Phytotoxicity of the new antifouling compound Irgarol 1051 and a major degradation product

The phytotoxicity of the new antifouling compound Irgarol 1051 (2-methylthi o-4-tert-butylamino-6-cycloamino-s-triazine) and its degradation product M1 (2-methylthio-3-tert-butylamino-6-amino-s-triazine) was assessed by a batt ery of bioassays with marine and freshwater species, Both compounds at low concentrations affected aquatic plant species such as the red macroalga Por phyra yezoensis conchospores, the brown macroalga Eisenia bicyclis gametoph ytes, the freshwater green microalga Closterium ehrenbergii, the floating m acrophytes Lemna gibba G3 and Lemna minor 1769, The toxicity of Irgarol 105 1 was higher than that of M1 for all the aquatic plant species tested, but MI showed a higher toxicity to root elongation of a terrestrial plant. The NOEC (0.3 mu g/l) of Irgarol to the brown seaweed was identical to the maxi mum concentration (0.296 mu g/l) detected in Japanese coastal waters, and t he maximum concentration of M1 (1.87 mu g/l) detected amounted to only 20% of the NOEC value. The bioassay results suggest the possibility that both I rgarol 1051 and M1 may influence the primary producer community in the aqua tic environment, (C) 2000 Elsevier Science Ltd. All rights reserved.