Multiple Evaluation of Typical Heavy Metals Pollution in Surface Soil and Road Dust from Beijing and Hebei Province, China.

Soil and road dust are important receptors of heavy metals in the environment. Meanwhile, heavy metal could transfer to the atmosphere through resuspension. Due to the serious consequences and atmospheric haze in Jing-Jin-Ji area, it's important to evaluate the pollution level, particle size distribution and sources of heavy metals. For heavy metals in soil samples, similar concentrations to the background values and no obvious pollution or low-level pollution was presented. Higher concentration of Cu (78.9 mg/kg) and Zn (261 mg/kg) were found in road dust. The source appointment results showed that Mn, Co, Cr, Ni, Zn and Pb in soils and Cr, Co and Mn in road dust were mainly from the natural sources, while traffic source contributed to most of Cu, Zn and Pb in road dust. Different particle size distribution patterns were found in soils and road dusts, and the finest particles presented the highest heavy metal concentrations.

Assessment of the Bioavailability of Mercury Sulfides in Paddy Soils Using Sodium Thiosulfate Extraction - Results from Microcosm Experiments.

Mercury sulfides (HgS), one of the largest Hg sinks in the lithosphere, has long been considered to be highly inert. Recently, several HgS speciation (e.g., nano- or micro-sized HgS particles) in paddy soils have been found to be reactive and bioavailable, increasing the possibility of methylation and bioaccumulation and posing a potential risk to humans. However, a simple and uniform method for investigating HgS bioavailability is still lacking. To address this issue, we extracted dissolved Hg from HgS particles by sodium thiosulfate (Na2S2O3) in paddy soils and analyzed the correlation between extracted Hg and soil methylmercury (MeHg). Results showed that the amounts of Hg extracted by Na2S2O3 had a strong positive correlation with the levels of soil MeHg (R 2 adj = 0.893, p < 0.05). It is suggested that Na2S2O3 extraction may be a good method of predicting Hg bioavailability in paddy soils. Our results would help to give clues in better predicting Hg risk in natural environments.

Early-life exposure to three size-fractionated ultrafine and fine atmospheric particulates in Beijing exacerbates asthma development in mature mice.

BACKGROUND: Epidemiological studies have suggested that elevated levels of air pollution contribute to an increased incidence or severity of asthma. Although late-onset adult asthma seems to be more attributable to environmental risk factors, limited data is available on the impact of early-life exposure to size-fractionated ambient particulate matter (PM) on asthma in adults. We aimed to determine the effect on the development and exacerbation of asthma in the adult after the mice were exposed as juveniles to three size-fractionated ambient particulates collected from Beijing. METHODS: The three size-fractionated ambient particulates were collected from urban Beijing in winter, heavily affected by traffic and coal-fired emissions. The typical morphological and major chemical components of the PM were characterized first. Oxidative stress and expression of DNA methyltransferases (DNMTs) were then examined in vitro and in the lungs of mouse pups 48 h after exposure to PM by oropharyngeal aspiration. When the exposed and control juvenile mice matured to adulthood, an antigen-induced asthma model was established and relevant bio-indices were assessed. RESULTS: PM with different granularities can induce oxidative stress; in particular, F1, with the smallest size (< 0.49 µm), decreased the mRNA expression of DNMTs in vitro and in vivo the most significantly. In an asthma model of adult mice, previous exposure as juveniles to size-fractionated PM caused increased peribronchiolar inflammation, increased airway mucus secretion, and increased production of Th2 cytokines and chemokines. In general, F1 and F2 (aerodynamic diameter < 0.95 µm) particulates affected murine adult asthma development more seriously than F3 (0.95-1.5 µm). Moreover, F1 led to airway inflammation in the form of both increased neutrophils and eosinophils in BALF. The activation of the TGF-ß1/Smad2 and Smad3/Stat3 signaling pathways leading to airway fibrosis was more profoundly induced by F1. CONCLUSION: This study demonstrated that exposure to ambient PM in juvenile mice enhanced adult asthma development, as shown by increased Th2 responses, which might be associated with the persistent effects resulting from the oxidative stress and decreased gene expression of DNMTs induced by PM exposure. The observed differences between the effects of three size-fractionated particulates were attributed to particle sizes and chemical constituents, including heavy metals and also PAHs, since the amounts of PAH associated with more severe toxicity were enriched equivalently in the F1 and F2 fractions. Relative to the often mentioned PM2.5, PM with an aerodynamic diameter smaller than 0.95 µm had a more aggravating effect on asthma development.

