Peter E. Holm

The potential of willow for remediation of heavy metal polluted calcareous urban soils

Growth performance and heavy metal uptake by willow (Salix viminalis) from strongly and moderately polluted calcareous soils were investigated in field and growth chamber trials to assess the suitability of willow for phytoremediation. Field uptakes were 2-10 times higher than growth chamber uptakes. Despite high concentrations of cadmium (>/=80 mg/kg) and zinc (>/=3000 mg/kg) in leaves of willow grown on strongly polluted soil with up to 18 mgCd/kg, 1400 mgCu/kg, 500 mgPb/kg and 3300 mgZn/kg, it is unsuited on strongly polluted soils because of poor growth. However, willow proved promising on moderately polluted soils (2.5 mgCd/kg and 400 mgZn/kg), where it extracted 0.13% of total Cd and 0.29% of the total Zn per year probably representing the most mobile fraction. Cu and Pb are strongly fixed in calcareous soils.

Cu Exposure under Field Conditions Coselects for Antibiotic Resistance as Determined by a Novel Cultivation-Independent Bacterial Community Tolerance Assay

Environmental reservoirs of antibiotic resistance are important to human health, and recent evidence indicates that terrestrial resistance reservoirs have expanded during the antibiotic era. Our aim was to study the impact of Cu pollution as a selective driver for the spread of antibiotic resistance in soil. Bacteria were extracted from a well-characterized soil site solely contaminated with CuSO₄ more than 80 years ago and from a corresponding control soil. Pollution-induced bacterial community tolerance (PICT) to Cu and a panel of antibiotics was determined by a novel cultivation-independent approach based on [³H]bromodeoxyuridine (BrdU) incorporation into DNA and by resistance profiling of soil bacterial isolates on solid media. High Cu exposure selected for Cu-tolerant bacterial communities but also coselected for increased community-level tolerance to tetracycline and vancomycin. Cu-resistant isolates showed significantly higher incidence of resistance to five out of seven tested antibiotics (tetracycline, olaquindox, nalidixic acid, chloramphenicol, and ampicillin) than Cu-sensitive isolates. Our BrdU-PICT data demonstrate for the first time that soil Cu exposure coselects for resistance to clinically important antibiotics (e.g., vancomycin) at the bacterial community-level. Our study further indicates that Cu exposure provides a strong selection pressure for the expansion of the soil bacterial resistome.

Selection for Cu-tolerant bacterial communities with altered composition, but unaltered richness, via long-term Cu exposure.

ABSTRACT Toxic metal pollution affects the composition and metal tolerance of soil bacterial communities. However, there is virtually no knowledge concerning the responses of members of specific bacterial taxa (e.g., phyla or classes) to metal toxicity, and contradictory results have been obtained regarding the impact of metals on operational taxonomic unit (OTU) richness. We used tag-coded pyrosequencing of the 16S rRNA gene to elucidate the impacts of copper (Cu) on bacterial community composition and diversity within a well-described Cu gradient (20 to 3,537 μg g−1) stemming from industrial contamination with CuSO4 more than 85 years ago. DNA sequence information was linked to analysis of pollution-induced community tolerance (PICT) to Cu, as determined by the [3H]leucine incorporation technique, and to chemical characterization of the soil. PICT was significantly correlated to bioavailable Cu, as determined by the results seen with a Cu-specific bioluminescent biosensor strain, demonstrating a specific community response to Cu. The relative abundances of members of several phyla or candidate phyla, including the Proteobacteria, Bacteroidetes, Verrumicrobia, Chloroflexi, WS3, and Planctomycetes, decreased with increasing bioavailable Cu, while members of the dominant phylum, the Actinobacteria, showed no response and members of the Acidobacteria showed a marked increase in abundance. Interestingly, changes in the relative abundances of classes frequently deviated from the responses of the phyla to which they belong. Despite the apparent Cu impacts on Cu resistance and community structure, bioavailable Cu levels did not show any correlation to bacterial OTU richness (97% similarity level). Our report highlights several bacterial taxa responding to Cu and thereby provides new guidelines for future studies aiming to explore the bacterial domain for members of metal-responding taxa.

