Contamination investigation and risk assessment of molybdenum on an industrial site in China

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<ul><li><p>Contamination investigation and risk assessm</p><p>a The Ecological Technique and Engineering College, Shanghb Institute of Urban Environment, Chinese Academy of Scienc Institute of Soil Science, Chinese Academy of Sciences, 71 Ed Shanghai Academy of Environmental Sciences, 508 Qinzhoe College of Environmental Studies, China University of Geosf Department of Earth and Environmental Sciences, The Univ</p><p>a r t i c l e i n f o</p><p>Article history:Received 13 April 2013Accepted 29 December 2013Available online xxxx</p><p>Keywords:</p><p>from the toxicity data for Mo. Among the 35 assessment locations, Mo in 14 locations was determined to pose un-</p><p>Journal of Geochemical Exploration xxx (2014) xxxxxx</p><p>GEXPLO-05275; No of Pages 9</p><p>Contents lists available at ScienceDirect</p><p>Journal of Geochem</p><p>j ourna l homepage: www.e lsacceptable non-cancer risk for on-site children,with a hazard quotient from 1.2 to 433when children directly drinkgroundwater. In addition, Mo in groundwater which is transported off-site by lateral migrationwill pose unaccept-able non-cancer risks for off-site children, with a hazard quotient of up to 45.8 fromdirectwater drinking. AlthoughMo concentrations in the bounding rivers ranged from4 to6,053 g/L, toxicity data indicated that the ecological riskis minimal for aquatic biota in the surface water. A site-specic target level for Mo in groundwater was establishedas 75.1 g/L. Further work will be conducted regarding remediation feasibility at this site; permeable reactive bar-riers may be an effective option given the predominant distribution of Mo in the groundwater in the site.</p><p> 2014 Elsevier B.V. All rights reserved.</p><p>1. Introduction Corresponding author at: College of EnvironmentaGeosciences, Wuhan 430074, PR China. Tel.: +1 86 27 66235.</p><p>E-mail addresses: gengchunnv@hotmail.com (C. Gengpaparikier@hotmail.com (D. Li), jianxuping@gmail.com (X(Q. Hu).1 Tel./fax: +86 592 6190 560.2 Tel.: +86 21 6408 5119; fax: +86 21 021 64840680.</p><p>0375-6742/$ see front matter 2014 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.gexplo.2013.12.014</p><p>Please cite this article as: Geng, C., et al., CoGeochem. Explor. (2014), http://dx.doi.org/1would be consumption of the groundwater by local residents, and lateral Mo migration to bounding rivers. Onlynon-carcinogenic riskwas assessed, becauseMo has no known carcinogenic effect on living organisms, as indicatedMo contaminationSoilGroundwaterRisk assessmentTransportd,2, Dan Li d,2, Xuping Jian b,1, Qinhong Hu e,f,ai Institute of Technology, No. 100 Haiquan Road, Fengxian District, Shanghai 201418, Chinaces, 1799 Jimei Road, Xiamen 361021, PR Chinaast Beijing Road, Nanjing 210008, PR Chinau Road, Shanghai 200233, Chinaciences, Wuhan 430074, PR Chinaersity of Texas at Arlington, 500 Yates Street, Arlington, TX 76019, USA</p><p>a b s t r a c t</p><p>Because certied reference standards onmolybdenum (Mo) in soil are not available, and drafted risk assessmentprocedures in China have not includedMo. Assessment of the potential risks posed byMo in soil and groundwa-ter is the key to establishing the extent of the contamination and deriving achievable remedial targets, should re-mediation deemed to be necessary. This paper reports the rst investigation of Mo contamination in soil andgroundwater from an incandescent light-bulb manufacturing facility in China. Though the plant was built in1971, the contamination ofMo in the site received little attention until the 1994 and 2008monitoring campaigns;soil Mo concentrations ranged from not-detectable to 15 mg/kg in 1994, and from 0.25 to 252 mg/kg in 2008. Inaddition, groundwater Mo concentrations ranged from not-detectable to 362 g/L in 1994, and 1 to 32, 500 g/Lin 2008. Simulation by Visual MINTEQ software showed thatMo speciation in the groundwaterwould be limitedto MoO42. Detailed site investigation showed that the high concentrations of Mo in groundwater could beadequately explained by the predominant presence of anionic MoO42 at the measured average soil pH of 8.65,and given the small adsorption coefcient 112 L/kg forMo onto eld soil samples. Amodied three-step sequen-tial extraction procedure showed that residual percentages of soil Mo at this industrial site ranged from 69.8 to81.0%, indicating that Mo in the soil was mostly present in the mineral lattice. Bounding of Mo onto the minerallattice is not available to living organisms and thus the risk from soil contamination was considered minimal.A conceptual site model developed for quantitative risk assessment indicated that the main exposure pathwaysChunnu Geng a,b,c,d,1, Yangjun Gaoin Chinal Studies, China University of788 3512; fax: +1 86 27 8743</p><p>), yngyj@163.com (Y. Gao),. Jian), water19049@gmail.com</p><p>ghts reserved.