Copper oxide nanoparticles (CuO-NP) are used as an efficient alternative to conventional Cu in agriculture and might end up in soils. They show a high toxicity towards cells and microorganisms, but only low toxicity towards soil invertebrates. However, most existing soil ecotoxicological studies were conducted in a sandy reference soil and at test concentrations ≥100 mg Cu/kg soil. Therefore, there is a knowledge gap concerning the effect of soil texture on the toxicity of CuO-NP at lower, more realistic test concentrations. In our study, a sandy reference soil and three loamy soils were spiked with CuO-NP at up to four concentrations, ranging from 5 to 158 mg Cu/kg. We investigated 28-day reproduction as well as weight and Cu content after 14-day bioaccumulation and subsequent 14-day elimination for the springtail Folsomia candida. For the first time we analysed the size distribution of CuO-NP in aqueous test soil extracts by single particle-ICP-MS which revealed that the diameter of CuO-NP significantly increased with increasing concentration, but did not vary between test soils. Negative effects on reproduction were only observed in loamy soils, most pronounced in a loamy-acidic soil (−61%), and they were always strongest at the lowest test concentration. The observed effects were much stronger than reported by other studies performed with sandy soils and higher CuO-NP concentrations. In the same soil and concentration, a moderate impact on growth (−28%) was observed, while Cu elimination from springtails was inhibited. Rather than Cu body concentration, the diameter of the CuO-NP taken up, as well as NP-clay interactions might play a crucial role regarding their toxicity. Our study reports for the first time toxic effects of CuO-NP towards a soil invertebrate at a low, realistic concentration range. The results strongly suggest including lower test concentrations and a range of soil types in nanotoxicity testing.

Land application of biosolids is a major route for the introduction of silver (Ag) into the terrestrial environment. Previous studies have focused on the risks from Ag to the human food chain but there is still a lack of quantitative information on the flow of biosolid-borne Ag in the soil-crop system. Two long-term field experiments were selected to provide contrasting soil properties and tillage crops to investigate the fate of Ag from sequentially applied biosolids. Biosolid-borne Ag accumulated in the soil and < 1‰ of applied Ag was taken up by the crops. The biosolid-borne Ag also migrated down and accumulated significantly (p < 0.05) in the soil profile to a depth of 60–80 cm at an application rate of 72 t biosolids ha⁻¹. Soil texture significantly affected the downward transport of biosolid-borne Ag and the migration of Ag appeared to be more pronounced in a soil profile with a low clay content. Moreover, loss of Ag by leaching may not be related to the biosolid application rate. Leaching losses of Ag may have continued for some time after biosolid amendment was suspended. The results indicate that soil texture may be a key factor affecting the distribution of biosolid-borne Ag in the soil-crop system.

Knowledge of the transport and fate of pathogenic Escherichia coli, especially in the areas contaminated with crude oil, is required to assess contamination of shallow groundwater resources. The present study aims to investigate the effect of crude oil-mediated water repellency on the movement of nalidixic acid-resistant Escherichia coli strain (E. coli NAR) and bromide (Br) as an inert tracer in two soil types. The soils were contaminated at three levels of 0, 0.5 and 1% w/w of total petroleum hydrocarbons (TPHs) using crude oil. Steady-state saturated flow in the soil columns was controlled using a tension infiltrometer. Leaching experiments were conducted through the columns of repacked (un-weathered) and physically-weathered clay loam (CL) and sandy loam (SL) soils. The columns leachate was sampled at specific times for 4 pore volumes. The shape of breakthrough curves for the E. coli NAR and Br depended on soil texture and structure and the TPHs level. Preferential flow in the crude oil-mediated water-repellent soils facilitated the transport of contaminants especially E. coli NAR. Filtration coefficient and relative adsorption index of bacteria were greatest in the repacked CL soils and were lowest in the weathered SL soils. Discontinuity of soil pores and lower flow velocity resulted in greater filtration of E. coli NAR in the repacked CL soil than other treatments. Physical weathering induced the formation of aggregates which reduced soil particle surfaces available for retention of water-repellent oil and contaminants. Movement of both bacteria and Br tracer in the weathered SL soil with 1% TPHs was higher than other treatments. This finding was attributed to low specific surface area, continuity of the pores and water repellency-mediated preferential pathways in the weathered SL soil columns. Our findings implied that shallow groundwater resources could be very sensitive to microbial contamination particularly in the oil-mediated water-repellent soils.

