William H. Hendershot

Copper solubility and speciation of in situ contaminated soils : Effects of copper level, pH and organic matter

This study attempts to identify the soil properties controlling the fractionation of copper into various soil pools and determine the influence of pH and metal loading on soil-solution free copper activity (pCu2+). The pCu2+ was determined in 0.01 M CaCl2 soil extracts using a copper ion selective electrode. We analyzed a wide variety of soils: urban, agricultural and forest soils from the Province of Québec, New York State and Denmark. The pCu2+ ranged from 12.21 to 6.18. The relationships among pCu2+, total soil copper, total dissolved copper and soil pH are studied for their variability within and between sites as well as for the whole data set. Regression equations are presented for predicting soluble copper as a function of total soil copper and also for predicting pCu2+ as a function of total soil copper and soil pH.

Linking plant tissue concentrations and soil copper pools in urban contaminated soils

Copper tissue concentrations of radish (Raphanus sativa cv. Cherry Belle), lettuce (Lactuca sativa cv. Buttercrunch) and ryegrass (Lolium perenne cv. Barmultra) grown in a greenhouse in urban contaminated soils are compared to total, soluble and free ion copper pools. The tissue concentrations of copper vary between 8.1 and 82.6 mg Cu kg(-1) dry tissue and the total soil copper content varies between 32 and 640 mg Cu kg(-1) dry soil. The linear regressions with cupric ion activity and total soil copper are both significant (p < 0.01), but cupric ion activity yields a higher level of statistical significance in every case. The results support the hypothesis that free metal in the soil solution is a better indicator of plant metal bioavailability than either total or soluble metal.

The effects of antecedent moisture conditions on the relationship of hydrology to hydrochemistry in a small forested watershed

The relationship between stream discharge and the concentration of different solutes reflects the hydrological processes occurring in a catchment, but is also strongly affected by antecedent moisture conditions. In this study, the effects of antecedent conditions were examined for a small forested watershed near Montreal (Quebec) by comparing data from sequences of fall events for two years of contrasting antecedent moisture conditions. The relationship between discharge and stream water chemistry was also quantified using cross-correlation analysis. Results show that concentrations of dissolved organic carbon, nitrate and calcium increased during storm events with dry antecedent conditions but that the relationships were weaker under wet conditions. For both years, concentrations of sulfate, silicon and sodium and the pH were negatively correlated with discharge (cross-correlations from −0·20 to −0·53). With dry antecedent conditions, there was a general decrease in the concentration of all solutes with time, whereas concentrations remained at about the same level under wet conditions. The concentration–discharge relationships for sulfate shifted frequently from higher concentrations during the rising limb to higher concentrations during the falling limb from one event to another as a result of changing antecedent conditions. Although the contrast in antecedent moisture conditions between the two years was moderate in comparison with that reported in other studies (25% dryer than average in 1995 and 12% wetter than average in 1996), the hydrochemistry of the stream was markedly different. Copyright

Ion-selective electrode measurements of copper(II) activity in contaminated soils

A method is presented for the use of a cupric ionselective electrode to determine the free copper activity in 0.01 M CaCl2 soil solution extracts. Ionic strength variations and the presence of aluminum caused no significant interferences. The method was applied to 18 soils with wide-ranging copper levels. The pCu2+ varied between 6.33 and 12.20. Acidic soils have a very high cupric ion activity even though they are not considered to be contaminated with copper. Soils considered contaminated with respect to total copper also have free pCu2+ activities below 10, which is close to the toxicity threshold determined in aquatic ecotoxicological studies. All mineral soils have free copper activities close to or below the values expected from pH-dependent soil equilibration studies.

Removal of trace metals from contaminated soils using EDTA incorporating resin trapping techniques

Abstract A series of experiments was conducted using two urban soils from Montreal contaminated with high levels of trace metals. The experiments were aimed at removing and recuperating trace metals from the contaminated soils using ethylene diamine tetraacetic acid (EDTA) and HCl. Acid washing with 1×10 −3 M HCl was found to be ineffective in removing trace metals from the soils. In contrast, the extraction with EDTA is a promising approach; at a low concentration it removed large amounts of metals. In one soil we were able to decrease Cd concentration from 6.2 to 1.4 mg kg −1 ; the corresponding results for Cu were 700 to 330 mg kg −1 , Pb 800 to 410 mg kg −1 , and Zn 2600 to 431 mg kg −1 after 12 times 24-h extraction with 2.74×10 −3 M EDTA. These represent decreases of 76% for Cd, 53% for Cu, 49% for Pb, and 84% for Zn. In a second, less contaminated soil, the Cu concentration was reduced from 130 to 85 mg kg −1 after three 24-h extractions with 2.74×10 −3 M EDTA. We have also developed a procedure to remove metal–EDTA complexes from the leachates using an anion exchange resin. With this technique we were able to trap up to 99% of the Cd, Cu, and Zn, and 93% of the Pb in the soil leachates.

