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The effect of water hardness on the toxicity of uranium to a tropical freshwater alga Chlorella sp.
Aquat Toxicol. 2002 Oct 02; 60(1-2):61-73.AT

Abstract

Uranium (U) derived from mining activities is of potential ecotoxicological concern to freshwater biota in tropical northern Australia. Few data are available on the effects of water hardness (Ca and/or Mg), which is elevated in U mine wastewaters, on the toxicity and bioavailability of U to freshwater biota, particularly algae. This study determined the effect of water hardness (8, 40, 100 and 400 mg CaCO(3) x l(-1), added as calcium (Ca) and magnesium (Mg) sulphate) on the toxicity (72 h growth rate inhibition) of U to the unicellular green alga, Chlorella sp., in synthetic freshwater, at constant pH (7.0) and alkalinity (8 mg CaCO(3) x l(-1)), similar in chemical composition to sandy coastal streams in tropical northern Australia. A 50-fold increase in water hardness resulted in a 5-fold decrease (P<or =0.05) in the toxicity of U to Chlorella sp. (i.e. the 72 h EC(50) increased from 56 to 270 micro g U l(-1)). Possible explanation for the ameliorative effect of water hardness includes: (i) competition between U and Ca and/or Mg for binding sites on the cell surface; and (ii) a change in U speciation, and hence, bioavailability. Results showed that extracellular (cell-surface) and intracellular U concentrations significantly (P<0.05) decreased (2-5-fold) as water hardness increased from 8 to 400 mg CaCO(3)x l(-1). Calculation of U speciation using the geochemical model HARPHRQ showed that there were no significant (P>0.05) differences in the predicted speciation (% distribution) of U amongst the four water hardness levels. The reduction in U toxicity with increasing water hardness was most likely due to competition between U and Ca and/or Mg for binding sites on the algal cell surface. The minimum detectable effect concentrations of U were approximately 3 and 24 times higher (at 8 and 400 mg CaCO(3)x l(-1) hardness, respectively) than the national interim U guideline value (0.5 micro g x l(-1)) for protecting aquatic ecosystems. Overall, the results reinforce the need for a more flexible U guideline based on a hardness-dependent algorithm, which may allow environmental managers to relax the national guideline for U on a site-specific basis.

Authors+Show Affiliations

Charles AL
Environment Division, Australian Nuclear Science and Technology Organisation, PMB 1, Menai NSW 2234, Australia. amanda.charles@ansto.gov.au
Markich SJ
No affiliation info available
Stauber JL
No affiliation info available
De Filippis LF
No affiliation info available

MeSH

Biological AvailabilityCalciumChlorellaDose-Response Relationship, DrugGuidelines as TopicMagnesiumMiningUraniumWaste Disposal, FluidWater Pollutants, RadioactiveWater Pollution

Pub Type(s)

Journal Article

Language

eng

PubMed ID

12204587

Citation

Charles, Amanda L., et al. "The Effect of Water Hardness On the Toxicity of Uranium to a Tropical Freshwater Alga Chlorella Sp." Aquatic Toxicology (Amsterdam, Netherlands), vol. 60, no. 1-2, 2002, pp. 61-73.
Charles AL, Markich SJ, Stauber JL, et al. The effect of water hardness on the toxicity of uranium to a tropical freshwater alga Chlorella sp. Aquat Toxicol. 2002;60(1-2):61-73.
Charles, A. L., Markich, S. J., Stauber, J. L., & De Filippis, L. F. (2002). The effect of water hardness on the toxicity of uranium to a tropical freshwater alga Chlorella sp. Aquatic Toxicology (Amsterdam, Netherlands), 60(1-2), 61-73.
Charles AL, et al. The Effect of Water Hardness On the Toxicity of Uranium to a Tropical Freshwater Alga Chlorella Sp. Aquat Toxicol. 2002 Oct 2;60(1-2):61-73. PubMed PMID: 12204587.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The effect of water hardness on the toxicity of uranium to a tropical freshwater alga Chlorella sp. AU - Charles,Amanda L, AU - Markich,Scott J, AU - Stauber,Jennifer L, AU - De Filippis,Lou F, PY - 2002/9/3/pubmed PY - 2002/10/17/medline PY - 2002/9/3/entrez SP - 61 EP - 73 JF - Aquatic toxicology (Amsterdam, Netherlands) JO - Aquat Toxicol VL - 60 IS - 1-2 N2 - Uranium (U) derived from mining activities is of potential ecotoxicological concern to freshwater biota in tropical northern Australia. Few data are available on the effects of water hardness (Ca and/or Mg), which is elevated in U mine wastewaters, on the toxicity and bioavailability of U to freshwater biota, particularly algae. This study determined the effect of water hardness (8, 40, 100 and 400 mg CaCO(3) x l(-1), added as calcium (Ca) and magnesium (Mg) sulphate) on the toxicity (72 h growth rate inhibition) of U to the unicellular green alga, Chlorella sp., in synthetic freshwater, at constant pH (7.0) and alkalinity (8 mg CaCO(3) x l(-1)), similar in chemical composition to sandy coastal streams in tropical northern Australia. A 50-fold increase in water hardness resulted in a 5-fold decrease (P<or =0.05) in the toxicity of U to Chlorella sp. (i.e. the 72 h EC(50) increased from 56 to 270 micro g U l(-1)). Possible explanation for the ameliorative effect of water hardness includes: (i) competition between U and Ca and/or Mg for binding sites on the cell surface; and (ii) a change in U speciation, and hence, bioavailability. Results showed that extracellular (cell-surface) and intracellular U concentrations significantly (P<0.05) decreased (2-5-fold) as water hardness increased from 8 to 400 mg CaCO(3)x l(-1). Calculation of U speciation using the geochemical model HARPHRQ showed that there were no significant (P>0.05) differences in the predicted speciation (% distribution) of U amongst the four water hardness levels. The reduction in U toxicity with increasing water hardness was most likely due to competition between U and Ca and/or Mg for binding sites on the algal cell surface. The minimum detectable effect concentrations of U were approximately 3 and 24 times higher (at 8 and 400 mg CaCO(3)x l(-1) hardness, respectively) than the national interim U guideline value (0.5 micro g x l(-1)) for protecting aquatic ecosystems. Overall, the results reinforce the need for a more flexible U guideline based on a hardness-dependent algorithm, which may allow environmental managers to relax the national guideline for U on a site-specific basis. SN - 0166-445X UR - https://www.unboundmedicine.com/medline/citation/12204587/The_effect_of_water_hardness_on_the_toxicity_of_uranium_to_a_tropical_freshwater_alga_Chlorella_sp_ DB - PRIME DP - Unbound Medicine ER -