Characterization of benthic biofilms in mangrove sediments and their variation in response to nutrients and contaminants.

Diatom-dominated biofilms and associated extracellular polymeric substances (EPS) may adapt to the stress of long-term exposure to nutrients and anthropogenic contaminants. However, such interactions in contaminated mangrove sediments have rarely been reported. Based on the in situ characterization of biofilm components and environmental factors, the present study aimed to explore the key factors involved in shaping sediment biofilms through correlational and multivariate analyses. The pennate diatom Navicula is the core taxon that plays a crucial role in balancing the abundance of Nitzschia and Cyclotella, and is the main producer of bound-polysaccharides. The taxa composition shifts in a high N/P matrix, with the populations of pennate diatoms increasing but that of centric diatoms decreasing. High nutrient concentrations yield more number of diatoms and elevated levels of EPS. Bacteria are the main consumers of EPS and tend to be more symbiotic with Nitzschia than the other two diatom taxa. Some bound-polysaccharides dominated by arabinose and glucose units are transformed into the colloidal fraction, whereas other conservative ones serve as structural materials in concert with the bound-proteins. The planktonic phase of Cyclotella breaks down the structural EPS secreted by pennate diatoms in a process that directly affects the dynamic renewal of benthic biofilms. Most heavy metals as well as bisphenol A inhibit the abundance of bacteria and diatoms but enhance most EPS fractions except bound-polysaccharides. The response of structural EPS to specific contaminants varies, exhibiting increases in Co and Ni levels but decreases in nonylphenol and methylparaben levels. The present study improves our understanding of the microbial carbon loop of benthic biofilms in mangrove ecosystems under stress by nutrients and mixed contaminants.

Aggregation of Fe2O3 nanoparticle in the presence of organophosphate esters (OPEs).

Aggregation is a key process for determining the environmental behavior and impact of a nanoparticle (NP). Since organophosphate esters (OPEs), which are recognized as emerging contaminants, are distributed widely in the natural aquatic environment, they may contribute to interacting with NPs and ultimately influence their transport and fate. Here, we investigated two typical organophosphate esters OPEs on aggregation the Fe2O3 NP in aquatic environments. The results showed that both tri-ethylhexyl phosphate (TEHP) and tris (chloroisopropyl) phosphate (TCPP) improved the colloidal stability of Fe2O3 NP in artificial water and environmental matrices. TEHP exhibited an obvious effect than TCPP on the Zeta potential and aggregation rates of Fe2O3 NP in artificial water. In the presence of electrolyte, 10 mg/L TCPP and TEHP increased the critical coagulation concentration (CCC) by 3.6 times and 17.4 times, respectively. Compared with pore-water, the aggregation rates of Fe2O3 NP in river water were slightly higher than those in pore-water, which can be attributed to the higher DOC in pore-water. We suggested that the high hydrophobicity and molecular weight of OPEs were considered important factors against the aggregation of Fe2O3 NP in water. Greater surface charge and steric hindrance originating from TCPP and TEHP dominated the colloidal stability of Fe2O3 NP.

Enhancement effect of nanoscale zero-valent iron addition on microbial degradation of BDE-209 in contaminated mangrove sediment.

Chemical and biological methods have been employed to remedy polybrominated diphenyl ether contamination, but the removal of decabromodiphenyl ether (BDE-209) by either method still has limitations. The present study aims to evaluate the combined effect of nanoscale zero-valent iron (nZVI) (from 0.1 to 10%) reduction and microbial debromination on BDE-209 removal in mangrove sediments under an anaerobic condition. During the 12-months incubation, nZVI significantly enhanced BDE-209 removal, with 17.03% to 41.99% reduction in sterilized sediments. The reduction was even higher in non-sterilized sediments with living indigenous microorganisms, achieving 15.80%, 33.50%, 55.83% and 66.95% removal of BDE-209 at 0 (control without nZVI), 0.1%, 1% and 10% nZVI, respectively. In control sterilized sediments, no debromination was found, and debromination occurred according to spiked levels of nZVI, with BDE-153 being the dominant congener. The concentrations of debrominated congeners in non-sterilized sediments also increased with nZVI levels, but were significantly higher than the respective sterilized sediment. The relative proportions of different debrominated congeners in non-sterilized sediments depended on nZVI levels, with BDE-99 being the dominant congener in low nZVI amended sediments but shifted to BDE-153 under high nZVI. Higher concentrations of ferrous iron (Fe2+) were detected in both sterilized and non-sterilized sediments spiked with more nZVI, and their concentrations significantly correlated with BDE-209 removal. Growth of total bacteria in sediments with 1% and 10% nZVI was inhibited within first two months, but their numbers resumed to that in the control at the end of 12 months. The present study demonstrates the synergy between chemical and microbiological methods, and a combination of nZVI and indigenous microorganisms could be an efficient and feasible mean to remedy BDE-209 in contaminated sediments.

