evaluating the exchange of ddts between sediment and water in a major lake in north china

RESEARCH ARTICLE

Evaluating the exchange of DDTs between sediment and waterin a major lake in North China

Guo-Hua Dai & Xin-Hui Liu & Gang Liang &

Wen-Wen Gong

Received: 30 August 2013 /Accepted: 25 November 2013# Springer-Verlag Berlin Heidelberg 2013

Abstract A large-scale sampling program was conducted tosimultaneously collect surface water, overlying water, porewater, and sediment samples at monthly intervals betweenMarch and December 2010 from Baiyangdian Lake, NorthChina to assess the distribution of DDTs and determine the netdirection of sediment–water exchange. Total DDT concentra-tions ranged 2.36–22.4 ng/L, 0.72–21.9 ng/L, 2.25–33.7 ng/L,and 4.42–7.29 ng/g in surface water, overlying water, porewater, and sediments, respectively, which were at the interme-diate levels compared to those of other area around the world.Seasonal variations of DDTs were featured by higher concen-tration in summer. This was likely associated with (a) theincrease of land runoff in the summer and (b) application ofdicofol and DDT-containing antifouling paints for ships insummer. Sediment–water fugacity ratios of the DDT isomerswere used to predict the direction of the sediment–waterexchange of these isomers. The sediment–surface water, sed-iment–overlying water, and sediment–pore water fugacityratios of DDT isomers averaged 0.34, 0.44, and 0.1, whichare significantly lower than the equilibrium status (1.0), sug-gesting that the net flux direction were from the water tosediment and the sediment acted as a sink for the DDTs. Thedifference of DDT concentrations between sediment and wa-ter samples was found to be an important factor affecting thediffusion of DDT from the water to sediment.

Keywords DDT .Water . Sediments . Sediment–waterexchange . Baiyangdian Lake

Introduction

Dichlorodiphenyltrichloroethanes (DDTs, including p ,p ′-DDT, p ,p ′-DDE, p ,p ′-DDD, o ,p ′-DDT, o ,p ′-DDE, ando ,p ′-DDD) are typical persistent organic pollutants (POPs),which have received wide attention because of their persis-tence, lipophilicity, and toxic biological effects (Tanabe et al.1994; Doong et al. 2002; Serrano et al. 2003). Studies havesuggested that DDTs may affect the normal function of theendocrine system of humans and wildlife and increase the riskof human liver, pancreatic, and breast cancers (Snedeker2001; Turusov et al. 2002).

Technical DDT has been widely applied in China over thepast decades. Considering the persistence and toxicity ofDDTs, Chinese government partly banned the agricultureusage of DDTs in 1982. However, high DDT levels in variousenvironmental media were still being observed recently inChina (Wong et al. 2005; Wei et al. 2008; Yang et al. 2008;Zheng et al. 2010; He et al. 2012; Liu et al. 2013). This may behighly attributable to the potential sources of DDTs includingdicofol usage for crops (Qiu et al. 2005), DDT-containingantifouling paints for fishing boats (He et al. 2012), technicalDDT usage for disease control (Wong et al. 2005), and evenillegal agriculture purpose (Wei et al. 2008).

It has been found that the freshwater ecosystem is one ofthe major sinks for contaminants (Doong et al. 2002; He et al.2012; Hellar-Kihampa et al. 2013). DDTs can enter the aquat-ic environment through sewage inputs, runoff, and atmospher-ic deposition. Once introduced into water, DDTs with lowwater solubility and high octanol/water partition coefficients(Kow) are easily accumulated in sediment (Doong et al. 2002).Other than being an important sink for pollutants, sediment

Responsible editor: Roland Kallenborn

G.<H. DaiState Key Joint Laboratory of Environment Simulation and PollutionControl (SKLESPC), POPs Research Center, School ofEnvironment, Tsinghua University, Beijing 100084, China

G.<H. Dai :X.<H. Liu (*) :G. Liang :W.<W. GongState Key Laboratory of Water Environment Simulation, School ofEnvironment, Beijing Normal University, Beijing 100875, Chinae-mail: [email protected]

Environ Sci Pollut ResDOI 10.1007/s11356-013-2400-8

can potentially act as a significant long-term secondary sourceof DDTs in water by diffusion of dissolved pollutants andresuspension of particles.

Information on direction across the sediment and waterinterface is frequently important in water quality assessmentor prediction (Jurado et al. 2007). Sediment–water exchangeis one of the most important processes determining the envi-ronmental fate and direct or indirect human exposure to DDTs(Chau 2005). In recent years, numerous studies have focusedon air–water and air–soil exchanges of many persistent toxicpollutants such as polychlorinated biphenyls (PCBs),polybrominated diphenyl ethers (PBDEs), and organochlorinepesticides (OCPs) (Cetin and Odabasi 2007; Dickhut et al.2005; Rowe et al. 2007). However, the sediment–water ex-change of hydrophobic organic contaminants (HOCs) wasscarcely reported in the previous studies. Sediment–waterexchange includes two main processes: (a) particle-phaseHOCs deposition and resuspension and (b) the diffusion ofdissolved HOCs between sediment and the water column(Lun et al. 1998). Meijer et al. (2006) studied the PCBsdynamic flux model of internal lake processes and found thatthe flux of sediment–water diffusion was larger than that ofsettling and resuspension for the low molecular weight PCB28, while, for the high molecular weight PCB 153, the flux ofsettling and resuspension was more important than those ofsediment–water diffusion. Dalla Valle et al. (2003) studied thePCDD/F flux in the Venice Lagoon and the process of sedi-ment–water exchange of PCDD/F was included. Their resultsindicated that the net sediment to water movement (i.e., remo-bilization) is suggested for the lighter congeners. In contrast,net deposition (water to sediment) occurred for the heaviest(hepta- and octa-) substituted PCDD/Fs. These results indicatethat the physicochemical properties of HOCs play a vital rolein controlling the sediment–water exchange. To our knowl-edge, few studies have investigated the sediment–water ex-change of DDTs between sediment and water using fieldexperiments. The objectives of this study were to investigatethe seasonal variations of DDT and its metabolites in waterphase and sediment and to determine the direction of DDTs'sediment–water exchange.

