In the field of water cycle monitoring or natural disaster management, it is assumed that performing a controlled exposure of organisms is a relevant way to appraise the effects of pollutants in natural waters. The approach is also very well adapted to soil characterization where specific biomarkers might be used.
In order to assess the toxicological status of an aquatic ecosystem, in situ exposures under controlled conditions are often carried out with plants (e.g. moss), invertebrates (e.g. mussels) or vertebrates (e.g. fishes). Nonetheless, these controlled exposures are difficult to achieve when using microorganisms although they represent relevant bioindicators for determining the health or the toxicological status of natural waters. The main reason comes from the difficulty for designing an exposure device that isolates the micro-organisms while enabling the system to quickly equilibrate with the medium; assuming natural waters are dynamic.
To address this challenge, the Stirred Underwater Biouptake System (SUBS) was developed by the University of Montréal within ECODIS. This project was funded by the European Commission under the sixth framework programme (FP 6), a grant funding programme..
The SUBS device is composed of two cylindrical compartments that fit into each other: the control compartment and the diffusion chamber. The upper control compartment contains a water-tight battery pack and a stirring motor. The lower compartment houses the microorganisms within a continuously stirred medium. This compartment is surrounded by a semi-permeable membrane, through which both contaminants and nutrients can diffuse.
The SUBS functioning principle is based on the diffusion of ionic species through the semi-permeable membrane so that both the bio-availability and the bio-accumulation of chemical contaminants (e.g. metals) can be measured in real-time conditions. The semi-permeable membrane consists of a 0.45 µm porosity polycarbonate filter. This physical filtrating capability allows the device to maintain the concentrations outside and inside the chamber at the same level. In practice, the diffusion of metals through the semipermeable membrane is measured via a microelectrode.
The approach of the SUBS technology consists in transplanting laboratory cultures (i.e. microorganisms) to measure the bioavailability and bioaccumulation of metals into natural environments. In order to ensure experimental reproducibility, a set of three SUBS are attached to a rack. This rack is weighed to achieve a constant immersion of all diffusion chambers. A set of 7 racks, thereby gathering 21 SUBS, may routinely be deployed so as to either conduct consecutive time-series analysis or to carry out multi-site experiments.
The prototype was tested in laboratory and in field. Experiments were carried out in Switzerland, Canada and France. The technology readiness level is estimated to be 6 on the TRL scale, according to the scope of the sixth framework programme, which provides public grant partial funding for R&D. Various laboratory and field experiments were conducted to verify the diffusion through the polycarbonate membrane, the bio-accumulation and the cellular viability. The prototype was validated over short deployment periods with a minimal exposure of two hours (using fresh water green algae Chlamydomonas reinhardtii as organisms). The period of exposure can be extended up to six hours.
The SUBS technology was developed for environmental applications. The system is particularly well suited for analysing the biological dynamic uptake in a disaster scenario where the concentration profiles of the pollutants are constantly evolving over short periods. Further development should deal with substituting laboratory organisms with natural plankton communities, thereby leading to noteworthy improvements in the field of ecotoxicology.