Recycling EDTA solutions used to remediate metal-polluted soils.

The objective of this research was to investigate the recycling of ethylenediamine-tetraacetic acid (EDTA) used for the removal of trace metals from contaminated soils. We successfully used Na2S combined with Ca(OH)2 to precipitate the trace metals allowing us to recycle the EDTA. The results of batch and column leaching experiments show that both Ca-EDTA and Na-EDTA are powerful chelating agents with a similar soil remediation potential. The major advantage of Ca-EDTA is the preservation of soil organic matter. We found that Na2S was capable of separating the metals Cd, Cu and Pb from EDTA; however, the precipitation of Zn required the addition of Ca(OH)2. After reusing the reclaimed EDTA seven times, over a 14-day period, EDTA reagent losses ranged from 19.5% to 23.5%. Successive washing cycles enhanced the removal of trace metals from contaminated soils. The metal sulfide precipitates contain high concentrations of metals and could potentially be recycled.

Environmental risk assessment of metals: tools for incorporating bioavailability.

In this paper, some of the main processes and parameters which affect metal bioavailability and toxicity in the aquatic environment and its implications for metal risk assessment procedures will be discussed. It has become clear that, besides chemical processes (speciation, complexation), attention should also be given to physiological aspects for predicting metal toxicity. The development of biotic ligand models (BLMs), which combine speciation models with more biologically oriented models (e.g. GSIM), has offered an answer to this need. The various BLMs which have been developed and/or refined for a number of metals (e.g. Cu, Ag, Zn) and species (algae, crustaceans, fish) are discussed here. Finally, the potential of the BLM approach is illustrated through a theoretical exercise in which chronic zinc toxicity to Daphnia magna is predicted in three regions, taking the physico-chemical characteristics of these areas into account.

Prediction of uptake of copper from solution by lettuce (Lactuca sativa Romance).

We studied effects of free copper ion activity and total copper concentration on copper uptake by lettuce from nutrient solution and a model was developed. In ethylenediaminetetraacetic acid and dissolved organic matter treatments, when pH and free copper ion activity were the same, root copper concentration did not change with the total copper concentration. However, at fixed pH and total copper concentration, root copper concentration increased with, and was log-log linearly related to free copper ion activity. Copper uptake by plant roots is affected by free copper ion activity, pH, and the concentration of other competing ions such as Ca2+. Based on the free-ion activity model, we developed a model to predict copper concentrations in lettuce root and shoot. The parameters in this model are the binding constant of lettuce root surface site for copper times the site density, log(nK(Cu)) = 11.29 +/- 0.10; for protons, log(K(H)) = 6.80 +/- 0.12; and for calcium, log(K(Ca)) = 8.49 +/- 0.30. Copper concentration in lettuce shoot was much lower than that of lettuce root. The translocation coefficient (k) is (2.36 +/- 0.37) x 10(-2).

Biotic ligand model of the acute toxicity of metals. 1. Technical basis.

The biotic ligand model (BLM) of acute metal toxicity to aquatic organisms is based on the idea that mortality occurs when the metal-biotic ligand complex reaches a critical concentration. For fish, the biotic ligand is either known or suspected to be the sodium or calcium channel proteins in the gill surface that regulate the ionic composition of the blood. For other organisms, it is hypothesized that a biotic ligand exists and that mortality can be modeled in a similar way. The biotic ligand interacts with the metal cations in solution. The amount of metal that binds is determined by a competition for metal ions between the biotic ligand and the other aqueous ligands, particularly dissolved organic matter (DOM), and the competition for the biotic ligand between the toxic metal ion and the other metal cations in solution, for example, calcium. The model is a generalization of the free ion activity model that relates toxicity to the concentration of the divalent metal cation. The difference is the presence of competitive binding at the biotic ligand, which models the protective effects of other metal cations, and the direct influence of pH. The model is implemented using the Windermere humic aqueous model (WHAM) model of metal-DOM complexation. It is applied to copper and silver using gill complexation constants reported by R. Playle and coworkers. Initial application is made to the fathead minnow data set reported by R. Erickson and a water effects ratio data set by J. Diamond. The use of the BLM for determining total maximum daily loadings (TMDLs) and for regional risk assessments is discussed within a probabilistic framework. At first glance, it appears that a large amount of data are required for a successful application. However, the use of lognormal probability distributions reduces the required data to a manageable amount.

Biotic ligand model of the acute toxicity of metals. 2. Application to acute copper toxicity in freshwater fish and Daphnia.

The biotic ligand model (BLM) was developed to explain and predict the effects of water chemistry on the acute toxicity of metals to aquatic organisms. The biotic ligand is defined as a specific receptor within an organism where metal complexation leads to acute toxicity. The BLM is designed to predict metal interactions at the biotic ligand within the context of aqueous metal speciation and competitive binding of protective cations such as calcium. Toxicity is defined as accumulation of metal at the biotic ligand at or above a critical threshold concentration. This modeling framework provides mechanistic explanations for the observed effects of aqueous ligands, such as natural organic matter, and water hardness on metal toxicity. In this paper, the development of a copper version of the BLM is described. The calibrated model is then used to calculate LC50 (the lethal concentration for 50% of test organisms) and is evaluated by comparison with published toxicity data sets for freshwater fish (fathead minnow, Pimephales promelas) and Daphnia.

