In situ quantitative and visual investigation of the retention of polycyclic aromatic hydrocarbons on the root surface of Kandelia obovata using a microscopic fluorescence spectral analysis method

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Polycyclic aromatic hydrocarbons (PAHs) in surface soils of tropical reef islands in China under external plant and soil introduction: Occurrence, sources, risks, and relationships with soil properties, vegetation cover, and soil source

This study explored the levels, sources, and risks of PAHs in soils from Yongle Atoll (YLA) and Xuande Atoll (XDA) of the Xisha Islands (XSIs) in the South China Sea, China, under different vegetation cover types and soil sources. The results clearly showed that the levels of 16 US EPA priority PAHs (Σ₁₆PAHs) are relatively low in XDA and YLA, with concentrations ranging from not detected (ND) to 151 ng/g (average 15.7 ng/g) and ND to 5.8 ng/g (average 2.1 ng/g), respectively. Three- and four-ring PAHs (62.3% and 53.8%) were widely distributed in YLA and XDA. The average concentration of Σ₁₆PAHs in soils with shrub cover was 1.4, 1.8, 4.8, and 5.0 times higher than that in soils with herbaceous cover, vegetable cover, arbor cover, and no plant cover, respectively. Source analysis using binary diagnostic ratios and the positive matrix factorization (PMF) model suggested that PAHs have similar sources (gasoline/coal combustion, coke production, and biomass combustion), but different contributions in native soil and introduced soil. Moreover, diesel-related vehicular emission was identified to be an additional source of PAHs in native soil. Pearson's correlations revealed strong relationships between PAHs and organic matter or total organic carbon. The cancer risk of PAHs varied among different vegetation cover types and soil sources, following the orders herbaceous cover > vegetable cover > shrub cover > arbor cover > no plant cover and introduced soil > mixed soil > native soil. Nevertheless, the risk remained lower than the risk threshold (10^-6), suggesting low carcinogenesis risk in the two atolls. Our findings provide new evidence for the introduction of external vegetation/soil acting as a driver of changes in the characteristics of PAHs in islands, and also underline the negligibility of the PAH increase in soils in the South China Sea, China, from the perspective of health hazards.

The distribution and retained amount of benzo[a]pyrene at the micro-zones of mangrove leaf cuticles: Results from a novel analytical method

Plant leaf cuticles play a critical role in the accumulation and transport of atmospheric polycyclic aromatic hydrocarbons (PAHs). The relationship between the distribution and retained amount of PAHs on the leaf cuticles and the leaves micro-zone structures is still unclear. In this study, a confocal microscopic fluorescence spectral analysis (CMFSA) system with a spatial resolution of 200 nm was established as a direct and noninvasive means to determine the microscopic distribution and quantify the retained amount of benzo[a]pyrene (B[a]P) at Aegiceras corniculatum (Ac), Kandelia obovata (Ko) and Avicennia marina (Am) leaf cuticle micro-zones (0.096 mm²). The linear ranges for the established method were 10-1900 ng spot^-1 for Ac, 15-1700 ng spot^-1 for Ko and 30-1800 ng spot^-1 for Am, and the detection limits were 0.06 ng spot^-1 for Ac, 0.06 ng spot^-1 for Ko and 0.07 ng spot^-1 for Am. Notably, B[a]P formed clusters and unevenly distributed at the leaf cuticles. On the adaxial cuticles, B[a]P was mainly accumulated unevenly along the epidermis cell wall, and it was also distinctively distributed in the secretory cells around salt glands for Ac and Am. On the abaxial leaf cuticles, B[a]P was concentrated in the salt glands and stomata apart from being unevenly distributed in the epidermis cell wall. Moreover, the amount of B[a]P retained presented a negative correlation with the polarity of leaf cuticles, which resulted in the amount of B[a]P retained on the adaxial leaf cuticles being significantly higher than that on abaxial leaf cuticles. Our results provide a potential in situ method for investigating the distribution and retained amount of PAHs at plant leaf surface micro-zones, which would contribute to further studying and understanding the mechanism of migration and transformation of PAHs by plant leaves from a microscopic perspective.

