Vital roles of soil microbes in driving terrestrial nitrogen immobilization.

Nitrogen immobilization usually leads to nitrogen retention in soil and, thus, influences soil nitrogen supply for plant growth. Understanding soil nitrogen immobilization is important for predicting soil nitrogen cycling under anthropogenic activities and climate changes. However, the global patterns and drivers of soil nitrogen immobilization remain unclear. We synthesized 1350 observations of gross soil nitrogen immobilization rate (NIR) from 97 articles to identify patterns and drivers of NIR. The global mean NIR was 8.77 ± 1.01 mg N kg-1  soil day-1 . It was 5.55 ± 0.41 mg N kg-1  soil day-1 in croplands, 15.74 ± 3.02 mg N kg-1  soil day-1 in wetlands, and 15.26 ± 2.98 mg N kg-1  soil day-1 in forests. The NIR increased with mean annual temperature, precipitation, soil moisture, soil organic carbon, total nitrogen, dissolved organic nitrogen, ammonium, nitrate, phosphorus, and microbial biomass carbon. But it decreased with soil pH. The results of structural equation models showed that soil microbial biomass carbon was a pivotal driver of NIR, because temperature, total soil nitrogen, and soil pH mostly indirectly influenced NIR via changing soil microbial biomass. Moreover, microbial biomass carbon accounted for most of the variations in NIR among all direct relationships. Furthermore, the efficiency of transforming the immobilized nitrogen to microbial biomass nitrogen was lower in croplands than in natural ecosystems (i.e., forests, grasslands, and wetlands). These findings suggested that soil nitrogen retention may decrease under the land use change from forests or wetlands to croplands, but NIR was expected to increase due to increased microbial biomass under global warming. The identified patterns and drivers of soil nitrogen immobilization in this study are crucial to project the changes in soil nitrogen retention.

Vertical distributions and potential contamination assessment of seldom monitored trace elements in three different land use types of Yellow River Delta.

The Yellow River Delta (YRD) is the second largest petrochemical base in China and the impact of human activities has been continuously increasing in recent decades, however, the contamination status of seldom monitored trace elements (SMTEs) in YRD has rarely been reported. This study evaluated the levels, vertical distributions, contamination status and sources of SMTEs in soil samples of three different land use types in YRD. The results indicated that the vertical distributions of SMTEs contents showed a gradually upward increasing trend for the soil profiles of black locust forest, while the SMTEs contents displayed a gradually upward decreasing trend for the soil profiles of cotton field. However, the SMTEs contents in the oil field area showed no significant difference among different depths. The vertical distributions of SMTEs were very likely related to the anthropogenic disturbance in the later stage. The environmental pollution status assessment of SMTEs showed obvious enrichment of Cs, Sn, and U in the soils of YRD. Moreover, the potential source analysis based on multivariate statistical methods indicated that Ga, Rb, Cs, Sc, Sn, Tl, Be, Bi, Ca and Mo were clustered together and positively correlated with Al, Fe, Mg and K, and may be mainly associated with geochemical weathering process, while the Ce, La, Th, U, Nb, Ta, and Hf may be impacted by both natural process and human activities. Though the SMTEs pollution status was not very serious, our results highlighted the non-negligible influence of anthropogenic activities on vertical distributions of SMTEs in three different land use types from YRD. Our results provide valuable information for understanding the vertical distribution and pollution status of SMTEs in YRD.

Polycyclic aromatic hydrocarbons and their halogenated derivatives in soil from Yellow River Delta: Distribution, source apportionment, and risk assessment.

The distribution of polycyclic aromatic hydrocarbons (PAHs) and halogenated PAHs (HPAHs) in surface soils from the petroleum industrial area of the Yellow River Delta (YRD) in China were investigated. The total concentrations of 16 PAHs ranged from 19.6 to 1560 ng/g, while 22 HPAHs ranged from 2.44 to 14.9 ng/g. Moreover, a high degree of spatial distribution heterogeneity was observed for both PAHs and HPAHs, which is likely attributed to the distinct industrial activities in studied area. The combustion of biomass and petroleum were identified as primary sources of soil PAHs and HPAHs in the YRD. Furthermore, benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[g,h,i]perylene exhibited high ecological risks (with risk quotients of 1.47, 1.44, and 1.02, respectively) in specific sites within the YRD. Considering the high toxicity of HPAHs and their potential joint environmental effects with PAHs, continuous attention should be directed towards the environmental risks associated with both PAHs and HPAHs.

Biotoxicity responses of zebrafish in environmentally relevant concentration of di (2-ethylhexyl) phthalate.

As an emerging environmental contaminant, di (2-ethylhexyl) phthalate (DEHP) is widely present in the aquatic environment, however, the effects and underlying mechanisms of DEHP on the aquatic organisms are poorly understood. This study systematically investigated the ecotoxicity induced by chronic exposure to environmental relevant concentrations of DEHP (0.03 mg/L, 0.1 mg/L, and 0.3 mg/L) on zebrafish brain. Results indicated that DEHP exposure significantly increased the levels of ROS and disturbance of the antioxidant enzymes activities in the brain, which may further enhance lipid peroxidation and DNA damage. Furthermore, acetylcholinesterase activity was first stimulated and inhibited by exposure to DEHP, and the antioxidant and apoptosis related genes were mainly upregulated. Risk assessment indicated that the ecotoxicity of DEHP on the zebrafish showed an "enhancement-reduction" trend as the exposure time was prolonged. Overall, these results provided new insights and useful information to ecological risk assessment and environmental management of DEHP pollution.

Comprehensive assessment of seldom monitored trace elements contamination and its anthropogenic impact record in a sediment core from the North Yellow Sea.

The environmental status of seldom monitored trace elements (SMTEs) has rarely been reported in the North Yellow Sea (NYS). This study investigated the levels, sources and ecological risks of 18 SMTEs in a 209-cm-long sediment core from NYS. The concentrations of SMTEs exhibited a gradual increasing trend in the upper 70 cm. Based on the assessment results of enrichment factor (EF), geo-accumulation index (Igeo) and contamination factor (CF), obvious enrichment of Cs, Li, and U was observed for the NYS sediments, indicating possible anthropogenic sources, which are consistent with the geochemical background normalized patterns. Moreover, the pollution load index (PLI) values ranged from 0.93 to 1.24 and showed a steadily increasing trend in the upper 70 cm part, indicating gradual deterioration of environment in NYS. Combined with the multivariate statistical analysis results and PLI variations, the first principal component (PC1) with high positive loading on Be, Cs, Ga, Hf, In, Li, Nb, Rb, Sc, Ta and Tl was very likely an "anthropogenic factor". Therefore, the historical anthropogenic impact record in the NYS was reconstructed based on the PC1 scores, which indicated significant anthropogenic influence over the past 300 years. This study provides valuable information for understanding the pollution history of SMTEs and historical record of anthropogenic impact in the NYS.

Oxidative stress and DNA damage in earthworms induced by methyl tertiary-butyl ether in natural soils.

Adverse effects of methyl tertiary-butyl ether (MTBE) have been noticed at different trophic levels by international researchers. However, there was unclear evidence about its effects on oxidative stress and DNA damage in earthworms. In this study, earthworms were cultivated in various doses of MTBE (0.0 mg/kg, 10.0 mg/kg, 30.0 mg/kg, and 60.0 mg/kg) contaminated agricultural soil for 7 days, 14 days, 21 days, and 28 days, respectively. The result showed that the reactive oxygen species (ROS) content of earthworms significantly increased in MTBE treatment groups compared to the control group. In MTBE treatment groups, the activities of superoxide dismutase, catalase, peroxidase, and glutathione S-transferase were significantly activated at the exposure of 7 days, which increased by 36.3-78.9%, 51.8-97.3%, 36.5-61.9%, and 12.0-54.8%, respectively. Then, the activities of these defense enzymes showed various changes following the changes in exposure times and MTBE concentrations. Especially in the 60.0 mg kg-1 group, both antioxidant enzymes and GST were still significantly activated at the exposure of 14 days and then significantly inhibited at the exposure of 28 days. The analysis of olive tail moment showed significant DNA damage in the 10.0 mg kg-1 group at the exposure of 28 days, and this damage in 30.0 mg/kg and 60.0 mg/kg groups was found at the exposure of 7 days. This result was consistent with the malondialdehyde accumulation in earthworms. Additionally, the analysis of IBRv2 showed the effects of MTBE treatments on earthworms in dose- and time-dependent manners. This study helps better to understand the effects of MTBE on soil invertebrate animals and provide theoretical support for soil protection in governing MTBE application.

Evaluation of the biological response of propofol in zebrafish (Danio rerio): Focusing on biochemical, transcriptional, and molecular level.

