Investigating the formation, presence, and distribution of nanoplastics in aquatic environments

Nanoplastics (NPs), small (< 1 µm) polymer particles formed from bulk plastics, are a potential threat to human health and the environment. Orders of magnitude smaller than microplastics (MPs), they might behave different due to their larger surface area and small size, which allows them to diffuse through organic barriers. However, detecting NPs in the environment and organic matrices has proven to be difficult, as their chemical nature is similar to these matrices. Furthermore, as their size is smaller than the (spatial) detection limit of common analytic tools, they are hard to find and quantify. Here, we highlight different micro-spectroscopic techniques utilized for NP detection and argue that an analysis procedure should involve both particle imaging and correlative or direct chemical characterization of the same particles or samples. Finally, we highlight methods that can do both simultaneously, but have as downside that large particle numbers and statistics cannot be obtained.

Most marine plastic pollution originates on land. However, once plastic is at sea, it is difficult to determine its origin. Here we present a Bayesian inference framework to compute the probability that a piece of plastic found at sea came from a particular source. This framework combines information about plastic emitted by rivers with a Lagrangian simulation, and yields maps indicating the probability that a particle sampled somewhere in the ocean originates from a particular river source. We showcase the framework for floating river-sourced plastic released into the South Atlantic Ocean. We computed the probability as a function of the particle age at three locations, showing how probabilities vary according to the location and age. We computed the source probability of beached particles, showing that plastic found at a given latitude is most likely to come from the closest river source. This framework lays the basis for source attribution of marine plastic.

Nanoplastics can be classified into primary and secondary nanoplastics, where primary nanoplastics are industrially produced for specific purposes and secondary nanoplastics result from plastic waste via degradation processes. The origin of nanoplastic particles is an important consideration in nanotoxicological assays. Since nanoplastics are generally thought to be produced unintentionally from microscale plastic debris, it is likely that they form aggregates with other natural and/or anthropogenic materials. Nanoplastics can take on a new biological identity in the marine environment, often dictated by the biomolecular species on their surface. Freshwater nanoplastics may display differing surface functionalities and exist in different concentrations than marine nanoplastics. Phototrophs use light as their energy source to synthesize organic compounds and are widely distributed in marine environments. Though phototrophic microorganisms are vitally important to primary production in the marine environment, heterotrophs may also associate with nanoplastics in the marine environment, and trophic transfer is thus also possible.