Sorption hysteresis of Cd(II) and Pb(II) on natural zeolite and bentonite

Sorption hysteresis in natural sorbents has important environmental implications for pollutant transport and bioavailability. We examined sorption reversibility of Cd(II) and Pb(II) on zeolite and bentonite. Sorption isotherms were derived by sorption of Cd(II) and Pb(II) from solutions containing a range of the metal concentrations corresponding to 10-100% maximum sorption capacity (SCmax) of the sorbents. The desorption experiments were performed immediately following the completion of sorption experiments. Sorption and desorption isotherms of Cd(II) and Pb(II) were well described by the Freundlich model. The results revealed that the desorption isotherms of Cd(II) and Pb(II) from zeolite significantly deviated from the sorption isotherms indicating irreversible or very slowly reversible sorption. For bentonite sorption/desorption isotherms were similar indicating reversible sorption. The extent of hysteresis was evaluated from sorption and desorption Freundlich parameters (K(f) and n) through the apparent hysteresis index (HI = n(desorb)/n(sorb); n is the exponent in the Freundlich equation) and differences in Freundlich K(f) parameters. Higher sorption irreversibility was obtained for Pb(II) as compared to Cd(II). The amounts of Cd(II) and Pb(II) desorbed from bentonite were more than from zeolite, indicating that zeolite was a more effective sorbent for water and wastewater treatment.

Differential Capacity for High-Affinity Manganese Uptake Contributes to Differences between Barley Genotypes in Tolerance to Low Manganese Availability

There is considerable variability among barley (Hordeum vulgare) genotypes in their ability to grow in soils containing a low level of plant available manganese (Mn). The physiological basis for the tolerance to low Mn availability is unknown. In this work, Mn2+ influx and compartmentation in roots of the Mn-efficient genotype Vanessa and the Mn-inefficient genotype Antonia were investigated. Two separate Mn transport systems, mediating high-affinity Mn2+ influx at concentrations up to 130 nm and low-affinity Mn2+ influx at higher concentrations, were identified in both genotypes. The two genotypes differed only in high-affinity kinetics with the Mn-efficient genotype Vanessa having almost 4 times higher Vmax than the inefficient Antonia, but similar Km values. Online inductively coupled plasma-mass spectrometry measurements verified that the observed differences in high-affinity influx resulted in a higher Mn net uptake of Vanessa compared to Antonia. Further evidence for the importance of the differences in high-affinity uptake kinetics for Mn acquisition was obtained in a hydroponic system with mixed cultivation of the two genotypes at a continuously low Mn concentration (10–50 nm) similar to that occurring in soil solution. Under these conditions, Vanessa had a competitive advantage and contained 55% to 75% more Mn in the shoots than did Antonia. Subcellular compartmentation analysis of roots based on 54Mn2+ efflux established that up to 93% and 83% of all Mn was present in the vacuole in Vanessa and Antonia, respectively. It is concluded that differential capacity for high-affinity Mn influx contributes to differences between barley genotypes in Mn efficiency.

EFFECT OF ENDOPHYTIC FUNGI ON CADMIUM TOLERANCE AND BIOACCUMULATION BY FESTUCA ARUNDINACEA AND FESTUCA PRATENSIS

Endophytic fungi are a group of fungi that live asymptomatically inside plant tissue. These fungi may increase host plant tolerance to biotic and abiotic stresses. The effect of Neotyphodium endophytes in two grass species (Festuca arundinacea and Festuca pratensis) on cadmium (Cd) tolerance, accumulation and translocation has been our main objective. The plants were grown in a hydroponic system under different Cd concentrations (0, 5, 10, and 20 mg L−1) for 6 weeks. They were also grown in soil spiked with different concentrations of Cd (0, 10, 20, and 40 mg kg−1) for 2 months. The results from all Cd treatments showed higher biomass production (12–24%) and higher potential to accumulate Cd in roots (6–16%) and shoots (6–20%) of endophyte-infected plants than endophyte-free plants. Cadmium accumulation by plants indicated that the grasses were capable of Cd hyperaccumulation, a property that was augmented after endophyte infection. Maximum photochemical efficiency of photosystem II (Fv/Fm) revealed that Cd stress was significantly reduced in endophyte-infected plants compared to non-infected ones.