Propofol, one of the most widely used intravenous anesthetic in clinical practice, has been reported to impair cognitive and memory function. However, the toxicological effects of propofol on aquatic organisms are still poorly understood. This study explored the toxic effects of chronic propofol exposure (0.008, 0.04, and 0.2 mg L-1) on adult zebrafish from biochemical, transcriptional, and molecular level after 7, 14, 21 and 28 days of exposure. Results indicated that the reactive oxygen species (ROS) levels were significantly upregulated during the 28 days exposure period, and excessive ROS caused lipid peroxidation, resulting in increased malondialdehyde (MDA) contents in the zebrafish brain. In order to relieve the oxidative damage induced by the excessive ROS, the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT)) were significantly activated, and detoxification enzyme (glutathione S-transferase, GST) activities showed an "activation-inhibition" trend. However, the antioxidant enzymes and detoxification enzyme system could not eliminate the excessive ROS in time and thus caused DNA damage in zebrafish brain. The olive tail moment (OTM) values displayed a "dose-response" relationship with propofol concentrations. Meanwhile, the transcription of related genes of Nrf2-Keap1 pathway was activated. Further molecular simulation experiments suggested that propofol could directly combine with SOD/CAT to change the activity of its biological enzyme. These findings indicated that zebrafish could regulate antioxidant capacity to combat oxidative stress at the early exposure stage, but the activity of antioxidant enzymes were significantly inhibited with the increase of propofol exposure time. Our results are of great importance for understanding toxicological effects of propofol on aquatic organisms.

Environmentally relevant concentrations of butyl benzyl phthalate triggered oxidative stress and apoptosis in adult zebrafish (Danio rerio) liver: Combined analysis at physiological and molecular levels.

Butyl benzyl phthalate (BBP), a typical phthalate plasticizer, is frequently detected in aquatic environments, but its possible effects on fish liver are unknown. In this study, adult zebrafish were exposed to 5-500 µg/L BBP and cultured for 28 days. The toxicity mechanism of environmentally relevant concentrations of BBP in the liver was explored using integrated biomarker response (IBR), molecular docking, and histopathological analysis, based on the tests of oxidative stress, apoptosis, and tissue damage, respectively. The results revealed that exposure to 500 µg/L BBP caused lipid peroxidation and DNA damage and induced inflammatory responses in the liver and intestinal tissues. The accumulation of reactive oxygen species (ROS) is the primary manifestation of BBP toxicity and is accompanied by changes in the activities of antioxidant and detoxification enzymes. Notably, the pro-apoptotic genes (p53 and caspase-3) were still significantly upregulated in the 50 µg/L and 500 µg/L treatment groups on day 28. Moreover, BBP interfered with apoptosis by forming a stable complex with apoptosis proteins (P53 and Caspase-3). Our findings are helpful for understanding the toxicity mechanisms of BBP, which could further promote the assessment of the potential environmental risks of BBP.

Effects of diisononyl phthalate exposure on the oxidative stress and gut microorganisms in earthworms (Eisenia fetida).

Phthalate esters (PAEs) are widely used as plasticizers and can be ubiquitously detected in environment. However, the toxic effects and mechanisms of diisononyl phthalate (DINP) on earthworms are still poorly understood. In this study, earthworms (Eisenia fetida) were exposed to DINP at various doses (0, 300, 600, 1200, and 2400 mg/kg) to investigate their subchronic toxicity. The results demonstrated that the reactive oxygen species (ROS) levels displayed an "increase-decrease" trend with the increasing DINP doses after DINP exposure on days 7, 14, 21, and 28. The malondialdehyde (MDA) content increased with increasing DINP doses on days 7, 14, and then decreased on days 21, 28. The values of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) showed similar variation patterns and reached a maximum level on 21 d. Moreover, on day 28, the SOD and CAT gene expression levels were upregulated, while the GST gene expression levels were downregulated. Meanwhile, 16S rRNA genes of E. fetida gut bacteria and surrounding soil bacteria were measured after 28 days of exposure to DINP. The Chao index of E. fetida gut bacteria decreased when the treatment with the highest concentration (2400 mg/kg) was applied. At the phylum level, the abundance of Chloroflexi was significantly lower in the gut of E. fetida. In addition, the abundance of Proteobacteria at the phylum level and Ottowia at the genus level significantly increased in the surrounding soil. Overall, our results shed light on the toxic mechanism of DINP at biochemical, molecular, and omics levels, and contributed to a better understanding of the ecotoxicity of DINP.

