organochlorine pesticides in soils from the middle and lower sinú river basin (córdoba, colombia)

Organochlorine Pesticides in Soils from theMiddle and LowerSinú River Basin (Córdoba, Colombia)

José Luis Marrugo-Negrete &

Amado Enrique Navarro-Frómeta &

Iván D. Urango-Cardenas

Received: 15 February 2014 /Accepted: 25 June 2014 /Published online: 15 July 2014# Springer International Publishing Switzerland 2014

Abstract After decades of intensive application to thecroplands of the lower and middle Sinú River valleys inCórdoba Department, an area of important agriculturalactivity, organochlorine pesticides (OCPs) were official-ly banned from agricultural use in Colombia in the1990s. Until now, no studies of the OCP residue levelsand their vertical distributions in the soils of this areahad been conducted. In the present study, 83 represen-tative topsoil samples (0–20-cm depth) and four soilcores were collected. The OCP concentrations werequantified via gas chromatographywith electron capturedetection. The resulting data indicate that the principalpesticide residues in the soil samples from both themiddle and lower Sinú River basin were 4,4′-DDT(1.78±4.99 μg kg−1), 4,4′-DDD (3.55±8.27 μg kg−1),α-chlordane (80.0±200.0 μg kg−1), and lindane (280±870.0 μg kg−1), which accounted for approximately80% of the total residues detected in both regions. Otherpesticide residues, such as β-BCH and β-endosulfan

(0.11±0.4 and 2.91±20 μg kg−1, respectively), werealso detected. The presence of these organochloridepesticides could be attributed to past agricultural appli-cations and/or the adulteration of pesticides that are notbanned. Soil profiles from almost all sampled sitesindicate that organochlorine residues remain in surfacelayers. Because these compounds are highly toxic, per-sist in the environment, and are strongly enrichedthrough the food chain, these results indicate a substan-tial environmental risk from organochlorine pesticidesin the study area.

Keywords Soil contamination . Organochlorinepesticides . Agricultural soil . Colombia

1 Introduction

Because they are widely used in agriculture, publichealth vector control, and domestic and commercial pestcontrol, soil pesticides remain the most studied environ-mental contaminant. Despite a widespread ban in the1980s and 90s, organochlorine pesticides (OCPs) re-main a subject of interest for policy makers, researchers,and the general population due to the ubiquity, lowbiodegradability—thus, persistence in the environ-ment—and toxic effects of OCPs on animals andhumans (DTSC et al. 2010). These compounds mayaffect normal endocrine function and have been linkedto human breast and liver cancers, testicular tumors, andreduced sperm counts in humans (Cocco et al. 1997).Children are the group most sensitive to OCPs,

Water Air Soil Pollut (2014) 225:2053DOI 10.1007/s11270-014-2053-3

J. L. Marrugo-Negrete (*) : I. D. Urango-CardenasWater, Applied and Environmental Chemistry Group,Laboratory Toxicology and Environmental Management,University of Córdoba,Cra 6 # 76-103, 354 Montería, Colombiae-mail: [email protected]

I. D. Urango-Cardenase-mail: [email protected]

A. E. Navarro-FrómetaTechnological University of Izúcar de Matamoros,Prolongación Reforma # 168, Barrio Santiago Mihuacán,Izúcar de Matamoros, 74420 Puebla, Mexicoe-mail: [email protected]

especially in rural areas, where children may uninten-tionally ingest OCPs (Hong et al. 2011; Tao et al. 2011).DDT (dichlorodiphenyltrichloroethane) has been shownto have estrogen-like and possible carcinogenic activityin humans (Malik et al. 2009). In some developingcountries, OCPs are still used in agriculture becausethey have high potencies/efficacies and lower costscompared to alternative pesticides (Kumar et al. 2011;Aiyesanmi and Idowu 2012).

Soil serves as a reservoir for persistent organic pol-lutants and plays an important role in their global distri-bution (Meijer et al. 2003; Kookana 2009). Due to theirsemi-volatile character, OCPs can be re-emitted fromsoils and transported over long trans-boundary distancesvia air and ocean currents. These dangerous chemicalshave been detected in the Antarctic and other areas farfrom their sites of use (Bouwman 2004; Ssebugere et al.2010; Tao et al. 2011; Becker et al. 2012; Yang et al.2012). Thus, OCP use remains a global concern. TheOCP concentrations in surface soils are measured toestimate the burden of these pollutants in the soil. Thus,most research has been conducted using surface-layersoil samples (Wang et al. 2007b; Li et al. 2008; Zhanget al. 2009). However, OCPs transfer from soil surfacelayers to the underlying layers, and their downwardmigration may impact their volatilization rates fromsurface soil and impose potential risks for shallowgroundwater (Zhang et al. 2007; Weaver et al. 2012).The depth distributions of POPs (persistent organic pol-lutants) have been used to identify the transformationprocesses of these chemicals after deposition/application onto the soil surfaces (Krauss et al. 2000;Zhang et al. 2009).

