Patrick A.W. van Hees

The role of fungi in weathering

No rock at the Earths surface escapes weathering. This process is the primary source of all the essential elements for organisms, except nitrogen and carbon. Since the onset of terrestrial life, weathering has been accelerated under the influence of biota. The study of biological weathering started at the end of the 19th century. Although the role of bacteria (Eubacteria, Archaea) has attracted a lot of interest, until recently the role of fungi has largely been neglected. More recently, however, fungal weathering has become an increasingly important focus of biogeochemical research.

Laboratory and pilot scale soil washing of PAH and arsenic from a wood preservation site: Changes in concentration and toxicity

Soil washing of a soil with a mixture of both polycyclic aromatic hydrocarbons (PAH) and As was evaluated in laboratory and pilot scale, utilizing both single and mixtures of different additives. The highest level of decontamination was achieved with a combination of 0.213 M of the chelating agent MGDA and 3.2 x CMC* of a non-ionic, alkyl glucoside surfactant at pH 12 (Ca(OH)(2)). This combination managed to reach Swedish threshold values within 1 0 min of treatment when performed at elevated temperature (50 degrees C), with initial contaminant concentrations of As=105+/-4 mg/kg and US-EPA PAH(16)=46.0+/-2.3mg/kg. The main mechanisms behind the removal were the pH effect for As and a combination of SOM ionization as a result of high pH and micellar solubilization for PAHs. Implementation of the laboratory results utilizing a pilot scale equipment did not improve the performance, which may be due to the shorter contact time between the washing solution and the particles, or changes in physical characteristics of the leaching solution due to the elevated pressure utilized. The ecotoxicological evaluation, Microtox, demonstrated that all soil washing treatments increased the toxicity of soil leachates, possibly due to increased availability of contaminants and toxicity of soil washing solutions to the test organism.

Remediation of heavy metal contaminated soil washing residues with amino polycarboxylic acids

Removal of Cu, Pb, and Zn by the action of the two biodegradable chelating agents [S,S]-ethylenediaminedisuccinic acid (EDDS) and methylglycinediacetic acid (MGDA), as well as citric acid, was tested. Three soil samples, which had previously been treated by conventional soil washing (water), were utilized in the leaching tests. Experiments were performed in batches (0.3 kg-scale) and with a WTC-mixer system (Water Treatment Construction, 10 kg-scale). EDDS and MGDA were most often equally efficient in removing Cu, Pb, and Zn after 10-60 min. Nonetheless, after 10d, there were occasionally significant differences in extraction efficiencies. Extraction with citric acid was generally less efficient, however equal for Zn (mainly) after 10d. Metal removal was similar in batch and WTC-mixer systems, which indicates that a dynamic mixer system could be used in full-scale. Use of biodegradable amino polycarboxylic acids for metal removal, as a second step after soil washing, would release most remaining metals (Cu, Pb and Zn) from the present soils, however only after long leaching time. Thus, a full-scale procedure, based on enhanced metal leaching by amino polycarboxylic acids from soil of the present kind, would require a pre-leaching step lasting several days in order to be efficient.

Separation of organic low molecular weight aluminium complexes in soil solution by liquid chromatography

Abstract A size exclusion chromatography method was developed for the separation of Al complexes of low molecular weight organic acids in soil solution. Bio-Gel P2 was used in a 1.6 x 30 cm column and the mobile phase consisted 0f 0.l M NaSCN of pH 4. The low molecular weight acids were determined by HPLC. The results show that 28–37% of the Al in the soil solution of the 0-horizon was bound t0 these acids. In the lower horizons Al coincided with the UV-trace at 400 run indicating organic complexes. Si was found in one major peak which was assumed to be a low molecular weight compound possibly silicic acid. As a compliment ultrafiltration was employed for characterisation

Quantitative analysis of root and ectomycorrhizal exudates as a response to Pb, Cd and As stress

We examined exudation of low molecular weight (LMW) organic compounds of ectomycorrhizal (ECM) and non-mycorrhizal (NM) seedlings in relation to metals. Scots pine seedlings, either colonized by one of six different ECM fungi or NM, were grown in Petri dishes containing glass beads and liquid growth medium and exposed to elevated concentrations of Pb, Cd and As. Exudation of LMW organic compounds (LMW organic acids (LMWOAs), amino acids and dissolved monosaccharides) and dissolved organic carbon (DOC) was determined qualitatively and quantitatively and exudation rates were calculated. Metals had a significant impact on exudation, especially of oxalate. For Pb and Cd treatments, exudation of oxalate and total LMWOAs generally increased by 15–45% compared to nutrient controls. Production of amino acids, dissolved monosaccharides and DOC was not significantly stimulated by exposure to metals; however, there were non-significant trends towards increased exudation. Finally, exudation generally increased in the presence of mycorrhizal seedlings compared to NM seedlings. The results suggest that ECM fungi may reduce the toxicity of metals to plants through significant increases in the production of organic chelators. Axenic conditions are required to assess the full potential for production of these molecules but their overall significance in soil ecosystems needs to be determined using additional experiments under more ecologically realistic conditions.

