Exploring the potential of earthworm gut bacteria for plastic degradation.

The use of plastic mulch films in agriculture leads to the inevitable accumulation of plastic debris in soils. Here, we explored the potential of earthworm gut-inhabiting bacterial strains (Mycobacterium vanbaalenii (MV), Rhodococcus jostii (RJ), Streptomyces fulvissimus (SF), Bacillus simplex (BS), and Sporosarcina globispora (SG) to degrade plastic films (⌀ = 15 mm) made from commonly used polymers: low-density polyethylene film (LDPE-f), polylactic acid (PLA-f), polybutylene adipate terephthalate film (PBAT-f), and a commercial biodegradable mulch film, Bionov-B® (composed of Mater-Bi, a feedstock with PBAT, PLA and other chemical compounds). A 180-day experiment was conducted at room temperature (x̄ =19.4 °C) for different strain-plastic combinations under a low carbon media (0.1× tryptic soy broth). Results showed that the tested strain-plastic combinations did not facilitate the degradation of LDPE-f (treated with RJ and SF), PBAT-f (treated with BS and SG), and Bionov-B (treated with BS, MV, and SG). However, incubating PLA-f with SF triggered a reduction in the molecular weights and an increase in crystallinity. Therefore, we used PLA-f as model plastic to study the influence of temperature ("room temperature" & "30 °C"), carbon source ("carbon-free" & "low carbon supply"), and strain interactions ("single strains" & "strain mixtures") on PLA degradation. SF and SF + RJ treatments significantly fostered PLA degradation under 30 °C in a low-carbon media. PLA-f did not show any degradation in carbon-free media treatments. The competition between different strains in the same system likely hindered the performance of PLA-degrading strains. A positive correlation between the final pH of culture media and PLA-f weight loss was observed, which might reflect the pH-dependent hydrolysis mechanism of PLA. Our results situate SF and its co-culture with RJ strains as possible accelerators of PLA degradation in temperatures below PLA glass transition temperature (Tg). Further studies are needed to test the bioremediation feasibility in soils.

Microplastic appraisal of soil, water, ditch sediment and airborne dust: The case of agricultural systems.

Although microplastic pollution jeopardizes both terrestrial and aquatic ecosystems, the movement of plastic particles through terrestrial environments is still poorly understood. Agricultural soils exposed to different managements are important sites of storage and dispersal of microplastics. This study aimed to identify the abundance, distribution, and type of microplastics present in agricultural soils, water, airborne dust, and ditch sediments. Soil health was also assessed using soil macroinvertebrate abundance and diversity. Sixteen fields were evaluated, 6 of which had been exposed to more than 5 years of compost application, 5 were exposed to at least 5 years of plastic mulch use, and 5 were not exposed to any specific management (controls) within the last 5 years. We also evaluated the spread of microplastics from the farms into nearby water bodies and airborne dust. We found 11 types of microplastics in soil, among which Light Density Polyethylene (LDPE) and Light Density Polyethylene covered with pro-oxidant additives (PAC) were the most abundant. The highest concentrations of plastics were found in soils exposed to plastic mulch management (128.7 ± 320 MPs.g-1 soil and 224.84 ± 488 MPs.g-1 soil, respectively) and the particles measured from 50 to 150 µm. Nine types of microplastics were found in water, with the highest concentrations observed in systems exposed to compost. Farms applying compost had higher LDPE and PAC concentrations in ditch sediments as compared to control and mulch systems; a significant correlation between soil polypropylene (PP) microplastics with ditch sediment microplastics (r2 0.7 p < 0.05) was found. LDPE, PAC, PE (Polyethylene), and PP were the most abundant microplastics in airborne dust. Soil invertebrates were scarce in the systems using plastic mulch. A cocktail of microplastics was found in all assessed matrices.

Alginate films functionalized with silver sulfadiazine-loaded [Mg-Al] layered double hydroxide as antimicrobial wound dressing.

Alginate (ALG) is an abundant, biocompatible, regenerative, and nontoxic polysaccharide that has potential applications in tissue engineering. Silver sulfadiazine (SDZ) is a topical antibiotic used to control bacterial infection in burns. Aiming to combine the intrinsic alginate characteristics and silver sulfadiazine antimicrobial properties, hydrotalcite ([Mg-Al]-LDH) was used as a host matrix to obtain a system efficient in delivering SDZ from alginate films. SDZ was successfully intercalated in [Mg-Al]-LDH through structural reconstruction. Different solutions were prepared using sodium alginate at 10 wt%, glycerol at 10 wt% as a plasticizer and [Mg-Al]-LDH and [Mg-Al]-LDH/SDZ as fillers at 1 wt% and 5 wt%. Films were obtained by continuous casting and further characterized for their microstructural, mechanical, water barrier and antimicrobial properties. Cytotoxicity tests were also performed on fibroblasts cells. The incorporation of [Mg-Al]-LDH and [Mg-Al]-LDH/SDZ presented neither negative nor positive effects on the mechanical properties and morphology of the alginate films. Moreover, samples containing SDZ exhibited inhibitory activity against S. aureus, E. coli, and S. enterica. The addition of [Mg-Al]-LDH/SDZ even at the highest concentration did not afford a very significant cytotoxicity to the alginate-[Mg-Al]-LDH/SDZ films. These results describe a suitable approach for preparing innovative active wound dressings integrated to efficient drug delivery.