Abstract

The historical records of organochlorine pesticides (OCPs) in a sediment core are essential for understanding the circulation of them in the global context. In this study, we measured the concentrations of 22 OCPs in the sediment core from the Huaihe River, China by gas chromatography mass spectrometry (GC-MS). The total concentration of 18 kinds of 22 OCPs in the sediment core were in the range of 0.01–7.18 ng g−1 with an average concentration of 4.53 ng g−1. The average detection rate was up to 51.60%. Dichlorodiphenyltrichloroethanes (DDTs) were the predominant species in the sediment core. The different categories of OCPs were in the following order: DDTs > hexachlorocyclohexane (HCHs) > Chlordanes > Endosulfans > hexachlorobenzene (HCB). Drins were all lower than detection limits. The temporal trends of OCPs were influenced by their different historical usages, different properties or different degradation conditions in the environment. There was an obvious decreasing trend for OCPs in the core in recent years. The findings suggested there was also no new pollution source input in recent years and OCPs could not cause adverse biological risk in the environment.

INTRODUCTION

Organochlorine pesticides (OCPs) are known for the toxicity and persistence because of their biological accumulation through the food chain (Yang et al. 2015; Bajwa et al. 2016). OCPs were used widely as insecticides in agriculture before the 1980s around the world (Barhoumi et al. 2014; Mumtaz et al. 2015). In China, a large amount of OCPs were used to obtain high yields of crops from 1952 to 1983 (Dewan et al. 2013; Da et al. 2015). The extensive use of OCPs has led to ubiquitous OCPs pollution in different environmental media (such as air, soil, plant and sediment) because of their persistence. Sediment eventually became the storage vault because of the high lipotropy and low water solubilities of OCPs (Wu et al. 2015). A sediment core is very useful for evaluating and reconstructing historical records of OCPs in the environment media (Alonso-Hernández et al. 2015). Well-laminated sediments can provide historical archives for historical environmental conditions and evaluate the influence of humanity activities on local environments (Lin et al. 2016).

The Huaihe River, one of the seven largest rivers in China, has become increasingly vulnerable to contamination owing to increasing discharges of industrial and agriculture garbage with rapid development of the local economy (Wang et al. 2014). The Huaihe River has attracted the attentions of many scholars due to its pollution. Wang et al. (2009) have reported an ecological risk assessment of OCPs in water from the Huaihe River. Residues of OCPs in the upper reaches of the Huaihe River were studied by Feng et al. (Feng et al. 2011). The distribution characteristics and the sources identification of OCPs in sediments from the upper reaches of the Huaihe River were analyzed by Sun et al. (Sun et al. 2010). The author has also studied OCPs in surface sediment from Anhui Reach of Huaihe River (Da et al. 2017). Therefore, it is important to conduct studies to further understand the historical contamination trends of OCPs in the Huaihe River. The objectives of the present research were to: (1) reconstruct the history of OCPs pollution in the Huaihe River; (2) elucidate the pollution source and vertical distribution of these compounds; (3) study the impact of anthropogenic activities on the environment. The finding of this research will supplement the data on the year tendency of OCPs and help to apprehending their circulation in the global scope.

MATERIALS AND METHODS

Sampling

A sediment core was sampled in July 2015. The map of the sampling location is displayed in Figure 1. The sediment core sample was collected using a stainless steel static gravity corer with an 8 cm inner diameter. The depth of the sample core was 38 cm. The sediment core sample was cut at 1 cm segments immediately from the top-down at the sampling site and wrapped in precleaned aluminum foil (baked at 450 °C before use). All wrapped samples were sealed in the plastic bags and stored at −20 °C before further study.

Figure 1

Map of sampling locations of the sediments.

Figure 1

Map of sampling locations of the sediments.