Role of miR164 in the growth of wheat new adventitious roots exposed to phenanthrene

Polycyclic aromatic hydrocarbons (PAHs), ubiquitous organic pollutants in the environment, can accumulate in humans via the food chain and then harm human health. MiRNAs (microRNAs), a kind of non-coding small RNAs with a length of 18-30 nucleotides, regulate plant growth and development and respond to environmental stress. In this study, it is demonstrated that miR164 can regulate root growth and adventitious root generation of wheat under phenanthrene exposure by targeting NAC (NAM/ATAF/CUC) transcription factor. We observed that phenanthrene treatment accelerated the senescence and death of wheat roots, and stimulated the occurrence of new roots. However, it is difficult to compensate for the loss caused by old root senescence and death, due to the slower growth of new roots under phenanthrene exposure. Phenanthrene accumulation in wheat roots caused to generate a lot of reactive oxygen species, and enhanced lipoxygenase activity and malonaldehyde concentration, meaning that lipid peroxidation is the main reason for root damage. MiR164 was up-regulated by phenanthrene, enhancing the silence of NAC1, weakening the association with auxin signal, and inhibiting the occurrence of adventitious roots. Phenanthrene also affected the expression of CDK (the coding gene of cyclin-dependent kinase) and CDC2 (a gene regulating cell division cycle), the key genes in the cell cycle of pericycle cells, thereby affecting the occurrence and growth of lateral roots. In addition, NAM (a gene regulating no apical meristem) and NAC23 may also be related to the root growth and development in wheat exposed to phenanthrene. These results provide not only theoretical basis for understanding the molecular mechanism of crop response to PAHs accumulation, but also knowledge support for improving phytoremediation of soil or water contaminated by PAHs.

Accumulation and transformation of benzo[a]pyrene in Haplic Chernozem under artificial contamination

Polycyclic aromatic hydrocarbons (PAHs) have been a major concern because of their carcinogenicity, mutagenicity, teratogenicity and wide distribution in the environment. Over 90% of PAHs in the environment exist on soil surface/sediment. Benzo[a]pyrene (BaP) is one of the predominant PAHs in soil. Thus, it is critically important to understand the patterns of BaP accumulation and transformation peculiarities in soil for the risk assessment. The studies were conducted in model experiment with Haplic Chernozem spiked with various doses of BaP (20, 200, 400 and 800 µg kg^-1) equivalent to 1, 10, 20 and 40 levels of maximum permissible concentrations. The unique properties of Haplic Chernozem were studied allow to accumulate and transform BaP as well as barley plants ability to absorb of some BaP concentration. Extraction of BaP from the soil was carried out by the saponification method. The qualitative and quantitative determination of BaP and other polycyclic aromatic hydrocarbons (PAHs) was performed by high-performance liquid chromatography with fluorescence detection (Agilent 1260 Germany, 2014). BaP accumulation in soil depended on the applied BaP concentrations in Haplic Chernozem. Studying the features of PAHs transformation in the soil of a model experiment 1 year after the compound application showed the BaP content in the soil decreased up to 11-40%. Two years after the BaP application the content in the soil decreased up to 15-44% from the initial BaP content in the soil. The percentage of BaP concentration reduction in Haplic Chernozem increased with an increase in the dose of the applied xenobiotic. An increase in the dose of the applied pollutant to the soil of the model experiment contributed to an increase in all PAHs, which indicated a rapid BaP transformation in Haplic Chernozem. The PAHs content in the soils of model experiment in the first year of the research formed the following descending series: pyrene > chrysene > fluoranthene > phenanthrene. In the second year of research the phenanthrene content became higher than the fluoranthene content. The content of these compounds exceeded 20% of the total PAHs content in the soil samples in the first and second years of the model experiment. The features of PAHs accumulation and transformation in soils under artificial pollution showed the degradation of large-nuclear PAHs, starting from 5-ring polyarenes, and their structural reorganization into the less-nuclear polyarenes, such as 4-, 3-, and 2-ring PAHs. During the 2 years of the model experiment the BaP concentration in the soil decreased up to 15-44% from the initial BaP content in the soil.

Nickel uptake and distribution in Agropyron cristatum L. in the presence of pyrene

PAHs affect the uptake of heavy metal by plants. The uptake pathway, distribution and detoxification of nickel (Ni) in Agropyron cristatum L. (A. cristatum) were investigated in the presence of pyrene in this study. Most of Ni was adsorbed on the cell wall in the insoluble phosphate (57.31-72.18%) form and pectate and protein integrated (38.27-38.98%) form. Ni was transferred to the organelle (from 37.84% to 40.52%) in the presence of pyrene. The concentration of Ni in A. cristatum decreased by 27.42%; it was affected by the ATP production inhibitor and 29.49% by the P-type ATPase inhibitor. The results indicated that the uptake of Ni related closely to the synthesis and decomposition of ATP and was an active uptake process. Contents of phytochelatins (PCs) in A. cristatum in Ni contaminated soils increased by 19.97%, and an additional 4.13% increase occurred in the presence of pyrene when compared to single Ni contamination. The content of malic acid in A. cristatum was the highest for 262.78 mg g^-1 in shoots and 46.81 mg g^-1 in roots with Ni contamination. Besides, acetic acid in shoots and roots increased by 40.25% and 102.63% with Ni contamination, and by 61.59% and 185.71% with Ni-pyrene co-contamination. This study preliminarily explored the inhibitory mechanism of pyrene on plant uptake of Ni.

