Biochars induced modification of dissolved organic matter (DOM) in soil and its impact on mobility and bioaccumulation of arsenic and cadmium.

Biochar application has attracted great attention due to its diverse uses and benefits in the fields of environmental management and agriculture. Biochar modifies the composition of dissolved organic matter (DOM) in soil, which directly or indirectly controls the mobility of metal contaminants and their bioaccumulation. In this study, ten different hydrothermal biochars pyrolysed from mushroom waste (MSBC), soybean straw (SBBC), sewage sludge (SSBC), peanut shells (PNBC) and rice straw (RSBC) at two pyrolysis temperatures (200 °C and 350 °C) were used to investigate DOM changes in soil solution and their effects on metal availability and bioaccumulation. Biochar induced modification of soil DOM which was characterized by spectroscopic analysis of water soluble organic carbon, specific absorbance (SUVA254), UV-vis absorption, spectral slope (SR) and the absorption coefficient. Regarding rice plant growth, the biochar effects on biomass were greatly varied. Biochars (except for RSBC and MSBC) prepared at high temperature significantly (P ≤ 0.05) suppressed the availability of As and Cd in soil and their subsequent bioaccumulation in rice plants. The highest reduction (88%) in bioaccumulated As was observed in rice grown on soil amended with SBBC prepared at 350 °C (the highest temperature for hydrothermal technique). The addition of biochars (except RSBC and MSBC) prepared at high temperature markedly (p < 0.05) decreased AsIII (30-92%), while the effects on dimethylarsenic acid (DMA) and arsenate (AsV) concentrations were not significant except for SSBC350 (prepared at 350 °C) treatment. These results highlight the potential of biochar-DOM interactions as an important mechanism for suppressing the mobility and bioaccumulation of As and Cd in biochar-amended paddy agricultural systems.

Roles of abiotic losses, microbes, plant roots, and root exudates on phytoremediation of PAHs in a barren soil.

Phytoremediation is an emerging technology for the remediation of polycyclic aromatic hydrocarbons (PAHs). In this study, pot experiments were conducted to evaluate the efficacy of phytoremediation of phenanthrene and pyrene in a typical low organic matter soil (3.75 g kg(-1)), and the contribution proportions of abiotic losses, microbes, plant roots, and root exudates were ascertained during the PAHs dissipation. The results indicated that contribution of abiotic losses from this soil was high both for phenanthrene (83.4%) and pyrene (57.2%). The contributions of root-exudates-enhanced biodegradation of phenanthrene (15.5%) and pyrene (21.3%) were higher than those of indigenous microbial degradation. The role of root exudates on dissipation of phenanthrene and pyrene was evident in this experiment. By the way, with the increasing of ring numbers in PAHs structures, the root-exudates-enhanced degradation became more and more important. BIOLOG-ECO plate analysis indicated that microbial community structure of the soil receiving root exudates had changed. The removal efficiency and substrate utilization rate in the treatment with plant roots were lower than the treatment only with root exudates, which suggested that possible competition between roots and microbes for nutrients had occurred in a low organic matter soil.

Application of bioassays to evaluate a copper contaminated soil before and after a pilot-scale electrokinetic remediation.

Remediation programmes are considered to be complete when human risk-based criteria are met. However, these targets are often unsatisfied with the ecological parameters that may be important with regard to future soil use. Five soil subsamples, collecting along a pilot-scale soil column after electrokinetic treatment, were studied, from which about 42.0%-93.3% soil Cu had been successfully removed. A series of biological assays including soil microbial biomass carbon, basal soil respiration, soil urease activity, earthworm assays, and seed assays were used to evaluate their ecological risks. The results showed that the bioassay data from the treatment variants did not supposedly reflecting the decreased soil Cu concentrations after the electrokinetic treatment, but were highly correlated with some soil physicochemical characteristics. It suggests that bioassays are necessary to assess the ecotoxicity of soil after electrokinetic treatment.