Soil microbial activities and community diversity during the rhizoremediation of a pyrene contaminated soil

A greenhouse pot experiment was conducted to evaluate pyrene degradation, microbial biomass, basal soil respiration, metabolic quotient （qCO2）, soil enzyme activities, and the FAME patterns of rhizospheric soil and nonrhizospheric soil. The results showed that the pyrene concentrations in soil decreased with time extending and were very significant less in rhizospheric soil grown with maize plants （p〈0.01）. At the end of the 45-day experiment, the ratios of pyrene degradation were 61.25% and 35.58% in rhizospheric and nonrhizospheric soil, respectively. Maize enhanced the decrease of pyrene concentration and increased the degradation rate of pyrene in soil. During the experimental period, a relatively large amount of microbial biomass biomass （Craig）, basal soil respiration, the Cmic/Corg ratio, enzyme （urease, dehydrogenase, polyphenol oxidase, and catalase） activities were detected in rbizospheric soil. Metabolic quotient was lower in rhizospheric soil than in nonrhizospheric soil at the whole experimental period. Soil microbial communities in rhizospheric soil and nonrhizospheric soil were characterized using fatty acid methyl ester （FAME） analysis. Fatty acid profiles demonstrated that soil microbial community structure was significantly altered in pyrene contaminated soil with maize. Fatty acid indicators for fungi and the ratio of fungi to bacteria significant increased, and fatty acid indicators for bacteria and Gram-negative bacteria significantly decreased. The effect gradually increased and got very significant （p〈0.01） with the time extending. The differences of fatty acid indicators for arbuscular mycorrhizal fungi （AMF）, Gram-positive bacteria and actinomycetes gradually increased, and the differences reached significant level （p〈0.05） at the end of the experiment （45 d）.

Improved rhizoremediation for decabromodiphenyl ether(BDE-209)in E-waste contaminated soils

An experiment was conducted to improve rhizoremediation for decabromodiphenyl ether(BDE-209)contaminated soil from typical E-waste dismantling areas.Plants of ryegrass(Lolium perenne L.)and rice(Oryza sativa L.)were cultivated in aged-contaminated(initial concentration of 346.3μg BDE-209·kg^(-1))and freshly-spiked(initial concentration of 3127μg BDE-209·kg^(-1))soils,coupling with the agricultural modification strategies of compost addition and/or arbuscular mycorrhizal fungi(AMF)infection,respectively.60 days’growth of ryegrass significantly facilitated the dissipation of BDE-209,with the most effective in its rhizosphere in treatment inoculated with AMF;the BDE-209 dissipation rates achieved 51.9% and 22.8% in rhizosphere,and 43.5% and 19.8% in non-rhizosphere,for aged-contaminated and freshlyspiked soils,respectively.120 days’growth of rice with simultaneous inoculation of AMF and addition of compost was the most effective in facilitating BDE-209 dissipation in agedcontaminated soil,with the removal rates of 53.3% and 48.1% in rhizosphere and nonrhizosphere soils respectively;while for freshly-spiked soils,the most effective removal was achieved by compost addition only,with the BDE-209 dissipation rates of 27.9% and 26.6% in rhizosphere and non-rhizosphere soils,respectively.High throughput sequencing analysis of rhizosphere soil DNA showed that responses in microbial communities and their structure differed with plant species,soil pollution dose,AMF inoculation and/or compost addition.Actinomycetales,Xanthomonadales,Burkholderiales,Sphingomonadales,Clostridiales,Cytophagales,Gemmatimonadales and Saprospirales were the sensitive responders and even possibly potential functional microbial groups during the facilitated removal of BDE-209 in soils.This study illustrates an effective rhizoremediation pattern for removal of BDE-209 in pollution soils,through successive cultivation of rice and followed by ryegrass,with rice growth coupled with AMF inoculation and compost addition,while ryegrass growth coupled with AMF inoculation only.

Available Approaches of Remediation and Stabilisation of Metal Contamination in Soil: A Review

Anthropogenic activities, such as mining of natural resources, manufac-turing industries, modern agricultural practices and energy production have resulted in the release of heavy metals with resultant harmful im-pacts in some natural environments. Toxic heavy metals are harmful to living organisms even at low concentrations. Therefore, heavy metal contaminated sites should be remediated as heavy metals do not decompose into less harmful substances and are retained in the soil. Conventional methods are used for remediation of heavy metal contaminated soils such as heavy metal extraction, immobilization and removal of soils to landfill produce large quantities of toxic products including insoluble hydroxides and are rarely cost effective. The advent of bioremediation technologies like biosparging, bioventing and bioaugmentation has provided an alternative to conventional methods for remediating heavy metal contaminated soils. A subset of bacteria found in the rhizosphere has been found to increase the tolerance of plants to heavy metals in soil. These bacteria commonly known as plant growth promoting rhizobacteria or Plant Growth Promoting Rhizobacteria (PGPR) are showing promise as a bioremediation technique for the stabilisation and remediation of heavy metal contami-nated sites. PGPR can improve plant growth via a variety of mechanism including fixing atmospheric N to improve N status and making plants more tolerant of heavy metals. Scattered literature is harnessed to review the principles, advantages and disadvantages of the available technologies for remediating heavy metal contaminated soils and is presented.