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Distribution of HCHs and DDTs in the soil–plant system in tea gardens in Fujian, a major tea-producing province in China
Agriculture, Ecosystems and Environment 171 (2013) 19–24
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Short communication
Distribution of HCHs and DDTs in the soil–plant system in tea gardens in Fujian, a major tea-producing province in China Zhigang Yi ∗ , Pingping Guo, Lili Zheng, Xingran Huang, Junqi Bi College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
a r t i c l e
i n f o
Article history: Received 5 October 2012 Received in revised form 5 February 2013 Accepted 8 March 2013 Available online 17 April 2013 Keywords: Hexachlorocyclohexane Dichlorodiphenyltrichloroethane Organochlorine pesticides Soil–plant relationship Tea gardens
a b s t r a c t The distribution of HCHs and DDTs were investigated in tea gardens in Fujian, a major tea-producing province in China. HCHs ranged from 0.56 ± 0.32 ng g−1 in soils to 4.1 ± 2.6 ng g−1 in old leaves, and
DDTs ranged from 1.0 ± 0.73 ng g−1 in soils to 4.1 ± 4.3 ng g−1 in old branches. ␥-HCH was the major HCH isomers, with the percentages of 36–83%, and p,p -DDT and o,p -DDT accounted for 40–49% and 17–36% in total DDTs in plant tissues. Tea plants could accumulate HCHs and DDTs, with the highest ␥HCH bioconcentration factor in old leaves and p,p -DDT in old branches. HCHs and DDTs concentrations between soil and plant suggested that HCHs tended to accumulate in most of the plant tissues, while DDTs mainly accumulate in the roots. Low ratios of ␣-/␥-HCH and -/(␣ + ␥)-HCH indicated new input of lindane in tea gardens. High ratios of DDT/(DDD + DDE) indicated fresh introduction of DDT, and high ratios of o,p -DDT/p,p -DDT suggested the input of dicofol in these gardens. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Organochlorine pesticides (OCPs), including hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), have caused great concerns for decades and have been banned for about 30 years in China due to their persistence in the environment, bioaccumulation through food chains (Nakata et al., 2002), and high toxicity to humans and biota (Willett et al., 1998). A total of 4.9 million tons of HCHs and 0.4 million tons of DDTs were produced from the 1950s through 1983 in China (Li et al., 2006). The spatial distribution characteristic of pesticide application in China has been reported as follows: southeast > central > northwest (Wang et al., 2005). Many HCHs and DDTs were disposed of in an uncontrolled manner in most of the farmland, causing contamination to nearby ecosystems. Vegetation constitutes an important OCPs sink in the ecosystems, and OCPs can accumulate in different plant tissues (Simonich and Hites, 1994). OCPs come into plants through two possible routes: (i) root uptake and adsorption from the soil and subsequent transfer to the aerial tissues (Pereira et al., 2006, 2008; Mikes et al., 2009), (ii) vapor uptake from the surrounding atmosphere and then translocation into various plant parts (Bacci et al., 1990; Simonich and Hites, 1995b; Barber et al., 2004). The first pathway is usually
∗ Corresponding author at: College of Resources and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China. Tel.: +86 591 83789471; fax: +86 591 83776849. E-mail addresses: [email protected], [email protected] (Z. Yi). 0167-8809/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2013.03.002
the predominant one for low-volatility organic contaminants, especially the adsorption on roots for those with high n-octanol–water partitioning coefficients (log Kow > 3). In the terrestrial environment, the uptake of semivolatile lipophilic compounds into plants has been studied by numerous studies (Simonich and Hites, 1995a; McLachlan, 1999; Mikes et al., 2009). High levels of contaminants in plant tissues have been attributed to accumulation of contaminants from the atmosphere (McLachlan, 1999; Barber et al., 2004). The uptake of contaminants from soil to root surfaces, however, has been investigated far less. Tea (Camellia sinensis L.) is a traditional Chinese merchandize for export. The area of tea plantations and the scale of tea production in China rank first in the world, and tea production of Fujian, locating at the southeastern China, ranks top in China in 2010. The leaves of the tea plant are thin and tender, and the surface area per unit weight of leaf is relatively larger than that of other crops. Thus compared to other crops, the residue level of pesticide on tea leaves is higher under the same concentration of contaminants (Chen and Wan, 1997). European Tea Committee (ETC) have established very stringent maximum residue levels (MRL) of pesticides in tea, with the MRL of 20 ng g−1 for HCH (sum of isomers except the ␥-HCH), 50 ng g−1 for lindane and 100 ng g−1 for total DDT (ETC, 2005). It is urgent to figure out the distribution and source of HCHs and DDTs in tea garden. In the present study, we sought to elucidate the possible source and distribution of HCHs and DDTs in tea gardens and the accumulation of these compounds in tea plants. To accomplish the goals, the concentrations of HCHs and DDTs were measured in soils and different tea plant tissues in 7 tea gardens.
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Fig. 1. The map of sampling tea gardens in Fujian province (site, location, altitude, sampling date: FD, Fuding, 27◦ 17 19 N, 120◦ 05 41 E, 390 m, July 22; FZ, Fuzhou, 26◦ 05 05 N, 119◦ 14 07 E, 40 m, July 29; YT Yongtai, 25◦ 51 27 N, 118◦ 43 54 E, 750 m, July 14; AX, Anxi, 24◦ 53 23 N, 117◦ 58 35 E, 850 m, July 6; SH, Shanghang, 24◦ 48 51 N, 116◦ 24 37“E, 280 m, July 11; ZH, Zhenghe, 27◦ 20’58 N, 118◦ 46 19 E, 200 m, July 14; YX, Youxi, 26◦ 09 81 N, 118◦ 13 63 E, 270 m, July 17).
2. Materials and methods 2.1. Site description and sample collection Seven tea gardens were selected in southeastern China’s Fujian province (Fig. 1). All the tea gardens distribute among the hills or low mountains and are far away from the pollution sources, and all seven gardens were operated for 5–7 years. Three sites were selected at the top, middle and foot of each tea garden, and root, old branch, young branch, old leaf and young leaf were collected from 20 tea plants at each site, then the plant samples were rinsed, lyophilized and ground for posterior analysis. Upper 0–30 cm of the soils were collected adjacent to the roots, then the soil samples were air-dried and sieved. All the samples were collected in July, 2009. 2.2. Extraction and analysis A mixture of 2,4,5,6-tetrachloro-m-xylene (TCmX) and decachlorobiphenyl (PCB209) was added as surrogate standards to 20 g soil samples. The spiked soil samples were Soxhlet-extracted with dichloromethane (DCM) for 72 h, then the extracts were concentrated, purified with silica–alumina cartridge, further concentrated to 0.2 ml, and added with appropriate amount of
pentachloronitrobenzene (PCNB) as an internal standard prior to instrument analysis. About 5 g plant samples spiked with TCmX and PCB209 were Soxhlet-extracted, concentrated to 2 ml for gel permeation chromatography (GPC) cleaning described as those reported by Hu et al. (2008). The cleaning extracts were concentrated and purified in a Silica–Alumina–Florisil cartridge, and then the cartridge were eluted and treated as the soil samples. GC-ECD (Model 7890, Agilent Technologies, USA) equipped with a HP-5 silica capillary column (30 m × 0.32 mm i.d. ×0.25 m film thickness) was employed for HCHs and DDTs analysis. Briefly, the oven temperature was maintained at 80 ◦ C for 0.5 min, and then increased to 180 ◦ C at 10 ◦ C min−1 , then to 280 ◦ C at 3 ◦ C min−1 , and finally to 315 ◦ C at 10 ◦ C min−1 for 15 min. Injector and detector temperature was maintained at 280 ◦ C and 315 ◦ C. Nitrogen (purity > 99.999%) was employed as the carrier gas at the flow rate of 1.5 ml min−1 . 2.3. Statistical analysis All statistical analysis was carried out using the SPSS. Student’s t test and analysis of variance (ANOVA) were applied to test for significant differences in the results.
