[Effects of Source Depletion on Vapor Intrusion Risk Assessment].

The current regulatory site investigation employs the J&E model to predict vapor intrusion risk. However, the J&E model assumes that the source concentration is constant for a given exposure period, which is not consistent with the actual site source under depletion. In this study, we compared the differences between the J&E model (constant source), SD source depletion model, and RBCA source depletion model for predicting indoor concentration variation as well as the risk levels during the exposure period with a case study in Beijing. The results showed that the source and indoor air concentrations predicted by the SD and RBCA models showed exponential decreases, whereas those predicted by the J&E model maintained high concentrations throughout the exposure period, which greatly overestimated the risk. The RBCA predicted source depletion at the fastest rate, but the predicted indoor air concentrations were still lower than those of the SD model, which was related to the fact that the RBCA did not consider the effect of buildings on source depletion and did not follow mass conservation. Further, the sensitivity analysis showed that the pressure difference (dP) had the greatest influence on the source concentration in the SD model. For the calculated carcinogenic risk and hazard quotients, the J&E constant source model, the SD source depletion model, and the RBCA source depletion model were ranked in descending order. The results indicated that in general the J&E model was too conservative, the RBCA model may have underestimated risk, and the SD model was more suitable for quantifying vapor intrusion risk in reality.

Refining health risk assessment by incorporating site-specific background concentration and bioaccessibility data of Nickel in soil.

Risk assessment of Nickel (Ni) in a brownfield site contaminated was refined by incorporating the site-specific background level (SSBL) derived using multiple lines of evidence technology and bioaccessibility measured by the Unified Bioaccessibility Method (UBM) and Inhalation Bioaccessibility Method (IBM). The results revealed that the SSBL was 80mg/kg, which was much higher than the general soil screening value (GSSL) (50mg/kg) and more than two times regional background level reported for Tianjing (33mg/kg). The average bioaccessibility for the gastric and intestinal phases was 24.2% (8.6%-54.4%) and 12.6% (7.7%-17.1%), respectively. In simulated lung fluid, only 2.1% (1.0%-4.6%) of Ni in the soil particle was bioaccessible. The amount of samples exceeding the acceptable level was reduced by 50% when SSBL, other than GSSL, was used as the screening value. Moreover, the site-specific target level (SSTL) under acceptable risk level was increased from 94mg/kg to 283mg/kg when bioaccessibility was considered, and the amount of samples above SSTL was reduced to 10%. The study indicated that incorporating site-specific background levels and bioaccessibility data of contaminants in a given site has the potential to support health risk assessment decisions and can reduce the remediation cost greatly.

Cadmium exposure via diet and its implication on the derivation of health-based soil screening values in China.

The cadmium (Cd) intake rates via diet of adults from different regions in China were between 0.160 and 0.557 µg/(kg BW·day), which were less than the provisional tolerable monthly intake (0.833 µg/(kg BW·day)) issued by Food and Agriculture Organization/World Health Organization in 2010, but higher than the one (0.365 µg/(kg BW·day)) issued by the European Food Safety Authority in 2011, to protect children, vegetarians and people living in heavily contaminated regions, and the intake rate of children (1.007 µg/(kg BW·day)) at the national scale was higher than the values recommended by the above institutes and those of adults. Vegetables were the critical contributors, followed by rice, flour, meats and aquatic products. Cd concentration in vegetable was the most sensitive factor in calculating the intake rate, followed by its contents in rice and aquatic products, and the intake rate of flour, indicating that more attention should be given to these parameters in future total diet surveys. When dietary exposure was incorporated, the derived national screening value of Cd under commercial scenario was reduced from 825 to 458 mg/kg, while the values of the north, south, Beijing and Shanghai were reduced to 627, 365, 693 and 489 mg/kg, respectively, indicating that the hazard would be underestimated if dietary exposure was not taken into account, especially for the south. The great variance between the screening values was due to the varied Cd intake rates, which indicated that deriving a screening value for each specific area based on its corresponding exposure characteristics was more appropriate. The national screening level for the residential scenario derived theoretically based on the dietary exposure characteristics of children was a negative value, meaning that the dietary intake rate was above the tolerable value. The method used in the United Kingdom to derive soil guideline values when non-soil exposure accounted for more than half of the maximum tolerable daily intake dose may be an appropriate estimate, but the exact ratio assigned to soil exposure should be assessed comprehensively based on a more sophisticated dietary exposure survey and the corresponding economic implications.

