Archives of Environmental Contamination and Toxicology

, Volume 62, Issue 2, pp 351–358

Assessment of DDT and DDE Levels in Soil, Dust, and Blood Samples From Chihuahua, Mexico

Authors

  • Fernando Díaz-Barriga Martínez
    • Departamento Toxicología Ambiental, Facultad de MedicinaUniversidad Autónoma de San Luis Potosí
  • Antonio Trejo-Acevedo
    • Departamento Toxicología Ambiental, Facultad de MedicinaUniversidad Autónoma de San Luis Potosí
    • Instituto Nacional de Salud Pública/Centro Regional de Investigación en Salud Publica
  • Angel F. Betanzos
    • Instituto Nacional de Salud Pública
  • Guillermo Espinosa-Reyes
    • Departamento Toxicología Ambiental, Facultad de MedicinaUniversidad Autónoma de San Luis Potosí
  • Jorge Alejandro Alegría-Torres
    • Departamento Toxicología Ambiental, Facultad de MedicinaUniversidad Autónoma de San Luis Potosí
    • Departamento Toxicología Ambiental, Facultad de MedicinaUniversidad Autónoma de San Luis Potosí
    • Unidad Académica Multidisciplinaria Zona MediaUniversidad Autónoma de San Luis Potosí
Article

DOI: 10.1007/s00244-011-9700-0

Cite this article as:
Martínez, F.D., Trejo-Acevedo, A., Betanzos, A.F. et al. Arch Environ Contam Toxicol (2012) 62: 351. doi:10.1007/s00244-011-9700-0

Abstract

The aim of this study was to assess levels of DDT and DDE in two environmental matrices (soil and dust) and to investigate the blood levels of these insecticides in exposed children living in a north Mexican state (Chihuahua) where DDT was sprayed several years ago during (1) health campaigns for the control of malaria and (2) agricultural activities. DDT and DDE were analyzed by gas chromatography/mass spectrometry. In general, lower levels were found in household outdoor samples. The levels in outdoor samples ranged from 0.001 to 0.788 mg/kg for DDT and from 0.001 to 0.642 mg/kg for DDE. The levels in indoor samples ranged from 0.001 to 15.47 mg/kg for DDT and from 0.001 to 1.063 mg/kg for DDE. Similar results to those found in indoor soil were found in dust, in which the levels ranged from 0.001 to 95.87 mg/kg for DDT and from 0.001 to 0.797 mg/kg for DDE. Moreover, blood levels showed that all of the communities studied had been exposed to DDT and/or DDE, indicating a general past or present exposure to DDT. It is important to note that the quotient DDT/DDE in all matrices was always >1. Whether the people living in our study area are at risk is an issue that deserves further analysis. However, applying precautionary principles, it is important to initiate a risk-reduction program to decrease exposure to DDT and its metabolites in people living in this area.

In the past, DDT [1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane] was the most widely used organochlorine pesticide in the world. It is considered a pollutant of high persistence due to its half-life of up to 15 years in the environment (ATSDR 2008; Turusov et al. 2002). In México, DDT was used in (1) health campaigns for the control of malaria and (2) agricultural activities.

Malaria has long been a public health problem in Mexico, where conditions in 60% (from sea level to 1800 meters above sea level) of the country are favorable for malaria transmission. This includes the Pacific coast, the Gulf of Mexico slopes, the Yucatan peninsula, and interior basins of the high plateau. Some 45 million people live in these areas (Díaz-Barriga et al. 2003). During the 1940s and 1950s, malaria caused an average of 24,000 lives each year and afflicted some 2.4 million people. The government introduced a malaria-eradication program that relied on extensive household spraying with DDT and antimalarial therapy. Cases of malaria decreased, but it proved impossible to completely rid the country of the disease. The problem was most stubborn in coastal areas, where control measures only succeeded in interrupting malaria transmission (Díaz-Barriga et al. 2003). The north region of Mexico was an important area of malaria, and from 1957 onward DDT was applied every 6 months indoors and outdoors with a coverage of 2 g/m2 (Direccion General 1996).

