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DDT Vertical Migration and Formation of Accumulation Layer in Pesticide-Producing Sites Li Liu, Liping Bai, Changgeng Man, Wuhong Liang, Fasheng Li, and Xiaoguang Meng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b02456 • Publication Date (Web): 01 Jul 2015 Downloaded from http://pubs.acs.org on July 10, 2015

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Environmental Science & Technology

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DDT Vertical Migration and Formation of Accumulation Layer in Pesticide-Producing Sites

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Li Liu1,2*, Liping Bai1, Changgeng Man2, Wuhong Liang2, Fasheng Li1, Xiaoguang Meng1,2

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1. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China 2. Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, USA

Corresponding author phone: +1-201-216-8014; (+86-10)84915216; email: [email protected]

Abstract

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Soil samples were collected at various depths (0.5-21.5m) from ten boreholes that were drilled with a

10

SH-30 Model Rig, four of which were at a dicofol production site while six were at a DDT

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(dichlorodiphenyltrichloroethane) production site. In industrial sites, the shallow soils at depths of 0-2m

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were mostly backfill soils, which cannot represent the contamination situation of the sites. The contaminated

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levels in the deep original soil can represent the situation in contaminated sites. All the soil samples

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investigated at the DDT and dicofol production sites were found to be seriously polluted. The contents of

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both DDT (0.6-6071 mg/kg) and dicofol (0.5-1440 mg/kg) were much higher at the dicofol production site

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than at the DDT production site (DDTs: 0.01-664.6 mg/kg, dicofol 1)4,5. Volatilization of DDTs from soil is a

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continuing source of atmospheric contamination, which can be transported and transformed in vivo or in the

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air6. They are normally considered persistent organic pollutants (POPs) that have more probability of 2

ACS Paragon Plus Environment

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impairing human health if the sites are reused in real estate development.

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DDT production in China began in the early 1950s, with about 435,200 metric tons of DDTs were

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produced between the 1950s and the 1980s7, accounting for 20% of total world production8,9. Although DDT

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was banned from application and application in most countries in the 1980s, it is still in use for malaria

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control and dicofol production in China10. From 1988 to 2002, nearly 54,000 tons of technical DDT were

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used to produce about 40,000 tons of dicofol in China10. In partial fulfillment of the Stockholm Convention

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on POPs, China endeavored to ban the open production of dicofol from DDT by 2009 and to accomplish

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environmentally sound management and disposal of DDT wastes by 201511.

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Most of the DDT contamination studies focused on agricultural areas12. It was reported that the ratio

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o,p’-DDT/p,p’-DDT (Ro,p’/p,p’) in technical DDT was typically ~0.2, and contamination of dicofol type

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was indicated when appeared with Ro,p’/p,p’ > 0.210,13. Widely differing Ro,p’/p,p’ values in dicofol

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formulations can be found in the literature, with average values ranging from 0.2 to 7.010,14. Several studies

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have investigated DDT in shallow soil at depths of 0 – 2 m in pesticide sites15,16. The soils within 2 m below

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surface were mostly backfill. The shallow soil cannot represent the contamination situation of the sites. Few

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studies referred to deep soil pollution of DDT production sites, especially that of dicofol production sites.

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However, investigation of contamination in the deep soil at production sites could better illustrates the

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vertical migration of contaminants and the sites situation.

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In this study, DDT and dicofol production workshops of a pesticide factory in East China were selected as

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typical contamination sites. This research presents the current status and the manner of migration and

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transformation of OCP residues on contamination sites, and aims to reveal the distribution and sources of

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OCP pollution in the pesticide production sites, which are different from agricultural soil, by examining

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concentrations of DDTs and dicofol. The dataset generated will enrich and provide scientific information for 3



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remediation technology screening at contaminated sites such as pesticide factories.