Z. Yi et al. / Agriculture, Ecosystems and Environment 171 (2013) 19–24
Fig. 2. Percentage distribution of HCHs and DDTs in soils and plant tissues (S = soil; R = root; OB = old branch; YB = young branch; OL = old leaf; YL = young leaf).
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Fig. 3. The concentration factors of HCHs and DDTs in different tissues of tea plants (R = root; OB = old branch; YB = young branch; OL = old leaf; YL = young leaf).
3. Results and discussion 3.1. HCHs 3.1.1. Levels and distribution of HCHs in soils and plants The concentrations of total HCHs ( HCHs) in soils varied within a wide range, with isomers ␥-HCH being the most abundant (Table 1), and the concentrations in soils were significantly lower than those in typical agricultural soils (Chen et al., 2005; Zhang et al., 2011; Yang et al., 2012). HCHs in plant tissues soils were significantly higher than those in soils (Table 1), and the concentrations of old leaves were significantly higher than those in other plant tissues, with ␥-HCH being the most abundant and having a wider range than those in soils (from 0.019 ng g−1 to 9.5 ng g−1 ), but they were much lower than the MRL of the ETC (50 ng g−1 ). The relative distribution of the different isomers to total HCHs differed significantly in soils and plant tissues, with ␥-HCH being the predominant one (36–83%) (Fig. 2). The ratios of ␥-HCH to total HCHs in soils were in agreement with those reported by Gong et al. (2007), who found that most of the ratios were higher than 0.5 in sediments from Quanzhou Bay in Fujian. The relative distribution of -HCH was the lowest for all the HCH isomers and decreased in the plant tissues (Fig. 2), which might be explained by the fact that, -HCH is the most persistent isomer to transfer and has the lowest volatility (Willett et al., 1998). 3.1.2. Accumulation and sources of HCHs Linear regressions can be used to quantify relations between concentrations in soil and plants. The slope of the regression between the soil and the plant concentrations can be interpreted as the plant bioconcentration factor (BCF), and the correlation
coefficient (r) describes how much of the concentration variance in plants is explained by the concentration variance in soil (Mikes et al., 2009). In the present study, the slopes of the regression HCHs in root, old branch, young (BCF) were 2.7, 1.2, 1.5, 3.1 for branch and young leaf respectively, and the correlations were significant (Table 2), especially those for root and young leaf. The results suggested that the HCH concentrations in plant tissues highly depended on soil concentrations, especially for root and young leaf (Pereira et al., 2006; Mikes et al., 2009). The measured BCF (the concentration in plant tissues to that in soil) differed in different compounds. As shown in Fig. 3, high BCFs were found for ␣- and -HCH in roots, with the measured BCFs of 3.9, 3.8, 1.9 and 2.9 for ␣-, -, ␥- and ␦-HCH in root. Plots of HCH concentrations in roots against HCH concentrations in soils showed that correlations were significant between them, and the predicted BCFs were 4.0, 3.5, 3.2, and 2.3 for ␣-, -, ␥- and ␦-HCH. Combined with the higher relative distribution of ␣- and ␦-HCH in roots than that in soils, it could be inferred that the roots had the isomer-selective accumulation of ␣- and ␦-HCH. The accumulation of HCHs in the roots occurs mainly as a result of the hydrophobic partitioning between the aqueous solution and the root surfaces, and Kow was usually employed to estimate the BCF in root. The greater the hydrophobicity of the organic compound, the greater the tendency for it to move from the aqueous solution to the root (Dietz and Schnoor, 2001). According to the log Kow (Pereira et al., 2006), the values of each HCH isomers are quite similar, with ␦-HCH being a little higher. However, the BCFs were not exactly consistent with the tendency for HCH isomers to the roots. This difference may be explained by the fact that soil conditions is much complex, as in the soil, in addition to water, other components such as clays
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Table 1 Mean, standard deviation, minimum and maximum concentrations (ng g−1 ) of HCHs and DDTs in soil and different plant tissues.
Soil ␣-HCH -HCH ␥-HCH ␦-HCH HCH p,p -DDT p,p -DDE p,p -DDD o,p -DDT o,p -DDE o,p -DDD DDT
0.11 (0.095, 0.02–0.33) 0.11 (0.14, n.d.−0.66) 0.23 (0.067, 0.13–0.35) 0.12 (0.073, 0.026–0.32) 0.56 (0.32, 0.18–1.6) 0.16 (0.12, 0.017–0.45) 0.13 (0.18, 0.010–0.74) 0.17 (0.19, 0.016–0.76) 0.45 (0.38, 0.070–1.4) 0.052 (0.079, n.d.−0.30) 0.049 (0.049, n.d.−0.15) 1.0 (0.73, 0.24–2.8)
Root
Old branch
Young Branch
Old leaf
Young leaf
0.36 (0.82, 0.012–3.6) 0.095 (0.11, n.d.−0.38) 0.47 (0.56, 0.034–2.5) 0.33 (0.27, 0.045–1.3) 1.3 (1.6, 0.18–7.5) 1.3 (1.3, 0.023–4.5) 0.33 (0.44, n.d.−1.5) 0.42 (0.76, n.d.−3.3) 0.37 (0.31, 0.022–1.3) 0.056 (0.084, n.d.−0.29) 0.063 (0.068, 0.010–0.25) 2.5 (1.8, 0.21–6.6)
0.14 (0.13, 0.015–0.62) 0.12 (0.15, n.d.−0.71) 0.63 (0.39, 0.019–1.3) 0.30 (0.25, 0.017–1.2) 1.2 (0.67, 0.19–2.9) 2.4 (3.5, 0.070–17) 0.17 (0.16, 0.010–0.62) 0.75 (0.80, 0.016–2.7) 0.61 (0.38, 0.067–1.5) 0.13 (0.38, n.d.−1.8) 0.12 (0.19, n.d.−0.71) 4.2 (4.3, 0.20–21)
0.15 (0.12, 0.014–0.46) 0.13 (0.15, n.d.−0.57) 1.2 (0.61, 0.096–2.4) 0.26 (0.15, 0.042–0.64) 1.7 (0.85, 0.26–3.3) 1.4 (1.3, 0.062–4.6) 0.22 (0.19, 0.016–0.73) 0.40 (0.44, 0.018–1.8) 0.90 (0.75, 0.085–2.6) 0.038 (0.036, n.d.−0.13) 0.076 (0.079, n.d.−0.27) 3.1 (1.8, 0.24–6.9)
0.14 (0.11, 0.011–0.46) 0.068 (0.055, 0.013–0.25) 3.7 (2.6, 0.16–9.5) 0.15 (0.10, 0.018–0.36) 4.1 (2.6, 0.38–10) 1.0 (1.3, 0.040–5.3) 0.22 (0.25, 0.027–1.1) 0.22 (0.10, n.d.−1.7) 1.3 (0.39, 0.023–15) 0.04 2(0.034, n.d.−0.14) 0.041 (0.027, n.d.−0.093) 2.9 (1.4, 0.31–19)
0.10 (0.090, n.d.−0.34) 0.081 (0.088, n.d.−0.29) 1.2 (0.98, 0.13–3.9) 0.28 (0.21, 0.032–0.76) 1.7 (1.2, 0.25–4.5) 1.1 (1.3, 0.085–5.1) 0.19 (0.21, 0.014–0.77) 0.26 (0.32, n.d.−1.1) 1.2 (1.0, 0.032–3.9) 0.072 (0.14, n.d.−0.65) 0.17 (0.37, n.d.−1.7) 3.0 (2.1, 0.31–7.4)
Concentration is presented as mean (standard deviation, minimum–maximum). n.d.: not detected.
