Adult breams (Abrama brama L.) were caught in October 1992 at seven stations in the river Elbe and at one nonpolluted reference site, the Belauer See. The locations of the sampling stations extended from the city of Steti (Tschechien Republic) to the city of Hamburg. Indices of biochemical effects in microsomal and cytosolic fractions of livers were studied by measuring cytochrome P450-dependent monooxygenases and glutathione-S-transferase (GST) activities. In addition, levels of mercury and 35 polychlorinated biphenyl (PCB) congeners were analyzed in livers of breams. Fish caught in the River Elbe exhibited a significant increase of cytochrome P450-mediated monooxygenase activities and the detoxifications enzyme GST compared to the reference site. At two stations of the river Elbe (Steti and Dresden) elevated activities of ethoxyresorufin-O-deethylase (EROD) were analyzed. These effects were discussed as effects from the pulp mill industries at station Steti and high concentrations of PCBs in the livers of breams at station Dresden. A significant reduction of GST activities was observed at station Dresden compared to those at Steti. These findings were probably a synergistic effect of high mercury concentrations at Dresden. The results presented in this study suggest that breams can be successfully employed for monitoring biological effects in the river Elbe.

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The reaction rates of the muonium (Mu) atom with HBr and HI in ∼1 atm N2 moderator have been measured over the temperature range 160–490 K using the μSR technique. While both abstraction and exchange reactions are possible, only the abstraction reaction should be observable, being moderately exothermic. Comparisons with the corresponding H(D) reactions reveal small kinetic isotope effects in both reactions, which do not vary strongly with temperature (kMu/kH≊3.5 near 300 K), consistent with the (classical) ratio of mean velocities. Surprisingly, quantum tunneling, normally facile for similarly exothermic reactions of the ultralight Mu atom (mMu/mH≊1/9), appears to be of little importance here. This despite the fact that the (temperature-independent) experimental activation energies are much less than the expected vibrationally adiabatic barrier heights (estimated to be ≊1.5 kcal mol−1) and, particularly in the case of Mu+HI, much less than the corresponding H-atom activation energy: 0.13±0.03 vs 0.70±0.3 kcal mol−1. In the case of reactions with HBr, the experimental Mu- and H-atom activation energies are much more similar: 0.51±0.03 and 0.74±0.12 kcal mol−1, respectively, over comparable temperature ranges. These data pose a conundrum in which several compensating effects related to the much lighter Mu-atom mass seem to be involved. Theoretical calculations are urgently required. In our view the topography of the potential-energy surface(s) for H2X is poorly known, particularly in the region of the barrier. It may be that the abstraction barriers for both Mu+HI and Mu+HBr are considerably later and even smaller than current calculations indicate, resulting in a cancellation of the effects of zero-point-energy shifts and quantum tunneling at the transition state. Differences in skewing angles between Mu and H+HX could favor a shorter tunneling path for the H-atom reaction, possibly compensating for its heavier mass. Steric or rebound effects from ‘‘bottlenecks’’ on the (mass-weighted) potential surfaces for Mu reactivity may also play some role. An upper limit for the 300 K reaction rate of Mu+HCl is given as well. In contrast to both HBr and HI, this reaction is quite endothermic and hence exhibits an inverse kinetic isotope effect (kMu≪kH).

The phase information of triplet muonium signals has been used to measure the slowing down times of the positive muon in Ar. The results agree well with calculated stopping power based on proton data with the assumption that the positive muon and proton have the same stopping power at the same projectilew velocity (velocity scaling).

Gas-phase mu-SR studies of dense methane up to 10 mol L-1 and of propane at low densities, up to 0.2 mol L-1, are reported. It is found that the diamagnetic polarization, P(D), increases in both gases with pressure, with a related decrease seen in the muonium polarization, P(Mu). The initial increase seen in P(D) at low densities is attributed to hot-atom (Mu*) abstraction and substitution reactions. Comparisons with both hot-tritium (T*) and epithermal H* reactions in the alkanes reveal substantial isotope effects. In the case of CH4, a continued increase in P(D) at higher densities is likely due to a proton-transfer reaction from the molecular ion CH4Mu+ in the radiolysis track, forming CH3Mu, rather than to hot-atom reactions. Extrapolation of the present trend with density gives agreement with the value of P(D) found in liquid CH4, indicating that the diamagnetic muon polarization in dense alkanes depends primarily on density rather than on temperature or phase.

Results of the first μSR studies using Merck FO Optipur silica powder, which contains paramagnetic impurities at the ppb level and has a surface area of 610±20 m2/g. are reported. Above 20 K, the transverse field muonium relaxation rate is roughly constant at 0.5 μs−1. Upon the addition of oxygen at ppm levels, the relaxation rate increases linearly with O2 concentration in the temperature range from 40–100 K yielding two-dimensional depolarization rate constants on the order of 10−4 cm2 molecule−1 s−1. As the temperature is increased further, both oxygen and muonium desorb from the surface yielding a three-dimensional rate constants at 300 K of 3.1(3)×10–10−10 cm3 molecule−1 s−1, in agreement with the gas phase value. Longitudinal field measurements suggest that MuO2 is formed and is able to spin exchange with other oxygen molecules.

Results of muon polarization studies in xenon and argon up to 60 atm are reported. In argon for pressures up to 10 atm, the muon polarization is best explained by an epithermalcharge exchange model. Above this pressure, the decrease inPD and increase inPL are ascribed to charge neutralization and spin exchange reactions, respectively, in the radiolysis track. Measurements with Xe/He mixtures with a xenon pressure of 1 atm indicate that the lost polarization in the pure xenon at this pressure is due to inefficient moderation of the muon. As the pressure in pure xenon is increased above 10 atm, we find thatPL remains roughly constant andPD begins to increase. The lost fraction may be due to the formation of a XeMu Van der Waals type complex, whilePD is ascribed to XeMu+ formation. This suggests that spur processes appear to be less important in xenon than in argon.