Removal of polycyclic aromatic hydrocarbons from water by migration into polyethylene

Direct visualization of pyrene diffusion in polyethylene and polyoxymethylene passive samplers

While passive sampling of ultra-low aqueous concentrations of hydrophobic organic compounds in environmental aqueous media has emerged as a promising analytical technique, there is a lack of good understanding of the fundamental diffusive processes. In this research, we used a fluorophore, pyrene, as a model compound to track diffusion in polymers through absorption and environmental media exchange processes. We directly tracked the penetration of pyrene into polyethylene (PE) and polyoxymethylene (POM) rods during absorption from water by sectioning the rod after different stages of absorption and observing the fluorescence signal through a microscope. Diffusion profiles of pyrene in polymers were simulated by numerical integration of Fickian diffusion. The results indicated that the uptake process in PE is governed by Fick's law and the absorption and desorption kinetics are similar in this polymer. However, the observed uptake profiles of pyrene in POM were non-Fickian and the release kinetics out of POM was slower compared to uptake into the polymer. We show that slower desorption from POM makes corrections for nonequilibrium using performance reference compounds (PRCs) problematic for deployments in water or sediment where there is significant advection. However, for static sediment deployments, the overall kinetics of exchange is controlled by slow transport through sediment and the hysteretic behavior of POM may not preclude the use of PRCs to interpret equilibrium status.

Plastic ingestion by the Wels catfish (Silurus glanis L.): detailed chemical analysis and degradation state evaluation

Plastic ingestion by various organisms within different trophic levels, including humans, is becoming a serious problem worldwide. Plastic waste samples are often found concentrated in an organism's digestive tract and can be degraded and further translocate to the surrounding tissue or circulatory systems and accumulate in food chains. In the present work, we report a detailed chemical analysis and degradation state evaluation of a relatively large piece of plastic waste found in the gastrointestinal tract of a Wels catfish (Silurus glanis L.) caught in the Bodrog River (Danube River basin), eastern Slovakia. Chemical analysis by surface-sensitive X-ray photoelectron spectroscopy (XPS) was performed to identify the surface composition of the digested plastic piece. Micro-Fourier transform infrared (μFTIR) spectroscopy showed that the plastic waste was oxidized low-density polyethylene (LDPE), with some nylon fibers adhered on the surface. Glyceraldehyde adhered onto LDPE was also detected, which might come from the carbohydrate metabolism of that fish. A morphology study by digital optical microscopy indicated solid inorganic particles attached to the surface of LDPE. A degradation study by differential scanning calorimetry (DSC) showed considerable oxidation of LDPE, leading to fragmentation and disintegration of the plastic waste material.

Uptake and Release Kinetics of Organic Contaminants Associated with Micro- and Nanoplastic Particles

A generic theoretical framework is presented for describing the kinetics of uptake and release of organic compounds that associate with plastic particles. The underlying concepts account for the physicochemical features of the target organic compounds and the plastic particles. The developed framework builds on concepts established for dynamic speciation analysis by solid-phase microextraction and the size-dependent reactivity features of particulate complexants. The theoretical framework is applied to interpretation of literature data, thereby providing more rigorous insights into previous observations. The presented concepts enable predictions of the sink/source functioning of plastic particles and their impact on the dynamic chemical speciation of organic compounds in aqueous environmental media and within biota. Our results highlight the fundamental influence of particle size on the uptake and release kinetics. The findings call for a comprehensive description of the physicochemical features of plastic particles to be provided in experimental studies on micro- and nanoplastics in different types of aquatic environmental media.

Modern Procedures for Removal of Hazardous Compounds From Foods

This chapter deals with interactions between foods or food additives and plastic package materials oriented to elimination of hazardous compounds from foods. As found, polycyclic aromatic hydrocarbons (PAHs) can be effectively eliminated from liquid smoke flavors and smoked meat products by migration of PAHs into low-density polyethylene (LDPE), when the limiting factor of the elimination is diffusion in food matrix. After leaving food bulk, PAHs migrate deeper into LDPE bulk what brings about permanent renewal of material imbalance on LDPE/food matrix interface that maintains the migration process in an intensive regime causing extensive lowering of PAH content in food matrix. To the opposite, polyethylene terephthalate (PET) in contact with vegetable oils is able to absorb only PAHs on active center deposited on its surface without deeper migration into plastic bulk and therefore this type of elimination process is less effective. Overall, migration processes are affected by polarity of food matrix and package materials, presence of compounds able to compete for adsorption center on PET surface, the time of interactions, and, of course, imbalance of PAH chemical potentials in individual systems.

