Low-density Polyethylene Microplastics Research Articles

Toxicological assessment of dietary exposure of polyethylene microplastics on growth, nutrient digestibility, carcass and gut histology of Nile Tilapia (Oreochromis niloticus) fingerlings.

This study was conducted to ascertain the negative effects of dietary low-density polyethylene microplastics (LDPE-MPs) exposure on growth, nutrient digestibility, body composition and gut histology of Nile tilapia (Oreochromis niloticus). Six sunflower meal-based diets (protein 30.95%; fat 8.04%) were prepared; one was the control (0%) and five were incorporated with LDPE-MPs at levels of 2, 4, 6, 8 and 10% in sunflower meal-based diets. A total of eighteen experimental tanks, each with 15 fingerlings, were used in triplicates. Fish were fed at the rate of 5% biomass twice a day for 60 days. Results revealed that best values of growth, nutrient digestibility, body composition and gut histology were observed by control diet, while 10% exposure to LDPE-MPs significantly (P < 0.05) reduced weight gain (WG%, 85.04%), specific growth rate (SGR%, 0.68%), and increased FCR (3.92%). The findings showed that higher level of LDPE-MPs (10%) exposure in the diet of O. niloticus negatively affects nutrient digestibility. Furthermore, the results revealed that the higher concentration of LDPE-MPs (10%) had a detrimental impact on crude protein (11.92%) and crude fat (8.04%). A high number of histological lesions were seen in gut of fingerlings exposed to LDPE-MPs. Hence, LDPE-MPs potentially harm the aquatic health.

New insights into the size-independent bioactive potential of pristine and UV-B aged polyethylene microplastics

The present study investigates the morphological, physicochemical, and structural changes occurred by the UV-B aging process of low-density polyethylene microplastics (LDPE MPs), as well as the bioactive potential of both pristine and UVaged MPs towards healthy peripheral blood lymphocytes. Specifically, LDPE MPs (100–180 μm) prepared by mechanical milling of LDPE pellets, were UV-B irradiated for 120 days (wavelength 280 nm; temperature 25 °C; relative humidity 50 %) and further examined for alterations in their particle size and surface, their functional groups, thermal stability, and crystallinity (by means of SEM, FTIR spectroscopy, XRD patterns, and TGA measurements, respectively). In parallel, isolated human peripheral blood lymphocytes were treated with different concentrations (25–500 μg mL−1) of either pristine or aged MPs (UVfree and UV120d LDPE MPs) for assessing the cytogenotoxic (by means of trypan blue exclusion test and the cytokinesis-block micronucleus assay using cytochalasin-B) and oxidative effects (using the DCFH-DA staining) in both cases. According to the results, UVfree and UV120d-LDPE MPs, with a size ranging from 100 to 180 μm, can differentially promote cytogenotoxic and oxidative alterations in human lymphocytes. In fact, UVfree LDPE MPs not being able to be internalized by cells due to their size, could indirectly promote the onset of mild oxidative and cytogenotoxic damage in human peripheral lymphocytes, via a dose-dependent but size-independent manner. The latter is more profound in case of the irregular-shaped UV120d-LDPE MPs, bearing improved dispersibility and sharp edges (by means of cracks and holes), as well as oxygen-containing and carbonyl groups. To our knowledge, the present findings provide new data regarding the bioactive behavior of pristine and UV-B aged LDPE MPs, at least in the in vitro biological model tested, thus giving new evidence for their size-independent and/or indirect mode of action.

Low-density polyethylene microplastics partially alleviate the ecotoxicological effects induced by cadmium exposure on the earthworm Eisenia fetida

Low-density polyethylene microplastics partially alleviate the ecotoxicological effects induced by cadmium exposure on the earthworm Eisenia fetida

The characteristics and influencing factors of farmland soil microplastic in Hetao Irrigation District, China

