Humic substances influence sodium metabolism in the freshwater crustacean Daphnia magna

Chris N. Glover, Eric F. Pane, Chris M. Wood

Research output: Contribution to journalJournal Articlepeer-review

55 Citations (Scopus)


Humic substances are ubiquitous components of natural waters with important roles in alleviating metal toxicity to aquatic organisms. Recent literature reports suggest that humic substances may also exert direct influences on biota. This study investigated the influence of two commercially available humic substances on sodium metabolism in Daphnia magna, a hyperregulating freshwater crustacean. Environmentally realistic levels of Suwannee River natural organic matter (SRN) and Aldrich humic acid (AHA) significantly enhanced sodium transport. This effect was described as an uncompetitive stimulation of sodium influx, as characterised by an increased maximal sodium transport rate (J max), accompanied by a decreased uptake affinity (increased K m). SRN exposure also significantly promoted the unidirectional loss of sodium from the daphnids to the water, an effect not observed in the presence of AHA. A 24-h preexposure to AHA before influx measurement had no effect on AHA-induced stimulation of sodium influx. Conversely, 24-h preexposure to SRN resulted in influx values that returned to control (humic-free) levels. Whole-body sodium levels reduced by SRN exposure were also restored to control levels following 24-h SRN preexposure. The significance and potential mechanisms of these actions are discussed, and the toxicological implications of these findings are assessed.

Original languageEnglish
Pages (from-to)405-416
Number of pages12
JournalPhysiological and Biochemical Zoology
Issue number3
Publication statusPublished - May 2005


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