Dan Berggren Kleja

Effect of Acid Deposition on Quantity and Quality of Dissolved Organic Matter in Soil―Water

The aim of this study was to explore how acid deposition may affect the concentration and quality of dissolved organic matter (DOM) in soil-water. This was done by a small-scale acidification experiment during two years where 0.5 × 0.5 m(2) plots were artificially irrigated with water with different sulfuric acid content, and soil-water was sampled using zero-tension lysimeters under the O-horizon. The DOM was characterized using absorbance, fluorescence, and size exclusion chromatography analyses. Our results showed lower mobility of DOM in the high acid treatment. At the same time, there was a significant change in the DOM quality. Soil-water in the high acid treatment exhibited DOM that was less colored, less hydrophobic, less aromatic, and of lower molecular weight, compared to the low acid treatment. This supports the hypothesis that reduction in sulfur deposition is an important driver behind the ongoing brownification of surface waters in many regions.

Chromium(III) Complexation to Natural Organic Matter: Mechanisms and Modeling

Chromium is a common soil contaminant, and it often exists as chromium(III). However, limited information exists on the coordination chemistry and stability of chromium(III) complexes with natural organic matter (NOM). Here, the complexation of chromium(III) to mor layer material and to Suwannee River Fulvic Acid (SRFA) was investigated using EXAFS spectroscopy and batch experiments. The EXAFS results showed a predominance of monomeric chromium(III)-NOM complexes at low pH (<5), in which only Cr···C and Cr-O-C interactions were observed in the second coordination shell. At pH > 5 there were polynuclear chromium(III)-NOM complexes with Cr···Cr interactions at 2.98 Å and for SRFA also at 3.57 Å, indicating the presence of dimers (soil) and tetramers (SRFA). The complexation of chromium(III) to NOM was intermediate between that of iron(III) and aluminum(III). Chromium(III) complexation was slow at pH < 4: three months or longer were required to reach equilibrium. The results were used to constrain chromium-NOM complexation in the Stockholm Humic Model (SHM): a monomeric complex dominated at pH < 5, whereas a dimeric complex dominated at higher pH. The optimized constant for the monomeric chromium(III) complex was in between those of the iron(III) and aluminum(III) NOM complexes. Our study suggests that chromium(III)-NOM complexes are important for chromium speciation in many environments.

Modelling lead(II) sorption to ferrihydrite and soil organic matter

Lead(II) adsorption to soil organic matter and iron (hydr)oxides is strong, and may control the geochemical behaviour of this metal. Here, we report the adsorption of Pb(2+) (i) to 2-line ferrihydr ...

Fine root turnover and litter production of Norway spruce in a long-term temperature and nutrient manipulation experiment

Background and aimsIncreased soil temperature and nutrient availability enhance soil biological activity. We studied how these affect fine root growth and survival, i.e. below-ground litter production, in relation to above-ground foliage litter production of Norway spruce (Picea abies (L.) Karst.).MethodsThe treatments, irrigation (I), soil warming + irrigation (WI), fertilization + irrigation (FI) and soil warming + fertilization + irrigation (WFI) were started in 1987 (F, I) and in 1995 (W). The annual production of fine root litter was estimated from minirhizotrons (survival) and soil-cores (biomass) and the annual above-ground litter production from litter traps.Results and conclusionsThe number and elongation of fine roots tended to be higher in WI and I compared to the other treatments, which may indicate nutrient shortage. Fine roots in the WFI treatment had the lowest median longevity and from three to fourfold higher below-ground litter production compared to WI, FI or I - higher soil temperature increased the litter input particularly into the mineral soil. Only fertilization increased the above-ground litter production. As warmer and more nutrient-rich soil significantly shortened the fine root lifespan and increased the litter input, the storage of carbon in boreal forest soil may increase in the future.

Native Oxy-PAHs, N-PACs, and PAHs in Historically Contaminated Soils from Sweden, Belgium, and France : Their Soil-Porewater Partitioning Behavior, Bioaccumulation in Enchytraeus crypticus, and Bioavailability