210Pb dating

Details of the dating methods were elaborated in our previous research (Da et al. 2014). Briefly, the samples were weighed and poured into centrifuge tubes, which were sealed and placed for about 3 weeks before the samples were studied. The sediment age was dated for 210Pb using an Ortec GWL (a well-type E-series detector) HPGe gamma spectrometer. 210Pb was determined via gamma at 46.5 keV, while 137Cs was measured at 662 keV. Dates were calculated by a constant rate of supply dating pattern. The mean of sedimentation accumulation rates was 0.45 cm a−1. The sedimentation length of 38 cm was from the core-down date of 1956 to the core-top date of 2015.

Sample preparation and extraction

The methods for the preparation of OCPs in the samples were introduced in detail in our previous study (Da et al. 2015). In brief, the samples were freeze-dried for 48 h in the vacuum freeze drying machine and sieved using a 200-mesh sifter. 10 g of sample was used for Soxhlet extraction with 200 mL of dichloromethane (DCM) for 48 h at 46 °C. The activated copper was placed in the extraction flask for desulfurization. The sample extracts were evaporated to approximately 1 mL by rotary evaporation, 10 mL of n-hexane were added in the concentrated liquid to solvent-exchange, and then went on concentrating to 1 mL or so. The concentrated extracts were passed through an alumina/silica (1:2) gel column with about 1 g of anhydrous sodium sulfate covering the silica gel. The OCPs were collected by elution using 70 mL of DCM–hexane (v: v =3:7). The eluate was concentrated to 1 mL again and placed into the cell bottle until further instrumental analysis.

Analysis

The samples were measured using an Agilent 6890 Series GC equipped with an Agilent 5973 Network mass-selective detector (MS). All congeners were separated using a DB-5 MS fused silica capillary column (30 m*0.25 mm*0.25 mm) under the following conditions: samples (1 mL) were auto injected in splitless mode; the carrier gas was helium gas (99.99%) with a flow rate of 1.0 mL min−1; and the injection temperature started at 80 °C for 1 min; increased to 200 °C (held for 10 min) at a rate of 12 °C min−1; and then increased to 220 °C (held for 5 min) at a rate of 1 °C min−1 before being increased to the final temperature of 290 °C (held for 5 min) at a rate of 15 °C min−1. The components of the OCPs were obtained by comparison with the retention time of each standard and the internal standard peak area method was used for the concentrations of the individual OCPs.

Quality control

The residue of OCPs was quantitatively calculated using a peak area by the internal standard method. All data were subject to strict quality control procedures. The method detection limit (MDL) ranged from 0.001 to 0.21 ng g−1 for OCPs. The mean recoveries (R) for the surrogates of OCPs were 85.31 to 101.40%, and the relative standard deviation (RSD) ranged from 0.13 to 5.63%.