and organic matter compete with root surfaces for hydrophobic compounds (Riederer, 2005). The mechanism of foliar accumulation has been described for several semivolatile compounds in diverse studies, and it is most probably via air–plant partitioning, following volatilization from the soils (Mikes et al., 2009). The vapor pressure and the octanol–air partition coefficient (Koa ) may influence the behavior of HCH isomers. According to the log Koa of the different HCH isomers (Pereira et al., 2006), the affinities toward lipidic compounds would follow the order of ␦ >  > ␥ > ␣, but high accumulation capacity appeared for ␥-HCH in plant’s aerial tissues, especially in old leaf. It might be attributed to the long-term exposure to pesticides containing lindane. Pesticides used in the tea gardens were analyzed and ␥HCH could be detected, with the values ranging from 3.6 g ml−1 to 10.4 g ml−1 , but ␣-, - and ␦-HCH were lower than the detection limit. In the present study, HCH isomer concentrations in most of the plant tissues were closely related to those in soils (Table 2), suggesting that the process of root uptake and subsequent translocation to the aerial plant tissues could not be discarded. The ratios of ␣-/␥-HCH can be used to trace the source and the use history of HCHs. This ratio should be 4–7 for technical HCHs and nearly zero for lindane (Iwata et al., 1995). Low ␣-/␥-HCH ratios in the present study indicated the input of lindane in tea gardens (Table 3). Lower ratios in plant’s aerial tissues than those in the roots implied that aerial tissues were more readily expose to the lindane. -HCH is the most stable one among the HCH isomers and it is reluctant to degrade in the environment, thus -HCH will be the most abundance isomer in the environment (Willett et al., 1998).
The ratio of -/(␣ + ␥)-HCH can be used to identify the possible sources of HCHs, and also its input occurred recently or in the past. Low ratios of -/(␣ + ␥)-HCH in the present study (Table 3) indicated the possible input of technical HCHs or lindane as pesticide in tea gardens. As discussed above, if there existed recent input of technical HCHs, ␣-/␥-HCH ratios should be higher than those in the present study. However, ␥-HCH was found to be the major isomers in most of the compartments of the tea gardens, and thus there might be the input of ␥-HCH (lindane) in tea gardens. 3.2. DDTs 3.2.1. Levels and distribution of DDTs in soils and plants The concentrations of total DDTs ( DDTs) in soils ranged from 0.25 ng g−1 to 2.8 ng g−1 , with o,p -DDT being the most abundant one (Fig. 2), and the concentrations in tea garden soils were lower et al., than those in typical agricultural soils (Chen et al., 2005; Yang −1 2012). DDTs in the plant tissues (ranged from 0.20 ng g to 21 ng g−1 ) were significantly higher than those in soil (Table 1), but they were much lower than the MRL of the ETC (100 ng g−1 ). Significant differences were found for p,p -DDT and o,p -DDT among the plant tissues, with the highest value of 2.4 ± 3.5 ng g−1 for p,p DDT in old branches and 1.3 ± 0.39 ng g−1 for o,p -DDT in old leaves (Table 1). p,p -DDT and o,p -DDT were the most abundant in plants, with p,p -DDT ranging from 39.5% to 49.3% and o,p -DDT ranging from 17.4% to 35.7% (Fig. 2). The relative distribution of DDTs was partly in agreement with those reported by Sojinu et al. (2012), who found that o,p -DDT and p,p -DDT accounted for 39.3 ± 25.2% and 16.4 ± 18.7% in total DDTs in higher plants.
Table 2 Coefficients of correlation between HCHs and DDTs concentrations in the soil and different of tea plant tissues.
Soil
␣-HCH -HCH ␥-HCH ␦-HCH HCH p,p -DDT p,p -DDE p,p -DDD o,p -DDT o,p -DDE o,p -DDD DDT
n.s.: not significant; significant correlation. * P < 0.05. ** P < 0.01.
Root
Old branch
Young Branch
Old leaf
Young leaf
0.70** 0.77** 0.52* 0.66** 0.76** n.s. 0.74** 0.94** 0.52* 0.68** n.s. n.s.
0.70** 0.94** n.s. 0.61* 0.63* n.s. 0.97** n.s. n.s. n.s. n.s. n.s.
n.s. 0.65** 0.70* 0.60* 0.50* n.s. 0.73** n.s. n.s. n.s. n.s. n.s.
n.s. 0.83** n.s. 0.63* n.s. n.s. 0.81** 0.688** n.s. n.s. n.s. n.s.
n.s. 0.62* 0.61* 0.56* 0.79** n.s. n.s. n.s. n.s. n.s. n.s. n.s.
Z. Yi et al. / Agriculture, Ecosystems and Environment 171 (2013) 19–24
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Table 3 The ratios of HCHs and DDTs in soils and different plant tissues in tea gardens.* Soil ␣-/␥-HCH -/(␣ + ␥)-HCH DDT/(DDD + DDE) o,p -DDT/p,p -DDT *
0.44 0.29 1.8 3.8
Root ± ± ± ±
0.28 0.25 1.7 1.1
0.79 0.32 21 0.75
Old branch ± ± ± ±
0.60 0.30 34 0.71
0.40 0.36 8.0 0.82
± ± ± ±
0.39 0.64 8.9 0.89
Young Branch 0.18 0.10 6.0 1.2
± ± ± ±
0.17 0.08 7.5 0.96
Old leaf 0.07 0.06 17 1.7
± ± ± ±
Young leaf 0.08 0.08 39 1.4
0.11 0.07 9.9 3.4
± ± ± ±
0.06 0.03 10 4.7
Mean ± standard deviation.
3.2.2. Accumulation and sources of DDTs DDT concentrations in plants were higher than those in soils, and the measured BCFs were of 3.4, 5.6, 3.6, 3.1 and 3.9 for DDTs in root, old branch, young branch, old leaf and young leaf respectively. However, different from HCHs, there were no correlations between soil DDT concentrations and plant DDT concentrations, suggesting that total DDT concentration in plants did not depend on soil concentration. The BCF differed in different tissues for DDT and its metabolites, and the highest BCF were found for p,p -DDT (Fig. 3). High BCF for p,p -DDT and the higher relative distribution of p,p -DDT in plant tissues than that in soil indicated the selective accumulation of p,p -DDT in tea plants. As Table 2 showed, close correlations were only found between soil and root for most of the DDTs and its metabolites (Table 2), and the measured BCFs were 10.5, 3.0, 2.5, 1.1, 2.2, 1.2 for p,p -DDT, p,p -DDE, p,p -DDD, o,p -DDT, o,p -DDD and o,p -DDE respectively (Fig. 3). As mentioned above, Kow might be employed to estimate the accumulation of DDTs in roots. According to the log Kow values (US DHHS, 2003), the tendency should be p,p -DDT > o,p -DDT > p,p -DDE > p,p DDD ≈ o,p -DDE > o,p -DDD. However, the BCFs in root were not exactly consistent with the Kow , and it may also be attributed to the complex conditions in soils as mentioned above (Riederer, 2005). Vapor pressure could be employed to explain the relative content in the plant’s aerial tissues (Pereira et al., 2006, 2008). Vapor pressure of o,p -DDT and p,p -DDT is much lower compared to other DDTs, and so it is unlikely that tea plant’s aerial tissues absorb more o,p -DDT and p,p -DDT than other DDTs. The significantly higher p,p -DDT in aerial tissues, especially those in the young branches and leaves than those in soils might be attributed to the direct input of non-degraded DDTs into the aerial tissues. DDT/(DDD + DDE) ratio can be used to establish whether input occurred recently or in the past and whether degradation is significant or not. DDT/(DDD + DDE) ratio in contaminated soils after a long time of weathering is lower than 1 (Hitch and Day, 1992). The ratios in the present study ranged from 1.8 ± 1.7 in soils to 21 ± 34 in the roots, which were in the range of those reported in the agricultural soils in China (Chen et al., 2005; Yang et al., 2012), but much higher than those reported in the soils of USA (Pereira et al., 1996). The ratios in the soils in the present study indicated the new input of DDTs in the tea gardens. The ratios in the plant tissues were significantly higher than those in soils, which implied the selective accumulation of the DDTs, as shown in Fig. 3. o,p -DDT/p,p -DDT ratio is about 0.175 in the technical DDT and about 7 in dicofol (Qiu et al., 2005), and it can be employed to estimate the input of dicofol in the environment. The ratios in the present study ranged from 0.75 ± 0.71 in roots to 3.8 ± 1.1 in soils (Table 3), higher than those in technical DDT but lower than those in dicofol. The results implied the input of dicofol in the tea gardens. The pesticides used in the tea gardens were analyzed and the concentrations were 7.3–20.5 g ml−1 for o,p -DDT and 2.8–5.3 g ml−1 for p,p -DDT.
