Leaching of chemicals from microplastics: A review of chemical types, leaching mechanisms and influencing factors

It is widely known that microplastics are present everywhere and they pose certain risks to the ecosystem and humans which are partly attributed to the leaching of additives and chemicals from them. However, the leaching mechanisms remain insufficiently understood. This review paper aims to comprehensively and critically illustrate the leaching mechanisms in biotic and abiotic environments. It analyzes and synthesizes the factors influencing the leaching processes. It achieves the aims by reviewing >165 relevant scholarly papers published mainly in the past 10 years. According to this review, flame retardants, plasticizers and antioxidants are the three main groups of additives in microplastics with the potentials to disrupt endocrine functions, reproduction, brain development and kidney functions. Upon ingestion, the MPs are exposed to digestive fluids containing enzymes and acids which facilitate their degradation and leaching of chemicals. Fats and oils in the digestive tracts also aid the leaching and transport of these chemicals particularly the fat-soluble ones. Leaching is highly variable depending on chemical properties and bisphenols leach to a larger extent than other endocrine disrupting chemicals. However, the rates of leaching remain poorly understood, owing probably to multiple factors at play. Diffusion and partitioning are two main mechanisms of leaching in biotic and abiotic environments. Photodegradation is more predominant in the latter, generating reactive oxygen species which cause microplastic aging and leaching with minimal destruction of the chemicals leached. Effects of microplastic sizes on leaching are governed by Sherwood number, thickness of aqueous boundary layer and desorption half-life. This review contributes to better understanding of leaching of chemicals from microplastics which affect their ecotoxicities and human toxicity.

Optimization of an Aqueous Two-Phase System for the Determination of Trace Ethyl Carbamate in Red Wine

In this study, a novel method using gas chromatography-mass spectrometry coupled with ethanol and K₂HPO₄ aqueous two-phase system (ATPS) was established for the quantitative determination of trace ethyl carbamate (EC) in red wine. The parameters that influence EC extraction in an aqueous two-phase system, including extraction temperature, time, pH, and ethanol concentration, were optimized. Method validation results indicated that the regression coefficient of the proposed method was 0.9979 in the linear range of 10 to 100 μg/L, and the limits of detection and quantification were 2.8 and 9.2 μg/L, respectively. Four red wine samples made from different grape varieties were processed by the proposed method for the repeatability verification, and EC concentrations were between 15.8 and 37.3 μg/L, with the relative standard deviations ranging from 3.5 to 6.6%. Results of the precision assay showed the average recovery of EC in red wine at 95.4 to 107.1%, with the relative standard deviations ranging from 1.4 to 6.2%. This method proved to be simple and reliable for quantitative determination of trace EC in red wine and would give guidance for quality monitoring of various red wines in the production process.

Organic-free, versatile sessile droplet microfluidic device for chemical separation using an aqueous two-phase system

This work presents a novel portable, versatile sessile droplet microfluidic (SDMF) device to perform liquid manipulation operations such as confining, splitting and colorimetric detection. Furthermore, chemical isolations based on an aqueous two-phase system (ATPS) for separating an analyte of choice from a complicated sample matrix can be carried out. ATPS extractions can replace conventional liquid-liquid extractions and take away the need for harmful organic solvents. Superhydrophobic (SH) surfaces were fabricated from a commercially available material, Ultra-Ever Dry® (UED®). On these SH surfaces, surface energy traps (SETs) were produced either by air plasma treatment (simultaneously) or laser micromachining (sequentially) to dock/pin an ATPS containing droplet onto the surface. Splitting of droplets or removing a precise volume of the top phase from a pinned extraction system was achieved with a sandwich-chip approach. For this, an additional SET patterned substrate was placed on top of the droplet and subsequently lifted. This multipurpose platform was used to isolate Cd from a mixture of several other metal ions (i.e. Mn, Ni, Cu, Pb, Fe) for its subsequent interference-free detection. An ATPS consisting of sodium sulfate and polyethylene glycol (PEG) as phase forming components and potassium iodine as extractant allowed separation of cadmium with an extraction efficiency of q(Cd2+) = 98.5%. Using a portable, cost-effective, smartphone-based UV/vis spectrometer, Cd was detected with a LoD of 3.4 ppm. Alternatively, the multipurpose platform can also be used as sampling platform for a benchtop UV/vis spectrometer, where a LoD of 0.53 ppm was obtained. Potential applications of the presented platform include sample preparation and separation that can be achieved by aqueous two-phase extractions, such as proteins, antibodies, DNA, cells, organic molecules and metal ions.