Optimal chlorophyll fluorescence parameter selection for rapid and sensitive detection of lead toxicity to marine microalgae Nitzschia closterium based on chlorophyll fluorescence technology

Heavy metal pollution as one of the most serious pollution problems of marine environment, seriously threatens the safety of marine organism and human health, and will lead to potential risks for the marine ecological environment. In order to develop a rapid and sensitive toxicity detection method for marine heavy metals, in this study, marine diatom Nitzschia closterium was used as the test organism, and the effects of different concentrations of lead (Pb) on the five chlorophyll fluorescence parameters of N. closterium including the maximum photochemical quantum yield of PSII (Fv/Fm), the effective quantum yield of PSII photochemical energy conversion (ΦPSII), the effective absorption cross section of PSII photochemistry (σPSII′), the relative electron transfer rate of PSII (rP), and the PSII electron flux per unit volume (JVPII) at different exposure times were investigated based on chlorophyll fluorescence technology. By comparing with the photosynthetic activity fluorescence parameter Fv/Fm which is commonly used for toxicity analysis of pollutants using algae as test organisms, the optimal chlorophyll fluorescence parameter that could rapidly and sensitively determine Pb toxicity to N. closterium was selected. The results indicate that all the five chlorophyll fluorescence parameters of Fv/Fm, ΦPSII, σPSII′, rP and JVPII showed good dose-response relationships with Pb within 8 h exposure time, and they all could be used as endpoints to rapidly determine Pb toxicity to N. closterium. Among the five chlorophyll fluorescence parameters, JVPII was the most sensitive fluorescence parameter for detecting the toxicity of Pb to N. closterium within 6 h exposure. And for JVPII, the median effective concentration (EC50) values of Pb at 2, 4 and 6 h were 0.329, 0.068 and 0.040 mmol L−1, respectively. However, when the exposure time was 8 h, ΦPSII was the most sensitive fluorescence parameter for the toxicity detection of Pb, and the EC50 value of Pb at 8 h was 0.038 mmol L−1. This study will provide an important basis for the development of a rapid and sensitive detection method for the biological toxicity of marine heavy metals, and those results will be helpful for ecological risk assessment in marine environment.