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Osmoregulation in freshwater invertebrates in response to exposure to salt pollution
Expanded Title:The objective of this experiment was to compare sensitivities of three different mayfly species to MgSO4 and generate 96 h lethality data. These data, together with other lethality data from organisms exposed to MgSO4 in internationa studies, were used to calculate guideline values for MgSO4 using a species sensitivity distribution (SSD) approach. Nymphs of three different mayfly (Ephemeroptera) genera: Afronurus barnardi (Heptageniidae): Tricorythus discolor (Tricorythidae); and Euthraulus elegans (Leptophlebiidae) were collected from the Kat River, Eastern Cape, South Africa, and exposed to increasing concetrations of MgSO4 in recirculating channel systems on three different occassions. Toxicity tests were conducted over a 10 day (240 h) period with LC50 values determined after 96 h considered acute endpoints, and LC50 values determined after 240 h considered chronic endpoints. The experiment to compare sensitivities o fthree different mayfly species to MgSO4 and generate 96 h lethality data. A comparision of the current Reserve boundary values and the PCVs determined in this study show the PCVs to be more conservative at the Natural/Good boundary bur less conservative at the Good/Fair boundary and considerably so at the Fair/Poor boundary (Table 5.4). The PCV derivation approach should be investigated further in order to determine if it may provide more realistic boundary values for MgSO4. Although it is possible to use only acute lethality data in deriving guidelines and then apply an acute to chronic ratio (ARC), further research should investigate the use of chronic/sublethal data Fish responses to NaCI and Na2S04 exposure. The experiment to determine whether a change in dissolved oxygien (DO) could be used as a measure of the physiological response in guppies, Poecilia reticulata and zebra fish, Danio rerio when exposed to increasing concentrations of sodium chloride (NaCI) sand sodium sulphate (Na2S04) was also conducted. Data indicated little difference in the sensitivity of the used two species to either salt. As sublethal data were used in the derivation of the Natural/Good Reserve boundary values, physiological response data such as oxygen consumption data measured in D. rerio and P. reticulata could be used to evaluate this boundary value. For NaCI, a NOEC of 0.5 g/L was determined for both species. When compared with the sublethal toxicity data used by Jooste and Rossouw (2002) to derive the Reserve boundary values for NaDI (Table 5.5) it is evident that the physiological response of oxygen consumption has the potential to contribute as a sensitive endpoint in the determination of a realistic but protective guideline. The types of sublethal endpoints used in the derivation of the Reserve boundary values (e.g growth, reproduction etc) are not detailed in Jooste and Rossouw (2002) and thus it is difficult to interpret the significance of the difference in NOEC value obtained for D. rerio in the current study as compared to NOEC listed in Table 5.5. A NOEC could not be obtained for oxygen consumption as a physiological response in Na2SO4 exposed D. rerio and P. reticulata, although a LOEC could, allowing the calculation of a matc OF 0.188 g/L. The MATC (calculated by dividing the LOEC by half) is sometimes, in the absence of a NOEC, used as a sublethal endpoint in guideline derivation. When comparing this endpoint to the NOECs used by Jooste and Rossouw (2002) derive the Reserve boundary values for Na2SO4 (Table 5.5), it is again evident that oxygen consumption can contribute as a sensitive endpoint in the determination of suitable guidelines.
Date Published:01/03/2011
Document Type:Research Report
Document Subjects:Ecosystem - Biodiversity protection, Ecosystem - Invertebrates
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:1585/1/10
ISBN No:978-1-4312-0075-7
Authors:Holland AJ; Gordon AK; Muller WJ
Project No:K5/1585
Organizations:Unilever Centre for Environmental Water Quality Institute for Water Research Rhodes University
Document Size:619 KB
Attachments:EXECUTIVE SUMMARY for 1585.pdf
TABLE OF CONTENTS for 1585.pdf
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