Plastic additives in deep-sea debris collected from the western North Pacific and estimation for their environmental loads

Spectral analysis of environmental microplastic polyethylene (PE) using average spectra

In this study, microplastic samples from surface seawater of Tokyo Bay were collected, polyethylene (PE) microplastics were used to calculate carbonyl index (CI), and average spectra of PE were analyzed and compared with a previous study applying agitation during chemical treatment. It was found that PE and polypropylene (PP) were the predominant polymer type in the samples. Among PE samples, fragments were the most commonly observed shape, with white being the dominant color. Deviations were found in the average spectra among different shapes and colors when compared to the standard PE spectrum. A comparison of the average spectra between the two datasets suggests that pronounced peaks related to oxidation are most likely resulted from agitation during the chemical treatment. Additionally, it was found a closer spectral resemblance between the sample spectra and the spectrum of standard sample of oxidized PE (PEOx) than with the standard PE spectrum, suggesting that using the oxidized PE as a reference spectrum might be more effective for identification. These findings highlight the complex factors affecting the spectral properties of microplastics and highlight the importance of understanding these variations to enhance the accuracy of microplastic identification workflows and understanding of environmental fate of microplastics.

Analysis and remediation of phthalates in aquatic matrices: current perspectives

Phthalic acid esters (PAEs) are high production volume chemicals used extensively as plasticizers, to increase the flexibility of the main polymer. They are reported to leach into their surroundings from plastic products and are now a ubiquitous environmental contaminant. Phthalate levels have been determined in several environmental matrices, especially in water. These levels serve as an indicator of plasticizer abuse and plastic pollution, and also serve as a route of exposure to different species including humans. Reports published on effects of different PAEs on experimental models demonstrate their carcinogenic, teratogenic, reproductive, and endocrine disruptive effects. Therefore, regular monitoring and remediation of environmental water samples is essential to ascertain their hazard quotient and daily exposure levels. This review summarises the extraction and detection techniques available for phthalate analysis in water samples such as chromatography, biosensors, immunoassays, and spectroscopy. Current remediation strategies for phthalate removal such as adsorption, advanced oxidation, and microbial degradation have also been highlighted.

Organophosphate ester additives and microplastics in benthic compartments from the Loire estuary (French Atlantic coast)

We report the first empirical confirmation of the co-occurrence of organophosphate esters (OPEs) additives and microplastics (MPs) in benthic compartments from the Loire estuary. Higher median concentrations of MPs (3387 items/kg dw), ∑13tri-OPEs (12.0 ng/g dw) and ∑4di-OPEs (0.7 ng/g dw) were measured in intertidal sediments with predominance of fine particles, and under higher anthropogenic pressures, with a general lack of seasonality. Contrarily, Scrobicularia plana showed up to 4-fold higher ∑tri-OPE concentrations in summer (reaching 37.0 ng/g dw), and similar spatial distribution. Polyethylene predominated in both compartments. Tris(2-ethylhexyl) phosphate (TEHP), its degradation metabolite (BEHP) and tris-(2-chloro, 1-methylethyl) phosphate (TCIPP) were the most abundant OPEs in sediments, while TCIPP predominated in S. plana. The biota-sediment accumulation factors suggest bioaccumulation potential for chlorinated-OPEs, with higher exposure in summer. No significant correlations were generally found between OPEs and MPs in sediments suggesting a limited role of MPs as in-situ source of OPEs.

Leaching and transformation of chemical additives from weathered plastic deployed in the marine environment

Plastic pollution causes detrimental environmental impacts, which are increasingly attributed to chemical additives. However, the behaviour of plastic additives in the marine environment is poorly understood. We used a marine deployment experiment to examine the impact of weathering on the extractables profile, analysed by liquid chromatography-mass spectrometry, of four plastics at two locations over nine months in Aotearoa/New Zealand. The concentration of additives in polyethylene and oxo-degradable polyethylene were strongly influenced by artificial weathering, with deployment location and time less influential. By comparison, polyamide 6 and polyethylene terephthalate were comparatively inert with minimal change in response to artificial weathering or deployment time. Non-target analysis revealed extensive differentiation between non-aged and aged polyethylene after deployment, concordant with the targeted analysis. These observations highlight the need to consider the impact of leaching and weathering on plastic composition when quantifying the potential impact and risk of plastic pollution within receiving environments.

Microplastics Distribution in Sediments Collected from Myanmar

Microplastics (MPs) distributions have been increasingly reported in the terrestrial areas worldwide, but little information is available for ASEAN regions. In this study, 68 sediment samples of drainage channels, lakes, rivers and beaches from Myanmar were collected between 2014 and 2018, and analyzed to investigate the status of MPs concentration and prevalence. The high concentrations of MPs in sediments were found in urban cities called Yangon (13,855 pieces/kg dry weight), Mandalay (11,946 pieces/kg), and Pathein (12,583 pieces/kg), which were two orders of magnitude greater than the MPs concentrations in sediments collected in rural towns called Wundwin. These results suggested that the difference in high population densities and high municipal solid waste generation rates are related to the MPs contamination in sediments. Polyethylene, polypropylene and polyethylene terephthalate with fragments, lines/fibers and films/sheets were major polymers and shape in the sediment samples analyzed from Myanmar. To our knowledge, this is the first study to report the distribution of MPs in sediments from Myanmar.