Materials and methods

Study area and sample collection

Baiyangdian Lake is the largest shallow freshwater body inNorth China Plain and is also considered as the Kidney ofNorth China due to its unmatchable contribution to the sur-rounding area's groundwater supplies and the ecological en-vironment of Beijing, Tianjin, and North China at large.Currently, there are more than 243,000 people living in 39villages scattered around the lake. As an important base of

aquaculture in North China, Baiyangdian Lake providesaquatic products for nearly seven million people, and, as afamous tourist resort in China, it received more than 850,000tourists every year. Diesel boats are the most important trans-portation means in the lake. The lake, with a surface area of366 km2 and an average depth of about 2 m, consists of morethan 100 small and shallow lakes linked by ditches. Therewere eight rivers in the upstream of Baiyangdian Lake in thepast, and most of them have dried up in the recent years. Theonly surviving tributary, the Fuhe River, carries large amountsof municipal and industrial effluents from Baoding city intothe lake. However, with the rapid economic development andpopulation rise, the water quality of the Baiyangdian Lake hasdeteriorated and water contamination has threatened the watersupply.

Six sites were chosen based on hotspots of pollution aroundBaiyangdian Lake (Fig. 1). Site 1 (Shaochedian, SCD) wasclose to the core area of the nature preserve and is farthestfrom the sewage sources. Site 2 (Beiliuzhuang, BLZ) was atthe mouth of Fuhe River, which was mainly stressed by thesewage from Baoding city. Site 3 (Wangjiazhai, WJZ) was onthe entrance way of Fuhe River and close to villages. Site 4(Zaolinzhuang, ZLZ) was situated near the central area of thelake. Site 5 (Duancun, DC) was near the largest fishery culturearea and a town of about 10,000 people. Site 6 (Caiputai,CPT) was close to villages and also affected by farmlanddischarge. FromDecember to February, the Baiyangdian Lakeis frozen. The sample collection was carried out monthly fromMarch to December 2010. Surface water samples were col-lected at approximately 0.5 m below the water surface using astainless steel submersible pump. Overlying water sampleswere collected at approximately 0.2 m off the bottom using aperistaltic pump in order to make sure that the surface sedi-ments would not be disturbed. In situ pore water samples werecollected using Rhizon In Situ Sampler (RISS) (RhizosphereResearch Products, Wageningen, The Netherlands). At thesame time, surface sediments (0–5 cm deep) were collectedat the water sampling sites using a stainless steel static gravitycorer. All samples were transported on ice to the laboratoryimmediately. Sediment samples were freeze-dried using afreeze drier (FD-1A, China), and water samples were storedat −20 °C. Freeze-dried sediments were grounded with amortar and sieved through a 100-mesh sieve and then storedat −20 °C in pre-cleaned dark glass bottles before extraction.

Chemicals and materials

Standard solutions of six DDT congeners including p ,p ′-DDT, p ,p ′-DDE, p ,p ′-DDD, o ,p ′-DDT, o ,p ′-DDE and o ,p ′-DDD were obtained from Labor Dr. Ehrenstorfer, Germany.Internal standard pentachloronitrobenzene (PCNB) and surro-gate of 4,4′-dichlorobiphenyl were all purchased fromAccuStandard (AccuStandard, USA). Acetone, n-hexane,

Environ Sci Pollut Res

ethyl acetate, methanol, and dichloromethane used for sampleprocessing and analysis, were of HPLC grade and purchasedfrom Fisher Scientific International (USA). Silica gel (80–100mesh) was activated at 180 °C for 12 h in a muffle and thendeactivated with 3 % distilled water before use. Alumina(100–200 mesh) was activated at 250 °C for 12 h and thendeactivated with 3 % distilled water. Diatomaceous earth wasused after being heated at 400 °C for 6 h. Anhydrous sodiumsulfate was first washed with hexane and then heated at650 °C for 12 h prior to use. Powdered copper was used asthe desulfurizing agent and was treated with 1 mol/L HCL

before use. All glassware were treated with sulfochromicmixture at first and then washed with different solvents inthe order of water, acetone, and n-hexane prior to use.

