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The marine macroalga, Ulva lactuca, has been exposed for 48 h to different concentrations of Ag added as either silver nanoparticles (AgNP) or aqueous metal (AgNO(3)) and the resulting toxicity, estimated from reductions in quenching of chlorophyll-a fluorescence, and accumulation of Ag measured. Aqueous Ag was toxic at available concentrations as low as about 2.5 μg l(-1) and exhibited considerable accumulation that could be defined by the Langmuir equation. AgNP were not phytotoxic to the macroalga at available Ag concentrations up to at least 15 μg l(-1) and metal measured in U. lactuca was attributed to a physical association of nanoparticles at the algal surface. At higher AgNP concentrations, a dose-response relationship was observed that was similar to that for aqueous Ag recorded at much lower concentrations. These findings suggest that AgNP are only indirectly toxic to marine algae through the dissolution of Ag(+) ions into bulk sea water, albeit at concentrations orders of magnitude greater than those predicted in the environment.

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A method is given for calculating the spatial distribution of the production of a quantity, Q, averaged over many ions incident randomly on a solid for any energy dependent interaction between the ions and target atoms. The method is basically a two step method. First, the spatial distribution of the ions in the solid is followed as the ions lose energy. Then, at each intermediate energy the spatial distribution of Q-production is obtained and the result is integrated over the range of intermediate energies assumed by the ions. Saturation effqts are ignored in the procedure so that explicit consideration must be given to saturation effects when applying the method to high dose cases. Annealing and diffusion effects are also ignored, and the method is restricted in applicability to experimental conditions where annealing and diffusion are unimportant.Results of calculations by this method are presented of the depth distribution of energy ultimately deposited into atomic processes for Li7, Bll, Cia, N 1 ' , 0". Ne*O, Sip8, and P31 ions incident randomly on silicon with incident energies in the range of 30 to 400 keV. In this particular application of the method migration of the deposited energy through the recoil of struck target atoms has been neglected. Comparison of the results of calculations by this method with moments obtained by Sigmund and coworkers for the equal mass case indicate that for the ions listed above, and for the energy range considered, this approximation is valid. The calculated depth distributions thus represent the final depth distribution of energy deposited into atomic processes.