Herbert E. Allen

Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent.

Dissolved organic matter (DOM) was concentrated from natural waters and the effluent of a wastewater treatment plant using a portable reverse osmosis (RO) system. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fractions were isolated and purified by the XAD-8 resin combined with the cation exchange resin method. The FA fractions predominated in natural waters and accounted for 54-68% of the total amount of dissolved organic carbon (DOC), whereas the HA and HyI fractions constituted, respectively, 13-29 and 9-30% of the total DOC. The effluent of wastewater was almost devoid of HA and the HyI fraction exceeded FA. The elemental compositions of HA and FA were in the ranges typical for natural humic materials, but the HyI fractions did not exhibit humic character. 1H NMR spectra revealed that the HyI fractions were almost devoid of aromatic protons and the aliphatic region featured more sharp signals than HA and FA fractions, indicating that HyI fractions were consisted of more simple compounds and less complex mixtures. The aliphatic functional groups in these fractions of DOM samples followed the order HA < FA <HyI. Proton titrations indicated that HA. FA and HyI fractions of DOM samples from different sources had similar total acidity whose range was 9.0-11.6 meq/g C. This similarity may be due to the sample fractionation method. The copper titration results showed that the number of total Cu binding sites for the three fractions of different DOM samples were quite similar (1.46-1.60 mmol/g C), which was consistent with the similarity in total acidity from proton titrations. The affinity of copper with each isolated fraction followed the order HA approximately = FA > HyI. The rate of Cu complexation with the HyI fraction was faster than the rate with the HA or FA fraction of the Suwannee River DOM, implying that copper reacted with relatively weak ligands faster than with strong ligands.

Metal speciation. Effects on aquatic toxicity.

on Sensing of Elnvironmental Pollutants (Conf. Proc.) , 1978, p 697. (9) Jaklevic, J. M., Kirby, J . A., Klein, M. P., Robertson, A. S., Brown, G. S., Eisenberger, P., Solid S ta t e Commun. , 23,679 (1977). (10) Glen, G. L., Hurst , C. V., Der. A p p l . Spectrosc., 9, 307 (1971). Receiced for recieu, September 19,1979. Accepted January IO, 1980. Thi s work was supported in part by the Office of Health and Enoironmental Research o f the U.S. Department of Energy under Contract N o . W-7405-ENG-48. Some of the materials incorporated in this work were deceloped u i t h the financial support of the National Science Foundation under Contract No. DMR 77-27489.

The importance of organic matter distribution and extract soil:solution ratio on the desorption of heavy metals from soils.

The lability (mobility and bioavailability) of metals varies significantly with soil properties for similar total soil metal concentrations. We studied desorption of Cu, Ni and Zn, from 15 diverse, unamended soils. These studies included evaluation of the effects of soil:solution extraction ratio and the roles of soil properties on metal desorption. Dcsorption was examined for each metal by computing distribution coefficients (Kd) for each metal in each soil where Kd = [M]soil/[M]solution, Results from soil:solution ratio studies demonstrated that Kd values for the metals tended to increase with increasing soil:solution ratio. This result also held true for distribution of soil organic matter (SOM). Because the soil:solution ratio has a significant effect on measured metal distributions, we selected a high soil:solution ratio to more closely approach natural soil conditions. Copper showed strong affinity to operationally defined dissolved organic matter (DOM). In this study, DOM was operationally defined based on the total organic carbon (TOC) content in 0.45-microm or 0.22-microm filtrates of the extracts. The Kd of Cu correlated linearly (r2 = 0.91) with the Kd of organic matter (Kd-om) where the Kd-om is equal to SOM as measured by Walkley-Black wet combustion and converted to total carbon (TC) by a factor of 0.59. These values representing solid phase TC were then divided by soluble organic carbon as measured by TOC analysis (DOM). The conversion factor of 0.59 was employed in order to construct Kd-om values based on solid phase carbon and solution phase carbon. SOM plays a significant role in the fate of Cu in soil systems. Soil-solution distribution of Ni and Zn, as well as the activity of free Cu2+, were closely related to SOM, but not to DOM. Kd values for Ni, Zn and free Cu2+ in a particular soil were divided by the SOM content in the same soil. This normalization of the Kd values for Ni, Zn, and free Cu2+ to the SOM content resulted in significant improvements in the linear relationships between non-normalized Kd values and soil pH. The semi-empirical normalized regression equations can be used to predict the solubility of Ni and Zn and the activity of free Cu2+ as a function of pH.

Partitioning of organic matter in soils: effects of pH and water/soil ratio

Abstract The effects of pH and water/soil ratio on the soil–water partitioning of soil organic matter (SOM) in 15 New Jersey soils were investigated. The dissolved organic carbon (DOC) concentration stabilized within 24 h. An increase in pH increased dissolution of soil organic matter. The ratio of UV absorbance at 465 nm to that at 665 nm (E4/E6 ratio) of the dissolved organic matter decreased with increasing pH, indicating a greater fraction of high molecular weight of SOM being released into solution phase at higher pH values. A similar result was suggested by decreases in the fulvic/humic acid ratio with increasing pH. At a fixed pH, the partition coefficient (Kd) of SOM correlated with soil CEC. Normalization of Kd with CEC resulted in a linear correlation between the normalized Kd with pH.