Sample extraction and analysis

Surface water (1.0 L), overlying water (1.0 L), and pore water(500 mL) samples were extracted using a solid phase extrac-tion (SPE) system (Supelco, USA), following establishedprocedures (Zhou et al. 2000). Surrogate standard 4,4′-dichlorobiphenyl was added to each water sample (50 ng

Fig. 1 Sampling sites inBaiyangdian Lake and theirgeographical location (1–6denote six sampling sites inBaiyangdian Lake)


surrogate per liter of water sample). Each of C18 SPE car-tridge (500 mg, Waters, USA) was first washed with 5 mL ofethyl acetate then conditioned with 5 mL of methanol follow-ed by 2×5 mL of deionized water. Water samples were passedthrough the cartridges at a flow rate of 6 mL/min undervacuum. Following extraction, the cartridges were eluted with10 mL of ethyl acetate. Then, the extracts were dehydratedwith anhydrous Na2SO4 and finally concentrated to 0.5 mLusing a gentle nitrogen stream.

Sediment samples were extracted using accelerated solventextraction (ASE) (Dionex 300, CA, USA) with a mobile phaseof n-hexane/acetone (1:1, v /v ). Suitable amounts of surrogatestandard 4,4′-dichlorobiphenyl was added. Diatomaceousearth (DE) was used as a packing material (sediment samplewas homogenized with DE, with an additional layer of pureDE above and below). Active copper was added for desulfur-ization. The ASE conditions composed of the following:system pressure of 1,500 psi, oven temperature of 100 °C,oven heat up time at 5 min, static time at 5 min, flush volumeof 60 %, 1 min nitrogen purge, and 5 cycles per sample(Macgregor et al. 2010). ASE cells of 66 mL capacity wereused. After extraction, the solution was evaporated nearly todryness by a rotary evaporator and redissolved in 10 mL of n-hexane to remove acetone. The hexane extracts continued tobe concentrated to approximately 1 mL and were furthercleaned up and fractioned by a silica gel–alumina (2:1) col-umn (1 cm i.d.) with 15 mL n-hexane and 70 mL n-hexane/dichloromethane (7:3, v /v ) mixture, respectively. The n-hexane/dichloromethane elution was collected and concen-trated to 0.5 mL under a gentle stream of nitrogen gas.

Concentrations of p ,p ′-DDT, p ,p ′-DDE, p ,p ′-DDD, o ,p ′-DDT, o ,p ′-DDE, and o ,p ′-DDD in the extracts were deter-mined using an Agilent 7890A gas chromatograph (GC),equipped with an Agilent 5973 mass selective detector(MSD) (Agilent Technologies, CA, USA) under the selectedion monitoring mode. Separation was performed on a DB-5capillary column (30 m×0.25 mm i.d. 0.25-μm film thick-ness). The oven temperature was programmed from 60 °C(1.0 min hold) to 220 °C at the rate of 25 °C/min to 280 °C(5 min hold) at a rate of 6 °C/min. The injector and detectortemperatures were 230 and 305 °C, respectively. One micro-liter of the extract was injected in the splitless mode. Heliumwas used as carrier gas at a constant flow of 0.1 mL/min.PCNB was added as internal standard to each sample beforeGC injection, in order to quantify the concentration and re-coveries of surrogate.

Analysis of organic carbon

The analytical method of organic carbon in the sedimentsamples has been reported in reference (Mai et al. 2002).Briefly, about 5 g of freeze-dried sediment was treated with10 % HCl solution to remove inorganic carbon and dried

overnight at 60 °C. A portion of the sample was used todetermine total organic carbon (OC) by using an ElementarLiqui-TOC (Hanau, Germany). The dissolved organic carbon(DOC) contents in water phase were also measured by Liqui-TOC analyzer (Hanau, Germany) after filtration.

Quality assurance and quality control

All analytical procedures were carried out under strict qualityassurance and control measures to ensure data quality. Foreach batch of ten samples, procedural blanks (solvent blank),spiked blanks (standards spiked into solvent), matrix spikes/matrix spike duplicates, and sample duplicates were proc-essed. None of the target compounds were detected in theprocedural blanks. Recoveries of the six DDT congeners(p ,p ′-DDT, p ,p ′-DDE, p ,p ′-DDD, o ,p ′-DDT, o ,p ′-DDE,and o ,p ′-DDD) spiked to water and sediment were rangedfrom 45.9 to 102.7 % and 83.2 to 123.6 %, respectively. Thelimits of detection (LOD) were described as three times of thesignal-to-noise ratio. The LOD ranged from 0.01 to 0.5 ng/Lfor water phase and 0.01 to 0.63 ng/g for sediments. GC–MSanalysis was repeated twice for each replicate sample, and therelative standard deviation of replicate analyses was less than30 % for all samples.

Results and discussion

Residual levels of DDTs

The concentrations of DDT isomers (including p ,p ′-DDT,p ,p ′-DDE, p ,p ′-DDD, o ,p ′-DDT, o ,p ′-DDE and o ,p ′-DDD)in the surface water are shown in Table 1. The total concen-trations of DDTs were determined to be between 2.36 and22.4 ng/L with a mean of 7.67±7.0 ng/L during the samplingperiods. p ,p ′-DDE (2.68±1.37 ng/L) was the dominant iso-mer, followed by o ,p ′-DDT (2.63±2.75 ng/L) and p ,p ′-DDT(1.81±2.56 ng/L), with the average abundance of 35, 34, and24 %, respectively.

