ATSDR - Health Consultation - Calcasieu Estuary - MOSSVILLE, CALCASIEU PARISH, LOUISIANA

Residents of the community of Mossville in Calcasieu Parish, Louisiana, are concerned about current exposures to releases from neighboring chemical manufacturing plants.

The Agency for Toxic Substances and Disease Registry (ATSDR) conducted an Exposure Investigation (EI) which measured the blood dioxin (chlorinated dibenzodioxins [CDDs] and chlorinated dibenzofurans [CDFs]) levels of some residents [1]. This investigation showed elevated dioxin levels. To rule out current exposures as the cause of these elevated levels, ATSDR, its public health partners, and the community want to characterize the air pathway by conducting appropriate air sampling. This consultation uses dispersion modeling and seasonal weather patterns to identify optimal sampling locations.

Site Description and History

Dioxin may be emitted by any of several industrial facilities located in Calcasieu Parish. Calcasieu Parish contains a large number of manufacturing plants that produce chemicals such as chlorinated hydrocarbon solvents, vinyl chloride monomer, and petroleum-based chemicals. Chemical wastes from some of these industrial operations are burned in hazardous waste incinerators. Small amounts of dioxin are formed during the production of vinyl chloride [2], by the incineration of chlorinated hydrocarbon wastes, and during the regeneration of catalysts used in petroleum refining.

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

ATSDR has conducted an EI to determine if there was evidence for increased exposure to dioxins in residents of Mossville. Blood samples were collected from 28 residents of the community and were analyzed for chlorinated dibenzodioxins, chlorinated dibenzofurans, and co-planar polychlorinated biphenyls. The results of these samples indicated that blood dioxin in the EI participants were higher than a reference population.

Methods

A successful air sampling plan optimizes the possibility of both detecting the chemical and identifying its source. Air dispersion models allow scientists to optimize both of these objectives.

Air dispersion modeling was used to assist with the design of an air sampling plan. The air dispersion modeling will illustrate the transport of each facilities' air emissions. A diagram of the plume transport will provide scientists with conditions which prevent plumes from overlapping. When plumes do not overlap, the source of the emissions are more easily identified.

In an effort to evaluate dioxin exposures though air, it is essential to use the benefits of air dispersion modeling as well as atmospheric sampling. This review of the available data will assist with implementing the air sampling plan.

ATSDR requested an independent contractor (through the interagency agreement with the Environmental Protection Agency's Environmental Response Team [ERT] in Edison, NJ) to use meteorologic data collected at Lake Charles to model the plumes from the five chemical facilities nearest to Mossville to provide the plume impact locations.

Since the source content and magnitude is unknown, modeling only provides maximum impact zones of plumes. Should one of the plumes contain dioxin along with other chemicals, it may be identified through a sampling regime which includes: (1) sampling at the ideal locations identified in the modeling results; (2) measuring meteorologic data concurrent with the sampling; and (3) reconstructing the specific plume path after the samples are analyzed.

Results

A report of the modeling results is attached. The implications are illustrated in Figures 1- 12 which delineate the maximum impact regions for each month. Only a few unique wind directions will allow scientists to find the responsible source of the dioxin if it is found in the downwind samples. It is critical to consider the seasonal winds as well as the sampling locations to optimize sampling. The unique wind directions that will produce impacts that allow us to determine the responsible sources are illustrated in Figures 13 - 15. (** You may obtain a hardcopy of the figures by contacting the ATSDR Information Center, toll free, at (888) 42-ATSDR, that is (888) 422-8737.)

Discussion

The results from the modeling indicate that climate produces a few unique locations to optimize sampling goals. The locations that receive maximum plume impact are depicted on each of the figures. The figures can be used to site samplers to optimize the possibility of detecting dioxin from the potential sources.

Conclusions

1. Models indicate that emissions from the 5 closest facilities can be transported by the wind into Mossville (See Figures 1-12, for each month's relative impact).

2. Mossville is well-situated to detect emissions from the 5 facilities.

3. Model predicted impact zones indicate ideal sites in Mossville for locating samplers to discern the effects of emissions from each of the 5 facilities.

4. Meteorological conditions exist that will enable scientists to distinguish the source of chemicals unique to each of the facilities (See Figures 13 - 15).

Recommendations

1. Sample within the area between Mossville's 3^rd and 8^th Streets.

2. Consult the figures to help select sampling locations suitable for each season.

Collect meteorologic data during sampling.

If dioxin is detected, model the specific transport scenario to determine the source.

References

Agency for Toxic Substances and Disease Registry; Exposure Investigation for Mossville; November 12, 1999.

U.S. Environmental Protection Agency; Estimating Exposure to Dioxin-Like Compounds Volume II: Properties, Sources, Occurrence and Background Exposures; June 1994; EPA/600/6-88/005Cb.

Agency for Toxic Substances and Disease Registry; Health Consultation for Calcasieu Parish; October 16, 1998.

Agency for Toxic Substances and Disease Registry; Toxicological Profile for Chlorinated Dibenzo-p-Dioxins (Update); December 1998.

Preparer of report:
Gregory M. Zarus
Atmospheric Scientist
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

Reviewer of Report:
Susan Metcalf
Section Chief
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

Copies of ATSDR documents are available from the ATSDR Information Center.
Call toll-free, 1 (888) 42-ATSDR or e-mail ATSDRIC@cdc.gov.

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This page last updated on February 6, 2002

Joanne Cox / jdcox@cdc.gov