A simple paper-based colorimetric analytical device for rapid detection of Enterococcus faecalis under the stress of chlorophenols.

Bacteria detection and toxicity measurement are essential in many aspects. Becoming increasingly popular in recent years, paper-based analytical devices (PADs) have proven to be cost-effective, portable and eco-friendly with quantitative diagnostic results. In this work, by a straightforward soaking-drying method, a resazurin-deposited PAD has been developed for rapid bacteria detection and biotoxicity measurement. The colorimetric response on the PAD was generated from metabolic reduction of resazurin by Enterococcus faecalis, a facultative anaerobic bacterial strain. After recording and quantifying the colorimetric response with Hue value by a smartphone, the bioassay on PAD enables the detection of resazurin reduction kinetics difference among bacteria at various densities in 10 min. Thereby, the bioassay on PAD was applied to study the toxicity of two chlorophenols, i.e. pentachlorophenol (PCP) and 4-chlorophenol (4-CP), to E. faecalis. Compared to growth-based inhibition test, which takes 5 h, this assay shows higher efficiency, i.e. in 30 min, the biotoxicity difference between PCP and 4-CP can be identified.

Comparison of microbial community structure and function in sediment between natural regenerated and original mangrove forests in a National Nature Mangrove Reserve, South China.

Mangrove has been destroyed and reforestation is often undertaken, but whether a regenerated forest could restore its ecological function is not clear. This study compares microbial community structure and function in sediment of the 17-years old natural regenerated mangrove forest (Y17) with the original forest (Y74). No significant differences in phospholipid fatty acid (PLFA) profiles and microbial metabolism of most carbon substrates were found between these two forests. However, activities of dehydrogenase, protease, cellulase and phosphatase were lower in Y17 than Y74, and some specific microbial functions were also different. Both forests exhibited significant seasonal differences in enzyme activities and microbial characteristics, but such difference was larger in Y17 than Y74, indicating the regenerated forest was more sensitive to season. Correspondence analysis based on PLFA profiles and enzyme activities revealed the microbial community in Y17 was comparable to Y74, suggesting sediment microbial characteristics in natural regenerated mangroves could be restored.

Recovery of subtropical coastal intertidal system prokaryotes from a destruction event and the role of extracellular polymeric substances in the presence of endocrine disrupting chemicals.

Intertidal sediments constitute the micro-environment for the co-existence of endocrine disrupting chemicals (EDCs) and biofilms consisting of the microbial community and extracellular polymeric substances (EPS). However, the interactions and the resulting eco-function of this community are complex and poorly characterized, especially after a destruction event. This study evaluates the re-construction of biofilms in terms of the abundance of prokaryotic cells and related EPS characterization in two destroyed sedimentary matrices from subtropical environments simulated by sterilization in the presence of EDCs and investigates the role of EPS. The results show that benthic prokaryotes recover from the deposition of active prokaryotes in natural seawater and form biofilms after sterilization. Sterilization triggers the release of polysaccharides and protein from lysed native microbial cells and bound EPS in sedimentary organic matter, thus increasing their concentrations. The increased portion of EPS also acts as a persistent stress on re-colonizing prokaryotes and leads to the overproduction of sedimentary EPS. Due to the protective role mediated by EPS, the effect of EDCs on biofilm composition in sterilized sediment is not significant. The sedimentary matrix is the most important determinant of the composition of the biofilm and the occurrence of EDCs. At the end of an 84-day experiment, the abundance of prokaryotic cells and the concentrations of polysaccharides and protein in mangrove sediment are 1.6-1.8 times higher than those in sandflat sediment, regardless of EDCs. Sandflat sediment exhibits higher concentrations of nonylphenol and bisphenol A but a lower concentration of 17α-ethinylestradiol than mangrove sediment. This study enhances our understanding of the role of sedimentary biofilms and the fate of EDCs in intertidal systems and highlights the benefit of a destructive event in enhancing ecosystem function, particularly tolerance to EDC adversity due to EPS production.

