How do stream organisms respond to, and influence, the concentration of titanium dioxide nanoparticles? A mesocosm study with algae and herbivores

The biologically active properties of many nanomaterials, coupled with their rapidly expanding production and use, has generated concern that certain types of nanoparticles could have unintended impacts when released into natural ecosystems. In the present study, the authors report the results of an experiment in which they grew three common species of stream algae as monocultures and together as polycultures in the biofilms of stream mesocosms that were exposed to 0, 0.1, or 1.0ppm nanoparticle titanium dioxide (nTiO₂). The nTiO₂ did not alter the growth trajectory of any algal biofilm over 10+ generations. However, Ti accrual in biofilms not only differed among the algal species but was also higher in polycultures than in the average monoculture. Variation in accrual among species compositions was readily predicted by differences in the total biomass achieved by the different biofilms. When biofilms were fed to the herbivorous snail Physa acuta at the end of the experiment, initial concentrations of nTiO₂ did not alter short-term rates of herbivory. However, because of differences in palatability among the algae, biofilm composition influenced the amount of nTiO₂ that accumulated in the herbivore tissue. The results have important implications for understanding how efficiently nTiO₂ is removed from surface waters and the potential transfer of nanomaterials to higher trophic levels.