2.3.2. Ecotoxicological effects (4. เนม)
We tested the sediment samples for acute and chronic toxicity by luminescent bacteria Vibrio fischeri (ISO 21338, 2010) and Chironomus riparius midge (OECD, 2004), respectively. For the V. fischeri test, 1 g of freeze dried sediment sample was extracted with 5 ml 2% sodium chloride (NaCl) solution in two parallel extractions, and bacteria were exposed to the extract at concentrations ranging from 50% to 0.10% in two replicates. The test was performed as described in ISO standard 21338 (2010) standard, except that the extract was buffered with sodium bicarbonate (NaHCO3) to reduce the variation of pH, and to yield a test pH of 7. Extractswere dilutedwith 2% NaCl as two parallel dilutions series and each dilution stepwas tested for toxicity. Effective concentrations (EC50-values) expressed as percentage concentrations of the extract in the test were calculated with probit analysis using SPSS software version 20.0.0 (IBM, 2013).