In overlying water samples, the total concentration ofDDTs varied from 0.72 to 21.9 ng/L with a mean of 10.5±7.67 ng/L during the sampling periods. The dominant DDTmetabolites in the overlying water was p ,p ′-DDE (5.55±5.15 ng/L), which accounted for 55 % of total DDTs. p ,p ′-DDT (1.96±2.22 ng/L) and o ,p ′-DDT (1.85±1.89 ng/L) werethe primary pollutants in the remaining DDT isomers, with theaverage abundance of 19 and 15 % of total DDTs,respectively.

The total concentration of DDTs in the pore water variedfrom 2.25 to 33.7 ng/L with an average of 15.6±8.95 ng/Lduring the sampling periods, which were twofold higher thanthose in the surface water. As organochlorine pesticides arederived from anthropogenic inputs, their levels in pore water


are therefore determined by a number of closely related factorssuch as the transport processes (i.e., diffusion), reactions in thesediment column, and reactions across the sediment/waterinterface. In the six isomers of DDTs, p ,p ′-DDE (6.90±3.30 ng/L) was dominant, followed by p ,p ′-DDT (4.88±3.32 ng/L) and o ,p ′-DDT (1.67±3.67 ng/L), accounted for48, 31, and 10 % of total DDTs, respectively.

All DDT isomers were detected in 100 % of sedimentsamples during the sampling periods. The residual levels ofDDTs in sediments ranged from 4.42 to 7.29 ng/g, with amean value of 6.04±0.90 ng/g. The mean concentrations ofthe DDT isomers in sediments is in the following order: p ,p ′-DDE (3.17±0.72 ng/g)>p ,p ′-DDT (1.87±0.67 ng/g)>o ,p ′-DDT (0.71±0.46 ng/g)>p ,p ′-DDD (0.20±0.12 ng/g)>o ,p ′-DDE (0.06±0.04 ng/g)>o ,p ′-DDD (0.04±0.03 ng/g). Theisomers of p ,p ′-DDE, p ,p ′-DDT, and o ,p ′-DDT made up of52, 31, and 12 % of the total DDTs in sediment, respectively.

Overall, the six DDT isomers were detected in almost allsamples, indicating that the DDTs were ubiquitous in theBaiyangdian Lake. The concentrations of p ,p ′-DDE werehigher than the other isomers in each month, followed byo ,p ′-DDT and p ,p ′-DDT; the average abundance of the otherthree remaining isomers was generally less than 12% in watersamples and less than 5 % in sediment samples. The predom-inance of p ,p ′-DDE suggests that the p ,p ′-DDT in theBaiyangdian Lake was mostly degraded. In addition, relative-ly high levels of o ,p ′-DDT indicate that new input of o ,p ′-DDT into the Baiyangdian Lake might occur recently.

Compared with the previous studies of Baiyangdian Lake,in the present study, the mean concentration of DDTs in thesurface water of the Baiyangdian Lake was much lower thanthat found in 1995 (range 0–900 ng/L, mean 250 ng/L) (Douand Zhao 1998). Compared with other water bodies, theconcentration range of DDTs in the surface water from theBaiyangdian Lake was similar to those of Jiulong River Es-tuary and Lake Chaohu and slightly greater than those ofDaliao River Estuary, Ebro River in Spain, and Lake Baikalin Russia but was lower than those reported in the MinjiangRiver Estuary, Beijing Guanting Reservoir, and Gomti River

in India (Table 2). No research data on DDT residual levels inoverlying water has been presented in the previous studies, soit could not be compared with the other areas. For pore water,in comparison, the DDT level was lower than those observedin Minjiang River Estuary, Beijing Guanting Reservoir, whileit was similar to those in Daliao River Estuary and JiulongRiver Estuary in China. In sediments, the concentration ofDDTs in Baiyangdian Lake was comparable to those ofMinjiang River Estuary, Beijing Guanting Reservoir, DaliaoRiver Estuary, Lake Chaohu, and Ebro River in Spain, andgreater than those of Jiulong River Estuary and Lake Baikal inRussia, but much lower than those of Gomti River in India andHanoi area in Vietnam (Table 2). Compared with the previousstudies in Baiyangdian Lake, the DDT levels in sediment inthe present study were comparable to the levels in 1995 (0.69–2.26 ng/g) (Dou and Zhao 1998) and the levels in 2007 (2.2–3.1 ng/g) (Hu et al. 2010).

Spatial and temporal variation of DDTs

Temporally, the concentrations of DDTs varied considerablyin the surface water (Fig. 2). The greatest concentration ofDDTs was detected in July, and relatively higher concentra-tions were also found in August, June, and September. Threepossible explanations can be provided. First, the higher con-centration levels of DDTs found in the summer might bepartially attributed to the increase of land runoff during thewet season (June–September). A similar result was also ob-tained byYuan et al. (2013), indicating that the increasing landrunoff during the summer might bring the chemical residuesfrom soil to the water environment. Second, the high contam-ination level in the summer might be linked to the emission ofDDTs by ships since there are intensive boat activities fortourism and fishery in these months during sampling period.DDT, as the auxiliary material of an antifouling paint is still inuse. He et al. (2012) reported that in China, from 1950s to2005, approximately 1.1 million tons of DDT was used toproduce antifouling paints. Third, the higher levels of DDTs insummer might be related to the dicofol applications for crops

Table 1 Concentrations of DDTs in the surface water (ng/L), overlying water (ng/L), pore water (ng/L), and sediments (ng/g, dw) collected from theBaiyangdian Lake