In Colombia, large quantities of OCPs have beenused to control pests and thus improved crop yieldsduring the 1940s. Included in the group of OCP-pesticides were DDT, HCH, heptachlor, aldrin, dieldrin,and endrin, among which DDTand HCH were the mostextensively used. Although their use has beendiscontinued in Colombia in the 1990s because of theirpersistence in the environment, concentrations of OCPscan still be detected in various environmental matrices(Betancourt and Ramírez-Triana 2005).

Sinú Valley soils are primarily used for agriculture,and the main crops are cotton, corn, rice, and cassava.Therefore, pesticides are frequently applied to thesesoils, with little or no oversight in many cases. Theagricultural areas of the Sinú Valley are located inColombia’s Córdoba Department in which an

approximate area of 547.57 km2 is used for maize,227.37 km2 is used for cotton, and 95.80 ha is used forrice. Although regional surveys continue to monitorOCP residues in water and sediments (Marrugo 2005;Marrugo et al. 2008), few studies have documented thesoil concentrations and spatial patterns that havedeveloped.

The objectives of the present study are as follows: (1)to measure the concentrations of OCPs in soils of themiddle and lower Sinú River, Córdoba, Colombia, anddetermine how these OCP concentrations are related tophysicochemical characteristics of the soil (as texture,pH, and CEC) and (2) to investigate the levels anddistribution patterns of organochlorides in four typicalsoil profiles from the studied region. The results provideimportant information on the current contamination sta-tus in these regions and point out to the need of urgentactions to evaluate the long-term toxicity of such per-sistent compounds and a suitable strategy to improvethese areas.

2 Materials and Methods

2.1 Study Area

The Sinú River basin is located in northwest Colombia,South America, more specifically within the depart-ments of Córdoba and Antioquia in the southwesternregion of the Colombian Caribbean coast. The SinúRiver basin originates in the Paramillo massif locatedbetween 7° 8′ 9″–9° 27′ 2″ N and 75° 55′ 31″–75° 58′18″ W. The Sinú River is the primary water system inthe department of Córdoba, and its valley is home tointense agricultural and livestock activities (Feria et al.2010). Due to the annual flooding of the Sinú River, theSinú Valley has some of the most fertile soil in Colom-bia. Rainfall in this area is highly seasonal, with a dryperiod between January and March, a rainy seasonbetween April and December, and a short dry periodaround June. An average of 1,100 to 2,000 millimeters(mm) of rain falls in this region per year, with thesouthern parts of the valley being wetter than those inthe north. The average annual temperature is between 26and 30 °C (Ruiz et al. 2008).

The valley of the Middle Sinú covers an area of5.178 km2 and contains the municipalities of Monteria,Cereté, San Pelayo, Ciénaga de Oro, and San Carlos.Most of this subregion is composed of alluvial plains

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derived from the dynamics of the Sinú River. In general,the soils are deep or very deep with moderate to highfertility and are suitable for temporary or permanentcrops such as cotton, rice, maize, cassava, beans, andpasture.

The lower Sinú valley covers an area of 1,752 km2

and contains the municipalities of Cotorra, Chima,Momil, Lorica and Purísima. Soils are composed ofrecent alluvial deposits with moderate fertility and areused for agriculture and livestock. In this region, landuse is divided as follows: 70 % is used for livestock,23 % consists of a lagoon complex, and the remaining7 % is dedicated to agriculture (crops such as cotton,corn, and rice) (Viloria 2004).

2.2 Soil Sampling

Two sampling campaigns were performed in 2009, onein January (the dry season) in which soil samples werecollected from agricultural areas along the right marginof the Sinú River: 44 and 39 samples from the lower andmid Sinú, respectively (Fig. 1). The second campaignoccurred during the dry–wet transition season (April).Four soil profiles were selected from areas containingthe highest concentrations of pesticides measured dur-ing the first sampling campaign (two in both studyareas).

