Toxicity tests using developmental stages of Hormosira banksii (Phaeophyta) identify ammonium as a damaging component of secondary treated sewage effluent discharged into Bass Strait, Victoria, Australia

Developing Hormosira banksii embryos, used as bioassays in toxicity studies, identified ammonium as a toxicant in secondary treated sewage effluent discharged at Boags Rocks, Victoria, Australia. Ammonium did not affect fertilization but had a significant effect on germination at 48 h and cell division at 72 h with most damage occurring in the first 48 h. Ammonium showed a similar effect as whole effluent (when expressed as mg N l–1 ammonium), sampled in June, September and November 1997, on developing H. banksii embryos. This similarity is further confirmed with comparable EC50 (concentration causing an effect on 50% of the population tested) and LOEC (lowest observable effect concentration) values. Mean EC50 values for the ammonium bioassays were 3.19 mg N l–1 for germination and 6.14 mg N l–1 for cell division. The range of mean EC50 values for the 3 effluent samples were 3.15 to 5.28 mg N l–1 for germination and 3.53 to 6.43 mg N l–1 for cell division. These values are well below the median ammonium concentration (10.28 mg N l–1) calculated for Boags Rocks due to sewage effluent discharge.