Surface water Overlying water Pore water Sediments

Compounds Range Mean±SD Range Mean±SD Range Mean±SD Range Mean±SD

o ,p ′-DDT 0.05–8.55 2.63±2.75 0.04–4.72 1.85±1.89 0.20–3.38 1.67±0.92 0.15–1.80 0.71±0.46

p ,p ′-DDT 0.12–7.53 1.81±2.56 0.05–7.56 1.96±2.22 0.47–11.9 4.88±4.33 1.13–3.16 1.87±0.67

o ,p ′-DDE 0.04–0.34 0.19±0.12 0.05–0.79 0.35±0.24 0.13–0.65 0.35±0.19 0.02–0.15 0.06±0.04

p ,p ′-DDE 1.21–4.93 2.68±1.37 0.41–16.2 5.55±5.15 1.21–13.9 6.90±3.30 2.01–4.03 3.17±0.72

o ,p ′-DDD 0.06–1.09 0.46±0.44 0.17–1.20 0.64±.041 0.10–1.94 1.0±0.85 0.01–0.13 0.04±0.03

p ,p ′-DDD 0.02–0.34 0.14±0.12 0.02–2.66 0.58±0.87 0.37–2.82 1.33±0.88 0.02–0.41 0.20±0.12

ΣDDTs 2.36–22.4 7.67±7.0 0.72–21.9 10.5±7.67 2.25–33.7 15.6±8.95 4.42–7.29 6.04±0.90


in the summer season. Yang et al. (2008) reported that dicofolwith high impurity of DDT compounds is still widely used inagricultural practice such as cotton cultivation and becomes animportant source of DDT pollution in China. Statistical datashowed that from 1988 to 2002, the average annual DDTproduction was about 6,000 tons in China, of which nearly80 % was for dicofol production (Qiu et al. 2005). On thecontrary, lowest concentrations of DDTs in surface water werefound in April and November, followed by October, Decem-ber, and March. It is worth noting that during the months ofApril and November 2010, a great deal of fresh water wasallocated to the Baiyangdian Lake by the local government toimprove the hydrological and ecological conditions of the

lake. This resulted in a dilution of the concentrations of DDTsin the lake in the two months. The temporal variations of DDTsin the overlying water and pore water were somewhat similar tothat in the surface water, but the descending order for theaverage contents of DDTs was July>June>August>Septem-ber>May>October>December>March>April>November inthe overlying water, and the order was July>August>June>September>May>October>April>December>November>March in the pore water (Fig. 2). No obvious temporal varia-tions of DDT concentrations were observed in the sediment. Aslightly lower concentration occurred in sediment during theperiods of March and December compared to other samplingtimes (Fig. 2).

Table 2 Concentrations of DDTsisomers in surface water (ng/L),pore water (ng/L) and sediments(ng/g) from lakes and riversaround the world

nd not detected

Sampling area Surface water Pore water Sediment References

Baiyangdian Lake 2.36–22.35 2.25–33.68 4.42–7.29 This study

Minjiang River Estuary 40.61–233.5 466.7–1794 1.57–13.06 Zhang et al. 2003

Beijing Guanting Reservoir nd–528.8 5.01–174.35 2.77–17.22 Xue et al. 2006

Jiulong River Estuary <0.1–63.2 0.9–193 0.01–0.43 Maskaoui et al. 2005

Daliao River Estuary 0.02–5.2 2.0–107 0.3–12.6 Tan et al. 2009

Lake Chaohu 0.5–18.4 0.3–31.0 Liu et al. 2013

Gomti River, India nd–4,578 nd–509 Singh et al. 2005

Ebro River, Spain 2.0–6.8 0.9–9.0 Fernandez et al. 1999

Lake Baikal, Russia nd–0.02 0.014–2.7 Iwata et al. 1995

Hanoi area, Vietnam 1.3–384 Hoai et al. 2010

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Fig. 2 Distribution of DDT concentrations in surface water, overlying water, pore water, and sediments from Baiyangdian Lake


Overall, the concentrations of DDTs in the surface water,overlying water, pore water, and sediments varied with thesampling locations (Fig. 2). The greatest concentrations ofDDTs were found at site 2 in the surface water, at sites 2 and5 in the overlying water, and at site 2 in the pore water andsediment. Relatively higher levels were also found at sites 5and 6 in the surface water, at sites 3 and 6 in the overlyingwater, and at sites 3, 5, and 6 in the pore water and sediments.Two possible explanations can be provided. First, sites 2 and 3are located on the entrance of the Fuhe River. The higherconcentrations at these two sites might be caused by high ratesof influx of contaminants into the lake through the Fuhe River.This result can be confirmed by the fact that the concentrationof DDTs in the sediments from the Fuhe River (range 1.3–51.3 ng/g) was much higher than that in the Baiyangdian Lake(2.2–3.1 ng/g) (Hu et al. 2010). The Fuhe River, which runsthrough the heavy industrial city of Baoding, carries about250,000 tons of untreated industrial and domestic wastewaterper day produced by Baoding city into the Baiyangdian Lake(Hu et al. 2010). Second, sites 5 and 6 are all close to villagesand fish or duck aquaculture areas, and the high levels at thesesites may be the result of agricultural runoff entering the waterenvironment. In addition, the higher levels at sites 5 and 6(fish aquaculture area) may also be related to the fish feed.DDTs have been reported in commercial feed or trash fish(Meng et al. 2007; Guo et al. 2009), which will contaminatethe surrounding water body of aquaculture area. On the otherhand, in the relatively pristine site 4, levels of DDTs weremuch lower than the other sites.