Removal, seasonal variation, and environmental impact of parabens in a municipal wastewater treatment facility in Guangzhou, China.

The occurrence, seasonal variation, and environmental impact of five widely used parabens, methyl-(MeP), ethyl-(EtP), n-propyl-(n-PrP), n-butyl-(n-BuP), and benzyl-(BzP) parabens, were investigated in a municipal wastewater treatment plant (WWTP) located in Guangzhou, China, for 1 year. The concentrations of ∑5parabens in the influent and the effluent were 94.2-957 and 0.89-14.7 ng L-1, respectively. The influent paraben concentrations in autumn were significantly lower than in winter, spring, and summer, and the concentrations were generally higher in spring. The removal efficiencies of ∑5parabens in the dissolved phase were over 96%, with high efficiencies in MeP, EtP, and n-PrP. Risk assessment indicated that parabens in the effluent were not likely to pose an environmental risk to aquatic ecosystems. The present study indicates that the treatment processes employed in full-scale WWTPs are effective at removing parabens and highlights the possibility of utilizing WWTPs for restoring water quality in riverine and coastal regions heavily impacted by paraben contamination.

Microplastics in invertebrates on soft shores in Hong Kong: Influence of habitat, taxa and feeding mode.

Microplastic (MP) pollution in the marine environment has gained much concern in recent years. This study investigated the occurrence of MPs in invertebrates collected on 18 mudflats and sandy beaches in Hong Kong and its relationships to biological taxon, feeding mode and habitat. In total 38 species of gastropods, bivalves and crabs were collected and the mean number of suspected microplastics ranged from 0 to 9.68 particles g-1 wet weight or 0 to 18.4 particles individual-1. Around 26% of the suspected microplastics were confirmed to be synthetic polymers, including CP (cellophane), PET (polyethylene terephthalate), and PA (polyamide). Microplastic fibres were the most abundant type of MPs, followed by pellets. Significantly higher abundance of suspected microplastics was found in gastropods. Since MP abundance might vary with taxon, it is recommended to include different taxonomic groups in any ecological assessment of the impact of MPs.

Occurrence, composition and biological risk of organophosphate esters (OPEs) in water of the Pearl River Estuary, South China.

Since the production of brominated flame retardants has been gradually phased out, organophosphate esters (OPEs) are increasingly used as the substitutes. Given their toxicity and water solubility, OPEs may jeopardize the aquatic environment and organisms. Here, we examined the concentration, composition, and biological risk of OPEs in the water collected from the eight major waterways in the Pearl River Delta, a highly industrialized region in China. We found a widespread occurrence of OPEs in this region (∑9OPEs: 134 to 442 ng L-1), dominated by TCPP, TCEP, and TnBP. Halogenated OPEs were dominant over alkyl and aromatic OPEs. The biological risk of OPEs, mainly contributed by TPhP and TnBP, was low (RQ < 0.1). The contamination level of OPEs in the Pearl River Delta was likely associated with the degree of industrial activities. Although OPEs posed low risk to aquatic organisms, more attention should be paid to some OPEs in the future, such as TnBP, due to the high usage and toxicity. Considering the concentrations of OPEs worldwide and their usage, OPEs may become the emerging pollutants of global concern in the next decade.

Degradation of BDE-47 in mangrove sediments with amendment of extra carbon sources.

Polybrominated diphenyl ethers (PBDEs) are widely detected in coastal wetlands but their remediation is still difficult. In this study, different carbon sources, namely formate, acetate, pyruvate, lactate, succinate, methanol and ethanol, were added to mangrove sediments contaminated with BDE-47, a common PBDE congener, to enhance its degradation. After 2-month incubation, all carbon addition significantly enhanced degradation percentages. The residual BDE-47 percentage significantly correlated with the abundance of total bacteria and Dehalococcoides spp. The addition of methanol, acetate and succinate also achieved significantly higher degradation rates and shorter half-lives than sediments without carbon amendment at the end of 5-month incubation, although degradation percentages were comparable between sediments with and without extra carbon. The degradation pathway based on the profiles of degradation products was also similar among treatments. The results indicated the stimulatory effect of extra carbon sources on BDE-47 degradation in contaminated sediments was carbon- and time-specific.