Assessing contamination of smoked sprats (Sprattus sprattus) with polycyclic aromatic hydrocarbons (PAHs) and changes in its level during storage in various types of packaging

The analysis of material used in this study demonstrated that the amount of polycyclic aromatic hydrocarbons (PAHs) in smoked sprats varies from the level below the lowest detection limit in muscles up to 9.99 µg kg^-1 of benzo[a]pyrene (BaP) in fish skin. Such a high level of PAHs in skin was reported only in one of six batches of sprats, while mean BaP level was at 1.69 µg kg^-1. Regardless such a high BaP level in skin, its concentration in muscles did not exceed the maximum acceptable level. The study objective was to assess to what extent packaging materials adsorb PAH compounds from food. Changes in the PAH levels were monitored in fish during their storage in packages made of various materials. The storage time was from 0 to 168 hours. The obtained results varied considerably, therefore their scatter did not allow to confirm unequivocally the preliminary hypothesis about the reduction of PAHs due to their migration to packaging material. However, analysis of the packaging used in this study demonstrated a significant increase in the level of total 16 PAHs. When high-density polyethylene (HDPE) packaging was analysed, a six-fold increase in the total 16 PAHs was observed comparing to the blank sample.

Sorption of polycyclic aromatic hydrocarbons (PAHs) to low and high density polyethylene (PE)

BACKGROUND, AIM, AND SCOPE

According to their high sorption capacity polyethylene (PE) passive samplers are often used for the analysis of polycyclic aromatic hydrocarbons (PAHs) in the aquatic environment. PE is also one of the primary synthetic polymers found in oceans, and sorption of PAHs to marine PE debris may determine PAH exposure and therefore hazards in marine ecosystems. Thus, an understanding of the sorption process is of great importance. In the present study, the sorption of several PAHs with different polarities to low density polyethylene (LDPE) and high density polyethylene (HDPE) was studied in order to improve our understanding of the influence of material properties on the Fickian diffusion of PAHs into PE.

MATERIALS AND METHODS

Batch sorption experiments were performed with aqueous solutions containing acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and LPDE or HDPE pellets. Samples were shaken in the dark at 20 ± 1°C for 16 time intervals within one week. Concentrations of PAHs were determined in the aqueous samples using solid-phase microextraction coupled with gas chromatography-mass spectrometry. The distribution coefficients (K (PE)) between PE and water were estimated from different models reported in the literature. Kinetic sorption of the PAHs into the plastic pellets was described by a diffusion model based on Fick's second law in spherical coordinates.

RESULTS AND DISCUSSION

A comparison between different models describing the equilibrium distribution of PAHs between PE and water revealed that the sorption equilibrium seemed to be driven by parameters other than, or in addition to, organic carbon. For both plastic types, diffusion coefficients decreased while the molecular weight of the PAHs increased which indicates a hindered diffusion through the matrix as a result of a larger molecule size. Higher diffusion coefficients were derived for LPDE than for HDPE indicating a greater sorption velocity for LPDE according to the lower polymer density.

CONCLUSIONS

Our results revealed that equilibrium time could be shortened during passive sampling as polymer membranes of lower density are used. In some areas, marine ecosystems may not be in equilibrium with respect to concentrations of organic contaminants and abundance of marine plastic debris. In such cases, different polymer densities should be taken into account in risk assessments.

Critical review of low-density polyethylene's partitioning and diffusion coefficients for trace organic contaminants and implications for its use as a passive sampler

Polyethylene (PE)-water equilibrium partitioning constants, K(PEw), were reviewed for trace hydrophobic organic contaminants (HOCs). Relative standard deviations were <30% for phenanthrene, anthracene, fluoranthene, and pyrene implying excellent reproducibility of K(PEw) across laboratories and PE sources. Averaged K(PEw) values of various HOCs were best correlated with aqueous solubility, logC(w)(sat)(L): logK(PEw) = -0.99(±0.029)logC(w)(sat)(L) + 2.39(±0.096) (r(2) = 0.92, SE = 0.35, n = 100). For 80% of analytes, this equation predicted logK(PEw) within a factor of 2. A first-order estimation of K(PEw) can be obtained assuming constant solubility of the compounds in the PE, such that the variation in C(w)(sat)(L) determines the differences in K(PEw). For PE samplers, K(PEw) values do not change with the thickness of the PE sampler. The influence of temperature on K(PEw) seems dominated by solubility-changes of the compound in water, not in PE. The effect of salt is rather well understood, using a Schetschenow-style approach. The air-PE partitioning constant, K(PEa), can be approximated as the ratio of K(PEw)/K(aw) (the air-water partitioning constant). A critical review of diffusivities in PE, D(PE), suggests that best results are obtained when using the film-stacking method. A good correlation is then found between D(PE) and molar volume, V(m) (Ǻ(3)/mol): logD(PE) (m(2)/s) = 0.0145(±0.001)V(m) + 10.1(±0.20) (r(2) = 0.76, SE = 0.24, n = 74).

