Tissue accumulation of microplastics and potential health risks in human

Microplastics have become ubiquitous throughout the environment. Humans constantly ingest and inhale microplastics, increasing concerns about the health risks of microplastic exposure. However, limited data impedes a full understanding of the internal exposure to microplastics. Herein, to evaluate microplastic exposure via the respiratory and digestive systems, we used laser direct infrared spectroscopy to identify microplastics >20 μm in size in different human tissues. Consequently, 20-100 μm microplastics were concentrated in all tissues, with polyvinyl chloride (PVC) being the dominant polymer. The highest abundance of microplastics was detected in lung tissue with an average of 14.19 ± 14.57 particles/g, followed by that in the small intestine, large intestine, and tonsil (9.45 ± 13.13, 7.91 ± 7.00, and 6.03 ± 7.37 particles/g, respectively). The abundance of microplastics was also significantly greater in females than in males (p < 0.05). Despite significant diversity, our estimation showed that the lungs accumulated the highest amounts of microplastic. Moreover, PVC particles may cause potential health risks because of their high polymer hazard index and maximal risk level. This study provides evidence regarding the occurrence of microplastics in humans and empirical data to support assessments of the health risks posed by microplastics.

Occurrence of microplastics in edible tissues of livestock (cow and sheep)

Plastic contamination is widely recognized as a major environmental concern due to the entry of small plastic particles into the food chain, thereby posing potential hazards to human health. However, the current understanding of microplastic (MP; < 5 mm) particles in livestock, which serve as an important food source, is limited. This study aims to investigate the concentration and characteristics of MPs in edible tissues of cow and sheep, namely liver, meat, and tripe, obtained from butcher shops in five areas of Bushehr port, Iran. The mean concentration of MPs in different tissues of cow and sheep were 0.14 and 0.13 items/g, respectively. Among the examined tissues, cow meat exhibited the highest concentration of MPs, with a concentration of 0.19 items/g. Nylon and fiber were identified as the predominant polymer types and shapes of MPs found in cow and sheep tissues, respectively. Furthermore, no statistically significant difference was observed in MP concentration across different tissues of cow and sheep. Significantly, this study highlights the elevated hazards associated with exposure to MPs through the consumption of edible cow and sheep tissues, particularly for children who consume meat. The results underscore the potential transfer of MPs from the environment to livestock bodies through their food, contamination during meat processing, and subsequent health hazards for consumers.

Polystyrene nanoplastics induce developmental impairments and vasotoxicity in zebrafish (Danio rerio)

The exponential use of plastics has significantly increased environmental pollution by nanoplastics (NPs). In the aquatic environment, NPs interact and bioaccumulate in the biota, posing a potential ecotoxicological risk. The present study investigated the developmental toxicity, vasotoxicity, cytotoxicity, ROS induction, and behavioral impairments in zebrafish (Danio rerio) exposed to environmentally relevant polystyrene NPs (PS-NPs) concentrations (0.04, 34 ng L-1, and 34 μg L-1) for 144 h through multiple biomarkers response (mortality, frequency of spontaneous contractions, heart rate, and morphological changes). Furthermore, vasotoxicity (head, yolk sac, tail, and branchial vessels) was evaluated using the transgenic zebrafish tg(Fli1:eGFP). Results showed that PS-NPs interacted mainly with zebrafish chorion, gills, tail, and larvae head. PS-NPs at 34 ng L-1 and 34 μg L-1 induced neurotoxicity (decreased frequency of spontaneous contractions), cardiotoxicity (bradycardia), and morphological changes in the eyes and head, indicating that PS-NPs induce developmental impairments in zebrafish. In addition, cytotoxicity in the caudal region (34 ng L-1), ROS production, decreased mean swimming speed, and distance covered were observed in all tested concentrations. PS-NPs also induced vasotoxicity (yolk sac region) in transgenic zebrafish. Overall, the present study demonstrates the harmful effects of PS-NPs on the early developmental stages of freshwater fish, indicating their environmental risk.

