Direct and Indirect Toxic Effects of Engineered Nanoparticles on Algae: Role of Natural Organic Matter

Abstract

In order to assess the overall risk posed by engineered nanoparticles (ENPs), the biological effects of this emergent pollutant to aquatic ecosystems must be evaluated. We present findings from studies conducted with a diversity of ENPs (metallic, quantum dots) on a variety of freshwater and marine algae (phytoplankton) illustrating both their direct and indirect effects. We show that in general, while the surface properties of ENPs govern their aggregation behavior and ionic strength controls their dissolution, exopolymeric substances (EPS) produced by algae determine their potential to be toxic and thereby movement through the water column and food web. The production of EPS reduces the impact of ENPs (bioavailability and toxicity) and/or their ions on cellular activities of algae. It does not however directly reduce the aggregation and/or solubility of ENPs but rather affects their stability. Complicating understanding of these interactions is the great assortment of surface coatings for ENPs. This perspective is intended to highlight our current knowledge and the need for future research particularly focused on determining the fate and transport of ENPs in the aquatic environment.

Effect of magnetic iron oxide (Fe3O4) nanoparticles on the growth and photosynthetic pigment content of Picochlorum sp.

“…Similar findings were reported by Gong et al (2011). NPs are expected to be more soluble in freshwater with lower pH, while most will aggregate in marine waters (Klaine et al 2008;Batley et al 2013;Quigg et al 2013). Navarro et al (2008) explained that organic matter in the seawater might affect the surface speciation and charge of NPs and therefore affect their aggregation/deposition properties.…”

“…Furthermore, algae can produce substances that can induce NPs flocculation or metal ion chelation and thus reduce the bioavailability of both NPs and metal ions they released (Soldo et al 2005). Exopolymeric substances production may increase in algae upon exposure to NPs and may thus contribute to detoxification mechanisms (Miao et al 2007;Quigg et al 2013).…”

Cumulative effect of zinc oxide and titanium oxide nanoparticles on growth and chlorophyll a content of Picochlorum sp.

“…The ionic strength, the solution pH, and organic matter as well as the surface charge of NPs, all found to play key roles in the aggregation behavior of NPs (Gong et al 2011). NPs are expected to be more soluble in freshwater with low pH and are more likely to (Quigg et al 2013). Algae in this regard, can therefore promote sedimentation of NPs into the environment and are likely potential candidates for bioremediation and nanopollution (Gong et al 2011).…”

Effect of citric acid on toxicity of graphene towards freshwater algae (Chlorella pyrenoidosa)

“…On the other hand, it could inevitably be released into the environment, thus generating a negative effect [9]. Critic acid (CA), as a typical kind of dissolved organic matter (DOM), exists widely in the aquatic environment [10]. It is an important component in aquatic environment, which may interact with graphene in the water.…”