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2. Materials and methods

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2.1. Site characterization

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The pesticide factory is located in Shandong Province, East China, where the average annual temperature

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is 12.6-13.1°C and annual precipitation is 500-700 mm. It was one of the earliest companies producing DDT,

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which then stopped production according to the State Council’s directive in March 1983, and has not been

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cleaned up yet.

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A dicofol plant was built to produce 3000 ton/year of dicofol emulsifiable concentrate in December 1979

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and was upgraded in 1981. The plant was shut down in 2008. DDT was used in production as raw material

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for dicofol synthesis, which was firstly eliminated to DDE or chlorinated to Cl-DDT, then Cl-DDT was

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hydrolyzed to form dicofol10. The reactions are shown in Fig. S1. in Supporting Information. The dicofol

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products contained some DDT and Cl-DDT impurities. In order to reduce DDTs content in the products, the

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alkaline eliminating process was added in this factory in 2000.

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2.2. Soil sampling

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Site investigation showed that the groundwater flows from east to west. The groundwater is located at the

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silt layer or silty clay layer containing loess-doll with the depth of 4.2-8.5 m and the silty clay layer

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containing loess-doll layer with the depth of 10.5-13.2 m. The soil layers at the depths of 6.6 -10.5 m and

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12.5 - 16.0 m below the ground are aquicludes. The burial depth of the groundwater level is different in the

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study area.

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According to the groundwater flow and workshop distribution in the plant, a total of ten boreholes were

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drilled with a SH-30 Model Rig, four of which were at the dicofol production site while six were at the DDT 4


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production site (Fig. 1). Soil samples were collected at different depths of the boreholes for vertical

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migration study.

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The four borehole locations at the dicofol production site (named S1, S2, S3, S4) were originally covered

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with concrete that were 30 cm (S1), 150 cm (S2), 200 cm (S3) and 60 cm (S4) in thickness respectively. 31

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samples were collected from these four boreholes. Soil was sampled every 0.5 m deep after the concrete

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layer was removed and the soils exposed. Rocks were present at about 5 m deep in most of the boreholes.

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Location description of the sampling points is shown in Table S1 in Supporting Information.

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From the six boreholes (labeled D1, D2, D3, D4, D5, D6) at the DDT production site, 48 soil samples were

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collected at different depths (0-21.5 m), according to the soil texture, surface disturbance depth, and on-site

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test results by photoionization detector.

D1

S4

N

Dico fol pro (2002-20 ducing 08)

S1

Sampling

5

10 m

Pool

S2 Of fice

N

D6

Di cofol pr odu cin g (before 20 02 )

Trichloro methane

Drain 0

D4 Tank

Co nta ine r

Dicofol producing Po ol workshop

DDT producin g

Laboratory

D5

DDT producin g

S3 D3

DDT producing workshop

Packaging

Sampling 0

5

10 m

D2

99 Fig.1. Map of sampling sites.

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The 79 soil samples were placed into cylindrical aluminum boxes, sealed for transport, and stored in the

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laboratory at the temperature of 4°C. Each sample was tested for the concentrations of OCPs, including

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DDTs and dicofol.

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2.3. Sample extraction and preparation

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The soil samples were air-dried, sieved through a 2 mm mesh, and ground. The samples were spiked with

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2,4,5,6-tetrachloro-m-xylene (TCmX) and decachlorobiphenyl (PCB 209) as surrogate standards. In order to 5



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improve extraction efficiency, anhydrous sodium sulfate (5 g) and activated copper (2 g) were mixed with

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the soil samples to remove water and sulfur in the sample. 5.0 g soil was extracted by accelerated solvent

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extraction (ASE 300, Dionex, USA), using 100 mL 1:1 methylene chloride/acetone as extracting solvent.

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The extracted solution samples were concentrated to approximately 1 mL with a K-D concentrator, and then

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loaded onto a column (1 cm Φ) with a Florisil solid phase extraction cartridge (1 g, 6 mL, Supelco, USA)

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filled with anhydrous sodium sulfate (2 g) for further clean-up. The column was eluted with acetone/hexane

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(5/95, v/v, for about 5 min). Florisil and the anhydrous sodium sulfate were activated by heating at 400°C for

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4 h before use. The eluate was solvent-exchanged to n-hexane (50 ml) and concentrated to a final volume of

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1.0 mL under a gentle stream of nitrogen gas.

