The Effects of Antifouling Herbicide Irgarol 1051 on the Growth of Phytoplankton

Abstract

The antifouling algicide Irgarol 1051 is a s-triazine algicide which is an active ingredient in two antifouling formulations currently registered for distribution in New Zealand (at 20-25 gL-1 ). Primary colonization by microalgae on hull surfaces can be substantially reduced through the addition of Irgarol 1051 to ship paints. However, as a general photosystem II inhibitor, Irgarol 1051 also has toxic effects on the non-target periphyton community, reducing their growth rates after short-term and long-term exposure (Dahl, et al. 1996). This study evaluates the effects of Irgarol 1051 on the growth of two pelagic diatoms {Thalassiosira spp.) in pure culture, based on measuring the physiological and growth responses of the cultured algae to Irgarol 1051 addition. The results indicate that Irgarol 1051 can greatly increase fluorescence yield in cultured algae at a concentration of 1.00 μgL-1 during the short term physiological experiments. Fluorescence yield increase was probably caused by the inhibition of photosystem II electron transport by Irgarol 1051. Inhibition of photosynthetic activities consequently reduces the growth of these two coastal diatom species. Long term growth response showed that the growth of two Thalassiosira species would be significantly reduced at Irgarol 1051 of concentrations as low as 0.05 μgL-1. In this study EC50 in 96 hours for these two diatom species arc between 0.71 -2.23 μgL-1 which is in the range of the manufacturer's quoted levels for algal growth. Treated samples can resume growth in a clean medium, even after long-term (2 wk) exposure to Irgarol 1051. Further study on Irgarol 1051 degradation and phytoplankton recovery ability will reveal the extent of accumulation of Irgarol 1051 in the environment, and provide more information on the ecotoxicological effects of Irgarol 1051 on the phytoplankton community.