In agricultural areas, as many as 1000 tonnes DDT/y were used (Díaz-Barriga et al. 2003). Application rates in north México were among the highest in the world (Díaz-Barriga et al. 2003). However, the growing concern regarding DDT’s persistence has had a significant impact on agricultural practices in Mexico. During the early 1970s, the United States Food and Drug Administration (USFDA) began rejecting the importation of commodities due to high residue levels, especially those of DDT (Díaz-Barriga et al. 2003). Therefore, some agricultural areas changed to newer pesticides to comply with USFDA regulations. By 1990, DDT was limited to campaigns addressing public sanitation (Díaz-Barriga et al. 2003). In Mexico, DDT was used until the year 2000, and DDT and its metabolites have been found in the environment (Yáñez et al. 2002) as well as human tissues (Pérez-Maldonado et al. 2006; Yáñez et al. 2002) in Mexico.

The production and use of DDT are severely restricted by an international agreement known as the Stockholm Convention on persistent organic pollutants (POPs 2009). The convention’s objective is to protect both human health and the environment from POPs. DDT is one of 22 chemicals identified as a POP restricted by the convention (United Nations Environment Program (UNEP) 2011). In May 2007, 147 countries were parties to the convention. México signed the Stockholm Convention in May 2001 and was ratified in February 2003. However, one exemption clause allows malaria-endemic nations to use DDT strictly for disease vector control. UNEP estimates that approximately 25 countries will use DDT under exemptions from the DDT pesticide ban (POPs 2009).

Thus, in this regard the presence of DDT around the world can be divided into three scenarios: (1) sites where DDT is still in use; (2) sites where there is presence of DDT due to it being sprayed several years ago; and (3) sites where the presence of DDT is the result of long-range transport of DDT to areas where it was never used, such as the Antarctic. Therefore, the aim of this study was to assess the levels of DDT and its metabolites in two environmental matrices (soil and dust) and to investigate blood levels of these insecticides in exposed children living in a north Mexican state (Chihuahua) where DDT was sprayed several years ago during (1) health campaigns for the control of malaria (these areas were sprayed with DDT between 1957 and 2000 as part of the National Control Program for malaria) and (2) agricultural activities.

Materials and Methods

Population

To obtain a gradient of DDT and DDE exposure, three communities were selected (Fig. 1; Table 1). All children attending 1st to 6th grade in schools were screened for study eligibility through in-person interviews. During 2009, we studied a total of 101 healthy children (age 4–12 years) who were residents of community A (15 children), community B (39 children), and community C (47 children) in Chihuahua state (Fig. 1; Table 1). The children had similar ethnic and socioeconomic backgrounds. The children attending public schools at the sites were screened for study eligibility through personal interview with their parents. However, the samples were taken only from the children whose parents agreed to their participation in the study; for this reason we had differences in the number of children among communities. After informed consent agreement was signed by parents, a questionnaire was circulated and blood samples taken. The questionnaire registered certain characteristics, such as source of drinking water; occupational history of parents; child’s age, weight, and height; and child’s exposure to medicines, environmental tobacco smoke, and infectious diseases in the last month. The study was approved by the ethical committee of the School of Medicine, Universidad Autonoma de San Luis Potosi.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-011-9700-0/MediaObjects/244_2011_9700_Fig1_HTML.gif
Fig. 1

Location of communities studied

Table 1

Characteristics of sampled sites

City

Community

Characteristics

Agua Caliente

A

Rural community localized in an endemic malaria zone and with agriculture activity (27°12′37.68′′N; 107°55′3.16′′W)

San Juan de Dios

B

Rural community localized in an endemic malaria zone and with agriculture activity (27°1′31.65′′N; 107°44′35.76′′W)

Morelos

C

Rural community localized in an endemic malaria zone and with agriculture activity (26°40′17.27′′N; 107°40′37.32′′W)

Sampling Areas

The weight of sample collected in each point sampled in three communities was approximately 1000 g, whereas for dust samples the weight was approximately 100 g. To confirm the presence of DDT and DDE, indoor and outdoor surface soil samples (1–5 cm in depth) were collected with a metal blade. Soil samples were transported to the laboratory in glass containers and kept under refrigeration (4°C) until analysis. To have greater representation in the analysis, both samples indoor and outdoor were composed of five subsamples. Surface soil was collected outdoors in children’s recreational areas located next to the dwellings and indoors in the center of the room and next to the dwellings. Dust samples were taken by collecting material from the windows, the corners, and the center of the main room (one compound sample was obtained from each dwelling); they were obtained using brushes and foil. Dust samples were transported to the laboratory in foil containers and kept under refrigeration (4°C) until analysis.

