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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

What evidence would best support the conclusion that nano-iron is more toxic than iron ions?


High concentrations of iron ions have little effect on either growth rates or survival rates of plankton.


High concentrations of nano-ions reduce the growth rates and survival rates of plankton.


It takes lower concentrations of nano-ions than iron ions to reduce both the growth rates and survival rates of plankton.


It takes low concentrations of iron ions to affect the growth rates and survival rates of plankton.

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