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2.4. Chemical analysis

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Dicofol and isomers and metabolites of DDT (p,p′-DDE, p,p′-DDD, p,p′-DDT and o,p′-DDT) were

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quantified by a GC-ECD with dual columns. Analyses were done by an Agilent 6890 GC-ECD with

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split/splitless injector, columns DB-608 (30 m×0.25 mm×0.25 µm) and DB-1701 (30 m×0.25 mm×0.25 µm).

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The instrument oven program was as follows: initial temperature 100 °C held for 2 min, increased to 180 °C

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at 30 °C/min and held for 1.5 min, ramp to 230 °C at 2 °C/min and held for 1 min, ramp to 240 °C at 1 °C/min

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and held for 1 min, and then to 280 °C at 30 °C/min, maintained for 10 min. The sample injection volume

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was 2 µL.

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Physicochemical properties of the samples were rigorously examined including moisture content, pH,

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CEC, and organic carbon. Soil moisture content was measured according to the national standard (GB

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7172-1987, China). Soil pH was measured in water with the soil to water ratio of 1:2.5 (w/v). Soil organic

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carbon (SOC) contents were measured using a Shimadzu 5000A TOC analyzer (Japan). Soil cation exchange

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capacity (CEC) was the sum of Ca+Mg+K+Na extracted with 1 M NH4-acetate. CEC was measured by the 6


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method described by Yu et al3.

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2.5. Quality control

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Glassware was soaked in 5% K2Cr2O4 sulfuric acid solution overnight and then cleaned with distilled

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water, then further rinsed with acetone and hexane. Calibration was carried out every time the GC was

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restarted. For each OCP analysis, the correlation coefficients (r) of calibration curves were all higher than

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0.9995. For each compound, the relative standard deviation (RSD) of the response factor was less than 10%.

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All data were subject to strict quality control procedures, including the analysis of method blanks and

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laboratory control samples. The compounds in blanks were undetected. The average recovery ratios of the

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compounds obtained from the analysis of laboratory control sample were 70%-78%. Samples (n=10) were

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extracted and measured in duplicate to evaluate the reproducibility of the overall method. TCmX and PCB

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209 as recovery surrogates were added prior to extraction17. The average recovery ratios of surrogates were

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91.5±8% and 93.6±10% for TCmX and PCB209, respectively. The method detection limit (MDL) was 0.1

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mg/kg for the organochlorine pesticides.

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3. Results and discussion

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3.1. Vertical distributions of the contaminants at dicofol production site

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Figure 2 illustrates the vertical distributions of DDT and dicofol in the soil profiles. DDTs and dicofol

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were present in all samples, and the concentrations ranged from 0.6-6071 and 0.5-1440 mg/kg respectively.

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Although the production was banned about 15 years ago, these OCPs were still present at high levels in most

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of the soil layers. OCP residues remained in not only the top layer but also the deep layers, despite a long

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period of degradation and transport. The concentration of OCP was much lower in the deep layers than those

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in the top layer, which illustrated that OCP was difficult to migrate downward in soils.

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The total OCP concentrations of S2 and S3, which were located in the center of the workshop, were much 7



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higher than those of S1 and S4 in the same soil layer. They were much higher than those not only in urban or

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agricultural soils from various countries18-22, but also around a pesticide factory in Zibo city of China23,

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while close to those in a heavily contaminated site24. In particular, S3 showed very high concentration levels,

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among which the highest DDT concentration (6071 ppm) was in the soil layer at the depth of 2.0-2.5 m. The

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concentrations of DDTs and dicofol were hundreds to thousands of ppm at 2.5 m below the soil surface. For

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example, DDTs were 1217 ppm (3.0-3.5 m) while dicofol was 1440 ppm (2.5-3.0 m). Their concentrations

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also reached 349 ppm and 230 ppm even at 5.0 m deep, respectively. Soils in S3 were seriously contaminated,

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with much higher DDT and dicofol contents compared with the other three boreholes.

