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Organochlorine pesticides in adipose tissue of persons from El Paso, Texas.

Organochlorine compounds have become widely distributed in our environment, following their introduction as pesticides during World War II. In general, they are very resistant to metabolic breakdown, and they tend to become bio-magnified as they pass along food chains. They also have long half-lives in the environment, because they are resistant to physical factors, such as light and temperature.

As insect pests developed resistance to DDT, a wide variety of organochlorine compounds were developed. Those that were developed later, such as aldrin and heptachlor, generally were much more toxic than the original DDT. They were banned or restricted for use in the United States in 1972, following laboratory studies with animals which indicated that they may cause cancer. Levels found in the environment as well as in the human population of the United States generally have declined since that time (1, 2, 3). Pesticide monitoring activities of the U.S. Fish and Wildlife Service, however, have shown increasing organochlorine pesticide levels in starlings and waterfowl from New Mexico and Arizona since the ban (4, 5, 6). Very high levels have also been shown for birds and fish from the lower Rio Grande Valley of Texas (7). This may imply continued use of the banned organochlorine pesticides in the southwestern United States; although for the highly mobile species, such as waterfowl, the increase could also reflect increasing levels in Mexico. Because of the low cost of manufacture, great stability and ease of application, these compounds are still widely used in developing countries.

Research done at several locations in Mexico on organochlorine pesticide residues in human milk and adipose tissue have shown some of the highest levels ever reported in the literature (8, 9). Very high human tissue levels have also been reported for the lower Rio Grande Valley of Texas (10). These findings prompted the authors to initiate studies on organochlorine pesticide residues in the human population of El Paso, Texas, and adjacent Ciudad Juarez, Mexico. Results of this work, published earlier in this journal, showed that persons from Juarez also had very high levels of organochlorine pesticide residues in both blood (11) and adipose tissue (12). Residents of El Paso, however, had only moderate blood levels (13).

This work was continued to include adipose tissue levels for persons from El Paso. This was needed because blood levels reflect primarily recently ingested sources. Organochlorine compounds are lipid soluble and tend to accumulate in adipose tissue. Persons with moderate blood levels might still have high adipose levels. Then during periods of physical stress when adipose is metabolized, such as pregnancy or dieting, these compounds can be released into the blood.


Human adipose tissue samples were obtained from the El Paso County Coroner's office, primarily from persons involved in accidental death situations. Sampling continued from fall 1983 through spring 1984. None of the persons involved were known to have experienced occupational exposure to pesticides or pesticide intoxication. Samples were placed in foil-lined glass vials and refrigerated until processing. Samples were processed by standard FDA procedures, using Hexane extraction and Kontes co-distillation (14, 15). A Varian Aerograph series 1400 electron-capture gas chromatograph with 63Nickel detector was used to identify and quantify pesticide residues. Recovery studies using samples spiked with known concentrations of pesticides indicated that residue recoveries were over 90 percent. Minimum levels of detection were 0.01 ppm DDE and 0.02 ppm DDT. Identification of residue peaks was verified by thin-layer chromatography on glass plates (16).


Samples from 25 persons were included in the study. Nineteen were males and six were females. Average age was 46 years, with a range of nine to 58. The results are shown in Table 1. All residues are expressed as ppm of total extractable lipids. Data for males and females were pooled together, because the only significant difference in results between them was in heptachlor level, with females showing a higher level at 0-.31 ppm, compared to 0.06 ppm for males (a = 0.05). A fairly wide variety of organochlorine compounds was encountered: eight total, including aldrin, beta-BHC, TABULAR DATA OMITTED DDE, DDT, heptachlor, heptachlor epoxide, lindane and TDE. Pesticide residue levels generally were in the moderate range, though none of the samples was completely free of pesticides. Highest average levels found were for DDT-type compounds, which taken together totaled a moderate 6.70 ppm. DDT occurred in 72 percent of the samples, with an average level of 1.50 ppm and a maximum of 16.82 ppm. DDE, the first stable breakdown product of DDT, occurred in 100 percent of the samples, with an average level of 4.96 ppm, and a maximum of 18.85 ppm. TDE, a secondary breakdown product, occurred in 52 percent of the samples, with an average of 0.24 ppm, and a maximum of 1.14 ppm. Lindane occurred in 96 percent of the samples, with an average level of 0.20 ppm, and a maximum level of 1.01 ppm. Heptachlor occurred in 44 percent of the samples, with an average level of 0.12 ppm, and a maximum of 0.875 ppm. Heptachlor epoxide, the breakdown product of heptachlor, occurred in 12 percent of the samples, with an average level of of 0.01 ppm and a maximum of 0.28 ppm. This brought the total for heptachlor-type compounds to 0.13 ppm. Aldrin occurred in 16 percent of the samples, with an average level of 0.07 ppm, and a maximum of 1.10 ppm. Beta-BHC also occurred in 16 percent of the samples, with an average level of 0.04 ppm, and a maximum of 0.70 ppm. Average total organochlorine pesticide residue burden was 7.15 ppm.


