Di (2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) are important pollutants that contaminate agricultural soils. We determined the effects of di (2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) on the production of reactive oxygen species, photosynthesis, and activity of antioxidant enzymes in wheat planted in fluvo-aquic soils. DBP- and DEHP-induced oxidative stress decreased the values of the photosynthetic/fluorescence parameters (except for intercellular carbon dioxide concentration) and chlorophyll content at the seedling, jointing, and booting stages. Moreover, the non-stomatal factor responsible for the net decrease in photosynthetic efficiency was identified as the decrease in fluorescence resulting from the decreased amount of chlorophyll a returning from the excited to the ground energy state. The content of superoxide anions and hydrogen peroxide in wheat leaves and roots increased with increasing DBP and DEHP supplementation, compared to the control. Antioxidant enzyme activities in the leaves and roots at the seedling stage increased at DBP and DEHP levels of 10 and 20 mg kg⁻¹, respectively, and the enzyme activities at the jointing and booting stages increased with increasing concentrations of the chemicals, compared to the control. These results demonstrated that increased levels of antioxidant enzymes play a significant role in protecting plant growth under DBP and DEHP stress.

Effects of CeO2 NPs (200 mg.L−1) on rice (Oryza sativa L.) alone or co-exposure with cadmium (Cd) and salt (sodium chloride, NaCl) were investigated in hydroponic systems for two weeks. Physiological results show that rice biomass was significantly inhibited when NaCl or CdCl2 added alone or in co-exposure treatment. CeO2 NPs significantly relieve the chlorophyll damage under CdCl2 environmental stress. The presence of CeO2 NPs alleviated both stressors induced damages to rice as indicated by the reduced proline level. Additionally, CeO2 NPs triggered the antioxidant defense systems to counteract the oxidative stress caused by NaCl and CdCl2. The level of 8-OHdG, one of the most important indicators for genotoxicity, in rice suggest that the presence of CeO2 NPs reduced the DNA damage in NaCl treated rice. Elemental analysis indicated that co-exposure to NaCl and CdCl2 slightly decreased the Cd content as compared to the one in the CdCl2 alone treatment, and this co-exposure also significantly reduced the Na content when comparing with the NaCl alone treatment. Taken together, our findings suggest that CeO2 NPs could alleviate the CdCl2 and NaCl stresses, but could not completely change the phenotype of both contaminants treated rice.

The rapid emergence and dissemination of antibiotic resistance poses a threat to human health and to the marine environment. We have investigated the abundance and diversity of antibiotic resistance genes (ARGs) and of antibiotic-resistant bacteria (ARB), during the seedling period, rearing period, and harvesting period in seven marine fish cage-culture areas in Guangdong. Spatial and temporal variations of AGRs and ARB were also analyzed. Culture-based methods and quantitative PCR were used to detect ARB and ARGs. Bacterial resistance rates were no significantly different within farming periods. The proportion of antibiotic-resistant bacteria was extremely low (average on 1.15%), except for oxytetracycline-resistant bacteria (average on 34.15%). Vibrio was the most common ARB. Sul1, tetB, and ermB, had the highest relative abundance. The abundance of ARGs in the harvesting period was significant highest. The total abundance of ARGs was highest at Raoping and lowest at Dayawan and Liusha. Most ARGs were associated with opportunistic pathogens. The environmental factors effecting ARB and ARGs are complex, and no key factors were identified. This study provides a theoretical basis for assessing the harmfulness of ARGs and ARB to food safety and human health.

Organic pollutants are widely detected in surface water, groundwater and irrigation sewage in farmland soil, some of which can form complexes with heavy metal ions as ligands in the environment. Acesulfame (ACE), one of the most popular artificial sweeteners, has been found in wastewater sometimes at tens of microgram per liter. However, the combined effects of heavy metals and ACE are still unclear. In the present study, the effects of ACE on cadmium (Cd) absorption and translocation in rice seedlings (Oryza sativa L.) under different exposure conditions were investigated using hydroponic experiments. Under the combined exposure treatments of ACE and Cd, absorption of Cd and ACE in rice significantly decreased when compared with the single exposure treatments, while the alleviation of oxidative damage in rice was also found. Under the sequential exposure treatments of Cd and ACE, the post-exposed ACE activated the pre-absorbed Cd in plant, and accelerated the release of Cd to the environment as well as its translocation from the roots to shoots. In addition, compared with the single Cd exposure, the accumulated ACE can alleviate the oxidative damage in rice shoots induced by Cd, although the Cd concentrations in shoots changed little. In summary, the combined pollution of artificial sweetener ACE was beneficial to relieve the toxicological damage and ecological risk caused by Cd.

