Distribution of Phthalate Esters in Soil of E-waste Recycling Sites in China

中国环境学会  2011年 06月21日

  Distribution of Phthalate Esters in Soil of E-waste Recycling Sites in China
  W.L.Liu,C.B.Zhang, Z.Zhang


  School of Life Science, Taizhou University, 317000 Linhai, Zhejiang Province, China
  Abstract: 5 PAEs including DMP, DEP, DBP, DEHP and DnOP in the e-waste soils collected and analyzed from FJ, NS and MS in Taizhou city. The Σ5PAEs concentrations ranged from 12.566 to 46.669 mg/kg. DEHP, DBP and DEP were the major phthalates accounting for more than 94% of total phthalates studied. DEHP was the most frequently identified compounds in all samples varied from 0.236 to 6.761 mg/kg. DMP and DEP had relative high concentration at 5~15 cm depth, the others were decreased gradually with the increase of depth. DEHP have a higher level at 100 m distance. As compared to the results from other studies, the soils of Taizhou city were severely contaminated with PAEs. The environmental and human health risks posed by PAEs in the soils of Taizhou city may deserve further attention.
   
  1. Introduction


  Electrical and electronic equipment waste (e-waste) has contributed to the fastest growing waste problem in the world (Halluite, 2005). In China alone, approximately 4 million personal computers are discarded per year (UNEP, 2005). Taizhou, a city of south Chian, one of the largest e-waste disposal centers in China, which was involved in recycling for many years. Primitive methods used for e-waste recycling included mechanical shredding of electronic equipment, open burning of plastics and wires, and acid leaching of printed circuit boards. These have contributed to the release of hazardous chemicals including polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyls ethers (PBDEs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and heavy metals (e.g. Cr, Cd, Cu and Pb), which have caused severe pollution in air, dust, soil, river water and sediment in Taizhou (shen, 2008).
  Phthalate acid esters (PAEs) are the most common additives in the polyvinyl chloride (PVC) and are produced all over the world in large quantities (Simoneit, 2005). Since they are not chemically but only physically bound to the polymer chains, they may be leached into food and beverages from the plastic containers. In recent years, some research articles have appeared discussing the impact of PAEs on wild animals and human beings (Anderson, 2002; Silva, 2004). They suggested that increasing exposure to PAEs might be partially responsible for the recent decline in the male ratio, the premature breast development in young Puerto Rican girls, and the development of breast cancer in humans. Furthermore, it was found that they might persist in human body tissues for longer periods than previously assumed (Zeng, 2008). As highly lipophilic compounds, phthalate esters exhibited a strong potential for adsorption onto the particles, and when remained in the soil, they not only affected the crop growth and production quality but also could leach from soil into the ground water, thus becoming a threat to the aquatic environment. The US Environmental Protection Agency (EPA) and China National Environmental Monitoring Center classified the commonly occurring phthalates as priority pollutants. Up to now, we have not found studies about phthalate esters in e-waste soil in Taizhou, we expect that our study will contribute to more complete comprehension of the city soil quality.


  2. Materials and methods


  2.1. Chemicals and materials
  The standards of phthalate esters(dimethy phthalate(DMP), diethyl phthalate(DEP), di-butyl phthalate(DBP), di-(2-ethylhexyl) phthalate(DEHP) and di-n-octyl phthalate(DnOP)) were purchased from ULTRA Scientific. All solvents were of analytical purity (Tiantong Chemical Factory, China). Anhydrous sodium sulfat and silica gel (100-130 mesh) were activated for 16 h at 600℃ and 130℃, respectively, and trioxid alumina was heated at 250℃ for 12h to remove all the organic compounds. In order to avoid contamination by phthalate esters during the experiment, plastic tubing and containers were abstained and the solvents were redistilled in all –glass system before use. Glassware was treated successively in the following order: washed with acetone and water, soaked in 5%K2Cr2O4 sulfuric acid solution overnight, washed with water and distilled water, dried in oven and rinsed with acetone just before use.


  2.2. Sampling
  Three sites at different location on the e-waste disposal center and neighborhood of Taizhou city were chosen in March 2006. 27 soil samples were collected from FJ, NS and MS sites, respectively. In each site, nine samples collected in 0, 100 and 200 meters away from the disposal center, and at each distance, samples collected at 0-5 cm, 5-15 cm, 15-20 cm depth, respectively. A control sample was collected from farmland about 500 meters away. All samples were collected using a pre-cleaned stainless steel scoop into pre-cleaned aluminium foil envelopes. Each sample consisted of three sub-samples collected from each depth at different distance. The soil was dried at room temperature, ground to 30 mesh and stored in glass bottles at -4℃ until further processing. The remaining water content in the soil was determined gravimetrically after drying sample in an oven at 105℃ for 12h. All the results were reported as dried weight.
   
