Skip directly to search Skip directly to A to Z list Skip directly to site content


Exposure Investigation Report



Residents of the community of Mossville in Calcasieu Parish, Louisiana, expressed concern over potential health effects from exposure to chemical releases from chemical manufacturing plants in their neighborhood. To document their concerns, a private citizen provided ATSDR withblood dioxin test results that indicated that some residents of the Parish had elevated blooddioxin levels [1]. The individual with the highest dioxin level was a resident of Mossville.

In response to these preliminary findings, ATSDR conducted an Exposure Investigation (EI). The purpose of the EI was to determine if there was evidence for increased exposure to dioxins inresidents of Mossville. Blood samples were collected from 28 residents of the community andwere analyzed for chlorinated dibenzodioxins (CDDs), chlorinated dibenzofurans (CDFs), andco-planar polychlorinated biphenyls (PCBs). A limited investigation of environmentalcontamination was also conducted: four surface soil samples and two chicken eggs werecollected and analyzed for CDDS and CDFs. A breast milk sample from one resident was also analyzed.


Calcasieu Parish contains a large number of chemical manufacturing plants that producechemicals such as chlorinated hydrocarbon solvents, vinyl chloride monomer, and petroleum-based chemicals. Chemical wastes from some of these operations are burned in hazardous wasteincinerators operated by industries in the area. Small amounts of CDDs and CDFs are reportedlyformed during the production of vinyl chloride monomer [2]. The incineration of chlorinatedhydrocarbon wastes can also produce CDDs and CDFs. The regeneration of catalysts used inpetroleum refining is another potential source of CDDs and CDFs.

Mossville is located across the road from a large vinyl chloride monomer (VCM) plant. Severalflares at this facility intermittently burn unidentified materials. A representative of the plantreported that the flares do not burn chlorinated hydrocarbons or other materials that containchlorine. The plant also has two incinerators for chlorinated compounds that burn only gaseousvents from the VCM unit process. These incinerators have been sampled according to EPAmethods and reportedly emit less than 0.1 grams of total dioxin per year.

ATSDR recently reviewed the results of a study in which blood dioxin levels were determined in11 residents of Calcasieu Parish [1]. Three of the residents had blood dioxin levels that exceededthe reference range. The individual with the highest blood serum dioxin level (104 pg of dioxinTEQs/gram lipid or parts per trillion) was a resident of Mossville. This resident had no knownoccupational history of exposure to dioxins in the work place; therefore, it is suspected that this individual was exposed to dioxins from an unidentified environmental source.

In order to determine if other residents of Mossville have been exposed to dioxins, ATSDR conducted blood tests for dioxin-like compounds in residents of the community. In addition,surface soil and chicken egg samples were tested for dioxin contamination to identify possiblesources of human exposure.

There are 75 congeners of CDDs and 125 congeners of CDFs. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic chemical in this group. Some of the other CDDs and CDFs (i.e., those with chlorine atoms in the 2,3,7,8 positions) have TCDD-like toxicity. In addition,certain co-planar polychlorinated biphenyls (PCBs) have TCDD-like toxicity. Therefore, bloodsamples were analyzed for CDDs, CDFs, and PCBs with TCDD-like activity. In this report,"dioxin" or "dioxin like compounds" will be used as generic terms to refer to chemicals with TCDD-like toxicity.


    Target Population

ATSDR solicited the participation of residents who live in Mossville in the area bounded byVCM Plant Road (east), Center Street (south), Rigmaiden Avenue (west), and 8th Street (north). ATSDR staff worked with residents of the community to recruit the participants.

Participation was restricted to participants who were 18 years of age or older and who had livedin the designated area for at least five years. Preference was given to older people who had beenlong-term residents in the neighborhood. Since this investigation focused on exposure toenvironmental sources of dioxins, individuals with possible occupational exposure to dioxinswere excluded. There was one exception to this requirement: one participant had worked for achemical company four years prior to the EI.

Individuals were also excluded from testing if they were pregnant, or if they had a blood clottingdisorder or other medical condition that precluded them from donating a 70-ml blood sample. Ifthere was any question about the medical eligibility of a participant, the consent of their personalphysician was required.

Surface soil samples (0-3 inches) and chicken eggs were collected from private residences alongVCM Plant Road. ATSDR accepted a breast milk sample from one Mossville resident for analysis.

    Biological Sampling and Analyses

Participants were given an appointment to come to the Rigmaiden Community Center where theblood samples were collected. They were advised to avoid eating a fatty meal prior to donatingthe blood sample. A licensed phlebotomist collected a 70-ml blood sample by venipuncture from 28 participants. Blood samples were collected in 10-ml glass Vacutainer® tubes. Followingcollection, the blood samples were allowed to clot for 1 to 2 hours at room temperature. Thesamples were then stored on ice and hand-delivered to the laboratory at the National Center forEnvironmental Health (NCEH) in Atlanta, Georgia, for analyses.

The serum samples were analyzed for CDDs, CDFs, and co-planar PCBs by the NCEHlaboratory using gas chromatography/isotope dilution-high resolution mass spectroscopy [3]. The blood serum samples were also analyzed for total lipid content, so the results could beexpressed as a blood lipid concentration.

ATSDR provided glass bottles with Teflon-lined caps to women who requested breast milkanalyses. The women were advised to collect at least a 25 ml sample of milk in the bottle and tostore it in a freezer until an ATSDR staff person collected it. One breast milk sample wascollected and was stored on ice and hand-delivered to the laboratory at the National Center forEnvironmental Health (NCEH) for analyses.

