Intraspecific differences in effects of co-contamination of cadmium and arsenate on early seedling growth and metal uptake by wheat

A hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium （Cd） （0-10 mg/L） and arsenate （As（V）） （0-8 mg/L） on the growth parameters and accumulation of Cd and As in six wheat varieties Jing- 9428, Duokang- 1, Jingdong- 11, Jing-411, Jingdong-8 and Zhongrnai-8. The endpoints of wheat seedlings, including seed germination, biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties （p 〈 0.05）. The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongrnai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongrnai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.

Impacts of heavy metals on 1,2-dichloroethane biodegradation in co-contaminated soil

1,2-Dichloroethane （DCA）, a potential mutagen and carcinogen, is commonly introduced into the environment through its industrial and agricultural use. In this study, the impact of lead and mercury on DCA degradation in soil was investigated, owing to the complex co-contamination problem frequently encountered in most sites. 1,2-Dichloroethane was degraded readily in both contaminated loam and clay soils with the degradation rate constants ranging between 0.370-0.536 week-1 and 0.309-0.417 week-1, respectively. The presence of heavy metals have a negative impact on DCA degradation in both soil types, resulting in up to 24.11% reduction in DCA degradation within one week. Both biostimulation and treatment additives increased DCA degradation, with the best degradation observed upon addition of glucose and a combination of diphosphate salt and sodium chloride, leading to about 17.91% and 43.50% increase in DCA degradation, respectively. The results have promising potential for effective remediation of soils co-contaminated with chlorinated organics and heavy metals. However, the best bioremediation strategy will depend on the soil types, microbial population present in the soil matrices, nutrients availability and metal forms.

Synergetic and Antagonistic Effects of Cadmium on Adsorption of Atrazine on Surficial Sediments

Co-contamination of atrazine（AT） and cadmium（Cd） on the surficial sediments（SSs） and natural suface coating samples（NSCSs） was investigated via thermodynamic adsorption experiments. The results show that surface coatings have a stronger ability to adsorb AT owing to their higher active components compared with surficial sediments. Synergetic and antagonistic effects of Cd on the adsorption of AT were observed. Cd at a lower concentration（≤4.0 mg/L） in the solid/liquid phase enhanced AT adsorption onto the surficial sediments（surface coatings）, while the adsorption of AT would be inhibited at a Cd concentration of more than 8.0 mg/L： AT coordinates strongly to Cd, and AT-Cd complexes seem to be more strongly adsorbed on sediments than AT alone, and at the adsorption of AT can take place on the sites where Cd has been previously adsorbed and Cd acts as a bridge for the interaction be- tween sediments and AT. With the increase of Cd concentration, the superfluous Cd may hold much more adsorption sites and thus inhibits the adsorption of AT. Meanwhile, the effects of co-existed AT on Cd adsorption on SSs（NSCSs） were insignificant since Cd has a stronger competitive ability to be absorbed on SSs（NSCSs）. The present study could be useful in predicting interactions of the metal ions with herbicides and potentially aid the design of remediation strategies for contaminated sediments and groundwater.

A Large-Scale Identification of Sediment-Associated Risks of Contamination with Heavy Metals and Organics: Indicators and Algorithms

As mediators in key biotransformation processes, the complex enzyme activities (measured as a total of extracellular and intracellular activity on sub-organism, organism and supra-organism level) have a high potential to be used as reliable indicators for risk identification in co-contaminated sediments with organics and heavy metals. Two enzyme activities—dehydrogenase activity (TTC-DHA) and phosphatase activity index (PAI) were measured by use of methods with tetrazolium chloride and p-nitrophenyl phosphate in polluted sediments of Middle Iskar River part, Bulgaria. The environmental state of river sector has been strongly influenced by the organics, nutrients, xenobiotics pollutants and by the intensive hydrotechnical activity for construction of 9 micro-hydro power plants. The change of hydrological regime was a factor for intensive sediment accumulation and concentration of pollutants in the area of the cascade. Data for total activities of dehydrogenases and phosphatases in sediments were compared with total count of culturable sediment bacteria and pollutants concentrations. The results showed that the enzyme activities correlated positively with bacterial abundance in sediments and organics content in sediments and negatively with concentrations of xenobiotic pollutants (heavy metals). This approves a high potential of enzyme indicators for regulation of ecosystem self-purification capacity and for early assessment of sediment-associated risks of co-contamination. The correlative relations allow dividing the mathematical algorithms for control and management of processes in technologically influenced hydroecosystem.

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

This work investigates the influence of electrokinetic-bioremediation(EK-BIO)on remediating soil polluted by persistent organic pollutants(POPs)and heavy metals(mainly Cu,Pb and Ni),originated from electronic waste recycling activity.The results demonstrate that most of POPs and metals were removed from the soil.More than 60%of metals and 90%of POPs in the soil were removed after a 30-day EK-BIO remediation assisted by citrate.A citrate sodium concentration of 0.02 g/L was deemed to be suitable because higher citrate did not significantly improve treatment performance whereas increasing dosage consumption.Citrate increased soil electrical current and electroosmotic flow.After remediation,metal residues mainly existed in stable and low-toxic states,which could effectively lower the potential hazard of toxic metals to the surrounding environment and organisms.EK-BIO treatment influenced soil microbial counts,dehydrogenase activity and community structure.