DOC contents in water and total organic carbon (TOC) insediments were also investigated in this study, with the concen-trations ranging from 6.78 to16.23 mg/L in surface water, 7.12to 18.56 mg/L in overlying water, 7.28 to 22.08 mg/L in porewater, and 0.23 to 3.09 % in sediments, respectively, during thesampling periods. The distribution of HOCs such as PCBs hasbeen shown to be related by DOC contents in water and byTOC contents in sediments (Iwata et al. 1995). However, in thisstudy, distribution of DDTs did not show any correlation withDOC contents (r =0.415, p =0.272) in water phase and TOCcontents (r =0.423, p =0.112) in sediment. This relationshipwas also observed by Mai et al. (2002), suggesting that manyfactors contributed to the DDTs' distribution in water, and thesediment contamination in the study area may be dictated morepredominantly by anthropogenic inputs than by natural pro-cesses. The correlation of DDT concentrations with tempera-ture (r =0.536, p =0.09) and dissolved oxygen (r =0.322, p =0.302) was also investigated in this study, and no statisticallysignificant relationship was observed.

Possible sources of DDTs

The ratios of the parent compound to its metabolite canprovide useful information on the pollution source. The

portion of DDTmetabolic products is indicative of new inputsor historical usage. A ratio of DDT/(DDE+DDD) higher than1 is generally pointed to the fresh input of DDTs (Hitch andDay 1992). Otherwise, aged DDTs are suggested. There aretwo known sources of DDTs characterized by the o ,p ′-DDT/p ,p ′-DDT ratio of 0.2 in technical DDT mixture and ~7.0 indicofol products in China, respectively (Qiu et al. 2005).Therefore, the ratio of o ,p ′-DDT/p ,p ′-DDT is usually usedto distinguish technical DDT from dicofol-type DDT (Qiuet al. 2005; Yang et al. 2008; Liu et al. 2009), and an elevatedo ,p ′-DDT/p ,p ′-DDT is an indicative of the dicofol-type DDT.In the present study, the ratios of DDT/(DDE+DDD) were1.13±0.80, 0.66±0.48, 0.65±0.33, and 0.56±0.19 in surfacewater, overlying water, pore water, and sediments, respective-ly, during the sampling periods. As shown in Table 3, morethan 70 % of the DDT/(DDE+DDD) ratios were less than 1,suggesting that DDT in Baiyangdian Lake mostly stemmedfrom the historical input. On the contrary, for surface waterand overlying water, higher DDT/(DDE+DDD) ratios (>1.0)were found from April to September, indicating that freshinput of DDT occurred in the Baiyangdian Lake in thesemonths. Moreover, elevated o ,p ′-DDT/p ,p ′-DDT ratios, withthe mean value of 0.18±0.08 to 2.41±1.60 in different envi-ronment medium, were also observed. Recently, similar re-sults were also reported in water from Taihu Lake (Qiu et al.2008) and Chaohu Lake (He et al. 2012) in China, with o ,p ′-DDT/p ,p ′-DDT ratios of 1.6–5.6 and 0.40–2.18, respectively.Since o ,p ′-DDT metabolizes more readily than p ,p ′-DDT inthe environment (Martijn et al. 1993; Qiu et al. 2005), thedegradation of technical DDT is unlikely to cause increase ofo ,p ′-DDT/p ,p ′-DDT ratio in the environment that is higherthan that of technical DDT. Therefore, the relatively highervalues of o ,p ′-DDT/p ,p ′-DDT in Baiyangdian Lake clearlydemonstrates that the new input of DDT was from dicofol-type DDT. In summary, mixed sources of DDTs, i.e., bothhistorical input of technical DDT and new input of dicofol-type DDT, were obvious in Baiyangdian Lake. According tothe formula proposed by Liu et al. (2009), the contributions oftechnical DDT and dicofol-type DDT were 85 and 15 %,respectively, in the Baiyangdian Lake.

Fugacity ratios calculation

Fugacity is a measure of the tendency of a chemical toescape from its medium. A convenient way to estimatethe net flux direction is to compare fugacity values of achemical among the different compartments (Mackay2001; Rowe et al. 2007). The fugacity (f ) of a chemicalin any phase is defined as the concentration (C ) of thechemical in the phase divided by the fugacity capacity(Z ) of the phase (Mackay 2001):

f ¼ C=Z ð1Þ


Z values are obtained from the following relationship(Mackay 2001):