    Environmental Sampling and Analyses

ATSDR staff collected surface soil (0-3 inches) samples from three residences on VCM PlantRoad. At two of the houses, the soil sample was collected from the drip line of the house; at thethird house, the soil sample was collected next to the front steps. At one house, a second soilsample was collected inside a large wire coop where the owner was raising poultry. The soilsamples were placed in pre-cleaned, amber glass jars and shipped by overnight express to thelaboratory for analyses.

ATSDR staff also collected two chicken eggs from a resident on VCM Plant Road who wasraising poultry on his property. The eggs were broken into pre-cleaned glass jars with Teflon-lined caps. The eggs were stored on ice and shipped on ice packs by overnight express to thelaboratory for analyses.

Soil samples and eggs were analyzed for CDDs and CDFs by the Midwest Research Institute(MRI) in Kansas City, Missouri. MRI also analyzed a control egg purchased from a local (Kansas City) supermarket.

    Consent Form

Prior to biological and environmental testing, each participant in the investigation signed an informed consent form.


In order to assess the health impact of a mixture of dioxin-like compounds, risk assessors oftenconvert the toxicity of individual congeners to TCDD toxicity equivalents (TEQs) using ToxicityEquivalent Factors (TEFs) [4]. The toxicity of the mixture is then assumed to be equal to thesum of the individual components. The World Health Organization recently evaluated newscientific data and recommended revised TEFs for some dioxin-like compounds [5].

In the draft report for this Exposure Investigation (May 7, 1999), blood TCDD-TEQconcentrations were calculated using the previous TEFs so that the results could be compared toreference values that were also calculated using the old TEFs. In this report, the blood TCDD-TEQ concentrations were calculated using the new TEFs, which results in higher TEQ values. The new TEF values were used so the results could be compared to updated comparison valuesthat were calculated with the new TEF values (see Appendix 1).

The use of TEFs only affects the calculated TCDD-TEQ concentrations (the bottom line in Table 1). The concentrations of individual dioxin congeners are not affected by TEFs and remainunchanged from the draft report.

In this report, as well as in the draft report, the dioxin TEQ concentrations in soil, egg, and breastmilk samples were calculated using the TEFs previously recommended by the EPA [4]. TheseTEFs values were used so that the TEQ levels in egg, soil, and breast milk samples could becompared to reference values in the scientific literature that were calculated using the previous TEFs.

Biological Samples


Blood serum samples from 28 adults were analyzed for dioxin-like compounds. Dioxin TEQs inthe blood serum samples ranged from 3.8 to 186 parts per trillion (ppt) on a lipid-adjusted basis. The median dioxin TEQ concentration was 54.8 ppt, and the mean dioxin TEQ concentrationwas 68.3 ppt. Table 1 contains the median, mean, and 95th percentile concentrations of dioxin-like compounds for the EI participants and a comparison population. The derivation ofbackground dioxin levels in the comparison population is discussed in Appendix 1.

Table 1.

Concentrations of dioxin-like compounds (pg/g lipid or ppt) in blood serum samples from EI participants
Analyte Residents-
Population -
- mean
Population -
- 95th
- 95th
2378D 7.3 2.0 7.6 2.3 18.2 4.8
12378D 19.2 4.8 28.8 5.1 77.1 9.1
1234/678D 99.1 61.0 131.8 58.2 306 106
123789D 13.6 6.3 17.8 6.4 37.1 11.9
1234678D 102.7 65.2 126.9 71.3 351.3 143.8
1234679D 4.25 3.0 4.2 3.2 13.1 9.2
OCDD 906 556 1126 626 2429 1288
2378F 0.0 0.9 0.2 0.7 1.2 1.8
12378F 0.0 0.8 0.2 0.7 1.6 1.8
23478F 8.1 5.6 11.9 5.9 38.0 11.5
1234/678F 16.8 10.5 22.3 10.7 76.7 19.9
123789F 0.0 0.8 1.2 0.6 4.9 2.0
234678F 1.7 2.3 3.1 2.0 15.4 4.1
1234678F 19.6 11.3 25.2 12.2 67.2 24.5
1234789F 0.0 1.4 0.4 1.1 2.3 3.0
OCDF NR 11.0 NR 7.7 NR 70.2
3344-PCB ND 38.9 ND 34.7 ND 100.7
3445-PCB 0.0 3.2 1.2 3.2 8.2 7.4
33445-PCB 31.7 16.9 59.7 20.5 172 55.7
334455-PCB 27.0 20.2 39.9 20.5 105.7 39.4
TCDD-TEQs(1) 54.8 19.9 68.3 21.0 162.3 37.5

NR - not reported due to analytical interference
ND - not detected
(1) calculated using TEFs recommended by the World Health Organization [5]

    Breast Milk

A human breast milk sample contained 13.5 ppt of dioxin TEQs on a lipid-adjusted basis.

Environmental Samples


Surface soil samples were collected from three residential yards located across the street from aVCM plant. The concentrations of dioxin TEQs in the three samples were 0.004, 0.019, and 0.028 parts per billion (ppb). At one house, a surface soil sample from the front yard contained0.019 ppb dioxin TEQs, and a surface soil sample from the owner's chicken coop contained 0.0006 ppb dioxin TEQs.


Two chicken eggs given to ATSDR by a Mossville resident and a control egg from a Kansas City supermarket were analyzed for dioxin-like compounds. The results were reported as picograms dioxin TEQs per gram of wet weight and picograms dioxin TEQs per gram of egg lipid.

Table 2.

Dioxin TEQ concentrations in chicken eggs
Kansas City egg 0.101 pg/g (wet weight) 0.946 pg/g (egg lipid)
Mossville egg # 1 0.200 2.09
Mossville egg # 2 0.235 1.76

Next Section          Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #