Straw-return methods that neither negatively impact yield nor bring environmental risk are ideal patterns. To attain this goal, it is necessary to conduct field observation to evaluate the environmental influence of different straw-return methods. Therefore, we conducted a 2-year field study in 2015–2017 to investigate the emissions of methane (CH₄) and nitrous oxide (N₂O) and the changes in topsoil (0–20 cm) organic carbon (SOC) density in a typical Chinese rice-wheat rotation in the Eastern China. These measurements allowed a complete greenhouse gas accounting (net GWP and GHGI) of five treatments including: FP (no straw, plus fertilizer), FS (wheat straw plus fertilizer), FB (straw-derived biochar plus fertilizer), FSDI (wheat straw with straw-decomposing microbial inoculants plus fertilizer) and CK (control: no straw, no fertilizer). Average annual SOC sequestration rates were estimated to be 0.20, 0.97, 1.97 and 1.87 t C ha⁻¹ yr⁻¹ (0–20 cm) for the FP, FS, FB and FSDI treatments respectively. Relative to the FP treatment, the FS and FSDI treatments increased CH₄ emissions by 12.4 and 17.9% respectively, but decreased N₂O emissions by 19.1 and 26.6%. Conversely, the FB treatment decreased CH₄ emission by 7.2% and increased N₂O emission by 10.9% compared to FP. FB increased grain yield, but FS and FSDI did not. Compared to the net GWP (11.6 t CO₂-eq ha⁻¹ yr⁻¹) and GHGI (1.20 kg CO₂-eq kg⁻¹ grain) of FP, the FS, FB and FSDI treatments reduced net GWP by 12.6, 59.9 and 34.6% and GHGI by 10.5, 65.8 and 37.7% respectively. In rice-wheat systems of eastern China, the environmentally beneficial effects of returning wheat straw can be greatly enhanced by application of straw-decomposing microbial inoculants or by applying straw-derived biochar.

Marine polychaetes and fish are known to ingest polystyrene microparticles in the environment. Laboratory microplastic feeding experiments have demonstrated that plastic may release endocrine-disrupting compounds such as diethylhexyl phthalate (DEHP), which can cause adverse effects in both vertebrates and invertebrates. In order to determine the influence of size and digestive conditions on the desorption of DEHP and other plasticizers to polychaetes and fish, we exposed polystyrene particles of various sizes under invertebrate and vertebrate digestive conditions (vertebrate mimic; pepsin, pH = 2.0, 24 °C, invertebrate mimic; Na taurocholate pH = 7, 18 °C). Estrogen receptor activation and concentrations of 12 plasticizers were measured in the extracts. DEHP, bisphenol S and 4-tert-octylphenol were the only compounds detected. Simulated vertebrate gut digestion did not significantly enhance the release of chemicals nor estrogenic activity. However, a 6.3 ± 2.0-fold increase in the concentration of DEHP was observed in extracts from invertebrate gut conditions (Mean ± SD; N = 24, p < 0.0001). Additionally, estimated particle surface area was positively correlated with estrogenic activity across all treatment types (r = 0.85, p < 0.0001). Overall, these data indicate an elevated bioaccessibility of DEHP may occur in invertebrates, and size-dependent desorption of uncharacterized estrogenic compounds from plastic suggest additional complexity when considering the risks of MP to aquatic organisms.

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.

Rapid industrialization in China during the last three decades has resulted in widespread contamination of Cd in agricultural soils. A considerable proportion of the rice grain grown in some areas of southern China has Cd concentrations exceeding the Chinese food limit, raising widespread concern regarding food safety. In this review, we summarize rice grain Cd concentrations in national Chinese markets and in field surveys from contaminated areas, and analyze the potential health risk associated with increased dietary Cd intake. For subsistence rice farmers living in some contaminated areas of southern China who mainly consume locally-produced Cd-contaminated rice, their estimated dietary Cd intake is now comparable to that for the population in the region of Japan where the Itai-Itai disease was first reported. Interventions must be taken urgently to reduce Cd intake for these farmers. We also analyze i) the main reasons causing elevated grain Cd concentrations in southern China, ii) the dominant biogeochemical processes controlling the solubility of Cd in paddy soils, and iii) molecular mechanisms for the uptake and translocation of Cd in rice plants. Based on these analyses, we propose a number of countermeasures to address soil Cd contamination, including i) mitigation of Cd transfer from paddy soils to rice grain, and ii) intervention in those farmers who consume home-grown Cd-contaminated rice. Liming to increase soil pH to 6.5 and gene editing biotechnology are effective strategies to decrease Cd accumulation in rice grain. For these local farmers with high-Cd exposure risk, local governments should monitor the Cd concentration in their home-grown rice and exchange those high-Cd rice with low-Cd rice in order to reduce their dietary Cd intake.

