An official website of the United States government
Abstract Microplastics (MPs) are an emerging class of pollutants in air, soil and especially in all aquatic environments. Secondary MPs are generated in the environment during fragmentation of especially photo-oxidised plastic litter. Photo-oxidation is mediated primarily by solar UV radiation. The implementation of the Montreal Protocol and its Amendments, which have resulted in controlling the tropospheric UV-B (280–315 nm) radiation load, is therefore pertinent to the fate of environmental plastic debris. Due to the Montreal Protocol high amounts of solar UV-B radiation at the Earth’s surface have been avoided, retarding the oxidative fragmentation of plastic debris, leading to a slower generation and accumulation of MPs in the environment. Quantifying the impact of the Montreal Protocol in reducing the abundance of MPs in the environment, however, is complicated as the role of potential mechanical fragmentation of plastics under environmental mechanical stresses is poorly understood.
more »
« less
Insights into the mechanism of plastics’ fragmentation under abrasive mechanical forces: An implication for agricultural soil health
Abstract The application of agricultural plastic products such as mulch, greenhouse covers, and silage films is increasing due to their economic benefits in providing an early and better‐quality harvest. However, mechanical abrasion of these plastic materials by soil particles could result in generation of microplastic (MP) pollutants that could harm soil organisms and impact food safety. This study aims to better understand the physicochemical mechanisms resulting in the fragmentation of low‐density polyethylene (LDPE). Herein, we used pellets and films to study the impacts of abrasive wear forces on their surface morphology variations and fragmentation behavior. An innovative laboratory approach was developed to abrade the plastic surface under controlled normal loadings and abrasion durations. The investigation of the plastics’ surface morphology variations due to the abrasion process revealed microcutting as the dominant process at low normal force (4 N). However, a combination of microploughing and microcutting occurred for new LDPE films by increasing the normal force to 8 N. Despite the significant surface morphology variations of the new LDPE film due to the abrasion process; the water contact angle did not alter. Furthermore, the fragmentation behavior of photodegraded LDPE pellets and films was compared to the new plastics. The extent of MPs (3 µm < dp < 162 µm) generation due to fragmentation was studied using fluorescence microscopy imaging. The localized stress and strains at the contact sites of plastic and sand particles resulted in abrasion of the plastic surface. According to the results, the normal loadings and duration of abrasion played a significant role in the degree of fragmentation of plastics. Increasing the normal loading applied during the abrasion process from 2 to 8 N linearly increased the number of generated plastic fragments by more than five times for pellets and more than three times for film. Photodegradation significantly enhanced the extent of MPs fragmentation. Moreover, the limitations of this study and the implications for agricultural soil health were discussed.
more »
« less
- Award ID(s):
- 2305189
- PAR ID:
- 10441934
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- CLEAN – Soil, Air, Water
- Volume:
- 51
- Issue:
- 8
- ISSN:
- 1863-0650
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Plastics have become an integral component in agricultural production as mulch films, nets, storage bins and in many other applications, but their widespread use has led to the accumulation of large quantities in soils. Rational use and reduction, collection, reuse, and innovative recycling are key measures to curb plastic pollution from agriculture. Plastics that cannot be collected after use must be biodegradable in an environmentally benign manner. Harmful plastic additives must be replaced with safer alternatives to reduce toxicity burdens and included in the ongoing negotiations surrounding the United Nations Plastics Treaty. Although full substitution of plastics is currently not possible without increasing the overall environmental footprint and jeopardizing food security, alternatives with smaller environmental impacts should be used and endorsed within a clear socio-economic framework. Better monitoring and reporting, technical innovation, education and training, and social and economic incentives are imperative to promote more sustainable use of plastics in agriculture.more » « less