Each sample contained a mixture of five subsamplescollected from five areas of approximately 10×10 m2.All soil subsamples were collected from a depth of 0–20 cm using a stainless steel shovel. Grass and othersundries were removed from the surface of each samplelocation prior to sample collection. Soil cores wereobtained from the surface downward; samples werecollected from 0 to 5, 5 to 10, 10 to 20, and 20 to30 cm. The soil samples were air dried at room temper-ature (25–28 °C) for approximately 10 days, sieved to<2 mm, and stored at 4 °C in pre-cleaned glass jars untilanalyzed for pesticides. The principal soil characteris-tics, including pH, soil organic content, cation exchangecapacity (CEC), and texture, were determined.

2.3 Soil Extraction and Cleanup

Soils were extracted according to the procedure describedin the US EPA manual, “Analysis of Pesticide Residuesin Human and Environmental Samples” (EPA 1980).

Approximately 5 g of soil (dry weight) was placed ina pre-extracted Soxhlet thimble. The thimble was placed

in a Soxhlet apparatus, and the sample was extracted for8 h with a mixture of hexane and acetone (1:1 v/v). Theacetone-hexane extract was placed in a separatory fun-nel, and 150 mL of distilled deionized water was added.The lipid-soluble material remained in the hexane layer.After washing the hexane layer several times with water,the acetone–water extracts were discarded, and the hex-ane extract was dried over anhydrous sodium sulfate for2 h. The extract was concentrated to approximately5 mL using rotary evaporation and was transferred to aFlorisil column, which had been pre-rinsed with 50 mLof n-hexane (the Florisil had been activated at 130 °C for24 h). The column was then eluted with a 4:96 v/v ether/hexane mixture. This mixture was used to collect thefirst fraction, which contained most of the organochlo-rine pesticides (Aldrin, heptachlor, heptachlor epoxide,α-BHC, lindane, β-BHC, 4,4′-DDD, 4,4′-DDT, γ-chlordane, and α-chlordane). Fraction two was obtainedusing ether/hexane (15:85 v/v), and this fractioncontained oxygenated organochlorine pesticides (δ-BHC, endrin, α-endosulfan, and β-endosulfan). Thevolume of each fraction was reduced to less than 5 mL(to concentrate the pesticides) and analyzed using gaschromatography with electron capture detection (GC-ECD).

2.4 Chromatographic Analysis

The samples were analyzed using a Perkin ElmerAutoSystem XL gas chromatograph equipped with anECD. Separation of the organochlorine compounds wasaccomplished using an Rtx®-5 fused silica capillarycolumn (30 m×0.25 mm (id)) with a liquid-phase thick-ness of 0.25 μm. The temperature regimen was asfollows: 100 °C for 2 min, 15 °C/min to 160 °C,160 °C for 6 min, 3 °C/min to 250 °C, and 250 °C for30 min. Helium was used as the carrier gas at a pressureof 12 psi. Nitrogen was used as the make-up gas for theelectron capture detector, and injections were made inthe splitless mode. The injector and detector tempera-tures were 200 and 300 °C, respectively. The OCPswere identified by matching their retention times tostandards and were quantified using peak areaintegration.

2.5 Quality Control

For quality assurance and control, procedural blanks andmatrices spiked with standard solutions were analyzed.

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Fig. 1 Study area and soil sampling locations in the middle and lower Sinú River basin


None of the target compounds were detected in theprocedural blanks. All solvents used were distilled inglass (PR grade) and were checked for interferences orcontamination prior to use. Table 1 presents the qualityassurance and control parameters for the OCP analysis.The OCPs were quantified by comparing the peak areasof the experimental solutions and the external standardsolutions (supplied by AccuStandard). The correlationcoefficients (r) for the OCP calibration curves were all>0.998. The method detection limits calculated as threestandard deviations of the mean from ten blank solutions(MDL) for the measured OCPs ranged from 0.01 to0.39 μg/kg. The spiked recoveries of the OCPs rangedfrom 79.8–94.3 %, and the relative standard deviations(RSD) ranged from 0.6–4.2 %. These parameters con-firmed the applicability of the analytical protocol usedherein for determining OCPs in soils.