</p><p>ntamination investigation a0.1016/j.gexplo.2013.12.014ent of molybdenum on an industrial site</p><p>ical Exploration</p><p>ev ie r .com/ locate / jgeoexpDue to the rapid urbanization in China, many factories have beenrelocated from the urban area to the suburb, where the factory sitesare redeveloped for residential or municipal use. Some regulationshave been drafted in China for site investigation, monitoring, risk as-sessment and remediation. However, most of these regulations are di-rectly taken from other countries, not adapted to specic Chineseconditions. Some case studies have been addressing these open issues(Chen et al., 2006; Geng et al., 2010).</p><p>nd risk assessment of molybdenum on an industrial site in China, J.</p></li><li><p>2 C. Geng et al. / Journal of Geochemical Exploration xxx (2014) xxxxxxMolybdenum (Mo) is a necessary plant and human micronutrient(O'Connor et al., 2001; Sequi, 1973), but Mo in the high concentrationmay cause copper deciency in cattle (Elliott &amp; Taylor, 2000; O'Connoret al., 2001). Receiving less attention in contaminated sites, the regula-tion of Mo in soil and water has not been a priority in the past due tothe relatively low concentrations found in most groundwater and soils(Ecometrix Inc., 2007). However, Mo has been found at elevated con-centrations in the irrigation drainage of arid agricultural soils (Lemly,1994; O'Connor et al., 2001). Though Mo concentration in soils andgroundwater near, and in contact with, Mo ore has been investigatedin China, these investigations have produced no risk assessment forMo (Cong et al., 2009; Qu et al., 2007) largely because certied referencestandards on soil were not available in the current laws and regulationsin China (MEP, 1995).</p><p>Furthermore, Mo concentrations can be high at sites where Mo isused as the main industrial material and subsequently discharged intowastewater. For example, during the manufacturing of tungsten la-ments for electric lamps, tungsten coils are double-wound around Momandrel wire or rods, which are then separated from the coil by the dis-solution of Mo in a reagent composed of nitric and sulfuric acids. Suchoperation results in the generation of large volumes of spent acid con-taining dissolved Mo (Mukherjee et al., 1988). Although some effortshave been extended to recover Mo from such spent acid, much Mohas been discharged into the environment as wastewater (Liu, 2006;Mukherjee et al., 1988).</p><p>However, little or no information is currently available on Mo con-centrations in soils and groundwater of lamp-making plants, especiallyfor plants built in the 1990s in China. Moreover, in the current Chinesestandards on Mo, the only available certied reference standards arefor groundwater and drinking water; no certied reference standardsare available for soil and surface water. Therefore, the objectives of thepresent work are to: 1) investigate the occurrence and concentrationsof Mo in soils and groundwater in an industrial site in Shanghai whereMo was historically and widely used during incandescent light-bulbmanufacturing processes; 2) identifyMo fractions in soil and speciationin groundwater; 3) propose and analyze the possible mechanism of Moaccumulation in groundwater; 4) undertake quantitative risk assess-ments to evaluate the potential risks of the site to human health andecological receptors, and to identify exposure pathways that may besubject to possible groundwater remediation; and5) derive site-specictarget level (SSTL) for remediation validation.</p><p>2. Materials and methods</p><p>2.1. Environmental settings of the industrial site</p><p>The general area inwhich the site is located includes both residentialand industrial zones in Shanghai, China. The site and its surroundingarea are generally at. The east side of the site is immediately boundedby a paved-road, and the south is bounded by residential areas, beyondwhich is a surface water body; both the west and the north sides arebounded by a surface water body (Fig. 1). Site reconnaissance revealsthat no groundwater abstraction well is present onsite, but ground-water has been used in surrounding residential areas for washingpurposes.</p><p>2.2. Field sampling and chemical measurements</p><p>The site was used for incandescent light-bulb manufacturing from1971 to 2008; the operational layout of the site is shown in Fig. 1. Theprimary operations at the site were coil production and light-bulb as-sembly. Detailed site investigations were performed in 1994 and 2008.</p><p>The selection of soil borings and groundwater monitoring wellswere based on the detailed phase I investigation of due diligence andthe characterization of contamination sources, such as near waste</p><p>dumping areas or leaching areas. In 1994, 6 soil bores were drilled,</p><p>Please cite this article as: Geng, C., et al., Contamination investigation aGeochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2013.12.014and 3 groundwater monitoring wells were installed to the depth of5 m. In 2008, 70 soil borings were drilled to the groundwater levelwith a maximum depth of 6 m, and one soil sample was collectedfrom each soil boring at the depth of 0.11.5 m based on the results ofX-ray uorescent analyzers. Following the drilling, 35 of the soil boringswere converted to groundwater monitoring wells with 75-mm diame-ter PVC casing, in accordance with the U.S. Environmental ProtectionAgency's RCRA Orientation Manual (USEPA, 2003). The layout of these35 monitoring wells is shown in Fig. 1. During the 2008 site investiga-tion, one groundwater sample was collected from each monitoringwell. In 2010, groundwater samples were collected again from eachmonitoring well and analyzed for Mo.