Published online 9 January 2007
Published in J Environ Qual 36:272-279 (2007)
DOI: 10.2134/jeq2006.0053
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORTS
Organic Compounds in the Environment
Accidental Organochlorine Pesticide Contamination of Soil in Porriño, Spain
F. A. Vega,
E. F. Covelo and
M. L. Andrade*
Dep. de Biología Vegetal y Ciencia del Suelo, Univ. de Vigo, Lagoas, Marcosende, 36310 Vigo, España
* Corresponding author (mandrade{at}uvigo.es)
Received for publication February 7, 2006.
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ABSTRACT
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In the 1960s at Porriño, Spain, soil from a pesticide factory dump was placed in an uncontrolled land infill during demolition. Since then, organochlorine pesticides have degraded and migrated from their original location. Concentrations of lindane, DDT, dicofol, and related side products or degradation products were determined at depths of 0 to 20, 20 to 60 and 60 to 100 cm along a 300-m transect running between the land infill and a nearby river. Depthwise nonmonotonicities (lowest concentrations of DDT and dicofol were found in the 20- to 60-cm layer) were attributed to the occurrence of several successive spill episodes; in general, concentrations were highest or near-highest in the 0- to 20-cm layer. At the dump site, the analyte contents of the 0- to 20-cm layer were as follows: 
-hexachlorocyclohexane (-HCH), 25 mg kg–1; ß-HCH, 15 mg kg–1; 
-HCH (lindane), 1.3 mg kg–1; 
-HCH, 0.5 mg kg–1; DDT, 2.5 mg kg–1; dicofol, 0.05 mg kg–1; DDD + DDE, 2.2 mg kg–1. The -HCH/-HCH ratio was higher than in commercial products, and the DDT/(DDD + DDE) ratio lower, suggesting the degradation of lindane and DDT with time. In general, the concentrations of HCH isomers, DDT, and dicofol fell with increasing distance from the dump site; in particular, the rapid fall in HCH concentrations illustrates the marked immobility of these species in the soil. By contrast, the combined concentration of the DDT degradation products DDD and DDE rose with distance from the dump site, which is attributed to their higher mobility.
Abbreviations: CECe, effective cation exchange capacity • PCA, principal components analysis
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INTRODUCTION
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THE organochlorine insecticides put on the market in the 1940s and 50s, notably DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and lindane (-1,2,3,4,5,6-hexachlorocyclohexane,-HCH), initially played important roles in the control of pests and disease vectors (WHO, 1990). By the 1960s, however, evidence was beginning to accumulate regarding their undesirable side effects. It is now well established that these liposoluble compounds, which are readily absorbed by and toxic to fish and mammals as well as insects, accumulate in organisms undergoing repeated or chronic exposure and are passed up the food chain to higher animals (including human beings), in which their toxic actions include the disruption of hormone systems and alteration of the central nervous system (Jones and de Voogt, 1999; Miglioranza et al., 1999; Plimmer, 2001; Zhu et al., 2005; Gaw et al., 2006).
Organochlorine pesticides not only accumulate in animal tissues: many are extremely stable and persist in the soil and in plants, and if soluble enough can also reach groundwater or surface waters (Ritter, 1990). They can therefore enter the food chain not only via their target organisms, but also via imbibed water and via plants eaten by herbivores, including cattle (WHO, 1990). Their persistence in soils depends both on the nature of the soil and their own physicochemical properties. Whereas light soils facilitate the water-borne transport of soluble pesticides (Walker et al., 1999), soils with high clay and organic matter contents tend to retain both the more soluble pesticides (because of their high water storage capacity) and the more hydrophobic pesticides (because of their high specific surface area and other sorption-favoring properties) (Letey and Farmer, 1974; Weed and Weber, 1974; Chassin and Calvet, 1984).
Because of the dangers they pose to non-target organisms, DDT and a number of other organochlorine pesticides were banned in most countries in the 1970s and 1980s, at least for agricultural use. However, because of their resistance to degradation processes and immobility, many are still found in high concentrations in soils to which they were formerly applied, where they constitute a reservoir capable of ongoing contamination of waters, wildlife, and crops (Harner et al., 1999; Gong et al., 2004; Andrade et al., 2005; Zhu et al., 2005; Wang et al., 2006). The transnational nature of these problems eventually led to the Stockholm Convention on Persistent Organic Pollutants of 2001, the signatories of which undertook to ban a number of organochlorine pesticides and limit the uses of others, including DDT.
