Numerical Simulation of Plant–microbial Remediation for Petroleum-polluted Soil

This paper presents a numerical analysis of the migration and transformation mechanism of petroleum hydrocarbons (PHs) pollutants in soil. The mathematical model of the solute migration and plant–microbial remediation for PH polluted soil was established. The model was verified by field experimental data. Then, the software Hydrus-1D was employed to simulate the processes of diffusion, adsorption, desorption, microbial degradation, and plant adsorption of PHs in the soil–water system. The process of plant–microbial remediation for PH-contaminated soil was also simulated. The space-time change of PHs in soil was obtained, and the fate and remediation efficiency of PHs in soil were revealed in different remediation conditions. The results indicated that the Hydrus-1D model can adequately simulate the process of plant–microbial remediation. Plant–microbial remediation appears to be more efficient than the application of bacteria or Suaeda salsa. The majority of PH pollutants are degraded in the upper soil levels. For long-chain petro-alkane-contaminated soil, plant–microbial remediation is a more efficient method. A suitable moisture level in soil is important for improving the bioremediation effect of plant–microbial remediation technology.     

黄河口盐地碱蓬湿地土壤-植物系统重金属污染评价

以黄河口盐地碱蓬湿地为例,评价了淹水和非淹水区湿地表层土壤As、Cd、Cu、Cr、Pb和Zn 6种重金属的污染程度及其在土壤-植物系统中的迁移、富集特征,分析了不同积水深度和土壤理化性质对研究区土壤重金属含量的影响.研究结果表明,与土壤或沉积物质量标准相比,黄河口盐地碱蓬湿地土壤受As和Cd污染最严重,而其它重金属污染较轻;非淹水土壤Cd、Cr和Zn含量高于淹水湿地,而As、Cu和Pb则较低;而且淹水土壤As含量随积水深度增加而呈下降趋势,但积水深度对其他重金属含量的影响不明显.相关性分析结果表明,按照受土壤关键影响因子的不同重金属(除As外)可以分为两类:第一类为Cd、Cr和Zn,这些重金属含量受土壤pH值和盐分影响较大,且相互间存在显著正相关关系,表明它们可能有相同的来源;第二类为Pb和Cu,它们受土壤pH值、盐分和有机质的影响,且Pb和Cu之间存在显著正相关关系.除Cr、Cu和Zn外,重金属在盐地碱蓬的根系内一般不发生显著富集,但绝大多数重金属都表现出地上部分的含量比根系更高的现象.     

Assessing the applicability of phytoremediation of soils with mixed organic and heavy metal contaminants

Soil pollution is a major environmental problem and many contaminated sites are tainted with a mixture of organic and heavy metal contaminants. Compared to other remedial strategies, phytoremediation is a low cost, environmentally-friendly, sustainable means of remediating the contamination. This review first provides an overview of phytoremediation studies where the soil is contaminated with just one type of pollutant (heavy metals or organics) and then critically evaluates the applicability of phytotechnologies for the remediation of contaminated sites where the soil is polluted by a mixture of organic and heavy metal contaminants. In most of the earlier research studies, mixed contamination was held to be detrimental to plant growth, yet there were instances where plant growth was more successful in soil with mixed contamination than in the soil with only individual contaminants. New effective phytoremediation strategies can be designed for remediation of co-contaminated sites using: (a) plants species especially adapted to grow in the contaminated site (hyperacumulators, local plants, transgenic plants); (b) endophytic bacteria to enhance the degradation in the rizhosphere; (c) soil amendments to increase the contaminants bioavailability [chelating agents and (bio)surfactants]; (d) soil fertilization to enhance the plant growth and microbial activity in the soil; and (e) coupling phytoremediation with other remediation technologies such as electrokinetic remediation or enhanced biodegradation in the rhizosphere.     

