Simultaneous removal of Cd(II) and As(V) by ferrihydrite-biochar composite: Enhanced effects of As(V) on Cd(II) adsorption.

The coexistence of cadmium (Cd(II)) and arsenate (As(V)) pollution has long been an environmental problem. Biochar, a porous carbonaceous material with tunable functionality, has been used for the remediation of contaminated soils. However, it is still challenging for the dynamic quantification and mechanistic understanding of the simultaneous sequestration of multi-metals in biochar-engineered environment, especially in the presence of anions. In this study, ferrihydrite was coprecipitated with biochar to investigate how ferrihydrite-biochar composite affects the fate of heavy metals, especially in the coexistence of Cd(II) and As(V). In the solution system containing both Cd(II) and As(V), the maximum adsorption capacities of ferrihydrite-biochar composite for Cd(II) and As(V) reached 82.03 µmol/g and 531.53 µmol/g, respectively, much higher than those of the pure biochar (26.90 µmol/g for Cd(II), and 40.24 µmol/g for As(V)) and ferrihydrite (42.26 µmol/g for Cd(II), and 248.25 µmol/g for As(V)). Cd(II) adsorption increased in the presence of As(V), possibly due to the changes in composite surface charge in the presence of As(V), and the increased dispersion of ferrihydrite by biochar. Further microscopic and mechanistic results showed that Cd(II) complexed with both biochar and ferrihydrite, while As(V) was mainly complexed by ferrihydrite in the Cd(II) and As(V) coexistence system. Ferrihydrite posed vital importance for the co-adsorption of Cd(II) and As(V). The different distribution patterns revealed by this study help to a deeper understanding of the behaviors of cations and anions in the natural environment.

Cadmium threshold for acidic and multi-metal contaminated soil according to Oryza sativa L. Cadmium accumulation: Influential factors and prediction model.

Cadmium (Cd) contamination in soil-rice systems has become a global public concern. However, influencing factors and the contamination threshold of Cd in soils remain largely unknown owing to soil heterogeneity, which limits our ability to assess the risk to human health and to draft appropriate environmental policies. In this study, we selected the soil-rice system of Longtang and Shijiao town in southern China, which was characterized by multi-metal acidic soil contamination due to improper electronic waste recycling activities, as a case to analyze the influence of different soil properties on the Cd threshold in the soil and Cd accumulation in rice. The results showed that soil organic matter (SOM) was the main factor regulating Cd accumulation in the soil-rice system. Moreover, compared with the total Cd concentration, the DTPA-extractable Cd concentration in the soil was a better predictor of Cd transportation in the soil-rice system. According to the prediction model, when SOM was < 35 g kg-1, the CdDTPA threshold was 0.16 mg kg-1 with a 95% likelihood of Cdrice accumulation above the Chinese food standard limit (0.2 mg kg-1). Conversely, when SOM was ≥ 35 g kg-1, the CdDTPA threshold was only 0.03 mg kg-1. This study of the influence of SOM on Cd accumulation in a soil-rice system confirms that SOM is a crucial parameter for better and safer rice production, especially in multi-metal contaminated acidic soils.

Application of phosphorus amendments reduces metal uptake and increases yield of Oryza saliva L. (rice) in Cd/Cu-contaminated paddy field.

To alleviate worldwide food safety issues caused by metal contamination, an easily available material is urgently needed for extensive application. In this study, calcium magnesium phosphate fertiliser (Pcm) was applied to a Cd/Cu co-contaminated paddy field in comparison with limestone and organic fertiliser. The results showed that only Pcm is effective in simultaneously reducing Cd uptake by 56.7% and Cu uptake by 36.2% in Oryza saliva L. (rice). The rice yield, reduced mainly by Cu, also increased by 30.1% with respect to the enhancement of soil pH, cation exchange capacity and availability of phosphorus, as well as the reduction in availabilities of Cd and Cu. Additionally, Pcm dramatically shaped the bacterial community structure, with Proteobacteria and Firmicutes predominant in the soils. The beneficial genera Exiguobacterium, Citrobacter, and Acinetobacter, which are vital for phosphate dissolution and Cd/Cu immobilisation, were also enriched. The results demonstrated that the application of Pcm at 0.4% (w:w) was able to enhance both crop quantity and quality in Cd/Cu co-contaminated paddy fields by reducing Cu/Cd availability, promoting rice yield, and reshaping bacterial community structures.

Field study on the soil bacterial associations to combined contamination with heavy metals and organic contaminants.