Spatial distribution, sources and risk assessment of potentially toxic elements contamination in surface soils of Yellow River Delta, China.

The contamination status and ecological risk of soil potentially toxic elements (PTEs) in Yellow River Delta (YRD) are still poorly understood. Thirty surface soil samples were collected in YRD, determined for contents of PTEs, and assessed using four kinds of proxies. Results indicated that PTEs contents basically met the Environmental Quality Standard for Soils, and spatial heterogeneity of PTEs was not distinctive except for a few sampling sites. Results of geo-accumulation index (Igeo) and enrichment factor (EF) indicated significant enrichment of As and Sb in YRD. The multivariate analysis results distinguished the possible sources of these PTEs and demonstrated that sources of Ag, As, Cd, Cu, Pb, Sb and Zn could be influenced by anthropogenic activities (industrial and agricultural sources). Moreover, Ni, Cr and As had relatively high contributions to sum of toxicity units (ΣTUs). This study provides basic information for understanding soil PTEs contamination status of YRD.

Reconstruction, assessment, and calibration of potential toxic elements (PTEs) in a 3500-year-long sedimentary record off the northern coast of Shandong Peninsula, China.

The marine environment of coastal Shandong Peninsula has been significantly influenced by anthropogenic activities due to the rapid industrialization and economic development in the past decades. However, the sedimentary records of PTEs in the North Yellow Sea have rarely been reported. In this study, a 209-cm-long sediment core was collected off the northern coast of Shandong Peninsula, analyzed for grain size and elemental compositions, and assessed using EF, Igeo and several numerical Sediment Quality Guidelines (SQGs). The EF and Igeo results suggested that sediment profile could be slightly to moderately polluted with As and Sb, while ecological risk assessment using SQGs showed that As, Cr, Sb and Ni in the sediment profile may have a moderate incidence of toxicity. Our results highlighted the nonnegligible ecological risk of Sb in sediments of North Yellow Sea, and great importance should be attached to the fact that many PTEs may also pose a potential ecological risk to the aquatic organisms, even though their concentrations meet the standards of the Marine Sediments Quality (MSQ). Moreover, the reconstructed PTEs record showed a dramatic increase over the past 250 years, which could be related to the intense anthropogenic activities since the Industrial Revolution. The multivariate statistical analysis results indicated that Co, Cr, Cu, Pb, Ni and Zn may be mainly related to the natural origin, while As and Sb could be influenced by both natural weathering sources and anthropogenic activities. This study provides more insights into the historical record of PTEs in the North Yellow Sea, and lays foundation for future comparison of PTEs sedimentary records.

Potential influence of rapid climate change on elemental geochemistry distributions in lacustrine sediments-A case study at a high Arctic site in Ny-Ålesund, Svalbard.

Metal contamination has become an increasingly severe environmental issue due to intense anthropogenic activities in recent decades. Many studies have reported a rapidly increasing trend of heavy metal contents in sedimentary records. In this study, two lacustrine sediment cores (LDL and YL) far away from scientific research stations were collected in Ny-Ålesund and analyzed for the vertical distributions of 17 elemental concentrations (Cu, Zn, Pb, Co, Ni, Cr, Sr, Ba, Mn, P, Ti, K2O, Na2O, CaO, MgO, Fe2O3, Al2O3), CIA and TOC contents. The results indicated that only the proxies Pb, P, CaO, TOC, and CIA showed an increasing trend in the upper 7 cm section of the sediment cores, while most of the elements' concentrations decreased towards the surface. The rapid increase of TOC contents is likely related to the climate warming over the past 200 years, which promotes the prosperity of vegetation and thus leads to more input of organic matter into the lakes. Moreover, a large number of seabirds live around the sampling position and the seabird guano contains high concentrations of P, which could be regarded as an important nutrient source for vegetation. Additionally, the rapid climate warming could accelerate the chemical weathering rates, and thus lead to increased CaO contents in the sediment profiles according to its geological background. Therefore, the concentrations of other elements are very likely diluted by the high contents of organic matter and CaO in the upper part of the sediment cores. It is noteworthy that the rapidly increasing trend of Pb contents are related to the gas-oil powered generators in Ny-Ålesund and long-range atmospheric transport from Europe. This study highlighted the nonnegligible influence of climate warming on the inorganic elemental geochemistry distributions in remote lakes.