Beyond PM2.5: The role of ultrafine particles on adverse health effects of air pollution.

BACKGROUND: Air pollution constitutes the major threat to human health, whereas their adverse impacts and underlying mechanisms of different particular matters are not clearly defined. SCOPE OF REVIEW: Ultrafine particles (UFPs) are high related to the anthropogenic emission sources, i.e. combustion engines and power plants. Their composition, source, typical characters, oxidative effects, potential exposure routes and health risks were thoroughly reviewed. MAJOR CONCLUSIONS: UFPs play a major role in adverse impacts on human health and require further investigations in future toxicological research of air pollution. GENERAL SIGNIFICANCE: Unlike PM2.5, UFPs may have much more impacts on human health considering loads of evidences emerging from particulate matters and nanotoxicology research fields. The knowledge of nanotoxicology contributes to the understanding of toxicity mechanisms of airborne UFPs in air pollution. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

A hidden demethylation pathway removes mercury from rice plants and mitigates mercury flux to food chains.

Dietary exposure to methylmercury (MeHg) causes irreversible damage to human cognition and is mitigated by photolysis and microbial demethylation of MeHg. Rice (Oryza sativa L.) has been identified as a major dietary source of MeHg. However, it remains unknown what drives the process within plants for MeHg to make its way from soils to rice and the subsequent human dietary exposure to Hg. Here we report a hidden pathway of MeHg demethylation independent of light and microorganisms in rice plants. This natural pathway is driven by reactive oxygen species generated in vivo, rapidly transforming MeHg to inorganic Hg and then eliminating Hg from plants as gaseous Hg°. MeHg concentrations in rice grains would increase by 2.4- to 4.7-fold without this pathway, which equates to intelligence quotient losses of 0.01-0.51 points per newborn in major rice-consuming countries, corresponding to annual economic losses of US$30.7-84.2 billion globally. This discovered pathway effectively removes Hg from human food webs, playing an important role in exposure mitigation and global Hg cycling.

Application countermeasures of non-incineration technologies for medical waste treatment in China.

By the end of 2012, there were 272 modern, high-standard, centralized medical waste disposal facilities operating in various cities in China. Among these facilities nearly 50% are non-incineration treatment facilities, including the technologies of high temperature steam, chemical disinfection and microwave. Each of the non-incineration technologies has its advantages and disadvantages, and any single technology cannot offer a panacea because of the complexity of medical waste disposal. Although non-incineration treatment of medical waste can avoid the release of polychlorinated dibenzo-p-dioxins/dibenzofurans, it is still necessary to decide how to best meet the local waste management needs while minimizing the impact on the environment and public health. There is still a long way to go to establish the sustainable application and management mode of non-incineration technologies. Based on the analysis of typical non-incineration process, pollutant release, and the current tendency for technology application and development at home and abroad, this article recommends the application countermeasures of non-incineration technologies as the best available techniques and best environmental practices in China.

Research progress on the analysis and application of radioactive hot particle.

Radioactive hot particle is the particulate form of nuclear material that exists in the environment. The U, Pu, Am, Cs, and other radionuclides isotope in the hot particle contain abundant and accurate fingerprint information, such as the origin and age of the nuclear material. The acquisition and analysis of the key information in the hot particle can be equivalent to the analysis of bulk nuclear material, which could directly reflect the real situation of nuclear activities. Therefore, the single particle analysis of hot particles has become an irreplaceable key technology in nuclear safeguards inspection. The rapid identification, screening, locating, and accurate isotope analysis of hot particles from a large number of particles dispersed in environmental media or on the surface of other materials are one of the most important research field in nuclear emergency. In this review, the research process of the analytical methods for hot particles in the last decade was summarized, including the physical character of hot particles, and the techniques of localization, screening, and extraction of hot particles. Furthermore, we also focused on the mass spectrometry technology for the analysis of hot particle. The advantages and disadvantages of the most used mass spectrometry were summarized. Finally, the research trend for hot particle analysis methods was proposed.

