Toxicological effects of microplastics and heavy metals on the Daphnia magna.

Microplastics (MPs) are gradually spreading around the world and becoming a ubiquitous environmental contamination in aquatic environments. Due to its unique physicochemical properties, MPs are considered to be strong adsorbents for environmental pollutants and may affect their fate and toxicity in the environment. In this study, the adsorption behaviors of four typical heavy metal ions (Pb2+, Cu2+, Cd2+, and Ni2+) on two sizes of polystyrene MPs (10 μm and 50 μm) were investigated based on batch experiments, and the combined effects of heavy metals and MPs were assessed using Daphnia magna as model. The results showed that smaller MPs (SMPs) exhibited higher adsorption capacities for metal ions (0.261-0.579 mg/g) than that of the larger MPs (LMPs) (0.243-0.525 mg/g), and the affinity sequence of heavy metals on MPs is Pb2+ > Cu2+ > Cd2+ > Ni2+. There are better admirable agreements for pseudo-second-order model and Langmuir model to fit the adsorption kinetics and adsorption isotherms, respectively. Additionally, the combined toxicity of MPs and heavy metals was negatively correlated with the adsorption capacity between them. The combined effects of mixtures toward D. magna changed from antagonism to additive effect with increasing MPs concentrations, and SMPs exhibited higher toxicological risk than LMPs. Our findings compared the accumulative effects of various heavy metals on MPs and can contribute to understanding the combined effects of plastics and heavy metals on biota.

Yuan W ，Zhou Y ，Chen Y ，Liu X ，Wang J ... -  《-》

Microplastics as a vehicle of heavy metals in aquatic environments: A review of adsorption factors, mechanisms, and biological effects.

Microplastics (MPs) have recently attracted much attention due to their widespread distribution in the aquatic environment. Microplastics can act as a vector of heavy metals in the aquatic environment, causing a potential threat to aquatic organisms and human health. This review mainly summarized the occurrence of microplastics in the aquatic environment and their interaction with heavy metals. Then, we considered the adsorption mechanisms of MPs and heavy metals, and further critically discussed the effects of microplastics properties and environmental factors (e.g., pH, DOM, and salinity) on the adsorption of heavy metals. Finally, the potential risks of combined exposure of MPs and heavy metals to aquatic biota were briefly evaluated. This work aims to provide a theoretical summary of the interaction between MPs and heavy metals, and is expected to serve as a reference for the accurate assessment of their potential risks in future studies.

Liu S ，Huang J ，Zhang W ，Shi L ，Yi K ，Yu H ，Zhang C ，Li S ，Li J ... -  《-》

A critical review on the interactions of microplastics with heavy metals: Mechanism and their combined effect on organisms and humans.

Although individual toxicity of microplastics (MPs) to organism has been widely studied, limited knowledge is available on the interactions between heavy metals and MPs, as well as potential biological impacts from their combinations. The interaction between MPs and heavy metals may alter their environmental behaviors, bioavailability and potential toxicity, leading to ecological risks. In this paper, an overview of different sources of heavy metals on MPs is provided. Then the recent achievements in adsorption isotherms, adsorption kinetics and interaction mechanism between MPs and heavy metals are discussed. Besides, the factors that influence the adsorption of heavy metals on MPs such as polymer properties, chemical properties of heavy metals, and other environmental factors are also considered. Furthermore, potential combined toxic effects from MPs and heavy metals on organisms and human health are further summarized.

Cao Y ，Zhao M ，Ma X ，Song Y ，Zuo S ，Li H ，Deng W ... -  《-》

The types of microplastics, heavy metals, and adsorption environments control the microplastic adsorption capacity of heavy metals.

Anthropogenic development has released large amounts of microplastics (MPs), which are carriers of migratory heavy metals, into the environment, and heavy metal adsorption by MPs may have strong combined toxic effects on ecosystems. However, until now, a comprehensive understanding of the factors influencing these adsorption capacities of MPs has been lacking. Thus, we used 4984 experimental data points to systematically assess the factors influencing the adsorption strength of 8 types of MPs on 13 types of heavy metals. We found that (1) the types of MPs, heavy metals, and adsorption environments significantly impacted the heavy metal adsorption capacities of MPs; (2) polyvinyl alcohol (PVA) showed a higher adsorption capacity for lead (Pb) and cadmium (Cd) than did other MPs, by 2810.62 mg/kg and 2732.84 mg/kg, respectively; (3) the adsorption capacities of MPs for heavy metal were regulated by multiple variables, with heavy metal concentration, MP quality, solution amount, adsorption time, and pH being the most important; and (4) MPs had a higher adsorption capacity in aquatic environments (except for seawater) than which in soil environments. Overall, our study clearly showed that the types of heavy metals, adsorption environments, and MPs influenced the heavy metal adsorption capacities of MPs and may exacerbate their combined environmental toxicity, which would help better characterize the severity of MP pollution.

Zhu G ，Yue K ，Ni X ，Yuan C ，Wu F ... -  《-》

Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river.

Microplastics (MPs) and heavy-metal contamination in freshwater is an increasing concern. Fe, Mn, Pb, Zn, Cr, and Cd are common heavy metals that can easily flow into rivers causing water pollution. Microplastics act as carriers for heavy metals and increase the transport of contaminants in freshwater systems. We investigated the adsorption mechanisms of three kinds of MPs having similar particle sizes, namely polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), with respect to trace heavy metals of Pb, Cu, Cr, and Cd under different temperature and salinity conditions. The reaction kinetics of the adsorption of different trace heavy metals on different MPs were consistent with both the quasi primary and quasi secondary kinetic models, indicating the complexity of heavy metal adsorption by MPs. The adsorption rate of heavy metal on MPs was mainly controlled by intra-particle diffusion, and the isotherm model indicated that the adsorption of Pb, Cu, Cr, and Cd by MPs occurred in the form of monolayer physical adsorption. Additionally, an increase in temperature and decrease in salinity were favourable to improve the affinity of MPs toward heavy metals (through adsorption). Zeta potential measurements and Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that electrostatic force interaction was the main mechanism of the adsorption process; oxygen-containing functional groups, π-π interaction, and halogen bonds played important roles in the process of adsorption. Furthermore, the growth inhibition and oxidative stress of microalgae Chlorella vulgaris (GY-D27) due to PP, PS, and PVC were analysed; notably, MPs or Pb inhibited the growth of Chlorella vulgaris. However, the reduced toxicity to Chlorella vulgaris, with respect to a mixture of Pb and MPs, was confirmed using superoxide dismutase and catalase enzyme activities. Our results can be applied for the risk assessment of heavy metals and MPs in aquatic environments.

Liu Q ，Wu H ，Chen J ，Guo B ，Zhao X ，Lin H ，Li W ，Zhao X ，Lv S ，Huang C ... -  《-》