Ecotoxicological effects of titanium dioxide nanoparticles and Galaxolide, separately and as binary mixtures, in radish (Raphanus sativus)

Galaxolide-contaminated soil and tolerance strategies in soybean plants using biofertilization and selenium nanoparticle supplementation

The current study aimed to address the response of soybean (Glycine max) plants to biofertilization and selenium supplementation treatments under galaxolide contamination of soil. In this regard, a pot experiment was carried out where the soybean plants were treated with the plant growth-promoting Actinobacteria (Actinobacterium sp.) as a biofertilizer (PGPB treatment) and/or selenium nanoparticles (Se treatment; 25 mg L-1) under two non-polluted and galaxolide-polluted soils (250 mg galaxolide per kg of soil) to assess the modifications in some plant physiological and biochemical traits. Although higher accumulation of oxidative biomarkers, including hydrogen peroxide (+180%), malondialdehyde (+163%), and protein oxidation (+125%), indicating oxidative stress in galaxolide-contaminated plants, an apparent decline in their contents was observed in response to biofertilization/supplementation treatments in contaminated soil, especially. It was mainly related to the higher detoxification of ROS in PGPB- and Se-treated plants under galaxolide-induced oxidative stress, in which the direct ROS-scavenging enzymes (+44 -179%), enzymatic (+34 - 293%) and non-enzymatic (+35 - 98%) components of the ascorbate-glutathione pathway, and antioxidant molecules (+38 - 370%) were more activated than in control plants. In addition, a higher accumulation of detoxification activity markers, including phytochelatins (+32%) and metallothioneins (+79%), were found in the combined treatments (PGPB+Se) under galaxolide contamination. Moreover, combined treatment with PGPB and Se ameliorated the levels of chlorophyll a content (+58%), stomatal conductance (+57%), the maximum efficiency of photosystem II (PSII) (+36%), and photorespiratory metabolism (including +99% in glycolate oxidase and +54% in hydroxypyruvate reductase activity) in leaves under galaxolide contamination, which resulted in higher photosynthesis capacity (+36%) and biomass production (+74%) in galaxolide-stressed plants as compared to control group. In conclusion, the application of beneficial Actinobacteria and selenium nanoparticles as biofertilization/supplementation is expected to be useful for improving plant toleration and adaptation against galaxolide contamination.

Effect of HHCB and Cd on phytotoxicity, accumulation, subcellular distribution and stereoselectivity of chiral HHCB in soil-plant systems

The toxicity of HHCB in the growth and development of plants is well known, but its uptake, subcellular distribution, and stereoselectivity, especially in a co-contamination environment, is not fully understood. Therefore, a pot experiment was performed to research the physiochemical response, and the fate of HHCB in pakchoi when the Cd co-existed in soil. The Chl contents were significantly lower, and the oxidative stress was aggravated under the co-exposure of HHCB and Cd. The accumulations of HHCB in roots were inhibited, and those in leaves were elevated. The transfer factors of HHCB in HHCB-Cd treatment increased. The subcellular distributions were analyzed in the cell walls, cell organelles, and cell soluble constituents of roots and leaves. In roots, the distribution proportion of HHCB followed cell organelle > cell wall > cell soluble constituent. In leaves, the distribution proportion of HHCB was different from that in roots. And the co-existing Cd made the distribution proportion of HHCB change. In the absence of Cd, the (4R,7S)-HHCB and (4R,7R)-HHCB were preferentially enriched in roots and leaves, and the stereoselectivity of chiral HHCB was more significant in roots than leaves. The co-existing Cd reduced the stereoselectivity of HHCB in plants. Our findings suggested that the fate of HHCB was affected by the co-existing Cd, so the risk of HHCB in the complicated environment should be paid more attention.