</p><p>Soil sampleswere digested by acid and the concentrations ofMo andarsenic were analyzed by inductively coupled plasma-mass spectrome-try (ICP-MS, Agilent 7500cx, Agilent Inc., USA); the concentrations ofMo and arsenic in groundwater were directly analyzed by ICP-MSafter ltration with 0.45 m membrane. Soil was extracted by Milli-Qwater, and measured by pH meter (Lu, 1999), while groundwater pHvalue was directly analyzed by pH meter (MEP, 2002b). In addition,two additional soils (#1 and #2)were sampled from the site by the dig-ging bucket when the sitewas remediated, with the depth of 0.51.0 m.Samples #1 and #2 were near MW31 and MW19, respectively, whichare located in the north-east and south-west areas of the site, respec-tively (shown in Fig. 1). The soil samples were air-dried, sieved through2 mm screens, and analyzed for basic properties (results are shownin Table 1). Carbon (C), nitrogen (N), and sulfur (S) were analyzed byVario Max CNS analyzer (Elementar Inc., Germany), following ap-proaches of Guo et al. (2011), Lin et al. (2004) and Zhang (2004). Solu-ble bromine (Br) and chlorine (Cl) were extracted byMilli-Q water andanalyzed by ICP-MS according to Lu and Liu (2011) and SBQTS (2010).Soil texture was analyzed, according to Li et al. (2011) and Jiang et al.(2005), by the following procedure: the soilwasrst treatedwith sodiumhexametaphosphate for dispersion, then carbon was removed by adding6% H2O2 and dilute HCl in succession, and nally the treated soil was an-alyzed by the laser particle sizer (Mastersizer 2000,Malvern Inc., UK). Themeasurement of cation exchange capacity (CEC) followed the method ofLu (1999). CEC ranged from 17.4 0.6 to 21.7 0.1 cmol/kg and soilswere predominantly silty in texture.</p><p>2.3. Geology and hydrogeology</p><p>The surface and subsurface prole encountered in the boreholesconsisted of a layer of ll material (including concrete surface base),consisting of silty clay with gravel and/or cobbles/boulders or coal ash,extending to depths of 0.53.0 m below ground surface (bgs). The lllayer was underlain by clay to depth of at least 6 m, the maximumdepth of the boreholes. The clay can be further divided into upper andlower clay layers. The upper clay is brown to gray-brown, rm, of highplasticity, and appears saturated or nearly so. The lower clay layer isgenerally gray, soft, saturated and of high plasticity.</p><p>Groundwater levels encountered in the boreholes ranged from0.6 to2.7 m bgs. Static groundwater levels in the monitoring wells gauged on16 June 2008 ranged from 0.35 to 2.91 m bgs. Based on the staticgroundwater elevations in the wells, the shallow groundwater ow inthe immediate vicinity of the site appears to be toward the surroundingareas and local rivers. More regional groundwater and surface waterow is assumed to be from southwest to northeast, towards the YangtzeRiver about 100 km away from the site.</p><p>2.4. Mo fractionation in soil</p><p>Amodied three-step sequential extraction procedure recommend-ed by the Commission of European Communities Bureau of Reference(BCR), and proposed by emberyov et al. (2010), was used to deter-mine Mo fractions in the two industrial soil samples (soils #1 and #2).</p><p>In addition, pseudo-total metal contents, both for the original soils and</p><p>nd risk assessment of molybdenum on an industrial site in China, J.</p></li><li><p>3C. Geng et al. / Journal of Geochemical Exploration xxx (2014) xxxxxxfor the residue after the three-step sequential extraction, were deter-mined by digestion with aqua regia using the following steps: a soilamount of 0.15 g was weighed into a reaction vessel; 5 ml aqua regiawas then added and allowed to stand for 16 h (overnight) at room tem-perature, to permit slow oxidation of the organic matter in the soil; thesamples were then digested at 120 C for 13 h; after cooling, 4 ml con-centrated HClO4 was added and digested at 140 C for another 13 h;</p><p>Fig. 1. The site layout of monitoring wells for the light-bulb plant. Circles are themonitoring weings andmonitoring wells based on the year 1994 monitoring campaign. Arrows near the mon(For interpretation of the references to color in this gure legend, the reader is referred to the</p><p>Table 1Properties of the soils.</p><p>Soil #1 #2</p><p>C (g/kg) 19.7 0.2 9.7 0.6N (g/kg) 0.93 0.03 0.87 0.07S (g/kg) 0.88 0.00 0.25 0.00pH 8.5 0.04 8.3 0.01CEC (cmol/kg) 21.7 0.1 17.4 0.6Cl (mg/kg) 140 10.6 5.67 1.31Br (mg/kg) 0.45 0.11 0.30 0.00K (mg/kg) 302 9.96 326 22.8Clay (%) 12 10Silt (%) 86 87Sand (%) 2 3</p><p>Please cite this article as: Geng, C., et al., Contamination investigation aGeochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2013.12.014Northafter another cooling period, 2 ml concentrated H2...</p></li></ul>

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