Energy and exergy performances of low-density polyethylene plastic particles assisted by microwave heating

Plastic waste can exist naturally for hundreds of thousands of years and harm humans, animals, and the environment. In this study, the energy and exergy performances (absorbed energy, energy efficiency, absorbed exergy, and exergy efficiency) of LDPE (low-density polyethylene) plastic particles assisted by microwave heating based on the experimental data as affected by microwave power, feeding load, and chamber volume were evaluated and analyzed. The results showed that as the microwave power raised from 500 to 900 W, the feeding load changed from 10 to 30 g, and the chamber volume decreased from 200 to 100 ml, (a) the absorbed energy at the heating time of 60 min increased from 19.73 kJ, 5.84 kJ, and 22.71 kJ to 37.69 kJ; (b) the energy efficiency for the whole heating process increased from 1.10%, 0.32%, and 1.26% to 2.09%; (c) the absorbed exergy at the heating time of 60 min increased from 0.308, 0.091, and 0.091 to 0.724 kJ; and (d) the exergy efficiency for the whole heating process increased from 0.017, 0.005, and 0.023 to 0.040%, respectively.

Dose effect of polyethylene microplastics on nitrous oxide emissions from paddy soils cultivated for different periods

The presence of microplastics (MPs) under flooded conditions is beneficial for nitrifiers and denitrifiers to produce nitrous oxide (N₂O), but their dose effect remains unclear. This study evaluated the impact of different doses of polyethylene (PE) MPs on the release of N₂O from paddy soils cultivated for different years. Compared with unpolluted soils, low doses of MPs (≤ 0.1%) had a negligible influence on N₂O emissions, and high amounts of MPs (≥ 0.5%) significantly (p < 0.05) increased N₂O emissions from the paddy soils cultivated for 3, 15 and 40 years by 2.5-4.3, 3.9-8.5 and 8.9-27.7 times, respectively. Moreover, an exponential model indicated that a 0.2% concentration of PE MPs appeared to be the dose threshold that accelerated the release of N₂O from the all soils. Increased MP concentrations accelerated N₂O emissions by affecting microbial functional genes involved in N₂O production and reduction, but microbial taxonomic attributes involved in nitrogen cycling played an insignificant role in controlling N₂O emissions. Overall, our results indicated that high doses (≥ 0.5%) of PE MPs essentially accelerated the emission of N₂O from rice soils, and a longer cultivation period (40 years) enhanced the positive effect of MPs on N₂O emissions.

Co-exposure to nanoplastics and acetaminophen causes skeletal dysplasia and behavioral abnormalities in zebrafish

Nanoplastics (NPs) and acetaminophen (APAP) are thought to be common contaminants and are invariably detected in the environment. Despite the increasing awareness of their toxicity to humans and animals, the embryonic toxicity, skeletal development toxicity, and mechanism of action of their combined exposure have not been clarified. This study was performed to investigate whether combined exposure to NPs and APAP induces abnormal embryonic and skeletal development in zebrafish and to explore the potential toxicological mechanisms. All zebrafish juveniles in the high-concentration compound exposure group showed some abnormal phenomena such as pericardial edema, spinal curvature, cartilage developmental abnormality and melanin inhibition together with a significant downward trend in body length. Behavioral data also implicated that the exposure of APAP alone, as well as the co-exposure of NPs and APAP, caused a depression in the total distance, swimming speed and the maximum acceleration. Furthermore, real-time polymerase chain reaction analysis showed that compared with exposure alone, the expression level of genes related to osteogenesis, runx2a, runx2b, Sp7, bmp2b and shh was significantly reduced with compound exposure. These results suggest that the compound exposure of NPs and APAP has adverse impacts on zebrafish embryonic development and skeletal growth.