Microplastic pollution, a major global concern, has garnered increasing attention in agricultural ecosystem research. China’s Hetao Irrigation District, vital for grain production in the Yellow River Basin, lacks sufficient research on microplastic pollution of agricultural soils. This study, based on a detailed background investigation and testing of 47 samples, is the first to elucidate the characteristics and potential influencing factors of microplastics in the Hetao Irrigation District. The abundance of microplastics in the farmland soil ranged from 1810 to 86331 items/kg, with 90% measuring below 180 µm and mainly in film and fragment forms. Predominant polymers were polyethylene (PE, 43.0%) and polyamide (PA, 27.8%). Key pollution influencers were identified as agricultural inputs, with low-density polyethylene (LDPE) being the most extensively used plastic type. The carbonyl index and hydroxyl indices of the detected LDPE microplastics ranged from 0.041 to 0.96 and 0.092 to 1.20, respectively. The study highlights the significance of mulching management and agronomic practices in shaping microplastic characteristics. Potential pollution sources include agricultural inputs, irrigation equipment, domestic waste, and tire wear. Proposed effective strategies include responsible plastic use, robust waste management, and irrigation system upgrades, establishing a foundation for future ecological risk assessments and effective management approaches in the Hetao Irrigation District. Environmental implicationThe harmful substances studied in this paper are microplastics, which are widely distributed in the environment and have potential ecological risks. This study is the first to investigate the characteristics of microplastics in farmland soil within the Hetao Irrigation Area, a region that is of critical importance to agricultural production in the Yellow River Basin of China. The study provides comprehensive insights into the factors influencing the characteristics of microplastics and speculates on their sources. These findings offer a novel perspective on the assessment of microplastic contamination in the area and provide valuable recommendations for prevention and control measures.

Optimizing biocoagulant aid from shrimp shells (Litopenaeus vannamei) for enhancing microplastics removal from aqueous solutions

The escalating concern over microplastic pollution in surface water has led to the exploration of effective removal methods, including coagulation and flocculation (CF). This study investigates the potential of chitosan, derived from shrimp shell waste (Litopenaeus vannamei), as a promising biocoagulant aid for pollutant and microplastic removal. The characteristics of chitosan were analyzed for moisture, ashes, protein content, the degree of deacetylation (DD), solubility, pH, viscosity, and Fourier Transform Infrared (FTIR). Systematic examinations of coagulant, biocoagulant aid dosages and pH levels were conducted to optimize the removal efficiency for various pollutants. Subsequently, Low Density Polyethylene (LDPE) microplastics with particle sizes of 1.00, 0.30, and 0.090 mm were employed to assess the efficacy of CF for microplastic removal. The results demonstrated that the optimal dosages of 20 mg/L of alum, 1 mg/L of chitosan, and pH 5, exhibited the highest efficiency for pollutant removal, encompassing turbidity, total suspended solids (TSS), and chemical oxygen demand (COD). Furthermore, the size of LDPE microplastics significantly influenced their removal efficiency, with smaller microplastics (0.090 mm) exhibiting higher removal rates compared to larger ones (0.30 mm and 1.00 mm). The maximum removal efficiencies for LDPE microplastics were 92.13 ± 1.41% for sizes of 0.090 mm. The removal mechanisms for LDPE microplastics involved charge neutralization, inter-particle bridging, and hydrophobic flocculation between LDPE and the coagulant/biocoagulant aid. This study highlights the potential of chitosan from shrimp shell waste as a sustainable and efficient biocoagulant aid for pollutants and microplastic removal in aqueous solutions.

Low-density polyethylene microplastics alter chemical properties and microbial communities in agricultural soil