4. Conclusions Tea plants can accumulate HCHs and DDTs, with the selective accumulation of ␣-HCH, ␦-HCH and p,p -DDT in roots. Higher
concentrations of HCHs in the tea plant tissues, especially ␥-HCH in the old leaves than those in soils, and the lower ratios of ␣-/␥HCH implied the possible source and process of HCHs in tea plants. Pesticides containing lindane in tea garden were adsorbed on the plant aerial tissues, and some of the ␥-HCH came into the soils and then absorbed by the roots. Higher DDTs concentrations, especially p,p -DDT and o,p -DDT in plant tissues than those in soils, and the high ratios of DDT/(DDD + DDE) and o,p -DDT/p,p -DDT indicated the fresh input of DDTs and dicofol in pesticides in tea gardens. The correlation of HCHs and DDTs concentration between soils and plant tissues suggested that most of the plant HCH concentrations highly depended on soil HCH concentration, and soil HCHs tended to accumulate in all the plant tissues. However, only root DDT concentrations depended on soil DDT concentration. The results implied that the process of root uptake and subsequent translocation to the aerial plant tissues could not be discarded.
Acknowledgments This work was funded by the National Natural Science Foundation of China (40971260, 41173090) and the Program for New Century Excellent Talents in Fujian Province University (JA12087).
References Bacci, E., Calamari, D., Gaggi, G., Vighi, M., 1990. Bioconcentration of organic chemical vapors in plant leaves: experimental measurement and correlation. Environ. Sci. Technol. 24, 885–889. Barber, J.L., Thomas, G.O., Kerstiens, G., Jones, K.C., 2004. Current issues and uncertainties in the measurement and modelling of air–vegetation exchange and within-plant processing of POPs. Environ. Pollut. 128, 99–138. Chen, L.G., Ran, Y., Xing, B.S., Mai, B.X., He, J.H., Wei, X.G., Fu, J.M., Sheng, G.Y., 2005. Contents and sources of polycyclic aromatic hydrocarbons and organochlorine pesticides in vegetable soils of Guangzhou, China. Chemosphere 60, 879–890. Chen, Z.M., Wan, H.B., 1997. Degradation of pesticides on plant surface and its prediction – a case study on tea plant. Environ. Monit. Assess 44, 301–313. Dietz, A.C., Schnoor, J.L., 2001. Advances in phytoremediation. Environ. Health Perspect. 109, 163–167. European Tea Committee, 2005. Code of Practice-Pesticide Residues in Tea. Hamburg, Germany. Gong, X.Y., Qi, S.H., Wang, Y.X., Julia, E.B., Lv, C.L., 2007. Historical contamination and sources of organochlorine pesticides in sediment cores from Quanzhou Bay, Southeast China. Mar. Pollut. Bull. 54, 1434–1440. Hitch, R.K., Day, H.P., 1992. Unusual persistence of DDT in some western USA soils. Bull. Environ. Contam. Toxicol. 48, 264–295. Hu, B.Z., Song, W.H., Xie, L.P., Shao, T.F., 2008. Determination of 33 pesticides in tea using accelerated solvent extraction/gel permeation chromatography and solid phase extraction/gas chromatography–mass spectrometry. Chin. J. Chromatogr. 26, 22–28. Iwata, H., Tanabe, S., Ueda, K., Tatsukawa, R., 1995. Persistent organochlorine residues in air, water, sediments, and soils from the Lake Baikal Region, Russia. Environ. Sci. Technol. 29, 792–801. Li, J., Zhang, G., Qi, S.H., Li, X.D., Peng, X.Z., 2006. Concentrations, enantiomeric compositions, and sources of HCH, DDT and chlordane in soils from the Pearl River Delta, South China. Sci. Total Environ. 372, 215–224. McLachlan, M.S., 1999. Framework for the interpretation of measurements of SOCs in plants. Environ. Sci. Technol. 33, 1799–1804. Mikes, O., Cupr, P., Trapp, S., Klanova, J., 2009. Uptake of polychlorinated biphenyls and organochlorine pesticides from soil and air into radishes (Raphanus sativus). Environ. Pollut. 157, 488–496. Nakata, H., Kawazoe, M., Arizono, K., Abe, S., Kitano, T., Shimada, H., Li, W., Ding, X., 2002. Organochlorine pesticides and polychlorinated biphenyl residues in foodstuffs and human tissues from China: status of contamination, historical trend, and human dietary exposure. Arch. Environ. Contam. Toxicol. 43, 473–480.
24
Z. Yi et al. / Agriculture, Ecosystems and Environment 171 (2013) 19–24
Pereira, R.C., Camps-Arbestain, M., Garrido, B.R., Macias, F., Monterroso, C., 2006. Behaviour of ␣-, -, ␥-, and ␦-hexachlorocyclohexane in the soil–plant system of a contaminated site. Environ. Pollut. 144, 210–217. Pereira, R.C., Monterroso, C., Macias, F., Camps-Arbestain, M., 2008. Distribution pathways of hexachlorocyclohexane isomers in a soil–plant–air system. A case study with Cynara scolymus L. and Erica sp. plants grown in a contaminated site. Environ. Pollut. 155, 350–358. Pereira, W.E., Domagalski, J.L., Hostettler, F.D., 1996. Occurrence and accumulation of pesticides and organic contaminants in river sediment, water and clam tissues from the san Joaquin River and tributaries, California. Environ. Toxicol. Chem. 15, 172–180. Qiu, X.H., Zhu, T., Yao, B., Hu, J.X., Hu, S.W., 2005. Contribution of dicofol to the current DDT pollution in China. Environ. Sci. Technol. 39, 4385–4390. Riederer, M., 2005. Uptake and transport of xenobiotics. In: Hock, B., Elstner, E.F. (Eds.), Plant Toxicology. Marcel Dekker, New York, pp. 131–150. Simonich, S.L., Hites, R.A., 1994. Vegetation–atmosphere partitioning of polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 28, 939–943. Simonich, S.L., Hites, R.A., 1995a. Global distribution of persistent organochlorine compounds. Science 269, 1851–1854.
Simonich, S.L., Hites, R.A., 1995b. Organic pollutant accumulation in vegetation. Environ. Sci. Technol. 29, 2905–2914. Sojinu, O.S., Wang, J.Z., Sonibare, O.S., Zeng, E.Y., 2012. Assessment of organochlorine pesticides residues in higher plants from oil exploration areas of Niger Delta, Nigeria. Sci. Total Environ. 433, 169–177. U.S. Department of Health and Human Services, 2003. Toxicological profile for DDT, DDE and DDD. Atlanta, Georgia. Wang, T.Y., Lu, Y.L., Zhang, H., Shi, Y.J., 2005. Contamination of persistent organic pollutants (POPs) and relevant management in China. Environ. Int. 31, 813–821. Willett, K.L., Ulrich, E.M., Hites, R.A., 1998. Differential toxicity and environmental fates of hexachlorocyclohexane isomers. Environ. Sci. Technol. 32, 2197–2207. Yang, D., Qi, S.H., Zhang, J.Q., Tan, L.Z., Zhang, J.P., Zhang, Y., Xu, F., Xing, X.L., Hu, Y., Chen, W., Yang, J.H., Xu, M.H., 2012. Residues of organochlorine pesticides (OCPs) in agricultural soils of Zhangzhou city, China. Pedosphere 22, 178– 189. Zhang, A.P., Liu, W.P., Yuan, H.J., Zhou, S.S., Su, Y.S., Li, Y.F., 2011. Spatial distribution of hexachlorocyclohexanes in agricultural soils in Zhejiang province, China, and correlations with elevation and temperature. Environ. Sci. Technol. 45, 6303–6308.