Degradation of BDE-47 in mangrove sediments under alternating anaerobic-aerobic conditions.

Polybrominated diphenyl ethers (PBDEs) resistant to degradation have significant environmental impacts. Anaerobic reductive debromination and aerobic oxidation of PBDEs by microorganisms are main removal mechanisms during natural attenuation, but previous studies often focused on the process under either aerobic or anaerobic condition leading to unsatisfactory removal. The present study aims to remove PBDEs by employing alternating anaerobic-aerobic condition, which is common in inter-tidal mangrove sediments, and elucidate the degradation pathways. During 40-week experiment, BDE-47 reduced with an accumulation of tri-BDEs and di-BDEs as debromination products in all sediments. However, the removal percentages of BDE-47 and the concentrations of debromination congeners varied among flushing regimes. Sediments under less frequent flushing regime (longer duration of aerobic period) had significantly lower concentration and proportion of debromination products, especially BDE-17, than that under more frequent regime (longer anaerobic period). BDE-17 then went through aerobic degradation pathway, as evidenced by the accumulation of its hydroxylation form. Microbial analyses further revealed that less frequent regime favored accumulation of biphenyl dioxygenase gene for aerobic degradation, while more frequent tidal regime promoted growth of dehalogenating bacteria for reductive debromination. This study first time demonstrated that PBDEs in contaminated sediments could be removed under alternating anaerobic-aerobic conditions.

Contamination of polybrominated diphenyl ethers (PBDEs) in watershed sediments and plants adjacent to e-waste sites.

Polybrominated diphenyl ethers (PBDEs) are one of the persistent toxic organic pollutants in watersheds near electrical and electronic waste (e-waste) sites (EWS). Spatial redistribution, translocation and bioaccumulation of PBDEs in natural sediment-plant ecosystems, however, are still unclear. The contamination and distribution of PBDEs in core sediments and wetland plants from two EWS and two mangrove forest sites (MFS) were investigated. The eight PBDE congeners were all detected in plant tissue and sediment samples, indicating PBDE contamination was common and severe, and their spatial variations were significant. Although sediments from EWS had higher PBDE concentrations than those in MFS, with an extremely high value of 36392 ±â€¯5992 ng g-1 dw, mangroves could be the sink of PBDEs, as high concentrations (327 ±â€¯48 ng g-1 dw) were also detected in mangrove sediments. The historical usage of PBDEs was reflected by their distribution in mangrove sediment core but not so in e-waste sediment core. PBDEs were taken up and accumulated in six wetland plants, with more accumulation in mangrove plants. These results demonstrated that PBDEs were not only contaminated in sediments adjacent to e-waste sites but also plant tissues. PBDEs could enter other environments via plant littering and/or herbivorous processes that must not be neglected.

Changes in microbial community during removal of BDE-153 in four types of aquatic sediments.

Indigenous microorganisms in sediments could degrade polybrominated diphenyl ethers (PBDEs), but how the microbial communities respond to PBDEs was seldom reported. The effect of BDE-153, a common congener in aquatic environments, on the microbial communities in four types of aquatic sediments was evaluated during the 150days' incubation under an anaerobic condition. The intrinsic potential to remove BDE-153 varied significantly among four sediment types, and the removal rates of mangrove, mudflat, marine and freshwater sediments were 0.013, 0.013, 0.011, and 0.009day-1, respectively. The observed microbial species, Simpson, Shannon, and Chao1 indices in all sediments were rather stable and were not changed significantly by BDE-153 amendment. However, BDE-153 amendment altered the microbial community compositions in three saline sediments at the end of the incubation period. Distance-based multivariate multiple regression analysis revealed that salinity, total organic carbon (TOC) and BDE-52, the major debromination product of BDE-153, were the three main factors explaining the variations in microbial community compositions in BDE-treated sediments; whereas salinity, TOC and pH were the main contributing factors in control sediments without BDE-153. The daughter congeners generated during anaerobic debromination process need more attention, especially their effect on the microbial communities in aquatic sediments.

Overproduction of microbial extracellular polymeric substances in subtropical intertidal sediments in response to endocrine disrupting chemicals.