Characterization of copper complexation with natural dissolved organic matter (DOM)—link to acidic moieties of DOM and competition by Ca and Mg

We investigated Cu complexation by three dissolved organic matters (DOMs) collected by reverse osmosis (RO). Alkalimetric titration, pH-stat Cu and Ca titrations, pH edges of Cu-DOM complexation, and Ca/Mg-Cu exchange experiments were investigated at 1 = 109-2)M for DOM samples of 10mg C/L. The proton and Cu binding characteristics indicated similarity for all three DOMs. All Cu titrations employed ion selective electrode measurement and indicated the presence of relatively small amounts of strong Cu-binding sites. Four distinct classes of Cu binding sites are required for FITEQL 4.0 to provide good fits to the entire curves. The estimated total Cu binding site density is 4.55 mmol/g C, much less than the total acidity but very close to the phenolic site content. Cu-DOM complexation increases approximately 10-fold per pH unit, even at relatively high pH (> 8). We suggest that sites characterized as phenolic based on alkalimetric titration, not carboxyl sites, account for the majority of Cu complexation under natural water conditions, and Cu-DOM complexation is principally through the replacement of H + by Cu2+ at the phenolic binding sites. The Cu-H exchange ratio is 1:1 for the first three sites and about 1:2 for the 4th site. This 4-site model describes well the pH dependency of Cu-DOM complexation and provides good estimates of free Cu concentrations throughout wide total copper (Cu(T)) and pH ranges. Comparison between Ca-DOM and Cu-DOM complexation demonstrated that (i) Ca-DOM complexation increases much less than an order of magnitude per pH unit and decreases at higher Ca concentration, different from that of Cu-DOM complexation; and (ii) Cu-DOM complexation is highly non-linear, in contrast to the much reduced extent of non-linearity of Ca-DOM complexation. Ca/Mg-Cu exchange experiments showed small competition effect, less than expected by a simple competition model, and the competition tended to reduce with increasing Ca or Mg concentrations. The extent of the competition by Mg and Ca are essentially comparable. Put all together, it suggests that Ca and Mg are preferably bound by carboxyl sites, especially at relatively high concentrations, resulting in a weakened apparent competition effect.

Sediment pore water collection methods for trace metal analysis: A review

Collection and analysis of pore water has become an important aspect of many environmental programs. Pore water analyses are used for toxicity identification, sediment quality assessment and diagenetic studies. This paper reviews the four commonly used methods for collection of pore water and potential artifacts from their use, particularly in the preparation of samples for trace metal analysis. Two of the methods, centrifugation and squeezing, are ex situ, requiring the removal of sediment from the natural environment. The other two, dialysis and suction filtration, are used in situ. Each method has its advantages and disadvantages, and usage must be determined by the individual researcher. The handling of most samples should be conducted in an inert atmosphere until pore water samples are acidified because oxidation has been shown to significantly alter sample speciation. Significant errors have also been found to result from temperature alteration. Sample contamination by fine particles is important in all methods as differentiation of particulate and soluble components is based on membrane pore size.

Correlation of the partitioning of dissolved organic matter fractions with the desorption of Cd, Cu, Ni, Pb and Zn from 18 Dutch soils

Eighteen Dutch soils were extracted in aqueous solutions at varying pH. Extracts were analyzed for Cd, Cu, Ni, Pb and Zn by ICP-AES. Extract dissolved organic carbon (DOC) was also concentrated onto a macroreticular resin and fractionation into three operationally defined fractions: hydrophilic acids (Hyd), humic acids (HA) and fulvic acids (FA). In this manner, change in absolute solution concentration and relative percentage for each fraction could be calculated as a function of extraction equilibrium pH. The soils were also analyzed for solid phase total organic carbon and total recoverable metals (EPA Method 3051). Partitioning coefficients were calculated for the metals and organic carbon (OC) based on solid phase concentrations (less the metal or OC removed by the extraction) divided by solution concentrations. Cu and Pb concentrations in solution as a function of extract equilibrium pH are greatest at low and high pH resulting in parabolic desorption/dissolution curves. While processes such as proton competition and proton promoted dissolution can account for high solution metal concentrations at low pH, these processes cannot account for higher Cu and Pb concentrations at high pH. DOC increases with increasing pH, concurrently with the increase in Cu and Pb solution concentrations. While the absolute concentrations of FA and HA generally increase with increasing pH, the relative proportional increase is greatest for HA . Variation in HA concentrations spans three orders of magnitude while FA concentrations vary an order of magnitude over the pH range examined. Correlation analysis strongly suggests that HA plays a major role in increasing the concentration of solution Cu and Pb with increasing pH in the 18 soils studied. The percentage of the OC that was due to FA was nearly constant over a wide pH range although the FA concentration increased with increasing pH and its concentration was greater than that of the HA fraction at lower pH values (pH = 3-5). Thus, in more acidic environments, FA may play a larger role than HA in governing organo-metallic interactions. For Cd, Ni, and Zn, the desorption/dissolution pattern shows high metal solution concentrations at low pH with slight increases in solution concentrations at extremely high pH values (pH>10). The results presented here suggest that the effects of dissolved organic carbon on the mobilization of Cd, Ni, and Zn may only occur in systems governed by very high pH. At high pH, it is difficult to distinguish in this study whether the slightly increased solution-phase concentrations of these cations is due to DOC or hydrolysis reactions. These high pH environments would rarely occur in natural settings.