RESULTS AND DISCUSSION

Concentrations of OCPs in the sediment core

Concentrations of 22 kinds of OCPs in the sediment core from the Huaihe River are shown in Table 1. Eighteen kinds of OCPs (o′p-DDE, o′p-DDD, o′p-DDT, p′p-DDE, p′p-DDD, p′p-DDT, α-HCH, β-HCH, γ-HCH, δ-HCH, Heptachlor, Heptachlor epoxide, Cis-chlordane, Trans-chlordane, Endosulfan I, Endosulfan II, HCB and Mirex) were detected. Particularly, the detection frequencies for β-HCH, γ-HCH and o′p-DDT compounds in the sediment core were up to 100%; second, the detection frequencies of p′p-DDD were up to 81.45%, which reflected a wide occurrence of the four kinds of OCPs in Huaihe River. The total concentrations of the OCPs were in the range of 0.01–7.18 ng g−1 with an average concentration of 4.53 ng g−1. The mean of detection rate was up to 51.60%. The average concentration of OCPs in the core was less than those of OCPs in the surface sediment from the upstream and downstream parts of river in our previous study (Da et al. 2017). The results suggested that the DDTs (including o′p-DDE, o′p-DDD, o′p-DDT, p′p-DDE, p′p-DDD and p′p-DDT) were the predominant pesticides in the sediment core. The concentrations of DDTs ranged from 0.01 to 2.18 ng g−1 (mean = 1.67 ng g−1), with average detection frequencies of 67.32%. The high levels and detection frequencies of DDTs indicated that they were widely used in the past in the Huaihe River. The concentrations of HCHs (including α-HCH, β-HCH, γ-HCH and δ-HCH) were 0.01–0.51 ng g−1 (mean = 0.81 ng g−1), with the mean of detection rates of 61.36%. The residues of HCHs in the sediment core were much less than those of DDTs. The same finding was also recorded in a sediment core from the Beibu Gulf, the South China Sea, the northeastern Chinese river and the Gulf of Batabanó, Cuba (Wang et al. 2013a, 2013b; Li et al. 2014; Alonso-Hernández et al. 2015) but was different from the contamination of OCPs in sediment cores from Lake Baiyangdian, China and the Old Yellow river estuary, China (Da et al. 2014; Guo et al. 2014). The high concentrations of DDTs and HCHs were detected in sediment cores, corresponded to a more extensive use of DDTs and HCHs from the 1950s to 1983 in China. Within Chlordane compounds, cis-chlordane (mean = 0.36 ng g−1) was much higher than heptachlor, heptachlor epoxide and its isomeric compound trans-chlordane. The mean concentration of HCB was 0.39 ng g−1, with a detection frequency of 30.10%. The mean concentrations of different categories of OCPs were in following the order: DDTs > HCHs > Chlordanes > Endosulfans (including Endosulfan I and Endosulfan II) >HCB. Drins (including aldrin, dieldrin, Endrin) were all below detection limits, probably relating to their zero production in the past in China (Zhao et al. 2013). Other OCP compounds, such as mirex, only were in the range of 0.1 ng g−1–1.21 ng g−1, with a mean value of 0.19 ng g−1. Mirex was mainly used to kill termites in China and was also used as a flame retardant in industry (Guo et al. 2014).

Table 1

Concentrations (ng g−1) of individual OCPs in the sediment core

CompoundsRangeMeanDetection rate (%)
α-HCH 0.01–0.39 0.13 20.22 
β-HCH 0.10–0.51 0.34 100 
γ-HCH 0.09–0.47 0.29 100 
δ-HCH 0.01–0.15 0.05 25.20 
o′p-DDE 0.01–0.13 0.07 45.12 
o′p-DDD 0.02–0.42 0.31 44.35 
o′p-DDT 0.03–1.23 0.17 100 
p′p-DDE 0.03–2.12 0.69 65.54 
p′p-DDD 0.09–0.38 0.27 81.45 
p′p-DDT 0.01–2.18 0.16 67.50 
Heptachlor 0.13–2.01 0.22 8.75 
Aldrin BDL BDL BDL 
Heptachlor epoxide 0.04–1.03 0.11 3.52 
Trans-chlordane 0.02–1.07 0.09 5.89 
Cis-chlordane 0.21–1.25 0.36 8.15 
Endosulfan I 0.03–0.88 0.10 33.56 
Endosulfan II 0.18–1.04 0.59 24.10 
HCB 0.01–0.64 0.39 40.10 
Dieldrin BDL BDL BDL 
Methoxychlor BDL BDL BDL 
Mirex 0.1–1.21 0.19 5.28 
Endrin BDL BDL BDL 
DDTs 0.01–2.18 1.67 67.32 
HCHs 0.01–0.51 0.81 61.36 
OCPs 0.01–7.18 4.53 51.60 
CompoundsRangeMeanDetection rate (%)
α-HCH 0.01–0.39 0.13 20.22 
β-HCH 0.10–0.51 0.34 100 
γ-HCH 0.09–0.47 0.29 100 
δ-HCH 0.01–0.15 0.05 25.20 
o′p-DDE 0.01–0.13 0.07 45.12 
o′p-DDD 0.02–0.42 0.31 44.35 
o′p-DDT 0.03–1.23 0.17 100 
p′p-DDE 0.03–2.12 0.69 65.54 
p′p-DDD 0.09–0.38 0.27 81.45 
p′p-DDT 0.01–2.18 0.16 67.50 
Heptachlor 0.13–2.01 0.22 8.75 
Aldrin BDL BDL BDL 
Heptachlor epoxide 0.04–1.03 0.11 3.52 
Trans-chlordane 0.02–1.07 0.09 5.89 
Cis-chlordane 0.21–1.25 0.36 8.15 
Endosulfan I 0.03–0.88 0.10 33.56 
Endosulfan II 0.18–1.04 0.59 24.10 
HCB 0.01–0.64 0.39 40.10 
Dieldrin BDL BDL BDL 
Methoxychlor BDL BDL BDL 
Mirex 0.1–1.21 0.19 5.28 
Endrin BDL BDL BDL 
DDTs 0.01–2.18 1.67 67.32 
HCHs 0.01–0.51 0.81 61.36 
OCPs 0.01–7.18 4.53 51.60 

