Effects of lanthanum and lanthanum-modified clay on growth, survival and reproduction of Daphnia magna

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Abstract

The novel lanthanum-modified clay water treatment technology (Phoslock) seems very promising in remediation of eutrophied waters. Phoslock is highly efficient in stripping dissolved phosphorous from the water column and in intercepting phosphorous released from the sediments. The active phosphorous-sorbent in Phoslock is the Rare Earth Element lanthanum. The purpose of this study was: 1) to establish a dose response relationship between Phoslock and the growth of Daphnia magna, 2) to determine the amount of lanthanum released from Phoslock, and 3) to test the effects of lanthanum on life-history characteristics of D. magna in artificial P-free and P-containing medium.
The novel lanthanum-modified clay water treatment technology (Phoslock (R)) seems very promising in remediation of eutrophied waters. Phoslock (R) is highly efficient in stripping dissolved phosphorous from the water column and in intercepting phosphorous released from the sediments. The active phosphorous-sorbent in Phoslock (R) is the Rare Earth Element lanthanum. A leachate experiment revealed that lanthanum could be released from the clay, but only in minute quantities of 0.13-2.13 mu g l(-1) for a worst-case Phoslock (R) dosage of 250 mg l(-1). A life-history experiment with the zooplankton grazer Daphnia magna revealed that lanthanum, up to the 1000 mu g l(-1) tested, had no toxic effect on the animals, but only in medium without phosphorous. In the presence of phosphorous, rhabdophane (LaPO4 center dot nH(2)O) formation resulted in significant precipitation of the food algae and consequently affected life-history traits. With increasing amounts of lanthanum, in the presence of phosphate, animals remained smaller, matured later, and reproduced less, resulting in lower population growth rates. Growth rates were not affected at 33 mu g La l(-1), but were 6% and 7% lower at 100 and 330 mu g l(-1), respectively, and 20% lower at 1000 mu g l(-1). A juvenile growth assay with Phoslock (R) tested in the range 0-5000 mg l(-1), yielded EC50 (NOEC) values of 871 (100) and 1557 (500) mg Phoslock (R) l(-1) for weight and length based growth rates, respectively. The results of this study show that no major detrimental effects on Daphnia are to be expected from Phoslock (R) or its active ingredient lanthanum when applied in eutrophication control. (C) 2009 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)309-319
JournalWater Research
Volume44
Issue number1
DOIs
Publication statusPublished - 2010

Keywords

  • water quality
  • lakes
  • clay
  • eutrophication
  • daphnia magna
  • lanthanum
  • rare earth elements
  • phosphorus
  • aquatic ecology
  • water treatment
  • phosphorus binding clay
  • rare-earth-elements
  • microcystis-aeruginosa
  • cyanobacterial toxins
  • suspended clay
  • waters
  • blooms
  • phosphate

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