AquaSentinel. In a similar laboratory setup with a Walz XE-PAM fluorometer (Heinz Walz GmbH, Effeltrich, Germany), the standard fluorescence cuvette in the fluorometer was replaced with a flow-through model (Hellma Cells, Inc., Model QS-131, Plainview, NY). The cuvette inlet was connected to a glass-bottle reservoir that contained the water samples, and the outlet drained to waste. The system is designed to mimic the flow of river or lake water through the fluorescence detection system. This experimental arrangement allowed continuous monitoring and replacement of water samples in a manner similar to that for the contemplated operation of a real-world biosensor system. Fluorescence induction curves were measured before and during exposure to toxic agents. Fluorescence excitation and emission wavelengths were 660 and 685 nm, respectively. A halogen lamp actinic light source illuminated the cuvette at an intensity of 500 µE-m−2·s−1 via a fiber-optic cable through direct connection to the cell chamber.
Fluorescence induction curves were recorded every 5 minutes, and data collection for each curve was completed within 10 seconds. Data extracted from the fluorescence induction curves were used to calculate Fs, Fmax, Fv (variable fluorescence = Fmax − Fs), and the efficiency of PSII photochemistry (Fv/Fmax). A 200-mL water sample was placed in a jacketed reservoir. The sample was stirred continuously and maintained in darkness with a black cloth. The reservoir was connected to the flow-through fluorescence cell with flexible tubing. To obtain a homogeneous sample before each recording, the volume in the fluorescence cell was replaced three times. After control data were collected, the volume in the reservoir was adjusted to 100 mL and the toxic agent was added. The toxic agents were prepared as stock solutions prior to addition to the reservoir and were injected directly into the top of the vessel and immediately mixed with the sample. Spent samples were drained into a waste bottle. Upon arrival in the laboratory from collection sites at the rivers, the water samples were kept under a fluorescent lamp at an illumination of 50 µE-m−2-s−1 until use.
Experiments were performed with field samples drawn from the Clinch River at Clark Center Recreation Park in Oak Ridge, Tennessee. The Clinch is the main source of drinking water supply for the city of Oak Ridge. Figures 6.2a through 6.2d show the effect of KCN, MPt, DCMU, and Paraquat, respectively, on naturally occurring algae from the Clinch River.
The results shown here demonstrate that naturally occurring freshwater algae can be used as biosensor material for the detection of toxic agents in sunlight-exposed primary drinking water supplies. These agents block electron transport, impair light energy transfer, or generate toxic secondary photoproducts, all of which provide signals that can trig-