Microorganisms and their extracellular polymeric substances (EPS) in sediments are important in sediment stabilization and the fate of pollutants. However, how toxic organic pollutants affect bacteria and EPS in sediments, particularly in subtropical intertidal zones is poorly known. The present study aims to investigate the bacterial abundance and related EPS in simulated intertidal sandflat and mangrove sediments under the stress of endocrine disrupting chemicals (EDCs). Results showed that the temporal changes of the bacterial number in both sandflat and mangrove sediments were similar, increased from days 0 to 56 then became steady during the 84-days incubation. Bacteria exhibited an important role in the production of high molecular weight (HMW) EPS protein and the degradation of the low molecular weight (LMW) EPS protein. During incubation, the EPS polysaccharides changed from a colloidal-LMW fraction at the beginning to a more complex-HMW fraction at the end of the experiment. The increases in the concentration of HMW polysaccharides might contribute to sediment stabilization. Among different spiked EDCs, nonylphenol (NP) and 17α-ethinylestradiol (EE2) tended to accumulate in both sandflat and mangrove sediments and posed stresses to bacterial growth, especially the latter sediment. The persistent EDCs promoted a higher production of EPS polysaccharides and proteins in both sediments when compared to the respective control, but the EPS in the sandflat sediment was mainly in the colloidal fraction while the bound fraction was more abundant in the mangrove sediment. The present results enhance our understanding of the effects of EDCs on sediment biofilms in intertidal systems. This study also demonstrates the significance of EPS polysaccharides and proteins in sediment stabilization and provides a fundamental basis for future microbiology studies.

Growth and Cd uptake by rice (Oryza sativa) in acidic and Cd-contaminated paddy soils amended with steel slag.

Contamination of rice (Oryza sativa) by Cd is of great concern. Steel slag could be used to amend Cd-contaminated soils and make them safe for cereal production. This work was conducted to study the effects of steel slag on Cd uptake and growth of rice plants in acidic and Cd-contaminated paddy soils and to determine the possible mechanisms behind these effects. Pot (rhizobag) experiments were conducted using rice plants grown on two acidic and Cd-contaminated paddy soils with or without steel slag amendment. Steel slag amendment significantly increased grain yield by 36-45% and root catalase activity, and decreased Cd concentrations in brown rice by 66-77% compared with the control, in both soils. Steel slag amendment also markedly decreased extractable soil Cd, Cd concentrations in pore-water and Cd translocation from roots to above-ground parts. It also significantly increased soil pH, extractable Si and Ca in soils and Ca concentrations in roots. Significant positive correlations were found between extractable soil Cd and Cd concentrations in rice tissues, but it was negatively correlated with soil pH and extractable Si. Calcium in root tissues significantly and negatively correlated with Cd translocation factors from roots to straw. Overall, steel slag amendment not only significantly promoted rice growth but decreased Cd accumulation in brown rice. These benefits appear to be related to improvements in soil conditions (e.g. increasing pH, extractable Si and Ca), a reduction in extractable soil Cd, and suppression of Cd translocation from roots to above-ground parts.

Performance and bacterial community structure of a 10-years old constructed mangrove wetland.

Constructed mangrove wetland has been used for wastewater treatment but its long-term performance has not been reported. One-year monitoring of a 10-years old horizontal subsurface-flow constructed mangrove wetland consisting of three belts, two with mangrove plants and one without, revealed that the system maintained high and stable removal percentages of organic matter and nutrients, and planted belts performed better than unplanted control. Substrates in belts planted with Aegiceras corniculatum or Kandelia obovata had higher abundance of ammonifiers, nitrifiers and denitrifiers but lower total heterotrophic bacteria than unplanted substrate. Denaturing gradient gel electrophoresis showed that microbial diversity in planted substrate was significantly lower than that in unplanted one. The bacteria in substrates, irrespective to belts, were phylogenetically related to Proteobacteria (most dominant), Acidobacteria, Firmicutes, Nitrospirae, Gemmatimonadetes, Chloroflexi and Cyanobacteria. The steady performance of this 10-year old constructed mangrove wetland was affected by the abundance and diversity of bacterial community in substrate.

Impact of habitat management on waterbirds in a degraded coastal wetland.