[Application of multiple lines of evidence analysis technology in the assessment of sites contaminated by heavy metals].

A multiple lines of evidence analysis technology was applied to assess whether sites were contaminated by heavy metals (HMs). Firstly, the baseline upper limit concentration for As and Cr6+ were derived for the two investigated sites based on the analysis of the relative cumulative probability plots of the two metals and their spatial distribution in the soil. The results indicated that the baseline upper limit concentrations for As and Cr6+ at site 1 were 29. 8 mg x kg(-1) and 76. 1 mg x kg(-1), respectively, which were much higher than those reported for the local area by others. But at site 2, the baseline upper limit concentrations for As and Cr6+ were 10.6 mg x kg(-1) and 33 mg x kg(-1), respectively, which were only a little higher than the reported values. Taken the derived baseline concentrations as the assessment criteria, both sites were contaminated by the heavy metals to some degree, which is consistent with the site historical activities review results and element correlation analysis results. At site 1, the As concentration in 3.8% samples exceeded the derived baseline concentration, while the Cr6+ concentration in 6.0% samples exceeded the baseline concentration. At site 2, only the concentration of As in 5.2% samples exceeded the derived baseline value. All the above exceeding rates were much lower than those based on the reported baseline values, which were 77.7% and 96.7% for As and Cr6+ at site 1, respectively and 41.9% for As at site 2. The difference indicates that for a specific site, the baseline concentrations for heavy metals reported in literatures should not be directly applied as the criteria to assess whether the site is contaminated or not, which may cause the results to lose the objectivity and leading to the misallocation of lots of rare resource to remediate soil that maybe not contaminated.

[Application of tiered approach to assess the impact of backfilling remediated soil on groundwater].

The tiered approach for assessing the impact of backfilling treated contaminated soil on groundwater was presented in details with a case study. The soil was contaminated by 1,2-dicholorenthane and 9 other organic pollutants and had been remediated before backfilling to meet the pre-set remediation goals based on health risk assessment. The results from tiered I assessment indicate that the concentrations of 8 contaminants in the leachate of the backfilling soil layer would exceed the assessment standards probably leading to groundwater contamination. However, the results from tiered II assessment, in which the adsorption and retardation of vadose zone soil was taken into account and the concentrations of pollutants reaching the groundwater table were predicated, reveal that only the concentrations of 6 contaminants would exceed the assessment standards. Further, taking the dilution and mixing of the groundwater into consideration, tiered III assessment was adopted and the results reveal that only 4 contaminants were beyond the standards. Finally, tiered IV assessment, aiming at predicting the concentration at the target well downstream, was carried out by considering the retardation of contaminants in saturated layer, and the results indicate only 1 pollutant was above the assessment standard. Therefore, it can be seen that the predicted concentrations of the target pollutants at advanced assessment levels will be closer to those at the target drinking water well and the amount of contaminants whose initially-set remediation goals need to be modified will decrease correspondingly, indicating the reduction in pollution prevention cost, although more efforts should be made and more field data should be collected to implement the advance assessment level.

[Application and benefit evaluation of tiered health risk assessment approach on site contaminated by benzene].

The procedures of implementing tiered health risk assessment approach were introduced in detail, and took a large-scale site polluted by benzene in Beijing as an example, the difference on the remediation target of benzene in soil, as well as the corresponding soil remediation volume and costs, were compared. The results indicate that the benzene concentration in soil within 1.5 m in depth and the one below should be remediated to 0.26 mg x kg(-1) and 0.15 mg x kg(-1), respectively, in order to keep the cumulative carcinogenic health risk below 1 x 10(-6) based on tiered II assessment. However, according to tiered III assessment result, which is based on the benzene in soil gas within the contaminated areas in the investigated site, the soil in the corresponding depth should only be remediated to 2.6 mg x kg(-1) and 1.5 mg x kg(-1), respectively. That means the soil remediation volume delimited on tiered III assessment result is less than the one on tiered II by 139 537 m3 and the corresponding remediation costs will be reduced by 57 million Yuan, meaning the enormous economic benefits compared to the costs (around 100 thousands Yuan) spent to carry out tiered III assessment in the site.

