Effects of alumina refinery wastewater and signature metal constituents at the upper thermal tolerance of: 1. The tropical diatom Nitzschia closterium

Ecotoxicological studies, using the tropical marine diatom, Nitzschia closterium (72-h growth rate), were undertaken to assess potential issues relating to the discharge from an alumina refinery in northern Australia. The studies assessed: (i) the species' upper thermal tolerance; (ii) the effects of three signature metals, aluminium (Al), vanadium (V) and gallium (Ga) (at 32 degrees C): and (iii) the effects of wastewater (at 27 and 32 degrees C). The critical thermal maximum and median inhibition temperature for N. closterium were 32.7 degrees C and 33.1 degrees C, respectively. Single metal toxicity tests found that N. closterium was more sensitive to Al compared to Ga and V. with IC(50)s (95% confidence limits) of 190 (140-280), 19,640 (11,600-25,200) and 42,000 (32,770-56,000) mu g L-1, respectively. The undiluted wastewater samples were of low toxicity to N. closterium (IC(50)s > 100% wastewater). Environmental chemistry data suggested that the key metals and discharge are a very low risk to this species. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.