Impact of sewage sludge spreading on heavy metal speciation in tropical soils (Réunion, Indian Ocean)

Behavior of trace metals during composting of mixed sewage sludge and tropical green waste: a combined EDTA kinetic and BCR sequential extraction study in New Caledonia

The aim of the study was to assess the impact of composting on the release dynamics and partitioning of geogenic nickel (Ni), chromium (Cr) and anthropogenic copper (Cu) and zinc (Zn) in a mixture of sewage sludge and green waste in New Caledonia. In contrast to Cu and Zn, total concentrations of Ni and Cr were very high, tenfold the French regulation, due to their sourcing from Ni and Cr enriched ultramafic soils. The novel method used to assess the behavior of trace metals during composting involved combining EDTA kinetic extraction and BCR sequential extraction. BCR extraction revealed marked mobility of Cu and Zn: more than 30% of the total concentration of these trace metals was found in the mobile fractions (F1 + F2) whereas Ni and Cr were mainly found in the residual fraction (F4). Composting increased the proportion of the stable fractions (F3 + F4) of all four trace metals studied. Interestingly, only EDTA kinetic extraction was able to identify the increase in Cr mobility during composting, Cr mobility being driven by the more labile pool (Q1). However, the total mobilizable pool (Q1 + Q2) of Cr remained very low, < 1% of total Cr content. Among the four trace metals studied, only Ni showed significant mobility, the (Q1 + Q2) pool represented almost half the value given in the regulatory guidelines. This suggests possible environmental and ecological risks associated with spreading our type of compost that require further investigation. Beyond New Caledonia, our results also raise the question of the risks in other Ni-rich soils worldwide.

Phosphate-solubilizing bacteria improve the phytoremediation efficiency of Wedelia trilobata for Cu-contaminated soil

In a controlled experiment, we assessed the effect of phosphate-solubilizing bacterium (PSB) on the soil metal (Cu²⁺) phytoremediation by Wedelia trilobata and examined the effect of the interaction of Cu contamination and PSB on the growth of W. trilobata. We also explored the effect of the interaction of Cu contamination and PSB on the soil microflora. The results showed that the removal efficiency of Cu from soil by W. trilobata increased with an increase in the concentration of PSB, and the translocation factors of Cu (i.e., leaf:root and stem:root) were both significantly upregulated by PSB. The PSB significantly promoted the growth of W. trilobata; however, the effect of the Cu-PSB interaction on the leaf net photosynthetic rate (Pn) of W. trilobata was not significant, whereas copper contamination had a significant negative influence on the soil microflora, PSB had a significant positive influence on the soil microflora. Thus, PSB improved the phytoremediation efficiency of W. trilobata in Cu-contaminated soil because of the positive influence on the soil microflora, improving soil quality, which then increased the growth of W. trilobata in Cu-contaminated soil. The vigorous growth of W. trlobata led to higher of Cu absorption and translocation from soil as the ultimate result.

Fractionation, Bioaccessibility, and Risk Assessment of Heavy Metals in the Soil of an Urban Recreational Area Amended with Composted Sewage Sludge

A composted sewage sludge (CSS) was added to the soil of an urban garden at 5%, 10%, and 25% (w/w soil) and stabilised for 180 days. Samples were then collected and analysed for total heavy metal concentrations, chemical fractions, and bioaccessibility, together with some physicochemical properties. The results showed that the total chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) concentrations were increased with CSS addition rate. The CSS addition decreased the residual fractions of these four elements. The exchangeable Cr, Cu, and Pb fractions were very small or not detected, while Zn exhibited an increasing trend in its exchangeable fraction with CSS addition rate. The bioaccessibility of these four elements was increased with the CSS addition rate. Moreover, the Cr, Cu, and Zn bioaccessibility correlated positively with the total concentration, while the bioaccessibility of these four elements exhibited a negative correlation with the residual fraction. The fractionation and bioaccessibility of heavy metals may have also been influenced by pH, cation exchange capacity, and organic matter. The risk assessment code reflected the amended soil showed no or low environmental risks for Cr, Cu, and Pb and a medium risk for Zn. The hazardous index values and cancer risk levels indicated that the heavy metals in the soil amended with 25% CSS posed negligible potential noncarcinogenic and carcinogenic risks to children and adults via incidental ingestion.

