Are We Speaking the Same Language? Recommendations for a Definition and Categorization Framework for Plastic Debris

The accumulation of plastic litter in natural environments is a global issue. Concerns over potential negative impacts on the economy, wildlife, and human health provide strong incentives for improving the sustainable use of plastics. Despite the many voices raised on the issue, we lack a consensus on how to define and categorize plastic debris. This is evident for microplastics, where inconsistent size classes are used and where the materials to be included are under debate. While this is inherent in an emerging research field, an ambiguous terminology results in confusion and miscommunication that may compromise progress in research and mitigation measures. Therefore, we need to be explicit on what exactly we consider plastic debris. Thus, we critically discuss the advantages and disadvantages of a unified terminology, propose a definition and categorization framework, and highlight areas of uncertainty. Going beyond size classes, our framework includes physicochemical properties (polymer composition, solid state, solubility) as defining criteria and size, shape, color, and origin as classifiers for categorization. Acknowledging the rapid evolution of our knowledge on plastic pollution, our framework will promote consensus building within the scientific and regulatory community based on a solid scientific foundation

The composition of bacterial communities associated with plastic biofilms differs between different polymers and stages of biofilm succession

Once in the ocean, plastics are rapidly colonized by complex microbial communities. Factorsaffecting the development and composition of these communities are still poorly understood.Additionally, whether there are plastic-type specific communities developing ondifferent plastics remains enigmatic. We determined the development and succession ofbacterial communities on different plastics under ambient and dim light conditions in thecoastal Northern Adriatic over the course of two months using scanning electron microscopyand 16S rRNA gene analyses. Plastics used were low- and high-density polyethylene(LDPE and HDPE, respectively), polypropylene (PP) and polyvinyl chloride with two typicaladditives (PVC DEHP and PVC DINP). The bacterial communities developing on the plasticsclustered in two groups; one group was found on PVC and the other group on all theother plastics and on glass, which was used as an inert control. Specific bacterial taxa werefound on specific surfaces in essentially all stages of biofilm development and in both ambientand dim light conditions. Differences in bacterial community composition between thedifferent plastics and light exposures were stronger after an incubation period of one weekthan at the later stages of the incubation. Under both ambient and dim light conditions, onepart of the bacterial community was common on all plastic types, especially in later stages ofthe biofilm development, with families such as Flavobacteriaceae, Rhodobacteraceae,Planctomycetaceae and Phyllobacteriaceae presenting relatively high relative abundanceson all surfaces. Another part of the bacterial community was plastic-type specific. The plastic-type specific fraction was variable among the different plastic types and was more abundantafter one week of incubation than at later stages of the succession

NO2 and natural organic matter affect both soot aggregation behavior and sorption of <em>S</em>-metolachlor.

Soot is an important carbonaceous nanoparticle (CNP) frequently found in natural environments. Its entry into surface waters can occur directly via surface runoff or infiltration, as well as via atmospheric deposition. Pristine soot is likely to rapidly undergo aggregation and subsequent sedimentation in aquatic environments. Further, soot can sorb a variety of organic contaminants, such as S-metolachlor (log K-D = 3.25 +/- 0.12). During atmospheric transport, soot can be chemically transformed by reactive oxygen species including NO2. The presence of natural organic matter (NOM) in surface waters can further affect the aquatic fate of soot. To better understand the processes driving the fate of soot and its interactions with contaminants, pristine and NO2-transformed model soot suspensions were investigated in the presence and absence of NOM. NO2-oxidized soot showed a smaller particle size, a higher number of particles remaining in suspension, and a decreased sorption of S-metolachlor (log K-D = 2.47 +/- 0.40). In agreement with findings for other CNPs, soot stability against aggregation was increased for both pristine and NO2 transformed soot in the presence of NOM

Environmental Degradation of Microplastics: How to Measure Fragmentation Rates to Secondary Micro- and Nanoplastic Fragments and Dissociation into Dissolved Organics

Understanding the environmental fate of microplastics is essential for their risk assessment. It is essential to differentiate size classes and degradation states. Still, insights into fragmentation and degradation mechanisms of primary and secondary microplastics into micro- and nanoplastic fragments and other degradation products are limited. Here, we present an adapted NanoRelease protocol for a UV-dose-dependent assessment and size-selective quantification of the release of micro- and nanoplastic fragments down to 10 nm and demonstrate its applicability for polyamide and thermoplastic polyurethanes. The tested cryo-milled polymers do not originate from actual consumer products but are handled in industry and are therefore representative of polydisperse microplastics occurring in the environment. The protocol is suitable for various types of microplastic polymers, and the measured rates can serve to parameterize mechanistic fragmentation models. We also found that primary microplastics matched the same ranking of weathering stability as their corresponding macroplastics and that dissolved organics constitute a major rate of microplastic mass loss. The results imply that previously formed micro- and nanoplastic fragments can further degrade into water-soluble organics with measurable rates that enable modeling approaches for all environmental compartments accessible to UV light