Degradation of platinum electrocatalysts for methanol oxidation by lead contamination

Platinum exhibits high electrocatalytic activity toward various reactions but might be poisoned by some species. This communication reports a new finding that the electrocatalytic activity of platinum for methanol oxidation will be largely lost in a lead-contaminated environment. This activity loss is demonstrated in an electrochemical cell using a lead counter electrode for measuring the activity of platinum electrode towards methanol oxidation. The recorded methanol oxidation current in this cell is significantly decreased compared with that using a platinum counter electrode. The possible mechanism is related to the adsorption of trace lead ions from the lead counter electrode, as confirmed by comparing the calculated binding energies of platinum and lead ions with oxygen ion. This report is of great importance for reliably designing and efficiently managing direct methanol fuel cells, because trace lead might be present in various components in the fuel cell systems or in air and attention should be paid to its negative effect.

Effect of Lead Contamination on Soil Microbial Activity Measured by Microcalorimetry

Microcalorimetry was used to investigate the microbial activity in three types of soil （orchard soil, crop soil, forest soil） in Wuhan, China, and to evaluate the influence of different concentrations of lead （Pb^2＋） on soil microbial activity. The experimental results revealed that due to different physical and chemical characteristics of the soils, soil microbial activity in three soil samples were in a descending sequence： orchards soil, crops soil, forest soil. Six levels ofPb viz. 0, 10, 20, 40, 80, 160 μg·g^-1 were applied in these soils, and the results showed that an in- crease of the amount of Pb^2＋ is associated with a decrease in microbial activity in the soils due to the toxic effect of Pb^2＋. In order to gain further insight of the sequential change of microorganisms, determination of colony forming units （CFU） was performed to provide a negative linear correlation between the heat effect and the respective number of microorganisms in the system.

Identification and quantification of lead source in sediment in the northern East China Sea using stable lead isotopes

Stable Pb isotopes in surface and core sediments were determined to identify the sources of Pb contaminants in the northern East China Sea(ECS).The Bayesian stable isotope mixing model was used to quantify the contributions of Pb sources.The results show that since the late 1980 s,ratios of^(207)Pb/^(206)Pb and^(208)Pb/^(206)Pb increased in the top 34-cm sediment shown in the coastal core samples,reflecting elevated anthropogenic Pb input in coastal sea.Seaward increase of^(207)Pb/^(206)Pb and^(208)Pb/^(206)Pb ratios in surface sediments reveals that anthropogenic Pb came mainly via atmospheric transmission into the ECS.Anthropogenic sources accounted for 12.0%-21.1%of the total Pb in sediments after the 1990 s.Coal combustion was the largest anthropogenic contributor(47.5%±18.8%),and Pb mining and smelting,cement production,and vehicle exhaust/gasoline contributed 23.2%±7.1%,19.0%±13.0%,and 10.3%±6.9%,respectively.The proportions of the anthropogenic sources gradually increased while geogenic source(riverine sediment)decreased from the coast to the outer shelf.This study demonstrated that the significant influence of atmospheric input of Pb contaminants into the ECS,and also the urgent need to control coal combustion and Pb discharge from industrial dust and fume emission in China.It also highlights the promising application of the Simmr model to quantify the proportions of multiple sources of trace elements in an environment.

Natural and anthropogenic sources of lead, zinc, and nickel in sediments of Lake Izabal, Guatemala

Sediments in Lake Izabal,Guatemala,contain substantial lead (Pb),zinc (Zn),and nickel (Ni).The lack of historical data for heavy metal concentrations in the sediments makes it difficult to determine the sources or evaluate whether inputs of metals to the lake have changed through time.We measured the relative abundances and concentrations of Pb,Zn,and Ni by X-Ray Fluorescence core scanning and by Inductively Coupled Plasma Optical Emission Spectrometry in three sediment cores to explore stratigraphic distributions of metals in the lake deposits.High amounts of Pb and Zn in the core taken near the Polochic Delta suggest that galena and sphalerite mining increased Pb and Zn delivery to Lake Izabal between ~1945 and 1965 CE.An up-core Ni increase in the core taken near a different mine on the north shore of Lake Izabal suggests that recent nickel mining operations led to an increase in Ni concentrations in the local sediments,but amounts in the other cores indicate that Ni is not widely distributed throughout the lake.Sediment cores from Lake Izabal are reliable recorders of heavy metal input to the lake,and were measured to establish background metal levels,which would otherwise be unavailable.Concentrations of Pb,Zn,and Ni in older,pre-20th-century Lake Izabal sediments reflect input from natural erosion of bedrock.Our results provide previously unavailable estimates of background metal concentrations in Lake Izabal before the onset of mining.These results are necessary for future monitoring related to mining contamination of the lake ecosystem.

Remediation mechanism of“double-resistant”bacteria—Sedum alfredii Hance on Pb-and Cd-contaminated soil

Background:Concentrations of heavy metals continue to increase in soil environments as a result of both anthro-pogenic activities and natural processes.Cadmium(Cd)and lead(Pb)is one of the most toxic heavy metals and pose health risks to both humans and the ecosystem.Therefore,effectively solving the problem of heavy metal pollution is the concern of soil workers.Among the existing remediation techniques,only the combined use of microorganisms and plants for remediation of heavy metal-contaminated soil is the greenest and most developed one.Consequently,based on this background,this study investigates the remediation mechanism of Pb and Cd heavy metals using the combined action of bacteria and Sedum alfredii Hance.Methods:In order to enrich the research theory of combined plant and microorganism remediation of heavy metal-contaminated soil,we constructed a heavy metal composite pollution remediation system by combining Pb and Cd-tolerant bacteria with the Pb and Cd hyperaccumulator plant—Sedum alfredii Hance to investigate its combined remediation effect on Pb and Cd composite contaminated soil.Results:The results showed that resistant bacteria were able to promote enrichment of Pb and Cd in Sedum alfredii Hance and J2(200 ml of bacterial solution)was significantly(P<0.05)more effective than J1(100 ml of bacterial solution).The resistant bacteria were able to alleviate the toxic effects of Pb and Cd heavy metals on Sedum alfredii Hance and promote growth while reducing rhizosphere soil pH.The resistant bacteria were able to significantly reduce the effective state of Pb and Cd in the rhizosphere soil(P<0.05),with the greatest reduction in the effective state of Pb in treatment A(Cd7Pb100 mg/kg),where J2 was reduced by 9.98%compared to J0,and the greatest reduction in the effective state of Cd in treatment C(Cd28Pb400 mg/kg),where J2 was 43.53%lower than J0.In addition,the resistant bacteria were able to increase the exchangeable state Cd content by 0.97 to 9.85%.The resistant bacteria had a weakly promoting effect and a highly inhibitory effect on the absorption of Pb by Sedum alfredii Hance.Conclusions:The resistant bacteria can change the rhizosphere environment and significantly improve the remedia-tion effect of Sedum alfredii Hance on heavy metal cadmium.The role of“double-resistant”bacteria in promoting the accumulation of Cd was greater than that of Pb.