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Aggregation, sedimentation, dissolution and bioavailability of quantum dots in estuarine systems.
Citation:
Xiao, Y., K. Ho, R. Burgess, AND M. Cashman. Aggregation, sedimentation, dissolution and bioavailability of quantum dots in estuarine systems. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 51(3):1357-1363, (2017).
Impact/Purpose:
Because of their increasing use and value to society, cadmium-based quantum dots (QDs) will inevitably find their way into marine systems. In an effort to understand the fate and transport of CdSe QDs in estuarine systems, the aggregation, sedimentation dissolution and toxicity of CdSe QDs in seawater was investigated. The sedimentation rate of CdSe QDs aggregates in seawater was measured to be 1-10 mm/day, which was slow considering their relatively large size. Light played a vital role in promoting the dissolution of CdSe QDs and the release of dissolved Cd. Our results demonstrate that the benthic zone in marine systems is the most probable long-term destination of CdSe QDs due to aggregation and sedimentation, despite being affected by slower transport processes than expected. In addition, the benthic community might be exposed to both particulate and ionic form of CdSe QDs. This work indicates that further study of the role of particulate QDs in causing toxicity to estuarine organisms is critical.
Description:
To understand their fate and transport in estuarine systems, the aggregation, sedimentation, and dissolution of CdSe quantum dots (QDs) in seawater were investigated. Hydrodynamic size increased from 40 to 60 nm to >1 mm within 1 h in seawater, and the aggregates were highly polydispersed. Their sedimentation rates in seawater were measured to be 4–10 mm/day. Humic acid (HA), further increased their size and polydispersity, and slowed sedimentation. Light increased their dissolution and release of dissolved Cd. The ZnS shell also slowed release of Cd ions. With sufficient light, HA increased the dissolution of QDs, while with low light, HA alone did not change their dissolution. The benthic zone in estuarine systems is the most probable long-term destination of QDs due to aggregation and sedimentation. The bioavailability of was evaluated using the mysid Americamysis bahia. The 7-day LC50s of particulate and dissolved QDs were 290 and 23 μg (total Cd)/L, respectively. For mysids, the acute toxicity appears to be from Cd ions; however, research on the effects of QDs should be conducted with other organisms where QDs may be lodged in critical tissues such as gills or filtering apparatus and Cd ions may be released and delivered directly to those tissues.
