Comparative study of toxicological responses of chlorophyllrelated parameters in the marine diatom Skeletonema sp. exposed to tributyltin and Irgarol

Abstract

We investigated the growth and chlorophyll-related parameters of the marine diatom Skeletonema marinoi-dohrnii complex （NIES-324） exposed to tributyltin （TBT） or photosystem （PS） II inhibitor Irgarol as a reference chemical for elucidating the effect of TBT on photosynthetic activity. Fifty percent effective concentrations for growth （EC₅₀） were 2.14 μg/L in TBT and 1.14 μg/L in Irgarol. Chlorophyll a content per one cell （pg/cell） was significantly decreased at the highest Irgarol concentration （1.0 μg/L） but chlorophyll c content was not affected. Following TBT treatment, however, both chlorophyll a and c content per cell increased significantly at the highest concentration （2.0 μg/L）. The ratio of chlorophyll a and c content （chl. a/c ratio） decreased significantly and the minimum level of chlorophyll fluorescence （F_o） per μg/mL of chlorophyll a （F_o/chl. a） increased significantly in all Irgarol treatment groups, but TBT had no effect on either parameter. The present results suggest that TBT has no direct effect on electron flow in the photosystem and that the chl. a/c ratio and F_o/chl. a are sensitive bio-markers for detecting the effect of the PSII inhibitor in diatoms.