Polyethylene microplastics alter the microbial functional gene abundances and increase nitrous oxide emissions from paddy soils

The accumulation of microplastics (MPs) in terrestrial ecosystems can affect greenhouse gases (GHGs) production by changing soil structure and microbial functions. In this study, microcosm experiments were conducted to investigate the impact of polyethylene (PE) MP addition on soil carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from paddy soils and their associated microbial functional genes. Methane was not considered due to the negligible emissions throughout the incubation. The amendment of both virgin and aged PE MPs did not significantly (p > 0.05) affect soil CO₂ emissions, but significantly (p < 0.05) increased the abundances of microbial functional genes encoding enzymes involved in hemicellulose (abfA) and lignin (mnp) decomposition, indicating plastic particle has potential to stimulate soil organic carbon decomposition. The presence of PE MP significantly increased N₂O emissions by 3.7-fold, which was probably due to PE MP increased the abundances of nirS gene involved in nitrite reductase. In addition, compared with virgin PE MP treatment, artificially aged PE MP did not significantly (p > 0.05) influence soil CO₂ and N₂O emissions. Our results provide evidence that PE MP likely cause a high risk of N₂O emission from paddy soils, this factor should be considered in future estimates of GHGs emissions from rice fields.

On the prediction of settling velocity for plastic particles of different shapes

Transport processes of plastic particles in freshwater and marine environments are one of the relevant advances of knowledge in predicting the fate of plastic in the environment. Here, we investigated the effect of different shapes on the settling velocity, finding a representative reference diameter which encompasses three-dimensional shapes like pellets or spherules, two-dimensional shapes like fragments or disks, and one-dimensional shapes like filaments or fibers. The new method is able to predict the settling velocity of plastic and natural particles given the representative size and the Corey shape factor coefficient, over the entire range of viscous to turbulent flow regime. The calibration of the method with experimental data, and the validation with an independent dataset, support its application in a wide range of hydraulic conditions.

Microplastic characteristics in organisms of different trophic levels from Liaohe Estuary, China

Microplastics are a growing concern globally due to their small size and easy ingestion by terrestrial and aquatic organisms, resulting in potential adverse impacts on wildlife. However, current data regarding microplastics in wild organisms in different trophic levels is limited. This study investigated microplastic characteristics, including their abundance, size, shape and polymer type, in estuarine invertebrates and vertebrates. Resultantly, polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) were the predominant microplastics found, as confirmed by a Fourier transform infrared spectrometer (FT-IR). An average microplastic abundance of 0.83 ± 0.99 to 3.87 ± 2.18 items/individual was detected across all species, including sandworm, mollusks, crustacean and fish, but they were not found in all individuals. Microplastics ranged from 52 μm to 5392 μm in size, and the shapes were consisted of fiber, fragment, and pellet. Moreover, the detection ratio (91.95%) and abundance (3.34 ± 2.17 items/individual) of microplastics in fish were significantly higher than in sandworm (42.86%, 0.88 ± 1.04 items/individual), mollusks (66.97%, 1.42 ± 1.41 items/individual) and crustaceans (66.66%, 1.33 ± 1.32 items/individual) (p < 0.05). Furthermore, a positive relationship was identified between microplastic abundance and the trophic level of organisms. These findings imply that microplastics might transfer along the food chain and accumulate at organisms in higher trophic levels.

Effects of food presence on microplastic ingestion and egestion in Mytilus galloprovincialis

Plastic wastes are widespread pollutants in marine environments and several studies have focused on their impacts on different ecosystems. Microplastics (MPs, < 5 mm) have been the focus of a particularly extensive investigation because of their ubiquity, large surface area, interactions with organisms, and the challenges they present in terms of disposal and management. However, studies regarding their fates and life cycle in ecosystems are still limited. This study examined the effects of presence of food (the green microalga Dunaliella salina) on egestion rate of polyethylene MPs in the mussel Mytilus galloprovincialis. Ingestion and egestion rates were calculated after 6, 12, 18, and 24 h of depuration. The results suggest that MPs exposed to algal food persisted in the mussels. A single exposure of MPs without food induced relatively rapid excretion by the mussels compared to MPs exposure with food. This could be attributed to the ability of mussels to distinguish between nutritive foods and unusable suspended particles. Thus, environmental factors, such as food abundance, can affect the cycle or fate of MPs in marine environments.