  2.3. Sample extraction and fractionation
  About 5g of soil was ground with anhydrous sodium sulfate into free flowing powder. The sample was ultrasonically extracted in centrifuge tube with 30 ml of 1/1(v/v) acetone/hexane for 5 min and then the extract was separated by centrifugation. The process was repeated for three times. The solvents in combined extract were evaporated by K.D. apparatus with a gentle stream of nitrogen, and then hexane was added as solvent. The concentrated extract was transferred to a chromatograph column (30 cm×10 cm id) containing 5 g of activated Florisil and about 1 g of anhydrous sodium sulfate on the column top. The fraction eluted by 60 mL of 50/50 (v/v) n-hexane/diethyl ether contained all the phthalates analyzed. Then the extracts were concentrated using a rotary evaporator, and reduced to 0.1 mL under a gentle stream of nitrogen for GC analysis.
   
  2.4. Instrumental analysis  
  The identification and quantification of phthalate esters was carried out on a Agilent 7890 ( United States) GC system equipped with a flame ionization detector and a fused silica capillary HP-5 column (30m×0.25mm id, 0.25μm film thickness). The carrier gas was heloum with a flow of 1 mL/min.1μL of sample was injected in splitless mode. The injector and detector temperature were 280 ℃ and 300℃, respectively. The temperature program was as follows: initial temperature 50℃, from 5o to 280℃ at 4℃/min , and finally 280℃ for 10 min.
  The limit of detection (LOD) for the phthalate esters, estimated as three times response of signal-to-noise of 3:1 in blank sample, ranged from 0.02 mg/kg for DMP to 0.236 mg/kg for DEHP. The average recovery experiments of three times were done by spiking known concentration standards (2.0 mg/kg) in uncultured soil (previously found containing very low amounts of phthalate esters), ranged from 85% for DMP to 115% for DnOP and the relative standard deviation was 7%-13%.


  2.5. Soil physical and chemical analyses
   Soil pH was measured by pH meter with a soil/water ratio of 1:2.5. Total organic carbon (TOC) was measured with an Elementar Vavio EL III elemental analyzer (Hanau, Germany). Total nitrogen and total phosphorus were measured with ammonium molybdate spectrophotometry and alkaline potassium persulfate spectrophotometry.


  2.6. Statistical analysis
  Statistical analysis was performed with SPSS 13.0 for Windows (SPSS Inc., Chicago, IL).
   
  3.Results and discussion
   
  3.1. Major characteristics of the different soils
  The properties of the different soils collected from FJ, NS and MS of Taizhou city, including soil pH, TOC (%), total nitrogen (%), total phosphorus(%), P2O5 were presented in Table 1.
  Table 1: Major characteristics of the different soils

Soil properties          FJ soils n=9       NS soils n=9       MS soils n=9

pH (H2O)               5.90±0.461       6.57±0.820         6.08±0.532

TOC (%)               3.40±0.548       3.28±0.521         2.71±0.817

Total nitrogen(%)        0.910±0.939       1.12±1.047          0.841±1.051

Total phosphorus(%)     0.271±0.0432      0.135±0.0205       0.265±0.0632

   
  3.2. Concentrations of PAEs in soils
  The relative proportions of the 5 PAEs including DMP, DEP, DBP, DEHP and DnOP in the soils collected from FJ, NS and MS were presented in Figure 1 and in the following order: DEHP > DBP >DEP > DMP>DnOP. DEHP, DBP and DEP were the major phthalates accounting for more than 94% of total phthalates studied. The trend of high DBP, DEHP and DEP values in soil was due to their high production. This result was consistent with the commonly reported findings that DBP and DEHP were the dominant components of the PAEs in air (Xie, 2006; Teil, 2006?), water (Fromme, 2002; Yuan, 2002; Peijnenburg ,2006; Fernandez,2007), sediment (Fromme, 2002; Peijnenburg , 2006; Klamer, 2005) and biota (Yuan ,2002).
  Of all the samples, the total concentration of phthalates (ΣPAEs) in soils from FJ, NS and MS sites varied from 12.566 to 46.669 mg/kg, which was higher than that in the control. The highest ΣPAEs concentration was found at FJ (46.669 mg/kg), which was close to a large e-waste disposal site, where a significant amount of plastics and wires were burned to get copper or other metals in it, lots of PAEs may be released from plastics and wires and came into the soil due to local contamination caused by human activities such as its improper electric and electronic waste (e-waste) disposal.

