Aquatic Toxicology 174 (2016) 82–91 Contents lists available at ScienceDirect Aquatic Toxicology j o ur na l ho me pag e: www.elsevier.com/locate/aquatox Toxicity of dissolved and precipitated aluminium to marine diatoms Megan L. Gillmore a,b,∗ , Lisa A. Golding a , Brad M. Angel a , Merrin S. Adams a , Dianne F. Jolley b a CSIRO Land and Water, Lucas Heights, NSW 2234, Australia b University of Wollongong, Wollongong, NSW 2522, Australia a r t i c l e i n f o Article history: Received 23 November 2015 Received in revised form 19 January 2016 Accepted 13 February 2016 Available online 16 February 2016 Keywords: Metal Speciation Solubility Microalgae Membrane permeability Water quality guidelines a b s t r a c t Localised aluminium contamination can lead to high concentrations in coastal waters, which have the potential for adverse effects on aquatic organisms. This research investigated the toxicity of 72-h exposures of aluminium to three marine diatoms (Ceratoneis closterium (formerly Nitzschia closterium), Minutocellus polymorphus and Phaeodactylum tricornutum) by measuring population growth rate inhibition and cell membrane damage (SYTOX Green) as endpoints. Toxicity was correlated to the time-averaged concentrations of different aluminium size-fractions, operationally defined as <0.025 m filtered, <0.45 m filtered (dissolved) and unfiltered (total) present in solution over the 72-h bioassay. The chronic population growth rate inhibition after aluminium exposure varied between diatom species. C. closterium was the most sensitive species (10% inhibition of growth rate (72-h IC10) of 80 (55–100) g Al/L (95% confidence limits)) while M. polymorphus (540 (460–600) g Al/L) and P. tricornutum (2100 (2000–2200) g Al/L) were less sensitive (based on measured total aluminium). Dissolved aluminium was the primary contributor to toxicity in C. closterium, while a combination of dissolved and precip- itated aluminium forms contributed to toxicity in M. polymorphus. In contrast, aluminium toxicity to the most tolerant diatom P. tricornutum was due predominantly to precipitated aluminium. Preliminary investigations revealed the sensitivity of C. closterium and M. polymorphus to aluminium was influenced by initial cell density with aluminium toxicity significantly (p < 0.05) increasing with initial cell density from 10 3 to 10 5 cells/mL. No effects on plasma membrane permeability were observed for any of the three diatoms suggesting that mechanisms of aluminium toxicity to diatoms do not involve compromis- ing the plasma membrane. These results indicate that marine diatoms have a broad range in sensitivity to aluminium with toxic mechanisms related to both dissolved and precipitated aluminium. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Over the past few decades, localised inputs of aluminium to marine ecosystems have increased as a consequence of anthro- pogenic activities, such as coastal mining and dredging operations, discharges associated with alumina production, the disturbance or drainage of acid sulphate soils for coastal development and the use of aluminium in sacrificial anodes for the protection of offshore assets. These activities can increase aluminium concen- trations above the natural background concentrations of coastal waters. Open ocean dissolved aluminium concentrations are typi- cally <0.7 g/L (Kramer et al., 2004; Measures et al., 2005; Middag et al., 2011), while in coastal waters they range from 0.1 to 16.7 g/L ∗ Corresponding author. E-mail addresses: mg997@uowmail.edu.au, megan.gillmore@csiro.au (M.L. Gillmore). (Angel et al., 2016) and can be as high as 83 g/L in heavily indus- trialised harbours such as Port Curtis, QLD, Australia (Angel et al., 2012). An important distinction between aluminium speciation in sea- water compared to freshwater is the absence of cationic species (Al 3+ , AlOH 2+ and Al(OH) 2 + ) which dominate under acidic pH con- ditions (Wilson, 2011). In the marine environment (pH 8.0–8.3, 35 PSU), aluminium speciation is dominated by the aluminate anion (Al(OH) 4 - ) and to a lesser extent neutral aluminium hydroxide (Al(OH) 3 ◦ ) (Millero et al., 2009) with insignificant amounts of col- loidal aluminium (Angel et al., 2016; Moran and Moore, 1989). At high total aluminium concentrations (above approximately 500 g/L) precipitation of dissolved aluminium, mostly as Al(OH) 3 and to a lesser extent as hydrotalcite (Mg 6 Al 2 CO 3 (OH) 16 .4H 2 O), increases and dominates speciation (Angel et al., 2016). The change in aluminium speciation with pH, time and con- centration is an important consideration when performing toxicity tests as bioavailability and hence toxicity is directly related to metal http://dx.doi.org/10.1016/j.aquatox.2016.02.004 0166-445X/© 2016 Elsevier B.V. All rights reserved.