Toward a Biotic Ligand Model for Freshwater Green Algae: Surface-Bound and Internal Copper Are Better Predictors of Toxicity than Free Cu2+-Ion Activity When pH Is Varied
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- 作者：Karel A. C. De Schamphelaere ; Jennifer L. Stauber ; Karyn L. Wilde ; Scott J. Markich ; Paul L. Brown ; Natasha M. Franklin ; Nicola M. Creighton ; and Colin R. Janssen
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：April 1, 2005
- 年：2005
- 卷：39
- 期：7
- 页码：2067 - 2072
- 全文大小：120K
- 年卷期：v.39,no.7(April 1, 2005)
- ISSN：1520-5851
文摘
The freshwater green microalgae Chlorella sp. andPseudokirchneriella subcapitata (P. subcapitata) werechronically (48 and 72 h, respectively) exposed to copperat various pH levels, i.e., pH 6-7.5 and pH 5.9-8.5,respectively. Concentrations resulting in 50% inhibition ofexponential growth rate (EC50) were determined asdissolved Cu, estimated chemical activity of the free Cu2+ion (as pCu = - log{Cu2+ activity as molarity}), and asexternal (surface-bound) Cu and internal Cu in the algal cells.With increasing pH, EC50dissolved decreased from 30 to1.1 
g of Cu L-1 for Chlorella sp. and from 46 to 18 g ofCu L-1 for P. subcapitata. The pH effect on copper toxicitywas even more obvious when expressed as Cu2+ activity.The EC50pCu increased on average 1.4 pCu unit per pHunit for Chlorella sp. and 1.1 pCu unit per pH unit for P.subcapitata, thus indicating a marked increase of Cu2+ toxicityat higher pH (more than 1 order of magnitude per pHunit). In contrast, it was found that EC50 values expressedas surface bound or external copper (EC50external) and asinternal copper (EC50internal) did not vary substantially whenpH was increased. External Cu was operationally definedas the Cu fraction removable from the algal cell by short-term contact with ethylenediaminetetraacetic acid; internalcopper was defined as the nonremovable fraction. ForChlorella sp. the EC50external varied between 5 and 10 fg ofCu/cell (factor of 2 difference) and the EC50internal between 25and 40 fg of Cu/cell (factor of 1.6 difference). For P.subcapitata the EC50external varied between 10 and 28 fgof Cu/cell (factor of 2.8 difference) and the EC50internal between42 and 71 fg of Cu/cell (factor of 1.7 difference). Becausethe observed variation in EC50external and EC50internal ismuch less than the variation in EC50Cu2+, it is concludedthat both external and internal copper are better predictorsof copper toxicity than Cu2+ when pH is varied. From theperspective of toxicity modeling, this observation is the firststep toward considering the use of the cell surface asthe algal biotic ligand for Cu in a similar way as fish gillsfulfill this role in the biotic ligand model for predictingmetal toxicity to fish species.
g of Cu L-1 for Chlorella sp. and from 46 to 18 g ofCu L-1 for P. subcapitata. The pH effect on copper toxicitywas even more obvious when expressed as Cu2+ activity.The EC50pCu increased on average 1.4 pCu unit per pHunit for Chlorella sp. and 1.1 pCu unit per pH unit for P.subcapitata, thus indicating a marked increase of Cu2+ toxicityat higher pH (more than 1 order of magnitude per pHunit). In contrast, it was found that EC50 values expressedas surface bound or external copper (EC50external) and asinternal copper (EC50internal) did not vary substantially whenpH was increased. External Cu was operationally definedas the Cu fraction removable from the algal cell by short-term contact with ethylenediaminetetraacetic acid; internalcopper was defined as the nonremovable fraction. ForChlorella sp. the EC50external varied between 5 and 10 fg ofCu/cell (factor of 2 difference) and the EC50internal between 25and 40 fg of Cu/cell (factor of 1.6 difference). For P.subcapitata the EC50external varied between 10 and 28 fgof Cu/cell (factor of 2.8 difference) and the EC50internal between42 and 71 fg of Cu/cell (factor of 1.7 difference). Becausethe observed variation in EC50external and EC50internal ismuch less than the variation in EC50Cu2+, it is concludedthat both external and internal copper are better predictorsof copper toxicity than Cu2+ when pH is varied. From theperspective of toxicity modeling, this observation is the firststep toward considering the use of the cell surface asthe algal biotic ligand for Cu in a similar way as fish gillsfulfill this role in the biotic ligand model for predictingmetal toxicity to fish species.