[Determination of nine hazardous elements in textiles by inductively coupled plasma optical emission spectrometer after microwave-assisted dilute nitric acid extraction].

Textiles are easily contaminated by heavy metals in the course of processing. In order to monitor the quality of textiles, a new method was developed for simultaneous determination of arsenic, antimony, lead, cadmium, chromium, cobalt, copper, nickel and mercury in textiles by inductively coupled plasma optical emission spectrometry (ICP-OES) after microwave-assisted dilute nitric acid extraction. After optimizing extraction conditions, we ultimately selected 5% nitric acid as extractant and 5 min as extraction time with the extraction temperature of 120 degrees C and instrument power of 400W in the microwave-assisted extraction procedure. Nine hazardous elements were detected sequentially by ICP-OES. The results showed that the detection limits were 0.3-15 microg x L(-1) and the recoveries 73.6%-105% with the RSDs (n = 3) of 0.1%-3%. The proposed method was successfully used to determine nine elements in cotton, wool, terylene and acrylic.

A review of anthropogenic radionuclide 236U: Environmental application and analytical advances.

236U is an anthropogenic radionuclide that is produced from nuclear reactions of 235U(n, γ) and 238U(n, 3n). It has gained extensive attention in the field of environment, geology, nuclear emergency, and nuclear forensics. Due to the unique physical and chemical character and the distinct fingerprint character from different sources, 236U has been successfully applied in the environmental tracer, nuclear material source appointment, and environmental assessment. Until now, few reviews were published about the database, application, and the latest analytical technology development of 236U. In this review, the 236U concentration and 236U/238U isotope ratio were summarized, and the data were classified into four categories, including soil and seawater samples affected by global fallout and nuclear incidents. Furthermore, the development of environmental application and pretreatment methods were also summarized. The advanced pretreatment technology using alkali fusion and flow injection was especially discussed to introduce the development of a rapid analytical method. Finally, the research challenge and direction of 236U were proposed for further research, such as the tracer application combining 236U with other radionuclides in the terrestrial environment and the precise analysis of minor isotopes in ultra-trace uranium samples. We hope this review will help scholars to have a deep research on the analysis and application of 236U.

Inactivation of porcine epidemic diarrhea virus with electron beam irradiation under cold chain conditions.

The many instances of COVID-19 outbreaks suggest that cold chains are a possible route for the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, owing to the low temperatures of cold chains, which are normally below 0 °C, there are limited options for virus inactivation. Here, high-energy electron beam (E-beam) irradiation was used to inactivate porcine epidemic diarrhea virus (PEDV) under simulated cold chain conditions. This coronavirus was used as a surrogate for SARS-CoV-2. The possible mechanism by which high-energy E-beam irradiation inactivates PEDV was also explored. An irradiation dose of 10 kGy reduced the PEDV infectious viral titer by 1.68-1.76 log10TCID 50 / 100 µ L in the cold chain environment, suggesting that greater than 98.1% of PEDV was inactivated. E-beam irradiation at 5-30 kGy damaged the viral genomic RNA with an efficiency of 46.25%-92.11%. The integrity of the viral capsid was disrupted at 20 kGy. The rapid and effective inactivation of PEDV at temperatures below freezing indicates high-energy E-beam irradiation as a promising technology for disinfecting SARS-CoV-2 in cold chain logistics to limit the transmission of COVID-19.

Detection and remediation of mercury contaminated environment by nanotechnology: Progress and challenges.

Hg pollution is a global concern due to its high ecotoxicity and health risk to human beings. A comprehensive understanding of the fast-developed technology applied in determining and controlling Hg pollution is beneficial for risk assessment and field remediation. Herein, we mainly assembled the recent progress on Hg treatment in the environment by nanotechnology. The advantages and disadvantages of the conventional and nanotechnology-based methods commonly used in water-/soil-Hg remediation were compared and summarized. Specifically, green nanomaterials derived from plant tissues (e.g., nanocellulose) have prominent merits in remediation of Hg contaminated environments, including high efficiency in Hg removal, low cost, environment-friendly, and easily degradable. Based on the theories of Hg biogeochemistry and existed researches, four promising pathways are proposed, 1) developing surface-modified green nanocellulose with high selectivity and affinity towards Hg; 2) designing effective dispersants in preventing nanocellulose from agglomeration in soil; 3) mediating soil properties by adding green nanomaterials-based fertilizers; 4) improving plant-Hg-extract capacity with green nanomaterials addition. Briefly, more efficient and available approaches are still expected to be developed and implemented in the natural environment for Hg remediation.