2.6 Soil Characteristics

The soil texture was determined by measuring the pro-portions of clay, silt, and sand particles present in thesoil. These constituents were measured using the pipettemethod, and the soil type was classified using the soiltexture triangle. The soil pH was measured with a po-tentiometric glass electrode using a soil/water ratio of

1:2.5. The cation exchange capacity (CEC) of the min-eral soils was calculated as the sum of Ca + Mg + K +Na + Fe + Al +Mn extractable with 1M of NH4-acetate,and organic matter (% OM) was determined followingWalkley–Black method (Reeuwij 2002).

2.7 Statistical Analysis

For statistical analysis of the OCP soil concentrations,we determined their arithmetic means, and all valuesbelow the MDL (limits of detection) were set to zero forstatistical purposes. Because the data were non-normally distributed, non-parametric Mann–Whitneytests were used to identify the differences in OCP con-centrations between regions. The Spearman correlationcoefficients were obtained to determine if the correla-tions between the different OCPs were statistically sig-nificant. Principal component analysis was used to ex-plore the sources and fates of the OCPs. All statisticalanalyses were performed using Minitab 16.0.

3 Results and Discussion

Average values of soil physicochemical properties aresummarized in Table 2. Soil texture was generally sandyclay in the study area. Soil pH was predominately acidwith an average of 6.38, % OM (organic matter, per-centage) was relatively low and the CEC of the soil ismoderate, with an average of 26.2 meq/100 g.

The OCP residue levels in soil samples from the midand lower Sinú River valley are summarized in Table 3.Despite being eliminated from the market in theCórdoba department for more than two decades, organ-ochlorine pesticide residues were found in 35 % of the

Table 1 Detection limits and recoveries of this method

Organochloridepesticide

LDM(μg kg−1 d.w.)

Recovery(%)

RSD(%)

Aldrin 0.39 79.8 1.4

Heptachlor epoxide 0.09 89.8 2.6

α–BCH 0.16 94.3 0.9

β–BCH 0.05 92.8 2.1

δ–BCH 0.03 88.9 5.4

Lindane 0.01 86.5 3.4

Endrin 0.02 83.1 0.7

Heptachlor 0.03 87.7 0.7

4,4′-DDD 0.02 86.1 2.1

4,4′-DDT 0.08 91.2 0.3

α-Chlordane 0.01 83.8 0.6

γ–Chlordane 0.03 92.3 2.7

α-Endosulfan 0.01 86.9 3.0

β–Endosulfan 0.01 88.4 4.2

Endrin Aldehido 0.04 87.4 2.1

Table 2 Physical–chemical properties of soil from the mid andlower Sinú River valley

Variable Mean ± SD Min Max

MO (%) 1.86±0.64 0.17 3.55

CEC (meq/100 g suelo) 26.2±5.27 17.6 40.4

% Sand 55.0±13.3 32.0 86.0

% Clay 30.0±11.0 3.0 49.0

% Silt 15.0±7.83 4.0 49.0

pH 6.38±0.66 4.58 8.82


samples collected, which confirms the persistent char-acter of these molecules and their adsorption to soil,showing that a latent risk of exposure remains (Maliket al. 2009; Wang et al. 2007a).

The organochlorine most often detected in the soilsamples was α-chlordane, which was found in 25 % ofthe samples analyzed with concentrations ranging from30 to 1,120 μg kg−1 and a mean value of 240±280 μg kg−1. This pesticide was used extensively oncotton and rice crops in this area during the late 1970sand 80s and can persist in the soil for over 20 years.Chlordane adheres strongly to surface soil particles andis not likely to enter groundwater. Several studies havefound chlordane residues indicating that more 10 % ofthe initially applied quantity remains 10+years afterapplication. Concentrations of α-chlordane in the mid-dle and low Sinú valley (arithmetic average 80±208 μg kg−1) are significantly higher than those foundin agricultural soils from Shanghai, China (which con-tain from <0.02 to 1.86 μg kg−1 chlordane), in archivedsoil from the UK (which contains from <0.05 to 1.6 andfrom <0.07 to 1.0 μg kg−1 chlordane), and in soil fromthe USA (for which the mean concentration of chlor-dane is 0.49 and 0.43 μg kg−1) (Jiang et al. 2009).