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Short communication
Distribution of HCHs and DDTs in the soil–plant system in tea gardens in Fujian, a major tea-producing province in China Zhigang Yi ∗ , Pingping Guo, Lili Zheng, Xingran Huang, Junqi Bi College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
a r t i c l e
i n f o
Article history: Received 5 October 2012 Received in revised form 5 February 2013 Accepted 8 March 2013 Available online 17 April 2013 Keywords: Hexachlorocyclohexane Dichlorodiphenyltrichloroethane Organochlorine pesticides Soil–plant relationship Tea gardens
a b s t r a c t The distribution of HCHs and DDTs were investigated in tea gardens in Fujian, a major tea-producing province in China. HCHs ranged from 0.56 ± 0.32 ng g−1 in soils to 4.1 ± 2.6 ng g−1 in old leaves, and
DDTs ranged from 1.0 ± 0.73 ng g−1 in soils to 4.1 ± 4.3 ng g−1 in old branches. ␥-HCH was the major HCH isomers, with the percentages of 36–83%, and p,p -DDT and o,p -DDT accounted for 40–49% and 17–36% in total DDTs in plant tissues. Tea plants could accumulate HCHs and DDTs, with the highest ␥HCH bioconcentration factor in old leaves and p,p -DDT in old branches. HCHs and DDTs concentrations between soil and plant suggested that HCHs tended to accumulate in most of the plant tissues, while DDTs mainly accumulate in the roots. Low ratios of ␣-/␥-HCH and -/(␣ + ␥)-HCH indicated new input of lindane in tea gardens. High ratios of DDT/(DDD + DDE) indicated fresh introduction of DDT, and high ratios of o,p -DDT/p,p -DDT suggested the input of dicofol in these gardens. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Organochlorine pesticides (OCPs), including hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), have caused great concerns for decades and have been banned for about 30 years in China due to their persistence in the environment, bioaccumulation through food chains (Nakata et al., 2002), and high toxicity to humans and biota (Willett et al., 1998). A total of 4.9 million tons of HCHs and 0.4 million tons of DDTs were produced from the 1950s through 1983 in China (Li et al., 2006). The spatial distribution characteristic of pesticide application in China has been reported as follows: southeast > central > northwest (Wang et al., 2005). Many HCHs and DDTs were disposed of in an uncontrolled manner in most of the farmland, causing contamination to nearby ecosystems. Vegetation constitutes an important OCPs sink in the ecosystems, and OCPs can accumulate in different plant tissues (Simonich and Hites, 1994). OCPs come into plants through two possible routes: (i) root uptake and adsorption from the soil and subsequent transfer to the aerial tissues (Pereira et al., 2006, 2008; Mikes et al., 2009), (ii) vapor uptake from the surrounding atmosphere and then translocation into various plant parts (Bacci et al., 1990; Simonich and Hites, 1995b; Barber et al., 2004). The first pathway is usually
∗ Corresponding author at: College of Resources and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China. Tel.: +86 591 83789471; fax: +86 591 83776849. E-mail addresses: [email protected], [email protected] (Z. Yi). 0167-8809/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2013.03.002
the predominant one for low-volatility organic contaminants, especially the adsorption on roots for those with high n-octanol–water partitioning coefficients (log Kow > 3). In the terrestrial environment, the uptake of semivolatile lipophilic compounds into plants has been studied by numerous studies (Simonich and Hites, 1995a; McLachlan, 1999; Mikes et al., 2009). High levels of contaminants in plant tissues have been attributed to accumulation of contaminants from the atmosphere (McLachlan, 1999; Barber et al., 2004). The uptake of contaminants from soil to root surfaces, however, has been investigated far less. Tea (Camellia sinensis L.) is a traditional Chinese merchandize for export. The area of tea plantations and the scale of tea production in China rank first in the world, and tea production of Fujian, locating at the southeastern China, ranks top in China in 2010. The leaves of the tea plant are thin and tender, and the surface area per unit weight of leaf is relatively larger than that of other crops. Thus compared to other crops, the residue level of pesticide on tea leaves is higher under the same concentration of contaminants (Chen and Wan, 1997). European Tea Committee (ETC) have established very stringent maximum residue levels (MRL) of pesticides in tea, with the MRL of 20 ng g−1 for HCH (sum of isomers except the ␥-HCH), 50 ng g−1 for lindane and 100 ng g−1 for total DDT (ETC, 2005). It is urgent to figure out the distribution and source of HCHs and DDTs in tea garden. In the present study, we sought to elucidate the possible source and distribution of HCHs and DDTs in tea gardens and the accumulation of these compounds in tea plants. To accomplish the goals, the concentrations of HCHs and DDTs were measured in soils and different tea plant tissues in 7 tea gardens.
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Fig. 1. The map of sampling tea gardens in Fujian province (site, location, altitude, sampling date: FD, Fuding, 27◦ 17 19 N, 120◦ 05 41 E, 390 m, July 22; FZ, Fuzhou, 26◦ 05 05 N, 119◦ 14 07 E, 40 m, July 29; YT Yongtai, 25◦ 51 27 N, 118◦ 43 54 E, 750 m, July 14; AX, Anxi, 24◦ 53 23 N, 117◦ 58 35 E, 850 m, July 6; SH, Shanghang, 24◦ 48 51 N, 116◦ 24 37“E, 280 m, July 11; ZH, Zhenghe, 27◦ 20’58 N, 118◦ 46 19 E, 200 m, July 14; YX, Youxi, 26◦ 09 81 N, 118◦ 13 63 E, 270 m, July 17).
2. Materials and methods 2.1. Site description and sample collection Seven tea gardens were selected in southeastern China’s Fujian province (Fig. 1). All the tea gardens distribute among the hills or low mountains and are far away from the pollution sources, and all seven gardens were operated for 5–7 years. Three sites were selected at the top, middle and foot of each tea garden, and root, old branch, young branch, old leaf and young leaf were collected from 20 tea plants at each site, then the plant samples were rinsed, lyophilized and ground for posterior analysis. Upper 0–30 cm of the soils were collected adjacent to the roots, then the soil samples were air-dried and sieved. All the samples were collected in July, 2009. 2.2. Extraction and analysis A mixture of 2,4,5,6-tetrachloro-m-xylene (TCmX) and decachlorobiphenyl (PCB209) was added as surrogate standards to 20 g soil samples. The spiked soil samples were Soxhlet-extracted with dichloromethane (DCM) for 72 h, then the extracts were concentrated, purified with silica–alumina cartridge, further concentrated to 0.2 ml, and added with appropriate amount of
pentachloronitrobenzene (PCNB) as an internal standard prior to instrument analysis. About 5 g plant samples spiked with TCmX and PCB209 were Soxhlet-extracted, concentrated to 2 ml for gel permeation chromatography (GPC) cleaning described as those reported by Hu et al. (2008). The cleaning extracts were concentrated and purified in a Silica–Alumina–Florisil cartridge, and then the cartridge were eluted and treated as the soil samples. GC-ECD (Model 7890, Agilent Technologies, USA) equipped with a HP-5 silica capillary column (30 m × 0.32 mm i.d. ×0.25 m film thickness) was employed for HCHs and DDTs analysis. Briefly, the oven temperature was maintained at 80 ◦ C for 0.5 min, and then increased to 180 ◦ C at 10 ◦ C min−1 , then to 280 ◦ C at 3 ◦ C min−1 , and finally to 315 ◦ C at 10 ◦ C min−1 for 15 min. Injector and detector temperature was maintained at 280 ◦ C and 315 ◦ C. Nitrogen (purity > 99.999%) was employed as the carrier gas at the flow rate of 1.5 ml min−1 . 2.3. Statistical analysis All statistical analysis was carried out using the SPSS. Student’s t test and analysis of variance (ANOVA) were applied to test for significant differences in the results.