Historical records and contamination assessment of potential toxic elements (PTEs) over the past 100 years in Ny-Ålesund, Svalbard.

Ny-Ålesund has been significantly impacted by anthropogenic activities (e.g. coal mining, scientific research, tourist shipping) over the past 100 years. However, the studies of potential toxic elements (PTEs) contamination in Ny-Ålesund currently mainly focus on surface soil or surface fjord sediments, and little is known about the history and status of PTEs contamination over the past 100 years. In this study, we collected a palaeo-notch sediment profile YN, analyzed the contents of six typical PTEs (Cu, Pb, Cd, Hg, As, Se) in the sediments, and assessed the historical pollution status in Ny-Ålesund using the pollution load index, geo-accumulation index and enrichment factor. The results showed that the contents of PTEs over the past 100 years increased rapidly compared with those during the interval of 9400-100 BP. In addition, Pb, Cd and Hg showed a clear signal of enrichment and were the main polluters among the PTEs analyzed. The contamination was likely linked to gas-oil powered generators, coal mining, research station, tourist shipping and long-range transport of pollutants.

Levels, sources and influence mechanisms of heavy metal contamination in topsoils in Mirror Peninsula, East Antarctica.

Heavy metal contaminants in Mirror Peninsula, East Antarctica, have rarely been studied and the source and influencing factors are poorly understood. We sampled a grid of 189 topsoil samples from Mirror Peninsula and analyzed the concentrations of Zn, Cu, U, Cr, Ga, Pb, Hg, Se and As; we also calculated the chemical index of alteration (CIA), a proxy of weathering. The results show that the distributions of Cr, Ga, Cu, and Zn are associated with weathering; the distributions of As and Pb are related to vehicle use and unloading activities at the wharfs, respectively; and the distribution of Hg is likely associated with both anthropogenic impacts and biological activity. The contamination level of these heavy metals in Mirror Peninsula is relatively low and within the controllable range. Both weathering processes and anthropogenic impacts can cause the enrichment of heavy metals; thus reliable source apportionment is crucial in studying heavy metal enrichment and contamination.

Holocene ENSO variability in the South China Sea recorded by high-resolution oxygen isotope records from the shells of Tridacna spp.

The El Niño-Southern Oscillation (ENSO) is the principal climatic system in the modern Pacific Ocean, and it potentially influences the global climate. The South China Sea (SCS), in the western tropical Pacific, is significantly affected by ENSO activity. We have conducted a high-resolution oxygen isotope study of the shells of one modern and four fossil Tridacna from the Xisha Islands in the SCS. The results for the modern sample reveal that the shells of Tridacna are a good proxy of ENSO variability. We used the results of the oxygen isotope composition of four fossil Tridacna to produce high-resolution records of ENSO activity during four time slices in the Holocene. The results indicate that ENSO variability in the early Holocene was comparable to that of today, and that a minimum in the frequency and intensity of ENSO activity occurred in the mid Holocene. These findings are consistent with paleoclimatic results from corals, mollusks and sedimentary records. However, the observed extremely low frequency and moderate ENSO intensity at 4.7 ka indicate an anomalous pattern of ENSO changes within this interval of climatic transition. In addition, seasonal temperature variations during the Holocene were different from those of today and extreme seasonality may also occur during warmer periods.

Assessment of heavy metal contamination from penguins and anthropogenic activities on Fildes Peninsula and Ardley Island, Antarctic.

Fildes Peninsula, with a high density of scientific stations, has been significantly impacted by anthropogenic activities. However, the contamination from penguins, a biovector that transports pollutants from ocean to land, has seldom been assessed. In this study, 32 lacustrine surface sediment samples on Fildes Peninsula and 8 lacustrine surface sediment samples on Ardley Island were collected to determine Cu, Zn, Pb, Ni, Cr, Cd, Co, Sb, Hg and P levels. The results showed that the heavy metal contents of lacustrine sediments on Ardley Island are significantly higher than those on Fildes Peninsula. The contaminants on Fildes Peninsula are mainly derived from anthropogenic activities, while the contaminants on Ardley Island are transported to the lacustrine sediments in the form of penguin guanos after a series of biomagnification in the food chain. The results indicated that the impact of penguin-transported contamination on Antarctic environment outweighs human activities near scientific stations in some areas. Therefore, more attention should be paid to the impacts of Antarctic animals on the Antarctic environment.