Combined use of photosynthetic enzyme complexes and microalgal photosynthetic systems for rapid screening of wastewater toxicity

Abstract

Because of the often episodic nature of wastewater toxicity, routine monitoring using expensive and time consuming tests can constitute an inefficient means of toxicity evaluation, particularly when negative results are generated. Cost-effective screening tests enabling the rapid detection of effluent toxicity are clearly needed, and they should be used to rapidly determine where in-depth investigations should be focused. The LuminoTox is a recently-developed screening test enabling the rapid determination of wastewater toxicity. This test is based on the inhibition of chlorophyll fluorescence emitted by photosynthetic systems. The combined use of photosynthetic enzyme complexes (PECs), isolated from higher plants, and whole photosynthetic organisms (algae) allows a wide range of toxic inhibitors to be detected within 10-15 min. The detection thresholds obtained for individual toxic chemicals indicate that algae are less sensitive to metal cations than PECs, because of the algal cell wall being ion selective. However, other toxic chemicals, such as phenolic compounds and nitrogen ammonia, acting on the last constituents of the photosynthetic enzyme complex that are degraded during the PEC extraction process, are more easily detected with algae after just 10 min of exposure. The combination of PECs and algae is not only useful for rapid toxicity screening, but yields results that are as sensitive as those of standard bioassays. Toxicity data generated with mining industry effluents demonstrate that PECs routinely prove to be as sensitive as daphnia, while algal sensitivity is comparable to that of the standard trout bioassay. An important feature of LuminoTox and algal photosynthetic system testing, however, resides in the production of their rapid and sensitive responses (10-15 min) in comparison with those of the more traditional tests (48-96 h for daphnia and trout, respectively).