Effect of dissolved organic matter source on acute copper toxicity to Daphnia magna

The protective effect of dissolved organic matter (DOM) on metal toxicity to aquatic organisms has been reported by numerous authors. Bioavailability models such as the biotic ligand model (BLM) thus account for this factor to predict metal toxicity to aquatic organisms. Until now, however, few attempts have been made to assess the effect of the DOM source on metal speciation and toxicity and, accordingly, on BLM predictions. The aims of this study were to investigate to what extent DOMs differ in their ability to decrease acute copper toxicity to the cladoceran Daphnia magna and to evaluate if ultraviolet (UV) absorbance measurements may be a simple and effective method to incorporate DOM variability into the acute Cu-BLM for D. magna. Acute toxicity tests were carried out in artificial test water enriched with DOMs isolated from six locations in Europe and North America and in seven natural European surface waters. The acute Cu-BLM for D. magna was then used to estimate the copper complexing capacity of each DOM (expressed as % active fulvic acid, %AFA). A factor of 6 difference was observed between the lowest and the highest copper complexing capacity. A significant linear relationship was observed between the UV-absorbance coefficient at 350 nm (epsilon350) and the %AFA. Linking this relationship to the acute Cu-BLM resulted in a significant improvement of the predictive capacity of this BLM. Without accounting for this relationship, 90% of the predicted 48-h 50% effective concentrations (EC50) were within a factor of 2 of the observed EC50s; taking this relationship into account, 90% of the EC50s were predicted with an error of less than factor 1.3. The present study and other studies seem to indicate that UV absorbance may be a good measure of biologically and toxicologically relevant differences in copper binding behavior of DOM.

Adsorption Of Cadmium And Copper By Manganese Oxide

Cadmium and copper adsorption by δ-MnO2 was investigated by potentiometric titration over a range of pH. Adsorption increased with increasing pH because of hydrolysis of metal cations and/or variable charge sites on δ-MnO2 δ-MnO2. The surface acidity constant for δ-MnO2 was determined using the Triple Layer Model to be pKint,a2 = 5.34. The data from titrations with pH as master variable were analyzed to determine the Triple Layer Model intrinsic stability constants, p*Kint,cd2+ = 0.81, p*Kint.cdoH+ = 6.89, p*Kint,cd2+ = 1.66, and p*K+int,CuOH+ = 3.79 for cadmium and copper adsorption onto δ-MnO2. Titrations with metal ion as the master variable were performed at constant pH to estimate the adsorption capacities. The data conformed to a Langmuir isotherm and could be modeled with the Triple Layer Model constants. For cadmium, at pH 5.5, 7.0, and 8.0, the adsorption capacity is 0.434, 1.08, and 1.92 mmol/g, respectively. The affinity of δ-MnO2 for Cu, 1.54 mmol/g at pH 5.5, is greater than that for cadmium. The results show δ-MnO2 has high adsorption capacities and high adsorption affinities for cadmium and copper even in acidic conditions.

Assessing potential bioavailability of metals in sediments: A proposed approach

Due to anthropogenic inputs, elevated concentrations of metals frequently occur in aquatic sediments. In order to make defensible estimates of the potential risk of metals in sediments and/or develop sediment quality criteria for metals, it is essential to identify that fraction of the total metal in the sediments that is bioavailable. Studies with a variety of benthic invertebrates indicate that interstitial (pore) water concentrations of metals correspond very well with the bioavailability of metals in test sediments. Many factors may influence pore water concentrations of metals; however, in anaerobic sediments a key phase controlling partitioning of several cationic metals (cadmium, nickel, lead, zinc, copper) into pore water is acid volatile sulfide (AVS). In this paper, we present an overview of the technical basis for predicting bioavailability of cationic metals to benthic organisms based on pore water metal concentrations and metal-AVS relationships. Included are discussions of the advantages and limitations of metal bioavailability predictions based on these parameters, relative both to site-specific assessments and the development of sediment quality criteria.