Conference Agenda

Plastic use in baby food packaging, handling, preparation, and storage increases the risk of directly releasing microplastics and nanoplastics into the food. This study investigated the release of microplastics and nanoplastics from plastic containers and reusable food pouches under different usage scenarios, using DI water and 3% acetic acid as food simulants for aqueous foods and acidic foods. We found that microwave heating caused the highest release of microplastics and nanoplastics into food than other usage scenarios, such as refrigeration or room temperature storage. For some containers, three minutes of microwave heating can release as many as 4.27 billion microplastic and 2.29 trillion nanoplastic particles in one liter of water. Refrigeration and room temperature storage can also release millions to billions of microplastics and nanoplastics. Raman spectroscopic analysis confirmed that the released microplastics and nanoplastics matched with the plastic containers' properties. The polyethylene-based food pouch released more particles than polypropylene-based plastic containers, due to the lower thermal stability of polyethylene. Our exposure modeling found that the highest estimated daily intake was 20.3 ng/kg‧day for infants drinking microwaved water and 22.1 ng/kg‧day for toddlers consuming microwaved dairy products from polypropylene containers. An in vitro study conducted to assess the cell viability showed that the extracted microplastics and nanoplastics released from the plastic container can cause the death of 76.70% and 77.18% of human embryonic kidney cells (HEK293T) at 1000 µg/ml concentration after exposure of 48 hours and 72 hours, respectively.

Microplastics pollution is growing pollution concern for the state of Rhode Island, especially given the high urban land cover and importance of the surrounding marine environment to the local economy. Several local studies have focused on quantifying and characterizing microplastic pollution and its impacts to wildlife in the Narragansett Bay, however, there is a lack of data from inland freshwater and atmospheric inputs to the bay. Knowledge of the extent of microplastic pollution in rivers and streams is important, since microplastics are transported through inland river systems to the bay. Atmospheric deposition of microplastics is a growing area of interest, especially in urban areas, however there is very limited data on this globally and none in New England. The goal of this study was to start a long-term microplastic sampling campaign to develop a database of freshwater and atmospheric microplastic measurements in Rhode Island. An additional goal of this project was to make the sampling and analysis methods accessible to all engineering undergraduate students in the program to encourage their participation in the work. Various river sample locations were identified in collaboration with local stakeholders. An atmospheric microplastic fallout collector was designed, built, and installed on campus to collect atmospheric dry deposition samples. Sample analysis included sample digestion and microscopic enumeration based on plastic shape and color. Sample results help provide baseline microplastic data from freshwater and atmospheric sources to the Narragansett Bay and provide a starting point for a long-term monitoring program.

Wastewater treatment plants (WWTPs) are the most significant receptors and distributors of microplastics in the environment. Although occurrence and discharge of microplastics from WWTPs have been extensively studied, the behaviour, fate, and transport pathways of microplastics in terms of their types and shapes across WWTPs have not been understood thoroughly. This study addresses the aforementioned gap and offers a more controlled approach for determining the behaviour and transport pattern of microplastics by conducting a tracer study using two typical microplastics - Acrylic fiber and Polyvinyl Chloride (PVC) spheres stained with Nile Red in the University of Connecticut WWTP. Those tracer microplastics were added in the influent of the disinfection tank (volume of one tank: 43,000 gallons) and collected at the final disposal point after the minimum hydraulic retention time (24 minutes) in several batches. The results indicated that the presence of fiber-shaped microplastics in the effluent is only 5%, contrary to the higher percentages reported by previous studies, most likely due to rapid mixing and fragmentation which cause overestimation of fiber counts in effluent. In contrast, 77% of sphere-shaped PVC particles remain in the effluent, which mainly attributed to the short retention time of the disinfection tank unable to retain the PVC microparticles which are moderately denser (density: 1.4 g/cm3) than chlorination tank water. This tracer study provides a crucial framework elevating the understanding of the transport behavior of microplastics across treatment units in WWTPs, and bolsters treatment efficiency to mitigate microplastic pollution.

Abrasive wear by sand or soil particles is one the major pathways for nanoplastics release in the atmospheric and aquatic environment, where polyesters are frequently used and leaked. It remains unclear how polymer chemistry of polyesters impacts the environmental degradation behavior of plastics. In our work, photo-oxidation of linearly structured aliphatic polyesters, poly-hydroxybutyrate (PHB) and poly-lactic acid (PLA) and an aromatic polyester, polyethylene terephthalate (PET), were carried out following ASTM G154 standard. We hypothesize that the ratio of chain scission and crosslinking during photooxidation dictates the nanomechanical properties of polyesters and their propensity of releasing micro/nanoplastics. After 7 days, we found that Norrish chain scission has occurred in all polyesters using ATR-FTIR, particularly in semicrystalline PET, where we also observed an increase in the crystallinity from 21% to 30%, due to destruction of amorphous regions during photo-oxidation. In contrast, for PHB and PLA, only small decline in crystallinity was observed, implying that the aromatic polyesters are likely more prone to photochemical reactions compared to aliphatic polyesters. Nanoindentation and lateral force microscopy (LFM) experiments revealed that after 7 days of oxidation, the nanomechanical properties and friction coefficient of all polyesters changed minimally. We will continue the UV irradiation of plastics up to 50 days. Furthermore, nanoscale abrasion will be performed using our recently developed nanoscratch test to explore the influence of photo-oxidation on the nanoplastic release. These results will elucidate a major gap in our understanding of chemistry-structure-degradability relationship, particularly for nanoplastic release under coupled photo-oxidation and mechanical abrasion stress.

Of the approximately 4.8 to 12.7 million metric tons³ of plastic annually emitted to the ocean, larger polymers are likely to fragment into smaller microplastics or nanoplastics incidentally produced and not accounted for. However, there is a limitation of systematic approaches to comprehend the influence of water conditions on the fragmentation, degradation, and leaching of polymers. This presentation introduces a modeling framework for describing additive release from plastics that considers the role of plastic fragmentation in increasing surface area and release rates over time and methods for parameterizing the models from plastic abrasion and additive leaching experiments using an adaptation to Fick’s model. For hydrolysis experiments, the influence of temperature, pH, and salinity on six pristine microplastic powders and larger polymer coupons were evaluated (PA-6, TPU, PLA, PET, LDPE, and PP) in various media (pH 4, pH 9, pH 7, artificial seawater) for three-time points and temperatures (5 day, 30 day, 100 days and 4°C, 22°C, and 65°C). For microplastic fragmentation, preliminary results show that PLA and PA-6 are the most susceptible to hydrolysis both exhibiting larger mass loss than the other polymers while PA-6 and TPU show larger amounts of particles in the 1-10 µm range in the high-temperature seawater. Although much of the plastic that enters water bodies is already weathered, this study provides a mechanistic approach to understand the behavior of microplastics under various hydrolysis conditions and enables us to parametrize a model for fragmentation and additive release for risk assessment.