Evaluation of the Bioavailability of Metals in Sediment from the Southern Coastal Wetland of the Qiantang Estuary by Using Diffusive Gradients in Thin Films Technique

Metal pollution has become an major issue governing the wetland ecosystem health.The southern coastal wetland of the Qiangtang Estuary are facing unusual perturbation due to rapid development along the embayment in recent decades.This study evaluated the bioavailability of metals(Cu,Pb,Cd,Cr and Zn)in the sediment of the southern coastal wetland of the Qiangtang Es-tuary using diffusive gradients in thin films(DGT)techniques and compared with several methods based on total metal content.The results showed that the contents of Cr,Pb,Cd and Cu in sediment,as detected using DGT,were considerably correlated with the exchangeable fraction and the content in Phragmites australis roots,while a weak correlation was observed for Zn.Therefore,DGT analysis could be used to evaluate the bioavailability and potential risk of Cr,Cd,Pb and Cu for P.australis.Quantitative indices,such as DGT concentration,bioaccumulation in P.australis,geoaccumulation index(Igeo)and potential ecological risk index(RI),revealed that Cd was a major potential ecological risk factor along the southern coast wetland of the Qiantang Estuary,especially in the upstream region,which is potentially more vulnerable to the anthropogenic pollution.

Diffusive gradients in thin films using molecularly imprinted polymer binding gels for in situ measurements of antibiotics in urban wastewaters

Urban wastewater is one of main sources for the introduction of antibiotics into the environment.Monitoring the concentrations of antibiotics in wastewater is necessary for estimating the amount of antibiotics discharged into the environment through urban wastewater treatment systems.In this study,we report a novel diffusive gradient in thin films(DGT)method based on molecularly imprinted polymers(MIPs)for in situ measurement of two typical antibiotics,fluoroquinolones(FQs)and sulfonamides(SAs)in urban wastewater.MIPs show specific adsorption toward their templates and their structural analogs,resulting in the selective uptake of the two target antibiotics during MIP-DGT deployment.The uptake performance of the MIP-DGTs was evaluated in the laboratory and was relatively independent of solution pH(4.0-9.0),ionic strength(1-750 mmol/L),and dissolved organic matter(DOM,0-20 mg/L).MIP-DGT samplers were tested in the effluent of an urban wastewater treatment plant for field trials,where three SA(sulfamethoxazole,sulfapyridine,and trimethoprim)and one FQ(ofloxacin)antibiotics were detected,with concentrations ranging from 25.50 to 117.58 ng/L,which are consistent with the results measured by grab sampling.The total removal efficiency of the antibiotics was 80.1%by the treatment plant.This study demonstrates that MIP-DGT is an effective tool for in situ monitoring of trace antibiotics in complex urban wastewaters.

Diffusive gradients in thin films(DGT) probe for effectively sampling of per-and polyfluoroalkyl substances in waters and sediments

The passive sampling technique, diffusive gradients in thin films(DGT) has attracted increasing interests as an in-situ sampler for organic contaminants including per-and polyfluoroalkyl substances(PFAS). However, its effectiveness has been questioned because of the small effective sampling area(3.1 cm^(2)). In this study, we developed a DGT probe for rapid sampling of eight PFAS in waters and applied it to a water-sediment system. It has a much larger sampling area(27 cm^(2)) and as a result lower method quantification limits(0.15 –0.21 ng/L for one-day deployment and 0.02 – 0.03 ng/L for one-week deployment) and much higher(by > 10 factors) sampling rate(100 m L/day) compared to the standard DGT(piston configuration). The sampler could linearly accumulate PFAS from wastewater, was sensitive enough even for a 24 hr deployment with performance comparable to grab sampling(500m L). The DGT probe provided homogeneous sampling performance along the large exposure area. The use of the probe to investigate distributions of dissolved PFAS around the sediment-water interface was demonstrated. This work, for the first time, demonstrated that the DGT probe is a promising monitoring tool for trace levels of PFAS and a research tool for studying their distribution, migration, and fate in aquatic environments including the sediment-water interface.

Distr ibution, risk and bioavailability of metals in sediments of Lake Yamdrok Basin on the Tibetan Plateau, China

Total contents of metals in soil and sediments on the Tibetan Plateau of China have been widely analyzed,but existing information is insufficient to effectively evaluate metal ecological risk because of a lack of metal bioavailability data.In this study,distribution,potential risk,mobility and bioavailability of metals in sediments of Lake Yamdrok Basin in Tibet of China were explored by combined use of total digestion,sequential extraction and the diffusive gradient in thin-films(DGT).Average concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb in surface sediments were 31.25,30.31,22.00,45.04,31.32,0.13 and 13.39 mg/kg,respectively.Higher levels of metals were found near the inflowing rivers.Residual form was dominant in Cr,Ni,Zn,Cd and Pb,and reducible form was dominant in As and Cd.Metals in surface sediments showed a low enrichment degree overall,but Cd and As had higher ecological risk levels than the other metals.Furthermore,there was a larger average proportion of exchangeable form of As(20.4%)and Cd(9.0%)than the other metals(1.7%-3.3%),implying their higher mobility and release risk.Average DGT-labile concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb were 0.5,4.5,0.7,25.1,60.0,0.22 and 1.0μg/L,respectively.The DGT-labile As was significantly correlated with extractable As forms(p<0.01),suggesting that extractable As in sediments acts as a"mobile pool"for bioavailable As.These results suggest potential risks of As and Cd,especially As,deserve further attention in Lake Yamdrok Basin.