Phytoremediation of fuel oil and lead co-contaminated soil by Chromolaena odorata in association with Micrococcus luteus

Phytoremediation is widely promoted as a cost-effective technology for treating heavy metal and total petroleum hydrocarbon (TPH) co-contaminated soil. This study investigated the concurrent removal of TPHs and Pb in co-contaminated soil (27,000 mg kg^?1 TPHs, 780 mg kg^?1 Pb) by growing Siam weed (Chromolaena odorata) in a pot experiment for 90 days. There were four treatments: co-contaminated soil; co-contaminated soil with C. odorata only; co-contaminated soil with C. odorata and Micrococcus luteus inoculum; and co-contaminated soil with M. luteus only. C. odorata survived and grew well in the co-contaminated soil. C. odorata with M. luteus showed the highest Pb accumulation (513.7 mg kg^?1) and uptake (7.7 mg plant^?1), and the highest reduction percentage of TPHs (52.2%). The higher TPH degradation in vegetated soils indicated the interaction between the rhizosphere microorganisms and plants. The results suggested that C. odorata together with M. luteus and other rhizosphere microorganisms is a promising candidate for the removal of Pb and TPHs in co-contaminated soils.     

Biostimulation and Phytoremediation Treatment Strategies of Gasoline-Nickel Co-Contaminated Soil

This study investigated the potential effect of poultry dung (biostimulation) and stubborn grass (Sporobolus pyramidalis) (phytoremediation) on microbial biodegradation of gasoline and nickel uptake in gasoline-nickel-impacted soil. In addition, the potential stimulatory effects of nickel on hydrocarbon utilization were investigated over a small range of nickel concentrations (2.5–12.5 mg/kg). The results showed that an increase in nickel concentration increased hydrocarbon degraders in soil by a range of 8.4–17.2% and resulted in a relative increase in gasoline biodegradation (57.5–62.4%). Also, under aerobic conditions, total petroleum hydrocarbons’ (TPH) removal was 62.4% in the natural gasoline-nickel microcosm (natural attenuation), and a maximum of 78.5%, 85.7%, and 95.8% TPH removal was obtained in phytoremediation, biostimulation, and a combination of biostimulation- and phytoremediation-treated microcosms, respectively. First-order kinetics described the biodegradation of gasoline and nickel uptake very well. Half-life times obtained were 28.88, 18.24, 14.44, and 8.56 days for gasoline degradation under natural attenuation, phytoremediation, biostimulation, and combined biostimulation and phytoremediation treatment methods, respectively. The results indicate that these remediation methods have promising potential for effective remediation of soils co-contaminated with petroleum hydrocarbons and heavy metals.     

盐和重金属复合胁迫对翅碱蓬萌发与生长的影响及调控措施

为探究Zn、Cu与盐复合胁迫对翅碱蓬(Suaeda salsa)萌发生长的影响机理及其调控措施,以翅碱蓬为研究对象,采用水培试验方法,测定Zn、Cu和盐复合胁迫条件下翅碱蓬种子发芽率、萌发速率和幼苗渗透调节物质含量等指标,分析1.5 mg/L吲哚乙酸(IAA)、100 mg/L赤霉素(GA)和0.3%硝酸钾(KNO₃)处理对Zn、Cu与盐复合胁迫条件下翅碱蓬萌发与生长的影响。结果表明：(1) Zn、Cu与高盐复合胁迫极显著降低翅碱蓬种子的发芽率,中高浓度的Zn、Cu与盐复合胁迫极显著降低翅碱蓬种子的萌发速率,Zn、Cu和盐复合胁迫对翅碱蓬种子的萌发生长影响表现为低促高抑效应,影响因子间存在明显的协同效应;(2)Zn、Cu和盐复合胁迫条件下,随着盐浓度的升高,翅碱蓬幼苗体内过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)3种抗氧化酶活性呈先升高后降低的变化趋势,Zn、Cu和高盐复合胁迫使翅碱蓬幼苗体内丙二醛(MDA)含量增加近2.5倍;(3)1.5 mg/L IAA溶液浸种12 h可显著提高Zn、Cu与高盐复合胁迫条件下翅碱蓬种子的发芽率和萌发速...     

Red mud (RM)-Induced enhancement of iron plaque formation reduces arsenic and metal accumulation in two wetland plant species

Human activities have resulted in arsenic (As) and heavy metals accumulation in paddy soils in China. Phytoremediation has been suggested as an effective and low-cost method to clean up contaminated soils. A combined soil-sand pot experiment was conducted to investigate the influence of red mud (RM) supply on iron plaque formation and As and heavy metal accumulation in two wetland plant species (Cyperus alternifolius Rottb., Echinodorus amazonicus Rataj), using As and heavy metals polluted paddy soil combined with three rates of RM application (0, 2%, 5%). The results showed that RM supply significantly decreased As and heavy metals accumulation in shoots of the two plants due to the decrease of As and heavy metal availability and the enhancement of the formation of iron plaque on the root surface and in the rhizosphere. Both wetland plants supplied with RM tended to have more Fe plaque, higher As and heavy metals on roots and in their rhizospheres, and were more tolerant of As and heavy metal toxicity. The results suggest that RM-induced enhancement of the formation of iron plaque on the root surface and in the rhizosphere of wetland plants may be significant for remediation of soils contaminated with As and heavy metals.     

