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Uncharged nanoparticles of iron are being investigated as a potential way to reduce the mobility of toxic metal ions. The iron nanoparticles are pumped into the ground and they reduce the heavy metals dramatically, lowering the metal's mobility. However, the iron particles have been known to seep into ground water, and might end up in marine ecosystems. To understand the impacts of nano-iron, researchers need to study the effects of the iron particles on aquatic organisms. The researchers conducted several studies on the growth rates and survival rates of both phytoplankton and zooplankton in conditions with various concentrations of uncharged nanoparticles of iron.

Study 1

The researchers measured the growth rate of I.galbana, a marine phytoplankton species, at varying concentrations of either neutral iron nanoparticles or iron ions.

Study 2

In a second study, the survival rate of the zooplankton grazer Daphnia magna (D. magna) was measured at various concentrations of both nano-iron and iron ions.

Adapted from: Keller AA, Garner K, Miller RJ, Lenihan HS (2012) Toxicity of Nano-Zero Valent Iron to Freshwater and Marine Organisms. PLoS ONE 7(8): e43983. doi:10.1371/journal.pone.0043983

Which of the following statements could be supported by the data in Study 2?


Iron ion concentrations at or above 0.25 mg/L do not change zooplankton survival rates.


Nano-iron concentrations at or below 0.50 mg/L do not change zooplankton survival rates.


Nano-iron is more toxic to zooplankton than iron ions.


When nano-iron concentrations reach 1.0 mg/L, there is a significant change in the growth rate of phytoplankton.

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