Rapid expansion of nanoparticle research demands new technologies that will enable better interpretation of experimental data and assistance in the rational design of future nanoparticles. The use of physiologically based pharmacokinetic (PBPK) models may serve as powerful tools to meet these needs. PBPK models have been successfully applied for the study of the absorption, distribution, metabolism, and excretion (ADME) of small molecules, such as drugs. Preliminary application of PBPK models to nanoparticles illustrated their potential usefulness for nanoparticle ADME research. However, due to the differences between nanoparticles and small molecules, modifications are needed to build appropriate PBPK models for nanoparticles. This review is divided into two sections, with the first discussing nanoparticle ADME research, emphasizing the interaction of nanoparticles with living systems, including transportation kinetics across biobarriers. In the second section, the basic principles of PBPK model development are introduced, and research pertaining to PBPK models of nanoparticles is reviewed. Factors that need to be considered for developing PBPK models for nanoparticles are also discussed. Finally, perspective applications of nanoparticle PBPK models are summarized.

SUMMARYWe investigated mycorrhizal infections caused by Glomus etunieatum Becker & Gerd. n-i sunflower (Helianthus annuus L.) plants given small concentrations of phosphate. In pure sand given no additional phosphate, infection was only poorly developed. As phosphate availability was increased, the e.xtent of infection also initially increased. We hypothesized that the extent of infection should be regulated by the nutritional status of the shoot. However, by performing a split-root experiment, we found that the root rather than the shoot was responsible for this regulation.

SunHower {Helianthus ciniiuus L.) and mustard {Bras,':ica hirta Moench.) plants were grown in autoclaved soil to which -was added various components of soil inoculum. LIse of inocula containing mycorrhizal propagules ultimately resulted in growth promotions which were related to improved phosphorus nutrition. Inoculation with soil containing mycorrhizal propagules caused an initial growth depression in comparison with plants receiving no inoculation, but inoculation with washed spores did not. For several reasons, the growth depression caused by inoculation with soil was not attributable to mycorrhizal infection. Pirst, the growth depression was evident before mycorrhizal infections had become established. Second, the growth depression was also evident w-hen either soil or soil sievings, both lacking mycotrhizal propagules, were used. Third, similar growth depressions were observed in mu.stard. The results suggest that careful selection of appropriate controls for mycorrhizal plants must be made, particularly if the emphasis is on early phases of plant growth. Use of non-sterile soil reduced the extent of mycorrhizal infection.