The tissue burdens of organochlorine pesticides observed in this study for persons from El Paso, Texas, were moderate, and generally comparable to those found in other areas of the United States (1, 2, 3). DDT-type compounds were the most abundant, followed by lindane and heptachlor. DDE tissues levels were more than three times higher than DDT levels. This reinforces our findings on DDT and DDE in blood of persons of El Paso (13). Since DDE is a stable breakdown product of DDT, this indicates mainly past ingestion. Another possibility is low-level indirect exposure from food and water coming from areas of past use, where DDE persists in the environment. DDT was widely used in the Rio Grande Valley of El Paso, both for agriculture and domestic household purposes prior to the ban. Since El Paso makes considerable use of both locally grown food products and surface water, the observed tissue burdens would be expected. The 100 percent occurrence rate for DDE in particular supports this explanation. It should be noted here that the relatively high maximum level found for DDT of 16.82 ppm, while only one instance, does indicate that direct exposure has occurred.

The other organochlorine compounds taken together totaled 0.45 ppm. While they are more toxic than DDT, these levels still are in the low to moderate range. Lindane showed a high percent occurrence at 96 percent, and had an average tissue level of 0.21 ppm. This could indicate a widespread low-level exposure to a dispersed source, such as food and water, or perhaps widespread domestic use. Since the breakdown product for lindane was not found, this could represent recent exposure. Heptachlor was more than 10 times more abundant than its breakdown product, heptachlor-epoxide. This may indicate more recent exposure as well. The occurrence for the heptachlor-type compounds taken together was 44 percent, indicating moderately widespread exposure.

These results for heptachlor were comparable to the blood study. The moderately widespread occurrence of heptachlor in both blood and tissue may imply an area-related exposure. Since females had significantly higher levels of heptachlor than men, this would indicate a domestic source, such as termite control. The low percent occurrences and low levels of aldrin and beta-BHC could reflect low-frequency food sources, or restricted environmental contamination.

For purposes of comparison, the results of our study in Juarez, Mexico showed a much higher level of 20.78 ppm total organochlorine pesticides in adipose tissues (12). The major difference was in total DDT-type compounds, which averaged 20.59 ppm for the Juarez population, compared to 6.70 ppm for El Paso. For the Juarez studies, DDT and its isomers were combined, because the DDT being used in Mexico was primarily a mixture of DDT and DDE. It wasn't possible to use a ratio of DDE to DDT as an indicator of recent exposure for Juarez. However, blood levels of DDT-type compounds found in our Juarez study also were very high, averaging 21.7 ppm (11). Finding very high levels in both blood and tissue in Juarez indicated recent high-level exposure, possibly through domestic use of readily available DDT in addition to food and water sources.

Other differences were much less important. Aldrin was much more prevalent in Juarez, while heptachlor was more prevalent in El Paso. Lindane and beta-BHC were observed in the El Paso study but were not found in Juarez, while endrin was found in Juarez but not in El Paso. Some spillover exposure between El Paso and Juarez may have been involved. The one instance of high-level tissue DDT found in El Paso may have come from exposure sources in Juarez. Also, low levels of aldrin in El Paso may reflect exposure sources across the border. Similarly, low levels of heptachlor found in the Juarez tissue study may reflect exposure from sources in El Paso.


