Developing and interpreting aqueous functional assays for comparative property-activity relationships of different nanoparticles

Highlights: • A framework to compare ENM properties to their environmental behavior was proposed. • There is a high reproducibility of functional assay results for all nanomaterials tested. • Some functional assays may be surrogates for other assays, reducing experimental time and cost. • Activity-profiling radar plots provide a unique way to visualize potential hazards of ENMs. It is difficult to relate intrinsic nanomaterial properties to their functional behavior in the environment. Unlike frameworks for dissolved organic chemicals, there are few frameworks comparing multiple and inter-related properties of engineered nanomaterials (ENMs) to their fate, exposure, and hazard in environmental systems. We developed and evaluated reproducibility and inter-correlation of 12 physical, chemical, and biological functional assays in water for eight different engineered nanomaterials (ENMs) and interpreted results using activity-profiling radar plots. The functional assays were highly reproducible when run in triplicate (average coefficient of variation [CV] = 6.6%). Radar plots showed that each nanomaterial exhibited unique activity profiles. Reactivity assays showed dissolution or aggregation potential for some ENMs. Surprisingly, multi-walled carbon nanotubes (MWCNTs) exhibited movement in a magnetic field. We found high inter-correlations between cloud point extraction (CPE) and distribution to sewage sludge (R² = 0.99), dissolution at pH 8 and pH 4.9 (R² = 0.98), and dissolution at pH 8 and zebrafish mortality at 24 hpf (R² = 0.94). Additionally, most ENMs tend to distribute out of water and into other phases (i.e., soil surfaces, surfactant micelles, and sewage sludge). The activity-profiling radar plots provide a framework and estimations of likely ENM disposition in the environment.