Partitioning of copper onto suspended particulate matter in river waters.

Suspended particles and river water from the Susquehanna River, White Clay Creek and the Delaware River were collected to experimentally study the partitioning of copper. The effects of many factors that may influence the partitioning coefficient (Kd) including pH, total suspended solids (TSS), total copper concentration ([Cu]T), dissolved organic matter (DOM), particulate organic matter (POM), hardness, and ionic strength were investigated by performing batch adsorption experiments. The results implied that organic matter binding sites in both the aqueous and solid phases play the most important role in controlling copper partitioning. Other major factors governing the partitioning are pH and TSS. Kd increases with pH in the pH range 3-8. TSS increases caused decreases in Kd values, which may be attributed to the decrease in the quantity of available binding sites caused by interparticle interactions, rather than by the redistribution of organic matter between solid and solution phases with the variation of TSS. Kd decreases slightly when total Cu concentration increases; however, Kd can be considered to be independent of Cu concentration when TSS is high. The effects of calcium competition and ionic strength on partitioning are small.

Comparison of trace metals in the intake and discharge water of power plants using "clean" techniques.

Once-through, noncontact condenser cooling water at power plants is frequently discharged back to the fresh or saline water body used for its intake water. This study evaluated the potential effect that trace metals, collected using "clean" sampling and analytical techniques and discharged from a once-through, noncontact cooling water system from a power plant, have on receiving water bodies. A paired t-test was used to compare the intake and discharge concentrations of the metals. The metals analyzed were antimony, arsenic, barium, beryllium, boron, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, and zinc. "Clean" is a term applied to field and analytical procedures that are designed to reduce or eliminate ubiquitous metal contamination from samples collected for environmental monitoring. Study results indicate that there is no measurable difference between intake and discharge samples from a noncontact cooling water system, and, therefore, there is no net contribution of metals to receiving water bodies from this system.

Physicochemical factors affecting the sensitivity of Ceriodaphnia dubia to copper.

The effects of physicochemical conditions, such as pH, water hardness, flow rates and natural organic substances on the sensitivity of Ceriodaphnia dubia to the toxic effects of copper were investigated using static bioassay cups and specially designed flow-through bioassay chambers. We found that C. dubia was very sensitive to pH changes and the total copper LC50 values of C. dubia neonates increased by 15-fold as the pH increased from pH 7 to 10. It was also observed that the LC50 values increased sharply upon increasing the water hardness value to 2.4 meq. In addition, increasing flow rates from zero to 50 mL hr(-1) also increased its sensitivity to copper, which was possibly due to hydrodynamic stress. The presence of natural organic substances (humic acid and dissolved organic matter) and suspended particles decreased the toxic effect of copper. This significant decrease in the toxicity of copper in the presence of natural organic materials can be explained by a reduction in the free ion concentration due to complexation. Furthermore, we observed that the kinetics of copper interactions with natural organic materials are a significant factor in the toxic effect of copper and that the acute LC50 values increased with increasing reaction time between solubilized copper and water-borne organics.

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. 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.

Relationship between soil copper content and copper content of selected crop plants in central Chile.

A survey of copper levels in agricultural soils of central Chile revealed two soil clusters-one with a mean copper level of 162 mg/kg and one with a mean copper level of 751 mg/kg of soil. Samples of soils from both soil clusters were characterized on the basis of physicochemical characteristics, and copper extractability was compared by saturation and CaCl2 extraction as well as an acid-leaching procedure (TCLP). We also measured the copper content of various tissues of tomato (Lycopersicon esculentum) and onion (Allium cepa) crops growing on these soils. Other than copper levels, soils from the two clusters were quite similar, with slightly greater levels of molybdenum and cadmium in the high-copper soils. Within each cluster, extracted copper levels and total soil copper levels were not correlated. However, the three extraction procedures solubilized significantly more copper from the high-Cu soils. Mineralogical characterization of the soil particles and depth profiles of soil metal levels in a subsample of sites suggested that highly insoluble copper ore and mining wastes might account for the high copper levels. Neither total nor extractable copper levels allowed statistical prediction of the levels of copper in plant tissue. The edible tissues of both crops had the same mean copper content, regardless of the copper soil level. However, copper contents of stems and leaves were significantly higher for plants growing on the high-Cu soils. These results show that in these soils, high copper levels are associated with very insoluble copper species and thus low bioavailability of copper to crop plants.

Novel model describing trace metal concentrations in the earthworm, Eisenia andrei.