Rhizospheric microbes play important roles in plant growth and heavy metals (HMs) transformation, possessing great potential for the successful phytoremediation of environmental pollutants. In the present study, the rhizosphere of Elsholtzia haichowensis Sun was comprehensively studied to uncover the influence of environmental factors (EFs) on the whole microbial communities including bacteria, fungi and archaea, via quantitative polymerase chain reaction (qPCR) and high-throughput sequencing. By analyzing molecular ecological network and multivariate regression trees (MRT), we evaluated the distinct impacts of 37 EFs on soil microbial community. Of them, soil pH, HMs, soil texture and nitrogen were identified as the most influencing factors, and their roles varied across different domains. Soil pH was the main environmental variable on archaeal and bacterial community but not fungi, explaining 25.7%, 46.5% and 40.7% variation of bacterial taxonomic composition, archaeal taxonomic composition and a-diversity, respectively. HMs showed important roles in driving the whole microbial community and explained the major variation in different domains. Nitrogen (NH4-N, NO3-N, NO2-N and TN) explained 47.3% variation of microbial population composition and 15.9% of archaeal taxonomic composition, demonstrating its influence in structuring the rhizospheric microbiome, particularly archaeal and bacterial community. Soil texture accounted for 10.2% variation of population composition, 28.9% of fungal taxonomic composition, 19.2% of fungal a-diversity and 7.8% of archaeal a-diversity. Rhizosphere only showed strong impacts on fungi and bacteria, accounting for 14.7% and 4.9% variation of fungal taxonomic composition and bacterial a-diversity. Spatial distance had stronger influence on bacteria and archaea than fungi, but not as significant as other EFs. For the first time, our study provides a complete insight into key influential EFs on rhizospheric microbes and how their roles vary across microbial domains, giving a hand for understanding the construction of microbial communities in rhizosphere.

Generic biomarkers are needed to assess environmental risks in metal polluted soils. We assessed the strength of the relationship between earthworm energy reserves and metal availability under conditions of cocktail of metals at low doses and large range of soil parameters. Aporrectodea caliginosa was exposed in laboratory to a panel of soils differing in Cd, Pb and Zn total and available (CaCl2 and EDTA-extractable) concentrations, and in soil texture, pH, CEC and organic-C. Glycogen, protein and lipid contents were recorded in exposed worms. Glycogen contents were not linked to the explaining variables considered. Variable selection identified CaCl2 extractable metals concentrations and soil texture as the main factors affecting protein and lipid contents. The results showed opposite effects of Pb and Zn, high inter-individual variability of biomarkers and weak relationships with easily extractable metals. Our results support the lack of genericity of energy reserves in earthworms exposed to field-contaminated soils.

Nitrogen (N) and phosphorous (P) enrichment play an important role in regulating soil N₂O emission, but their interactive effect remains elusive (i.e. whether the effect of P or N enrichment on soil N₂O emission varies between ambient and elevated soil N or P conditions). Here, we conducted a Bayesian meta-analysis across the global natural ecosystems to determine this effect. Our results showed that P enrichment significantly decreased soil N₂O emission by 13.9% at ambient soil N condition. This N₂O mitigation is likely due to the decreased soil NO₃⁻-N content (−17.6%) derived by the enhanced plant uptake when the P limitation was alleviated by P enrichment. However, this P-induced N₂O (and NO₃⁻-N) mitigation was not found at elevated soil N condition. Additionally, N enrichment significantly increased soil N₂O emission by 101.4%, which was associated with the increased soil NH₄⁺-N (+41.0%) and NO₃⁻-N (+82.3%). However, the effect of N enrichment on soil N₂O emission did not differ between ambient and elevated soil P subgroups, indicating that the P-derived N₂O mitigation could be masked by N enrichment. Further analysis showed that manipulated N rate, soil texture, soil dissolved organic nitrogen, soil total nitrogen, soil organic carbon, soil pH, aboveground plant biomass, belowground plant biomass, and plant biomass nitrogen were the main factors affecting soil N₂O emission under N enrichment. Taken together, our study provides evidence that P enrichment has the potential to reduce soil N₂O emission from natural ecosystems, but this mitigation effect could be masked by N enrichment.