BDL: below detection limit; Detection rate: the number of samples that were analytically detected for specific compound; DDD: dichlorodiphenyldichloroethane; DDE: dichlorodiphenyldichloroethylene; DDT: dichlorodiphenyltrichloroethane; HCB: hexachlorobenzene; HCH: hexachlorocyclohexane.

These results suggested that the concentrations of different kinds of OCPs were influenced by their different historical usages or their diverse degradation conditions in the environment.

Temporal tendency of OCPs

DDTs and HCHs

The temporal tendency of OCPs could provide meaningful information for past contamination. The temporal trends of OCPs are listed in Figures 24; as shown in Figure 2(a), the recorded HCHs concentrations varied significantly by sediment years (from 1956 to 2015). A gradual increasing residue of HCHs was displayed from 1956 to the 1960s until peaking in 1971, and then there was a steady variation until the other peaking in 2002. The HCH levels were close to zero in 1998. Approximately 4,000 kt of technical HCHs were produced and used from the 1950s to 1983 in China, and then lindane (including 99.9% γ-HCH) was used for controlling pests since the 1990s (Wang et al. 2013a, 2013b). The gradual increasing levels of HCHs from 1956 to the 1960s may be related to the beginning of the use of HCHs in the past in the Huaihe River basin of the Anhui reach. The first peak-time periods of HCH concentrations were observed in 1971, corresponding to the widespread use of HCHs during this period. The second peak was observed in 2002, which coincided with the peak of the technical lindane production and usage in the region. It was interesting that the HCH residues were close to zero in 1998. As far as we know, there was a catastrophic flooding in 1998 in Anhui Province. Therefore, HCHs may be washed away by the flood because of the high water solubility of HCHs. It was worth noting that the HCH residue levels rapidly decreased from 2008 to 2015, which may be related to the degradation of the ‘old’ HCHs and the fewer new input sources. It has been reported that the time is approximately 20 years for the degradation of 95% of the HCHs in the environment (Yang et al. 2008). Therefore, the residues of HCHs have decreased gradually from 2008 to 2015.

Figure 2

Time trends of HCHs and DDTs concentrations in the sediment core.

Figure 2

Time trends of HCHs and DDTs concentrations in the sediment core.

Figure 3

Time trends of CHLs and endosulfan concentrations in the sediment core.

Figure 3

Time trends of CHLs and endosulfan concentrations in the sediment core.

Figure 4

Time trends of HCB concentrations in the sediment core.

Figure 4

Time trends of HCB concentrations in the sediment core.