Bioavailability and methylation of bulk mercury sulfide in paddy soils: New insights into mercury risks in rice paddies.

Mercury sulfide (HgS) constitutes the largest Hg reservoir in the lithosphere but has long been considered to be not bioavailable and a minor participant in Hg biogeochemical cycling. Herein, we report that bulk α-HgS can be dissolved and methylated in paddy soils, especially with rice culture. Bulk α-HgS exposure did not affect rice growth compared to the control group but significantly increased methylmercury (MeHg) contents in the rhizospheric soils (e.g., 80.15% and 108.71% higher for bulk α-HgS treatment vs. control at the seedling and maturation stages, respectively). Moreover, bulk α-HgS exposure induced an apparent accumulation of MeHg (50% higher for bulk α-HgS treatment vs. control) and markedly elevated total Hg (THg) in rice grains. The presence of DOM and reduced sulfide in paddy soils was further evidenced to drive the mobilization and dissolution of bulk α-HgS, thereby resulting in THg and MeHg accumulation in rice grains. These findings highlight the bioavailability of HgS in rice paddies and suggest that bulk HgS should be considered when assessing Hg health risks and developing efficient remediation approaches in Hg-contaminated croplands.

Mobilization and methylation of mercury with sulfur addition in paddy soil: Implications for integrated water-sulfur management in controlling Hg accumulation in rice.

Sulfur-fertilizer is commonly applied in croplands and in immobilizing Hg in contaminated soil. However, there is still great uncertainty and controversy concerning Hg transportability and transformation when supplying sulfur in paddies with complex conditions. Herein, we explored the effect of adding sulfate in paddy soil at different rice growth stages on soil Hg release and MeHg accumulation in rice and uncovered the correlation between sulfur induced MeHg production and the dynamically changed soil Eh, dissolved Fe, and dissolved organic carbon (DOC). In specific, sulfate addition at early stages (flooding period) triggered the decrease of Eh and increase of DOC and dissolved Fe, which in turn promoted Hg release and favored MeHg generation (increased by 235.19-555.07% vs control). Interestingly, adding sulfate at late stages (drainage condition), as compared with that at early stages, alleviated Hg release and MeHg production accompanied by the increase of Eh and decrease of dissolved Fe and DOC. The microcosmic experiment further confirmed the reduction of sulfate to sulfide promoted the change of Eh, thereby stimulating HgS dissolution in soil extract. The results give clues on the rational application of sulfur-fertilizer and through the water-sulfur fertilizer management considering the correspondingly changed soil conditions to diminish Hg bioavailability and MeHg production in paddies and paddy-like environments.

Nano-silica particles synergistically IgE-mediated mast cell activation exacerbating allergic inflammation in mice.

Background: Allergic respiratory diseases have increased dramatically due to air pollution over the past few decades. However, studies are limited on the effects of inorganic components and particulate matter with different particle sizes in smog on allergic diseases, and the possible molecular mechanism of inducing allergies has not been thoroughly studied. Methods: Four common mineral elements with different particle sizes in smog particles were selected, including Al2O3, TiO2, Fe2O3, and SiO2. We studied the relationship and molecular mechanism of smog particle composition, particle size, and allergic reactions using mast cells, immunoglobulin E (IgE)-mediated passive cutaneous anaphylaxis (PCA) model, and an ovalbumin (OVA)-induced asthmatic mouse model in vitro and in vivo, combined with transmission electron microscopy, scanning transmission X-ray microscopy analysis, and transcriptome sequencing. Results: Only 20 nm SiO2 particles significantly increased ß-hexosaminidase release, based on dinitrophenol (DNP)-human serum albumin (HSA) stimulation, from IgE-sensitized mast cells, while other particles did not. Meanwhile, the PCA model showed that Evan's blue extravasation in mice was increased after treatment with nano-SiO2 particles. Nano-SiO2 particles exposure in the asthmatic mouse model caused an enhancement of allergic airway inflammation as manifested by OVA-specific serum IgE, airway hyperresponsiveness, lung inflammation injury, mucous cell metaplasia, cytokine expression, mast cell activation, and histamine secretion, which were significantly increased. Nano-SiO2 particles exposure did not affect the expression of FcϵRI or the ability of mast cells to bind IgE but synergistically activated mast cells by enhancing the mitogen-activated protein kinase (MAPK) signaling pathway, especially the phosphorylation levels of the extracellular signal-regulated kinase (ERK)1/2. The ERK inhibitors showed a significant inhibitory effect in reducing ß-hexosaminidase release. Conclusion: Our results indicated that nano-SiO2 particles stimulation might synergistically activate IgE-sensitized mast cells by enhancing the MAPK signaling pathway and that nano-SiO2 particles exposure could exacerbate allergic inflammation. Our experimental results provide useful information for preventing and treating allergic diseases.