At a small chemical plant near the town of Porriño in Galicia (northwest Spain; see Fig. 1), production of DDT began in 1942 and production of lindane in the mid 1950s. Following the closure of the plant in the mid 1960s, land leveling for the extension of the industrial area and the construction of a small adjacent housing estate included infill operations using demolition rubble and soil from the old factory site, including soil from areas that had been used to dump excess HCH isomers and possibly other products. Years later, a study to delimit the polluted zone detected high levels of HCH isomers in soil and springs in an area of 136000 m2 around an area of 41000 m2 identified as the main recipient of polluted infill (Crespo et al., 2001). However, products other than HCH were not considered; the depthwise distribution of HCH was only determined at the spill site, where greatest pollution was found in the top meter; and there was no specific investigation of whether HCH was leaching into the River Louro, 300 m from the main spill site, which other studies had shown to contain high HCH levels (Xunta de Galicia, 2000). In this study, we evaluated if organochlorine pesticides were migrating toward the River Louro. We determined the concentrations of four HCH isomers (, ß, , and ), dicofol, DDT, and the DDT degradation products DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] and DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] in the 0- to 20-, 20- to 60- and 60- to 100-cm soil layers along a transect running between the main spill site and the Louro River.
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MATERIALS AND METHODS
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Samples were taken at seven points located at intervals of 50 m on a transect with a 5% downward slope between the main spill site and the River Louro (Fig. 1). The whole transect is contained within the 136 000 m2 area identified as polluted by Crespo et al. (2001). At each sampling point, five samples were taken with an Eijkelkamp Mod.04.20.SA sampler from each of three soil layers: 0 to 20 cm, 20 to 60 cm and 60 to 100 cm. The samples were introduced in glass flasks and were transported to the laboratory in darkness at 4°C. In the laboratory they were air-dried and passed through a 2-mm mesh sieve, and the five samples from each combination of site and depth were pooled and homogenized in a Fritsch Laborette 27 vibratory homogenizer. All analyses were performed on five subsamples of the pooled sample for each site and depth.
Soil pH was measured using a soil/water ratio of 1:2 and an equilibration period of 10 min (Guitián and Carballas, 1976). Particle size distribution was determined following oxidation of organic matter with hydrogen peroxide; the fraction >50 µm was removed by sieving, and the sub-50-µm fraction was fractionated using the international method (Day, 1965). Organic carbon content was determined as per Walkley and Black (1934). Cation exchange capacity (CEC) and exchangeable cation content were determined as per Hendershot and Duquette (1986). Aluminum, Ca, K, Mg, and Na were extracted with 0.1 M BaCl2 and determined by inductively coupled plasma optical emission spectrometry on a PerkinElmer Optima 4300 DV apparatus.
-, ß-, - and -HCH, dicofol, DDT, DDD, and DDE were determined in accordance with USEPA protocol 8081A (USEPA, 1996). Soil samples (20 g) were extracted three times with 50 mL of 1:1 hexane/acetone using ultrasound, and to remove interferences the pooled extracts were concentrated, washed, and purified by gel permeation chromatography using toluene as eluent (DFG Pesticide Commission, 1987). The purified extract was analyzed by gas chromatography on a Thermo Electron TRACE 2000 apparatus with a POLARIS-Q ion trap mass detector, using splitless injection (275°C, 1 min) and helium as carrier gas (1.5 mL min–1). The typical limit of quantification under these conditions was 0.1 µg kg–1.
The statistical significance of differences among group means was estimated by analysis of variance (ANOVA) with subsequent least significant difference (LSD) tests. Pesticide contents were related to soil properties by correlation analyses, regression analyses, and principal components analysis (PCA) (Neter et al., 1996). All statistical analyses were performed using SPSS version 14.0 for Windows (Norussis, 1992).
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RESULTS AND DISCUSSION
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At the dump site and 50 m along the transect (sample point DS-50), organic matter content increased with depth (Table 1). At the other sample points organic matter content was greatest in the surface layer, but was slightly greater at 60 to 100 cm than at 20 to 60 cm. This pattern, like with other irregularities in the data of Table 1, is consistent with sample points DS-0 and DS-50 lying within the area where infilling is known to have taken place, and is suggestive of successive spills and infills with different materials.
In the 0- to 20-cm layer, the concentration of -HCH fell from about 1.3 mg kg–1 at the spill site to about 0.2 mg kg–1 beside the river (Fig. 2). Similarly, -HCH content fell from 25 to 2.5 mg kg–1, ß-HCH content from 15 to 5 mg kg–1, and -HCH content from 0.5 to 0.2 mg kg–1. The concentration of each isomer in the 20- to 60-cm layer was generally quite similar to its concentration in the 60- to 100-cm layer and appreciably lower than its concentration in the 0- to 20-cm layer, with a similar but less pronounced dependence on distance from the spill site. The exception was the -HCH content of the 60- to 100-cm layer at the spill site, which was the same as the content of the 0- to 20-cm layer. In no sample was the concentration of any isomer less than about five times the official Spanish threshold, 0.01 mg kg–1 for each isomer (BOE, 2005).
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Fig. 2. Concentrations of HCH isomers in the 0- to 20-, 20- to 60-, and 60- to 100-cm layers along the transect.
