The impacts of polyethylene terephthalate microplastics (mPETs) on ecosystem functionality in marine sediment

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

Microplastic concentrations and risk assessment in water, sediment and invertebrates from Simon's Town, South Africa

Plastic pollution is an ever-increasing threat globally and poor waste management in South Africa has caused an increase in plastic leakage into the environment. Plastic waste in the environment are categorized according to size and plastic particles smaller than 5 mm in size are regarded as microplastics (MPs), and little to no research has been done on MPs pollution within the marine coastal environment and rocky shores in South Africa. Sampling was done in February 2020 at a rocky shore within Simon's Town Marina, Cape Town. MPs were extracted from collected water (n = 5), sediment (n = 5) and biota (n ≤ 30) samples. The extracted MPs were further classified based on shape, colour, size and an attenuated total reflectance Fourier-transform infrared (ATR-FTIR) instrument was utilized for polymer type identification The risks posed by MPs because of concentration at which they occurred and chemical composition were assessed in all the sample types. As expected, MPs were higher in sediment (38 ± 2 MP/kg) than in water (0.37 ± 0.06 MP/L) as the area has low water energy, allowing MP particles to settle within the sediment. Filter-feeding organisms had the lowest average MP particle concentrations (0.28 ± 0.04 MP/g) but displayed the highest variation of MP particle colours due to the non-selective feeding strategy, where other feeding strategies ingested mostly black/grey particles. The dominant MP size was between 100 μm and 500 μm in size for all samples combined, with the most abundant MP polymer type being nylon (27.27 %), polyethylene terephthalate (PET) (18.18 %) and natural MP particles such as cotton (18.18 %). The risk assessment indicated that polymer type poses a greater risk of MP pollution than MP concentrations.

Biodegradation of poly(ethylene terephthalate) through PETase surface-display: From function to structure

Polyethylene terephthalate (PET) is one of the most used plastics which has caused some environmental pollution and social problems. Although many newly discovered or modified PET hydrolases have been reported at present, there is still a lack of comparison between their hydrolytic capacities, as well as the need for new biotechnology to apply them for the PET treatment. Here, we systematically studied the surface-display technology for PET hydrolysis using several PET hydrolases. It is found that anchoring protein types had little influence on the surface-display result under T7 promoter, while the PET hydrolase types were more important. By contrast, the newly reported FAST-PETase showed the strongest hydrolysis effect, achieving 71.3% PET hydrolysis in 24 h by pGSA-FAST-PETase. Via model calculation, FAST-PETase indeed exhibited higher temperature tolerance and catalytic capacity. Besides, smaller particle size and lower crystallinity favored the hydrolysis of PET pellets. Through protein structure comparison, we summarized the common characteristics of efficient PET-hydrolyzing enzymes and proposed three main crystal structures of PET enzymes via crystal structural analysis, with ISPETase being the representative and main structure. Surface co-display of FAST-PETase and MHETase can promote the hydrolysis of PET, and the C-terminal of the fusion protein is crucial for PET hydrolysis. The results of our research can be helpful for PET contamination removal as well as other areas involving the application of enzymes. SYNOPSIS: This research can promote the development of better PET hydrolase and its applications in PET pollution treatment via bacteria surface-display.

Uncovering the intricate relationship between plant nutrients and microplastics in agroecosystems

Recent scientific and media focus has increased on the impact of microplastics (MPs) on terrestrial and soil ecosystems. However, the interactions between MPs with macronutrients and micronutrients and their potential consequences for the agroecosystem are not well understood. Wheat (Triticum aestivum) is a staple food grown globally and has special importance for nations economies. Different elements can cause dangerous outcomes for wheat quality and production yield. In this study, batch adsorption experiments were done using 1 g of polyethylene tetra phthalate MP particles (PET-MPs) in varying concentrations of thirteen elements. The adsorption data were fitted by two common adsorption models (Langmuir and Freundlich). The effect of pH on the speciation of elements in aqueous solutions was investigated. The non-invasive characterization methods indicate the importance of O- and H-containing groups as the main component of selected MPs in controlling the adsorption of the elements ions. In the current study, adsorption and potential transport of the adsorbed macronutrients (K and Na) and micronutrients (Ni, Co, Cu, Al, Ba, Se, Fe, As, B, V and Ag) which include some beneficial (Na, Se, V), and non-essential or toxic elements (Al, As, Ag, Ba) onto MPs to the simulated roots of wheat were evaluated. The maximum sorption capacities of K+> Ni+2> Na+ > Co2+> Cu2+>Al+3 >Ba+2 >Se4+>Fe2+ >As5+ >B3+ >V5+> Ag + on PET-MPs at pH 5.8 and 25 ± 1 °C were 290.6 > 0.52> 0.51 > 0.20> 0.10 > 0.051> 0.024 > 0.003> 0.003 > 0.0015> 5.05 × 10-4> 1.7 × 10-4>3.7 × 10-6 mg g-1, respectively. The results highlight the importance of PET-MPs in controlling element adsorption in the rhizosphere. Our observations provide a good start for understanding the adsorption of multiple elements from the soil rhizosphere zone by PET-MPs.

Modelled broad-scale shifts on seafloor ecosystem functioning due to microplastic impacts on bioturbation

Bioturbating species play an essential role in regulating nutrient cycling in marine sediments, but their interaction with microplastics (MP) remains poorly understood. Here we investigated the linkage between MP and ecosystem functioning using experimental observations of luminophore distribution in the sediment to parametrize bioturbation coefficients (Db). this information as fed into a simplified transport-reaction model, allowing us to upscale our experimental results. We found that the composition of bioturbators modulated shifts in the ecosystem functioning under microplastic stress. Maldanid worms (Macroclymenella stewartensis), functionally deep burrowing and upward-conveyor belt feeders, became less active. The Db of M. stewartensis reduced by 25% with the addition of 0.002 g MP cm-2 at surface sediment, causing accumulation of organic matter in the oxic sediment zone and stimulating aerobic respiration by 18%. In contract, the tellinid bivalve Macomona liliana, functionally a surface -deposit feeder that excretes at depth, maintained particle mixing behaviour in MP-contaminated systems. This study provides a mechanistic insight into the impacts of MP and indicates that the functional role of bioturbating species should be involved in assessing the global impact of MP. The model allowed us to understand the broad-scale impact of MP on seafloor habitat.

Real-world impacts of microplastic pollution on seafloor ecosystem function

Emerging research shows that microplastic pollution could be impacting seafloor ecosystem function, but this has been primarily demonstrated without environmental and ecological context. This causes uncertainty in the real-world effects of microplastic pollution and leaves out essential information guiding policy and mitigation. In this study, we take a well-supported sampling design and statistical approach commonly employed in benthic ecology to evaluate real-world effects of microplastic pollution on coastal, benthic ecosystem function. We utilised environmental gradients in the Waitemata Harbour of Auckland, New Zealand to evaluate the importance of commonly assessed biological, chemical, and geological sediment variables and the characteristics of microplastic contaminants in driving essential ecosystem functions. Our results showed that models including microplastic terms were more accurate and explained more variability than those without microplastic terms, highlighting that microplastics impact real-world seafloor ecosystem function. Specifically, microplastic fibers significantly influenced oxygen flux (p < 0.03) and the diverse forms of microplastics (i.e., richness) significantly influenced ammonium flux (p < 0.02). Additionally, interactions between microplastic fiber concentrations and mollusc abundances significantly contributed to oxygen flux (p < 0.02). These results provide the first evaluation of in situ relationships between microplastics and ecosystem function. Even more importantly, this study suggests the value of environmental and ecological context for addressing microplastic impacts on benthic ecosystems and argues for further field examination.

Long-term exposure of a free-living freshwater micro- and meiobenthos community to microplastic mixtures in microcosms

Microplastics in a wide range of shapes and polymer types (MPs; <5 mm) accumulate in freshwater sediments, where they may pose an environmental threat to sediment-dwelling micro- and meiobenthos. To date, the effects of MPs on those organisms have mostly been studied in single-species experiments exposed to high particle concentrations. By contrast, there have been few investigations of the effects resulting from the long-term exposure of natural communities to environmental relevant MPs. This research gap was addressed in the present study. A microcosm experiment was conducted to examine the impact of a mixture of MPs of varying polymer composition, shape, and size (50% polystyrene (PS) beads: 1-μm diameter; 37% polyethylene terephthalate (PET) fragments: 32 × 21 μm in size, and 13% polyamide (PA) fibers 104 × 15 μm in size; % based on the total particle number) provided at two concentrations (low: 4.11 × 10⁵ MPs/kg sediment dw and high: 4.11 × 10⁷ MPs/kg sediment dw) and two exposure durations (4 and 12 weeks) on a micro- and meiobenthic community collected from a freshwater sediment. MPs exposure did not alter the abundance of protozoa (ciliates and flagellates) as well as the abundance and biomass of meiobenthic organisms (nematodes, rotifers, oligochaetes, gastrotrichs, nauplii), whereas the abundance and biomass of harpacticoid copepods was affected. Neither nematode species diversity (species richness, Shannon-Wiener index, and evenness) nor the NemaSPEAR[%]-index (pollution-sensitive index based on freshwater nematodes) changed in response to the MPs. However, changes in the structure of the meiobenthic and nematode community in the presence of environmentally relevant MPs mixtures cannot be excluded, such that microcosms experiments may be of value in detecting subtle, indirect effects of MPs.

A call to evaluate Plastic's impacts on marine benthic ecosystem interaction networks

Plastic pollution continues to seep into natural and pristine habitats. Emerging laboratory-based research has evoked concern regarding plastic's impact on ecosystem structure and function, the essence of the ecosystem services that supports our life, wellbeing, and economy. These impacts have yet to be observed in nature where complex ecosystem interaction networks are enveloped in environmental physical and chemical dynamics. Specifically, there is concern that environmental impacts of plastics reach beyond toxicity and into ecosystem processes such as primary production, respiration, carbon and nutrient cycling, filtration, bioturbation, and bioirrigation. Plastics are popularly regarded as recalcitrant carbon molecules, although they have not been fully assessed as such. We hypothesize that plastics can take on similar roles as natural recalcitrant carbon (i.e., lignin and humic substances) in carbon cycling and associated biogeochemistry. In this paper, we review the current knowledge of the impacts of plastic pollution on marine, benthic ecosystem function. We argue for research advancement through (1) employing field experiments, (2) evaluating ecological network disturbances by plastic, and (3) assessing the role of plastics (i.e., a carbon-based molecule) in carbon cycling at local and global scales.