Zw waterð Þ ¼ 1=H ð2Þ

Zs sedimentð Þ ¼ 0:41 OCð Þ Kowρs=H ð3Þ

so that the fugacities of a chemical in water and sediment are:

f w ¼ CwH ð4Þ

f s ¼ CsH=0:41 OCð ÞKowρs ð5Þ

where fw and fs are the fugacities in water and sediment (Pa),Cw

andCs are the concentrations of DDT isomer inwater (ng/L) andsediment (ng/g),H is the Henry's law constant at the temperatureof the water (Pa m3/mol), OC is the organic carbon content(fraction ranging from 0 to 1),Kow is the octanol–water partitioncoefficient, and ρs is the sediment density (kg/L). The measuredaverage density of sediment solids (2.0±0.3 kg/L) was used forthe calculations in this study. The Kow values for o ,p ′-DDT,p ,p ′-DDT, p ,p ′-DDE, and p ,p ′-DDD were taken from UNEPChemicals (2002). The sediment–water fugacity ratio (fs/fw) is:

f s f w ¼ Cs Cw � 0:41 OCð ÞKowρsð Þ: ð6Þ

Here, fs/fw=1.0 implies that the DDTs in water and sedimentare at equilibrium, the net flux is zero, although DDTs areexchanged between water and sediment at the same rate. Valuesof fs/fw>1.0 and <1.0 indicate net diffusion from the sediment tothe water and net deposition from the water to the sediment.

Sediment–surface water exchange

The sediment–surface water fugacity ratio (f s/f sw) was obtain-ed using concentration values calculated for DDT isomers insediments and surface water during the sampling periods. Thefugacity ratio values ranged from 0.002 to 0.356, 0.007 to0.758, 0.08 to 0.57, and 0.07 to 2.08 for o ,p ′-DDT, p ,p ′-DDT,p ,p ′-DDE, and p ,p ′-DDD, with mean values of 0.09, 0.29,0.28, and 0.70, respectively (Fig. 3a). The uncertainty inindividual fugacity ratios was estimated by propagation of

errors in water and sediment concentrations. Replicate analy-ses in the laboratory have shown that the analytical reproduc-ibility in measurements of water and sediment are typically≈30%. Therefore, a propagation of the errors that are associatedwith the calculation indicated that the equilibrium is repre-sented by an f s/f sw of 1.0±0.21 (i.e., a range of 0.79–1.21).The fugacity ratios of the four DDT isomers (except the ratiosfor p ,p ′-DDD for two samples) fall outside this uncertaintyrange and it can be confident that for these compounds, thesurface water and sediment are not in equilibrium (Fig. 3a).Fugacity ratios for o ,p ′-DDT, p ,p ′-DDT, p ,p ′-DDE, and p ,p ′-DDD were generally <1.0 indicating net transfer of DDTisomers from surface water to sediment, while the ratios forp ,p ′-DDD in April (f s/f sw=2.08) and October (f s/f sw=1.53)indicated diffusion to surface water.

Temporally, the lowest fugacity ratio (f s/f sw) of DDT iso-mers was found in July and August, and relatively lower valueswere also found in May, June, and September in 2010. Theresults may be associated with the smaller difference of DDTconcentration between sediment and surface water in thesemonths (shown in Fig. 2). A similar result was also observedin the previous work (Zhang et al. 2003), showing that thedifference of the DDT concentration between water and sedi-ment can affect their transfer trend. Pearson's correlation be-tween sediment–surface water fugacity ratio (f s/f sw) and phys-icochemical parameters was also performed, and neither signif-icant correlation between f s/f sw and organic carbon (r =0.231,p =0.205) nor f s/f sw and temperature was obtained (r =0.403,p =0.187). This suggests that the transport trends of DDTsbetween sediment and water were not dependent on the contentof organic carbon and the temperature in Baiyangdian Lake.Spatially, there was no significant difference for the sediment–surface water fugacity ratios among the six sampling sites(p >0.05), and the slightly lower fugacity ratios occurred at siteBLZ (Fig. 4a). This might be due to slightly higher concentra-tions of DDTs in the surface water at this site.

Sediment–overlying water exchange

The sediment–overlying water fugacity ratio (f s/fow) rangedfrom 0.008 to 1.54 (mean 0.39) for o ,p ′-DDT, 0.005 to 1.98

Table 3 Ratios used in sourceidentification of DDTwith itsmetabolites in Baiyangdian Lakefrom March to December

W surface water, OW overlyingwater, PW pore water, SEDsediments

Ratios Mar Apr May Jun Jul Aug Sep Oct Nov Dec

DDT/(DDE+DDD) W 0.77 1.04 1.55 1.84 2.56 1.75 1.14 0.28 0.08 0.28

OW 0.24 0.31 0.53 1.05 1.35 1.31 0.18 0.40 1.02 0.17

PW 0.48 0.24 0.44 0.85 1.13 1.05 0.48 0.82 0.20 0.86

SED 0.37 0.80 0.25 0.83 0.54 0.50 0.47 0.52 0.77 0.57

o ,p ′/p ,p ′-DDT W 1.82 1.14 3.00 2.19 4.86 5.03 3.18 1.67 0.42 0.78

OW 0.85 0.15 1.80 1.48 1.77 1.83 0.16 2.44 0.09 0.75

PW 0.52 0.37 0.24 0.64 0.35 0.21 0.64 0.71 0.37 0.94

SED 0.07 0.12 0.27 0.23 0.09 0.17 0.24 0.20 0.14 0.28


0.001

0.01

0.1

1

10


f s/f

sw

op-DDT pp-DDT

pp-DDE pp-DDD

a

0.001

0.01

0.1

1

10


fs/f

ow

op-DDT pp-DDT

pp-DDE pp-DDD

b

0.001

0.01

0.1

1


fs/f

pw

op-DDT pp-DDT

pp-DDE pp-DDDc

Fig. 3 Seasonal variations of a sediment–surface water fugacity ratios, b sediment–overlying water fugacity ratios, and c sediment–pore water fugacityratios in the Baiyagndian Lake

