Does the aging of nanoparticles modulate the ecotoxicity of metals?

In this blog post, Rajdeep Roy and his colleagues address the impacts of titanium dioxide nanoparticles (nTiO2)-aging on the ecotoxicity of metals. This is done by employing acute waterborne and multigenerational dietary exposures. 

Motivation for our assessments

Because of rising production volumes, nTiO2 are expected to enter the surface waters via wastewater effluents. nTiO2 may interact with co-existing metal ions and natural organic matter (NOM) during their aquatic life cycle, justifying the consideration of their joint environmental risks. Coexisting metal ions can be cations or anions with positive or negative charges, respectively. Moreover, the duration of interaction between nTiO2 and co-existing substances can also impact the outcome of the joint environmental risks. We use the terminology “aging” to define this duration of interaction. So far, researchers highlighted the importance of nTiO2 and NOM individually or as a combination in regulating the ecotoxicity of metals. However, reports on the ecotoxicological consequences (via different exposure pathways) considering aging in surface waters were limited.

Overview of our study designs

Acute waterborne exposure study design 
Figure 1: Acute waterborne exposure study design 

In the laboratory, we assessed the individual and joint acute impacts of NOM, nTiO2, and metals, with copper (Cu), silver (Ag), cadmium (Cd), and arsenic (As) representing varying toxic ionic species (for instance Cu2+, Ag+, Cd2+, and HAsO42-) following several aging durations. At the same time, we considered two types of aging scenarios (Figure 1). In one scenario (Type 1), we aged nTiO2 together with NOM and one of the metals, while in another scenario (Type 2), we added metal following the aging of nTiO2 and NOM. Subsequently, we evaluated the ecotoxicity of the aged medium on Daphnia with immobilization as the endpoint.  

Multigenerational dietary exposure study design
Figure 2: Multigenerational dietary exposure study design 

In contrast, we assessed the impacts of multigenerational dietary exposure by exposing alga to nTiO2 aged in a medium with Cu and NOM. Subsequently, we fed Daphnia those exposed alga over two generations (Figure 2) and monitored survival, reproduction, and body length as endpoints. Parallelly, we evaluated Cu accumulation and depuration from Daphnia.

We observed 

As a consequence of acute waterborne exposure, nTiO2 elevated the toxicity of metals (Cu, Ag, and Cd) with mainly cationic toxic species. Furthermore, NOM reduced metal toxicity only for Cu and Ag, and aging duration had a limited impact on the test outcome, suggesting that relevant interactions between metal and nTiO2 occur quickly. The data suggests that the charge of metals’ most toxic species and its interaction with nanoparticles are the determining factors for the observed acute ecotoxic effects.

Moreover, multigenerational dietary Cu exposure in combination with nTiO2 impaired offspring production of Daphnia with the effect size depending on the nTiO2-aging duration and generation. Interestingly, NOM had a negligible impact on the observed effects. We think nTiO2-aging is an important factor when assessing the effects of Cu exposure through diet. 

The studies:

Rajdeep Roy, Simon Lüderwald, Asawer Alawi Ahmed Maknoon, George Metreveli, Ralf Schulz and Mirco Bundschuh. Effects of copper in Daphnia are modulated by nanosized titanium dioxide and natural organic matter: what is the impact of aging duration? .

Rajdeep Roy, Vinod Kumar Kandrapu, Lucas Kempter, Rezaul Islam, Gabriela Kalčíková, Ralf Schulz and Mirco Bundschuh. Nanosized titanium dioxide elevates toxicity of cationic metals species for Daphnia – have aging and natural organic matter an unexpected impact?

Rajdeep Roy, Lucas Kempter, Allan PhilippeEric Bollinger, Lea Grünling, Mugilvannan Sivagnanam, Frederik MeyerAlexander Feckler, Frank Seitz, Ralf Schulz and Mirco Bundschuh. Aging of nanosized titanium dioxide modulates the effects of dietary copper exposure on Daphnia magna – an assessment over two generations