Higher concentrations were found for lindane, whichwas detected in 15 % of sampling points with concen-trations ranging from 350.0 to 5600.0 μg kg−1 and amean value of 1850.0±1440.0 μg kg−1. Lindane con-centrations measured in agricultural soils in Northern

France ranged from 2–5 μg kg−1, with a mean value of0.83 μg kg−1 (Villanneau et al. 2009). In soils fromIndia, lindane was found at concentrations ranging from0.01–94.73 μg kg−1 in the Delhi region (Kumar et al.2011) and 0.098–1.945 mg kg−1 in two districts ofAssam (Mishra et al. 2012). Most of the samples ana-lyzed herein (Table 2) exhibited higher lindane valuesthan those obtained in highly contaminated soils such asthose from Tanjin, China (mean value of 9.3 μg kg−1)(Gong et al. 2004), Beijing, China (mean value of1.96 μg kg−1) (Li et al. 2006), and Bauru, Sao PauloBrazil (mean value of 0.15 μg kg−1) (Rissato et al.2006). Even higher values have been reported for theYaqui andMayo valleys inMéxico (mean value of 19.2,ranging from ND to 938.5 mg kg−1) (Cantu-Soto et al.2011) and in agricultural soils from Saudi Arabia(0.290–394 mg kg−1) (Al-Wabel et al. 2011). Table 4summarizes the concentrations of DDTs and HCHsmeasured in several locations.

In contrast, levels of heptachlor epoxide, heptachlor,endrin, and endrin aldehydo were below the detectionlimit (MDL). According to Cavanagh et al. (1999),organochlorine concentrations in soils from tropical re-gions were observed to be low due to rapid evaporationat the higher temperatures typical in these regions. Healso claimed that volatilization of persistent organiccompounds such as organochlorine occurs in climateof tropical regions. Hence, it is possible that the majorloss of many organochlorine pesticides used in Colom-bia occurs through volatilization

ΣDDT (sum of 4,4′-DDD and 4,4′-DDT) was detect-ed in 16 samples with 8 and 9 samples originating fromthe middle and lower Sinú, respectively. TheΣDDTsoilconcentrations ranged from <MDL to 62 μg kg−1 with amean value of 5.3±13.0 μg kg−1. The DDT levels in themiddle Sinú soils were higher than those in the lowerSinú soils due to the previous extensive application ofDDT on cotton crops. Cotton is one of the most impor-tant commercial crops grown in the middle Sinú; thus,the highest DDT concentration (62 μg kg−1) was foundin soil sampled from a cotton production area in themiddle Sinú. The DDT (mainly consisting of 2,4′-DDTand 4,4′-DDT) in the soil can easily be broken downinto DDE and DDD, thereby becoming more stable andpersistent compounds and therefore more abundant(Bossi et al. 1992; Thomas et al. 2008). The mean soilconcentrations of 4,4′-DDD were greater than those of4,4′-DDT. Various studies indicate that DDT is reduc-tively dechlorinated to DDD under reducing conditions

Table 3 Concentrations of organochlorine pesticides (μg kg−1) inthe studied soils

OCP Mean ± SD Min Max

α–BCH ND ND ND

β–BCH 0.113±0.44 ND 3.16

Lindane 280.0±870.0 ND 5600.0

δ–BCH ND ND ND

Endrin ND ND ND

Heptachlor ND ND ND

α-Chlordane 80.0±200.0 ND 1120.0

γ–Chlordane ND ND ND

β-Endosulfan 3.0±16.0 ND 103.0

Endrin Aldehyde ND ND ND

4,4′-DDD 3.55±8.27 ND 41

4,4′-DDT 1.78±4.99 ND 25

ΣDDT 5.33

ND not detected


(Loganathan and Lam 2011). Due to the annual floodingof the Sinú River, the soils in the Sinú valley are largelyanaerobic indicating that the sampling sites generallyexhibit reducing condition and that DDT is largelydegrading to DDD. DDD was also manufactured andused as an insecticide, but to a much lesser extent thanDDT (DDE concentrations were not determined, butlow DDE levels were expected due probably to thegreater volatility of DDE especially in tropical areas(Xu et al. 1994) and that under flooded (reducing)conditions, DDD is the more common degradationproduct of DDT than DDE). A small DDT:(DDE +DDD) ratio indicates aged (microbiologically degraded)DDT, while a value greater than 1.0 indicates that DDThas recently been applied, also the use of Dicofol, whereimpurities of DDTappear in the manufacturing process-es (10 % or more) could be other fresh DDT input. TheDDT/DDD ratios ranged from 0 to 0.8, implying theexistence of aged DDT in most of the soils sampledfrom the study area. This result was similar to thoseobtained in tropical regions (Rissato et al. 2006).