Microplastic (MP) pollution in agricultural soils, resulting from the use of plastic mulch, compost, and sewage sludge, jeopardizes the soil microbial populations. However, the effects of MPs on soil chemical properties and microbial communities remain largely unknown. Here, we investigated the effects of different concentration levels (0, 0.1, 1, 3, 5, and 7%; w:w) of low-density polyethylene (LDPE) MPs on the chemical properties and bacterial communities of agricultural soil in an incubation study. The addition of LDPE MPs did not drastically change soil pH (ranging from 8.22 to 8.42). Electrical conductivity increased significantly when the LDPE MP concentrations were between 1 and 7%, whereas the total exchangeable cations (Na+, K+, Mg2+, and Ca2+) decreased significantly at higher LDPE MP concentrations (3–7%). The highest available phosphorus content (2.13 mg kg−1) was observed in 0.1% LDPE MP. Bacterial richness (Chao1 and Ace indices) was the lowest at 0.1% LDPE MP, and diversity indices (Shannon and Invsimpson) were higher at 0 and 1% LDPE MP than at other concentrations. The effect of LDPE MP concentrations on bacterial phyla remained unchanged, but the bacterial abundance varied. The relative abundance of Proteobacteria (25.8–33.0%) was the highest in all treatments. The abundance of Acidobacteria (15.8–17.2%) was also high, particularly in the 0, 0.1, and 1% LDPE MPs. With the increase in LDPE MP concentration, the abundance of Actinobacteria gradually increased from 7.80 to 31.8%. Our findings suggest that different MP concentration levels considerably alter soil chemical properties and microbial composition, which may potentially change the ecological functions of soil ecosystems.

Middle concentration of microplastics decreasing soil moisture-temperature and the germination rate and early height of lettuce (Lactuca sativa var. ramosa Hort.) in Mollisols

Microplastics (MPs) have been widely found in soils, however, the mechanism of MPs influencing plant growth is still debated and possibly attributed to the soil environment changed by MPs. In this study, 0.0 %, 0.1 %, 0.5 %, 1.0 %, 2.0 %, and 5.0 % (w/w) content of low-density polyethylene MPs (LDPE-MPs) with the particle sizes of 75–2000 μm was used to test how MPs alter the germination and the early growth of lettuce (Lactuca sativa var. ramosa Hort.) in Mollisols under both natural condition and regular incubation condition. Soil temperature (ST), soil moisture (SM) and the ratio of cracks area to surface soil area (CA) and cracks length to surface soil area (CL) were monitored. As well, the dynamics of water and nutrient infiltration reported by our previous publication were combined to analyze the relationship between soil properties and crop growth influenced by MP concentration. The main results showed that: (1) compared with CK (0.0 %), the germination and plant height of lettuce were lowest in treatments with the middle concentration of MPs (0.5 % and 1 %, w/w), but was highest in treatments of high concentration of MPs (5.0 %, w/w) during the whole 14 days of incubation; (2) increasing MP concentration weakened the influence of SM on ST in Mollisols; (3) the average of SM and ST were highest at 5 % of MP concentration, while was lowest at 0.5 % and 1 % of MP concentration from the 2nd to the 9th day; (3) compared with CK and other treatments, the CA and CL were lowest in 1.0 % MP concentration, but were highest in 0.1 % and 5.0 % of MP concentration. This study provides insight that middle, rather than high and low levels of MP concentration, significantly decrease the SM and ST and increase nitrogen leaching which further leads to negative impacts on emergent and early growth of crops in soils with heavy texture (Mollisols).

Low-density polyethylene microplastics and biochar interactively affect greenhouse gas emissions and microbial community structure and function in paddy soil

Paddy soils are susceptible to microplastics (MPs) contamination. As a common soil amendment, biochar (BC) has been extensively applied in paddy fields. The co-occurrence of MPs and BC may cause interactive effects on soil biogeochemical processes, which has yet been well studied. In this study, a 41-days of microcosm experiment was conducted using paddy soil added with 0.5–1.5 wt% of low-density polyethylene (LDPE) and 5 wt% of BC individually or jointly. Application of BC, LDPE, or their mixture into soil significantly increased the emission of methane (CH4), but suppressed the emission of carbon dioxide (CO2). LDPE addition lowered soil nitrous oxide (N2O) emissions, while BC exerted an opposite effect. Proteobacteria was the most dominant phylum with a relative abundance range of 35.1–51.0%, followed by Actinobacteria (19.3–30.9%) and Acidobacteria (7.5–23.5%). The abundances of the mcrA gene and pH values were increased in soils added with BC or/and LDPE, which were the possible reasons for the higher CH4 emissions in these treatments. The emission of N2O was positively related to the abundances of norB and narG genes, suggesting denitrification was a major pathway to produce N2O. Results of structural equation modeling demonstrated that addition of BC or/and LDPE MPs could affect greenhouse gas emissions from paddy soil by altering soil chemical properties, microbial community structure, and functional gene abundances.