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Fig. 2. Percentage distribution of HCHs and DDTs in soils and plant tissues (S = soil; R = root; OB = old branch; YB = young branch; OL = old leaf; YL = young leaf).
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Fig. 3. The concentration factors of HCHs and DDTs in different tissues of tea plants (R = root; OB = old branch; YB = young branch; OL = old leaf; YL = young leaf).
3. Results and discussion 3.1. HCHs 3.1.1. Levels and distribution of HCHs in soils and plants The concentrations of total HCHs ( HCHs) in soils varied within a wide range, with isomers ␥-HCH being the most abundant (Table 1), and the concentrations in soils were significantly lower than those in typical agricultural soils (Chen et al., 2005; Zhang et al., 2011; Yang et al., 2012). HCHs in plant tissues soils were significantly higher than those in soils (Table 1), and the concentrations of old leaves were significantly higher than those in other plant tissues, with ␥-HCH being the most abundant and having a wider range than those in soils (from 0.019 ng g−1 to 9.5 ng g−1 ), but they were much lower than the MRL of the ETC (50 ng g−1 ). The relative distribution of the different isomers to total HCHs differed significantly in soils and plant tissues, with ␥-HCH being the predominant one (36–83%) (Fig. 2). The ratios of ␥-HCH to total HCHs in soils were in agreement with those reported by Gong et al. (2007), who found that most of the ratios were higher than 0.5 in sediments from Quanzhou Bay in Fujian. The relative distribution of -HCH was the lowest for all the HCH isomers and decreased in the plant tissues (Fig. 2), which might be explained by the fact that, -HCH is the most persistent isomer to transfer and has the lowest volatility (Willett et al., 1998). 3.1.2. Accumulation and sources of HCHs Linear regressions can be used to quantify relations between concentrations in soil and plants. The slope of the regression between the soil and the plant concentrations can be interpreted as the plant bioconcentration factor (BCF), and the correlation
coefficient (r) describes how much of the concentration variance in plants is explained by the concentration variance in soil (Mikes et al., 2009). In the present study, the slopes of the regression HCHs in root, old branch, young (BCF) were 2.7, 1.2, 1.5, 3.1 for branch and young leaf respectively, and the correlations were significant (Table 2), especially those for root and young leaf. The results suggested that the HCH concentrations in plant tissues highly depended on soil concentrations, especially for root and young leaf (Pereira et al., 2006; Mikes et al., 2009). The measured BCF (the concentration in plant tissues to that in soil) differed in different compounds. As shown in Fig. 3, high BCFs were found for ␣- and -HCH in roots, with the measured BCFs of 3.9, 3.8, 1.9 and 2.9 for ␣-, -, ␥- and ␦-HCH in root. Plots of HCH concentrations in roots against HCH concentrations in soils showed that correlations were significant between them, and the predicted BCFs were 4.0, 3.5, 3.2, and 2.3 for ␣-, -, ␥- and ␦-HCH. Combined with the higher relative distribution of ␣- and ␦-HCH in roots than that in soils, it could be inferred that the roots had the isomer-selective accumulation of ␣- and ␦-HCH. The accumulation of HCHs in the roots occurs mainly as a result of the hydrophobic partitioning between the aqueous solution and the root surfaces, and Kow was usually employed to estimate the BCF in root. The greater the hydrophobicity of the organic compound, the greater the tendency for it to move from the aqueous solution to the root (Dietz and Schnoor, 2001). According to the log Kow (Pereira et al., 2006), the values of each HCH isomers are quite similar, with ␦-HCH being a little higher. However, the BCFs were not exactly consistent with the tendency for HCH isomers to the roots. This difference may be explained by the fact that soil conditions is much complex, as in the soil, in addition to water, other components such as clays
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Table 1 Mean, standard deviation, minimum and maximum concentrations (ng g−1 ) of HCHs and DDTs in soil and different plant tissues.
Soil ␣-HCH -HCH ␥-HCH ␦-HCH HCH p,p -DDT p,p -DDE p,p -DDD o,p -DDT o,p -DDE o,p -DDD DDT
0.11 (0.095, 0.02–0.33) 0.11 (0.14, n.d.−0.66) 0.23 (0.067, 0.13–0.35) 0.12 (0.073, 0.026–0.32) 0.56 (0.32, 0.18–1.6) 0.16 (0.12, 0.017–0.45) 0.13 (0.18, 0.010–0.74) 0.17 (0.19, 0.016–0.76) 0.45 (0.38, 0.070–1.4) 0.052 (0.079, n.d.−0.30) 0.049 (0.049, n.d.−0.15) 1.0 (0.73, 0.24–2.8)
Root
Old branch
Young Branch
Old leaf
Young leaf
0.36 (0.82, 0.012–3.6) 0.095 (0.11, n.d.−0.38) 0.47 (0.56, 0.034–2.5) 0.33 (0.27, 0.045–1.3) 1.3 (1.6, 0.18–7.5) 1.3 (1.3, 0.023–4.5) 0.33 (0.44, n.d.−1.5) 0.42 (0.76, n.d.−3.3) 0.37 (0.31, 0.022–1.3) 0.056 (0.084, n.d.−0.29) 0.063 (0.068, 0.010–0.25) 2.5 (1.8, 0.21–6.6)
0.14 (0.13, 0.015–0.62) 0.12 (0.15, n.d.−0.71) 0.63 (0.39, 0.019–1.3) 0.30 (0.25, 0.017–1.2) 1.2 (0.67, 0.19–2.9) 2.4 (3.5, 0.070–17) 0.17 (0.16, 0.010–0.62) 0.75 (0.80, 0.016–2.7) 0.61 (0.38, 0.067–1.5) 0.13 (0.38, n.d.−1.8) 0.12 (0.19, n.d.−0.71) 4.2 (4.3, 0.20–21)
0.15 (0.12, 0.014–0.46) 0.13 (0.15, n.d.−0.57) 1.2 (0.61, 0.096–2.4) 0.26 (0.15, 0.042–0.64) 1.7 (0.85, 0.26–3.3) 1.4 (1.3, 0.062–4.6) 0.22 (0.19, 0.016–0.73) 0.40 (0.44, 0.018–1.8) 0.90 (0.75, 0.085–2.6) 0.038 (0.036, n.d.−0.13) 0.076 (0.079, n.d.−0.27) 3.1 (1.8, 0.24–6.9)
0.14 (0.11, 0.011–0.46) 0.068 (0.055, 0.013–0.25) 3.7 (2.6, 0.16–9.5) 0.15 (0.10, 0.018–0.36) 4.1 (2.6, 0.38–10) 1.0 (1.3, 0.040–5.3) 0.22 (0.25, 0.027–1.1) 0.22 (0.10, n.d.−1.7) 1.3 (0.39, 0.023–15) 0.04 2(0.034, n.d.−0.14) 0.041 (0.027, n.d.−0.093) 2.9 (1.4, 0.31–19)
0.10 (0.090, n.d.−0.34) 0.081 (0.088, n.d.−0.29) 1.2 (0.98, 0.13–3.9) 0.28 (0.21, 0.032–0.76) 1.7 (1.2, 0.25–4.5) 1.1 (1.3, 0.085–5.1) 0.19 (0.21, 0.014–0.77) 0.26 (0.32, n.d.−1.1) 1.2 (1.0, 0.032–3.9) 0.072 (0.14, n.d.−0.65) 0.17 (0.37, n.d.−1.7) 3.0 (2.1, 0.31–7.4)
Concentration is presented as mean (standard deviation, minimum–maximum). n.d.: not detected.