Extractability and phytotoxicity of heavy metals and essential elements from plastics in soil solutions and root exudates

Plastic waste is increasing and is a serious environmental problem. Among the threats associated with plastics is the release of contaminants into the environment. This study aimed to evaluate the efficiency of metals release from plastics (low-density polyethylene (LDPE), polyethylene terephthalate (PET), and polypropylene (PP)) as affected by different soil solution types, artificial root exudates, and distilled water. The extent of metal release varied depending on the type of solution and plastic used. Metals were leached most effectively from plastics in soil solutions, followed by root exudates, and least effectively by distilled water. LDPE released the highest concentrations of Cu and Na into solution, PP released the greatest amount of Fe, and PET released the most Cr. The efficiencies of Mg and Zn release from the plastics (PP and PET) varied by solution type. Among the plastics studied, LDPE exhibited the strongest ability to adsorb metals, such as Fe, Cr, Mg, and Zn from soil solutions. The amount of metal released from the plastics was also dependent on pH, dissolved organic carbon (DOC) concentrations, and the electrical conductivity (EC) of the solutions. Moreover, plastic extracts were found to have negative effects on germination and growth in Lepidium sativum.

Structural modeling of cytochrome P450 51 from a deep-sea fish points to a novel structural feature in other CYP51s

Cytochromes P450 (CYP), enzymes involved in the metabolism of endogenous and xenobiotic substrates, provide an excellent model system to study how membrane proteins with unique functions have catalytically adapted through evolution. Molecular adaptation of deep-sea proteins to high hydrostatic pressure remains poorly understood. Herein, we have characterized recombinant cytochrome P450 sterol 14α-demethylase (CYP51), an essential enzyme of cholesterol biosynthesis, from an abyssal fish species, Coryphaenoides armatus. C. armatus CYP51 was heterologously expressed in Escherichia coli following N-terminal truncation and purified to homogeneity. Recombinant C. armatus CYP51 bound its sterol substrate lanosterol giving a Type I binding spectra (KD 15 μM) and catalyzed lanosterol 14α-demethylation turnover at 5.8 nmol/min/nmol P450. C. armatus CYP51 also bound the azole antifungals ketoconazole (KD 0.12 μM) and propiconazole (KD 0.54 μM) as determined by Type II absorbance spectra. Comparison of C. armatus CYP51 primary sequence and modeled structures with other CYP51s identified amino acid substitutions that may confer an ability to function under pressures of the deep sea and revealed heretofore undescribed internal cavities in human and other non-deep sea CYP51s. The functional significance of these cavities is not known. PROLOGUE: This paper is dedicated in memory of Michael Waterman and Tsuneo Omura, who as good friends and colleagues enriched our lives. They continue to inspire us.

Crack Patterns of Environmental Plastic Fragments

Secondary microplastics usually come from the breakdown of larger plastics due to weathering and environmental stress cracking of plastic wastes. In the present study, 5013 plastic fragments were collected from coastal beaches, estuary dikes, and lake banks in China. The fragment sizes ranged from 0.2 to 17.1 cm, and the dominant polymers were polypropylene and polyethylene. Cracks were observed on the surfaces of 49-56% of the fragments. Based on the extracted crack images, we proposed a general crack pattern system including four crack types with specific definitions, abbreviations, and symbols. The two-dimensional spectral analysis of the cracks suggests that the first three patterns showed good regularity and supported the rationality of the pattern system. Some crack metrics (e.g., line density) were closely correlated with the carbonyl index and additives (e.g., phthalate esters) of fragments. For crack investigation in field, we proposed a succinct protocol, in which five crack ranks were established to directly characterize the degree of cracking based on the line density values. The system was successfully applied to distinguish the differences in crack features at two representative sites, which indicates that crack pattern is a useful tool to describe the morphological changes of plastic surfaces in the environment.

Effects of microplastics and food particles on organic pollutants bioaccumulation in equi-fugacity and above-fugacity scenarios

