Common occurrence of a positive δ53Cr shift in Central European waters contaminated by geogenic/industrial chromium relative to source values.

Carcinogenic effects of hexavalent chromium in waters are of concern in many countries worldwide. We explored Cr isotope systematics at 11 sites in the Czech Republic and Poland. Geogenic Cr pollution was associated with serpentinite bodies at former convergent plate margins, while anthropogenic Cr pollution resulted from electroplating, tanning, and the chemical industry. Cr(VI) concentration in geogenic waters was less than 40 ppb. Anthropogenic waters contained up to 127,000 ppb Cr(VI). At both geogenic and anthropogenic sites, where known, the source of pollution had a low δ53Cr (<1‰). δ53Cr of geogenic and anthropogenic waters was up to 3.9 and 5.8‰, respectively. At both serpentinite-dominated and industrial sites, δ53Cr(VI)aq was shifted toward higher values, compared to the pollution source. At the industrial sites, this positive δ53Cr shift was related to Cr(VI) reduction, a process known to fractionate Cr isotopes. At geogenic sites, the origin of high δ53Cr(VI)aq is tentatively ascribed to preferential release of 53Cr during oxidation of soil Cr(III) and its mobilization to water. δ53Cr(VI) of industrially contaminated waters was significantly higher (p<0.001) compared to δ53Cr of waters carrying geogenic Cr(VI), implying that either the effective fractionation factor or process extent was greater for Cr(VI) reduction than for Cr(III) oxidation.

Evaluation of the potential for the natural attenuation of hexavalent chromium within a sub-wetland ground water.

In this work, the potential for natural attenuation (NA) of Cr(VI) is evaluated for sub-wetland ground water at a chromium-contaminated site in Connecticut, incorporating the experimental findings of previous work at the site. Experimental data is assessed through long-term attenuation capacity calculations and modeling, which incorporates statistical uncertainty of parametric values. The NA evaluation yielded the following results: (1) Significant increases in Cr(VI) concentration and extremely long chromium source dissolution timeframes are required to exceed the attenuation capacity of the sub-wetland region soils studied in this work; and (2) Based on the 1-D transport modeling and incorporating input parameter uncertainty, there is an approximately 92% and 98% probability that the applicable regulatory criteria will not be exceeded at Point C, near a river which serves as the receptor, for the cases of (1) sorption of Cr(VI) only and (2) pseudo first order disappearance of Cr(VI) from the aqueous phase only, respectively.

Studies of hexavalent chromium attenuation in redox variable soils obtained from a sandy to sub-wetland groundwater environment.

Laboratory experiments were conducted to characterize and quantify the capacity and kinetics of the combined effects of natural attenuation processes, such as adsorption, reduction, and precipitation, for hexavalent chromium [Cr(VI)] in a variable geochemical (i.e. fraction of organic carbon [foc], redox) environment of glaciated soils. Equilibrium attenuation terms: linear sorption (K(d)), estimated capacity, and non-linear Langmuir (K(L), Q) sorption parameters; varied over several orders of magnitude. The pseudo-first-order rate of disappearance of Cr(VI) from aqueous:soil slurries ranged from approximately 10(-5) to approximately 10(-1)/min. An operationally defined kinetic attenuation term, attenuation capacity (AC), describing the quantity of Cr(VI) disappearing from the slurries, ranged from 1.1 to approximately 12 microg Cr(VI)/g soil/7 days. The linear K(d)'s and estimated attenuation capacities were indirectly and directly related to increasing soil pH and foc, respectively. The AC values decreased and increased as a function of increasing soil pH and foc, respectively. The parameters determined in this work were used to evaluate the kinetics, capacity, and stability of chromium attenuation in the sub-wetland saturated soils in Hellerich (2004. A field, laboratory, and modeling study of natural attenuation processes affecting the fate and transport of hexavalent chromium in a redox variable groundwater environment. Ph.D. Dissertation, Department of Civil and Environmental Engineering, University of Connecticut-Storrs) using a statistical simulation framework.

Sorption studies of mixed chromium and chlorinated ethenes at the field and laboratory scales.

The sorption and desorption behavior of hexavalent chromium and chlorinated ethenes in a sandy ground water aquifer with a low reduction capacity was evaluated by performing a variety of analyses and experiments at the laboratory (batch and column studies) and field (in situ injection-withdrawal experiment) scales. The partitioning coefficients determined from the field and laboratory experiments are generally similar. Both sets of experiments yielded relatively low partition coefficients for chromium and chlorinated ethenes. The column studies and injection-withdrawal experiment indicate that chromium has the potential to leach from aquifer sediments and act as a secondary source of contamination. However, the magnitude of the secondary source effect is not significant due to low concentrations of leachable contamination. The chromium sorption isotherm data were also simulated using the triple layer surface complexation model (TLM). The isotherm data were modeled using the TLM, illustrating the applicability of geochemical modeling for sorption of chromium to these sediments under variable pE-pH conditions.