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S2 was located between the two production workshops (Fig.1). In borehole S2, DDT and dicofol

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concentrations were as high as 1196 ppm and 589 ppm at the depth of 1.5-2.0 m respectively, while they

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were less than tens of ppm and kept falling below 2 m depth. DDT and dicofol contents in the soil from S4

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were no higher than 20 ppm, 1.1-17 ppm and 0.5-14 ppm respectively, much lower than those of S2 and S3.

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This reveals that it is difficult for DDTs and dicofol in soil to disseminate or migrate horizontally.

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DDT and dicofol concentrations were high in each soil layer of S2, S3, and S4, illustrating serious leaks of

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both production materials (DDTs) and completed products (dicofol) during the dicofol production process.

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DDT and dicofol concentrations decreased with depth in S2, and S3. The contents of the contaminants in the

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top layers were very high, and both their contents were higher at 2.5-3.0 m in S4. These boreholes shared

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similar distribution patterns, revealing that the DDT and dicofol pollution here had the same pollution

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sources, and that all resulted from leaks during dicofol production, not only before the year of 2000, but also

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from recent production between 2000 (making dicofol) and 2008 (plant shutdown).

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Borehole S1 was located in the area surrounding the original dicofol production workshop, and near the

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wastewater pond. DDT and dicofol concentrations were less than tens of ppm, 0.6-61 ppm and 1.3-17 ppm 8


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respectively, significantly lower than those in the same layer of S2 and S3. As the result of a leak of the

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wastewater pond, the vertical distributions pattern of DDT and dicofol contents in S1 were different from

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those in the other three boreholes. The distribution patterns of DDTs and dicofol also had significant

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differences in S1. The DDT concentration exhibited its highest value (61.2ppm) in the 0.3-0.6 m soil layer

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and decreased with depth. In contrast, the dicofol content was comparatively low at this layer and increased

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with depth, showing an opposite trend to that of DDTs. This suggested that they might have arisen from two

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different pollution sources. S1 was located next to the wastewater pond, and its soil samples were deep grey,

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soaked in liquid, and smelled pungent. Therefore, it can be deduced that there was penetration of wastewater

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from the pond. Since these two pollutants exhibited different distributions, there was also leakage of DDTs

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during the dicofol production process. In addition, the significantly high concentration of DDE proved that

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degradation of OCPs was faster in wet soils when compared with dry soils25.

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Fig. 2. Vertical distribution of dicofol and DDTs at dicofol production site

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3.2. DDT isomers and metabolites at dicofol production site

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In the dicofol production site, the DDE contents in soils made up the majority of total DDT concentrations, 9



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compared to the DDD contents (Fig. 2). In particular, the p,p'-DDE content in S1 soil constituted 87%. It was

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not only higher than p,p'-DDD, but also higher than p,p'-DDT and o,p'-DDT. DDT present in the

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environment could degrade to DDD and DDE through chemical and biological processes. Under anaerobic

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conditions, the main metabolite is DDD, whereas under aerobic conditions, DDE is the most representative

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metabolite26. So the DDD:DDE ratio can be selected as an index to indicate whether DDT is degraded under

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aerobic or anaerobic conditions. Although the p,p'-DDE content was much higher than that of p,p'-DDD in

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all samples in this study, ratios of DDE/DDD cannot indicate the DDT degradation condition in a dicofol

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production site, which is different from agriculture soil, because DDE is an intermediate product in the

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dicofol production process using DDT as starting material. The high content DDTs in the soil of the dicofol

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production site suggested the source was leakage of the materials and products in the dicofol production

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process.

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In the dicofol production site, the DDE content generally decreases with depth from 2.0 m to 4.0 m in the

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soil, probably because oxygen entered the soil largely by diffusion and gradually declined with the depth27.

