Behavior and mechanisms of ciprofloxacin adsorption on aged polylactic acid and polyethlene microplastics

Different impacts of oil-based and bio-based microplastics on isotopic composition and stoichiometry of a model freshwater grazer

Microplastic pollution has become a pervasive environmental challenge due to their global distribution and putatively harmful effects on organisms at different ecotoxicological endpoints. However, in some cases, the effects of microplastics are similar to, or even less harmful than those of naturally occurring particles. Bioplastics, developed as a more sustainable alternative to traditional plastics, still have unclear effects compared with oil-based microplastics. This study uses a laboratory-controlled experiment to compare the physical effects of oil-based high-density polyethylene (HDPE) and bio-based biodegradable polylactic acid (PLA) on the consumption rate, isotopic composition, respiration rate, stoichiometry, and growth rate of model freshwater snail Radix balthica. The experiment included a positive control using silica sand (Si) to simulate natural particles and a control with no experimental additions. It was hypothesised that exposure to microplastics affects the snails solely through the physical influence of the particles, and that the effects of microplastics depend on their composition. The results show that the effects of HDPE were attributable solely due to the physical presence of the particles, but this was not the case for PLA. Exposure to PLA led to increased growth (as final mass). Consumption, respiration, and growth rates were not significantly affected when exposed to the experimental additions. However, the isotopic composition and C:N of snails was altered after exposure to HDPE and Si compared with control. The isotopic composition of snails exposed to PLA did not show significant changes, but they did have higher phosphorous content in their tissues. In this study, HDPE microplastics were not more harmful than naturally occurring particles, and PLA microplastics appeared to influence growth patterns differently than expected. Further research is needed to confirm these observations and fully assess the environmental and biological implications of these contaminants.

Surfactant-mediated transport behavior of zinc oxide nanoparticles in porous media

Nanomaterials and surfactants are widely detected in soil-groundwater environments, while the surfactant-mediated transport behavior of nanoparticles has not been sufficiently investigated. In this study, the transport of ZnO nanoparticles (nZnO) in quartz sand (QS) in the presence of cetyltrimethylammonium bromide (CTAB) is investigated by adsorption and column experiments in combination with XDLVO analysis and numerical simulation. The adsorption of nZnO on QS is investigated by adsorption experiments under the environmental concentration of CTAB (50 mg·L-1). The results of adsorption experiments indicate that the adsorption efficiency of QS is related to the concentration of nZnO and primarily exhibits multilayer adsorption, and the Freundlich model can effectively fit the experimental data of isothermal adsorption. Additionally, the adsorption process is dominated by several factors, among which chemical adsorption is the primary controlling factor. The column experiment results indicate that at higher initial concentrations, the transport capacity of nZnO is weakened due to the occupation of adsorption sites on the QS and the increased collision opportunities between particles. The addition of ionic strength promotes the aggregation of nZnO by reducing electrostatic repulsion, thus inhibiting nZnO transport. Significantly, the inhibition of divalent Ca2+ is stronger than that of monovalent Na+. Interestingly, HA binds mainly to CTAB to form a hydrophobic complex, which reduces the repulsive force between nZnO and QS and inhibits the transport of nZnO. Increasing the pH, nZnO mobility first increases and then decreases, and begins to be inhibited at pH= 9 near the zero-point charge of nZnO. Moreover, at pH= 10, nZnO particles acquire a positive charge due to the adsorption of CTAB, and consequently, they are retained by QS through the hydrophobic interaction between the adsorbed CTABs. In addition, nZnO transport capacity does not increase with CTAB concentration. When a certain concentration of nZnO is reached, nZnO transport capacity is inhibited with CTAB concentration.