Recent increased use of agricultural machines elevated the atmospheric pollutant emissions in the Yangtze River Delta (YRD) region in eastern China. Given the potentially large environmental and health impacts in busy seasons with enhanced machinery usage, it is important to accurately estimate the magnitude, spatial and temporal distributions of the emissions. We developed a novel method to estimate the real-world in-use agricultural machinery emissions, by combining satellite data, land and soil information, and in-house investigation. The machinery usage was determined based on the spatial distribution, growing and rotation pattern of the crops. The varied requirement of machinery power by heterogeneous soil texture, which was ignored in the previous studies, was considered in our methodology. The spatiotemporal pattern of machinery usage was determined based on the explored quantitative correlation between the local agricultural activity duration and the geographic location of the activity. A “grid-based” (30 × 30 m) inventory with daily emissions was then obtained, achieving significant improvement on spatial and temporal resolution. It substantially diminished the bias of previous inventories based on the machinery population or power installation census data. The emissions of NOX, PM₂.₅, CO and THC were estimated at 36300, 2000, 36900 and 8430 metric tons in YRD, with the majority contribution from Anhui and Jiangsu. Ten cities locating in northern and central Anhui and Jiangsu contributed the largest machinery emissions, accounting for 60% of the total emissions in YRD. Harvesting was found to have the largest emissions, followed by tilling and planting. Regarding the crops, the emissions from wheat and rice related machinery usage were the largest. In the busy seasons (spring and autumn), larger daily NOX and PM₂.₅ emissions were found from machinery than on-road vehicles in 42% of counties in Anhui and Jiangsu, highlighting the necessity of careful strategy making on controls of priority emission source.

This study examined the influences of three subsets of environmental factors (i.e. soil physicochemical properties including pH, organic matters and soil texture, landscape patterns, and parent materials) on the spatial variations and sources of soil trace metal contamination across an urban-rural environmental gradient in Guangzhou City, southern China. We collected 318 surface soil samples from forests, orchards, farmlands, and urban lawns using a random tessellation design for selecting sample sites. The geo-accumulation indices showed that 18%–88% of soil samples were contaminated: moderate to high contamination with Cd and Hg, low to moderate contamination with Cu, Pb, Zn and Ni, and low contamination with As and Cr. However, less than 13% of soil samples were considered to have exceeded the national standards causing environmental and human health concerns. The mean geo-accumulation indices increased in the order of forest, paddy field/orchard, vegetable, road/residential, and park/residential areas for As, Cd, Ni, Pb, Zn, closely following a land disturbance gradient. Spearman Correlation and Cluster Analyses showed that Pb-Cu-Zn had traffic-related origins, Cd-Hg were mainly influenced by fertilization or industrial emissions, and As-Cr-Ni had geogenic origins for agricultural soils. In contrast, the Ni, Hg and Cd contamination sources for urban soils included both anthropogenic and geogenic origins. The Stepwise Regression and Partial Redundancy Analyses showed that three subsets of environmental factors explained 43%–87% of variations of soil contamination for both agricultural and urban soils. We concluded that soil contamination was mainly controlled by soil physiochemical properties followed by landscape patterns. Soil absorption of aerial loads of trace metal pollutants dominated the soil contamination processes. Our findings implied that improving soil physiochemical properties and landscape designs can strengthen environmental buffering and carrying capacity, thus alleviating soil contamination and reducing non-point-source pollution in the study region.

Application of controlled release urea (CRU) is recommended to reduce the undesirable environmental effects resulting from urea application. However, the overall effects of CRU on maize productivity and reactive nitrogen (N) losses remain unclear. Our global meta-analysis based on 866 observations of 120 studies indicated that application of CRU instead of urea (same N rate) increased maize yield by 5.3% and nitrogen use efficiency (NUE) by 24.1%, and significantly decreased nitrous oxide (N₂O) emission, N leaching and ammonia (NH₃) volatilization by 23.8%, 27.1% and 39.4%, respectively. The increase of NUE and reduction of N₂O emission by CRU application were greater with medium and high N rates (150 ≤ N < 200 and N ≥ 200 kg N ha⁻¹) than with low N rates. The reduction in N₂O emission and N leaching with CRU application were enhanced when soil organic carbon (SOC) content was <15.0 g kg⁻¹, and soil texture was medium or coarse. The reduction in N₂O emission and NH₃ volatilization with CRU were greater in soils with pH ≥ 6.0. We concluded that use of CRU should be encouraged for maize production, especially on light-textured soils with low organic matter content.