The understanding of soil microbial associations to combined contamination would substantially benefit the restoration of damaged ecosystems, which is currently limited at the field scale. In this study, we investigated the soil bacterial associations to combined contamination with metals (Cd, Cu, Hg, Pb, and Zn), polyaromatic hydrocarbons (PAHs), and polybrominated diphenyl ethers (PBDEs). Samples were collected from field sites under five land-use patterns with electronic waste recycling. Results showed that the contents of Cd (0.22-12.86 mg/kg), Cu (17-14,136 mg/kg), Pb (4.6-77,014 mg/kg), Hg (0.28-22 mg/kg), Zn (26-42,495 mg/kg), PAHs (4.6-1753 µg/kg), and PBDEs (1.9-1079 µg/kg) varied significantly across sites. We observed positive correlations between catalase activity and heavy metals, indicative of a resistance response to the oxidative stress induced by metals. Furthermore, the bacterial community diversity was found to be determined primarily by PBDEs, whereas acenaphthylene, available phosphorus, and 2,2',3,3',4,5,6-heptabrominated diphenyl ether (BDE-183) were the three major drivers affecting community composition. The co-occurrence network constructed for bacterial communities exposed to combined contamination was non-random with scale-free, small-world and modularity features. We further proposed functional roles of the modules including stress resistance, hydrocarbon degradation, and nutrient cycling. Overall, the findings of redundancy analysis, variation partition analysis and the co-occurrence network indicated that soil bacterial community under combined contamination cooperated to survive. Members including Rhodoplanes and Nitrospira were capable of degrading PAHs and PBDEs in various pathways, while others, including Acinetobacter, Citrobacter, and Pseudomonas, reduced the metal toxicity to the community. Our findings provide new insights into the responses of soil bacteria, particularly in terms of inter-specific relationships, under combined contamination at the field scale.

Groundwater contaminated with short-chain chlorinated paraffins and microbial responses.

The vertical migrations of toxic and persistent short-chain chlorinated paraffins (SCCPs) in soils as well as the microbial responses have been reported, however, there is a paucity of data on the resulting groundwater contamination. Here, we determined the concentration and congener profile of SCCPs in the groundwater beneath a production plant of chlorinated paraffins (CPs) and characterized the microbial community to explore their responses to SCCPs. Results showed that SCCPs ranged from not detected to 70.3 µg/L, with C13-CPs (11.2-65.8%) and Cl7-CPs (27.2-50.6%), in mass ratio, as the dominant groups. Similar to the distribution pattern in soils, SCCPs in groundwater were distributed in hotspot pattern. CP synthesis was the source of SCCPs in groundwater and the entire contamination plume significantly migrated downgradient, while there was an apparent hysteresis of C13-CP migration. Groundwater microbial community was likely shaped by both hydrogeological condition (pH and depth) and SCCPs. Specifically, the microbial community responded to the contamination by forming a co-occurrence network with "small world" feature, where Desulfobacca, Desulfomonile, Ferritrophicum, Methylomonas, Syntrophobacter, Syntrophorhabdus, Syntrophus, and Thermoanaerobaculum were the keystone taxa. Furthermore, the interrelations between bacterial taxa and SCCPs indicated that the microbial community might cooperate to achieve the dechlorination and mineralization of SCCPs through either anaerobic organohalide respiration mainly functioned by the keystone taxa, or cometabolic degradation processes functioned by Aquabacterium and Hydrogenophaga. Results of this study would provide a better understanding of the environmental behavior and ecological effects of SCCPs in groundwater systems.

Distributions of chlorinated paraffins and the effects on soil microbial community structure in a production plant brownfield site.

The distributions of chlorinated paraffins (CPs) in soils and their ecological effects attract much attention, while site-scale data are still scarce. In this study, a comprehensive investigation was performed to understand the CP distributions at a CP production plant brownfield site, as well as their effects on soil microbial community. Short-, medium- and long-chain CPs (SCCPs, MCCPs, LCCPs) were detected in most samples with total contents ranging ND-5,090, ND-6,670, and ND-1450 ng g-1 (dw), respectively. A CP-hotspot was observed 10 m beneath the synthesis workshop, indicating the downward migration of CPs. The consistence of soil SCCP congener profiles with commercial product CP-52 suggested the leakage of CP products as the contamination source. Besides CPs, petroleum hydrocarbons (PHC) contamination also occurred beneath the synthesis workshop. Soil microbial community composition and diversity were significantly influenced by SCCPs (p < 0.05) despite their lower contents compared to other concerned contaminants. Microbial network analysis indicated nonrandom co-occurrence patterns, with Acinetobacter, Brevibacterium, Corynebacterium, Microbacterium, Stenotrophomonas, and Variibacter as the keystone genera. Genera from the same module showed significant ecological links (p < 0.05) and were involved in the degradation of PHCs and chlorinated organic contaminants. This study provides the first phylogenetic look at the microbial communities in CP contaminated soils, indicating that the long-term exposure to CPs and PHCs may lead to microbial group assemblages with the potential for degradation.