Simultaneous dissipation of trichloroethene and arsenic from co-contaminated groundwater by coupling biodechlorination and biodetoxification with assistance of biochar

Co-contamination of groundwater with trichloroethene(TCE)and arsenic(As)is a widespread problem in industrial sites.The simultaneous biological removal of As and TCE has not yet been developed.This study incorporated biochar into anaerobic dechlorination system to achieve a greatly accelerated dissipation and co-removal of TCE and As.Biochar eliminated microbial lag(6 days)and achieved a 100%TCE removal within 12 days even at a relatively high initial concentration(TCE:30 mg L^(−1);As(V):4 mg L^(−1)),while without biochar,only 75%TCE was removed until day 18.Bio-char adsorbed TCE and the intermediate products allowing them to be degraded on its surface gradually,maintaining a high metabolic activity of microbes.Biochar facilitated the preferential colonization of its surfaces by dechlorinating microorganisms(Clostridium and Dehalococcoides)and suppressed hydrogen-competing microorganisms(Desulfo-vibrio)in water.Biochar itself cannot adsorb As,however,separation of biochar carrying the As-laden microorgan-isms achieved 50-70%As-removal from groundwater.The biochar-amended incubations were found to be enriched with microbes possessing more crucial As-transforming genes(K00537-arsC and K07755-AS3MT),and upregulated amino acid metabolism,thus enhancing the self-detoxification ability of microorganisms to transform As(Ⅴ)to As(Ⅲ)or volatile organic As.This study proposes a strategy of regulating microbes’metabolic activity by biochar to achieve simultaneous removal of coexisting contaminations,which is an important step prior to examining the feasibility of biochar application for enhanced bioremediation.

Biochar alleviates metal toxicity and improves microbial community functions in a soil co-contaminated with cadmium and lead

Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils.Yet,it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals.The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar(SCB)in cadmium(Cd)-lead(Pb)co-contaminated soils.SCBs(400 and 600°C)decreased the available concentrations of Cd and Pb,increased organic carbon(OC)and dissolved organic carbon(DOC)contents in soil.The decrease of metal availability was greater with 600°C SCB than with 400°C SCB,and metal immobilization was greater for Cd(16%)than for Pb(12%)in co-spiked soils amended with low-temperature SCB.Biochar application improved microbial activity and biomass,and enzymatic activity in the soils co-spiked with metals,but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils.SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobili-zation of metals.Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB.The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB,due to its higher labile C fraction.Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.

Simultaneous adsorption of As(Ⅲ) and Pb(Ⅱ) by the iron-sulfur codoped biochar composite:Competitive and synergistic effects

Simultaneous elimination of As(Ⅲ) and Pb(Ⅱ) from wastewater is still a great challenge.In this work,an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(Ⅲ) and Pb(Ⅱ).The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction.The mechanism of As(Ⅲ) removal could be illustrated by surface complexation,oxidation and precipitation.In addition to precipitation and complexation,the elimination mechanism of Pb(Ⅱ) also contained ion exchange and electrostatic interactions.Competitive and synergistic effects existed simultaneously in the co-contamination system.The suppression of As(Ⅲ) was ascribed to competitive complexation of the two metals on Fe/S-BC,while the synergy of Pb(Ⅱ) was attributed to the formation of the PbFe2(AsO_(4))2(OH)2.Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(Ⅲ) and Pb(Ⅱ),regardless of pH dependency and interference by various coexisting ions.The maximum adsorption capacities of the Fe/S-BC for As(Ⅲ) and Pb(Ⅱ) were 91.2 mg/g and 631.7 mg/g,respectively.Fe/S-BC could be treated as a novel candidate for the elimination of As(Ⅲ)-Pb(Ⅱ) combined pollution.

Effects of biochars on the bioaccessibility of phenanthrene/pyrene/zinc/lead and microbial community structure in a soil under aerobic and anaerobic conditions

The immobilization of co-contaminants of organic and inorganic pollutants by biochar is an efficient remediation strategy. However, the effect of biochar amendments on the bioaccessibility of the co-contaminants in dry versus flooded soils has rarely been compared. In batch experiments, bamboo-derived biochar（BB） had a higher sorption capacity for phenanthrene（Phe）/pyrene（Pyr）/zinc（Zn） than corn straw-derived biochar（CB）, while CB had a higher sorption capacity for lead（Pb） than BB. After 150 days of incubation, the amendments of 2% CB, 0.5% BB and 2% BB effectively suppressed the dissipation and reduced the bioaccessibility of Phe/Pyr by 15.65%/18.02%, 17.07%/18.31%and 25.43%/27.11%, respectively, in the aerobic soils. This effectiveness was more significant than that in the anaerobic soils. The accessible Zn/Pb concentrations were also significantly lower in the aerobic soils than in the anaerobic soils, regardless of treatments.The Gram-negative bacterial biomass and the Shannon–Weaver index in the aerobic soil amended with 2% CB were the highest. The soil microbial community structure was jointly affected by changes in the bioaccessibility of the co-contaminants and the soil physiochemical properties caused by biochar amendments under the two conditions. Therefore, dry land farming may be more reliable than paddy soil cultivation at reducing the bioaccessibility of Phe/Pyr/Zn/Pb and enhancing the soil microbial diversity in the short term.