A flow-through chamber for toxicity testing of 80–200 μm organisms

A flow-through chamber was developed for toxicity testing of mobile species that require microscopic observation to assess viability and development; no sub-sampling was required in this method. Organisms were held in 1.5 mL volumes in 30 mm plastic petri plates adapted with two side sections containing 35 μm screening to provide drainage. Test solutions continuously entered via a drip tube; five 1.5 mL volumes were exchanged per hour. The 30 mm organism dish was housed in an outer dish (60 mm petri plate) that captured effluent for water quality measurements. Direct observation of organisms in the thin water layer occurred without refocusing the microscope. The flow-through chamber was used to test the toxicity of copper to Mercenaria mercenaria (hard clam) as they developed from free swimming larvae ( 80+μm) through metamorphosis to the settlement stage ( 200 μm). The flow-through chamber performed well and good water quality was maintained throughout the assay. Metamorphosis occurred at the appropriate developmental time with relatively low variability between replicates. Copper, at a concentration of 14 μg/L Cu, was shown to significantly increase mortality and inhibit metamorphosis after 36 h of exposure.