Adsorption and Desorption Behavior of Cr(VI) on Two Typical UV-Aged Microplastics in Aqueous Solution

Microplastics (MPs) are novel pollutants that can adsorb heavy metals in water environments and migrate together as carriers and are prone to aging due to the light in water. However, few reports have been published on the synergistic behavior and effects of these different types of aged MPs on the adsorption and desorption of Cr(VI). Here, two MP types─polyamide (PA) and polylactic acid (PLA)─were aged by UV irradiation, and the adsorption and desorption behaviors of MPs on Cr(VI) were studied. The results indicated that UV light can rapidly age MPs. After the MPs were exposed to UV light, their specific surface area, negative charge, and oxygenic groups increased, resulting in enhanced hydrophilicity. The aged MPs depicted a markedly enhanced adsorption capacity for Cr(VI) compared with the results of aged-PA > pristine-PA > aged-PLA > pristine-PLA. The process followed the Langmuir and pseudo-second-order models, confirming that chemical and monolayer adsorption are the primary processes involved in the adsorption of Cr(VI) by aged MPs. Cr(VI) was more easily desorbed in the simulated gastric fluid environment. The desorption rate of aged MPs was lower than that of pristine MPs because of their stronger binding forces to Cr(VI). The binding of Cr(VI) to MPs mainly depends on synergistic mechanisms such as electrostatic attraction, reduction reactions, and chelation of oxygenic groups. This study clarifies the reciprocity mechanism between aging MPs and Cr(VI) and provides further insights and guidance for controlling the joint pollution between MPs and heavy metal pollutants in the future.

Ecotoxicological Effects of Microplastics Combined With Antibiotics in the Aquatic Environment: Recent Developments and Prospects

Both microplastics and antibiotics are commonly found contaminants in aquatic ecosystems. Microplastics have the ability to absorb antibiotic pollutants in water, but the specific adsorption behavior and mechanism are not fully understood, particularly in relation to the impact of microplastics on toxicity in aquatic environments. We review the interaction, mechanism, and transport of microplastics and antibiotics in water environments, with a focus on the main physical characteristics and environmental factors affecting adsorption behavior in water. We also analyze the effects of microplastic carriers on antibiotic transport and long-distance transport in the water environment. The toxic effects of microplastics combined with antibiotics on aquatic organisms are systematically explained, as well as the effect of the adsorption behavior of microplastics on the spread of antibiotic resistance genes. Finally, the scientific knowledge gap and future research directions related to the interactions between microplastics and antibiotics in the water environment are summarized to provide basic information for preventing and treating environmental risks. Environ Toxicol Chem 2024;43:1950-1961. © 2024 SETAC.

When antibiotics encounter microplastics in aquatic environments: Interaction, combined toxicity, and risk assessments

Antibiotics and microplastics (MPs), known as emerging pollutants, are bound to coexist in aquatic environments due to their widespread distribution and prolonged persistence. To date, few systematic summaries are available for the interaction between MPs and antibiotics in aquatic ecosystems, and a comprehensive reanalysis of their combined toxicity is also needed. Based on the collected published data, we have analyzed the source and distribution of MPs and antibiotics in global aquatic environments, finding their coexistence occurs in a lot of study sites. Accordingly, the presence of MPs can directly alter the environmental behavior of antibiotics. The main influencing factors of interaction between antibiotics and MPs have been summarized in terms of the characteristics of MPs and antibiotics, as well as the environmental factors. Then, we have conducted a meta-analysis to evaluate the combined toxicity of antibiotics and MPs on aquatic organisms and the related toxicity indicators, suggesting a significant adverse effect on algae, and inapparent on fish and daphnia. Finally, the environmental risk assessments for antibiotics and MPs were discussed, but unfortunately the standardized methodology for the risk assessment of MPs is still challenging, let alone assessment for their combined toxicity. This review provides insights into the interactions and environment risks of antibiotics and MPs in the aquatic environment, and suggests perspectives for future research.

Adsorption properties and mechanism of Cu(II) on virgin and aged microplastics in the aquatic environment

Microplastics (MPs) migrate by adsorbing heavy metals in aquatic environments and act as their carriers. However, the aging mechanisms of MPs in the environment and the interactions between MPs and heavy metals in aquatic environments require further study. In this study, two kinds of materials, polyamide (PA) and polylactic acid (PLA) were used as target MPs, and the effects of UV irradiation on the physical and chemical properties of the MPs and the adsorption behavior of Cu(II) were investigated. The results showed that after UV irradiation, pits, folds and pores appeared on the surface of aged MPs, the specific surface area (SSA) increased, the content of oxygen-containing functional groups increased, and the crystallinity decreased. These changes enhanced the adsorption capacity of aged MPs for Cu(II) pollutants. The adsorption behavior of the PA and PLA MPs for Cu(II) conformed to the pseudo-second-order model and Langmuir isotherm model, indicating that the monolayer chemical adsorption was dominant. The maximum amounts of aged PA and PLA reached 1.415 and 1.398 mg/g, respectively, which were 1.59 and 1.76 times of virgin MPs, respectively. The effects of pH and salinity on the adsorption of Cu(II) by the MPs were significant. Moreover, factors such as pH, salinity and dosage had significant effects on the adsorption of Cu(II) by MPs. Oxidative complexation between the oxygen-containing groups of the MPs and Cu(II) is an important adsorption mechanism. These findings reveal that the UV irradiation aging of MPs can enhance the adsorption of Cu(II) and increase their role as pollutant carriers, which is crucial for assessing the ecological risk of MPs and heavy metals coexisting in aquatic environments.

