Summary
Developing water quality guidelines for Antarctic marine environments requires understanding sensitivity of biota to contaminant exposure. Toxicity tests with Antarctic invertebrates have shown response times to metal exposure takes far longer than the durations of standard bioassay methods. Test methods which address the biological characteristics of these cold climate species and theenvironment need to be developed. This study investigated the effects of five metals on behaviour and survival of an Antarctic amphipod, Orchomenella pinguides, over 30 day exposures. Multiple observations were made assessing mortality rate response of this species to metal exposure. As traditional bioassay methods use probit analysis for individual period endpoints treated independently, a new statistical model that combines bioassay model with a survival time model was developed. Interval-censored survival times were modelled using a generalised additive model (GAM) with multiplicative effects for concentration level used to incorporate the bioassay component. The time period by concentration level interaction was included as a random effect term with this mixed model version of the GAM (called a GAMM) allowing model adequacy to be investigated. The advantages of this approach are that (i) it smooths through noisy periodic mortality data “gaining strength”by estimation of the trend across multiple observation periods exploiting all data simultaneously, (ii) the simple multiplicative model, if adequate, does not allow cross-overs of time trends across concentrations that make interpretation difficult, and (iii) it allows the uncertainty in estimates of lethal concentrations to be more adequately modelled. Response times vary between metals with amphipods exposed to copper producing behavioural changes and mortality at a faster rate than exposure to cadmium, lead or zinc. Nickel did not affect the behaviour or survival of the amphipod during the 30 day exposures despite using concentrations > 1mg/L. Results from comparisons of both approaches indicate that standard bioassay methods have serious limitations when applied to Antarctic species which are generally long lived, have longer developmental times, and slower metabolic processes and potentially metal uptake than species from other climatic regions. Recommendations are made for further toxicological assessments for the future development of Water Quality Guidelines to protect Antarctic marine environments.