Residual characteristics of HCHs and DDTs in soil and dust of some parks in Ulaanbaatar , Mongolia

The residual characteristics of HCHs and DDTs in park soils and dusts in Ulaanbaatar, Mongolia were determined by GC-ECD to evaluate their potential pollution risk. The residual concentrations of total HCHs and DDTs in the park soil samples were ranged in 11.36-53.14 ng·g -1 and 11.96-24.70 ng·g -1 while it was ranged in 32.28-92.68 ng·g -1 and 13.45-24.41 ng·g -1 in the park dust samples, respectively. We have studied the ratio of α-HCH/γ-HCH in order to determine pollution sources which may come from either technical HCHs or lindane. The study revealed that concentration of DDTs in soil has direct correlation on usage rate of the dicofol and technical DDT in the sampling area. The soil pollution assessments based on the single pollution index of HCHs and DDTs indicated that Ulaanbaatar city’s park soil and dust were not polluted with these compounds.The single pollution index of HCHs reached to 1.85 in A park dust samples，indicating the park dust environment was potentially polluted. DOI: http://doi.dx.org/10.5564/mjc.v15i0.315 Mongolian Journal of Chemistry 15 (41), 2014, p15-20


INTRODUCTION
Organochlorine pesticides (OCPs) are environment typical Persistent Organic Pollutants (POPs) [1][2][3][4][5].Although they has been observed to persist in the plants, animals, water, soil, sediment and other organisms due to refractory to highly chemical stability [3], biodegradation and long-term residual resistance to bioaccumulation along the food chain [5][6][7][8][9][10][11][12].The soil is the material basis of human survival, agricultural ecosystem carrier material and energy exchange [13].Therefore, the OCPs residue analysis in soil and dust contributed to reveal the deeper dynamics and pesticide contamination in the soil.So the environment risk assessments of OCPs in soil are great practical significance to the ecological environment.With the rapid industrialization, urbanization and population growth of Ulaanbaatar, more and more pollutants emit into the environment.The content of OCPs in the city parks soil was analyzed as a research object.This paper presents the current status of OCPs residual concentrations in soil and dust samples obtained from Botanical garden, Central Tower Public Park, Memorial status garden, Khar khorin children's garden and National Amusement Park in Ulaanbaatar city (Fig. 1).

Reagents and Standards:
Acetonitrilе, acetone, nhexane, methylene chloride, calcium chloride, pure anhydrous sodium sulfate, sulfuric acid, activated carbon, silica gel.Standard samples: HCHs, DDTs mixed standard sample (including: α-HCH, β-HCH, γ-HCH, δ-HCH; p,p'-DDT, o,p'-DDT, p,p'-DDE and p,p'-DDD), purity 93%-99%.Sample collection: Surface soil sampling (soil and dust) for analysis was conducted at four different spots from 0-30 cm depth in the circular area with a diameter of 50m in Ulaanbaatar city within the period of September to October in 2013.The soil samples were well mixed and the weight of each sample was 300 to 500g.The samples were packed in polyethylene bags.They were freeze-dried and stored at -20 o C until the extraction.Sample extraction and pre-treatment: Samples were extracted using accelerated solvent extractor (ASE-350) with n-hexane and acetone.A 5 g (dried through a 60 mesh sieve) soil and dust samples mixed with anhydrous Na 2 SO 4 were extracted in a 34 ml stainless steel vessel with n-hexane:acetone (1:1) at 120°C and 10.3 MPa for 5 min heat-up followed by 10 min static extraction [14].The extracts were concentrated to 2-3 mL using rotary evaporator (35°C-40°C), transfer to Florisil column for further purification.The extract is purified in a Florisil small column which have the layers of activated carbon with 1 cm deep and anhydrous Na 2 SO 4 with 1cm deep.The column was eluted with 15 ml nhexane and dichloromethane (1:1).The elution was done with 20 ml 1:1 n-hexane and dichloromethane.The extract was evaporated by nitrogen to 1-2 mL before gas chromatographic (GC-ECD) analysis and quantification.Sample Analysis: Samples were measured by an Agilent-7890A gas chromatograph using a 63 Ni electron capture detector and DB-5 fused silica capillary column (30m×0.25mm×0.25μm).The carrier gas was high purity nitrogen (0.6 ml/min).The injector and detector temperatures were 250°C and 280 o C, respectively.The oven temperature was initially set at
The ratio of α-HCH/γ-HCH has been used to identify whether the pollution source comes from technical HCH or lindane.The ratio of α-HCH/γ-HCH ranged in 3-7 is a source indicator for technical production and technical HCH [18,19], while it is close to 0 for Lindane [20,21].
In this study α-HCH/γ-HCH ratio were ranged from 0.2 to 3.6.The ratios were above 3 in most of park soils showing the sources can be a mixture of lindane and technical HCH.In the case of soil for park A, the ratio was the highest (3.dust samples，indicating the park dust environment was potentially polluted.However, individual pollution index for other park dust samples were less than 1.This is highly suggested that park dust environment was not polluted.The single pollution index of DDTs were 0.27-0.66,which presenting nonpolluting of DDTs in each park dust samples.