Content, distribution and fate of 33 elements in sediments of rivers receiving wastewater in Hanoi, Vietnam

Untreated industrial and domestic wastewater from Hanoi city is discharged into rivers that supply water for various agricultural and aqua-cultural food production systems. The aim of this study was to assess the content, distribution and fate of 33 elements in the sediment and pore water of the main wastewater receiving rivers. The sediment was polluted with potentially toxic elements (PTEs) with maximum concentrations of 73 As, 427 Cd, 281 Cr, 240 Cu, 218 Ni, 363 Pb, 12.5 Sb and 1240 Zn mg kg(-1) d.w. Observed distribution coefficients (log(10) K(d,obs)) were calculated as the ratio between sediment (mg kg(-1) d.w.) and pore water (mg L(-1)) concentrations. Maxima log(10) K(d,obs) were >4.26 Cd, >6.60 Cu, 4.78 Ni, 7.01 Pb and 6.62 Zn. The high values show a strong PTE retention and indicate the importance of both sorption and precipitation as retention mechanisms. Sulphide precipitation was a likely mechanism due to highly reduced conditions.

Multi-elemental speciation analysis of barley genotypes differing in tolerance to cadmium toxicity using SEC-ICP-MS and ESI-TOF-MS

Plants respond to Cd exposure by synthesizing heavy-metal-binding oligopeptides, called phytochelatins (PCs). These peptides reduce the activity of Cd2+ ions in the plant tissues by forming Cd chelates. The main objective of the present work was to develop an analytical technique, which allowed identification of the most prominent Cd species in plant tissue by SEC-ICP-MS and ESI-TOF-MS. An integrated part of the method development was to test the hypothesis that differential Cd tolerance between two barley genotypes was linked to differences in Cd speciation. Only one fraction of Cd species, ranging from 700–1800 Da, was detected in the shoots of both genotypes. In the roots, two additional fractions ranging from 2900–4600 and 6700–15 000 Da were found. The Cd-rich SEC fractions were heart-cut, de-salted and de-metallized using reversed-phase chromatography (RPC), followed by ESI-MS-TOF to identify the ligands. Three different families of PCs, viz. (γGlu-Cys)n-Gly (PCn), (γGlu-Cys)n-Ser (iso-PCn) and Cys-(γGlu-Cys)n-Gly (des-γGlu-PCn), the last lacking the N-terminal amino acid, were identified. The PCs induced by Cd toxicity also bound several essential trace elements in plants, including Zn, Cu, and Ni, whereas no Mn species were detected. Zn, Cu and Ni-species were distributed between the 700–1800 Da and 6700–15 000 Da fractions, whereas only Cd species were found in the 2900–4600 Da fraction dominated by PC3 ligands. Although the total tissue concentration of Cd was similar for the two species, the tolerant barley genotype synthesized significantly more CdPC3 species with a high Cd specificity than the intolerant genotype, clearly indicating a correlation between Cd tolerance and the Cd–PC speciation.

Coping with copper: legacy effect of copper on potential activity of soil bacteria following a century of exposure

Copper has been intensively used in industry and agriculture since mid-18(th) century and is currently accumulating in soils. We investigated the diversity of potential active bacteria by 16S rRNA gene transcript amplicon sequencing in a temperate grassland soil subjected to century-long exposure to normal (∼15 mg kg(-1)), high (∼450 mg kg(-1)) or extremely high (∼4500 mg kg(-1)) copper levels. Results showed that bioavailable copper had pronounced impacts on the structure of the transcriptionally active bacterial community, overruling other environmental factors (e.g. season and pH). As copper concentration increased, bacterial richness and evenness were negatively impacted, while distinct communities with an enhanced relative abundance of Nitrospira and Acidobacteria members and a lower representation of Verrucomicrobia, Proteobacteria and Actinobacteria were selected. Our analysis showed the presence of six functional response groups (FRGs), each consisting of bacterial taxa with similar tolerance response to copper. Furthermore, the use of FRGs revealed that specific taxa like the genus Nitrospira and several Acidobacteria groups could accurately predict the copper legacy burden in our system, suggesting a potential promising role as bioindicators of copper contamination in soils.

Bioavailability and toxicity of soil particle-associated copper as determined by two bioluminescent Pseudomonas fluorescens biosensor strains

We report the development and application of a novel, solid phase-contact bioassay based on two whole-cell bacterial biosensor strains. Our data indicate that a significant fraction of particle-associated Cu may be available to bacteria in dilute soil suspensions but also support the conventional view that mainly the soluble fraction of Cu is directly available to bacteria under more realistic soil conditions.