An assessment of the cage-culture turbidostat as an alternative algal bioassay

A computer controlled cage-culture turbidostat (CCT) is described as an alternative to batch algal bioassays. The CCT is designed to monitor algal growth changes in response to the addition of toxicants including chronic toxic effects in comparison to batch culture toxicity tests which are most successful in assessing acute responses. The system is easily and quickly set up, with minimum operator time required once assembled. The alga Phaeodactylum tricornutum (CCAP 1052/6) was used as the test species. Stable growth of the alga could be maintained in the CCT for 14 days, sufficient time to run bioassay experiments using both the herbicide Diuron™ (DCMU) and a complex industrial effluent. Additions of various concentrations of both toxins to the chamber caused changes in the growth rate and the chl-a concentration of the culture. The Median Inhibitory Concentration of effluent calculated to cause a 50% reduction in the growth rate (IC50) in the CCT was estimated to be 0.33 μM DCMU, and 15.33% of the effluent. Comparable results were obtained when using the standard algal growth inhibition toxicity (AGIT) test, the 72 h-IC50 values were 0.09 μM DCMU and 16.4% effluent. This study indicates a potential use for the CCT for water quality monitoring, which may provide more environmentally relevant information than the commonly used AGIT test.