ABSTRACT
The present study confirms that chlorate is toxic only to brown algae and not to species of other ecologically relevant taxa. The brown alga Ectocarpus variabilis exhibited a LOEC of 0.005 mM (0.4 mg ClO3-/liter) and an LC50 of 0.012 mM, when cultured with nitrate as a sole source of nitrogen. The toxicity to species other than brown algae as measured in growth inhibition tests ranged from 0.75 mM (96-h NOEC) for Selenastrum capricornutum to > or = 7.48 mM (48-h NOEC) for the fungus Trichoderma hamatum. The nitrogen source, nitrate or ammonium, did not significantly influence the toxicity to the nonsensitive species. The tests on brown algae found that as compared with ammonium, the toxicity to nitrate-grown cultures is higher by a factor of about 10. This confirms the hypothesis that nitrate reductase is involved in the toxic effects of chlorate on brown algae. Chlorite, tested as a potential toxic metabolite of chlorate, demonstrated high toxicity to many of the taxa tested and only low toxicity to E. variabilis. It may be concluded that brown algae are exceptionally sensitive to chlorate. It may also be concluded that various nitrogen sources could not induce toxicity in nonsensitive species. From these experiments no conclusions could be drawn as to the potential role of chlorite in chlorate toxicity. Furthermore it may be concluded that E. variabilis is a suitable laboratory test species for further investigations into the mechanism of chlorate toxicity to brown algae.