[Case study on health risk assessment based on site-specific conceptual model].

Site investigation was carried out on an area to be redeveloped as a subway station, which is right downstream of the groundwater of a former chemical plant. The results indicate the subsurface soil and groundwater in the area are both polluted heavily by 1,2-dichloroethane, which was caused by the chemical plant upstream with the highest concentration was 104.08 mg.kg-1 for soil sample at 8.6 m below ground and the highest concentration was 18500 microg.L-1 for groundwater. Further, a site-specific contamination conceptual model, giving consideration to the specific structure configuration of the station, was developed, and the corresponding risk calculation equation was derived. The carcinogenic risks calculated with models developed on the generic site conceptual model and derived herein on the site-specific conceptual model were compared. Both models indicate that the carcinogenic risk is significantly higher than the acceptable level which is 1 x 10(-6). The comparison result reveals that the risk calculated with the former models for soil and groundwater are higher than the one calculated with the latter models by 2 times and 1.5 times, respectively. The finding in this paper indicates that the generic risk assessment model may underestimate the risk if specific site conditions and structure configuration are not considered.

[Case study on groundwater health risk assessment and remediation strategy based on exposure pathway].

The carcinogenic risk originated from benzene in contaminated groundwater of a large-scale coke plant in Beijing was analyzed and assessed for different land use zones according to the site redevelopment plan. The results revealed that indoor vapor inhalation was the key exposure pathway for all the three zones. The carcinogenic risk in zone A as commercial area was 6.37 x 10(-8), below the maximum allowable level (1.0 x 10(-6)), but was 2.20 x 10(-4) in zone B as industrial park and 7.49 x 10(-5) in zone C as residential/commercial area, both beyond the acceptable level. Further, the remediation target for benzene was calculated at 118 microg x L(-1) and the corresponding remediation area was contoured to be 165 000 m2. Given the high permeability of the aquifer and the excellent volatility of benzene, air-sparging with a combination of engineering control measure was recommended to mitigate the risk of the groundwater contamination.

[Simulation on remediation of benzene contaminated groundwater by air sparging].

Air sparging (AS) is one of the in situ remedial technologies which are used in groundwater remediation for pollutions with volatile organic compounds (VOCs). At present, the field design of air sparging system was mainly based on experience due to the lack of field data. In order to obtain rational design parameters, the TMVOC module in the Petrasim software package, combined with field test results on a coking plant in Beijing, is used to optimize the design parameters and simulate the remediation process. The pilot test showed that the optimal injection rate was 23.2 m3 x h(-1), while the optimal radius of influence (ROI) was 5 m. The simulation results revealed that the pressure response simulated by the model matched well with the field test results, which indicated a good representation of the simulation. The optimization results indicated that the optimal injection location was at the bottom of the aquifer. Furthermore, simulated at the optimized injection location, the optimal injection rate was 20 m3 x h(-1), which was in accordance with the field test result. Besides, 3 m was the optimal ROI, less than the field test results, and the main reason was that field test reflected the flow behavior at the upper space of groundwater and unsaturated area, in which the width of flow increased rapidly, and became bigger than the actual one. With the above optimized operation parameters, in addition to the hydro-geological parameters measured on site, the model simulation result revealed that 90 days were needed to remediate the benzene from 371 000 microg x L(-1) to 1 microg x L(-1) for the site, and that the opeation model in which the injection wells were progressively turned off once the groundwater around them was "clean" was better than the one in which all the wells were kept operating throughout the remediation process.

[Simultaneous determination of trace arsenic and antimony in textile by intermittent flow-hydride generation-atomic fluorescence spectrometry with L-cysteine as a prereducer].

A method for the simultaneous determination of trace arsenic and antimony in textile by intermittent flow-hydride generation-atomic fluorescence spectrometry with L-cysteine as a prereducer was developed. The optimal instrument condition was established. The influence factors such as the acidity of sample solution and carrier liquid, the concentrations of KBH4 and L-cysteine, the flow rate of carrier, and the interference of coexistent elements were investigated. The method was convenient and rapid. Under the optimal condition, the detection limits were 0.35 and 0.22 microg x L(-1), the relative standard deviations were 1.3% and 2.8%, and the recoveries were in the ranges of 93.6% - 98.4% and 92.2% - 103.6% for As and Sb respectively.