DDT Analysis in Human Blood

Quantification of DDT and DDE was performed as reported by Trejo-Acevedo et al. (2009). Briefly, a 2-ml aliquot of plasma was first extracted with a mixture of ammonium sulfate/ethanol/hexane (1:1:3), and the extract was then concentrated and cleaned up on Florisil columns. The quantification was performed using a HP 6890 gas chromatograph coupled with a HP 5973 mass spectrometer as described later in the text. Internal standards used were α-hexachlorocyclohexane-C13, endrin-C13, and PCB-141-C13.

DDT Analysis of Soil and Dust

Soil (indoor and outdoor) and dust samples (1 g) were microwave-extracted in acetone and hexane (1:1) as described by Yáñez et al. (2002). After extraction, samples were evaporated under nitrogen to 0.2 ml, and the extract was resuspended to 2.0 ml with hexane. Finally, the samples were cleaned on a Florisil column packed in a 6-ml solid-phase extraction cartridge, where the extraction was performed with 6% ethyl ether in hexane, and the Florisil eluate was concentrated under nitrogen to 1 ml. We performed analytical determination of the target analytes using a Hewlett Packard (HP) 6890 gas chromatograph coupled with an HP 5973 mass spectrometer as described later in the text. Internal standards used were PCB-141 or PCB-29.

Quantitative Analysis

DDT and DDE were analyzed in all matrices. Quantitative analyses were performed by gas chromatography coupled with mass spectrometry (MS). An HP5-MS column, 60 m × 0.25 mm ID, 0.25-μm film thickness, was used (J&W Scientific, Bellefonte, PA). Column temperatures were as follows: initial 100°C (2 min) and final 310°C (rates: 20°C/min up to 200°C, 10.0°C/min up to 245°C, 4.0°C/min up to 280°C, and 30°C/min up to 310°C). Injector temperature was 270°C operated in pulsed splitless mode. Helium was used as the carrier gas at a linear velocity of 1.0 ml/min. MS was operated in selective ion mode. Ionization voltage in the ass spectrometer was 70 eV (electron ionization). The quadrupole was scanned at m/z 235 and m/z 246, the most abundant fragments for DDT and DDE, respectively. Under these conditions and using the data generated by seven replicates near the lowest concentration attainable at the calibration curve, the method detection limits for the pesticides were p′p-DDT 0.048 ng/ml, p′p-DDE 0.048 ng/ml, and p’p-DDD, 0.048 ng/ml. Quantification of DDT and DDE in blood was part of the Interlaboratory Comparison Program organized by the Institut National de Santé Publique du Quebec (Canada), and results were within the limits of tolerance. Our accuracy in this program was 80–120% for all tested analytes. For DDTs in soil, analytical reference material EC-2 (Environmental Canada, National Water Research Institute) was used. Our extraction efficiency was 90–110% for all tested analytes.

Statistics

To satisfy normality criteria, the levels for DDT and DDE in all matrices were logarithm-transformed. Therefore, all of the results are shown as geometric means. Mean levels of DDT and DDE in all matrices were compared between communities using one way analysis of variance followed by Tukey’s test. Multivariate analysis was performed using variables, such as child age, sex, height, and nutritional status, among others as independent variables, whereas exposure levels (DDT and DDE) were treated as dependent variables. For all statistical analyses, we used Jmpin Start Statistics Software 7.0 (SAS, Chicago, IL).

Results

DDT and DDE levels in outdoor and indoor surface soils are listed in Tables 2 and 3. In general, lower levels were found in household outdoor samples. The levels in outdoor samples ranged from 0.001 to 0.788 mg/kg for DDT and from 0.001 to 0.642 mg/kg for DDE, with greater mean levels of DDT and DDE found in community C (Table 2). Levels of indoor samples ranged from 0.001 to 15.47 mg/kg for DDT and from 0.001 to 1.063 mg/kg for DDE, with greater mean levels of DDT and DDE found in community C (Table 3). Similar results to those in indoor soil were found in dust; levels in dust ranged from 0.001 to 95.87 mg/kg for DDT and from 0.001 to 0.797 mg/kg for DDE, with greater mean levels of DDT and DDE found in community C (Table 4). It is important to note that the quotient DDT/DDE in all matrices at all sites sampled was always >1, suggesting recent use of the insecticides. Taking into account two guidelines for DDT in residential soil—0.7 mg/kg from Canada (Environment Canada 2007) and 1.6 mg/kg from the State of California in the United States (California Environmental Protection Agency 2005)—different scenarios were observed in our study. Regarding outdoor levels, community C (6%), community A (0%), and community B (10%) had samples with levels greater than the guidelines (Table 5). For indoor soils and dust samples, the percentage of samples greater than the guidelines were as follows: community C (approximately 70% for both matrices), community A (20% for both matrices), and community B (10% for both matrices (Table 5)).
Table 2