基于文献计量的细菌-生物炭协同修复重金属污染土壤研究进展

为提高重金属污染土壤可持续修复效能,研究生物炭与细菌对重金属污染土壤的协同修复作用。基于文献计量学分析及重金属污染土壤修复背景,总结了细菌与生物炭对土壤重金属的稳定化特征及菌炭间的相互作用,分析了单一生物炭或细菌对重金属污染土壤修复的局限性,强调了细菌-生物炭协同修复技术的优势,阐述了细菌与生物炭主要通过离子交换、固定作用、氧化还原作用和迁移作用等重要机制有效修复重金属污染土壤,揭示了细菌-生物炭协同作用在重金属污染土壤修复中的巨大应用价值。文献计量学研究表明,生物炭与细菌对重金属污染土壤的协同修复已得到广泛关注。目前认为:生物炭与细菌的协同作用可有效改良土壤理化性质及提高土壤修复效率,也可促进植物生长及植物修复进程;生物炭对细菌影响具有双重性质,可促进细菌生长,也可能对细菌产生毒害;细菌可改变生物炭的理化性质,进而强化生物炭的重金属固定性能;细菌协同生物炭联合修复重金属污染土壤过程中,生物炭主导吸附和固定,细菌则发挥活化和解毒等功能;优化细菌-生物炭组合形式,发展混合细菌与多种类生物炭协同技术,是复合重金属污染土壤可持续修复亟待解决的重要问题;进一步揭示细菌与生物炭对重金属污染土壤的耦合作用及长效作用机制,规避生物炭生产和应用中的潜在生态健康风险,研发新型高效能细菌与生物炭复合体是细菌协同生物炭可持续修复重金属污染土壤应用领域面临的挑战。     

Phytoremediation of soil co-contaminated with heavy metals and deca-BDE by co-planting of Sedum alfredii with tall fescue associated with Bacillus cereus JP12

Aim

The objective of this study was to develop a remediation strategy for soil co-contaminated with decabromodiphenyl ether (BDE-209) and heavy metals (Cd, Pb and Zn) using co-plantation of the hyperaccumulator plant (Sedum alfredii) with tall fescue (Festuca arundinaceae) associated with a BDE degrader (Bacillus cereus strain JP12).

Methods

A 120-day remediation experiment was conducted under greenhouse conditions. S. alfredii and tall fescue were grown in monoculture and intercropped in artificially contaminated soil. Plant biomass, concentration of polybrominated diphenyl ethers, density of soil bacteria, soil enzyme activity, and the physiological profile of the soil microbial community were determined.

Results and discussion

Inoculation with JP12 significantly increased BDE-209 dissipation in soil. Phytoextraction of metals was also enhanced by JP12 inoculation due to the improved plant growth. Planting of tall fescue significantly enhanced BDE-209 dissipation as compared to that in the bare soil because of the increased soil microbial activity. Tall fescue showed higher Pb phytoextraction efficiency than S. alfredii, but Pb was principally retained in the roots of tall fescue. BDE-209 dissipation and metal phytoextraction were highest when co-planting S. alfredii with tall fescue inoculated with strain JP12. Pyrosequencing analysis revealed that the inoculated JP12 could functionally adapt to the introduced soil, against competition with indigenous microorganisms in soil.

Conclusions

Co-planting of S. alfredii with tall fescue combined with BDE-degrading bacterial strain JP12 is promising for remediation of soil co-contaminated with BDE-209 and metals.     