Anaerobic Digestion Alters Copper and Zinc Speciation

Anaerobic digestion is a widely used organic waste treatment process. However, little is known on how it could alter the speciation of contaminants in organic waste. This study was focused on determining the influence of anaerobic digestion on the speciation of copper and zinc, two metals that generally occur at high concentration in organic waste. Copper and zinc speciation was investigated by X-ray absorption spectroscopy in four different raw organic wastes (predigestion) and their digested counterparts (postdigestion, i.e., digestates). The results highlighted an increase in the digestates of the proportion of amorphous or nanostructured copper sulfides as well as amorphous or nanostructured zinc sulfides and zinc phosphate as compared to raw waste. We therefore suggest that the environmental fate of these elements would be different when spreading either digestates or raw waste on cropland.

Increased zinc and copper availability in organic waste amended soil potentially involving distinct release mechanisms

This study aimed at determining the fate of trace elements (TE) following soil organic waste (OW) application. We used a unique combination of X-ray absorption spectroscopy analyses, to determine TE speciation, with incubation experiments for in situ monitoring of TE availability patterns over a time course with the technique of the diffusive gradients in thin films (DGT). We showed that copper (Cu) and zinc (Zn) availability were both increased in OW-amended soil, but their release was controlled by distinct mechanisms. Zn speciation in OW was found to be dominated by an inorganic species, i.e. Zn sorbed on Fe oxides. Zn desorption from Fe oxides could explain the increase in Zn availability in OW-amended soil. Cu speciation in OW was dominated by organic species. Cu release through the mineralization of organic carbon from OW was responsible for the increase in Cu availability.

Copper and zinc accumulation and fractionation in a clayey Hapludox soil subject to long-term pig slurry application

Pig slurry (PS) recycling as fertilizer is commonly practiced as an option for minimizing livestock waste. Successive PS applications on the soil can lead to crop toxicity and environmental risk. Despite extensive investigation of macronutrient behavior, the fate of trace metals remains uncertain and only a few long-term field studies have been reported to date. This study was designed to assess the impact of 11-year continuous PS spreading on Cu and Zn accumulation and fractionation in a Brazilian clayey Hapludox soil. Three different PS application rates--50, 100 and 200m3 ha(-1)year(-1)--were monitored at six soil depths in comparison to a non-amended control soil. The modified Geological Survey of Canada sequential extraction protocol was applied. A statistically significant increase in Cu and Zn total concentration (assessed by the sum of fractions) was noted only within the 0-5 cm soil layer for the 50 and 100 m3 ha(-1) year(-1) (PS50 and PS100) treatments, and up to 10-15 cm for the 200 m3 ha(-1)year(-1) (PS200) treatment. The mass balance, determined for the 22 PS amendments over the period, confirmed the overall exogenous Cu and Zn accumulation within the surface layers. More than 70% of the natural heavy metal content was originally in the residual fraction. However, this was the only fraction not influenced by the PS amendments. After PS input, the exogenous Cu was mainly detected in the fraction bound to organic matter (66.4%) within the PS200 0-5 cm soil layer. Exogenous Zn was mainly distributed between the adsorbed fraction (36.7%) and the organic matter fraction (32.0%) within the PS200 0-5 cm layer.

Heavy metal concentration and speciation of seven representative municipal sludges from wastewater treatment plants in Northeast China

The analysis of heavy metals is very important for assessing the feasibility of the agricultural utilization for the municipal sludge. In this paper, a four-step sequential extraction method was applied to extract heavy metals (Cu, Zn, Mn, Cr, and Ni) in municipal sludges from seven individual wastewater treatment plants located in Jilin and Heilongjiang Province, China, for estimating the mobility and bioavailability of the metal ions in the agricultural application. The total concentrations of heavy metals and their chemical fractions after the sequential extraction were determined. Principal component analysis (PCA) was applied to analyze the relations of heavy metals fractions in the municipal sludges. Experimental results indicated that the total concentrations of Cu, Zn, Cr, and Ni in all sludge samples were below the threshold values set out by the Chinese legislation (GB18918-2002). Specially, Zn had a high bioavailability and mobility, Cu and Cr had potential bioavailability, while Mn mainly existed in the residual fraction of municipal sludge. On the other hand, Ni had different mobility in different municipal sludge. PCA results were confirmed by the environmental behavior of heavy metals.