The loss of coastal wetlands in Hong Kong Mai Po Nature Reserve adversely affected wetland-depended species. To mitigate this impact, gei wai ponds were reconstructed according to a set of biodiversity management zones (BMZs). This study, based on Canonical Correspondence Analysis (CCA), investigated if waterbird distribution was related to BMZ characteristics. Based on habitat characteristics, ponds in the same BMZ generally clumped in the same quadrant or within a short distance on CCA scatter plots, indicating that a BMZ zone produced common habitat traits. Ponds in a close distance on the plot had similar bird abundance or community structure. Significant correlations were noted between the abundance of cormorants and tall tree, and between waders and bare ground areas within study ponds. This study indicated that the control of key habitat factors was important for the success of reconstruction of gei wais and management of waterbirds in Mai Po.

Degradation pathways of 1-methylphenanthrene in bacterial Sphingobium sp. MP9-4 isolated from petroleum-contaminated soil.

Alkylated polycyclic aromatic hydrocarbons (PAHs) are abundant in petroleum, and alkylated phenanthrenes are considered as the primary PAHs during some oil spill events. Bacterial strain of Sphingobium sp. MP9-4, isolated from petroleum-contaminated soil, was efficient to degrade 1-methylphenanthrene (1-MP). A detailed metabolism map of 1-MP in this strain was delineated based on analysis of metabolites with gas chromatograph-mass spectrometer (GC-MS). 1-MP was initially oxidized via two different biochemical strategies, including benzene ring and methyl-group attacks. Benzene ring attack was initiated with dioxygenation of the non-methylated aromatic ring via similar degradation pathways of phenanthrene (PHE) by bacteria. For methyl-group attack, mono oxygenase system was involved and more diverse enzymes were needed than that of PHE degradation. This study enhances the understanding of the metabolic pathways of alkylated PAHs and shows the significant potential of Sphingobium sp. MP9-4 for the bioremediation of alkylated PAHs contaminated environments.

Vertical distribution of dehalogenating bacteria in mangrove sediment and their potential to remove polybrominated diphenyl ether contamination.

The removal and degradation of polybrominated diphenyl ethers (PBDEs) in sediments are not clear. The vertical distribution of total and dehalogenating bacteria in sediment cores collected from a typical mangrove swamp in South China and their intrinsic degradation potential were investigated. These bacterial groups had the highest abundances in surface sediments (0-5cm). A 5-months microcosm experiment also showed that surface sediments had the highest rate to remove BDE-47 than deeper sediments (5-30cm) under anaerobic condition. The deeper sediments, being more anaerobic, had lower population of dehalogenating bacteria leading to a weaker BDE-47 removal potential than surface sediments. Stepwise multiple regression analysis indicated that Dehalococcoides spp. were the most important dehalogenating bacteria affecting the anaerobic removal of BDE-47 in mangrove sediments. This is the first study reporting that mangrove sediments harbored diverse groups of dehalogenating bacteria and had intrinsic potential to remove PBDE contamination.

Effects of alkaline and bioorganic amendments on cadmium, lead, zinc, and nutrient accumulation in brown rice and grain yield in acidic paddy fields contaminated with a mixture of heavy metals.

Paddy soils and rice (Oryza sativa L.) contaminated by mixed heavy metals have given rise to great concern. Field experiments were conducted over two cultivation seasons to study the effects of steel slag (SS), fly ash (FA), limestone (LS), bioorganic fertilizer (BF), and the combination of SS and BF (SSBF) on rice grain yield, Cd, Pb, and Zn and nutrient accumulation in brown rice, bioavailability of Cd, Pb, and Zn in soil as well as soil properties (pH and catalase), at two acidic paddy fields contaminated with mixed heavy metals (Cd, Pb, and Zn). Compared to the controls, SS, LS, and SSBF at both low and high additions significantly elevated soil pH over both cultivation seasons. The high treatments of SS and SSBF markedly increased grain yields, the accumulation of P and Ca in brown rice and soil catalase activities in the first cultivation season. The most striking result was from SS application (4.0 t ha-1) that consistently and significantly reduced the soil bioavailability of Cd, Pb, and Zn by 38.5-91.2 % and the concentrations of Cd and Pb in brown rice by 20.9-50.9 % in the two soils over both cultivation seasons. LS addition (4.0 t ha-1) also markedly reduced the bioavailable Cd, Pb, and Zn in soil and the Cd concentrations in brown rice. BF remobilized soil Cd and Pb leading to more accumulation of these metals in brown rice. The results showed that steel slag was most effective in the remediation of acidic paddy soils contaminated with mixed heavy metals.