Investigations of hemato-biochemical and histopathological parameters, and growth performance of walking catfish (Clarias batrachus) exposed to PET and LDPE microplastics

Fish inhabiting various trophic levels are affected differently as the presence of microplastic (MP) in the water column and their ingestion by fish varies. Walking catfish (Clarias batrachus) inhabits the bottom of the water bodies. To understand the effects of MP, we exposed C. batrachus to two types of MP – polyethylene terephthalate (PET) and low-density polyethylene (LDPE) for 60 days. After exposure, hematological indices, mainly red blood cells and hemoglobin levels decreased, and white blood cells increased significantly compared to the control group (p < 0.05). A significant increase in the levels of blood urea and glucose was observed, and serum glutamic pyruvate transaminase and serum glutamyl oxaloacetic transaminase activity remained elevated (p < 0.05). Histopathological examination of the liver, kidney, intestine, and gills showed morphological alterations. Moreover, MP exposure caused growth retardation (p < 0.05) in C. batrachus. Widespread pollution of water bodies by MP may impose serious ecological risks to bottom-feeding fish in Bangladesh.

Effects of Low-density Polyethylene Microplastics on the Growth and Physiology Characteristics of Ipomoea aquatica Forsk

Microplastic pollution in soil and its toxicological effects have attracted increasing attention from researchers, but the mechanisms of microplastics affecting crop growth and physiology remain unclear. A pot experiment was conducted to evaluate the impacts of various mass concentrations (0%, 0.2%, 5%, and 10%) of low-density polyethylene microplastics (LDPE MPs) on the germination rate, photosynthetic pigment content, biomass, antioxidant enzyme activity, soluble protein, and soluble sugar content of water spinach (Ipomoea aquatica Forsk). The results showed that LDPE MPs significantly inhibited (P<0.05) the seed vigor of water spinach, and the inhibitory effect increased with increasing concentration of LDPE MPs. However, the 5% LDPE MPs significantly promoted the aboveground biomass of water spinach. The 0.2% and 10% LDPE MPs significantly improved the superoxide dismutase (SOD) activity and catalase (CAT) and peroxidase (POD) activities, respectively. Further, malondialdehyde (MDA) content decreased with increasing concentration of LDPE MPs, and the reductions reached 15.53%-27.39% in comparison to that in the control. The LDPE MPs also significantly increased the soluble sugar content of water spinach leaves. In summary, LDPE MPs could inhibit the seed vigor and promote biomass accumulation in water spinach. Water spinach could relieve the oxidative stress caused by LDPE MPs by regulating antioxidant enzyme activity and soluble protein content. Therefore, this study may provide basic information for assessing the influences of microplastics on vegetables.

Interactive effects of microplastics and benzo[a]pyrene on two species of marine invertebrates

This study aimed to evaluate B[a]P and low-density polyethylene microplastics (MPs) toxicty, alone and in mixture (0.03 to 30 μg L−1 of B[a]P; and 5, 50 and 500 mg L−1 for MPs). Five mg L−1 of MPs is considerably higher than commonly reported environmental concentrations, although it has been reported for marine environments. Individual (sea urchin embryo-larval development and mortality of mysids) and sub-individual responses (LPO and DNA damage in mysids) were assessed. The toxicity increased as the B[a]P concentration increased, and microplastics alone did not cause toxicity. B[a]P toxicity was not modified by the lowest concentration of MPs (5 mg L−1), but at higher MPs concentrations (50 and 500 mg L−1), the effects of B[a]P on sea urchin development and in biomarkers in mysids were diminished. Microplastics interacted with B[a]P in seawater, reducing its toxicity, probably due to adsorption of B[a]P to the surface of microplastics.

