Can we use a biosensor to detect water pollution in real-time? Results of a pilot study in the Venice lagoon

In 2021, 214 million tons of chemicals hazardous to health were produced (4% more than in 2020; 1% more than in 2019), along with 85 million tons of chemicals hazardous to the environment (6% more compared with 2020; 2% more than in 2019) (EUROSTAT). A fraction of these chemicals reaches surface, ground, and marine waters in complex mixtures through different emission sources: industry, WWTPs, diffuse sources (leaching and runoff in agricultural fields, air deposition, etc.). In this challenging context, the European Commission adopted a proposal to review and modify the Water Framework Directive in 2022, in line with the objectives of the European Green Deal and the Zero Pollution Action Plan. To address these new stringent water quality requirements, we have developed a new monitoring device, called WATERSCAN that continuously tests water quality using a biosensor. WATERSCAN applies real-time PAM (Pulse Amplitude Modulated) fluorometry to detect changes in functional indicators of microbial biofilms exposed to a constant water flow and includes alocal clean reference. The device also included passive samplers POCIS (Polar Organic Chemical Integrative Samplers), specific for polar organic compounds, Diffusive Gradient in Thin film (DGT), for trace metals and a novel passive sampler to determine chemotaxonomical phytoplankton composition. The prototype, protected by a patent, has been tested in the field. Here are the results of the pilot study conducted at the Arsenale of the Venice lagoon from 17/7/23 to 27/7/23. First results indicate that the device can operate with minimal maintenance and provides highly sensitive results with a constant water flow during several days. Significant differences were detected between monitoring and reference chambers indicating possible water contamination events, in line with the results of passive sampling. A local reference was essential to discriminate significant divergences in PAM signals, especially during and after a storm event. The analysis of chlorophyll-a content indicates higher concentrations in the inflow compared to the outflow. This pattern is more pronounced during the afternoon, aligning with the day/night cycle of phytoplankton. HPLC and microscopy analysis confirm that colonization of the biofilm by external species is reduced to a minimal colonization by diatoms. Future developments will include the implementation of a standard monospecific biofilm to reduce variability in results.