Investigation of potential interferences on the measurement of dissolved reactive phosphate using zirconium oxide-based DGT technique

A diffusive gradients in thin films （DGT） technique based on hydrous zirconium oxide （Zr-oxide） has been recently developed for the measurement of dissolved reactive phosphate （DRP）. In this study, the detailed performance of the DGT technique is reported. Spiking experiments revealed that several orthophosphate monoester compounds contributed to the Zr-oxide DGT measurements of DRP. However, such a phenomenon is unlikely to occur during field conditions due to the low concentration of organic P in typical natural waters. The presence of Cl- （up to 106 g/L）, SO42- （up to 16 g/L）, HCO3- （up to 817 g/L）, and AsO2- and AsO 3 4 （both up to 1 mg As/L） in solutions had negligible effects on the measurement of DRP. The threshold concentrations of Cl-, SO42- and HCO3- have been increased from previous reports for the measurements of DRP using other adsorbent-based DGT techniques. The capacity for DGT measurements of DRP decreased with increasing solution pH （4.2-9.2）. The lowest capacity （95 μg P/m2 at pH 9.2） was still greater than that of other DGT techniques that are usually used for the measurement of DRP （2-12 μg P/cm2 ）. The Zr-oxide binding gel could be stored for up to 2 years without any aging effect. This period of validity was considerably longer than the ferrihydrite binding gel that is commonly used in present DGT devices （6 months）. The field application revealed that the concentrations of DRP measured in three fresh water samples using the Zr-oxide DGT technique were in agreement with those of the traditional colorimetric method.

Phosphorus removal from sediments by Potamogeton crispus:New high-resolution in-situ evidence for rhizosphere assimilation and oxidization-induced retention

Macrophytes are usually chosen for phytoremediation tools to remove P in eutrophic aquatic ecosystems,but the lack of test methods hinders the understanding of removal mechanism and application.In this study,we used the novel technologies combined of Diffusive gradients in thin films(DGT),Planar optode(PO),and Non-invasive micro-test technology(NMT)to explore P dynamics in water-sediment continuum and rhizosphere of Potamogeton crispus over time.Results of the high-resolution in situ measurement showed that labile P(LPDGT)fluxes at the surficial sediment significantly decreased from approximate 120,140,and 200 pg/(cm^(2)·sec)via 30 days incubation period to 17,40,and 56 pg/(cm2•sec)via that of 15 days.Obvious synchronous increase of LPDGT was not detected in overlying water,suggesting the intense assimilation of dissolve reactive P via root over time.PO measurement indicated that O_(2)concentration around the rhizosphere remarkably increased and radially diffused into deeper sediment until 100%saturation along with the root stretch downwards.NMT detection of roots showed the obvious O_(2)inflow into root tissue with the uppermost flux of 30 pmol/(cm2•sec)from surroundings via aerenchyma on different treatment conditions.Different from previous reports,gradually saturating O_(2)concentrations around the rhizosphere was principally driven by O_(2)penetration through interspace attributing to root stretch downward rather than root O_(2)leakage.Increased O_(2)concentrations in deep sediment over time finally induced the oxidization of labile Fe(II)into Fe(III)bound P and local P immobilization.

Mobility and sulfidization of heavy metals in sediments of a shallow eutrophic lake, Lake Taihu, China

The technique of DGT（diffusive gradients in thin films） using three diffusive gel thicknesses was applied to estimate the mobility and bioavailability of heavy metals in sediments and porewater of Lake Taihu, China. The DGT results showed significantly positive correlations between Co, Pb, Cd and Mn, and Ni and Fe concentrations in porewater. Cu and Zn showed a significantly negative correlation with Mn, due to Cu combination with carbonates and Zn derived from agricultural pollution, respectively. The rank order of average concentrations of Co, Ni and Cd at each station was DGT1.92〉DGT0.78〉 DGT0.39, suggesting stronger resupply from sediments to porewater when using thicker diffusive gels. Comparing centrifugation and DGT measurements, Co, Ni and Cd are highly labile; Mn and Fe are moderately labile; and Cu, Zn and Pb are slightly labile. The variations of AVS concentrations in sediment cores indicate that metal sulfides in deeper layers are easily diffused into surface sediments.