The results of this study have shown that persons from El Paso, Texas had much lower tissue burdens of organochlorine pesticides than their neighbors in adjacent Juarez, Mexico. Levels found in El Paso were moderate and similar to other areas of the United States, while levels in Juarez were very high, even by third-world standards. This reinforces results of our previous studies done on blood from the two cities.

The major difference between the two populations in both the tissue and blood studies was in DDT-type compounds, which were much higher in Juarez. DDT-type compounds still were the most abundant organochlorines in El Paso, followed by lower levels of lindane and heptachlor. Levels of the breakdown product, DDE, were much higher than DDT, indicating past exposure, or indirect current exposure sources from food or water coming from areas of past DDT use.

Lindane was very widespread and no breakdown products were detected. This indicates more recent exposure to lindane, possibly through a dispersed source such as water or food. Heptachlor was moderately widespread and present at higher levels than its breakdown product, indicating more recent, possibly area-related exposure.


1. Akerman, L.B. (1980), Overview of human exosure to dieldrin in the environment and current trends of residue levels in tissue, Pestic. Monit. J. 14:64-69.

2. Bloomer, A.W., S.I. Nash, H.A. Price and R.L. Welch (1977), A study of pesticide residues in Michigan's general population, Pestic. Monit. J. 11:111-115.

3. Kutz, F.W., A.R. Yobs, S.C. Strassman and J.F. Viar, Jr. (1977), Effects of reducing DDT usage on total DDT storage in humans, Pestic. Monit. J. 11:61-63.

4. Fleming, W. and B. Cain (1985), Areas of localized organochlorine contamination in Arizona and New Mexico, The Southwest Naturalist 30:269-277.

5. White, D.H. (1976), Nationwide residues of organochlorines in starlings, 1974, Pestic. Monit. J. 10:10-17.

6. White, D.H. (1979), Nationwide residues of organochlorine compounds in starlings (Sternus vulgaris), 1976, Pestic. Monit. J. 12:193-197.

7. White, D.H., A. Mitchell, H.D. Kennedy, A.J. Krynitsky and M.A. Ribick (1983), Elevated DDE and toxiphane residues in fish and birds reflect local contamination in the lower Rio Grande Valley, Texas, The Southwest Naturalist 28:325-333.

8. Albert, L., F. Mendoz, M. Cebrian and A. Portales (1980), Organochlorine pesticide residues in human adipose tissue in Mexico: Results of a preliminary study in three Mexican cities, Arch. Environ. Health 35:262-269.

9. Albert, L., P. Vega and A. Portales (1981), Organochlorine pesticide residues in human milk samples from Comarca Lagunera, Mexico, 1976, Pestic. Monit. J. 15:135-158.

10. Burnes, J.E. (1974), Organochlorine pesticide and polychlorinated biphenyl residues in biopsied human adipose tissue--Texas, 1969-1972, Pestic. Monit. J. 7:1922-1926.

11. Gonzalez, A.A., K.A. Redetzke and H.G. Applegate (1986), Organochlorine pesticides in blood of persons from Ciudad Juarez, Mexico, J. Environ. Health 47:189-191.

12. Redetzke, K.A., A.A. Gonzales and H.G. Applegate (1983), Organochlorine pesticides in adipose tissue of persons from Cuidad Juarez, Mexico, J. Environ. Health 46:25-27.

13. Mossing, M., K. Redetzke and H. Applegate (1985), Organochlorine pesticides in blood of persons from El Paso, Texas, J. Environ. Health 47:312-313.

14. Mills, P.A., J.H. Onley and R.A. Gaither (1963), Rapid method for chlorinated pesticide residues in non-fatty foods, J. Assoc. Offic. Agr. Chem. 46:186-191.

15. Thompon, J.F. (ed.) (1972), Analysis of Pesticide Residues in Human and Environmental Samples, Primate and Pesticides Effects Laboratory, U.S. Environmental Protection Agency, Perrine, FL.

16. Rodwell, V.W. (1975), Thin-layer Chromatography, American Chemical Society, Washington, DC.

Dr. Keith Redetzke, The University of Texas at El Paso, Dept. of Biological Sciences, El Paso, TX 79968-0519.
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Author:Applegate, Howard G.
Publication:Journal of Environmental Health
Date:Oct 1, 1993
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