-
While microplastics (MPs) are globally prevalent in marine environments, extending to the Arctic and sub-Arctic regions, the extent and distribution of MPs in terrestrial waters, drinking water sources, and recreational water in these areas remain unknown. This field study establishes a baseline for MPs in surface water sources, including lakes, rivers, and creeks, as well as in snow across three geo-locations (i.e., Far North, Interior, and Southcentral) in Alaska. Results (mean ± SE) show that the highest MP counts exist in snow (681 ± 45 L−1), followed by lakes (361 ± 76 L−1), creeks (377 ± 88 L−1), and rivers (359 ± 106 L−1). The smallest MPs (i.e., 90.6 ± 4 μm) also happened to have occurred in snow, followed by their larger sizes in lakes (203.9 ± 65 μm), creeks (382.8 ± 136.5 μm), and rivers (455.4 ± 212 μm). The physical morphology of MPs varies widely. MP fragments are predominant (i.e., nearly 62–74%) in these sites, while MP fibers (nearly 13–21%), pellets (nearly 13–18%), and films (<6%) also exist in appreciable quantities. Geolocation-wise, the Far North, where MPs were collected from off-road locations, shows the highest MP counts (695 ± 58 L−1), compared to Interior (473 ± 64 L−1) and Southcentral (447 ± 62 L−1) Alaska. Results also indicate that the occurrence of MPs in the source waters and snow decreases with increasing distance from the nearest coastlines and towns or communities. These baseline observations of MPs in terrestrial waters and precipitation across Alaska indicate MP pollution even in less-explored environments. This can be seen as a cause for concern with regard to MP exposure and risks in the region and beyond.more » « less
-
Abstract As the levels of plastic use in global society have increased, it has become crucial to regulate plastics of all sizes including both microplastics (MPs) and nanoplastics (NPs). Here, the published literature on the current laws passed by the US Congress and regulations developed by various federal agencies such as the US Environmental Protection Agency and the US Food and Drug Administration (FDA) that could be used to regulate MPs and NPs have been reviewed and analyzed. Statutes such as the Clean Water Act, the Safe Drinking Water Act, the Toxic Substances Control Act (TSCA), the Resource Conservation and Recovery Act, and the Clean Air Act can all be used to address plastic pollution. These statutes have not been invoked for MP and NP waste in water or air. The Federal Food, Drug, and Cosmetic Act provides guidance on how the FDA should evaluate plastics use in food, food packaging, cosmetics, drug packaging, and medical devices. The FDA has recommended that acceptable levels of ingestible contaminant from recycled plastic are less than 1.5 µg/person/day, which is 476 000 times less than the possible ingested daily dose. Plastic regulation is present at the state level. States have banned plastic bags, and several cities have banned plastic straws. California is the only state beginning to focus on monitoring MPs in drinking water. The future of MP regulation in the USA should use TSCA to test the safety of plastics. The other statutes need to include MPs in their definitions. For the FDA, MPs should be redefined as contaminants—allowing tolerances to be set for MPs in food and beverages. Through minor changes in how MPs are classified, it is possible to begin to use the current statutes to understand and begin to minimize the possible effects of MPs on human health and the environment. Integr Environ Assess Manag 2023;19:474–488. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).more » « less
-
The effect of precursor stoichiometry is reported on morphology, phase purity, and texture formation of polycrystalline diamond films. The diamond films were deposited on 100-mm Si (100) substrates using hot filament chemical vapor deposition at substrate temperature 720–750 °C using a mixture of methane and hydrogen. The gas mixture was varied with methane concentrations 1.5% to 4.5%. Diamond film thickness and average grain size both increase with increasing methane concentration. Diamond quality was checked using surface and cross-section by ultraviolet micro-Raman spectroscopy. The data show consistent diamond properties across the surface of the film and along the cross-section. XRD pole figure analyses of the films show that 3.0% methane results in preferential orientation of diamond in the〈111〉direction, whereas films deposited with 4.5% methane showed texture along the〈220〉direction in addition to〈111〉which was tilted ~ 23° with respect to the surface normal.more » « less