The total concentrations of endosulfan (as β-endosulfan mainly, probably because the α-isomer ismore volatile and dissipative, while the β-isomer isgenerally more adsorptive and persistent (Rice et al.2002; US EPA 2002)) in the soil samples analyzed inthe present study were between ND and 103.0 μg kg−1

with a mean value of 3.0±20.0μg kg−1. Endosulfan wasdetected in only a few soil samples (three samples).However, the concentrations measured were similar tothose found in Itirapina Sao Paulo, Brazil (where themean value was 2.48 μg kg−1) (Rissato et al. 2006),Shanghai, China (where the concentrations ranged from<0.018 to 3.68 μg kg−1) (Jiang et al. 2009), and Delhi,

India (where the concentrations ranged from <0.01 to7.57 μg kg−1) (Kumar et al. 2011). The concentrationsof endosulfan sulfate, a major degradation product ofendosulfan, were not determined in the soil samplesanalyzed; nevertheless, the low frequency of the detec-tion of endosulfan (α andβ) and the susceptibility of themetabolite to photolysis in natural tropical environmentsassume low levels of endosulfan sulfate. The technicaluse of endosulfan was restricted in many countriesbecause of its high toxicity. However, it was used oncotton and other crops in the studied region until 2001.

The lowest concentrations of organochlorines mea-sured in the soil samples from the middle and lower Sinúcorresponded to β-BCH, which had an average concen-tration of 0.11±0.43 μg kg−1. Greater values(~700 μg kg−1) were found in soil samples from agri-cultural lands in Mexico with low organic matter con-tents (Waliszewski and Infanzón 2003).

The results obtained herein suggest that the residuesof organochlorine pesticides used two decades ago stillexist in soils of the middle and low Sinú valley. Thepresence of these organochloride pesticides could beattributed to past agricultural applications and/or theadulteration of pesticides that are not banned and tothe fact that their degradation rates are slow.

Mann–Whitney tests indicated no significant “re-gional differences” in the organochlorine concentrations(between the middle and lower Sinú regions (p>0.05,Table 5)). The similar distributions of organochlorineresidue levels in these two regions indicate that theagricultural activities greatly influenced the initiationand use of pesticides in the two regions.

Table 6 lists the values of the Spearman correlationcoefficients between the organochlorines detected and

Table 4 Comparison of organochlorine concentrations (μg kg−1) in soil samples from numerous locations around the world

Locations Clima DDTs HCHs References

South California (USA) Mediterranean 0.11–44.8 <0.1–0.54 Kannan et al. 2003

Georgia (USA) Subtropical 0.34–33.6 <0.1–0.54 Kannan et al. 2003

Tanzania Tropical-temperate <0.1–97 <0.1–59 Kishimba et al. 2004

Shangai (China) Subtropical 18–142 <0.03–2.4 Nakata et al. 2005

Beijing (China) Temperate 0.77–2178 1.36–56.61 Zhu et al. 2005

São Paulo State (Brazil) Subtropical 0.12–11.01 0.05–0.92 Rissato et al. 2006

Tasman, Waikato, Auckland (New Zealand) Temperate 30–34500 – Gaw et al. 2006

Mexico Temperate ND–360 ND–0.14 Wong et al. 2010

ND not detected


the physical and chemical characteristics of the soilsfrom the two subregions considered in the present study.In the lower Sinú, the lindane and DDD levels signifi-cantly correlated with the OM (organic matter) (ρ=0.510 and ρ=0.491, respectively). (The rate at whichDDT is converted to DDD in flooded soils is dependenton the organic content of the soil (Racke et al. 1997)),while the α-chlordane significantly correlated with thepercentage of clay present (ρ=0.403). These resultsdemonstrate the affinity of these compounds for soilparticles (Edmunds 2007; Vig et al. 2001; Wang et al.2007a). The inverse correlation between α-chlordaneand the percentage of sand is also noteworthy and isconsistent with studies suggesting that the presence ofsand facilitates the volatilization of the pesticide(Bidleman and Leone 2004). Furthermore, a strongcorrelation exists between the pesticides α-chlordane,

DDT, and lindane in both areas, which may indicate theexcessive agricultural use of these pesticides decadesago in the study area, especially in transient crops. pHshowed no significant correlation with pesticidesevaluated.

Principal component analysis (PCA) was per-formed to reduce the set of original variables andto extract a small number of latent factors. In addi-tion, PCA could be used to determine the differentsources and degradation behaviors of environmentalOCPs.