Elemental concentrations of ambient aerosols are commonly sampled over 12–24 h, and the low time resolution puts a great limit on current understanding about the temporal variations and source apportionment based on receptor models. In this work, hourly-resolved concentrations of eighteen elements in PM₂.₅ at an urban site in Nanjing, a megacity in Yangtze River Delta of east China, were obtained by using a Xact 625 ambient metals monitor from 12/12/2016 to 12/31/2017. The influence of traffic activities was clearly reflected by the spikes of crustal elements (e.g., Fe, Ca, and Si) in the morning rush hour, and the firework burning and sandstorm events during the sampling periods were tracked by sharp enrichment of Ba, K and Fe, Ca, Si, Ti in PM₂.₅, respectively. To evaluate the advantage of hourly-resolved elements data in identifying impacts from specific emission sources, positive matrix factorization (PMF) analysis was performed with the 1-h data set (PMF₁₋ₕ) and 23-h averaged data (PMF₂₃₋ₕ), respectively. The 4- and 6-factor PMF₂₃₋ₕ solutions had similar factor profiles and consistent factor contributions as the corresponding PMF₁₋ₕ solutions. However, due to the limit in inter-sample variability, PMF analysis with 23-h average data misclassified some major (e.g., K, Fe, Zn, Ca, and Si) and trace (e.g., Pb) elements in factor profiles, resulting in different absolute factor contributions between PMF₂₃₋ₕ and PMF₁₋ₕ solutions. These results suggested the use of high time-resolved data to obtain valid and robust source apportionment results.

Atmospheric deposition, either dry or wet, has been identified as an important pathway of mercury (Hg) input to terrestrial and aquatic systems. Although East Asia is the major atmospheric Hg emission source region, very few studies have been conducted to quantify atmospheric Hg deposition in its downwind region. In this study, 8-year (2009–2016) atmospheric Hg dry deposition was reported at the Lulin Atmospheric Background Station (LABS), a high mountain forest site in central Taiwan. Dry deposition of speciated Hg was estimated using a bi-directional air-surface flux exchange model for gaseous elemental mercury (GEM) and dry deposition models for gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM), making use of the monitored speciated atmospheric Hg concentrations. Annual total Hg dry deposition ranged from 51.9 to 84.9 μg m−2 yr−1 with a multi-year average of 66.1 μg m−2 yr−1. Among the three forms of atmospheric Hg, GEM was the main contributor to the total dry deposition, contributing about 77.8% to the total, due to the high density of forest canopy as well as the much higher concentration of GEM than GOM and PBM at LABS. Mercury dry deposition is higher in winter and spring than in summer and fall, partly due to the elevated Hg concentrations associated with air masses from East and Southeast Asia where with high atmospheric Hg emissions. The mean annual dry/wet deposition ratio of 2.8 at LABS indicated that Hg deposition to forest landscape was governed by dry rather than wet deposition.

The effects of arsenic (As), cadmium (Cd) and zinc (Zn) on each other's uptake and oxidative stress in As-hyperaccumulator Pteris vittata were investigated. P. vittata plants were exposed to 50 μM As, Cd and/or Zn for 15 d in 0.2-strength Hoagland solution. When applied alone, P. vittata accumulated 185 mg kg⁻¹ As, 164 mg kg⁻¹ Cd and 327 mg kg⁻¹ Zn in the fronds. While Cd and Zn did not impact each other's uptake, As affected Cd and Zn uptake. Whereas As decreased Zn uptake, Zn affected As speciation in P. vittata fronds, with more arsenate (AsV) than arsenite (AsIII) being present. At 50 μM As, 75 μM Zn increased As accumulation in P. vittata fronds by 10 folds to 2363 mg kg⁻¹ compared to 50 μM Zn. Although AsV was the predominant As species in all tissues, Cd enhanced AsIII levels in the fronds but increased AsV in the roots. Co-exposure of Cd + Zn elevated oxidative stress basing on thiobarbituric acid reactive substances, H₂O₂ content, Evans blue dye uptake, membrane injury index and reactive oxygen species (ROS) relative to single metal. By lowering Cd and Zn concentrations in P. vittata fronds, As reduced the associated stress comparative to Cd or Zn treatment. The results enhance our understanding of the mechanisms underlying the interactions between As, Cd and Zn in As-hyperaccumulator P. vittata.