Uptake and Bioaccumulation of Pentachlorophenol by Emergent Wetland Plant Phragmites australis (Common Reed) in Cadmium Co-contaminated Soil

Despite many studies on phytoremediation of soils contaminated with either heavy metals or organics, little information is available on the effectiveness of phytoremediation of co-occurring metal and organic pollutants especially by using wetland species. Phragmites australis is a common wetland plant and its potential for phytoremediation of cadmium pentachlorophenol (Cd-PCP) co-contaminated soil was investigated. A greenhouse study was executed to elucidate the effects of Cd (0, 10, and 20 mg kg^?1) without or with PCP (0, 50, and 250 mg kg^?1) on the growth of the wetland plant P. australis and its uptake, accumulation and removal of pollutant from soils. After 75 days, plant biomass was significantly influenced by interaction of Cd and PCP and the effect of Cd on plant growth being stronger than that of PCP. Coexistence of PCP at low level lessened Cd toxicity to plants, resulting in improved plant growth and increased Cd accumulation in plant tissues. The dissipation of PCP in soils was significantly influenced by interactions of Cd, PCP and plant presence or absence. As an evaluation of soil biological activities after remediation soil enzyme was measured.     

黄河三角洲重度退化滨海湿地盐地碱蓬的生态修复效果

采用翻地、施肥和芦苇碎屑培肥等土壤改良方法,利用盐地碱蓬在黄河三角洲重度退化区进行生态修复实验研究。结果表明:重度退化湿地土壤改良后,盐地碱蓬能够成功生长,3种改良方法均可有效的降低重度退化盐碱地的土壤含盐量,改良后的土壤Na离子含量均显著低于对照组,土壤脲酶和磷酸酶活性与对照相比有了显著的提高,表明改良后土壤肥力得到了改善。3种改良方法比较,培肥处理组土壤Na离子含量显著低于其他两种方法;盐地碱蓬生物量达到最高值,说明增加有机物的培肥方法可有效的改良重度退化盐碱湿地土壤,达到较为理想的生态修复预期效果。     

Contents of volume 137 1991

The halophyte, Suaeda salsa, was grown in saline soil in pots and watered with a NaCl solution containing 0.2 g L^-1 Na-ions. S. salsa accumulated Na during a 120-day growing period and caused a net reduction in the Na content of the soil. S. salsa also decreased the Na content of saline soil in a field experiment. The Na content of the soil at depth 20–30 cm was reduced by 4.5% with S. salsa at a density of 15 plants m^-2 and by 6.7% with a density of 30 plants m^-2. In contrast, the Na content was decreased by only 1% with Medicago sativa at 15 plant m^-2 and increased by 3.8% with bare soil. The results confirm that S. salsa is an effective salt absorber in saline soils.     

The chelating effect of citric acid,oxalic acid,amino acids and Pseudomonas fluorescens bacteria on phytoremediation of Cu,Zn, and Cr from soil using Suaeda vera

Phytoextraction is a green technique for the removal of soil contaminants by plants uptake with the subsequent elimination of the generated biomass. The halophytic plant Suaeda vera Forssk. ex J.F.Gmel. is an native Mediterranean species able to tolerate and accumulate salts and heavy metals in their tissues. The objective of this study was to explore the potential use of S. vera for soil metal phytoextraction and to assess the impact of different chelating agents such as natural organic acids (oxalic acid [OA], citric acid [CA]), amino acids (AA) and Pseudomonas fluorescens bacteria (PFB) on the metal uptake and translocation. After 12 months, the highest accumulation of Cu was observed in the root/stem of PFB plots (17.62/8.19 mg/kg), in the root/stem of CA plots for Zn (31.16/23.52 mg/kg) and in the root of OA plots for Cr (10.53 mg/kg). The highest accumulation of metals occurred in the roots (27.33–50.76 mg/kg). Zn was the metal that accumulated at the highest rates in most cases. The phytoextraction percentages were higher for Cu and Zn (～2%) with respect to Cr (～1%). The percentages of metal removal from soil indicate the need to monitor soil properties, to recognize the influence of each treatment and to increase the concentration of bioavailable metals by the use of agricultural management practices aimed at promoting plant growth.     

碱蓬浮床对海水养殖尾水中氮磷修复效果研究

海水养殖尾水中总氮、总磷超标是引起沿海水体富营养化的主要原因,为研究碱蓬浮床对海水养殖尾水中氮磷的去除效果,该研究设计加入碱蓬(Suaeda salsa)浮床和不加浮床的两组对比实验,通过比较修复前后碱蓬株高、生物量、含水率、根长以及各部位氮、磷的含量变化,以及水体中总氮(TN)和总磷(TP)的去除效果,探究浮床中碱蓬对总氮和总磷的吸收及其生长特性,验证碱蓬浮床对海水养殖废水中氮、磷等的去除能力。结果表明:浮床中碱蓬株高、鲜重、干重、含水率、根长较修复前均有显著增加,说明浮床中盐生植物碱蓬能够适应含海水养殖尾水水培环境;经碱蓬浮床修复,水体中总氮、总磷均明显下降,其中碱蓬对海水养殖尾水中的总氮总磷去除贡献率分别为16.10%和78.15%,浮床中碱蓬会在叶片和根系中积累氮磷。     

