UC Riverside

The overall goal of this dissertation was to determine the effects of an emerging contaminant, nanomaterials, on microbial communities in engineered systems. Specifically, communities within a simulated human colon and model septic system were studied. Microbial communities in their natural environments represent realistic scenarios for toxicity testing versus assays with enriched growth media and single cell cultures; the two engineered systems used in this work approach “real” scenarios communities would experience.

This dissertation work has allowed for the following observations. The simulation of metal oxide nanomaterials ingestion with the model colon demonstrated these particles do significantly alter the phenotype of the gut microbial community within the model colon reactor. Next, dosing experiments with copper materials in the septic system established that the effluent had pulses of improper waste treatment and that incomplete organic breakdown was likely occurring. However, even with weekly fluctuations in water quality caused by the particles, data suggest that 100% of the time, water quality parameters and microbial composition were recovering towards baseline conditions. This indicates the system could maintain baseline conditions after perturbances, regardless of the particle type.

Finally, effluent containing copper emitted from the septic system was tested in a high throughput toxicity screening assay with zebrafish embryos. While “as-received” nanoscale copper materials caused the greatest embryo hatching interference, all three “processed” copper materials emitted from the model septic system demonstrated a decline in embryo toxicity, regardless of particle composition/size. Thus, the zebrafish screening in combination with the septic system, provide a novel way to study hazard potentials of commercial Cu-based particulates during partitioning, transformation, and speciation.

This collection of studies provides critical insights into the importance of understanding microbial communities more holistically and in realistic environments. These studies demonstrate the need to update toxicity tests such that they more accurately reflect real exposure scenarios simulating environmental conditions. This research also confirms the invalidity of using “as received” nanoparticles; toxicity tests must use particles reflective of those materials transformed in the environment. Future directions for toxicological studies need new useful testing combinations that provide additional information for complex matrices and microbial communities.