CONCLUSIONS
DDTs in soil and dust of some parks in Ulaanbaatar, Mongolia O.Khureldavaa 1* , Jiang He 2, 3 , Dekun Hou 2 , Ruiqing Zhang 3 , Fujing Zhang 4 , D.Oyuntsetseg 1 , J.Ganbaatar 1 100 o C and programmed to 160 o C (10 o C/min) to hold time of 2 min, and again ramped to 260 o C at 4 o C/min and held for 10 min.

Fig. 2 .Fig. 3 .
Fig. 2. The composition profiles of OCPs in park soil from Ulaanbaatar city

Fig. 4 .
Fig. 4. Comparison of soil pollution index values of HCHs and DDTs in park soil from Ulaanbaatar

Table 2
[18]: The concentrations of ∑DDTs (p,p'DDE, o,p'-DDT and p,p'-DDT) were ranged from 11..).The concentration of p,p'-DDE and o,p'-DDT isomers were higher than other isomers in the total DDTs.The concentration of p,p'-DDT was lower than that of other isomers in the park soils.The p,p'-DDE is a DDTs metabolic degradation products, DDT aerobic degradation to DDE and p,p'-DDT could be biodegraded to p,p'-DDE aerobic conditions [21].The DDT/DDE ratio was reported <0.8 in technical DDT[18].The ratio of o,p'-DDT/p,p'-DDT has been used to identify whether the soil pollution source of the technical DDT.The ratio of o,p'-DDT/ p,p'-DDT 2 while the o,p'-DDT/ p,p'-DDT ratio was varied from 3 to 6 which suggesting that pollution source comes from technical DDT and dicofol.Dicofol is potential substance and original drug

Table 3 .
The value of single pollution index and pollution degree[22] This study was investigated the distribution and concentrations of HCHs and DDTs in soil and dust from some parks in Ulaanbaatar city.Conclusions are as follows: 1.The total HCH conentrations were ranged from 11.36 to 53.14 ng•g -1 while the total DDT levels were varying from 11.96 to 24.7 ng•g -1 in these soil samples.A concentration of the HCHs and DDTs depends on human activity such as a usage of technical products or lindane and dicofol in the studied park soil samples.Soil environment was not contaminated by HCHs and DDTs. 2. The total concentrations of HCH and DDT were ranged from 32.28 to 92.68 ng•g-1 and from 13.45 to 24.41 ng•g -1 in the dust samples, respectively.The β-HCH and o,p′-DDT were dominant components.The HCHs and DDTs residues in the dust samples originated mainly from the use of lindane and dicofol. in agricultural soils from Guangzhou.J. Ecology and Environmental Sciences, 18(4), 1256-1260.21.Zhang Hong-yan., Gao Ru-tai., Jiang Shu-ren., et al. (2006) Spatial variability of Organochlorine pesticides (DDTs and HCHs) in surface soils of Farmland in Beijing, China.J. Scientia Agricultural Sinica, 39(7), 1403-1410.22. Hakanson L. (1980) Ecological risk index for aquatic pollution control.J.A sedimentological approach.Water Research, 14, 975-1001.