small crystals of cerium magnesium nitrate used as a refrigerant and as a thermometer. The phase separation appears as a discontinuity AC in the specific heat (Fig. 1), as was previously observed at higher temperatures by Ouboter, Beenakker, and Taconis. 5 We found such discontinuities in solutions withX = 0.08, 0.10, 0.12, and 0.15 but not with X = 0.04, 0....

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