Responses of earthworms exposed to low-density polyethylene microplastic fragments

The interest in the effect of microplastics (MPs) on the terrestrial environment has been increasing recently. Different species of earthworms have been used to study the effects of MPs on different aspects of earthworm health. However, there is still a need for more studies because different studies report different effects on earthworms depending on the properties (e.g., types, shapes, sizes) of MPs in the environment and exposure conditions (e.g., exposure period). This study used Eisenia fetida as a test earthworm species to investigate the effect of different concentrations of low-density polyethylene (LDPE) MPs (≤125 μm) in soil on the growth and reproduction of earthworms. The exposure of the earthworms to the different concentrations of LDPE MPs (0–3% w/w) for 14 d and 28 d neither caused death of the earthworms nor showed significant effects on the earthworm weights in this study. The number of cocoons produced by the exposed earthworms were also similar to that of the controls (i.e., no exposure to MPs). Some previous studies reported similar results to what have been observed in this study, while some studies reported different results. On the other hand, the number of ingested MPs by the earthworms increased with increasing MPs concentrations in soil, suggesting a potential for damage to digestive tract. Also, the earthworm skin surface was damaged after exposure to MPs. The ingested MPs and the skin surface damage suggest that there is a potential for adverse effects on the earthworm growth after a longer-term exposure. Overall, the results of this study show that the effects of MPs on earthworms need to be studied using various endpoints including growth, reproduction, ingestion, and skin damage and such effects can be different depending on the exposure conditions such as MPs concentration and exposure period.

Biodegradation of low-density polyethylene microplastic by new halotolerant bacteria isolated from saline mud in Bledug Kuwu, Indonesia

Biodegradation of low-density polyethylene (LDPE) microplastics by newly halotolerant bacteria from saline mud in Bledug Kuwu, Indonesia was investigated. Of the eight bacteria, S. maltophilia BK1 and Enterococcus sp. BK3 showed a clear zone in agar containing LDPE and degraded 5 % and 6 % (w/w) of LDPE in artificial seawater after 90 d. During the biodegradation, the bacterial growth rate, biofilm formation, and hydrophobicity significantly increased after 40 d when the glucose concentration in the media was limited. Scanning electron microscopy (SEM) analysis displayed the destruction of the LDPE surface after treatment. Fourier transform infrared (FTIR) analysis showed the removal of the CC group at 861 cm−1, the addition of alkyl at 1019–1058 cm−1, and hydroxyl groups at 3000–3500 cm−1, indicating biodegradation. X-ray diffraction (XRD) analysis corroborated the degradation by decreasing the crystallinity index from 36 % (control) to 23 % (BK1) and 24 % (BK3), respectively.

Partitioning of heavy metals in sediments and microplastics from stormwater runoff

Microplastics could act as vehicles for transporting heavy metals from urban environments to water resources via stormwater runoff. Although the transport of heavy metals by sediments has been widely studied, there is a lack of mechanistic understanding of their competition with microplastics (MPs) for heavy metal uptake. Therefore, this study was conducted to examine the partitioning of heavy metals in microplastics and sediments from stormwater runoff. For this purpose, new low density polyethylene (LDPE) pellets were selected as representative MPs, and accelerated UV-B irradiation experiments were conducted for eight weeks to generate photodegraded MPs. The competition of Cu, Zn, and Pb species for the occupation of available surface sites on sediments and new and photodegraded LDPE MPs was examined through 48 h kinetics experiments. Additionally, leaching experiments were conducted to identify the extent of organics released into the contact water by new and photodegraded MPs. Moreover, 24 h metal exposure experiments were conducted to identify the role of initial metal concentrations on their accumulation onto the MPs and sediments. The photodegradation process altered the LDPE MPs’ surface chemistry by creating the oxidized carbon functional groups [>CO, >C–O–C<], and it also enhanced their dissolved organic carbon (DOC) leaching into the contact water. The results showed significantly greater levels of Cu, Zn, and Pb accumulations on photodegraded MPs compared to the new MPs in either absence or presence of sediments. Heavy metal uptake by sediments when photodegraded MPs were present was significantly reduced. This might be due to the organic matter leached by photodegraded MPs into the contact water.

