Oral Presentation Society of Environmental Toxicology and Chemistry Australasia 2021

Copper toxicity assessed using a multispecies microalgal assay: influence of time-of-day and duration of pulse exposures (#128)

Sarah Stone 1 , Darren Koppel 2 , Monique T Binet 3 , Stuart L Simpson 3 , Dianne F Jolley 3
  1. School of Life Sciences, University of Technology Sydney, Sydney
  2. Curtin University, Perth
  3. CSIRO Land and Water, Lucas Heights

Aquatic organisms are often exposed to short-term discharges of contaminants in stormwater runoff or effluent discharge scenarios. The duration of exposure to contaminants can have a significant impact on observed toxicity, however, predicting the risk of toxicity from these exposures remains a significant challenge as water quality guideline values are based on data from continuous exposures. Copper is a common aquatic contaminant and is known to be highly toxic to freshwater microalgal species. Many aquatic species have been observed to tolerate higher concentrations of copper for shorter durations compared to continuous chronic exposures. This research aims to address knowledge gaps in risk assessments posed by short-term exposure to contaminants by investigating the pulse toxicity of copper in a multispecies assay.

Our study examined how changing exposure duration altered the toxicity of copper using a multispecies microalgal assay with three tropical, freshwater species; Monoraphidium arcuatum, Nannochloropsis-like sp., and Pediastrum duplex. Copper toxicity was assessed under four exposure scenarios: continuous 72-h exposure, 18-h pulse exposure and 3-h pulse exposures in either the photosynthesis phase (in the light) or the cell division phase (in the dark).

Exposure duration had a significant effect on toxicity for all species within the multispecies test, with microalgae tolerating 2-10× or 4-14× higher concentrations of dissolved copper in 18-h and 3-h pulse exposures respectively, compared to continuous 72-h exposures. Additionally, toxicity observed in the 3-h pulse exposures was dependant on whether cells were exposed in the dark or light. All microalgae were more or equivalently sensitive to copper when exposed in the dark, where cells were undergoing division, compared to the light when cells were photosynthesising.

These data highlight the need to consider the exposure duration and exposure photoperiod in toxicity testing to underpin the regulation of contaminants in aquatic ecosystems.