Optimistic effects of galaxolide and polystyrene microplastic stress on the physio-biochemical characteristics and metabolic profiles of an ornamental plant

Galaxolide (HHCB) and polystyrene (PS) microplastics or nanoplastics have been widely recognized as emerging pollutants. However, very few efforts have been made to remove these contaminants from the environment using eco-friendly materials such as plant materials. Therefore, this study sought to investigate the physiological and biochemical effects and tolerance mechanisms of Mirabilis jalapa L. upon exposure to HHCB and PS. Our findings demonstrated that this ornamental plant was tolerant to HHCB and PS exposure. HHCB treatment increased antioxidant enzyme activity. However, superoxide dismutase (SOD) activity increased by 206.85% when the plants were treated with 0.5 mg L^-1 HHCB alone, whereas co-exposure to 0.5 mg L^-1 HHCB and 500 nm PS increased SOD activity by 93.82%. Contaminant exposure also affected photosynthetic parameters such as stomatal conductance and transpiration rate. In contrast, net photosynthetic rate and photosynthetic pigment content were not significantly affected. HHCB aggregated heavily in the roots of the plant. Moreover, 500 nm PS could be absorbed by the root and transported to the shoot, and 5 μm PS would be transferred to the shoot under the carrying effect of HHCB. Co-exposure to HHCB and PS significantly changed the glyoxylate and dicarboxylate metabolism, alanine, aspartate, and glutamate metabolism, and glycine, serine, and threonine metabolism pathways, thus affecting carbohydrate synthesis and energy metabolism in M. jalapa. These results provide a basis for the development of HHCB and PS remediation strategies using M. jalapa, an ornamental plant that is not only tolerant to organic contaminants but can also beautify the environment.

The Acute and Chronic Effects of a Sediment-Bound Synthetic Musk, Galaxolide, on Hyalella azteca, Chironomus dilutus, and Lumbriculus variegatus

Galaxolide is one of the most frequently used synthetic polycyclic musks on the market and is commonly detected in aquatic waterways. Previous studies have mainly evaluated the toxicity of this emerging contaminant using water-only exposures; however, its high Log K_ow (5.9) suggests that this compound is likely to partition to sediments. Three benthic invertebrates, Chironomus dilutus, Hyalella azteca, and Lumbriculus variegatus, were exposed to sediment-bound Galaxolide using both acute (10 d; survival) and chronic (28 d; survival and growth) bioassays. The acute and chronic LC50s for Galaxolide ranged from 238 to 736 mg/kg sediment (2400-7430 µg/g organic carbon [OC]) for all three species, which were above concentrations commonly detected in the environment (< 2.5 mg/kg). Growth effects (i.e., weight and/or length) were noted in two of the three organisms (with C. dilutus being the exception); however, these effects were also noted at concentrations above those that are environmentally relevant. Molecular level evaluations were conducted with surviving L. variegatus and C. dilutus collected from treatments near the LC50 value. Markers of oxidative stress (glutathione-s-transferase) and endocrine disruption (estrogen-related receptor) in C. dilutus were significantly decreased in the treatment group compared to controls by 0.7-fold and 1.9-fold, respectively. Although acute and chronic effects were largely absent at environmentally relevant concentrations, changes in endocrine response suggest that more sensitive endocrine-based endpoints, such as emergence (for C. dilutus) and molting (for H. azteca), are needed to ensure that the risk of this emerging contaminant is low at environmentally relevant concentrations.

The impact of synthetic musk compounds in biofilms from drinking water bacteria

Musk fragrances have been detected in drinking water (DW) at trace concentrations. However, their impact on the microbial quality of DW has been disregarded. This work provides a pioneer evaluation of the effects of two synthetic musks contaminants, tonalide (AHTN) and galaxolide (HHCB), in microbial biofilms formed on two different surfaces, polyvinyl chloride (PVC) and stainless steel AISI 316 (SS316). Three bacterial species isolated from DW (Acinetobacter calcoaceticus, Burkholderia cepacia and Stenotrophomonas maltophilia), were used to develop 7-day-old single and mixed species biofilms. The impact of musks was assessed directly on biofilms but also on the bacteria motility, biofilm formation ability and biofilm susceptibility to chlorination. AHTN musk caused the most remarkable effects by increasing the cellular density and viability of mixed biofilms, and the extracellular polysaccharides content of biofilms on SS316. Most of the alterations caused by the direct exposure of biofilms to musks were observed when SS316 was used as an adhesion surface. In contrast, the ability to form biofilms and their susceptibility to chlorine were more affected for bacteria from HHCB-exposed biofilms on PVC. The overall results demonstrate that the presence of musks at residual concentrations influences DW bacterial dynamics, with the potential to impact the DW quality and safety. The type of plumbing material may further impact the effects of musks.