Utility of Delayed Fluorescence as Endpoint for Rapid Estimation of Effect Concentration on the Green Alga Pseudokirchneriella subcapitata

Abstract

Algal growth inhibition tests for environmental risk assessment require improved efficiency to evaluate large numbers of chemicals. As an endpoint for rapid estimation of the effect concentration of test chemicals, we propose the delayed fluorescence (DF) measurement from an alga 24 h after exposure. Eight chemicals (bifenox, bromoxynil, bensulfuronmethyl, diuron, diflufenican, thiobencarb, m-chlorophenylhydrazone and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) were tested. The EC50 values from the 24 h DF measurement were similar to those from the conventional 72 h growth test for seven tested chemicals excepting thiobencarb. We conclude that 24 h DF measurement is a possible endpoint for rapid estimation of the EC50 values obtained in the 72 h growth test for those seven chemicals.

Comparison of the Conventional Algal Growth Inhibition Tests Using Cell Counting and Algal Bioassay Using Delayed Fluorescence: Application to Industrial Effluents

“…The DF from algae in the tube was directly measured at 0 h (initial value), 1 h and 6 h after exposure by the high sensitivity luminometer (TYPE-7100 prototype, Hamamatsu Photonics, Japan). This luminometer was basically the same as the one that had used in our previous report (Katsumata et al, 2009). Samples were left to stand in the dark for 60 s and were then illuminated with excitation light condition for 30 s with a white LED light (500 μmol/m 2 /s), and let to stand in the dark for 5 s, followed by a 1 s exposure by a 700 nm LED light (20 μmol/m 2 /s).…”

“…The DF intensities in the 1 to 60 s period were integrated as an integrated delayed fluorescence (DFI). Since the DFI is inhibited through the influence of typical herbicides and photosynthetic inhibitors (Katsumata et al, 2009), DFI can be used in the same manner as cell density in the conventional evaluation method to calculate the EC 50 and NOEC. The Ecotox-Statics analysis software was used to determine the EC 50 and NOEC using the DFI data as was used for the conventional algal growth inhibition test.…”

“…First, the emission of DF is inhibited following exposure to certain chemical substances approximately 0.5 s after the excitation. In addition, the inhibition of DF can be used to estimate the 50% effective concentration (EC 50 ) that is obtained in the 72 h conventional growth inhibition test for typical herbicides, photosynthetic inhibitors and heavy metals even for exposure times less than 24 h (Katsumata et al, 2006(Katsumata et al, , 2009Berden-Zrimec et al, 2007). Second, it was also reported that the time profile of DF intensity (decay curve) shows characteristic behaviors that depend upon the substance (Schmidt and Senger, 1987;Bürger and Schmidt, 1988;Katsumata et al, 2006).…”

Microalgal cytometric analysis in the presence of endogenous autofluorescent pigments

“…Alternatively, different groups have exploited the measurement of the intrinsic fluorescence of chlorophyll [17,16,18] and other fluorescent pigments (green fluorescence) [19,20] for a number of applications such as viability evaluation, characterization of phytoplankton diversity, screening of microalgal strains for biotechnological processes, and evaluation of environmental toxicity [17,21]. However, chlorophyll continues to fluoresce in some non-viable cells, which may lead to inaccurate viability quantitation results using autofluorescence as the sole parameter of viability.…”

Thermoluminescence as a complementary technique for the toxicological evaluation of chemicals in photosynthetic organisms

“…To improve the efficiency in evaluating the hazard of a large number of chemicals, providing mechanistic information, it would be helpful to carry out batteries of rapid and mode of action based screening tests (Katsumata et al, 2009;Repetto, 2013).…”