Levels of DDT and DDE (mg/kg) in outdoor surface soil

Community

Compound

n

GM

SDs

Minimum concentration

Maximum concentration

DDT/DDE quotient

A

DDT

10

0.042

0.134

0.001

0.450

1.8

DDE

10

0.023

0.069

0.001

0.219

B

DDT

16

0.055

0.267

0.040

0.788

1.7

DDE

16

0.033

0.188

0.001

0.629

C

DDT

14

0.252*

0.229

0.040

0.528

1.5

DDE

14

0.171*

0.339

0.024

0.642

GM geometric mean, <LOD lower than detection limit (LOD = 0.0003 mg/kg), n number of soil samples analyzed

p < 0.05 compared with other communities

Table 3

Levels of DDT and DDE (mg/kg) in indoor surface soil

Community

Compound

n

GM

SDs

Minimum concentration

Maximum concentration

DDT/DDE quotient

A

DDT

10

0.110

0.154

0.001

1.732

1.9

DDE

10

0.059

0.110

0.001

1.063

B

DDT

16

0.124

0.094

0.016

15.470

4.4

DDE

16

0.028

0.025

0.001

0.685

C

DDT

14

0.708*

0.664

0.121

4.416

2.5

DDE

14

0.286*

0.157

0.141

1.054

GM geometric mean, <LOD lower than detection limit (LOD = 0.0003 mg/kg), n number of soil samples analyzed

p < 0.05 compared with other communities

Table 4

Levels of DDT and DDE (mg/kg) in dust

Community

Compound

n

GM

SDs

Minimum concentration

Maximum concentration

DDT/DDE quotient

A

DDT

10

0.160

0.590

0.016

1.788

4.1

DDE

10

0.039

0.143

0.001

0.376

B

DDT

16

0.026

0.376

0.001

1.113

1.7

DDE

16

0.015

0.233

0.001

0.682

C

DDT

14

0.942*

47.742

0.048

95.870

19.2

DDE

14

0.049

0.374

0.001

0.797

GM geometric mean, <LOD lower than detection limit (LOD = 0.0003 mg/kg), n number of soil samples analyzed

p < 0.05 compared with other communities

Table 5

Levels of total DDT (mg/kg) in outdoor and indoor soil and dust

Matrix

Community

n

GM

SDs

Minimum concentration

Maximum concentration

% >0.7

% >1.6

Outdoor soil

A

10

0.065

0.203

0.002

0.669

0

0

B

16

0.088

0.455

0.041

0.1417

0

0

C

14

0.423*

0.568

0.064

0.117

0

0

Indoor soil

A

10

0.169

0.264

0.002

2.795

30

10

B

16

0.152

0.119

0.017

16.155

37

19

C

14

0.994*

0.821

0.262

5.47

64

64

Dust

A

10

0.199

0.733

0.017

2.164

30

10

B

16

0.041

0.609

0.002

1.795

19

6

C

14

0.991*

48.116

0.049

96.667

78

57

GM geometric mean, <LOD lower than detection limit (LOD = 0.0003 mg/kg), n number of soil samples analyzed

p < 0.05 compared with other communities

Blood concentrations of DDT and DDE are listed in Table 6; the blood levels show that all of the communities studied were exposed to DDT and/or DDE, indicating a general past or present exposure to DDT. The highest concentrations of total DDT (DDT + DDE) were recorded in community A (approximately 35,000 ng/g lipid); in community B the levels were approximately half (14,500 ng/g lipid) those found in community A; and finally, children living in community C had levels of approximately 8900 ng/g lipid (Table 6). An important finding in our work is that we detected the 100% of DDT presence only 70–100% of DDE presence in blood samples and. It is also important to note that the quotient DDT/DDE in blood in children in community B and community C was >1, suggesting recent use of the insecticides. It is important to note that in multivariate analysis no significant effects were found for variables such as child age, sex, height, or nutritional status.
Table 6

DDT in blood samples of children (ng/g lipid)

