Other organic (carbon-based) chemicals are known to have an effect on the toxicity of pollutants to plant and animal life. But nanoparticles like C60 have unique and altered properties compared to larger particles, and so they may have a very different effect on the toxicity and availability of pollutant molecules.
The nanoparticles themselves may also be inherently toxic.
Researchers from the Technical University of Denmark and the University of Copenhagen, Denmark tested the effect of four common pollutant chemicals: atrazine, methyl parathion, pentachlorophenol (PCP) and phenanthrene on green algae and freshwater crustaceans ("Toxicity and bioaccumulation of xenobiotic organic compounds in the presence of aqueous suspensions of aggregates of nano-C60"). The researchers found that when C60 nanoparticles were present, they affected the availability of the toxic chemicals to the organisms.
- C60 made phenanthrene more toxic to algae at lower concentrations, for instance, but made it less toxic to the crustaceans.
- C60 made PCP less toxic to both algae and crustaceans.
- The C60 had little effect on the toxicity of the other two pollutants tested.
Nanoparticles also affected how quickly and how much of the pollutant was taken in by the organisms. Clumps of the C60 itself also stuck to the crustaceans' bodies and inside their digestive systems. The authors recommend that nanoparticle risk assessment take into account not just the toxicity of the particles themselves, but also the possible interaction with other environmental contaminants. They also suggest that further research into the effects of nanoparticles' different phases (in particular their behaviour in water as they form suspensions or clumps of molecules know as aggregates) is also relevant to their potential toxicity in the aquatic environment.
The potential of C60-nanoparticles (Buckminster fullerenes) as contaminant carriers in aqueous systems was studied in a series of toxicity tests with algae (Pseudokirchneriella subcapitata) and crustaceans (Daphnia magna). Four common environmental contaminants (atrazine, methyl parathion, pentachlorophenol (PCP), and phenanthrene) were used as model compounds, representing different physico-chemical properties and toxic modes of action. The aggregates of nano-C60 formed over 2 months of stirring in water were mixed with model compounds 5 days prior to testing. Uptake and excretion of phenanthrene in 4-days-old D. magna was studied with and without addition of C60 in aqueous suspensions. It was found that 85% of the added phenanthrene sorbed to C60-aggregates >200 nm whereas about 10% sorption was found for atrazine, methyl parathion, and pentachlorophenol. In algal tests, the presence of C60-aggregates increased the toxicity of phenanthrene with 60% and decreased toxicity of PCP about 1.9 times. Addition of C60-aggregates reduced the toxicity of PCP with 25% in tests with D. magna, whereas a more than 10 times increase in toxicity was observed for phenanthrene when results were expressed as water phase concentrations. Thus, results from both toxicity tests show that phenanthrene sorbed to C60-aggregates is available for the organisms. For atrazine and methyl parathion no statistically significant differences in toxicities could be observed in algal and daphnid tests as a result of the presence of C60-aggregates. In bioaccumulation studies with phenanthrene in D. magna it was found that the uptake of phenanthrene was faster when C60 was present in suspension and that a 1.7 times higher steady-state concentration was reached in the animals. However, a very fast clearance took place when animals were transferred to clean water resulting in no accumulation of phenanthrene. This study is the first to demonstrate the influence of C60-aggregates on aquatic toxicity and bioaccumulation of other environmentally relevant contaminants. The data provided underline that not only the inherent toxicity of manufactured nanoparticles, but also interactions with other compounds and characterisation of nanoparticles in aqueous suspension are of importance for risk assessment of nanomaterials.
Source: European Commission and Nanowerk News