The effect of water hardness on the toxicity of uranium to a tropical freshwater alga (Chlorella sp.)

Charles, Amanda L.; Markich, Scott J.; Stauber, Jennifer L.; Filippis, L.F. De

doi:10.1016/s0166-445x(01)00260-0

Cited by 73 publications

(41 citation statements)

References 24 publications

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“…In earlier studies, we found that the presence of H þ , Ca 2þ , and Mg 2þ reduced accumulation of uranium in L. gibba, and consequently toxicity (Mkandawire et al, 2004a). Similar results were obtained with algae where water hardness reduced toxicity of uranium (Charles et al, 2002). This indicates that in addition to phosphate, uranium toxicity to most aquatic organisms is influenced by the element's behavior in media where it readily interacts with other ions, and its speciation is readily influenced by physicochemical conditions in the milieu similar to factors that influence its bioaccumulation in L. gibba reported by Mkandawire et al (2004a).…”

Section: Influence Of Uranium-phosphate Concentration Ratios On Growthsupporting

confidence: 84%

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Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

Mkandawire

Vogel

Taubert

et al. 2007

Environmental Toxicology

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The influence of phosphate on the toxicity of uranium to Lemna gibba G3 was tested in semicontinuous culture with synthetic mine water developed as an analogue of surface water of two abandoned uranium mining and ore processing sites in Saxony, Germany. Six concentrations of uranium were investigated under five different supply regimes of PO 4 3À at constant pH (7.0 6 0.5) and alkalinity (7.0 6 1.6 mg L À1 total CO 3 2À). The results showed significant inhibition of specific growth rates in cultures exposed to the highest uranium concentrations (3500 and 7000 g U L À1 ) at lowest PO 4 3À supply of 0.01 mg LÀ1 . An increase of phosphate concentration from 0.01 to 8.0 mg L À1 resulted in an increase of EC 50 from 0.9 6 0.2 to 7.4 6 1.9 mg L À1 (significant with Student's t test, P > 0.05). The accumulation of uranium in L. gibba increased exponentially with the increase in uranium concentration in cultures with 0.01 and 0.14 mg PO 4 3À L À1. Accumulation also increased significantly when PO 4 3À supply was increased from 0.14 to 1.36 mg PO 4 3À L À1 for all uranium concentrations. However, as the supply of PO 4 3À gradually increased from 1.36 to 8.0 mg PO 4 3À L À1 , uranium bioaccumulation increased slightly but insignificantly before leveling off. Uranium speciation modeling with PhreeqC geochemical code predicted increases in the proportions of uranyl phosphate species when PO 4 3À concentrations increase in the media. Most of these uranyl phosphate species have a high probability of precipitation [saturation indices (SI) > 0.93]. Therefore, the alleviation of uranium toxicity to L. gibba with phosphates is due to interactions among components of the media, mainly uranyl and phosphate which results in precipitation. Consequently, bioavailable fractions of uranium to L. gibba are reduced. This might explain lack of consistent EC 50 values for uranium to most aquatic organisms. # 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 9-16, 2007.

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Section: Influence Of Uranium-phosphate Concentration Ratios On Growthsupporting

confidence: 84%

“…The contradiction in uranium toxicity is likely a result of recently observed influence from water quality. Charles et al (2002) found that toxicity of uranium to unicellular microalgae was alleviated by water hardness due presence of Ca 2þ or Mg 2þ…”

mentioning

confidence: 99%

Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

Mkandawire

Vogel

Taubert

et al. 2007

Environmental Toxicology

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“…Thus, the reduction in U toxicity with increased water hardness is most likely due to competition between U and Ca and/or Mg for binding sites on the cell surface of the organisms. In the study by Charles et al [100], both extracellular and intracellular U concentrations of U were lower at the highest water hardness, indicating that the decreased toxicity of U to Chlorella sp. was primarily due to a decrease in U binding at the cell surface, leading to a decreased cellular uptake of U.…”

Section: Effect Of Water Hardnessmentioning

confidence: 90%

“…Similarly, Charles et al [100] found that a 50-fold increase in water hardness (8 to 400 mg CaCO 3 l -1 ) resulted in a fivefold decrease in the toxicity (population growth) of U to the tropical freshwater alga, Chlorella sp. (i.e., an increase in the 72 h EC 50 from 56 µg l -1 at 8 mg CaCO 3 l -1 to 270 µg l -1 at 400 mg CaCO 3 l -1 ).…”

