China's soil and groundwater management challenges: Lessons from the UK's experience and opportunities for China.

There are a number of specific opportunities for UK and China to work together on contaminated land management issues as China lacks comprehensive and systematic planning for sustainable risk based land management, encompassing both contaminated soil and groundwater and recycling and reuse of soil. It also lacks comprehensive risk assessment systems, structures to support risk management decision making, processes for verification of remediation outcome, systems for record keeping and preservation and integration of contamination issues into land use planning, along with procedures for ensuring effective health and safety considerations during remediation projects, and effective evaluation of costs versus benefits and overall sustainability. A consequence of the absence of these overarching frameworks has been that remediation takes place on an ad hoc basis. At a specific site management level, China lacks capabilities in site investigation and consequent risk assessment systems, in particular related to conceptual modelling and risk evaluation. There is also a lack of shared experience of practical deployment of remediation technologies in China, analogous to the situation before the establishment of the independent, non-profit organisation CL:AIRE (Contaminated Land: Applications In Real Environments) in 1999 in the UK. Many local technology developments are at lab-scale or pilot-scale stage without being widely put into use. Therefore, a shared endeavour is needed to promote the development of technically and scientifically sound land management as well as soil and human health protection to improve the sustainability of the rapid urbanisation in China.

A lead isotopic study of the human bioaccessibility of lead in urban soils from Glasgow, Scotland.

The human bioaccessibility of lead (Pb) in Pb-contaminated soils from the Glasgow area was determined by the Unified Bioaccessibility Research Group of Europe (BARGE) Method (UBM), an in vitro physiologically based extraction scheme that mimics the chemical environment of the human gastrointestinal system and contains both stomach and intestine compartments. For 27 soils ranging in total Pb concentration from 126 to 2160 mg kg(-1) (median 539 mg kg(-1)), bioaccessibility as determined by the 'stomach' simulation (pH ~1.5) was 46-1580 mg kg(-1), equivalent to 23-77% (mean 52%) of soil total Pb concentration. The corresponding bioaccessibility data for the 'stomach+intestine' simulation (pH ~6.3) were 6-623 mg kg(-1) and 2-42% (mean 22%) of soil Pb concentration. The soil (206)Pb/(207)Pb ratios ranged from 1.057 to 1.175. Three-isotope plots of (208)Pb/(206)Pb against (206)Pb/(207)Pb demonstrated that (206)Pb/(207)Pb ratios were intermediate between values for source end-member extremes of imported Australian Pb ore (1.04)--used in the manufacture of alkyl Pb compounds (1.06-1.10) formerly added to petrol--and indigenous Pb ores/coal (1.17-1.19). The (206)Pb/(207)Pb ratios of the UBM 'stomach' extracts were similar (<0.01 difference) to those of the soil for 26 of the 27 samples (r=0.993, p<0.001) and lower in 24 of them. A slight preference for lower (206)Pb/(207)Pb ratio was discernible in the UBM. However, the source of Pb appeared to be less important in determining the extent of UBM-bioaccessible Pb than the overall soil total Pb concentration and the soil phases with which the Pb was associated. The significant phases identified in a subset of samples were carbonates, manganese oxides, iron-aluminium oxyhydroxides and clays.

Determination of the bioaccessibility of chromium in Glasgow soil and the implications for human health risk assessment.

The Unified Bioaccessibility Method (UBM), which simulates the fluids of the human gastrointestinal tract, was used to assess the oral bioaccessibility of Cr in 27 Glasgow soils. These included several contaminated with Cr(VI), the most toxic form of Cr, from the past disposal of chromite ore processing residue (COPR). The extraction was employed in conjunction with the subsequent determination of the bioaccessible Cr by ICP-OES and Cr(VI) by the diphenylcarbazide complexation colorimetric procedure. In addition, Cr(III)-containing species were determined by (i) HPLC-ICP-MS and (ii) ICP-OES analysis of gel electrophoretically separated components of colloidal and dissolved fractions from centrifugal ultrafiltration of extracts. Similar analytical procedures were applied to the determination of Cr and its species in extracts of the <10 µm fraction of soils subjected to a simulated lung fluid test to assess the inhalation bioaccessibility of Cr. The oral bioaccessibility of Cr was typically greater by a factor of 1.5 in the 'stomach' (pH ~1.2) compared with the 'stomach+intestine' (pH ~6.3) simulation. On average, excluding two COPR-contaminated soil samples, the oral bioaccessibility ('stomach') was 5% of total soil Cr and, overall, similar to the soil Cr(VI) concentration. Chromium(VI) was not detected in the extracts, a consequence of pH- and soil organic matter-mediated reduction in the 'stomach' to Cr(III)-containing species, identified as predominantly Cr(III)-humic complexes. Insertion of oral bioaccessible fraction data into the SNIFFER human health risk assessment model identified site-specific assessment criteria (for residential land without plant uptake) that were exceeded by the soil total Cr (3680 mg kg(-1)) and Cr(VI) (1485 mg kg(-1)) concentration at only the most COPR-Cr(VI)-contaminated location. However, the presence of measurable Cr(VI) in the <10 µm fraction of the two most highly Cr(VI)-contaminated soils demonstrated that inhalation of Cr(VI)-containing dust remains the most potentially harmful exposure route.

Calcium polysulfide remediation of hexavalent chromium contamination from chromite ore processing residue.

Past disposal of high-lime chromite ore processing residue (COPR) from a chemical works in S.E. Glasgow, UK, has led to continuing release of toxic and carcinogenic hexavalent chromium (Cr(VI)) to groundwaters which are highly contaminated with Cr(VI)O4(2-). Traditional methods of remediating Cr(VI)-contaminated land, e.g. using ferrous sulfate and organic matter, have had limited success in converting Cr(VI) to less harmful and insoluble Cr(III). This paper describes the first application of calcium polysulfide (CaS(x)) to the remediation of contaminated groundwater and high-lime COPR in a series of laboratory experiments, which have demonstrated the effectiveness of the treatment in quantitatively and rapidly reducing Cr(VI) to Cr(III) over the pH range (8-12.5) typically found at the sites. Cr(III)-organic complexes, present in groundwater at one location, were also effectively precipitated upon treatment with CaS(x). The potential for large-scale use of CaS(x) in the remediation of Cr(VI) from COPR is also discussed.