Antibiotics and microplastics in manure and surrounding soil of farms in the Loess Plateau: Occurrence and correlation

The wide use of animal manure in farmland operations is a source of soil nutrients. However, the return of manure affected antibiotics and microplastics in the soil, thus the potential ecological risks cannot be overlooked. This study investigated the distribution of different antibiotics and microplastics and their correlation. It was found that multiple classes of veterinary antibiotics and microplastics could be detected simultaneously in most manure and soil. In manure, the average concentration of tetracycline antibiotics was higher than fluoroquinolones and sulfonamides. A much lower concentration of antibiotics was found in the soil samples relative to manure. The abundance of microplastics ranged from 21,333 to 88,333 n/kg in manure, and the average abundance was 50,583 ± 24,318 n/kg. The average abundance was 3056 ± 1746 n/kg in the soil. It confirmed that applying organic fertilizer to agricultural soil and the application of plastic mulch in farmlands introduced microplastics. Moreover, microplastics were found to be significantly correlated with antibiotics (r = 0.698, p < 0.001). The correlation between microplastics and antibiotics in soil was significantly weaker than that in manure. Farms could be the hotspot for the co-spread of microplastics and antibiotics. These findings highlighted the co-occurrence of antibiotics and microplastics in agricultural environments.

Adsorption of azoxystrobin and pyraclostrobin onto degradable and non-degradable microplastics: Performance and mechanism

Microplastics (MPs) exist after agricultural operations and thus present potential hazards to the environment and human health. However, the ecological risks posed by MPs carrying pesticides remain unclear. In this study, the adsorption and desorption behaviors of two pesticides, azoxystrobin and pyraclostrobin, on degradable and non-degradable MPs of poly(butylene adipate-co-terephthalate) (PBAT) and polyethylene (PE) were compared before and after UV aging. Additionally, the bioaccessibility of MPs carrying pesticides within a condition simulating gastrointestinal fluids was evaluated. The results showed that, after UV aging, the adsorption capacity of PBAT for pesticides decreased, while that of PE increased. Moreover, PBAT possessed higher adsorption ability towards both the pesticides due to its higher specific surface area, pore volume, contact angle, and lower crystallinity, as well as stronger van der Waals forces, electrostatic interactions, and hydrogen bonding indicated by theoretical calculation. Bioaccessibility experiments showed that azoxystrobin and pyraclostrobin had a higher risk of desorption from PBAT than PE, which is mainly dependent on the LogKow of pesticides according to the random forest analysis. In brief, the study highlights the potential risks of degradable MPs carrying pesticides to human health and the ecosystem, especially when compared to their non-degradable counterparts, manifesting that the ecological risk posed by degradable MPs should not be ignored.

A review of the occurrence and degradation of biodegradable microplastics in soil environments

The use of plastics for manufacturing of products and packaging has become ubiquitous. This is because plastics are cheap, pliable, and durable. However, these characteristics of plastics have also led to their disposal in landfill, where they persist. To overcome the environmental challenge posed by conventional plastics (CPs), biodegradable plastics (BDPs) are increasingly being used. However, BDPs form residual microplastics (MPs) at a rate that far exceeds that of CPs, and MPs have negative impacts on the soil environment. This review aimed to evaluate whether the move away from CPs to BDPs is having an overall positive impact on the environment considering the formation of MPs. Topics focused on in this review include the degradation of BDPs in the soil environment and the impacts of MPs originating from BDPs on soil physical and chemical properties, microbial communities, animals, and plants. The information collated in this review can provide scientific guidance for sustainable development of the BDPs industry.