Impacts of polyethylene microplastics on the microalga, Spirulina (Arthrospira platensis)

Microalgae play a critical role in the food web and biogeochemical cycling and produce compounds that are commercially exploited. However, their reactions and responses to microplastic contamination are not well understood. In this study, the widely distributed and commercially important cyanobacterium, Spirulina (Arthrospira platensis), was exposed to different concentrations (1–100 mg L−1) of low-density polyethylene microplastics (<5 μm) over a 20-d period. Various end-points were combined with different microscopic techniques in order to examine physiological and biochemical effects and interactions between the plastic and microalga. Growth rate and photosynthetic activity decreased with increasing microplastic concentration, and a maximum inhibition ratio of about 9% was calculated from optical density measurements. Plastic concentrations above 10 mg L−1 resulted in oxidative stress and the intracellular production of proline. Fragmentation and swelling of trichomes and attachment of microplastics was observed in the exposures, and microplastics appeared to adhere or aggregate around fragmented or fragmenting regions. The latter effect may indicate trichome weakening by microplastics or their concentration around cytosolic debris; nevertheless, it provides a potential mechanism for internalisation of small particles. Although unrealistically high concentrations of well-defined microplastics have been employed, relatively small disruptions at the population level incurred by lower concentrations could have more serious implications for ecosystem services and functioning.

Fragmentation and depolymerization of microplastics in the earthworm gut: A potential for microplastic bioremediation?

The accumulation of microplastics poses potential risks to soil health. Here, we did a preliminary exploration on the potential of Lumbricus terrestris (Oligochaeta) to reduce low-density polyethylene (LDPE), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) microplastic (20–648 µm) contamination in soils. The ingestion of microplastics-contaminated soil (1% of microplastics, dw/dw) in a mesocosm system and the ingestion of pure microplastics in the Petri Dish by earthworms were studied. Results show that earthworms survived in the microplastics-contaminated soil (0% mortality in 35 days) but barely when exposed solely to microplastics (30–80% mortality in 4 days). Size-dependent ingestion of microplastics was not observed. The fragmentation of LDPE microplastics in the gizzard facilitated by soil was confirmed by the significantly increased ratio of small-sized (20–113 µm) microplastics from the bulk soil to the gut (from 8.4% to 18.8%). PLA and PBAT microplastics were fragmented by gizzard without the facilitation of soil, the ratios of small-sized (20–113 µm) PLA and PBAT microplastics in the gut were 55.5% and 108.2% higher than in respective pristine distributions. Substantial depolymerization of PLA (weight-average molar mass reduced by 17.7% with shift in molecular weight distribution) and suspected depolymerization of PBAT were observed in the worm gut, while no change in the molar mass was observed for PLA and PBAT microplastics buried in the soil for 49 days. Our results suggest that ingested microplastics could undergo fragmentation and depolymerization (for certain polymers) in the earthworm gut. Further research is needed to reveal the mechanisms of polymer depolymerization in the earthworm gut and to evaluate the feasibility of microplastic bioremediation with earthworms.

Wistar Rats Hippocampal Neurons Response to Blood Low-Density Polyethylene Microplastics: A Pathway Analysis of SOD, CAT, MDA, 8-OHdG Expression in Hippocampal Neurons and Blood Serum Aβ42 Levels

Low-density polyethylene microplastics are ingested into the bloodstream and distributed to all the organ tissue, including the hippocampus, causing toxic effects. This research aimed to elucidate the responses of hippocampal neurons to microplastic in the blood based on the expressions of superoxide dismutase (SOD), catalase (CAT) enzymes, malondialdehyde (MDA), 8-oxo-7,8-dihydro-2-deoxyguanosine (8-OHdG) in hippocampal neurons, and blood serum amyloid beta 1-42 (Aβ42) levels using SMART PLS pathway analysis. This was a pure experimental research on Wistar rats with a post-test control group design. Five experimental groups (X1, X2, X3, X4, X5) were given 0.0375 mg, 0.075 mg, 0.15 mg, 0.3 mg, and 0.6 mg of low-density polyethylene microplastics mixed in 2cc distilled water, respectively. Furthermore, except for control (C), the groups received microplastics an oral probe for 90 days. The molecular response of hippocampal neurons of Wistar rats to microplastics in the blood significantly decreased SOD enzyme expression, while CAT enzyme was unaffected. It considerably increased neuronal membrane damage (expression of MDA), increased considerably neuronal deoxyribonucleic acid damage (expression of 8-OHdG), and decreased blood serum Aβ42 levels (pathway analysis, all t-value >1.96). The pathway analysis showed that hippocampal neurons were significantly affected by microplastic particles in the blood.