Hydrogen gas (H₂) has been shown as an important factor in plant tolerance to abiotic stresses, but the underlying mechanisms remain unclear. In the present study, the effects of H₂ and its interaction with nitric oxide (NO) on alleviating cadmium (Cd) stress in Brassica campestris seedlings were investigated. NO donor (SNP) or hydrogen-rich water (HRW) treatment showed a significant improvement in growth of Cd-stressed seedlings. Cd treatment upregulated both endogenous NO and H₂ (36% and 66%, respectively), and the increase of H₂ was prior to NO increase. When treated with NO scavenger (PTIO) or NO biosynthesis enzyme inhibitors (L-NAME and Gln), HRW-induced alleviation under Cd stress was prevented. Under Cd stress, HRW pretreatment significantly enhanced the NO accumulation, and together up-regulated the activity of NR (nitrate reductase) and expression of NR. HRW induced lower reactive oxygen species (ROS), higher AsA content, enhanced activity of POD (peroxidase) and SOD (superoxide dismutase) in seedling roots were inhibited by PTIO, L-NAME and Gln. Through proteomic analysis, the level of 29 proteins were changed in response to H₂ and NO-induced amelioration of Cd stress. Nearly half of them were involved in oxidation-reduction processes (about 20%) or antioxidant enzymes (approximately 20%). These results strongly indicate that in Cd-stressed seedlings, pretreatment with HRW induces the accumulation of H₂ (biosynthesized or permeated), which further stimulates the biosynthesis of NO through the NR pathway. Finally, H₂ and NO together enhance the antioxidant capabilities of seedlings in response to Cd toxicity.

Although plants are often exposed to atmospheric nanoparticles (NPs), the mechanism of NP deposition and their effects on physiology and metabolism, and particularly in combination with other stressors, are not yet understood. Exploring interactions between stressors is particularly important for understanding plant responses in urban environments where elevated temperatures can be associated with air pollution. Accordingly, 3-year-old spruce seedlings were exposed for 2 weeks to aerial cadmium oxide (CdO) NPs of environmentally relevant size (8–62 nm) and concentration (2 × 10⁵ cm⁻³). While half the seedlings were initially acclimated to high temperature (35 °C) and vapour pressure deficit (VPD; 2.81 kPa), the second half of the plants were left under non-stressed conditions (20 °C, 0.58 kPa). Atomic absorption spectrometry was used to determine Cd content in needles, while gas and liquid chromatography was used to determine changes in primary and secondary metabolites. Photosynthesis-related processes were explored with gas-exchange and chlorophyll fluorescence systems. Our work supports the hypothesis that atmospheric CdO NPs penetrate into leaves but high temperature and VPD reduce such penetration due to stomatal closure. The hypothesis that atmospheric CdO NPs influences physiological and metabolic processes in plants was also confirmed. This impact strengthens with increasing time of exposure. Finally, we found evidence that plants acclimated to stress conditions have different sensitivity to CdO NPs compared to plants not so acclimated. These findings have important consequences for understanding impacts of global warming on plants and indicates that although the effects of elevated temperatures can be deleterious, this may limit other forms of plant stress associated with air pollution.

Herein, we investigated the effects of di-n-butyl phthalate (DBP) on photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) content, oxidative damage, and biomass accumulation of different tissues in wheat (Triticum aestivum L) planted in cinnamon soils. The photosynthetic or fluorescence parameters (except for the intercellular carbon dioxide concentration), chlorophyll content, RuBisCO content, and biomass of roots, stems, and leaves decreased at the seedling, jointing, and booting stages under the stress of DBP. Compared with the control, the content of superoxide anions and hydrogen peroxide in the roots, stems, and leaves increased with increasing DBP concentrations at the seedling, jointing, and booting stages. The activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, stems, and leaves increased under the 10 and 20 mg kg−1 DBP treatments; however, no significant changes were observed under the 40 mg kg−1 DBP treatment at the seedling stage (except for the SOD activity in roots). The increase in SOD and CAT activities in the roots, stems, and leaves with increasing DBP concentration at the jointing and booting stages suggested that an increase in the activities of these antioxidant enzymes may play an important role in defending against excess reactive oxygen species under DBP stress. The biomass of wheat roots, stems, and leaves decreased with an increase in DBP concentration, which was presumably caused by a decrease in photosynthesis and RuBisCO. The effect of DBP on wheat roots, stems, and leaves decreased with wheat growth.

