Maintenance of chemical concentrations during toxicity tests is essential to determine the intrinsic toxicity of a material. For compounds that are sorptive, rapidly biodegraded, volatile or chemically labile, static and/or static renewal exposure strategies may result in large fluctuations in exposure concentrations over time, particularly for chronic tests. This article describes the development and adequacy of a novel flow-through chronic toxicity test method for the cladoceran Ceriodaphnia dubia, using a rapidly biodegradable surfactant, dodecyl alkyl sulfate (C,,AS) as a model compound.
Organisms were exposed to &AS in polystyrene cups fitted with Nitex mesh on two opposing sides. Cups were placed in either piexiglass or glass flow-through channels. Alkyl sulfate solutions were delivered to the troughs via peristaltic pumps at one end and pumped through the individual test chambers in a linear fashion, exiting at the downstream end. Flow-through tests were conducted with both reconstituted and river water. Control mortality and reproduction met current U S . Environmental Protection Agency criteria (less than 20% mortality and greater than I5 neonates/femalej. Three advantages of this system are (1) the method provides an advance over current Ceriodaphnia dubia chronic test methods for sorptive and labile compounds, (2) it is compact and portable, and (3) it is useful for other small aquatic organism tests.