The Stirred Underwater Biouptake System (SUBS) was developed by the University of Montréal within the ECODIS project. The SUBS is a submersible sensing device using an in-situ bio-sensing technology to measure the bioavailability and the bioaccumulation of metals in natural environments. To develop such a device, various laboratory and field experiments were required.
When performing in situ exposures of microorganisms, the key point consists in not perturbing the balances between the contaminant uptake fluxes by the organisms and the contaminant resupply fluxes. Therefore, the approach consists in designing a chamber where the mass transport does not limit the biological uptake by the suspended organisms. To do so, diffusion across the filtrating membrane, bioaccumulation and cell viability were verified to develop a prototype exposure device that is as minimally perturbing as possible.
To validate these various technical parameters, a set of experiments were conducted in lab and in field. Thus, the objectives of these tests were (i) to verify the diffusion within the SUBS device (i.e. the diffusion chamber), (ii) to measure the metal bioaccumulation and (iii) to control the cellular viability.
The first concern deals with the diffusion into the SUBS. To ensure the diffusion into the device is not rate-limitating, Cd2+ diffusion through the semipermeable membrane was tested over 25 hours, with and without stirring and with and without microorganisms. It was shown that equilibration occurs between a 10 and 15 hours stirring period and that 89% of equilibration was reached after 25 h when not stirring. Moreover, experiments have shown that the Cd2+ resupplying through the semipermeable membrane was higher than the Cd2+ consumption by the microorganisms.
The second feature to be characterized handles metal bioaccumulation within the chamber. Measurements of Cd showed that its concentration nearly adds up to those found in the river water (between 90 and 95%) so that the risk of bulk depletion of Cd was negligible. As a result, it may be stated that the Biouptake of microorganisms within the SUBS chamber is likely to be representative of cells that might be exposed to natural waters.
Finally, the cellular viability (i.e. the possibility to maintain viable the cells during the exposures) was assessed. The viability test using formazan (i.e. chromogenic compounds proportional to the number of living cells) showed that microorganisms exposed in the river were alive during the entire exposure.
A novel in situ tool for the exposure and analysis of microorganisms in natural aquatic systems. Environ. Sci. Technol., 2009, 43, 8240-8244