典型重金属对氯苯类有机物生物转化影响及分子机制研究进展

重金属和有机物相互作用,形成共污染,是当今面临的重要环境问题之一。明晰重金属作用下氯苯类化合物（chlorobenzenes,CBs）的转化特性以及典型重金属对CBs生物降解的影响机制,对有效修复重金属-有机物共污染有重要意义。本文首先对CBs生物降解的研究现状进行了总结,明晰了当前CBs降解的主要功能菌属类型,包括伯克霍尔德菌（Burkholderia）,假单胞菌（Pseudomonas）,脱卤球菌（Dehalobium）和脱卤拟球菌（Dehalococcoides）等;而后概述了重金属与CBs的共污染现状,发现绝大多数污染中存在重金属与CBs共污染现象;随后系统综述了典型重金属对CBs生物转化的影响,表明好氧或厌氧条件下大多数重金属离子对CBs生物转化存在抑制作用,受金属离子种类、浓度、价态及pH影响显著;另外,对重金属影响下的CBs转化机制进行了分析,基于3方面影响构建了分子机制模型。最后对目前还存在的问题与局限性进行了分析,并对未来发展方向进行了展望,以期为重金属-有机物共污染的修复提供支撑。     

Siderophores mediate reduced and increased uptake of cadmium by Streptomyces tendae F4 and sunflower (Helianthus annuus), respectively

Aims: As a toxic metal, cadmium (Cd) affects microbial and plant metabolic processes, thereby potentially reducing the efficiency of microbe or plant‐mediated remediation of Cd‐polluted soil. The role of siderophores produced by Streptomyces tendae F4 in the uptake of Cd by bacteria and plant was investigated to gain insight into the influence of siderophores on Cd availability to micro‐organisms and plants. Methods and Results: The bacterium was cultured under siderophore‐inducing conditions in the presence of Cd. The kinetics of siderophore production and identification of the siderophores and their metal‐bound forms were performed using electrospray ionization mass spectrometry. Inductively coupled plasma spectroscopy was used to measure iron (Fe) and Cd contents in the bacterium and in sunflower plant grown in Cd‐amended soil. Siderophores significantly reduced the Cd uptake by the bacterium, while supplying it with iron. Bacterial culture filtrates containing three hydroxamate siderophores secreted by S. tendae F4 significantly promoted plant growth and enhanced uptake of Cd and Fe by the plant, relative to the control. Furthermore, application of siderophores caused slightly more Cd, but similar Fe uptake, compared with EDTA. Bioinoculation with Streptomyces caused a dramatic increase in plant Fe content, but resulted only in slight increase in plant Cd content. Conclusion: It is concluded that siderophores can help reduce toxic metal uptake in bacteria, while simultaneously facilitating the uptake of such metals by plants. Also, EDTA is not superior to hydroxamate siderophores in terms of metal solubilization for plant uptake. Significance and Impact of the Study: The study showed that microbial processes could indirectly influence the availability and amount of toxic metals taken up from the rhizosphere of plants. Furthermore, although EDTA is used for chelator‐enhanced phytoremediation, microbial siderophores would be ideal for this purpose.     

Biological technologies for the remediation of co-contaminated soil

Compound contamination in soil, caused by unreasonable waste disposal, has attracted increasing attention on a global scale, particularly since multiple heavy metals and/or organic pollutants are entering natural ecosystem through human activities, causing an enormous threat. The remediation of co-contaminated soil is more complicated and difficult than that of single contamination, due to the disparate remediation pathways utilized for different types of pollutants. Several modern remediation technologies have been developed for the treatment of co-contaminated soil. Biological remediation technologies, as the eco-friendly methods, have received widespread concern due to soil improvement besides remediation. This review summarizes the application of biological technologies, which contains microbial technologies (function microbial remediation and composting or compost addition), biochar, phytoremediation technologies, genetic engineering technologies and biochemical technologies, for the remediation of co-contaminated soil with heavy metals and organic pollutants. Mechanisms of these technologies and their remediation efficiencies are also reviewed. Based on this study, this review also identifies the future research required in this field.     

