Background Information

One of the main applications of nanotechnology in material science is the development of polymer nanocomposites, reinforced polymers with low quantities of nanosized organic or inorganic ingredients dispersed into a thermoplastic or thermoset polymer. The use of nanoparticles (NPs) in composites manufacturing offers enormous advantages over traditional macro- or microsized fillers and applications across a wide range of industrial sectors are currently on the market.
Information about the potential risks of an unintended release of ENMs (engineered nanomaterials) embedded into plastic composites along their life cycle is actually lacking, although evidence has emerged in the literature suggesting that some ENMs may have negative impacts in environment.
The risk is function of both exposure and hazard, and those can be influenced by the product life cycle and the product design. Moreover although guidelines to perform studies to evaluate the environmental safety data required for carrying out risk assessments are defined, they are developed for conventional chemicals and their suitability for ENMs is questioned. Parameters as environmental fate, properties (including degradation, environmental distribution and bioaccumulation), environmental hazards to organisms in the aquatic, terrestrial and atmospheric compartments, environmental exposure and environmental risk for different compartments must necessarily be taken into account. Additionally, it has already been demonstrated that the behaviour of ENMs in the environment is very different from the behaviour of bulk substances. Most ENPs will aggregate to some degree following release to the environment, but the degree of this aggregation and the size of the aggregates will depend on the characteristics of the particles, its concentration and the receiving environmental system.

NPs in Soil

The fate of nanoparticles (NPs) released to soil depends on the physical and chemical characteristics of the NP. NPs are small enough to fit into smaller spaces between soil particles, and might therefore travel further than larger particles before becoming trapped in the soil matrix. The strength of the sorption of the NPs to soil will depend on the size, chemistry of the applied surface treatment and the application conditions. Generally, NPs interact with microorganisms present in soil and groundwater through passive and active mechanisms that alter the chemical form and hence the groundwater transport and soil retention characteristics of the NPs.
There are very few data for the assessment of the ecotoxicity to soil biota, because, although some reports have examined ecotoxicity of NPs to soil organisms (root growth of plant species, spinach seed germination…) the media generally employed have been simple aqueous media and persistence of the NPs in the test media was not assessed. There are also few documents of bioaccumulation or trophic transfer to soil invertebrates or mammals.

NPs in Water

Fate of ENMs in aqueous environments is controlled by solubility or dispersability, interactions between the ENMs and natural and anthropogenic chemicals in the system and biological and abiotic processes. There is evidence to suggest that the impact of NPs on aquatic organisms differs compared to their macroparticle equivalents. Waterborne NPs generally settle down more slowly than the larger particles. However, due to the high surface area to mass ratios, nanosized particles have the potential to sorb to soil and sediment particles. The sorbed NPs can be more readily removed from the water column. Complexation by natural organic materials, such as humcolloids can facilitate reactions that transform metal in anaerobic sediment.
Toxicity to aquatic biota of ENMs has been studied in algae, invertebrate (Daphnia essentially) and fish (although normally fish would be expected to show less sensitivity to dissolved contaminants that algae or daphnids, this is not necessarily the case with ENMs and may be indicative of a different mechanism of toxicity) fundamentally.