Microplastics (MPs), as emerging contaminants, sorb organic pollutants from the environment or leach out additives, thereby altering the fate of co-existing pollutants to organisms. We chose equi-fugacity and above-fugacity concentrations of polychlorinated biphenyls (PCBs) as background contamination and plastic additive concentrations, respectively, to investigate the effects of MPs on PCB bioaccumulation; we compared the effects of MPs with those of food-borne particles (FBPs). Co-exposure to MPs and FBPs at both the equi-fugacity and above-fugacity PCB concentrations had no obvious toxic effects (ROS generation and cyp1a expression) on zebrafish. When the zebrafish were exposed to the equi-fugacity PCB concentrations, the PCB concentrations reached 177.7-400.5 ng/g after a 7-d uptake; the presence of MPs did not significantly enhance PCB bioaccumulation. The remaining PCB concentrations in the fish after a 4-d depuration were 58.4-125.1 ng/g; the effects of MPs were the same as those during the uptake period. However, at the above-fugacity PCB concentrations, the MPs markedly increased the PCB bioaccumulation (by 1.8-fold) to 712.9 ng/g. This is because at above-fugacity concentrations, PCBs on MPs migrate to organisms as there were high fugacity gradients. The FBPs enhanced PCB bioaccumulation in zebrafish more effectively than the MPs, even after depuration. In the presence of FBPs, PCB bioaccumulation increased by 2.8- and 4.2- fold after uptake in the equi-fugacity and above-fugacity scenarios, respectively, both of which were significantly higher than that observed for the MPs. This is probably because FBPs are easily assimilated by fish, making the associated PCBs more bioavailable. Finally, during the co-existence of MPs and FBPs, MPs facilitate the depuration of PCBs accumulated via FBP vectors; conversely, FBPs did not affect PCB accumulation via MP vectors. Thus, this study elucidated the effects of MPs and FBPs on the bioaccumulation of pollutants at equi-fugacity or above-fugacity concentrations in aquatic environments.

Microplastics in dumping site soils from six Asian countries as a source of plastic additives

The ubiquitous distribution of microplastics (MP) is a serious environmental issue in Asian countries. In this study, 54 open-dumping site soils collected from Cambodia, India, Indonesia, Laos, the Philippines, and Vietnam were analyzed for MP. Soil samples were also divided into light (floating) and heavy (sedimentation) fractions by density separation and analyzed for plastic additives. The highest abundance of MP was found in a soil from Cambodia at 218,182 pieces/kg. The median of MP in soils ranged from 1411 pieces/kg in India to 24,000 pieces/kg in the Philippines, suggesting that dumping sites are a major source of MP into the environment. Polyethylene, polypropylene, and polyethylene terephthalate were dominant polymers in soil samples analyzed. This indicates that daily-used plastic products are main sources of MP in dumping site soils in Asian countries. The high concentrations and burdens of phthalates and an antioxidant were detected in floating fraction accounting for 40 to 60% of the total additives in soils. Previous studies on soil pollution have assumed that the organic hydrophobic chemicals analyzed are adsorbed on the surface of soil particles. However, this result indicates that approximately half of the additives in dumping site soils were derived from MP, not soil particle. Monitoring study on soil pollution should be considered the occurrence of MP in the matrices.

Monitoring of polymer type and plastic additives in coating film of beer cans from 16 countries

Plastic debris has gained attention as anthropogenic waste in the environment, but less concerned given to metal waste despite its high abundance in aquatic environment. Metal packaging, such as can, utilizes polymeric coating films as barrier between metals and products which leads to be potential source of microplastic pollution. In this study, 27 beer cans from 16 countries for both body and lid parts as well as inside and outside layers were investigated. Despite the country’s origin, epoxy resin was the major polymeric coating used in all beer cans for lid (inside and outside) and body (inside). Whereas poly(1,2-butanediol isophthalate) was frequently used for outside layer of can body. DEHP and BHT were detected in almost all samples with the highest concentration of 5300 ng/g and 520 ng/g. Despite its lower detection frequency, DOA was detected as high as 9600 ng/g in Belgian beer can. There was no apparent relationship present between the home countries of beer cans and amount of additives used. Despite of being broken down, additives concentration in one environmental sample was found to be one to two orders of magnitude higher compared to the new can. This result proved that adsorption of chemical additives took place in the environment and degraded metal debris may become source of microplastic with higher risk of additives pollution in the environment.

The release inhibition of organic substances from microplastics in the presence of algal derived organic matters: Influence of the molecular weight-dependent inhibition heterogeneities

As the emerging contaminants, the behavior and fate of microplastics (MPs) were highly related to the interactions with surrounding organic matters. However, information on the effects of molecular sizes of organic matters on the interaction is still lacking. In this study, the bulk algal-derived organic matter (AOM) samples were obtained and further fractionated into high molecular weight (HMW-, 1kDa-0.45 μm) and low molecular weight (LMW-, < 1 kDa) fractions. The interaction between MPs [polyethylene (PE) and polystyrene (PS)] and these MW-fractionated AOMs were characterized by dissolved organic carbon, fluorescence and absorbance spectroscopy, and fourier transform infrared (FTIR) analysis. Results showed that presence of AOM could effectively inhibit the release of additives from MPs. Further analysis found that the inhibition extents decreased in the order of HMW- > bulk > LMW-AOM. The absorbance and fluorescence spectroscopy showed that aromatic protein-like substances in HMW fraction exhibited higher adsorption affinity to MPs than the bulk and LMW counterparts. The strong sorption of aromatic substances may offer more binding sites for additives to inhibit the release of organic substances. Moreover, two dimensional FTIR correlation spectroscopy revealed that the HMW non-aromatic substances were preferentially adsorbed onto PS, which led to an enhanced adsorption capacity to additives by forming H-bonding. Therefore, the MW- and component-dependent heterogeneities of AOM samples must be fully considered in evaluating the environmental behavior of MPs.