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Mechanism of acute silver toxicity in Daphnia magna
Author(s) -
Bianchini Adalto,
Wood Chris M.
Publication year - 2003
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620220624
Subject(s) - daphnia magna , sodium , toxicity , acute toxicity , chemistry , atpase , daphnia , environmental chemistry , toxicology , pharmacology , biochemistry , biology , biophysics , ecology , crustacean , enzyme , organic chemistry
Daphnids ( Daphnia magna ) were exposed to AgNO 3 at 0.303 ± 0.017 μg silver/L (46.9% as Ag + ), in the absence of food, in moderately hard synthetic water under static conditions for up to 48 h. Results from accumulation experiments demonstrated that silver body burden was inversely related to body mass. Daphnids exposed to silver exhibited ionoregulatory disturbance, which was characterized by decreases in whole‐body sodium concentration. This ionoregulatory disturbance was explained, at least in part, by a competitive inhibition of the whole‐body sodium uptake (six‐ to sevenfold increase in the Michaelis constant with no change in maximal velocity), which was complete by 1 h of exposure, and resulted in approximately 40% inhibition of sodium influx from the water. A rapidly developing inhibition of whole‐body Na + ,K + ‐dependent adenosine triphosphatase (Na + ,K + ‐ATPase) activity, significant by 2 h and complete at 90% blockade by 12 h, also was observed during exposure to AgNO 3 . Therefore, these findings clearly demonstrate that the key mechanism involved in acute Ag + toxicity in D. magna , the most sensitive freshwater organism tested to date, resembles that described for freshwater fish— that is, inhibition of active sodium uptake by blockade of Na + ,K + ‐ATPase. Furthermore, the results showed that Na + ,K + ‐ATPase inhibition was directly related to silver accumulation in the whole body of D. magna. However, the nature of the sodium uptake inhibition (competitive vs noncompetitive in fish) and the fact that whole‐body chloride concentration was not disturbed in daphnids was different from fish. With regard to the biotic ligand model (BLM) for silver, our results yielded a log K value of about 8.9. However, the current version of the BLM uses a rainbow trout log K value (7.3) but achieves the correct sensitivity of the model for daphnids by reducing the saturation of toxic sites needed to cause toxicity. An alternative way may be to use the log K value derived from the present results.