TOXICOLOGICAL VS ECOTOXICOLOGICAL TESTS FOR ENVIRONMENTAL SCREENING OF FRESHWATERS AFFECTED BY CYANOBACTERIA ALGAL BLOOM.

Introduction Cyanobacteria are a ubiquitous group of photosynthetic procariota. Blooms of non-toxin producing and toxin producing cyanobacteria are often observed in waters of lakes, reservoirs and slowly flowing eutrophic freshwater. Microcystin congeners are the most important group of cyanobacterial toxins and its determination is necessary in order to assess the health risk when such waters are used for recreational purposes or as tap waters. The WHO has established a provisional concentration limit of 1.0 μg/L for drinking water supply only for congener microcystin-LR. Some concern is raised also with respect to the chronic exposure to low cyanotoxin levels, whose effects remain a critical issue to be clarified. In Italy frequent blooms are reported from the lakes of many regions including Sicily. Some blooms, often caused by Plantotrix rubescens, were reported in Pozzillo Lake (EN), the largest lake in Sicily. Objective Aim of our study was asses the toxicity of waters sampled in Pozzillo Lake through both toxicological and ecotoxicological methodology to verify the most sensitive method in sub chronic exposure to microcystins. Methods Three pool of samples taken by center of Lake Pozzillo to 0.5 m, 10 m, and the bottom between May and September during 2014, were stored in sterile bottles (PET) 1L and maintained at 4 °C to prevent decay or growth of the occurring microorganisms. The samples were processed within 24 hours from collection. Determination of the acute toxicity were carried out trough two methods: 1. Vibrio fischeri (NRRL B-11177) luminescent bacteria in accordance with EN ISO 11348-3. The measuring unit was the natural luminescence of the Vibrio fischeri NRRL B-11177 detected by a Microtox Model 500 analyzer (SDIx, USA) carefully performing all the procedures described in the Microtox® standard protocol. 2. Artemia salina test (APAT 8060 ecotoxicological methods). For chronic toxicity we used the algal growth inhibition test using Pseudokirchneriella subcapitata. A commercially available certified microcystin enzyme-linked immunosorbent assay (ELISA) was used for detection of microcystin. Results and Conclusions The tested samples showed a concentration of microcystin always below the law limit of 10μg/L. How shows Table 1 the acute toxicity tests not are sensitive to exposure at subchronic doses of microcystin. The chronic toxicity algae test, instead, is very sensible already at very low microcystin concentrations, so this test could be a sensible test, useful if coupled with other chemical and toxicological assays for a better methodology of environmental screening of freshwaters affected by cyanobacteria algal bloom to protect human health. Table 1. 0.5 m Microcystin (µg/L) Vibrio f. (inibition %) Artemia s. (% of naupli vitality) Pseudokirchneriella s. (algal growth inhibition %) 0.05 <20 100 45 0.05 <20 100 7 0.05 <20 100 0 10 m 0.17 <20 100 46 0.05 <20 100 10 0.10 <20 100 5 bottom 0.05 59 100 0 0.14 <20 100 40 0.10 <20 100 12