Rapid toxicity assessment using ingestion rate of cladocerans and ciliates

Abstract

Ingestion rate of suspension feeding zooplankton is a useful endpoint for rapid toxicity assessment. Methods are presented for quantifying ingestion rate in single Ceriodaphnia dubia, Paramecium aurelia, and Brachionus plicatilis, using fluorescent beads and image analysis. Test organisms are exposed to toxicants for one hour, then allowed to feed on 2 μm fluorescent beads for 3 minutes. Toxicants reduced ingestion rate in a dose-dependent manner, permitting the calculation of NOECs. The NOECs for 7 toxicants are presented for the 3 species as well as comparative toxicity of pore water samples from 13 urban creeks. The sensitivity of the 1-h C. dubia ingestion rate test was compared to 48-h LC50 and 7-d reproductive tests for 2 and 4 compounds, respectively. The ingestion test was within a factor of 2 for 3 of the comparisons, but >8 times less sensitive for the other 3 comparisons. For B. plicatilis, 1-h ingestion rate NOEC was lower than the 24-h LC50s for 4 of the 5 compounds tested. The rotifer 48-h reproductive test was a more sensitive endpoint for 3 of 4 compounds. These methods are simple, rapid, and inexpensive, permitting several species to be incorporated into a test battery.