Toxicity of holmium-labelled clay to four benthic invertebrates / Lee Grapentine ... [et al.].: En83-9/07-541E-PDF

"Montmorillonite clay adsorbed with the rare earth element holmium (Ha-clay) is a new material produced for tracing movements of fine particles in aquatic systems. However, little is known about the toxicity of Ha-clay, and its potential environmental effects. To investigate effects of Ha-clay on aquatic biota, four benthic invertebrate species (Chironomus riparius, Hexagenia spp., Hyalella azteca, Tubifex tubifex) were exposed to Ha-clay alone and mixtures of 10, 25 and 50% Ha-clay with field-collected reference sediment for 10-28 days in standard laboratory toxicity tests. Overall, only the 100% Ha-clay treatment resulted in significantly higher toxicity than the reference sediment. Mean survival at the end of the exposures to 100% Ha-clay was 7, 53, 2 and 100% for Chironomus, Hexagenia, Hyalella and Tubifex, respectively. Exposure to a negative control treatment of 100% clay resulted in minor reductions in growth, but no lethal responses. Highest concentrations of Ho at which no toxicity was observed were 1400 ug/g for sediment and 11 ug/L for water. Potential impacts of Ha-clay released into natural waters would be expected only where Ha-clay persists in sediment at proportions >50% for at least several days"--Abstract, p. ii.

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