The results (Fig. 2) indicate that the first two factorsaccounted for 54.97 % of the total variance in the dataset. Factor 1 accounted for 37.68 % of the total variance.Most of the 4,4′-DDD (0.940) and 4,4′-DDT (0.915)and more than half of the lindane (0.603) detected wereinvolved in factor 1. Therefore, this factor was primarilyrelated to the degradation of “old” DDT and the use ofDDT and lindane in rice and cotton cultivation, particu-larly in the lower Sinú. Factor 2 accounted for 17.29 %of the total variance. The absolute loading of β-BCH(0.754) was positive, while the absolute loading valuesfor α-chlordane and endosulfan were negative (−0.432and −0.450, respectively). These results indicate thatfactor 2 was likely related to the combined use of thesechemicals in insecticides, especially for rice crops, andto differences in the volatilization rates of Lindane andchlordane.

Table 5 Mann–Whitneytests for the two regions(middle and lower Sinú)

Difference is nosignificant at the0.05 level

OCP pollutants Mann–Whitneytest

DDT 0.852

DDD 0.892

β-BCH 0.615

α-Chlordane 0.203

α-Lindane 0.887

Endosulfan 0.621

Table 6 Correlations between the soil OCPs in the study area(s)

Variables MO CIC %A %Ar %L pH DDT DDD Lindane α-Chlordane β-BCH Endosulfan

Middle Sinú

DDT 0.310 −0.170 −0.193 0.133 0.009 −0.146 1

DDD 0.491 −0.149 −0.137 0.061 0.055 −0.209 0.821 1

α-Lindane 0.510 −0.331 −0.154 0.194 −0.115 0.036 0.447 0.664 1

α-Chlordane 0.376 −0.187 −0.439 0.407 −0.040 0.158 0.518 0.595 0.632 1

β-BCH −0.073 0.118 −0.064 0.153 −0.035 0.082 0.054 0.121 0.005 0.166 1

Endosulfan 0.065 −0.108 −0.188 0.217 0.000 0.260 −0.062 −0.082 0.367 0.264 0.367 1

Lower Sinú

DDT −0.101 0.069 0.061 −0.140 0.019 −0.167 1

DDD −0.186 −0.084 0.156 −0.239 −0.013 −0.176 0.880 1

α-Lindane −0.124 0.170 −0.003 −0.169 0.211 −0.146 0.541 0.553 1

α-Chlordane −0.123 0.118 0.093 −0.208 0.107 −0.168 0.676 0.704 0.737 1

β-BCH −0.061 −0.002 −0.034 −0.064 0.271 0.038 0.230 0.317 0.431 0.294 1

Endosulfan 0.058 0.158 −0.142 0.081 0.133 0.065 −0.094 −0.110 −0.086 −0.110 −0.078 1

Correlation is significant at the 0.05 level (two-tailed)


4 Vertical Distribution of OCPs

The concentration and distribution of organochlorines insoil profiles are subject to physical, chemical, and bio-logical processes such as biodegradation, chemical deg-radation, photolyzing, leaching, adsorption, and volatil-ization. Thus, the OCPs present in soil may transfer tolower horizons or may remain in the surface soil layers,both of which can cause long-term harm to ecosystemsand human health.

Figure 3 shows the vertical distribution oforganochlorides in the four sampling sites: S69, S71,S27, and S34, among which similar patterns were noted.The highest concentrations were found at the surface ornear the surface horizons and decreased with depth.Fluctuations were observed in the plow layers of somecultivated soils, which could have resulted from fre-quent agricultural activities and batch irrigation(Castaneda and Bhuiyan 1996; Miglioranza et al. 2003).

Organochlorine residues in the soil were slightlylower than those obtained in the first sampling, indicat-ing a decrease in the organochlorine levels during thestudy. It implies that a small quantity of OCP residues

migrated away from or degraded within the surface soilafter the first sampling.

Low surface soil DDT concentrations were detectedonly in S71, indicating that most of the DDT residuesmigrated away from the surface soil via run-off ordegraded to low levels following the prohibition ofDDT two decades ago.