In-situ examination of graphene and graphene oxide impact on the depuration of phenanthrene and fluoranthene adsorbed onto spinach (Spinacia oleracea L.) leaf surfaces

To further assess the human being's exposure to polycyclic aromatic hydrocarbons (PAHs) through the dietary pathway, understanding the partitioning of these chemicals co-existed with nanomaterials in edible vegetable systems deserves specific consideration. In this study, the fiber-optic fluorimetry was applied to in situ examine the effects of graphene (GNS) and graphene oxide (GO) nanosheets on the quantification and depuration of three-ringed phenanthrene (Phe) and four-ringed fluoranthene (Fla) adsorbed individually onto the living spinach (Spinacia oleracea L.) surfaces. When the GNS and GO dosages separately increased to the maximum values: a respective red-shift of 4-5 nm and blue-shift of 2-3 nm occurred for the optimal detection emission wavelengths (λ_em) of the two PAHs, indicating that individual GNS and GO resulted in different changes to the epicuticular wax (ECW) polarity; GNS-inducing fluorescence quenching for the PAHs was about two times greater than GO, owing to the stronger π-π interactions between PAH molecules and GNS relative to GO; the volatilization coefficients (k_C1) were reduced by 31.1% versus 26.7% for Phe, and 51.6% versus 34.4% for Fla, mainly via providing an additional adsorbent and promoting the accessibility of the leaf cuticle; respective photolysis coefficients (k_P2) of Phe and Fla decreased by 42.9% and 50.0% with GNS, primarily owing to the enhancement of the ECW light-adsorption capacity, but increased by 33.3% and 40.0% with GO due to its photocatalytic activities; overall, total depuration coefficients (k_T1, k_T2) of the two PAHs decreased by 11.1-55.6%. These findings demonstrate that GNS and GO significantly alter the depuration behavior of PAHs in vegetable systems, potentially posing a threat to the safety of edible vegetables.

Development of a novel methodology for in vivo quantification of N/O/S-containing polycyclic aromatic hydrocarbons located on the epidermis of mangrove roots using graphene quantum dots as a fluorescence quencher

A novel approach for in vivo determination of typical N/O/S-containing PAHs located on the epidermis of mangrove roots was developed using graphene quantum dots (GQDs) as a fluorescence quencher. The decreasing fluorescence intensity from GQDs was attributed to the amount of N/O/S-containing PAHs introduced onto the epidermis of mangrove roots. The linear ranges of the proposed method were 10.3-980ngg^-1, 9.5-1350ngg^-1 and 7.8-1200ngg^-1 for DBF, DBT and CAR located on the epidermis of K. obovata roots, respectively. This method was also shown to be valid for quantifying the N/O/S-containing PAHs on the root epidermis in the presence of heavy metal (10mmolL^-1) and dissolved organic matter (1mgL^-1 C). Moreover, the death rates of epidermal cells were almost unchanged (p>0.05) after acquiring the fluorescence spectra, which is superior to the previously reported LITRF method with which the cell death rates increased to 42.6%.

Retention of CdS/ZnS Quantum Dots (QDs) on the Root Epidermis of Woody Plant and Its Implications by Benzo[a]pyrene: Evidence from the in Situ Synchronous Nanosecond Time-Resolved Fluorescence Spectra Method

The retention of CdS/ZnS QDs on the epidermis has been confirmed to be one of the core procedures during the root uptake process. However, the retention mechanisms of QDs on the epidermis of woody plant were poorly understood for lacking of an appropriate QD quantitative method. In this study, a novel method for in situ determination of CdS/ZnS QDs retained on the root epidermis was established using synchronous nanosecond time-resolved fluorescence spectroscopy. No correlations between K_f values of oleylamine-CdS/ZnS QDs retained on the epidermal tissues and the surface/bulk composition of mangrove root were observed (p > 0.05) due to the existence of endocytosis mechanisms during the QD uptake processes. Moreover, the difference of the CdS/ZnS QDs in water and further translocated to xylem/phloem of root rather than the combination with cell wall/membranes was the predominant reason that caused the K_f values to follow the sequence of PEG-COOH-CdS/ZnS QDs < PEG-NH₂-CdS/ZnS QDs ≪ oleylamine-CdS/ZnS QDs.