Interaction between beet vinasse and iron fertilisers in the prevention of iron deficiency in lupins

BACKGROUND

Recycling of organic byproducts for use as soil amendments or fertilisers may enhance the productivity of soils. The aim of this study was to investigate the potential of sugar beet vinasse to correct iron chlorosis in crops when applied in conjunction with Fe fertilisers such as vivianite and ferrous sulfate (FS). An experiment involving two factors (Fe source and dialysed sugar beet vinasse (DBV) rate) was performed using white lupin (Lupinus albus L.) and calcareous sand as growing medium.

RESULTS

Although vivianite provided lower chlorophyll contents than Fe-chelate, dry matter production was not significantly different between the two Fe sources. Vivianite was more effective than FS in preventing iron chlorosis in white lupin, but not when DBV was applied. DBV significantly increased chlorophyll content in plants treated with FS after 3 weeks of growth.

CONCLUSION

DBV increased the effect of FS in preventing iron deficiency chlorosis in white lupin. This was due, at least in part, to the inhibition of the precipitation of Fe oxides by organic compounds and to the increase in the content of Fe complexed by organic compounds in the growing medium, as revealed by sequential Fe fractionation.

Heavy metal and trace metal analysis in soil by sequential extraction: a review of procedures

Quantification of heavy and trace metal contamination in soil can be arduous, requiring the use of lengthy and intricate extraction procedures which may or may not give reliable results. Of the many procedures in publication, some are designed to operate within specific parameters while others are designed for more broad application. Most procedures have been modified since their inception which creates ambiguity as to which procedure is most acceptable in a given situation. For this study, the Tessier, Community Bureau of Reference (BCR), Short, Galán, and Geological Society of Canada (GCS) procedures were examined to clarify benefits and limitations of each. Modifications of the Tessier, BCR, and GCS procedures were also examined. The efficacy of these procedures is addressed by looking at the soils used in each procedure, the limitations, applications, and future of sequential extraction.

Influence of different organic amendments on the potential availability of metals from soil: a study on metal fractionation and extraction kinetics by EDTA

The effects of long-term application of different organic amendments, as compared to mineral fertilizer, on Zn, Cu and Pb content and leachability in a luvisol derived from loess were assessed. The organic fertilizers, applied since 1962, were compost (COM) - from green organic household waste, sewage sludge (SLU) - from municipal water treatment facilities, farmyard manure (FYM) and the doses applied since 1997 were 90tha(-1), 10tha(-1) and 9tha(-1), once in 3years, respectively. The kinetics of metals extraction with 0.05moldm(-3) EDTA at pH 6.0 has been studied. The two first-order reactions model was fitted to the kinetic data and allowed to distinguish two pools for each metal: a "labile" fraction (Q(1)), quickly extracted with a rate constant k(1), and a "moderately labile" fraction (Q(2)), more slowly extracted, with a rate constant k(2). Simultaneously, the pseudo-total metal contents in the soil samples were determined after digestion with aqua regia (3:1 HCl+HNO(3)). The obtained parameters Q(1), k(1), Q(2), k(2), for the kinetics of extraction of each metal in the three replicates of each fertilization mode, as well as the pseudo-total metal contents, were statistically analysed. COM and SLU application resulted in an increase of the total contents of Pb, Zn and Cu in soil. Further, the percentage of labile Zn and Pb also increased in consequence of the application of those amendments, particularly COM. The increase was more noticeable for Zn. FYM, despite not increasing the total content of Pb, Zn or Cu, did also have an effect on the leachability of Zn and Pb, increasing their labile fraction in soil. These results point to a potential risk of increasing metals mobility in soil, mainly Zn, associated to the use of organic amendments, particularly COM or SLU.

