An evaluation of recirculating artificial stream designs for acute toxicity testing using two South African Ephemeroptera species exposed to sodium sulphate

Binder, Markus (2000) An evaluation of recirculating artificial stream designs for acute toxicity testing using two South African Ephemeroptera species exposed to sodium sulphate. Masters thesis, Rhodes University.




Three artificial stream designs, tenned Large Artificial Stream Units (LASUs), Raceways, and Channels, at two major scales (1700 L, 12.5 L and 20 L recirculated volume) were developed at the Institute for Water Research, Rhodes University, Grahamstown, in order to explore the possibilities of using indigenous rheophilic macroinvertebrates in routine toxicity tests. This study compared these systems, using 96h-EC50 values from sodium sulphate toxicity tests as the experimental response. Two local Ephemeroptera (Leptophlebiidae: Adenophlebia auriculata Eaton, and Baetidae: Afroptilum sudafricanum Lestage) were evaluated for their suitability in routine toxicity tests; and the possible effects of elevated salinity levels in South African rivers on the test species were assessed. Two sets of experiments with each mayfly species were conducted, following an unreplicated regression design. Dechlorinated tap water was used as the water source. Experiments in the Channels were repeated to detennine experimental variability. Results were compared statistically by testing for overlap of 95% confidence limits (95%Cls) of EC50 values. The differences between A. auriculata EC50 values in the different systems were statistically significant (no overlap of 95%CLs), but they were not more varjable than has been considered nonnal for biological systems (Coefficient of variation 20.1 %; ratio of greatest EC50 / smallest EC50 1.63). The differences were not related to the scale or the average current velocity characteristic of each stream design (average current velocity LASUs - Raceways - Channels 0.090 - 0.083 - 0.038 mls). The Channels proved to be most efficient with regard to practical perfonnance as they are portable and easily transportable, user-friendly, reliable, splash-free, cost effective to construct, and can easily be adapted to specific requirements. These systems are therefore recommended for regular use. The suitability of the two mayfly species for routine toxicity testing was evaluated. A. auriculata EC50 values showed a significant negative correlation with the corresponding average body-size (range 1476 - 1610 11m, mean 1555 11m). The different average body-sizes probably reflected the abundance of a certain size range present in the Palmiet River at the time of collection. Both species reacted similarly to Na2S04 (similar slopes of the toxicity curves), identifying this salt as a slow acting toxicant. A. sudafricanum populations were more sensitive to Na2S04 (EC50 3.404 gIL) than A. auriculata (EC50 8.090 gIL), probably because of its smaller body-size (mean 709 11m) and a lack of extremely tolerant individuals. In comparison to other freshwater macro invertebrates, including the standard toxicity test organism Daphnia spp., both mayfly species seemed to be moderately tolerant of Na2S04; therefore there was no particular advantage to using these indigenous taxa rather than Daphnia spp. An assessment of the effects of elevated salinity/TDS levels on the test taxa yielded preliminary insights. A NaCI-EC50 for A. sudafricanum could be extrapolated and suggested a higher sensitivity to Na2S04 than to NaCl. When Na2S04 EC50 values of both species were compared to selected TDS levels of South African rivers, 4. auriculata would mostly not be affected, but A. sudafricanum might occasionally suffer frOm/ sub-lethal effects, depending on the SUlphate proportion of the TDS. The South African guideline for TDS seemed to protect both species sufficiently.

Item Type:Thesis (Masters)
Uncontrolled Keywords:Sodium sulfate, Water, Toxicology, Mayflies, Pollution
Subjects:Q Science > QL Zoology > Invertebrates > Insects
Divisions:Faculty > Faculty of Science > Zoology & Entomology
ID Code:2424
Deposited By: Mrs Carol Perold
Deposited On:31 Jan 2012 08:05
Last Modified:31 Jan 2012 08:05
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