Low-Density Polyethylene Microplastics in the Blood Seems not Induce Alzheimer’s Disease in Wistar Rat

Microplastic particles &lt;5 mm in the blood pose health problems to humans. One of the entry points for low density polyethylene microplastics in the human blood is through consumption of contaminated food. These low density polyethylene microplastic particles are found in table salt, canned sardines, beer, sea fish, honey, sugar, tea bags, minerals and drinking water. These findings estimated between 37 to as high as billion microplastic particles from those various food products. The number of low density polyethylene microplastic particles that contaminate food and beverages will continue to increase along with the increase in plastic debris in the environment.

The transport of microplastics by ants cannot be neglected in the soil ecosystem

Microplastics (MPs) are widespread in soils and continue to migrate in response to many abiotic and biotic factors. Although some studies have explored the effects of abiotic factors (e.g., wind and water) on MP migration and distribution, there is little information on the effects of biotic factors, especially soil fauna, on this process. Ants are among the most abundant fauna on Earth and play an important role in ecosystem health. Here, we tested whether ants could transport low-density polyethylene (LDPE) MPs in the field. We also investigated the effects of ants (Pheidole sp.) on the removal rates and distribution of LDPE MPs in the laboratory compared to other potential field materials (leaf fragments and tiny stones). We found that, in the field, two ant species (Pheidole sp. and Paratrechina sp.) could actively carry LDPE MPs; the mean removal distance was 75.34 ± 4.05 cm, and the curve had a long tail extending to 140 cm. In the laboratory, the mean number of removed leaf fragments and LDPE MPs was significantly greater than that of removed tiny stones. After 14 days, the proportions of LDPE MPs, leaf fragments, and tiny stones removed into the nests by ants were 15.8%, 19.15%, and 3.3%, respectively. The proportions of LDPE MPs in the original position (not removed by ants), inside the nests, and outside the nests were 18.4%, 15.8%, and 65.8%, respectively. These results indicate that ants play an important, but neglected, role in the transport and distribution of MPs in soil ecosystems. Given the abundance and diversity of ants worldwide, the ant-mediated transport of MPs may be common in soil ecosystems. We suggest that the transport of MPs by ants may expand the distribution of MPs and influence the exposure of other soil fauna to MPs in soil ecosystems.

Interactive adverse effects of low-density polyethylene microplastics on marine microalga Chaetoceros calcitrans

Low-density polyethylene (LDPE) is broadly utilized worldwide, increasing more dramatically during the COVID-19 pandemic, and the majority ends up in the aquatic environment as microplastics. The influence of polyethylene microplastics (LDPE-MPs) on aquatic ecosystems still needs further investigation, especially on microalgae as typical organisms represented in all aquatic systems and at the base of the trophic chain. Thereby, the biological and toxicity impacts of LDPE-MPs on Chaetoceros calcitrans were examined in this work. The results revealed that LDPE-MPs had a concentration-dependent adverse effect on the growth and performance of C. calcitrans. LDPE-MPs contributed the maximum inhibition rates of 85%, 51.3%, 21.49% and 16.13% on algal growth chlorophyll content, φPSII and Fv/Fm, respectively. The total protein content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased at 25 mg L−1 LDPE-MPs by 1.37, 3.52, 2.75 and 1.84 folds higher than those of the controls to sustain the adverse effects of LDPE-MPs. Extracellular polymeric substance (EPS) and monosaccharides contents of C. calcitrans were improved under low concentration of LDPE-MPs, which could facilitate the adsorption of MPs particles on the microalgae cell wall. This adsorption caused significant physical damage to the algal cell structure, as observed by SEM. These results suggest that the ecological footprint of MPs may require more attention, particularly due to the continuing breakdown of plastics in the ecosystem.