Biodegradation of low molecular weight organic compounds and their contribution to heterotrophic soil respiration in three Japanese forest soils

Low molecular weight (LMW) organic compounds in soil solution could be important substrates for heterotrophic soil respiration. The importance of LMW organic compound mineralization in heterotrophic soil respiration needs to be confirmed for different types of soils. The concentrations of LMW organic compounds in soil solution and mineralization kinetics of 14C-radiolabelled glucose, acetate, oxalate and citrate were studied in three Japanese forest soils (Andisol, Spodosol and Inceptisol) with varying adsorption capacities. Based on those results, the fluxes of LMW organic compound mineralization and their magnitude relative to heterotrophic soil respiration were quantified. Monosaccharides and organic acids comprised on average 5.9–11.2% and 0.9–1.4% of dissolved organic carbon in soil solution, respectively. Monosaccharide mineralization make up 49–74% of heterotrophic (basal) soil respiration at the soil-profile scale, while organic acid mineralization accounts for between 5% (Andisol) and 47–58% (Spodosol and Inceptisol) of heterotrophic soil respiration. The mineralization of LMW organic compounds is a substantial fraction of heterotrophic soil respiration regardless of soil type, owing to their rapid and continuous production and consumption. The specific contribution of organic acid mineralization to heterotrophic soil respiration varies depending on soil adsorption capacities, namely iron and aluminum oxides.

Re-cycling of remediated soil – Evaluation of leaching tests as tools for characterization

In Sweden, leaching tests with deionized water (D.W.) are utilized in risk assessment of materials entering landfills, but implementation of these results to evaluate the risk of spreading of pollutants in the environment is difficult. One problem is that most leaching procedures only consider heavy metals release, whereas organic pollutants are left out. The aim of the present study was to assess the possible pollutant mitigation in four remediated soils, three with heavy metals and one with polycyclic aromatic hydrocarbons (PAH) contamination. The mitigation was evaluated by standardized batch and column leaching tests utilizing three different leaching solutions: D.W., a weak ionic solution (0.001 M CaCl(2)) and an artificially made soil water (ASW). In general, batch leaching tests implied larger contaminant removal than column leaching test, possibly due to the more rough treatment of the soil particles, and guidelines would at times be exceeded by the batch leaching test but not by column leaching tests. Utilization of CaCl(2) was found to release less heavy metal than D.W., whereas the metals mobilized by ASW were removed from solution by the filtration of soil leachates. Low molecular weight PAH was most efficiently mobilized by CaCl(2), while D.W. worked better for high molecular weight PAH. Despite very low initial PAH-concentrations, tap- and groundwater criteria were exceeded by all leaching solutions.

Abundance and functions of natural organic matter species in soil and water

This special issue of Aquatic Sciences is the result of contributions in the field of aquatic science to the 9th meeting of the Nordic Chapter of the International Humic Substances Society held at Mid Sweden University, Sundsvall, Sweden, May 19-21, 2003. The conference focused on speciation of organic matter and its functions in nature and had themes ranging from analytical techniques to interpretation of ecosystem functions: 1. Characterization and identification of natural organic matter 2. Abundance and functions of organic matter species in terrestrial systems 3. Abundance and functions of organic matter species in aquatic systems 4. Natural organic matter in relation to climate change 5. Interaction of organic matter with heavy metals and xenobiotics

Occurrence and leachability of polycyclic aromatic compounds in contaminated soils : Chemical and bioanalytical characterization

An important concern regarding sites contaminated with polycyclic aromatic compounds (PACs) is the risk of groundwater contamination by release of the compounds from soils. The goal of this study was to investigate the occurrence and leachability of 77 PACs including polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic compounds (NSO-PACs) among total aryl hydrocarbon receptor (AhR) agonists in soils from historical contaminated sites. A novel approach combining chemical and bioanalytical methods in combination with characterization of leachability by use of a column leaching test was used. Similar profiles of relative concentrations of PACs were observed in all soils, with parent PAHs accounting for 71 to 90% of total concentrations in soils. Contribution of oxy-PAHs, alkyl-PAHs and N-PACs ranged from 2 to 9%, 3 to 9% and 1 to 14%, respectively. Although the contributions of groups of PACs were small, some compounds were found in similar or greater concentrations than parent PAHs. Leachable fractions of 77 PACs from soils were small and ranged from 0.002 to 0.54%. Polar PACs were shown to be more leachable than parent PAHs. The contribution of analyzed PACS to overall AhR-mediated activities in soils and leachates suggests presence of other AhR agonists in soils, and a potential risk. Only a small fraction of AhR agonists was available in soils, indicating an overestimation of the risk if only total initial concentrations in soils would be considered in risk assessment. The results of the study strongly support that focus on 16US EPA PAHs may result in inadequate assessment of risk and hazard of PACs in complex environmental samples.