Fluorescence fingerprints and Cu2+-complexing ability of individual molecular size fractions in soil- and waste-borne DOM

Land spreading of organic materials introduces large amounts of dissolved organic matter (DOM) into the soil. DOM has the ability to form stable complexes with heavy metals and can facilitate their transport towards the groundwater. The effects on soil processes are difficult to assess, because different DOM components might react differently towards metal ions. The objective of this study was to investigate the fluorescence signature and the Cu2+-binding capacity of individual molecular size fractions of DOM from various sources. DOM extracted from leaf compost, chicken manure, sugar cane vinasse and a fulvic hypercalcaric cambisol was fractionated by the means of dialysis into four molecular size classes: MW<500, 500<MW<3500, 3500<MW<12000-14000, and MW>12000-14000 Da. Vinasse and leaf compost contained around 80% and 70%, respectively, of the total organic carbon in the fractions with low molecular weight (MW<3500 Da); in chicken manure and soil these fractions accounted for 40% and 50% only. Fluorescence was highest in the fraction MW>12000 Da for leaf compost, chicken manure and soil. The opposite result was obtained for vinasse, where the fractions with low molecular weight showed highest fluorescence intensities, distinguishing it from all other samples. Vinasse showed the greatest ability to bind Cu2+ with a resulting complex concentration of 6.31mgl(-1) while in contact with an excess of Cu2+. Leaf compost, soil and chicken manure followed with 2.69, 1.12, and 0.85mgl(-1), respectively. Within vinasse, the fraction MW<500 Da was able to form the most DOM-Cu complexes, indicating the importance of low molecular weight fractions in metal binding.

Rapid screening of DOM's metal-binding ability using a fluorescence-based microplate assay

This note describes the development of a method to rapidly quantify the metal-binding ability of low-volume DOM samples based on their fluorescence properties. The method uses 96-well microplates to screen the fluorescence quenching observed when increasing concentrations of various metals are added to the pH-buffered DOM sample. Only 1.6 mL of DOM sample is required to quantify the binding affinity for each metal and the result is obtained in a few minutes. This study presents results for a surface soil DOM sample for which binding was assessed for Cu2+, Fe2+, Ni2+ at pH 5 and 9.

A fluorescence-based microplate assay to quantify DOM-induced catabolic activity

This note describes a novel method to quickly quantify the dissolved organic matter (DOM)-induced catabolic activity from low-volume samples. The concept is based on the catabolic response profiles (CRP) assay and is described as an inverse CRP, where the reactivity of a complex and diverse mixture of organic compounds towards single strains of bacteria is quantified. A strain of Pseudomonas fluorescens was grown and then transferred to an organic carbon-free mineral salt medium. 90 microL of a fluorogenic redox indicator was added to 90 microL of the bacterial suspension in a well on a 96-well microplate. The DOM sample (90 microL) was added to the well and the fluorescence emitted by the reduced indicator was read over the period of incubation. Only 0.8 mL of the DOM sample, including controls and replicates, was required to quantify the activity of each sample. Results are presented for a surface soil DOM sample and they were compared to glucose samples of various concentrations. The detection limit was reached for samples containing as little as 55 microM of glucose (0.3 mg C L(-1)). The assay showed that only 9% of the total carbon of the soil surface DOM sample was readily biodegradable.

Bioavailability of pentachlorophenol to acclimatised bacteria under batch and flow-through conditions

Biodegradation of organic contaminants in multi-phase systems, such as soils and aquifers, is often limited by the extent and the rate of contaminant sorption onto the solid matrix. However, information about biodegradation in complex matrices is largely limited to studies of closed systems under batch conditions in which potential bioavailability is characterised by the aqueous-phase concentration of a contaminant. There is little knowledge regarding the influence of flow-through conditions on the availability of contaminants to microbes (contaminant bioavailability). Thus, the aim of this study was to assess and compare contaminant bioavailability, in the presence of a sorptive medium, under both batch and flow-through conditions. Accordingly, experiments were designed in which pentachlorophenol (PCP) was introduced into a mixture of inoculated silica sand and a PCP-retaining resin, under either batch or flow-through (columns) conditions. The results indicated that an increase in the amount of resin (0.1-0.2 g) clearly lowered PCP availability to microbes after 170 h under batch conditions (30 and 45% respectively); whereas, the initial decrease in bioavailability observed under flow-through conditions (45 and 70% respectively) was reversed and no longer observable after 170 h. This increase in PCP availability was linked to an improvement in the contaminant biodegradation capacity from 0.03 to 0.13 mg x l(-1) x h(-1) over 200 h.