and organic matter compete with root surfaces for hydrophobic compounds (Riederer, 2005). The mechanism of foliar accumulation has been described for several semivolatile compounds in diverse studies, and it is most probably via air–plant partitioning, following volatilization from the soils (Mikes et al., 2009). The vapor pressure and the octanol–air partition coefficient (Koa ) may influence the behavior of HCH isomers. According to the log Koa of the different HCH isomers (Pereira et al., 2006), the affinities toward lipidic compounds would follow the order of ␦ >  > ␥ > ␣, but high accumulation capacity appeared for ␥-HCH in plant’s aerial tissues, especially in old leaf. It might be attributed to the long-term exposure to pesticides containing lindane. Pesticides used in the tea gardens were analyzed and ␥HCH could be detected, with the values ranging from 3.6 g ml−1 to 10.4 g ml−1 , but ␣-, - and ␦-HCH were lower than the detection limit. In the present study, HCH isomer concentrations in most of the plant tissues were closely related to those in soils (Table 2), suggesting that the process of root uptake and subsequent translocation to the aerial plant tissues could not be discarded. The ratios of ␣-/␥-HCH can be used to trace the source and the use history of HCHs. This ratio should be 4–7 for technical HCHs and nearly zero for lindane (Iwata et al., 1995). Low ␣-/␥-HCH ratios in the present study indicated the input of lindane in tea gardens (Table 3). Lower ratios in plant’s aerial tissues than those in the roots implied that aerial tissues were more readily expose to the lindane. -HCH is the most stable one among the HCH isomers and it is reluctant to degrade in the environment, thus -HCH will be the most abundance isomer in the environment (Willett et al., 1998).
The ratio of -/(␣ + ␥)-HCH can be used to identify the possible sources of HCHs, and also its input occurred recently or in the past. Low ratios of -/(␣ + ␥)-HCH in the present study (Table 3) indicated the possible input of technical HCHs or lindane as pesticide in tea gardens. As discussed above, if there existed recent input of technical HCHs, ␣-/␥-HCH ratios should be higher than those in the present study. However, ␥-HCH was found to be the major isomers in most of the compartments of the tea gardens, and thus there might be the input of ␥-HCH (lindane) in tea gardens. 3.2. DDTs 3.2.1. Levels and distribution of DDTs in soils and plants The concentrations of total DDTs ( DDTs) in soils ranged from 0.25 ng g−1 to 2.8 ng g−1 , with o,p -DDT being the most abundant one (Fig. 2), and the concentrations in tea garden soils were lower et al., than those in typical agricultural soils (Chen et al., 2005; Yang −1 2012). DDTs in the plant tissues (ranged from 0.20 ng g to 21 ng g−1 ) were significantly higher than those in soil (Table 1), but they were much lower than the MRL of the ETC (100 ng g−1 ). Significant differences were found for p,p -DDT and o,p -DDT among the plant tissues, with the highest value of 2.4 ± 3.5 ng g−1 for p,p DDT in old branches and 1.3 ± 0.39 ng g−1 for o,p -DDT in old leaves (Table 1). p,p -DDT and o,p -DDT were the most abundant in plants, with p,p -DDT ranging from 39.5% to 49.3% and o,p -DDT ranging from 17.4% to 35.7% (Fig. 2). The relative distribution of DDTs was partly in agreement with those reported by Sojinu et al. (2012), who found that o,p -DDT and p,p -DDT accounted for 39.3 ± 25.2% and 16.4 ± 18.7% in total DDTs in higher plants.
Table 2 Coefficients of correlation between HCHs and DDTs concentrations in the soil and different of tea plant tissues.
Soil
␣-HCH -HCH ␥-HCH ␦-HCH HCH p,p -DDT p,p -DDE p,p -DDD o,p -DDT o,p -DDE o,p -DDD DDT
n.s.: not significant; significant correlation. * P < 0.05. ** P < 0.01.
Root
Old branch
Young Branch
Old leaf
Young leaf
0.70** 0.77** 0.52* 0.66** 0.76** n.s. 0.74** 0.94** 0.52* 0.68** n.s. n.s.
0.70** 0.94** n.s. 0.61* 0.63* n.s. 0.97** n.s. n.s. n.s. n.s. n.s.
n.s. 0.65** 0.70* 0.60* 0.50* n.s. 0.73** n.s. n.s. n.s. n.s. n.s.
n.s. 0.83** n.s. 0.63* n.s. n.s. 0.81** 0.688** n.s. n.s. n.s. n.s.
n.s. 0.62* 0.61* 0.56* 0.79** n.s. n.s. n.s. n.s. n.s. n.s. n.s.
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Table 3 The ratios of HCHs and DDTs in soils and different plant tissues in tea gardens.* Soil ␣-/␥-HCH -/(␣ + ␥)-HCH DDT/(DDD + DDE) o,p -DDT/p,p -DDT *
0.44 0.29 1.8 3.8
Root ± ± ± ±
0.28 0.25 1.7 1.1
0.79 0.32 21 0.75
Old branch ± ± ± ±
0.60 0.30 34 0.71
0.40 0.36 8.0 0.82
± ± ± ±
0.39 0.64 8.9 0.89
Young Branch 0.18 0.10 6.0 1.2
± ± ± ±
0.17 0.08 7.5 0.96
Old leaf 0.07 0.06 17 1.7
± ± ± ±
Young leaf 0.08 0.08 39 1.4
0.11 0.07 9.9 3.4
± ± ± ±
0.06 0.03 10 4.7
Mean ± standard deviation.
3.2.2. Accumulation and sources of DDTs DDT concentrations in plants were higher than those in soils, and the measured BCFs were of 3.4, 5.6, 3.6, 3.1 and 3.9 for DDTs in root, old branch, young branch, old leaf and young leaf respectively. However, different from HCHs, there were no correlations between soil DDT concentrations and plant DDT concentrations, suggesting that total DDT concentration in plants did not depend on soil concentration. The BCF differed in different tissues for DDT and its metabolites, and the highest BCF were found for p,p -DDT (Fig. 3). High BCF for p,p -DDT and the higher relative distribution of p,p -DDT in plant tissues than that in soil indicated the selective accumulation of p,p -DDT in tea plants. As Table 2 showed, close correlations were only found between soil and root for most of the DDTs and its metabolites (Table 2), and the measured BCFs were 10.5, 3.0, 2.5, 1.1, 2.2, 1.2 for p,p -DDT, p,p -DDE, p,p -DDD, o,p -DDT, o,p -DDD and o,p -DDE respectively (Fig. 3). As mentioned above, Kow might be employed to estimate the accumulation of DDTs in roots. According to the log Kow values (US DHHS, 2003), the tendency should be p,p -DDT > o,p -DDT > p,p -DDE > p,p DDD ≈ o,p -DDE > o,p -DDD. However, the BCFs in root were not exactly consistent with the Kow , and it may also be attributed to the complex conditions in soils as mentioned above (Riederer, 2005). Vapor pressure could be employed to explain the relative content in the plant’s aerial tissues (Pereira et al., 2006, 2008). Vapor pressure of o,p -DDT and p,p -DDT is much lower compared to other DDTs, and so it is unlikely that tea plant’s aerial tissues absorb more o,p -DDT and p,p -DDT than other DDTs. The significantly higher p,p -DDT in aerial tissues, especially those in the young branches and leaves than those in soils might be attributed to the direct input of non-degraded DDTs into the aerial tissues. DDT/(DDD + DDE) ratio can be used to establish whether input occurred recently or in the past and whether degradation is significant or not. DDT/(DDD + DDE) ratio in contaminated soils after a long time of weathering is lower than 1 (Hitch and Day, 1992). The ratios in the present study ranged from 1.8 ± 1.7 in soils to 21 ± 34 in the roots, which were in the range of those reported in the agricultural soils in China (Chen et al., 2005; Yang et al., 2012), but much higher than those reported in the soils of USA (Pereira et al., 1996). The ratios in the soils in the present study indicated the new input of DDTs in the tea gardens. The ratios in the plant tissues were significantly higher than those in soils, which implied the selective accumulation of the DDTs, as shown in Fig. 3. o,p -DDT/p,p -DDT ratio is about 0.175 in the technical DDT and about 7 in dicofol (Qiu et al., 2005), and it can be employed to estimate the input of dicofol in the environment. The ratios in the present study ranged from 0.75 ± 0.71 in roots to 3.8 ± 1.1 in soils (Table 3), higher than those in technical DDT but lower than those in dicofol. The results implied the input of dicofol in the tea gardens. The pesticides used in the tea gardens were analyzed and the concentrations were 7.3–20.5 g ml−1 for o,p -DDT and 2.8–5.3 g ml−1 for p,p -DDT.