Presence of polychlorinated biphenyls (PCBs) in bottled drinking water in Mexico City

This paper describes the concentrations of seven polychlorinated biphenyls (PCBs) in bottled drinking water samples that were collected over 1 year from Mexico City in two sizes (1.5 and 19 L), using gas chromatography with an electron capture detector. PCBs 28 (0.018-0.042 μg/L), 52 (0.006-0.015 μg/L) and 101 (0.001-0.039 μg/L) were the most commonly found and were present in the majority of the samples. However, total concentrations of PCBs in bottled drinking water (0.035-0.039 μg/L) were below the maximum permissible level of 0.50 μg/L stated in Mexican regulations and probably do not represent a hazard to human health. PCBs were detectable in all samples and we recommend a monitoring program be established to better understand the quality of drinking bottled water over time; this may help in producing solutions for reducing the presence of organic contaminants.

Factors affecting elimination of polycyclic aromatic hydrocarbons from smoked meat foods and liquid smoke flavorings

This review deals with effects of environmental and physicochemical factors affecting polyaromatic hydrocarbon (PAH) elimination from smoked meat products and liquid smoke flavoring (LSF). In the introductory part, some essential information are aimed at principles of food smoking and PAH formation during smoke generation as a result of incomplete wood combustion. Also, an application of alternative technology for food aromatization using LSF is briefly mentioned. Similarly, latest European legislation, biological effects, and analytical aspects of PAHs are mentioned concisely. The main part is devoted to physicochemical factors affecting the PAH content in smoked meat products, such as light, additional cooking, and packaging, which are able to decrease considerably PAH content in some meat products. The most important effect on PAH concentration decrease in LSF has low-density polyethylene (LDPE) package due to sorption processes on a surface of the plastic with subsequent diffusion into the plastic bulk. A less effective material is polyethylene terephthalate (PET), when only a surface adsorption process comes into account. Moreover, this process is affected also by other compounds presented in liquid media able to compete for the adsorption center on the PET surface.

Composition and analysis of liquid smoke flavouring primary products

Smoke flavourings are produced on a large scale and have been applied to a variety of food products for more than 30 years. The use of them has many advantages compared to traditional smoking techniques. Among others, the amount of (known) toxic compounds deriving from combustion processes can be more easily controlled in smoke flavourings. In order to ensure safe products, a new European Regulation requests data on the composition and lays down, in particular, the maximum permitted concentrations for selected polycyclic aromatic hydrocarbons (PAHs). This review compiles results published on the chemical composition of liquid smoke flavouring primary products, partly in relation to production process parameters, and the analytical methods involved. The methods cover chromatographic techniques for analysis of specific compounds including extraction methods and clean-up procedures. Analysis of sensorial and bulk parameters such as acidity and total phenolic compounds are described as well as they are used as standard methods for analysis of liquid smoke flavourings. A special section is devoted to discussing the analysis of PAHs.

Use of passive samplers to mimic uptake of polycyclic aromatic hydrocarbons by benthic polychaetes

Experiments were conducted to test whether passive samplers made of low-density polyethylene (polyethylene devices, or PEDs) can estimate the extent of uptake of polycyclic aromatic hydrocarbons (PAHs) by benthic polychaetes (Nereis virens) in contaminated marine sediments. For a variety of PAHs, PEDs reached 90% equilibrium with sediment PAHs in 60 days or less. Using 60-day sediment bioaccumulation tests, we have demonstrated a significant relationship between PAH concentrations in the polychaetes and the PEDs (R2 = 0.67, p = 0.002), with the PEDs taking up less PAHs than the polychaetes. Because of this relationship, PEDs can potentially be used in a regulatory context to simulate uptake of bioavailable PAHs in contaminated marine sediments. The PED PAH concentrations were also used to calculate porewater PAH concentrations that allowed for the estimation of a linear free-energy relationship between the lipid-water distribution coefficient (Klip) and the octanol-water distribution coefficient (KOW) for PAH uptake in marine polychaetes (R2 = 0.94, p < 0.0001).