The biotic ligand model for plants and metals: Technical challenges for field application†

To improve predictions of phytoavailable metal, the mechanistic bases of bioaccumulation and toxicity of metals to plants can be integrated into a biotic ligand model (BLM). There are a number of significant challenges to the application of the BLM to plants in soils, including reliable measurements of free ion concentrations for the metals of interest in rhizospheric soil solution, as well as other free ions, and concentrations of ligands to which the ions could bind; identification of the simplest model that can adequately predict root accumulation, and the potential for more complex models to add accuracy to the predictions; incorporating the dissociation of labile metal complexes (i.e., nonequilibrium processes) into a BLM, which is an equilibrium model; application of factors in a BLM that adequately describe translocation, in order to estimate metal concentration and speciation in plant shoots. The review concluded that the ability to estimate trace metal speciation in samples of soil solution are not likely to be better than within one order of magnitude of actual, thus this would be an additional source of uncertainty to the predictions of toxicity. Further, regulatory use of the BLM would require mechanistic bases; and, until root ligands associated with toxicity are well characterized, incorporating the ameliorative effects of competitive cations cannot be mechanistically based. As well, a functional BLM for soils with lower metal free ion activities will have to include kinetic data for metal-ligand complexes, as their association/disassociation may constitute a greater metal supply to roots than what would be predicted by the free ion concentration in soil solution. To apply the BLM to trophic transfer where metal concentration in plant shoots is the main focus, a probabilistic approach using experimentally determined root-shoot partitioning of metals might permit estimates of shoot accumulation from root data, to within one or two orders of magnitude.

Earthworm Sublethal Responses to Titanium Dioxide Nanomaterial in Soil Detected by 1H NMR Metabolomics

¹H NMR-based metabolomics was used to examine the response of Eisenia fetida earthworms raised from juveniles for 20-23 weeks in soil spiked with either 20 or 200 mg/kg of a commercially available uncoated titanium dioxide (TiO(2)) nanomaterial (nominal diameter of 5 nm). To distinguish responses specific to particle size, soil treatments spiked with a micrometer-sized TiO(2) material (nominal diameter, <45 μm) at the same concentrations (20 and 200 mg/kg) were also included in addition to an unspiked control soil. Multivariate statistical analysis of the (1)H NMR spectra for aqueous extracts of E. fetida tissue suggested that earthworms exhibited significant changes in their metabolic profile following TiO(2) exposure for both particle sizes. The observed earthworm metabolic changes appeared to be consistent with oxidative stress, a proposed mechanism of toxicity for nanosized TiO(2). In contrast, a prior study had observed no impairment of E. fetida survival, reproduction, or growth following exposure to the same TiO(2) spiked soils. This suggests that (1)H NMR-based metabolomics provides a more sensitive measure of earthworm response to TiO(2) materials in soil and that further targeted assays to detect specific cellular or molecular level damage to earthworms caused by chronic exposure to TiO(2) are warranted.

The phenology of fine root growth in a maple-dominated ecosystem: relationships with some soil properties

A two-year study was undertaken in a maple-dominated watershed of southern Québec, Canada, to examine relationships between trends in fine root growth, stem diameter growth, soil moisture, soil temperature, mineralized-N and extractable-P. Until September, soil temperature was consistently higher in 1995 than in 1994. Apart from the first sampling in mid-May, soil moisture was higher in 1994 than in 1995. In 1994, most fine roots were produced before leaf expansion, whereas in 1995, fine root production peaked in July. Annual fine root production was estimated to be 2.7 times higher in 1994 than in 1995. Stem growth was strongly associated with the seasonal and annual variation in soil temperature. Root and diameter growth were asynchronous in 1994 but not in 1995. Fine root production was associated with two groups of variables: a soil fertility (mineralized-N and extractable-P) group and a physical soil environment (moisture and temperature) group. Our results are consistent with the negative effect of high soil-N fertility on fine root production but are inconclusive as to the positive effect of high soil-P fertility. Soil conditions that are detrimental to root growth such as high N availability and anaerobiosis could modify the normal dynamics of fine root growth.

Modeling of Cd and Pb speciation in soil solutions by WinHumicV and NICA-Donnan model

Abstract Speciation modeling is an essential tool to estimate the chemical composition of an aqueous sample and to assess the bioavailability and potential risks associated with metal contamination. It is also an indispensable alternative for quantifying the metal speciation when analytical techniques are not available. In this study, we tested the effectiveness of two models, WinHumicV and the Non-Ideal Competitive Adsorption (NICA)-Donnan model, in predicting the amount of Cd 2+ and Pb 2+ , which were originally measured by anodic stripping voltammetry (ASV). In general, with its default parameters, WinHumicV satisfactorily estimated the free Cd concentrations. For Pb, at high pH the model predictions were lower than the ASV measurements. The discrepancy between the measured and predicted free Pb concentrations may be attributed to the uncertainty of stability constants in WHAM model V for metal–DOC interactions, or the possible overestimation of free metals by ASV at high pH. Using the published generic parameters for fulvic acid (FA), the consistent NICA-Donnan model also made predictions comparable to the experimental data when Al and Fe competition was taken into account in the model. The agreement of model predictions and experimental data demonstrates that both models provide reasonable predictions of the metal speciation in soil solutions. However, the results stress the requirement of estimates or measurements of Al and Fe concentrations in soil solution speciation to provide reasonable estimates of trace element speciation.

Speciation of zinc in contaminated soils.

The chemical speciation of zinc in soil solutions is critical to the understanding of its bioavailability and potential toxic effects. We studied the speciation of Zn in soil solution extracts from 66 contaminated soils representative of a wide range of field conditions in both North America and Europe. Within this dataset, we evaluated the links among the dissolved concentrations of zinc and the speciation of Zn(2+), soil solution pH, total soil Zn, dissolved organic matter (DOM), soil organic matter (SOM) and the concentrations of different inorganic anions. The solid-liquid partitioning coefficient (K(d)) for Zn ranged from 17 to 13,100 L kg(-1) soil. The fraction of dissolved Zn bound to DOM varied from 60% to 98% and the soil solution free Zn(2+) varied from 40% to 60% of the labile Zn. Multiple regression equations to predict free Zn(2+), dissolved Zn and the solid-liquid partitioning of Zn are given for potential use in environmental fate modeling and risk assessment. The multiple regressions also highlight some of the most important soil properties controlling the solubility and chemical speciation of zinc in contaminated soils.