Background and fingerprint characteristics of anthropogenic 236U and137Cs in soil and road dust samples collected from Beijing and Zhangjiakou, China.

236U has attracted more attention as an environmental tracer in recent years. However, in-depth study of 236U in terrestrial environments is still rare in China. Data on 236U and 137Cs concentrations in soil and road dust samples collected from Beijing and Zhangjiakou, China were obtained to demonstrate the background and distinct characteristics of anthropogenic 236U and 137Cs. 236U and 137Cs were detected in the range of (1.10-7.90) × 107 atoms g-1 and below the method limits of detection to 5.30 Bq kg-1. A clear characteristic was observed in road dust, where 236U concentrations increased with decreasing of sample particle size. Soil samples showed an irregular characteristic, but the highest 236U concentrations were observed in particle size fraction of <0.053 mm in both samples. This phenomenon was caused by U chemical properties, higher specific surface areas and organic compounds in fine particles. Anthropogenic radionuclides fingerprint characteristics in <0.053 mm samples were specially discussed. 236U/238U atom ratios were detected in the range of (0.627-3.38) × 10-8. A weak correlation between anthropogenic 236U and natural U isotopes were observed. The intermediate correlation between 236U and 137Cs indicated somewhat distinct migration behavior of these two radionuclides in soil after release to the environment. The released amount of 236U from global fallout during the period of atmospheric nuclear weapons testing was roughly estimated to be 1300 ± 448 kg. These results could be used as fingerprint information for anthropogenic 236U migration behavior and tracer application in environment.

Distribution and potential human risk of organochlorine pesticides in market mollusks from Dalian, China.

Levels of organochlorine pesticides (OCPs) were analyzed in mollusk samples collected from markets in Dalian, China. Among 14 OCPs screened, chlordane (Chls), dichlorodiphenyltrichloroethane (DDT) and 1,2,3,4,5,6-hexachlorocyclohexane (HCH) were dominant compounds with the medians of 30.2, 5.31 and 2.03 ng/g wet weight (ww), respectively. Source analysis showed that, much higher concentrations of Chls in mollusk samples were the result of usage of the chemical in the city, HCH in samples were mainly due to historical technical HCH usage, and a small amount of fresh use of DDT might exist, causing high portion of p,p'-DDT in samples. Cumulative distribution functions for the concentrations of the selected OCPs were compared to several threshold criteria, indicating that concentrations in most mollusk samples were lower than the safe lines. The concentration data of selected OCPs were used for risk assessment, and human exposure levels were compared to noncancer and cancer benchmarks.

First report on global fallout 236U and uranium atom ratios in soils from Hunan Province, China.