4. Conclusions Tea plants can accumulate HCHs and DDTs, with the selective accumulation of ␣-HCH, ␦-HCH and p,p -DDT in roots. Higher
concentrations of HCHs in the tea plant tissues, especially ␥-HCH in the old leaves than those in soils, and the lower ratios of ␣-/␥HCH implied the possible source and process of HCHs in tea plants. Pesticides containing lindane in tea garden were adsorbed on the plant aerial tissues, and some of the ␥-HCH came into the soils and then absorbed by the roots. Higher DDTs concentrations, especially p,p -DDT and o,p -DDT in plant tissues than those in soils, and the high ratios of DDT/(DDD + DDE) and o,p -DDT/p,p -DDT indicated the fresh input of DDTs and dicofol in pesticides in tea gardens. The correlation of HCHs and DDTs concentration between soils and plant tissues suggested that most of the plant HCH concentrations highly depended on soil HCH concentration, and soil HCHs tended to accumulate in all the plant tissues. However, only root DDT concentrations depended on soil DDT concentration. The results implied that the process of root uptake and subsequent translocation to the aerial plant tissues could not be discarded.
Acknowledgments This work was funded by the National Natural Science Foundation of China (40971260, 41173090) and the Program for New Century Excellent Talents in Fujian Province University (JA12087).
References Bacci, E., Calamari, D., Gaggi, G., Vighi, M., 1990. Bioconcentration of organic chemical vapors in plant leaves: experimental measurement and correlation. Environ. Sci. Technol. 24, 885–889. Barber, J.L., Thomas, G.O., Kerstiens, G., Jones, K.C., 2004. Current issues and uncertainties in the measurement and modelling of air–vegetation exchange and within-plant processing of POPs. Environ. Pollut. 128, 99–138. Chen, L.G., Ran, Y., Xing, B.S., Mai, B.X., He, J.H., Wei, X.G., Fu, J.M., Sheng, G.Y., 2005. Contents and sources of polycyclic aromatic hydrocarbons and organochlorine pesticides in vegetable soils of Guangzhou, China. Chemosphere 60, 879–890. Chen, Z.M., Wan, H.B., 1997. Degradation of pesticides on plant surface and its prediction – a case study on tea plant. Environ. Monit. Assess 44, 301–313. Dietz, A.C., Schnoor, J.L., 2001. Advances in phytoremediation. Environ. Health Perspect. 109, 163–167. European Tea Committee, 2005. Code of Practice-Pesticide Residues in Tea. Hamburg, Germany. Gong, X.Y., Qi, S.H., Wang, Y.X., Julia, E.B., Lv, C.L., 2007. Historical contamination and sources of organochlorine pesticides in sediment cores from Quanzhou Bay, Southeast China. Mar. Pollut. Bull. 54, 1434–1440. Hitch, R.K., Day, H.P., 1992. Unusual persistence of DDT in some western USA soils. Bull. Environ. Contam. Toxicol. 48, 264–295. Hu, B.Z., Song, W.H., Xie, L.P., Shao, T.F., 2008. Determination of 33 pesticides in tea using accelerated solvent extraction/gel permeation chromatography and solid phase extraction/gas chromatography–mass spectrometry. Chin. J. Chromatogr. 26, 22–28. Iwata, H., Tanabe, S., Ueda, K., Tatsukawa, R., 1995. Persistent organochlorine residues in air, water, sediments, and soils from the Lake Baikal Region, Russia. Environ. Sci. Technol. 29, 792–801. Li, J., Zhang, G., Qi, S.H., Li, X.D., Peng, X.Z., 2006. Concentrations, enantiomeric compositions, and sources of HCH, DDT and chlordane in soils from the Pearl River Delta, South China. Sci. Total Environ. 372, 215–224. McLachlan, M.S., 1999. Framework for the interpretation of measurements of SOCs in plants. Environ. Sci. Technol. 33, 1799–1804. Mikes, O., Cupr, P., Trapp, S., Klanova, J., 2009. Uptake of polychlorinated biphenyls and organochlorine pesticides from soil and air into radishes (Raphanus sativus). Environ. Pollut. 157, 488–496. Nakata, H., Kawazoe, M., Arizono, K., Abe, S., Kitano, T., Shimada, H., Li, W., Ding, X., 2002. Organochlorine pesticides and polychlorinated biphenyl residues in foodstuffs and human tissues from China: status of contamination, historical trend, and human dietary exposure. Arch. Environ. Contam. Toxicol. 43, 473–480.
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Z. Yi et al. / Agriculture, Ecosystems and Environment 171 (2013) 19–24
Pereira, R.C., Camps-Arbestain, M., Garrido, B.R., Macias, F., Monterroso, C., 2006. Behaviour of ␣-, -, ␥-, and ␦-hexachlorocyclohexane in the soil–plant system of a contaminated site. Environ. Pollut. 144, 210–217. Pereira, R.C., Monterroso, C., Macias, F., Camps-Arbestain, M., 2008. Distribution pathways of hexachlorocyclohexane isomers in a soil–plant–air system. A case study with Cynara scolymus L. and Erica sp. plants grown in a contaminated site. Environ. Pollut. 155, 350–358. Pereira, W.E., Domagalski, J.L., Hostettler, F.D., 1996. Occurrence and accumulation of pesticides and organic contaminants in river sediment, water and clam tissues from the san Joaquin River and tributaries, California. Environ. Toxicol. Chem. 15, 172–180. Qiu, X.H., Zhu, T., Yao, B., Hu, J.X., Hu, S.W., 2005. Contribution of dicofol to the current DDT pollution in China. Environ. Sci. Technol. 39, 4385–4390. Riederer, M., 2005. Uptake and transport of xenobiotics. In: Hock, B., Elstner, E.F. (Eds.), Plant Toxicology. Marcel Dekker, New York, pp. 131–150. Simonich, S.L., Hites, R.A., 1994. Vegetation–atmosphere partitioning of polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 28, 939–943. Simonich, S.L., Hites, R.A., 1995a. Global distribution of persistent organochlorine compounds. Science 269, 1851–1854.
Simonich, S.L., Hites, R.A., 1995b. Organic pollutant accumulation in vegetation. Environ. Sci. Technol. 29, 2905–2914. Sojinu, O.S., Wang, J.Z., Sonibare, O.S., Zeng, E.Y., 2012. Assessment of organochlorine pesticides residues in higher plants from oil exploration areas of Niger Delta, Nigeria. Sci. Total Environ. 433, 169–177. U.S. Department of Health and Human Services, 2003. Toxicological profile for DDT, DDE and DDD. Atlanta, Georgia. Wang, T.Y., Lu, Y.L., Zhang, H., Shi, Y.J., 2005. Contamination of persistent organic pollutants (POPs) and relevant management in China. Environ. Int. 31, 813–821. Willett, K.L., Ulrich, E.M., Hites, R.A., 1998. Differential toxicity and environmental fates of hexachlorocyclohexane isomers. Environ. Sci. Technol. 32, 2197–2207. Yang, D., Qi, S.H., Zhang, J.Q., Tan, L.Z., Zhang, J.P., Zhang, Y., Xu, F., Xing, X.L., Hu, Y., Chen, W., Yang, J.H., Xu, M.H., 2012. Residues of organochlorine pesticides (OCPs) in agricultural soils of Zhangzhou city, China. Pedosphere 22, 178– 189. Zhang, A.P., Liu, W.P., Yuan, H.J., Zhou, S.S., Su, Y.S., Li, Y.F., 2011. Spatial distribution of hexachlorocyclohexanes in agricultural soils in Zhejiang province, China, and correlations with elevation and temperature. Environ. Sci. Technol. 45, 6303–6308.