Wheat yield prediction by zero sink and equilibrium-type soil phosphorus tests

Diffusive gradients in thin films(DGT)measurements have been shown to outperform other phosphorus(P)tests in soils with strong P sorption,but this has not been confirmed for moderately weathered European soils.We compared the performance of DGT in predicting wheat grain yield in Swedish long-term fertility experiments with those of standard intensity(water-extractable P(P-H2O))and quantity(ammonium lactate-extractable P(P-AL))tests.A Mitscherlich-type model was used to fit wheat yield response to P application rates(0,15,30 or 35,and 45 kg P ha-1 year-1)in each individual trial replicate to estimate the maximum yield.For trials with clear plateau-type yield responses and the goodness of fit(R2)>0.75,relative yields(RYs)were calculated for each P treatment and plotted against the soil P test results(n=143).The goodness of the Mitscherlich-type fits decreased in the following order:DGT-measured P(P-DGT)(R2=0.35)>P-H2O(R2=0.18)>P-AL(R2=0.13).When excluding soils with P-AL:P-DGT≥0.1 L g-1,R2 was considerably improved to 0.55 for P-AL,0.46 for P-H2O,and 0.65 for P-DGT(n=61).At 95%of maximum yield,the upper limit of P deficiency for P-DGT was 44.8(the soils with P-AL:P-DGT<0.1 L g-1)and 61.9μg L-1(all soils),falling within the range reported for other European and Australian soils(6.0–142μg L-1).We show that in the investigated Swedish soils,DGT performed better than the quantity and intensity tests,which is attributed to its ability to capture P diffusion and resupply from the soil solid phase,similar to plant roots in the rhizosphere.

Seasonal dynamics of iron and phosphorus in reservoir sediments in Eucalyptus plantation region

Background:Iron(Fe)and phosphorus(P)dynamics in sediments have direct and indirect impacts on water quality.However,the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear.This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode,the ZrO-Chelex DGT,and the DIFS model.Results:Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments(X2)compared to sediments without Eucalyptus species(X1).The mean concentration of labile P and Fe decreased by 25%and 42%from X1 to X2.The decrement was insignificant(p=0.20)in the surface sediment concentration for labile P.The significant disparity for DGT-Fe(Fe^(2+))(p=0.03)observed in the surface sediments could be attributed to the Eucalyptus species’elevated organic matter(tannins)concentration at X2,which reacted and consumed labile Fe.For both regions,the maximum concentration of labile P and Fe occurred in November(autumn).The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November.Low concentration of labile P and Fe was observed in December(winter)due to the adsorption of Fe/Mn oxides.The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship(r>0.8,p<0.01)in both regions.The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe.The fluxes of labile P and Fe in both regions were substantially higher(p<0.05)in the summer(anoxic period)than winter(aerobic period),indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe.From the DIFS model,the replenishment ability of reactive P was higher during the anoxic period(R=0.7,k_(1)=79.4 day^(-1),k_(-1)=0.2 day^(-1))than the aerobic period(R=0.4,k_(1)=14.2 day^(-1),k_(-1)=0.1 day^(-1)),suggesting that oxygen inhibited the efflux of P in the sediments.Conclusion:Our results indicated that hypoxia,Eucalyptus species(organic matter(tannins)),and redox conditions influenced the seasonal mobility of sediment labile P and Fe.Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and,moreover,serves as a reference for developing future studies on Eucalyptus-dominated sediments.

Synergistic effect of vermiculite and submerged plants on lake sediments

The synergistic effect of vermiculite and the submerged macrophytes Vallisneria spiralis and Hydrilla verticillata on lake sediment was studied using diffusive gradients in thin films(DGT)technology.The dynamics of phosphorus(P)fractions in sediment,the labile-P and labile-S in the water-sediment continuum,and the microbial community in the rhizosphere were studied.Vermiculite effectively promoted reproduction of microorganisms in the sediments Microbial abundance in treatments containing V.spiralis with sediments containing 10%added vermiculite,and H.verticillata containing 50%added vermiculite being 1.7 and 3.5 times higher than the controls which contained no added vermiculite.Acidobacteria and Proteobacteria populations,which are both beneficial for the sediment microenvironment,were higher in treatment groups containing vermiculite.The bioavailable-P in treatment groups containing added vermiculite was lower at the sediment-water interface,with a correlating decrease of TP by between 63%and 91%in the overlying water.This suggests that vermiculite can affect the release of labile P and facilitate the assimilation of nutrients by macrophyte roots.Additionally,vermiculite can improve the Oxidation-Reduction potential and further reduce sulfide toxicity to plants.These results provide theoretical guidance and technical support for the application of vermiculite combined with submerged plants for the remediation of eutrophic lakes.