The concentration variations of DDTs also reflected their application history in China. As seen from Figure 2(b), DDTs levels began to increase from 1956 until 1981, a period which was consistent with the history time of wide use in this country. During this time (1960s–1980s) the usage of DDTs was approximately 1900 tons (Yuan et al. 2013). The first maximal concentration was observed in 1981, which indicated a significant period for the wide use of these chemical compounds in this region. After the first peak, the levels of DDTs decreased gradually until the second peak in 1997. It has also been reported that more than 6000 tons of DDTs were produced and used as mosquito repellent, dicofol production, malaria control and anti-fouling paint from 1988 to 2002 in China (Yuan et al. 2013), perhaps which was another pollution source of DDTs in the environment. Therefore, it can be speculated that the second peak occurred due to the wide usage of DDTs during the period. It should be noted that the levels of DDTs at the top of the core decreased gradually in recent 10 years. It has been reported that it took approximately 30 years for 95% DDT degradation in the environment (Kim et al. 2008; Yang et al. 2008). One possible interpretation for these findings could be the constant degradation of DDTs during the recent decades.

As seen from Figure 2(a) and 2(b), the residues of HCHs were much less than those of DDTs. According to the previous reports, the usage of HCHs was much more than that of DDTs in the past (Wang et al. 2013a, 2013b). This result might be observed because of the lower persistence and higher solubility of HCHs than DDTs, as a number of HCHs have degraded, and another part of HCHs have been partitioned to the dissolved phase in the water. The temporal trend of HCHs was not the same as that of DDTs, which might be due to different degradation properties and vapor pressure. HCHs will be easier to partition in the atmosphere than DDTs because of the higher vapor pressure of HCHs. It was surprising that the concentrations of DDTs and HCHs have sharp decreases after approximately 2,000; the reason may be that the historical residue of HCHs and DDTs degraded gradually by sediment years and there were no new input sources in Huai River Basin in recent years. A similar recent decreasing trend of HCHs and DDTs residues was observed in the Yellow River Estuary and Chaohu Lake in China (Da et al. 2014; Li et al. 2014).

Chlordane compounds

It was reported that the Chlordane compounds (CHLs) were extensively used against termites during the 1960s and 2009 in China (Zhou et al. 2013). The vertical distribution of the total Chlordane compounds (including trans-chlordane, cis-chlordane, heptachlor and heptachlor epoxide) are listed in Figure 3(a). Total CHLs concentrations increased from the late 1950s to the late 1960s and kept varying steadily until 1998. The first peak year of CHLs was found in 1961, when Chlordane was first extensively used against termites in Anhui Province in China (Wang et al. 2014). It was followed by a steady variation between 1961 and 1998, which may be related to a relative constant usage during the period. It was worthwhile to note that the CHLs residue was close to zero in 1998. We speculated that the zero value in 1998 was attributed to the catastrophic flooding during this year, as CHLs may have been washed away by the flood. A progressive increase was shown between 1998 and 2009, a period during which termites were very serious in China, and there were not highly efficient and low cost substances to control termites. After 2009, CHLs were gradually forbidden to produce and use by the Chinese government (Yang et al. 2005). Therefore, a clear decreasing tendency was observed in recent years; it was also indicated that there was no new pollution source in recent years.

Endosulfan compounds

Endosulfan was used to kill pests in the crops between 1994 and 2004 in China. According to estimates, around 25,700 tons of endosulfans were used during this period (Zhou et al. 2012). The temporal trends of endosulfan (including Endosulfan I and Endosulfan II) residues are listed in Figure 3(b), which were consistent with the application history of endosulfan. It was noticeable that endosulfan residues were found before 1994, although no endosulfan had ever been used during this period, which may be related to transfer via long-distance atmospheric transportation from neighboring countries (such as India, the biggest user of endosulfans in the world). The reason may also be that endosulfans in the surface sediments can migrate downward. Similar findings were also recorded in the cores from the Yellow River Estuary, China (Da et al. 2014), the Beibu Gulf, the South China Sea (Li et al. 2014) and Quanzhou Bay, Southeast China (Gong et al. 2007). Gong et al. (2007) have also affirmed that organic pesticides in surface sediments can migrate downward. A gradual increase was observed between 1956 and 2002 when endosulfan application was allowed to expand in agriculture as an insecticide for the first time (Hu et al. 2009). The peak value was observed in 2002, when endosulfan was used widely for killing the pests in cotton in the Huaihe River basin. A sharp decline was observed since 2002, which was consistent with the banning of endosulfan since 2004 in China. Therefore, the residues decreased continuously until it was close to zero, and there was also no new pollution input in recent years.

