Aggregation-Based Growth and Reaction Mechanisms of Iron Oxyhydroxide Nanoparticles Christopher S. Kim, Department of Chemistry, Chapman University, Orange, CA 92866 Little is known about the extent and mechanisms of metal sorption to nanoparticles and corresponding effects on nanoparticle growth. Macroscopic studies show that uptake varies considerably as a function of metal species, while synchrotron-based X-ray diffraction studies show that the aggregation of particles aged at 75°C in the presence of these metals is considerably suppressed when metal(loid)s (e.g. Cu(II), As(V)) are sorbed rapidly. 4d Such sorption and incorporation effects have implications for the long-term fate and mobility of metals in contam- inated regions. 4d 4d 3d 3d 2d 3d 2d 2d 1d 1d 1d 0d 0d 0d