More nuclear power plants continue to be built in China. Due to its long half-life, radiotoxicity and potential application as an environmental tracer, 236U is one of the most important artificial radionuclides deserving more study since activity data are important for risk assessment. However, the ultra-trace activity of 236U and its dilution by natural uranium isotopes make it difficult to distinguish its sources and there are only limited global fallout 236U data for present in Chinese environmental samples. In order to understand the background levels for uranium isotopes, especially 236U, and clarify their sources, inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was applied to analyze uranium isotopes in 48 soil samples from Hunan Province, China. The 234U, 235U, 238U and 236U concentrations were measured as 9.91-33.7, 0.312-1.43, 6.63-28.7 Bq kg-1 and (1.61-21.3) × 107 atoms g-1, while, the 236U/238U, 234U/238U and 235U/238U atom ratios were (0.470-4.91) × 10-8, (5.10-9.31) × 10-5, and (7.11-7.82) × 10-3, respectively. The uranium isotopic fractionation may be due to irrigation of the agricultural lands where the samples were collected. Considering the facts that neither previous nuclear tests nor nuclear accidents had occurred in Hunan Province and the present 236U/238U atom ratios were included in the range of global fallout values in other areas, it may be concluded that 236U in soils from Hunan Province is mainly from global fallout. To the best of the authors' knowledge, the presence of global fallout 236U in soil samples from China has been confirmed for the first time, and these values may be useful as background data for risk assessment in the future.

A review of measurement methodologies and their applications to environmental 90Sr.

The high fission yield product 90Sr has been released into the environment in large amounts due to nuclear weapon tests, nuclear power plant accidents, and nuclear fuel reprocessing industries. It is a long half-life radionuclide (28.9 y), with serious consequences to human health; hence, it is desirable to perform routine monitoring of 90Sr in environmental samples. Many 90Sr radiometric methods have been developed in the past decades, which generally require complicated separation and purification steps with a relatively long analytical time. Moreover, some nominally rapid methods usually have high method detection limits, making them unsuitable for the environmental samples with ultra-low 90Sr levels. In this review, some rapid and practical methods for 90Sr routine monitoring are summarized. Different sample pretreatments and major purification procedures for 90Sr developed in recent years, such as variable digestion methods and extraction chromatography using Sr resin or DGA resin, are especially described. Additionally, four conventional and widely used ß spectrometric and mass spectrometric methods are demonstrated. Finally, 90Sr evaluations focusing on contaminated soil and seawater samples collected after the Fukushima Daiichi Nuclear Power Plant accident, and 90Sr application as tracers for environmental behavior are also reviewed.

Chlorine levels and species in fine and size resolved atmospheric particles by X-ray absorption near-edge structure spectroscopy analysis in Beijing, China.

An understanding of the species of chlorine is crucial in the metropolis-Beijing, which is suffering serious haze pollution with high frequency. Particulate Matters (PMs) with five different sizes were collected in Beijing from July 2009 to March 2016, and characterized non-destructively by X-ray absorption near edge structure spectroscopy. PM<0.2, PM0.2-0.5 and PM>2.5 contributed for the major PMs mass in spring and summer, PM0.5-1.0 and PM1.0-2.5 contributed for the major PMs mass in autumn and winter. The concentrations of the three chlorine species were in the order of inorganic chlorine (Clinorg) > aliphatic chlorine (Clali) > aromatic chlorine (Claro), indicating that Clinorg constituted the primary chlorine fraction and less toxic Clali constituted the primary total organic chlorine (Clali + Claro, abbreviated as Clorg) in the PMs in Beijing. In addition, these three chlorine species exhibited identical seasonal variation in PM2.5: winter > autumn > spring > summer. Wet precipitation is an important factor to result in the lower mass concentrations of these three chlorine species in summer. The temporal variations of both size resolved PM mass concentrations and chlorine species concentrations suggested that the air pollution prevention and control in Beijing has just won initial success.

Tyrosine phosphorylation/dephosphorylation regulates peroxynitrite-mediated peptide nitration.

Proteins are targets of reactive nitrogen species such as peroxynitrite and nitrogen dioxide. Among the various amino acids in proteins, tyrosine and tryptophan residues are especially susceptible to attack by reactive nitrogen species. On the other hand, protein tyrosine phosphorylation has gained much attention in respect to cellular regulatory events and signal transduction. Peroxynitrite-mediated nitration of peptide YPPPPPW and phosphopeptide pYPPPPPW were studied at pH 7.4. The predominant nitrated products were separated and identified by reverse phase high performance liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS). The nitration sites were established by tandem electrospray ionization-mass spectrometry (LC-MS/MS). A regulatory effect of tyrosine phosphorylation/dephosphorylation on peptide nitration was observed. YPPPPPW was predominantly nitrated at tyrosine residue while pYPPPPPW was nitrated at tryptophan one. Our results can help in understanding the biochemical significance of the relationship of tyrosine phosphorylation and nitration in proteins.