两株多环芳烃降解菌协同对菲-镉污染的去除特性北大核心

【目的】从污染土壤中分离筛选一株多环芳烃降解菌,并探究其与Pseudomonas aeruginosa B6-2构建的混菌体系对菲-镉复合污染的修复效能,以及微生物代谢特性对不同镉浓度赋存的响应特性,以期为复合污染的生物修复提供优良菌株资源及应用技术参考。【方法】采用富集驯化、筛选纯化方法得到一株多环芳烃降解菌,通过生理生化特征和16S rRNA基因序列分析进行鉴定。利用高效液相色谱法和电感耦合等离子体质谱法评估不同镉浓度赋存下各反应体系对菲和镉的去除效能;通过菌体细胞形态的扫描电镜观测及菌株代谢活性检测,探讨镉胁迫对菲生物降解过程的影响机制。【结果】筛选得到一株具有重金属耐受性和多环芳烃高效降解菌SZ-3,经鉴定为节杆菌属;降解菌协同体系(M)具有良好的菲降解效能和抗镉胁迫优势。镉胁迫浓度为0.5、10 mg/L时,M对菲和镉的去除率分别高于85%、80%;镉胁迫浓度为25、50 mg/L时,2种污染物的去除率均大于65%。扫描电镜分析表明,镉胁迫导致菌体表面粗糙且出现不同程度变形,菌体间黏附性和聚集性提高。反应周期内,邻苯二酚1,2-双加氧酶活性与电子传递体系活性随镉浓度增加而降低,两者变化与菲降解速率变化一致。【结论】Arthrobacter sp.SZ-3是一株PAHs高效降解菌,能与Pseudomonas aeruginosa B6-2协同高效修复菲-镉复合污染,随着初始镉胁迫浓度增加,混菌协同对目标污染物去除的优势显著。     

Heavy metal content in halophytic plants from inland and maritime saline areas

We investigated the concentration of Aluminium (Al), Cobalt (Co), Chromium (Cr), Copper (Cu), Iron (Fe), Manganese (Mn), Nickel (Ni) and Zinc (Zn) in the root and aboveground organs of four halophyte species (Salicornia europaea, Suaeda maritima, Salsola soda and Halimione portulacoides), as well as in the soil from maritime and inland saline areas. The aim of our research was to evaluate the capability of some halophyte species to absorb different heavy metals and to detect differentiation of heavy metal accumulation within populations from inland and maritime saline areas. Generally, the plant roots had significantly higher concentrations of metals when compared to stems and leaves. Zinc was the only metal with concentrations significantly higher in the leaves than in the root and stem. Populations from maritime saline areas had higher trace root and stem metal concentrations than populations from inland saline areas. Excepting zinc, populations from inland saline areas had higher heavy metal concentrations in the leaves. The factors that affected metal accumulation by halophytes included the percentage of salt in the soil. We also discuss the potential use of these halophytes in phytoremediation.     

Rhamnolipid-Enhanced Mineralization of Phenanthrene in Organic-Metal Co-Contaminated Soils

Successful remediation of soils co-contaminated with organics and metals may require a combination of technologies. This research addresses the organic component within co-contaminated sites. It is well known that metal contaminants in soil can partially or completely inhibit normal heterotrophic microbial activity and hence prevent in situ biodegradation of organics. Previous work has shown that a rhamnolipid biosurfactant can complex metals such as lead and cadmium. It has also been demonstrated, in pure culture, that rhamnolipid can mitigate metal inhibition during the degradation of naphthalene. The goal of this study was to investigate whether rhamnolipid could reduce the toxicity of a model metal, cadmium, to indigenous soil populations in two different soils, Brazito and Gila, during the mineralization of phenanthrene. Results show that cadmium inhibited phenanthrene mineralization in both soils at bioavailable cadmium concentrations as low as 27 µM. This inhibition was reduced by the addition of rhamnolipid. Since rhamnolipid is degraded by soil populations, a rhamnolipid pulsing strategy was used to maintain a constant level of rhamnolipid in the system. Using this strategy, phenanthrene mineralization levels comparable to the control (0 mM Cd/0 mM rhamnolipid) were achieved in the presence of toxic cadmium concentrations. This research demonstrates that pulsed application of rhamnolipid may allow bioremediation of organic contaminants in sites that are co-contaminated with organics and metals.