Community

Compound

n

% Positive

GM

SDs

Minimum concentration

Maximum concentration

DDT/DDE quotient

A

DDT

15

100

4494.4

8444.4

1062.9

36152.2

0.1

DDE

15

100

30485.0*

37958.2

8070.9

170596.2

B

DDT

39

100

12999.6*

14992.3

2033.4

68669.2

8.5

DDE

39

79

1521.4

4505.6

271.3

23069.6

C

DDT

47

100

7592.2

9403.5

711.0

37632.2

5.9

DDE

47

70

1295.3

2539.9

278.0

13616.6

GM geometric mean, <LOD lower than detection limit (LOD = 0.3 ng/ml, wet basis), n number of blood samples analyzed

p < 0.05 compared with other communities

Discussion

DDT was heavily used in Mexico in agriculture and in malaria-control programs. Therefore, human exposure to DDT has been reported in numerous communities due to the presence of this insecticide in different environmental media (Yáñez et al. 2002). In this work, we found high levels of this insecticide and its principal metabolite (DDE) in indoor soil and dust and in the blood of children living in three communities in Chihuahua located in the northern region of Mexico.

The communities studied are different in number of houses and families. For example, the community with high number of families, houses, and population is community C. Therefore, the amount of DDT applied in the past in that community is greater than that applied in communities A and B. In this regard, in our study community C was the town with greater DDT levels in environmental matrices. The above-mentioned result reflects the amount of DDT applied in the past. However, the levels of total DDT found in soil in this study (Table 5) were lower than those reported by Martinez-Salinas et al. (2011) in Chiapas in the southeastern region of Mexico. The levels in soil found by Martinez-Salinas et al. (2011) ranged from 0.002 to 27 mg/kg and in dust samples ranged from 0.002 to 2119 mg/kg. However, when the levels found in our study were compared with levels found in Mesoamerican countries (Pérez-Maldonado et al. 2010), it was noted that levels of total DDT in soil were similar or greater in the communities (Table 5) in our study than the levels assessed in soils in countries in Mesoamerica (mean levels <0.18 mg/kg; Pérez-Maldonado et al. 2010). For indoor dust samples (Table 5), the levels in all of the communities studied were similar or greater than those in six countries in Mesoamerica (Honduras, Nicaragua, El Salvador, Guatemala, Panama, and Mexico; mean levels <0.43 mg/kg). Only Costa Rica (14.0 mg/kg) had levels greater than the communities in our study.

Regarding blood samples (Table 6), levels found in this study were similar or greater than those previously reported in children from other communities of Chiapas (mean levels 22,284 and 613 ng/g lipid for DDE and DDT, respectively) and Quintana Roo (mean levels 10,767 and 2851 ng/g lipid for DDE and DDT, respectively) in two Mexican states located in the southeastern region of Mexico (Yáñez et al. 2002; Perez-Maldonado et al. 2004, 2006; Trejo-Acevedo et al. 2009). The southeastern region of Mexico was an important area for malaria, where DDT was applied indoors at a coverage of 2 g/m2 every 6 months from 1957 onward (Direccion General 1996). When comparing the levels found in this study with those found in children in the National Health and Nutrition Examination Survey (NHANES) III (12–19 years old), the difference is excessive for the children assessed in our study because they had DDE levels approximately 300 times greater than children in the United States (NHANES III 2005).

Furthermore, the ratio of DDT/DDE was calculated in all of the matrices tested and was always >1, with exception of blood samples from community A. It is important to mention that the ratio of DDT/DDE can be used as a rough indication of the period of application: A DDT/DDE ratio ≥1.0 indicates DDT use in the last 5 years (Tavares et al. 1999). Different explanations for this finding can be considered; however, it appears that recent use of this insecticide is the most reasonable explanation, which has also been suggested by Alegría et al. (2006). In this regard, it is important to take into account that in different countries, products used for the control of malaria are still available in some warehouses (for general pest control).Therefore, it is probable that the communities studied have deposits of DDT (used for malaria control several years ago), and it is possible that the people living in those communities are still using this store of DDT. In this regard, we detected 100% of DDT presence and only 70–100% of DDE presence in blood samples. That result could be explained by the recent use of DDT in those communities. These results are in concordance with studies performed in the southeastern region of México (Martinez-Salinas et al. 2011; Pérez-Maldonado et al. 2010).