  DnOP and DMP had been only detected in several soils, with concentrations ranging from   

  The concentration and distribution patterns in transverse distance and vertical depth were presented in Figure 2 and Figure 3. For DMP, had relative high concentration at 5~15 cm longitudinal depth, due to its low Kow, volatilization, and subsurface transport, as well as the same trend of DEP. DEHP, DBP and DnOP have the similar trend as with the increase of longitudinal depth, the concentration was decreased gradually. DEHP have a higher level at 100 m of transverse distance, indicating that it was much more easily moved.  
  PAEs are a class of chemical compounds, which vary in alkyl chain length and branching. This chemical class exhibits an eight order of magnitude increase in octanol-water partition coefficients (KOW) and a four order of magnitude decrease in vapor pressure (VP) as alkyl chain length increases from 1 to 13 carbons (Staples,1997), and PAEs with alkyl chain lengths greater than 8 carbon atoms are typically complex mixtures of isomers (Lin, 2003). Ritsema et al. (1989) separated SPM by centrifugation from surface water samples collected from Lake Yssel and the Rhine River (Netherlands). Based on the geometric mean of the range of SPM values, 33% of the DEHP was estimated to be dissolved while 67% was estimated to be SPM-bound. Laboratory and field studies show that partitioning to suspended solids, soils, sediments and aerosols increase as Kow increases and VP decreases (Staples, 1997). PAEs have several degradation pathways, e.g., photodegradation in the atmosphere, biodegradation in water, and anaerobic degradation in sediments and soil. Biodegradation is considered the dominant degradation mechanism for removal of PAEs entering sewage-treatment plants, or released to surface waters, soils and sediments. Higher molecular weight PAEs have a strong tendency to adsorb to soil and sediments, as their solubility in water is very low, which is a determining factor that influences the biodegradation of a chemical. However, it has been reported that soluble soil humic material associates strongly with these compounds, increasing their apparent water solubility and decreasing their apparent degree of soil sorption.


  Comparison of PAEs concentrations in the soils with other studies


  The content of PAEs in soils had been surveyed in some countries. PAEs concentrations in uncultured soil, soils, and sewage sludge-amended soil from Denmark (Vikelsøe, 2002), United Kingdom (Gibson, 2005), and Netherlands (Peijnenburg, 2006) were lower than those measured in this study. There were few investigations on phthalate esters in the greenhouse soil in China. The mean concentrations of DBP and DEHP in greenhouse soil were 2.96 mg/kg and 2.70 mg/kg, respectively, while those outside the greenhouse were 1.25 mg/kg and 1.15 mg/kg, respectively (Ma, 2003). Cai investigated twenty seven soil samples from nine typical vegetable field in areas of Guangzhou and Shenzhen of China, as a result that total contents of the six PAE compounds in all soils ranged from 3.00 to 45.67 mg/kg (Cai, 2006).
  The concentration of PAEs recorded in the present study was also used to assess the potential risk by comparing to the soil cleanup guidelines used in New York, USA (Table 2). In FJ, all PAE congener concentrations exceeded the recommended allowable value, and DMP and DBP exceeded cleanup objective value, it implied that the environmental and human health risks posed by PAEs in the soils of Taizhou city may deserve further attention. All PAE congeners except DnOP in NS and MS exceeded the recommended allowable value but were below the soil cleanup levels .
  Table 2  Soil allowable concentration and cleanup objective of PAE copmpounds in U.S.A

Compounds  Allowable soil concentration (mg/kg)   Value of soil cleanup objective (mg/kg)

DMP                  0.020                               2.0

DEP                   0.071                               7.1

DBP                   0.081                               8.1

DEHP                  4.35                                50.0

DnOP                  1.200                               50.0

   
  4. Conclusions


  This study had provided the first data on the levels of 5 PAEs in the e-waste disposal soils from Taizhou city. PAEs were detected in all soil samples in the present study with the ∑PAEs concentrations ranged from 12.566 to 46.669 mg/kg, mainly originating from e-waste improper disposal. PAEs concentrations in Taizhou soils had exceeded the recommended allowable value comparing to the soil cleanup guidelines used in New York, USA, it may deserve further attention. The ongoing rapid economical growth rate in China highlights the need for more detailed investigation on the levels of PAEs in various environmental matrices, people and food, as well as determining other routes of exposure of these compounds to the human.
   
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