Yibing Ma

An inventory of trace element inputs to agricultural soils in China

It is important to understand the status and extent of soil contamination with trace elements to make sustainable management strategies for agricultural soils. The inputs of trace elements to agricultural soils via atmospheric deposition, livestock manures, fertilizers and agrochemicals, sewage irrigation and sewage sludge in China were analyzed and an annual inventory of trace element inputs was developed. The results showed that atmospheric deposition was responsible for 43-85% of the total As, Cr, Hg, Ni and Pb inputs, while livestock manures accounted for approximately 55%, 69% and 51% of the total Cd, Cu and Zn inputs, respectively. Among the elements concerned, Cd was a top priority in agricultural soils in China, with an average input rate of 0.004 mg/kg/yr in the plough layer (0-20 cm). Due to the spatial and temporal heterogeneity of the sources, the inventory as well as the environmental risks of trace elements in soils varies on a regional scale. For example, sewage sludge and fertilizers (mainly organic and phosphate-based inorganic fertilizers) can also be the predominant sources of trace elements where these materials were excessively applied. This work provides baseline information to develop policies to control and reduce toxic element inputs to and accumulation in agricultural soils.

Long-term field application of sewage sludge increases the abundance of antibiotic resistance genes in soil

Sewage sludge and manure are common soil amendments in crop production; however, their impact on the abundance and diversity of the antibiotic resistome in soil remains elusive. In this study, by using high-throughput sequencing and high-throughput quantitative PCR, the patterns of bacterial community and antibiotic resistance genes (ARGs) in a long-term field experiment were investigated to gain insights into these impacts. A total of 130 unique ARGs and 5 mobile genetic elements (MGEs) were detected and the long-term application of sewage sludge and chicken manure significantly increased the abundance and diversity of ARGs in the soil. Genes conferring resistance to beta-lactams, tetracyclines, and multiple drugs were dominant in the samples. Sewage sludge or chicken manure applications caused significant enrichment of 108 unique ARGs and MGEs with a maximum enrichment of up to 3845 folds for mexF. The enrichment of MGEs suggested that the application of sewage sludge or manure may accelerate the dissemination of ARGs in soil through horizontal gene transfer (HGT). Based on the co-occurrence pattern of ARGs subtypes revealed by network analysis, aacC, oprD and mphA-02, were proposed to be potential indicators for quantitative estimation of the co-occurring ARGs subtypes abundance by power functions. The application of sewage sludge and manure resulted in significant increase of bacterial diversity in soil, Proteobacteria, Acidobacteria, Actinobacteria and Chloroflexi were the dominant phyla (>10% in each sample). Five bacterial phyla (Chloroflexi, Planctomycetes, Firmicutes, Gemmatimonadetes and Bacteroidetes) were found to be significantly correlated with the ARGs in soil. Mantel test and variation partitioning analysis (VPA) suggested that bacterial community shifts, rather than MGEs, is the major driver shaping the antibiotic resistome. Additionally, the co-occurrence pattern between ARGs and microbial taxa revealed by network analysis indicated that four bacterial families might be potential hosts of ARGs. These results may shed light on the mechanism underlining the effects of amendments of sewage sludge or manure on the occurrence and dissemination of ARGs in soil.

New insights into the sorption mechanism of cadmium on red mud

Effectiveness and mechanism of cadmium (Cd) sorption on original, acidified and ball milling nano-particle red muds were investigated using batch sorption experiments, sequential extraction analysis and X-ray absorption near edge structure (XANES) spectroscopy. The maximum sorption capacity of Cd was 0.16, 0.19, and 0.21 mol/kg for the original, acidified, and nano-particle red muds at pH 6.5, respectively. Both acidification and ball-milling treatments significantly enhanced Cd sorption and facilitated transformation of Cd into less extractable fractions. The Cd LIII-edge XANES analysis indicated the formation of inner-sphere complexes of Cd similar to XCdOH (X represents surface groups on red mud) on the red mud surfaces although outer-sphere complexes of Cd were the primary species. This work shed light on the potential application of red mud to remediate Cd-contaminated soils and illustrated the promising tool of XANES spectroscopy for speciation of multicomponent systems of environmental relevance.

Evaluation of impacts of soil fractions on phenanthrene sorption

Phenanthrene sorption to soils and soil fractions was investigated using two contrasting soils with different clay mineral and organic carbon (OC) contents in an attempt to evaluate the contribution of each soil fraction to phenanthrene sorption and the applicability of the carbon-normalized distribution constant (K(OC)) in soils. Sorbents were characterized using surface analysis, solid-state (13)C NMR analysis, and glass transition temperature (T(g)) analysis to gain a insight into the chemical nature of OC in soils. Dissolved organic carbon (DOC) in the soil solution impeded the phenanthrene sorption, while humins accounted for the predominant phenanthrene sorption in soils. The contribution of OC to phenanthrene sorption in soil would be overestimated if only a K(OC)-approach was adopted, since clay minerals could account for much of the sorption, especially when OC was low in soils. Nitrogen gas was shown to be inappropriate for probing non-polar sorption capacity. The results obtained highlight the importance of clay minerals in governing the sorption of phenanthrene in soil, and emphasize the inapplicability of the carbon-normalized distribution coefficient K(OC) in soils.