Section: Effect Of Water Hardnessmentioning

confidence: 92%

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Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

Markich

2002

The Scientific World JOURNAL

203

142

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The speciation of uranium (U) in relation to its bioavailability is reviewed for surface waters (fresh-and seawater) and their sediments. A summary of available analytical and modeling techniques for determining U speciation is also presented. U(VI) is the major form of U in oxic surface waters, while U(IV) is the major form in anoxic waters. The bioavailability of U (i.e., its ability to bind to or traverse the cell surface of an organism) is dependent on its speciation, or physicochemical form. U occurs in surface waters in a variety of physicochemical forms, including the free metal ion (U 4+ or UO 2 2+ ) and complexes with inorganic ligands (e.g., uranyl carbonate or uranyl phosphate), and humic substances (HS) (e.g., uranyl fulvate) in dissolved, colloidal, and/or particulate forms. Although the relationship between U speciation and bioavailability is complex, there is reasonable evidence to indicate that UO 2 2+ and UO 2 OH + are the major forms of U(VI) available to organisms, rather than U in strong complexes (e.g., uranyl fulvate) or adsorbed to colloidal and/or particulate matter. U(VI) complexes with inorganic ligands (e.g., carbonate or phosphate) and HS apparently reduce the bioavailability of U by reducing the activity of UO 2 2+ and UO 2 OH + . The majority of studies have used the results from thermodynamic speciation modeling to support these conclusions. Time-resolved laser-induced fluorescence spectroscopy is the only analytical technique able to directly determine specific U species, but is limited in use to freshwaters of low pH and ionic strength. Nearly all of the available information relating the speciation of U to its bioavailability has been derived using simple, chemically defined experimental freshwaters, rather than natural waters. No data are available for estuarine or seawater. Furthermore, there are no available data on the relationship between U speciation and bioavailability in sediments. An understanding of this relationship has been hindered due to the lack of direct quantitative U speciation techniques for particulate phases. More robust analytical techniques for determining the speciation of U in natural surface waters are needed before the relationship between U speciation and bioavailability can be clarified.

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Actinide Speciation and Bioavailability in Fresh and Marine Waters

Markich¹,

Brown²

2018

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The actinides comprise a group of 15 metals (with atomic numbers ranging from 89 to 103) that are all radioactive and occur as cations in natural surface waters. Only the first 10 actinides are covered in this study, as these are the most environmentally relevant, where the dominant oxidation states are as follow: actinium(III), thorium(IV), protactinium(V), uranium(VI), neptunium(V), plutonium(IV) and (V), americium(III), curium(III), berkelium(III), and californium(III). The physicochemical form, or speciation, of an actinide (e.g., free metal ion, or complexes with inorganic or organic ligands) in natural surface waters can be determined using a range of analytical techniques. However, such methods are seldom commercially available and rarely determine a complete distribution of all metal species. A complementary approach, which is more cost effective, time efficient, and predictive, is the application of geochemical speciation modeling, which calculates the percentage distribution of all actinide species based on known or postulated chemical reactions. The general consensus is that geochemical speciation models can provide useful results if applied correctly with an understanding of the differences between simulated and real systems. This is the first study to use an internally consistent equilibrium database within a geochemical model (WHAM) to calculate the speciation of the first 10 actinides across fresh, estuarine, and marine waters that incorporates natural dissolved organic matter (DOM) (i.e., fulvic acid). The speciation of a metal (actinide) largely governs its uptake and/or toxicity (bioavailability) in aquatic organisms. The general consensus is that bioavailability is best predicted by the concentration of the free metal ion (M z+ ) and that metals complexed with most inorganic ligands (e.g., carbonate or sulfate) or natural DOM, typically have low bioavailability. There is also evidence to suggest that colloidal thorium is bioavailable to freshwater organisms. The study correlates observed actinide speciation with bioavailability (where available) or utilizes predicted actinide speciation to determine the likely magnitude of bioavailability, as applied to aquatic organisms. This study also addresses the likely effects of global ocean acidification and increased natural DOM concentrations in fresh surface waters on actinide speciation and bioavailability.

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The effect of water hardness on the toxicity of uranium to a tropical freshwater alga (Chlorella sp.)

Cited by 73 publications

References 24 publications

Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

Actinide Speciation and Bioavailability in Fresh and Marine Waters

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