Hexachlorobenzene

Hexachlorobenzene (HCB) exists popularly as a byproduct in the industrial production process. It was reported that about 7,000 tons of HCB were produced since 1988 in China (Zhou et al. 2012). As seen in Figure 4, the vertical concentration of HCB maintained a low level before 1981, and began gradually increasing until a peak value appeared in 2004. Therefore, we speculated that large amounts of HCB came from the discharge in the process of industrial production from its adjacent region in 2004. HCB concentrations decreased gradually and a small amount was detected in recent years. Indeed, the production of industrial products containing HCB has been banned gradually in recent years in China.

Potential biological effects of OCPs

As shown in Table 2, two widely used sediment quality guidelines, the effects range-low value (ERL) and effects range-median value (ERM) guidelines and the threshold effects level (TEL) and probable effects level (PEL) guidelines, were applied to evaluate the possible ecotoxicological risks of OCPs (Da et al. 2013). Concentration levels of p′p-DDE, p′p-DDD and DDTs were all less than ERM and TEL and PEL. Concentration levels of DDTs were a little higher than ERL. Therefore, OCPs could not cause adverse biological risk in the environment.

Table 2

Assessments of potential biological risks of selected OCPs in sediments using two sediment quality guidelines

ChemicalMean (ng g−1)ERL (ng g−1)ERM (ng g−1)TEL (ng g−1)PEL (ng g−1)
p′p-DDE 0.69 2.2 27 1.22 7.81 
p′p-DDD 0.27 20 2.07 374 
DDTs 1.67 1.58 46.1 3.89 51.7 
γ-HCH 0.29 – – 0.32 0.99 
ChemicalMean (ng g−1)ERL (ng g−1)ERM (ng g−1)TEL (ng g−1)PEL (ng g−1)
p′p-DDE 0.69 2.2 27 1.22 7.81 
p′p-DDD 0.27 20 2.07 374 
DDTs 1.67 1.58 46.1 3.89 51.7 
γ-HCH 0.29 – – 0.32 0.99 

CONCLUSIONS

The sedimentary record of OCPs in a sediment core from the Huaihe River, China has been studied. The total concentrations of 18 kinds of 22 OCPs in the sediment core were in the range of 0.01–7.18 ng g−1 with an average concentration of 4.53 ng g−1. The mean of detection rates was up to 51.60%. DDTs were the predominant species found in the sediment core. The different categories of OCPs were in the following order: DDTs > HCHs > Chlordanes > Endosulfans > HCB. Drins were all below detection limits. The temporal tendency of OCPs was influenced by their different historical usages, different properties or different degradation conditions in the sediment environment. There was an obvious decreasing trend for OCPs in the core in recent years. The findings suggested there was also no new pollution source input in recent years and OCPs could not cause adverse biological risk in the environment.

ACKNOWLEDGEMENTS

This work is supported by the Anhui Provincial Natural Science Foundation (1608085 MD78), Key Projects of Natural Science Research of Universities in Anhui Province (KJ2015A201, KJ2017A546), the 2016 Hefei University Talent Research Fund Project (16YQ03RC) Key Projects of Anhui Province University Outstanding Youth Talent Support Program (gxyqZD2016274), and the National University Students Innovation and Entrepreneurship Training Program (201511059074, 201511059189). Special thanks are given to the anonymous reviewers for their useful suggestions and comments.

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