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The HCH-based pesticide produced at the old factory had a -HCH content of 13%, and a combined -, ß-, and -HCH content of 67%. These figures are compatible with reports that the /-HCH ratio in commercial lindane ranges from 4 to 7 (Kim et al., 2002; Zhang et al., 2005). The finding that the soil samples analyzed in this study had /-HCH ratios of between 8 (for the 20- to 60-cm layer beside the river) and 43 (for the same layer at the spill point) (Fig. 3) therefore suggests that the -HCH of dumped commercial lindane has undergone degradation to -HCH (and maybe other isomers also), and that -HCH was more mobile than -HCH along the transect.
Like the HCH concentrations, the concentrations of DDT and dicofol fell with distance from the spill site. In the 0- to 20-cm layer, for example, DDT content fell from 2.5 mg kg–1 at the spill site to 0.5 mg kg–1 beside the river, while dicofol content fell from 0.05 to 0.04 mg kg–1 (Fig. 4). However, unlike the HCH isomers, both these pesticides had roughly the same concentrations in the 60- to 100-cm layer as in the 0- to 20-cm layer, with lower concentrations in the 20- to 60-cm layer (practically zero in the case of DDT), which is suggestive of the use of successive spills with different pollution levels at the spill site. The official Spanish threshold for DDT in soil is 0.2 mg kg–1 (BOE, 2005).
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Fig. 4. Concentrations of (a) DDT and DDD + DDE and of (b) dicofol in the 0- to 20-, 20- to 60-, and 60- to 100-cm layers along the transect.
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The DDT degradation products DDD and DDE behaved similarly to HCH in that their combined concentration was at all sampling points considerably higher in the 0- to 20-cm layer than in the 20- to 60- and 60- to 100-cm layers (it was also consistently somewhat higher in the 60- to 100-cm layer than in the 20- to 60-cm layer); see Fig. 4. In the 0- to 20-cm layer, DDD concentration always exceeded the official Spanish threshold of 0.7 mg kg–1 (BOE, 2005). However, as DDT concentration fell with increasing distance from the spill site, DDD + DDE concentration rose, from 2.2 to about 2.8 mg kg–1 in the 0- to 20-cm layer and slightly more gradually in the other layers. These trends suggest that DDD and DDE were more mobile than DDT along the transect.
The DDT/(DDD + DDE) ratio, which is generally about 16 in commercial grade DDT (WHO, 1989), varied in the 60- to 100-cm layer from about 1 (beside the river) to 6.6 (at the spill site), and in the other layers never exceeded 1.2 (Fig. 3); even taking mobility differences into account, this suggests the degradation of DDT to DDD and DDE following dumping.
The above trends are nicely brought out by the results of principal components analysis of data for the total HCH concentration and the concentrations of DDT, DDD, DDE, and dicofol (Table 2). In the plane of the first two components (which together accounted for 87.5% of the total variance), the samples are neatly separated by layer, and as distance from the spill point increases in each layer group the value of Component 1 falls and that of Component 2 rises, except for the minor transposition of DS-50 and DS-100 (Fig. 5). Component 1 clearly represents overall pollution level, with greatest weight given to DDT, DDD, and HCH, while Component 2 reflects the balance between more mobile and less mobile pesticides. Component 1 was found to correlate with organic matter content (r = 0.46, P < 0.05), which may be due partly to the influence of distance from the spill point on pesticide levels coinciding with a natural organic matter gradient outside the spill area, and partly to high DDT content coinciding with high organic matter content in the deepest spill layer at the spill point. Component 2 correlated with soil pH (r = –0.76, P < 0.01), probably again due to coincidence: pH is high at the more disturbed spill site and lower in the more organic soil near the river (at least in the 0- to 20-cm layer), and this difference parallels the change in the balance between more mobile and less mobile pesticides (Table 3).
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Fig. 5. Soil samples plotted on the plane of the first two components extracted by principal components analysis of the data for the total HCH concentration and the concentrations of DDT, DDD, DDE, and dicofol.
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CONCLUSIONS
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The obtained results show clear evidence of organochlorine waste pollution in studied soils. Spanish official thresholds for pesticide levels in soil were exceeded by HCH isomers in all the soil samples taken in this study; by DDT in all 0- to 20- and 60- to 100-cm samples; and by DDD in all 0- to 20-cm samples. Irregularities in the horizontal or vertical distributions of organic matter, DDT, and dicofol suggest the occurrence of several successive spill episodes. The -HCH/-HCH ratio was higher than in commercial products, and the DDT/(DDD + DDE) ratio lower, suggesting the degradation of lindane and DDT with time. In general, the concentrations of HCH isomers, DDT, and dicofol fell with increasing distance from the dump site; in particular, the rapid fall in HCH concentrations illustrates the marked immobility of these species in the soil. By contrast, the combined concentration of the DDT degradation products DDD and DDE rose with distance from the dump site, which is attributed to their higher mobility. The presence of pollutants throughout the top meter of soil along the whole length of the transect confirms that this site must pollute the River Louro.
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ABSTRACT
INTRODUCTION