Evaluation of an electrostatic toxicity model for predicting Ni2+ toxicity to barley root elongation in hydroponic cultures and in soils

Assessing environmental risks of metal contamination in soils is a complex task because the biologically effective concentrations of metals in soils vary widely with soil properties. The factors influencing the toxic effect of nickel (Ni) on root growth of barley (Hordeum vulgare) were re-evaluated using published data from both soil and hydroponic cultures. The electrical potential (ψ(0) (o) ) and ion activities ({I(z) }(0) (o) ) at the outer surfaces of root-cell plasma membranes (PMs) were computed as the basis of the re-evaluation. The reanalyses demonstrated that root growth was related to: the Ni(2+) activity at the PM surface, ({Ni(2+) }(0) (o) ); calcium (Ca) deficiency (related to {Ca(2+) }(0) (o) ); osmotic effects; and modification of intrinsic Ni(2+) toxicity by magnesium (Mg(2+) ; this appeared to exert an intrinsic (specific) ameliorating effect on intrinsic Ni(2+) toxicity). Electrostatic toxicity models (ETM) were developed to relate root growth to these factors (R(2)  > 0.751). Based on the ETM developed in soil culture and a Ni(2+) solid-solution partitioning model, critical metal concentrations in soils linked to a biological effect were well predicted for 16 European soils with a wide range of properties, indicating the potential utility of ETM in risk assessment of metals in terrestrial ecosystems.

Copper toxicity thresholds in Chinese soils based on substrate-induced nitrification assay.

Copper toxicity in 17 Chinese soils was screened using a substrate-induced nitrification assay to generate information for the development of a terrestrial biotic ligand model (tBLM). The leaching effect on the Cu toxicity thresholds was investigated. Both the total Cu-based median effective concentration (EC50) values (46.9-2726 mg/kg) and the solution Cu-based EC50 values (0.04-2.91 mg/L) in unleached soils varied substantially among the soils in the present study. For unleached soils, linear stepwise multiple regression analysis showed that total Ca and soil pH were the best predictors for total Cu-based EC50, while electrical conductivity (EC) and soil pH were the best predictors for solution Cu-based EC50. The variation in solution Cu-based EC50 was largely (R(2) = 0.75) explained by Mg but not Ca and H(+) concentration in soil solution at EC50, suggesting a protective effect of Mg(2+) against Cu toxicity in the test soils. Leaching impacted Cu toxicity differently among the soils and apparently reduced the variations of both the total Cu-based and the solution Cu-based EC50. The predictability of the Cu EC50 by empirical models was decreased after leaching. The leaching effect on Cu toxicity, indicated by a leaching factor, was not predicted by any soil properties. There is a need to investigate quantitatively the mechanisms for the leaching effect on Cu toxicity in soils.

Selected dark sides of biomass-derived biochars as environmental amendments

With the rapid increase in the application of biochars as amendments, studies are needed to clarify the possible environmental risks derived from biochars to use safely the biomass resources. This work reported selected dark sides of maize straw- and swine manure-derived biochars pyrolyzed at 300 and 500°C. During the pyrolysis processes, total heavy metals in the biochars were enriched greatly accompanying with considerable emission of the heavy metals into atmosphere and the trends became increasingly obvious with pyrolysis temperature. Meanwhile, the biochars showed distinctly decreased available heavy metals compared with raw feedstocks, which could be mainly attributed to the sorption by the inorganics in the biochars. The water- and acid-washing treatments significantly increased the releasing risks of heavy metals from biochars into the environments. Electron paramagnetic resonance analysis indicated that persistent free radicals, emerged strongly in the biochars as a function of the aromatization of biomass feedstocks, were free from the influence of water-, acid-, or organic-washing of the biochars and could remain stable even after aged in soils for 30days. Dissolved biochars, highly produced during pyrolysis processes, showed distinct properties including lower molecular weight distribution while higher aromaticity compared with soil dissolved organic carbon. The results of this study provide important perspectives on the safe usage of biochars as agricultural/environmental amendments.

Long-term organic fertilization increased antibiotic resistome in phyllosphere of maize

Phyllosphere contains various microorganisms that may harbor diverse antibiotic resistance genes (ARGs). However, we know little about the composition of antibiotic resistome and the factors influencing the diversity and abundance of ARGs in the phyllosphere. In this study, 16S rRNA gene amplicon sequencing and high-throughput quantitative PCR approaches were employed to investigate the effects of long-term (over 10 years) organic fertilization on the phyllosphere bacterial communities and antibiotic resistome. Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes dominated in the phyllosphere bacterial communities. Long-term application of sewage sludge and chicken manure altered the phyllosphere bacterial community composition, with a remarkable decrease in bacterial alpha-diversity. A total of 124 unique ARGs were detected in the phyllosphere. The application of sewage sludge and chicken manure significantly increased the abundance of ARGs, with a maximum 2638-fold enrichment. Variation partitioning analysis (VPA) together with network analysis indicated that the profile of ARGs is strongly correlated with bacterial community compositions. These results improve the knowledge about the diversity of plant-associated antibiotic resistome and factors influencing the profile of ARGs in the phyllosphere.