ABSTRACT
There is much interest in converting natural nanoclay into modified forms for a variety of applications. Aquatic organisms have been exposed to natural nanoclay throughout their entire evolutionary history, but concerns have been raised about the effects of modified nanoclay on aquatic organisms. We investigated the potential toxicity of a natural nanoclay (Na+ montmorillonite) and two modified nanoclays (Cloisite® 30B and NovaclayTM) on survivorship and body growth of Daphnia magna and Chironomus dilutus. Natural nanoclay had no harmful effect on C. dilutus but reduced the survival (~1mgL-1) and body growth (~100 mgL-1) of D. magna. NovaclayTM had no harmful effects on C. dilutus or the body growth of D. magna but an intermediate concentration (1 mgL-1) caused a stronger reduction in D. magna survival during chronic exposure than did natural nanoclay. Cloisite® 30B adversely affected D. magna survival at concentrations as low as 0.01 mgL-1 and nearly all D. magna died when exposed to concentrations of Cloisite® 30B that exceeded 10 mgL-1 during acute exposure and 1 mgL-1 during chronic exposure. Though Cloisite® 30B appeared to have no effect on the body growth of surviving D. magna, Cloisite® 30B reduced C. dilutus body growth (100 mgL-1). Cloisite® 30B likely has higher toxic effects due to the presence of quaternary ammonium compounds and/or particle stability. Our work demonstrates that natural nanoclay has harmful effects on aquatic animals and that the different ways of converting natural nanoclay into different types of modified nanoclays augments the toxic effect of nanoclay to differing degrees.