Doctor of Philosophy
School of Chemistry
Ward, Daniel, The response of marine benthic fauna exposed to continuous and pulsed exposures of contaminated sediment: a study of avoidance and toxicity, Doctor of Philosophy thesis, School of Chemistry, University of Wollongong, 2013. http://ro.uow.edu.au/theses/4075
This study aimed to develop environmentally relevant chronic toxicity test methods to build on routine sediment quality assessment techniques currently in use. A series of experiments were used to assess the suitability of new Australian benthic invertebrate species for toxicity testing and investigate the use of chronic and behavioural endpoints to enable the development of more robust sediment quality guidelines.
Many researchers are evaluating representative benthic organisms for use in robust yet rapid toxicity tests to assess the sublethal and lethal effects of sediment contaminants. Four species of harpacticoid copepods, identified as Nitocra spinipes, Tisbe tenuimana, Robertgurneya hopkinsi and Halectinosoma sp., were assessed as potential test species. The influence of diet on life cycle progression (development) was assessed and the use of a mixed tri-algal diet was found to be superior to the use of commercial fish food alone. Water-only bioassays showed that the times required to cause 50% lethality (LT50) were 24 (22-27) h at 50 μg Cu/L for T. tenuimana; 114 (100-131) h and 36 (32-40) h for 200, and 400 Cu/L, respectively, for N. spinipes, and 119 (71-201) h and 7 (4-10) h for 200 and 800 μg Cu/L, respectively, for R. hopkinsi. 96-h lethal effects thresholds were also determined for N. spinipes exposed to Cd, Cu, Zn, ammonia and phenol in water-only exposures. Species were ranked based on ease of handling, culturing, rate of maturity, food selectivity and sensitivity to copper. N. spinipes was found to be the most suitable species to use in sediment bioassays as it was robust, easily cultured and was sensitive to dissolved copper.
The avoidance response of M. plumulosa, N. spinipes and the snail Phallomedusa solida when exposed to contaminated sediments was investigated. Test vessels were designed to allow the assessment of organisms moving between test sediments. Each species was observed to disperse evenly between test chambers that contained reference sediment. In the presence of contaminated sediment, test species avoided the contaminated sediment as early as 6, 6, and 24 h following exposure for N. spinipes, P. solida and M. plumulosa, respectively. Avoidance was generally greater for sediments which elicited greater 10-d lethality. Each species was observed to have the ability to respond to chemical cues in the environment and inhabit sediment that provided the best opportunity for survival. Rapid screening methods to assess sediment toxicity could be developed using avoidance as an endpoint.
Acute and chronic toxicity associated with short, intermittent exposure to four field collected contaminated sediments was assessed for M. plumulosa and N. spinipes. Increasing the duration of exposure caused a decrease in survival of M. plumulosa and N. spinipes during 10-d bioassays. In addition, reproduction decreased following exposure to contaminated sediment. For M. plumulosa, reduced fecundity appeared to occur from exposure to contaminated sediment and reproductive effects occurred follwoing shorter exposures than needed to sense and avoid contaminant exposure. Thus, while avoidance behaviours may prevent acute lethality, slow responses may not prevent sublethal effects.
This study indicates that sediment toxicity methods which utilise static continuous exposures may over-estimate the toxicity that would occur at a field location. However, by preventing organisms from avoiding unfavourable sediments, these methods provide a precautionary assessment of possible effects, which is usually the aim of most assessments frameworks.