Optimization and performance evaluation of the continuous algal toxicity test

Abstract

Responses of Selenastrum capricornutum to cadmium in a chemostat are evaluated under various test conditions defined by the nitrogen to phosphorus ratio, phosphate strength, dilution rate, and ethylenediaminetetraacetic acid content. Based on the test results, these parameters were optimized to achieve superior test sensitivity. This continuous system was also modified to allow testing on a weekly basis. The performance of the modified testing technique was evaluated, employing six different metal toxicants. Compared with batch test results reported by other researchers and our own experiment, the continuous test achieved superior sensitivities and reproducibility. The test method presented in this study is believed to be an ideal technique both for research and regulatory purposes.

Metal toxicity to Chlorella pyrenoidosa assessed by a short-term continuous test

“…The dilution rates for these tests were all maintained at D = 0.5 day −1 . The concentration of Na 2 EDTA·2H 2 O was reduced to 30 g/l following our previous approach [17,18]. One may find that the cell density dropped from 4.6 to 2.2 × 10 6 cells/ml as the PO 4 -P content decreased from 0.28 to 0.14 mg/l.…”

“…The author's previous works have proposed a short-term continuous algal toxicity test technique, whereby algae were grown and tested under nutrient-limited conditions. Toxicity tests employing different metal toxicants revealed that, with respect to both the median effective concentration (EC 50 ) and the no-observed-effect concentration (NOEC), algae cultured in a continuous reactor are more severely inhibited than those cultured by the batch technique [17,18]. Furthermore, batch and continuous techniques were found to depict completely different relationships in relative toxicity [19].…”

“…Therefore, their application in algal toxicity assessment is quite limited. On the other hand, our short-term technique evaluates the toxic response under non-steady state and the test duration is only 1 day [17]. The technique thus has a potential for more general applications such as routine checkup for regulatory purposes.…”

Use of Plants for Toxicity Assessment of Estuarine Ecosystems

“…Most phytotoxicity test methods have been designed to use the freshwater alga Selenastrum capricornutum [6], and many suggested modifications have been developed using this species. A continuous culture technique described and compared with batch culture techniques for S. capricornutum [59,60] is reputed to yield superior sensitivity and reproducibility in exposure tests. An in vivo fluorescence technique for measuring chlorophyll a in S. capricornutum was attempted [58], but this study produced inconclusive results.…”

Interferences of dark coloured waters and wastewater on algae toxicity assessment

“…Algae growth inhibition test (AGIT) is one of the most used test to assay effluent toxicity [1][2][3], to evaluate water quality [4,5] and for risk assessment 142 V. REGINATTO et al purposes [6]. Considering this wide range of applications it is expected that samples to be assayed could present different physical-chemical characteristics, like, different degree of colouration.…”