Spectroscopic characterization of organic matter of a soil and vinasse mixture during aerobic or anaerobic incubation

Mineralization potentials are often used to classify organic wastes. These methods involve measuring CO(2) production during batch experiments, so variations in chemical compounds are not addressed. Moreover, the physicochemical conditions are not monitored during the reactions. The present study was designed to address these deficiencies. Incubations of a mixture of soil and waste (vinasse at 20% dry matter from a fermentation industry) were conducted in aerobic and anaerobic conditions, and liquid samples obtained by centrifugation were collected at 2h, 1d and 28 d. Dissolved organic carbon (DOC) patterns highlighted that: there was a "soil effect" which increased organic matter (OM) degradation in all conditions compared to vinasse incubated alone; and OM degradation was faster under aerobic conditions since 500 mgkg(-1) of C remained after aerobic incubation, as compared to 4000 mgkg(-1) at the end of the anaerobic incubation period. No changes were detected by Fourier transform infrared spectroscopy (FTIR) between 2h and 1d incubation. At 28 days incubation, the FTIR signal of the aerobic samples was deeply modified, thus confirming the high OM degradation. Under anaerobic conditions, the main polysaccharide contributions (nu(C-O)) disappeared at 1000 and 1200 cm(-1), as also confirmed by the (13)C NMR findings. Under aerobic incubation, a 50% decrease in the polysaccharide proportion was observed. Under anaerobic conditions, significant chemical modifications of the organic fraction were detected, namely formation of low molecular weight organic acids.

Multiscale analysis of heavy metal contents in Spanish agricultural topsoils

This study characterized and mapped the spatial variability patterns of seven topsoil heavy metals (Cr, Ni, Pb, Cu, Zn, Hg and Cd) within the Ebro river basin (9.3 million ha) by Multivariate Factorial Kriging. The variograms and cross-variograms of heavy metal concentrations showed the presence of multiscale variation that was modeled using three variogram models with ranges of 20km (short-range), 100km (medium-range) and 225km (long-range). Our results indicate that the heavy metal concentration is influenced by bedrock composition and dynamics at all the spatial scales, while human activities have a notorious effect only at the short- and medium-range scale of variation. Sources of Cu, Pb and Zn (and secondary Cd) are associated with agricultural practices (at the short-range scale of variation), whereas Hg variation at the short- and medium-range scale of variation is related to atmospheric deposition.

Is there a future for sequential chemical extraction?

Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Concentration and speciation of heavy metals in six different sewage sludge-composts

This study presents the concentrations and speciation of heavy metals (HMs) in six different composts of sewage sludges deriving from two wastewater treatment plants in China. After 56 days of sludge composting with rice straw at a low C/N ratio (13:1), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) were enriched in sludge composts, exhibiting concentrations that varied from 0.75 to 2.0, 416 to 458, 66 to 168 and 1356 to 1750mgkg(-1) dry weight (d.w.), respectively. The concentrations increased by 12-60% for Cd, 8-17% for Cu, 15-43% for Pb and 14-44% for Zn compared to those in sewage sludges. The total concentrations of individual or total elements in the final composts exceeded the maximum permissible limits proposed for compost or fertilizer. In all the final composts, more than 70% of total Cu was associated with organic matter-bound fraction, while Zn was mainly concentrated in exchangeable and Fe-Mn oxide-bound fractions which implied the high mobility and bioavailability. Continuously aerated composting treatment exhibited better compost quality and lower potential toxicity of HMs, whereas inoculant with microorganism and enzyme spiked during composting had no obvious advantage on humification of organic matter and on reducing HM mobility and bioavailability.

New combination of EXAFS spectroscopy and density fractionation for the speciation of chromium within an andosol

Studying speciation of heavy metals instead of their total concentration in a complex matrix such as soil is a scientific challenge that requires a combination of different analytical techniques. We compared the speciation of Cr within an andosol (island of Réunion) by using X-ray absorption spectroscopy (XAS) and sequential extraction. Contradictory results were obtained since the fraction of Cr bound to organic matter was detected only with the latter method. As bulk soil is rather complex, its fractionation by a densimetric method decreased its heterogeneity. We found that 60% Cr was within chromite-type primary minerals. Weathering of these phases led to Fe and Cr release, eventually resulting in either coprecipitation as mixed FeCr oxyhydroxide (16% total Cr) or precipitation of a Cr oxyhydroxide (5% total Cr). Our results also revealed that 13% Cr was bound to organic matter. The organic matter was complexed with mineral phases to form organomineral complexes with a density ranging from 1.9 to 2.6. The use of an original density fractionation-based sample preparation allowed identification of the role of organic matter in chromium speciation within an andosol and to overcome the difficulties of EXAFS to detect light elements in the vicinity of heavy elements.