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This is in accordance with the conclusions of Zhao et al and Huang et al23,26. DDD is the anaerobic

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degradation product of DDT, so the degradation of DDT to DDD is expected to increase with depth 26, which

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is clearly because the oxygen content decreases with depth27.

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A parameter to assess the application time of DDT is theRp,p’/p,p’ with the reference value of 1.019,

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which is often used to indicate whether fresh technical DDT input is present28. A larger value means a longer

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time application of DDTs. Rp,p’/p,p’ in the dicofol production site ranged from 0.6 to 23.5 in this study, with

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an average value of 4.4. Most of the Rp,p’/p,p’ values were above 1.0, but not necessarily caused by old

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inputs, because DDE constituted a major percentage. Especially in S1, DDE exhibited significantly high

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values, even in the superficial layer (0.3-0.6 m). Technical DDT generally contains 75% p,p-DDT, 15% 10


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o,p-DDT, 5% p,p-DDE, and < 5% others29. The implementation of the Prohibition Directive 79/117/EEC by

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European Commissions strictly limited DDT contents in dicofol to less than 0.1% (Council Directive

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79/117/EEC, 1978). Two chemical industry sector standards of the People’s Republic of China

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(HG3699-2002 and HG3700-2002) require DDT impurity to be no more than 0.5% of technical dicofol or no

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more than 0.1% of formulated dicofol containing 20% dicofol. These standards had been implemented on

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July 1, 2003. Considering the degradation in soils is usually slow, the high DDE contents cannot result from

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degradation, but are probably due to the leak of some DDE intermediate products during the dicofol

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production process. In the reaction of DDT as raw material for dicofol production, DDT was firstly

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transformed to the intermediate DDE and Cl-DDT, then Cl-DDT was hydrolyzed to form dicofol as shown

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in the reactions Fig. S1. in Supporting Information. As seen from the vertical distributions (Fig. 2), each soil

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layer contained some dicofol, with the amount the same as the DDTs. This indicated that the contamination

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inputs occurred in the recent dicofol production period, which was in accordance with the practical reality.

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Therefore, the exact time of DDT inputs cannot be judged merely based on the value of Rp,p’/p,p’. The

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conversion of p,p’-Cl-DDT to p,p’-DDE could lead to high p,p’-DDE/p,p’-DDT ratios and could mislead the

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evaluation of p,p’-DDT residence time in the environment10.

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During the synthesis reactions, on average 93% p,p’-DDT was converted to p,p’-dicofol, while only 37%

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o,p’-DDT was converted to o,p’-dicofol. The o,p’-dicofol/p,p’-dicofol ratios were about 0.1, which was

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much lower than 0.2-0.3 for o,p’-DDT/p,p’-DDT in technical DDT10,30. The ratio Ro,p’/p,p’ =

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[o,p’-DDT]/[p,p’-DDT] can be used to distinguish technical DDT from “dicofol-type DDT”31, and can be

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considered as an indicator to discriminate between dicofol or technical DDT usage. The values of Ro,p’/p,p

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at the dicofol production site were generally between 0.4-5.8 in this study, further indicating the occurrence

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of leaks of dicofol and DDTs that contained a large amount of DDE during the dicofol production process. 11



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3.3. Vertical distributions of the contaminants at DDT production site

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Figure 3 illustrates the vertical distributions of DDTs and dicofol in the soil profiles at the former DDT

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production site, and it clearly shows that the concentrations of DDTs (0.01-664.6ppm) were much higher

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than those of dicofol, but much lower than in the soil of the former dicofol production site, especially in deep

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layer soil. They were also much lower than the average concentrations of DDTs (3800–7300 mg/kg) found

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in some reported heavily contaminated sites24, but much higher than in urban renewal soil in Beijing18. DDT

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concentrations at this site were much higher than that in soils from Hong Kong (0.007-0.31 µg/kg)19, the

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USA (

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