Dairy manure often has elevated concentrations of copper (Cu) that when applied to soil may create toxicity risks to seedlings and soil microbes. Manure application also increases dissolved organic matter (DOM) in soil solution. We hypothesize that high rates of dairy manure amendment over several years will cause increased DOM in the soil that complexes Cu, increasing its mobility. To test this hypothesis, this study investigated water soluble Cu concentrations and dissolved organic carbon (DOC) in soil samples from 3 years of manure-amended soils. Samples were collected at two depths over the first 3 years of a long-term manure-amendment field trial. DOC, Cu, Fe, and P concentrations were measured in water extracts from the samples. Ultraviolet/visible (UV/Vis) spectra were used to assess the DOC characteristics. After 3 years of manure application, extractable Cu concentration was approximately four times greater in the surface and two times greater in subsurface samples of manure-amended soils as compared to non-amended control soils and traditional mineral fertilizer-amended soils. The extractable Cu concentration was greatest in plots that had the highest manure amendment rates (35 t ha⁻¹ and 52 t ha⁻¹, dry weight). The UV/Vis parameters SUVA₂₅₄ and E₂/E₃ correlated with Cu concentration in the extracts (p < 0.05), suggesting that DOC characteristics are important in Cu-binding. The molecular characteristics of the DOC in the subsurface after 3 years of manure amendment were distinct from the DOC in the control plot, suggesting that manure amendment creates mobile DOC that may facilitate Cu mobilization through soil. The 10-fold increase in extractable Cu concentration after only 3 years of manure application indicates that repeated applications of the dairy manure sources used in this study at rates of 35 t/ha or greater may create risks for Cu toxicity and leaching of Cu into ground and surface waters.

Treated wastewater is increasingly used to meet agriculture's water needs; however, treated wastewater contains numerous contaminants of emerging concern (CECs). With exposure and uptake of CECs, phytotoxicity and health of crop plants is of concern, but is poorly understood. This study evaluated the effect of low-dose, chronic exposure to a mixture of 10 CECs, including 4 antibiotics, 3 anti-inflammatory drugs, 1 antiepileptic, 1 beta-blocker, and 1 antimicrobial, on lettuce (Lactuca sativa) and cucumber (Cucumis sativa L.) plants. The CEC mixture was added in nutrient media at 1 to 20X of their typical levels in treated wastewater effluents. Biological endpoints including germination, growth, phytohormone homeostasis, and CEC bioaccumulation were determined. Exposure to the CEC mixture did not affect the germination rate of lettuce seeds, but stimulated root elongation and increased the root-to-shoot biomass ratio during a 7 d cultivation. A dose-dependent decrease in biomass was observed in cucumber seedling after a 30 d exposure, with the highest rate CEC treatment resulting in decreases of 51.2 ± 20.9, 26.3 ± 34.1, and 33.2 ± 41.7% in the below-ground, above-ground, and total biomass, respectively. Levels of abscisic acid were significantly elevated (p < 0.05) in the leaves, but decreased (p < 0.05) in the roots. The dose-response of auxin was characterized by a hormesis effect. A significant 6-fold increase in the stem auxin level was observed at the 1X CEC rate, followed by a decrease to 2-fold the control at the 20X rate. Leaf auxin concentrations also significantly increased at the 1X CEC rate to 16-fold, followed by a decrease at the highest CEC rate. The results of this study suggeste that chronic exposure to low levels of CEC mixtures may compromise the fitness of plants, and the impairments are underlined by alterations in hormone balances.

Arsenic (As) in rice grains is a serious food safety concern. Some coexisting engineered nanoparticles (ENPs) were shown to alter the accumulation and speciation of As in rice grains. However, investigation on the effects of copper oxide nanoparticles (CuO NPs), a popular ingredient in pesticides, on the uptake and accumulation of As is rare. We explored the potentially different impact of CuO NPs and corresponding Cu(II) ions on the accumulation of two As species in rice seedlings in a hydroponic system. Rice seedlings were treated with a combinations of 1 mg/L of arsenite (As(III)) or arsenate (As(V)) and 100 mg/L of CuO NPs or Cu(II) for 6 days. Both forms of Cu significantly reduced the accumulation of total As in rice tissues, with Cu(II) exhibiting significantly greater effect than CuO NPs. As speciation in rice roots was markedly affected by both forms of Cu, and the impacts were Cu-form dependent. For example, the co-existence of As(V) with CuO NPs led to a 45% decrease of As(V) in rice roots, while the co-existence of As(V) with Cu(II) caused a 47% increase in As(V) in rice roots. As speciation in rice shoots was less affected by co-present Cu than in rice roots. Co-occurring As(III) or As(V) lowered Cu concentration in rice roots by 40% and 50% in treatments with CuO NPs, but did not affect Cu content in rice roots co-exposed to Cu(II). The study confirmed the reciprocal effect of co-occurring CuO NPs or Cu(II) and As in rice paddies and highlighted the unique “nano-effect” of CuO NPs. The results alsos showed that the initial oxidation state of As plays an important role in the interactions between As and Cu. The results shed light on the current debate on the safe applications of nano-enabled agrichemicals vs. conventional metal salts in agriculture.