Biochar application to fertilized paddy soils has been recommended as an effective countermeasure to mitigate methane (CH₄) emissions, but its mechanism and effective duration has not yet been adequately elucidated. A laboratory incubation experiment was performed to gain insight into the combined effects of fresh and six-year aged biochar on potential methane oxidation (PMO) in paddy soils with ammonium or nitrate-amendment. Results showed that both ammonium and nitrate were essential for CH₄ oxidation though high ammonium (4 mM) inhibited PMO as compared to low ammonium (1 mM and 2 mM), and that nitrate was better in promoting PMO than ammonium. Moreover, ammonium-amendment promoted type I pmoA, and nitrate-amendment enhanced type II pmoA abundance. Both fresh and aged biochar increased PMO as well as nitrification by enhancing the total, type I and type II methanotrophs as compared to the control. Increased soil PMO with mineral N input in both six-year aged biochar and fresh biochar amendment, indicating that biochar mitigated CH₄ by promoting PMO for prolonged period in fertilized paddy soils.

Microplastics (plastic particles <5 mm) are a contaminant of increasing ecotoxicological concern in aquatic environments, as well as for human health. Although microplastic pollution is widespread across the land, water, and air, these environments are commonly considered independently; however, in reality are closely linked. This study aims to review the scientific literature related microplastic research in different environmental compartments and to identify the research gaps for the assessment of future research priorities. Over 200 papers involving microplastic pollution, published between 2006 and 2018, are identified in the Web of Science database. The original research articles in ‘Environmental Sciences’, ‘Marine/Freshwater Biology’, ‘Toxicology’, ‘Multidisciplinary Sciences’, ‘Environmental Studies’, ‘Oceanography’, ‘Limnology’ and ‘Ecology’ categories of Web of Science are selected to investigate microplastic research in seas, estuaries, rivers, lakes, soil and atmosphere. The papers identified for seas, estuaries, rivers and lakes are further classified according to (i) occurrence and characterization (ii) uptake by and effects in organisms, and (iii) fate and transport issues. The results reveal that whilst marine microplastics have received substantial scientific research, the extent of microplastic pollution in continental environments, such as rivers, lakes, soil and air, and environmental interactions, remains poorly understood.

Microplastic (MP) pollution is everywhere. In terrestrial environments, microfibres (MFs) generated from textile laundering are believed to form a significant component of MPs entering soils, mainly through sewage sludge and compost applications. The aim of this study was to assess the effect of MFs on a keystone soil organism. We exposed the earthworm Lumbricus terrestris to soil with polyester MFs incorporated at rates of 0, 0.1 and 1.0 %w/w MF for a period of 35 days (in the dark at 15 °C; n = 4 for each treatment). Dried plant litter was applied at the soil surface as a food source for the earthworms. We assessed earthworm vitality through mortality, weight change, depurate production and MF avoidance testing. In addition, we measured stress biomarker responses via the expression of metallothionein-2 (mt-2), heat shock protein (hsp70) and superoxide dismutase (sod-1). Our results showed that exposure and ingestion of MFs (as evidenced by subsequent retrieval of MFs within earthworm depurates) were not lethal to earthworms, nor did earthworms actively avoid MFs. However, earthworms in the MF1.0% treatment showed a 1.5-fold lower cast production, a 24.3-fold increase in expression of mt-2 (p < 0.001) and a 9.9-fold decline in hsp70 expression (p < 0.001). Further analysis of soil and MF samples indicated that metal content was not a contributor to the biomarker results. Given that burrowing and feeding behaviour, as well as molecular genetic biomarkers, were modulated in earthworms exposed to MFs, our study highlights potential implications for soil ecosystem processes due to MF contamination.