Several studies have identified indoor house dust and soil as important pathways of toxicant exposure. Often the levels of pollutants found in house dust and soil, including compounds banned long ago (such as DDT), are significant sources of exposure for the general population, especially children (Butte and Heinzow 2002; Hwang et al. 2008; Rudel et al. 2003). Moreover, analyses of compounds in house dust and soil are a measure of indoor contamination, but they may also provide valuable information for the assessment of human indoor exposure (Butte and Heinzow 2002). In addition, outdoor soil is considered an important exposure pathway for the general population and children to compounds banned long ago (Herrera-Portugal et al. 2005a). However, it is important to note that longer residence times and increased contaminant concentrations in the indoor environment may increase the chance of exposure to these contaminants by 1000-fold compared with outdoor exposure (Hwang et al. 2008).

As shown by our results, the study of other exposure pathways in children is needed. We note that the community with the highest level of total DDT in environmental matrices was community C; however, the children with the highest levels of total DDT in blood were those living in community A. In this respect, we must point out the limitations of our assessment: We did not study pathways, such as breast milk, other food items, and other areas (only soil and dust samples around warehouses or in areas where DDT was used for agriculture), and the numbers of subjects for each sample site were low.

Nevertheless, to analyze the possibility of other sources of DDT, a comprehensive study of the environmental fate and distribution of the insecticide in tropical ecosystems must be conducted. Regarding, the number (few) of samples in each site, it can cause bias of the study, which can generate data that DDT levels vary among communities. However, the variability of DDT levels in environmental matrices has been reported in several studies (Yáñez et al. 2002; Martinez-Salinas et al. 2011; Pérez-Maldonado et al. 2010; Waliszewski et al. 2008; Zhang et al. 2011). In addition, although no significant effects were found for variables such as child age, sex, weight, height, or nutritional status, we must take account that those indicators have been associated with serum DDT/DDE levels. For example, body mass index has been associated with serum DDT/DDE levels (positive and inverse associations; Perry et al. 2005).

Taking into consideration the plasma concentrations of DDT and DDE found in children, and considering that greater concentrations of DDT than of DDE were found in environmental matrices, it is difficult to define specific health risks because the levels of concern for DDT or DDE in children’s plasma have not been established by either international or national health organizations. However, DDT and its metabolites have been associated with neurological effects (Dorner and Plagemann 2002; Fenster et al. 2007; Torres-Sánchez et al. 2007; Rocha-Amador et al. 2009), asthma (Sunyer et al. 2006), immunodeficiency (Dewailly et al. 2000; Vine et al. 2000, 2001; Belles-Isles et al. 2002; Bilrha et al. 2003; Cooper et al. 2004; Dallaire et al. 2004), apoptosis (Pérez-Maldonado et al. 2004), and DNA damage in immune cells in children (Yáñez et al. 2004; Herrera-Portugal et al. 2005b).

Compared with adults, children are more susceptible to the adverse effects of environmental degradation because of their physical, cognitive, and physiological immaturity (WHO 2006). In this regard, monitoring of toxins on a global scale can be the first step toward prevention of toxin-induced illnesses in this vulnerable population. For example, monitoring studies have been performed around the world as NHANES in the United States of America (NHANES III 2005): Among other, two are German studies, one in the federal state of Baden–Wuerttemberg in Southwest Germany (Gabrio et al. 2005; Link et al. 2005, 2007) and the other in North Rhine–Westphalia (Wilhelm et al. 2007).

Finally, our data indicate high levels of DDT and DDE in soil and dust in all communities studied when compared with studies around the world. Moreover, high exposure levels in children living in all communities also were found. In this regard, our research group has demonstrated contamination by DDT and its metabolites in the environment (Yáñez et al. 2002; Herrera-Portugal et al. 2005a; Martínez-Salinas et al. 2011; Pérez-Maldonado et al. 2010) and in human tissues (Pérez-Maldonado et al. 2006; Herrera-Portugal et al. 2005a; Yáñez et al. 2002, 2004; Rocha-Amador et al. 2009; Trejo-Acevedo et al. 2009) in Mexico. Moreover, the studies performed by our group screened all of the Mexican territories (Yáñez et al. 2002; Martínez-Salinas et al. 2011; Pérez-Maldonado et al. 2006, 2010; Herrera-Portugal et al. 2005a; Yáñez et al. 2002; Rocha-Amador et al. 2009; Trejo-Acevedo et al. 2009). Therefore, applying precautionary principles, it is important to initiate a risk-reduction program to decrease exposure to DDT and its metabolites in children in all Mexican territories.

Acknowledgments

This work was supported by grant from the Consejo Nacional de Ciencia y Tecnología, Mexico (CONACYT-SEP 24024).

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© Springer Science+Business Media, LLC 2011