Application of Short Sequential Extraction Procedure(SSEP) for the Determination of Zn, Cu, and Cd Contents in Riverbed Sludge in Hejiagou, Harbin, China

A short sequential extraction procedure（SSEP） was applied to the determination of more readily available metal fractions of Zn, Cu, and Cd in the riverbed sludge in Hejiagou, Harbin, China. From the results, a potential order of metal availability in seven sludge samples was proposed： Cd 〈 Cu 〈 Zn, and samples S1 , S2, and S4 were used for the determination of total Zn content, and sample S3 used for the determination of total Cu content in the mobile and the mobilizable fractions showed the highest pollution risk. The results with regard to metal mobility in sludge samples were confirmed by the individual and global contamination factors that were calculated from the nonresidual and residual metal contents. The results obtained from metal-release experiments after exposure of sludge to environmental conditions agreed well with those obtained from both SSEP and the individual and global contamination factors, indicating that the maximum metal release could be an additional factor to evaluate the heavy metal availability in contaminated sludge. A substantial time saving was achieved by using the metal-release method in the present study.

Investigation on Fe,Mn,Zn,Cu,Pb and Cd fractions in the natural surface coating samples and surficial sediments in the Songhua River,China

Natural surface coating samples （NSCSs） from the surface of shingles and surficial sediments （SSs） in the Songhua River, China were employed to investigate the relationship between NSCSs and SSs in fractions of heavy metals （Fe, Mn, Zn, Cu, Pb, and Cd） using the modified sequential extraction procedure （MSEP）. The results show that the differences between NSCSs and SSs in Fe fi＇actions were insignificant and Fe was dominantly present as residual phase （76.22% for NSCSs and 80.88% for SSs） and Fe-oxides phase （20.33% for NSCSs and 16.15% for SSs）. Significant variation of Mn distribution patterns between NSCSs and SSs was observed with Mn in NSCSs mainly present in Mn-oxides phase （48.27%） and that in SSs present as residual phase （45.44%）. Zn, Cu, Pb and Cd were found dominantly in residual fractions （〉48%）, and next in solid oxides/hydroxides for Zn, Pb and Cd and in easily oxidizable solids/compounds form for Cu, respectively. The heavy metal distribution patterns implied that Fe/Mn oxides both in NSCSs and SSs were more important sinks for binding and adsorption of Zn, Pb and Cd than organic matter （OM）, and inversely, higher affinity of Cu to OM than Fe/Mn oxides in NSCSs and SSs was obtained. Meanwhile, it was found that the distributions of heavy metals in NSCSs and SSs were similar to each other and the pseudo-total concentrations of Zn, Cu, Pb and Cd in NSCSs were greater than those in SSs, highlighting the more importance for NSCSs than SSs in controlling behaviours of heavy metals in aquatic environments.

Nutrient alterations following biochar application to a Cd-contaminated solution and soil

Biochars,when applied to contaminated solutions or soils,may sequester potentially toxic elements while releasing neces-sary plant nutrients.This purpose of this study focused on quantifying both phenomenon following wheat straw(Triticum aestivum L.)biochar application(0,5,and 15%by wt)to a Cd containing solution and a Cd-contaminated paddy soil using 240-day laboratory batch experiments.Following both experiments,solid phases were analyzed for elemental associations using a combination of wet chemical sequential extractions and synchrotron-based X-ray absorption spectroscopy(XAS).When wheat straw biochar was applied at 15%to Cd containing solutions,Cd and Zn concentrations decreased to below detection in some instances,Ca and Mg concentrations increased by up to 290%,and solution pH increased as compared to the 5%biochar application rate.Similar responses were observed when biochar was added to the Cd-contaminated paddy soil,suggesting that this particular biochar has the ability to sequester potentially toxic elements while releasing necessary plant nutrients to the soil solution.When significant,positive correlations existed between nutrient release over time,while negative correlations were present between biochar application rate,potentially toxic element sorption and pH.The latter suggests that potentially toxic elements were sorbed by a combination of organic functional groups or mineral precipitation based on whether pH was above or below~7.In support of this contention,the wet chemical sequential extraction procedure in conjunction with previously observed Cd or current Zn XAS showed that biochar application promoted the formation of layered double hydroxides,sorption to(oxy)hydroxides,and organically bound to biochar as Zn species.As a multi-functional material,biochar appears to play an important role in sequestering Cd while releasing essential plant nutrients.These findings suggest that biochar may be a‘win-win’for improving environmental quality in potentially toxic element contaminated agroecosystems.