Soil quality standards are based on partitioning and toxicity data for laboratory-spiked reference soils, instead of real world, historically contaminated soils, which would be more representative. Here 21 diverse historically contaminated soils from Sweden, Belgium, and France were obtained, and the soil-porewater partitioning along with the bioaccumulation in exposed worms (Enchytraeus crypticus) of native polycyclic aromatic compounds (PACs) were quantified. The native PACs investigated were polycyclic aromatic hydrocarbons (PAHs) and, for the first time to be included in such a study, oxygenated-PAHs (oxy-PAHs) and nitrogen containing heterocyclic PACs (N-PACs). The passive sampler polyoxymethylene (POM) was used to measure the equilibrium freely dissolved porewater concentration, Cpw, of all PACs. The obtained organic carbon normalized partitioning coefficients, KTOC, show that sorption of these native PACs is much stronger than observed in laboratory-spiked soils (typically by factors 10 to 100), which has been reported previously for PAHs but here for the first time for oxy-PAHs and N-PACs. A recently developed KTOC model for historically contaminated sediments predicted the 597 unique, native KTOC values in this study within a factor 30 for 100% of the data and a factor 3 for 58% of the data, without calibration. This model assumes that TOC in pyrogenic-impacted areas sorbs similarly to coal tar, rather than octanol as typically assumed. Black carbon (BC) inclusive partitioning models exhibited substantially poorer performance. Regarding bioaccumulation, Cpw combined with liposome-water partition coefficients corresponded better with measured worm lipid concentrations, Clipid (within a factor 10 for 85% of all PACs and soils), than Cpw combined with octanol-water partition coefficients (within a factor 10 for 76% of all PACs and soils). E. crypticus mortality and reproducibility were also quantified. No enhanced mortality was observed in the 21 historically contaminated soils despite expectations from PAH spiked reference soils. Worm reproducibility weakly correlated to Clipid of PACs, though the contributing influence of metal concentrations and soil texture could not be taken into account. The good agreement of POM-derived Cpw with independent soil and lipid partitioning models further supports that soil risk assessments would improve by accounting for bioavailability. Strategies for including bioavailability in soil risk assessment are presented.

Influence of particle size distribution, organic carbon, pH and chlorides on washing of mercury contaminated soil

Feasibility of soil washing to remediate Hg contaminated soil was studied. Dry sieving was performed to evaluate Hg distribution in soil particle size fractions. The influence of dissolved organic matter and chlorides on Hg dissolution was assessed by batch leaching tests. Mercury mobilization in the pH range of 3-11 was studied by pH-static titration. Results showed infeasibility of physical separation via dry sieving, as the least contaminated fraction exceeded the Swedish generic guideline value for Hg in soils. Soluble Hg did not correlate with dissolved organic carbon in the water leachate. The highest Hg dissolution was achieved at pH 5 and 11, reaching up to 0.3% of the total Hg. The pH adjustment was therefore not sufficient for the Hg removal to acceptable levels. Chlorides did not facilitate Hg mobilization under acidic pH either. Mercury was firmly bound in the studied soil thus soil washing might be insufficient method to treat the studied soil.

Phytotoxicity of trace metals in spiked and field‐contaminated soils: Linking soil‐extractable metals with toxicity

Soil tests have been widely developed to predict trace metal uptake by plants. The prediction of metal toxicity, however, has rarely been tested. The present study was set up to compare 8 established soil tests for diagnosing phytotoxicity in contaminated soils. Nine soils contaminated with Zn or Cu by metal mining, smelting, or processing were collected. Uncontaminated reference soils with similar soil properties were sampled, and series of increasing contamination were created by mixing each with the corresponding soil. In addition, each reference soil was spiked with either ZnCl2 or CuCl2 at several concentrations. Total metal toxicity to barley seedling growth in the field-contaminated soils was up to 30 times lower than that in corresponding spiked soils. Total metal (aqua regia-soluble) toxicity thresholds of 50% effective concentrations (EC50) varied by factors up to 260 (Zn) or 6 (Cu) among soils. For Zn, variations in EC50 thresholds decreased as aqua regia > 0.43 M HNO3  > 0.05 M ethylenediamine tetraacetic acid (EDTA) > 1 M NH4 NO3  > cobaltihexamine > diffusive gradients in thin films (DGT) > 0.001 M CaCl2 , suggesting that the last extraction is the most robust phytotoxicity index for Zn. The EDTA extraction was the most robust for Cu-contaminated soils. The isotopically exchangeable fraction of the total soil metal in the field-contaminated soils markedly explained the lower toxicity compared with spiked soils. The isotope exchange method can be used to translate soil metal limits derived from soils spiked with metal salts to site-specific soil metal limits.

