Chromium-contaminated site

Untreated industrial effluents India, chromium-contaminated site 5,000,000 11... 

Palmer CD, Wittbrodt PR. 1991. Processes affecting the remediation of chromium-contaminated sites. Environ Health Perspect 92 25-40. 

The remediation of chromium-contaminated sites requires knowledge of the processes that control migration and transformation of chromium. Chromium(VI) can be reduced to chromium(III) in the presence of ferrous iron, reduced sulfur compounds, or organic matter in soil. However, chromiu-m(III) also can be oxidized by manganese dioxide, a common mineral found in many soils (Bartlett 1991 Palmer and Wittbrodt 1991 Pandey etal. 2003). Usually, Part of any chromium(VI) added to a soil or sediment will be reduced very rapidly, especially under acid conditions. On the other hand, excess chromium(VI) may persist for years in soils or lagoons without reduction (Bolan et al. 2003). The addition of organic amendments such as manure enhanced the rate of reduction of chromium(VI) to chromium(III) in soils low in organic matter (Bolan et al. 2003). 

Soil. The first reported field trial of the use of hyperaccumulating plants to remove metals from a soil contaminated by sludge appHcations has been reported (103). The results were positive, but the rates of metal uptake suggest a time scale of decades for complete cleanup. Trials with higher biomass plants, such as B.juncea, are underway at several chromium and lead contaminated sites (88), but data are not yet available. 

In a very interesting and innovative study recently, the ultrasound-assisted microbial reduction of chromium [22], Mathur et al. reported the reduction of hexavalent chromium using Bacillus sp, isolated from tannery effluent contaminated site. The optimum reduction was found at pH 7 and 37°C. The percent reduction increased with an increase in biomass concentration and decreased with an increase in the initial concentration of hexavalent chromium. 

Chromium is a common anthropogenic contaminant in surface waters, therefore Cr isotope fractionations are of potential interest in tracking Cr + pollution in groundwaters. Ellis et al. (2002, 2004)) and Izbicki et al. (2008) analyzed ground-water samples from contaminated sites and observed an increase in Cr/ Cr ratios up to 6%c during the reduction of chromate. Equilibrium fractionations between Cr(VI) and Cr (III) have been estimated by Schauble et al. (2002), who predicted Cr isotope fractionations >l%c between Cr species with different oxidation states. 

Bacteria indigenous to Cr(VI)-polluted areas are Cr(VI) tolerant and/or resistant and have been considered as potential candidates for bioremediation of Cr(VI)-contaminated sites.16 However, the ability of bacteria to reduce Cr(VI) to the less-toxic Cr(III) compounds may produce reactive intermediates (such as Cr(V), Cr(IV), radicals), which are known to be active genotoxins and are likely to be carcinogenic.17 Therefore, the formation and lifetimes of Cr(V) intermediates, produced via bacterial reduction of Cr(VI), need to be evaluated carefully if microorganisms are to be employed as a means for remediation of chromium-polluted subsurface environments. Similarly, Cr(V) accumulation should first be monitored when considering plants and algae as biosorption materials for the bioremediation in the event of chromium pollution.18... 

According to the vendor, the costs of reagents, on-site technical support personnel, and onsite quality assurance personnel were 60 per ton of soil treated at a former electroplating facility in McPherson, Kansas. The reagents were applied to 1500 yd of chromium-contaminated soil (D113382, p. 15). 

Figure 5-1. Frequency of NPL Sites with Chromium Contamination... 

Quantitative chromium solid-state speciation in chromite ore processing residue (COPR) has defined the mineral species and the processes controlling the retention and release of Cr(VI) from CO PR-contaminated sites (Hillier et al, 2003). Information that, used within a process-based modelling framework, has helped to predict the impact of changes in physicochemical conditions on the COPR, to test the extent to which the system may be considered at equilibrium and that, therefore, need to be considered within the context of informed remediation (Geelhoed et al, 2001). 

There is concern that high concentrations of chromium in soil will also result in airborne chromium contamination. However, more than two-thirds of the 30 sites containing COPR in Hudson County, New Jersey,... 

With world production at almost 9.S X 10 tons, the disposal of the residue of spent ore has the potential to have a dramatic impact on our environment. This in fact presents a serious environmental problem as numerous chromium salts, at concentrations ranging fixim 0.7% to 5%, are slowly leached out of the residue. The movement of these salts by capillary action can be seen as chromate blooms in contaminated sites. These chromium salts can also enter the aquifer in areas where the depleted ore is dumped [5],... 

In the following sections, the original speciation of metals released during various industrial activities are reviewed, and possible changes in speciation in the environment outlined. The spatial location of metallic compounds at specific types of site is not discussed in detail the reader is referred to the Department of the Environment s Industry Profiles (Department of the Environment 995a-o). The present review is focused on cadmium, arsenic, chromium, mercury, lead, copper, nickel and zinc because they are conunon at industrially contaminated sites in forms which are considered hazardous. Cadmium, arsenic, chromium, mercury and lead were identified as groundwater contaminants representing threats to human health in a comprehensive US survey (Knox Canter 1996). 

Fig. 1. General fields of metal mobility at contaminated sites, (a) Copper, nickel, lead (b) zinc, cadmium, mercury (c) chromium and similar transition metals (i.e. metals with oxyanions that are soluble over a wide pH range). Dashed lines show region of water stability.

The second type of extraction involves removing metals from contaminated soil such that their concentration is below some defined level. Sometimes, this is called the actionable level. Above this level, some action needs to be taken to remove the contaminating metal. Below this level, no action need be taken. This type of extraction is limited to contaminated soil such as would be found at Superfund sites. Metals commonly of concern are chromium and cadmium other metals extracted are given in Table 11.2. At high levels, plant essential metals, mentioned earlier, are toxic and so may also be of concern under these conditions. 

The process can be used to immobilize heavy metals such as Cd, Zn, Cu, Pb, Ni and Co. Cr(VI) can be reduced by some metal-reducing bacteria to the less toxic and less soluble form Cr(III). Arsenate [As(V)] can be reduced to the more mobile arsenite [As(III)] which precipitates as AS2S3, and is insoluble at low pH. Several laboratory-scale tests (batch and column) are currently available to study the feasibility of this process. However, only a few field tests have been performed to date. Two such tests have been conducted in Belgium, one at a non-ferrous industrial site, where the groundwater was contaminated with Cd, Zn, Ni and Co, and the other which was treated by injection of molasses in order to reduce chromium (VI) to chromium (III). A third demonstration in The Netherlands has been performed at a metal surface treatment site contaminated by Zn. The outcomes of a batch test of a groundwater heavily contaminated by Zn, Cd, Co and Ni are presented in Table 5. The initial sulphate concentration was 506mg/l. With the addition of acetate, a nearly... 

The groundwater at the 2-acre Avco Lycoming Superfund site in Williamsport, Pennsylvania, was contaminated with chlorinated solvents, cadmium, and hexavalent chromium. Following a successful pilot-scale demonstration that lasted from 1995 through 1996, the technology was applied on a fuU-scale. The cost of the pilot-scale demonstration was approximately 145,000. The full-scale remediation system cost about 220,000 to construct. Operation and maintenance costs have been approximately 50,000 per year (D210571, p. 93 D213376, p. A-47). 

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