Our results also revealed that DDT residues presentin the subsoil (10–20 cm) and deep soil layers (20–30 cm) were less concentrated than those detected inthe surface soil samples (i.e., in site M71). Similarpatterns were observed among most sites. In some sites,the profiles had been disturbed by common agriculturalpractices like plowing. These results suggest that thevertical movement of DDT residues (in the soil profile)is not a major pathway. Surface water run-off, soilerosion, and degradation processes may be the mainroute by which the DDT residues are removed fromthe soil–water system.

DDT is strongly sorbed to soil, making it more diffi-cult for DDT to move to lower horizons and to accumu-late in organic matter-rich horizons (because of DDT’spersistence and affinity for soil organic matter). The

Fig. 2 Variable loads of in the first two principal components


surface soil of the Sinú valley is rich in organic matter,which decreases with depth. Thus, in the soil profile ofthis region, DDT levels correlate with the organic matterpatterns in the zone.

Our results show that along with organic matter andclay(s), α-chlordane and lindane tend to be retained inthe first 30 cm of the soil. In addition, their insolubilityin water and their slow degradation rates increase thepersistence of these pesticides. However, in La Doctrina(M34), residues were found at depths greater than 30 cmdue to the high percentage of sand (52 %), whichfacilitates evaporation in upper layers and shifts theresidues to lower layers (Bidleman and Leone 2004).In the M69 sample, in which the high clay contentfavors the persistence of these pesticide compounds,the tendency ofβ-BCH is similar to that ofα-chlordane.

Endosulfan has a high affinity for soil particles and isone of the pesticides that become concentrated in thesoil surface layer(s). Thus, endosulfan can be swept

along with dust particles during plowing, moving thecontaminant to the surfaces of water, and human settle-ments. Because endosulfan is insoluble in water, it canbe deposited on the floating dust particles stored insediments (Sethunathan et al. 2002; Kumar and Philip2006). Volatilization is one of the main routes by whichendosulfan is removed from surface soil. Approximatelyhalf of the amount of α- and β-endosulfan applied tosurface soils is dissipated via volatilization in 3–5 and5–8 days, respectively (Leys, et al. 1998). The degrada-tion of this contaminant is greatly reduced at lowertemperatures (20 °C, compared with 40 °C) and whenthe soil’s water content is low (15 %, compared with40 % or fully submerged) (Ghadiri and Rose 2001;Weber et al. 2010). When the pH value is less than 7,both α- and β-isomers are persistent to hydrolysis (USEPA 2002). Microbial oxidation becomes the predomi-nant degradation route. Half-lives in acidic to neutralsoils range from 1 to 2 months for α-endosulfan and

Fig. 3 Vertical distribution ofOCPs in the sampling sites


from 3 to 9 months for β endosulfan under aerobicconditions. Endosulfan sulfate is the main degra-dation product by oxidation in aerobic soils whileendosulfan diol is mainly formed by chemical orbiological hydrolysis in anaerobic soils (US EPA2001).

5 Conclusions

In this study, α-chlordane, lindane, β-BCH, β-endosulfan, and DDT were detected in soils from themiddle and lower Sinú valley. Our results indicate thatafter Colombia banned the use of OCPs almost20 years ago, OCP compounds can still be detectedin soil samples obtained in these regions. The resultsprovide further evidence that OCPs are persistentorganic pollutants in the environment. Soils of theSinú valley present higher α-chlordane, lindane, andβ-endosulfan concentrations than are found in agri-cultural soil surveys conducted in other parts of theworld. Past applications of pesticides in the Sinúvalleys are the greatest contributor of organochlorineaccumulation in soils of this region. The high concen-trations of α-chlordane and lindane revealed that thisarea is seriously contaminated. The OCP levels in thisregion could cause long-term ecotoxicological dam-age. No regional differences in the OCP pollutionwere detected most likely because both valleys arehome to intense agricultural activity, which led to theextensive use of organochlorine pesticides. The rela-tively low DDT concentrations measured in the soilsamples from tropical regions compared to temperateor cold regions might be evidence of the global trans-portation of this type of pollutant. Microbial biodeg-radation in soil with DDD production proved to be animportant mechanism for removal of toxic in the Sinuvalleys characterized by their anoxic conditions dueto flooding. The OCP concentrations peak at the sur-face and decline with soil depth depending largely onthe physicochemical properties of soils. Fluctuations,likely caused by frequent cultivation activities, wereobserved in the plow layers of some cultivated soils.

Acknowledgements The authors thank the University ofCordoba for financial support through the contract FCB-03-06.They also express their gratitude to the farmers in the region ofCordoba, Colombia for their special support.

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