Determination of polyoxymethylene (POM) - water partition coefficients for oxy-PAHs and PAHs

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are a class of ubiquitously occurring pollutants of which little is known. They can be co-emitted with PAHs or formed from PAHs in the environment. The environmental fate and risk of oxy-PAHs are difficult to assess due to a lack of methods to quantify their pore water concentrations. One sampler that can be used to determine freely dissolved concentrations of organic contaminants is polyoxymethylene (POM). In this study, POM - water partition coefficients (KPOM) were determined for 11 oxy-PAHs. KPOM values of 8 PAHs with similar hydrophobicities as the oxy-PAHs were determined for comparison. Results showed that logKPOM values ranged from 2.64 to 4.82 for the PAHs (2-4 rings), similar to previously determined values. LogKPOM values for investigated oxy-PAHs ranged from 0.96 to 5.36. The addition of carbonylic oxygen on a parent PAH generally lowered KPOM by 0.5 to 1.0 log units, which is attributable to the presence of carbonylic oxygens increasing water solubility. The KPOM values presented here will facilitate simultaneous assessments of freely dissolved water concentrations of oxy-PAHs and PAHs in environmental media.

Reactivity of dissolved organic matter in response to acid deposition

Fluvial export of organic matter from the terrestrial catchment to the aquatic system is a large and increasing carbon flux. The successful reduction in sulfuric acid deposition since the 1980s has been shown to enhance the mobility of organic matter in the soil, with more terrestrially derived dissolved organic matter (DOM) reaching aquatic systems. Changes in soil acidity also affect the quality of the DOM. In this study we explore the consequences this may have on the reactivity and turnover of the terrestrially derived DOM as it reaches the aquatic system. DOM of different quality (estimated by absorbance, fluorescence and size exclusion chromatography) was produced through extraction of boreal forest O-horizon soils from podzol at two sulfuric acid concentrations corresponding to natural throughfall in spruce forest in Southern Sweden around 1980 and today. Extraction was done using two different methods, i.e. field leaching and laboratory extraction. The DOM extracts were used to assess if differences in acidity generate DOM of different reactivity. Three reactivity experiments were performed: photodegradation by UV exposure, biodegradation by bacteria, and biodegradation after UV exposure. Reactivity was assessed by measuring loss of dissolved organic carbon and absorbance, change in fluorescence and molecular weight, and bacterial production. DOM extracted at lower sulfuric acid concentration was more susceptible to photooxidation, and less susceptible to bacterial degradation, than DOM extracted at a higher sulfuric acid concentration. Thus the relative importance of these two turnover processes may be altered with changes in acid deposition.

Sorption and dissolution of bare and coated silver nanoparticles in soil suspensions—Influence of soil and particle characteristics

The increasing use of silver nanoparticles (AgNPs) in consumer products triggers the need for investigations that improve the understanding of their chemical transformations upon environmental entry. Such knowledge provides crucial information for toxicological studies and risk assessments. Interactions with the soil compartment need to be explored as there are evident risks of the dispersion of both AgNPs and of released Ag ions/complexes present in wastewater-treated sludge that is distributed onto agricultural land. The dissolution and fractionation in solution of bare (AgNP-bare, noncoated) and coated AgNPs (AgNP-coat, stabilized with two nonionic surfactants, polyoxyethylene glycerol trioleate and Tween 20) were investigated after 4 and 48 h in suspensions of one sandy and one clayey soil of different pHs (3.3, 5.2). Parallel experiments were performed with soil suspensions spiked with easily soluble AgNO3. Silver in the water phase was separated in a dissolved fraction (mainly Ag ions/complexes) and a particle fraction (mainly AgNP/agglomerates/Ag adsorbed on organic matter) by means of ultracentrifugation. Bare AgNPs were nonstable and dissolved to a significantly larger extent in the sandy soil mixture compared to coated AgNPs. The concentration of dissolved Ag (ions/complexes) in the water phase was similar in the case of bare AgNPs and AgNO3 (at pH 3 and 5.2) after 24 h in sandy soil, which implies a high degree of dissolution of bare AgNPs (50–100%). In contrast, approximately 50% of the coated AgNPs remained in the water phase after 48 h of equilibration in the sandy soil at pH 5.2. The clayey soil had a significantly higher sorption capacity of Ag compared with the sandy soil, as Ag in the case of coated AgNPs was only detected in the water phase of pH 5.2 (<1 % of added Ag). Ultracentrifugation was proven more efficient compared with microfiltration to separate the dissolved Ag fraction (ions/complexes) and the particle fraction (AgNPs/agglomerates) of the water phase. This fractionation is not a measure of any potential toxicity.