We developed a novel model describing Eisenia andrei body concentrations for Cd, Cu, Pb, and Zn as a function of pH, metals, and soluble organic carbon (SOC) in soil extracts for potential use in predicting values in contaminated field sites. Data from 17 moderately contaminated Dutch field soils in which earthworms were cultured were used in model development. Model parameters quantify biological phenomena important for metal bioavailability, and soil variables quantify relevant soil chemistry characteristics. Earthworm body concentration (EBC) was modeled so that soil metal soluble at bulk soil pH was considered available for dermal exposure, and gut exposure was due to soil metal in solution near neutral regulated gut pH. The efficiency parameter values indicated that metals are biologically regulated in the following order (most to least): Zn - Cu > Pb > Cd. The values determined for the exposure-route constant indicate that Cd, Cu, and Pb EBCs are almost exclusively (>96%) due to dermal exposure and that only 18% of Zn EBC was due to gut exposure. The minimum healthful EBCs determined were Zn > Cu > Pb > Cd, and the values for Pb and Cd were near zero. The Cu model was normalized by soluble organic carbon to be meaningful. The model was most accurate in describing Zn behavior.

Mobilization of heavy metals from Le An River sediment.

The release of sediment-bound heavy metals can have a significant influence on river water quality. Generally speaking, variations of pH and oxygen are among the most important chemical factors that affect the mobility of sediment-bound metals. Recent research has indicated that sulfide, measured as acid-volatile sulfide (AVS), is an important partitioning component of heavy metals. We determined the metal release potential of sediments from the Le An River which receives drainage from a major copper mining operation. We found that the in-situ Cu, Pb, Zn, Cd and As concentrations of the Le An River sediments below the mine are much higher than are the global background values, but that Ni was not elevated. There is potential for mobilization of bound metals to the overlying water, the order of metal release ratio in terms of pH dependencies is Zn > Cu > Cd approximately Pb. Sulfide is not a major binding component for metals in Le An River sediment. It is more likely that the iron and manganese oxides are the most important metal binding components in the sediments of the Le An River.

A conceptual framework for implementation of bioavailability of metals for environmental management purposes.

Although bioavailability is an important issue, the scientific basis for its adequate use in the assessment of ecological risks is weak. What is often ignored is that bioavailability should be handled as a dynamic process that comprises two distinct phases: a physicochemically driven desorption process (also referred to as "environmental availability") and a physiologically driven uptake process (also referred to as "environmental bioavailability"). Since the internal concentration of the organism (also referred to as "toxicological bioavailability") is related with organ-effect levels, it is the latter that is determinant for the actual bioavailability. On the basis of contemporary ideas on equilibrium partitioning both within soils and between soils and organisms combined with a detailed literature review, in this contribution a framework is presented aimed at providing a guidance to necessary components of risk assessment procedures that take bioavailability into account. The framework provides suggestions with regard to the design and scope of studies to be carried out. It is based on knowledge on physico-chemical metal partitioning, in combination with models and concepts applied to analyse toxico-kinetics in exposed organisms. The conceptual dynamic framework boils down to a description of the system in the form of equilibria. It is assumed that each biotic species can be considered as one of the soil phases next to the particulate phase and the liquid phase. Each phase has a characteristic set of exposure routes. Equilibration processes are assumed to take place between all phases present. Essential is that the plan should result in validated procedures that, because they will explicitly address the issue of availability, will be predictive of effects in systems that have not been biologically tested.

Oligohydramnios sequence in a live-born infant following chorionic villus sampling.

We describe an infant born at 29 weeks' gestation with oligohydramnios sequence due to amniotic fluid leakage following chorionic villus sampling at 12 weeks. To our knowledge, this is the first such report.

Chemical composition of bottled mineral water.

Thirty-seven brands of domestic and imported mineral waters were analyzed for the following: alkalinity, aluminum, barium, beryllium, boron, cadmium, calcium, chloride, chromium, cobalt, copper, fluoride, iron, lead, lithium, magnesium, manganese, mercury, molybdenum, nickel, nitrate, pH, phosphate, potassium, silver, sodium, specific conductance, sulfate, tin, vanadium, and zinc. Of the waters examined in this study, 24 had one or more determinands that were not in compliance with the drinking water standards in the United States.

Effect of water treatment on mutagenic potential.

Enzymatic activation did not convert the compounds in the sample concentrates into mutagens. These results are in agreement with those of CHEH et al. (1979) that the mutagenic activity was two to three times greater without the activating system than with it. The dose response relationships demonstrated a low level of mutagenic activity for the concentrates of the Lake Michigan samples. The MAR increases for the completely treated potable water. The concentrates of the Calumet River water to which chlorine had been added produced more revertants per volume of concentrate than did the concentrates of water which had not been chlorinated. Chlorination of the water with no additional treatment produced the highest degree of activity. For the Calumet River samples, treatment with coagulants reduced the net number of revertants to one-third the value for the raw water. When chlorine was added as the final treatment step, the net number of revertants increased by a factor of ten.