0.001

0.01

0.1

1

SCD BLZ WJZ ZLZ CPT DC

fs/f

sw

op-DDT pp-DDT

pp-DDE pp-DDDa

0.001

0.01

0.1

1


fs/f

ow

op-DDT pp-DDT

pp-DDE pp-DDDb

0.001

0.01

0.1

1


f s/f

pw

op-DDT pp-DDT

pp-DDE pp-DDDc

Fig. 4 Spatial variations of a sediment–surface water fugacity ratios, b sediment-overlying water fugacity ratios, and c sediment–pore water fugacityratios in Baiyangdian Lake


(0.46) for p ,p ′-DDT, 0.037 to 1.17 (0.36) for p ,p ′-DDE and0.008 to 2.41 (0.53) for p ,p ′-DDD; and there were no signif-icant differences among the four DDT isomers (Fig. 3b). A ttest was used to judge whether the fugacity ratios were sig-nificantly different from steady state (1.0±0.21). The resultsindicated that the fugacity ratios for the four DDT isomerswere significantly lower than 1.0 (p <0.05) from April toOctober, suggesting a net flux from the overlying water tosediment in these months. Fugacity ratios for p ,p ′-DDE inMarch (f s/fow=1.07) and December (f s/fow=1.17) indicatedclose to the sediment–overlying water equilibrium; while theratios for p ,p ′-DDT inMarch (f s/fow=1.98) and December (f s/fow=1.97), o ,p ′-DDT in November (f s/fow=1.423) and De-cember (f s/fow=1.53), and p ,p ′-DDD in December (f s/fow=2.40) indicated diffusion from sediment to overlying water.Also, the sediment–overlying water fugacity ratios did notshow any correlation with temperature (r =0.321, p =0.219)and organic carbon contents (r =0.328, p =0.198). Spatially,there were no obvious spatial variations of sediment–overly-ing water fugacity ratios for four DDT isomers during thesampling periods (Fig. 4b).

Sediment–pore water exchange

The sediment–pore water fugacity ratios (f s/fpw) for four DDTisomers (except the ratios for o ,p ′-DDT and p ,p ′-DDE inDecember) were all much lower than 1.0, indicating that theseDDT isomers transferred from pore water to sediment and thesediment acted as a sink (Fig. 3c). The higher pore water DDTisomer concentrations suggest a stronger transfer tendencyfrom pore water to sediment than that from surface water oroverlying water to sediment for each DDT isomer. This phe-nomenon can also be found from the spatial variations ofsediment–pore water fugacity ratios in Fig. 4c. The highersediment–pore water fugacity ratios (f s/fow) occurred in Julyand August (Fig. 3c), which agreed with the fugacity ratiodistribution in sediment–overlying water and in sediment–surface water. Also, no significant correlations between f s/fpw and temperature (r =0.201, p =0.432) and f s/fpw and or-ganic carbon contents (r =0.398, p =0.252) were obtained.Spatially, there were no obvious spatial variations of sedi-ment–pore water fugacity ratios for four DDT isomers duringthe sampling periods, and this was similar to the spatialdistribution of sediment-overlying water fugacity ratios(Fig. 4). A likely explanation for this phenomenon is thatDDTs in the pore water and sediment mostly stemmed fromthe historical usage in the Baiyangdian Lake.

Conclusion

The distribution of hydrophobic organic contaminants in abi-otic compartments is essential for describing their transfer and

fate in aquatic ecosystems. This paper provided the firstsystemic data on the contamination status of DDTs in variousenvironmental media, including surface water, overlying wa-ter, pore water, and sediments from Baiyangdian Lake, NorthChina. Compared with the established reference values ofDDTs in surface water, pore water, and sediments, the con-centration of DDTs in the present study was at a middle level.Sources identification indicated that DDTs in BaiyangdianLake mostly stemmed from the historical usage of technicalDDT mixture, but a new source of DDT, i.e., dicofol-typeDDT, also occurred. Among the sampling sites, highest DDTconcentrations were observed at BLZ for different matrices,which may be due to the continued input of municipal andindustrial effluents from the Fuhe River. Temporally, the con-centrations of DDTs varied considerably in the surface water,overlying water, and pore water, with the higher concentra-tions occurring in summer months, while no obvious temporalvariation was observed in the sediment. The fugacity ratiocalculations in the sediment and water showed that the sedi-ment acts as a sink for the DDT isomers in the BaiyangdianLake. The difference of DDT concentrations between waterand sediment was an important factor affecting the sediment–water equilibrium status. An apparent disequilibrium betweenthe sediment and surface water was observed in this study, andthe tendency of DDT isomer deposition from the air to thesurface water was predicted. Further investigation of the air–water exchange of DDTs is needed to elucidate the role of theatmosphere in the input of DDT isomers from the air aroundBaiyangdian Lake.

Acknowledgments The research was financially supported by the Chi-na Postdoctoral Science Foundation (2013 M530640), the National Nat-ural Science Foundation of China ( 51108445), Major State Basic Re-search Development Program (2013CB430405), and the National Natu-ral Science Foundation for Innovative Research Group (51121003).

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evaluating the exchange of ddts between sediment and water in a major lake in north china

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