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Evaluation of Environmental Contamination and Potential Exposure Pathways Methodology

Quality Assurance

In preparing this report, ATSDR relied on the information provided in the referenced documentsand by contacts with the Alabama Department of Environmental Management (ADEM). ATSDRassumes that adequate quality assurance and control measures were taken during chain-of-custody, laboratory procedures, and data reporting. The validity of the analyses and conclusionsdrawn in this document are determined by the availability and reliability of the information.

Human Exposure Pathway Evaluation and the use of ATSDR Comparison Values

ATSDR assesses a site by evaluating the level of exposure in potential or completed exposurepathways. An exposure pathway is the way chemicals may enter a person's body to cause a healtheffect. It includes all the steps between the release of a chemical and the population exposed: (1) achemical release source, (2) chemical movement, (3) a place where people can come into contactwith the chemical, (4) a route of human exposure, and (5) a population that could be exposed. Inthis consultation, ATSDR evaluates the municipal water that people living in nearbyneighborhoods consume, which might cause a chemical exposure to compounds detected in thegroundwater.

Data evaluators use comparison values (CVs), which are screening tools used to evaluateenvironmental data that is relevant to the exposure pathways. Comparison values areconcentrations of contaminants that are considered to be safe levels of exposure. Comparisonvalues used in this document include ATSDR's environmental media evaluation guide (EMEG)and cancer risk evaluation guide (CREG). Comparison values are derived from available healthguidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor.

The derivation of a comparison value uses conservative exposure assumptions, resulting in valuesthat are much lower than exposure concentrations observed to cause adverse health effects; thus,insuring the comparison values are protective of public health in essentially all exposure situations.That is, if the concentrations in the exposure medium are less than the CV, the exposures are notof health concern and no further analysis of the pathway is required. However, whileconcentrations below the comparison value are not expected to lead to any observable healtheffect, it should not be inferred that a concentration greater than the comparison value willnecessarily lead to adverse effects. Depending on site-specific environmental exposure factors (forexample, duration of exposure) and activities of people that result in exposure (time spent in areaof contamination), exposure to levels above the comparison value may or may not lead to a healtheffect. Therefore, ATSDR's comparison values are not used to predict the occurrence of adversehealth effects.

The comparison values used in this evaluation are defined as follows: The CREG is aconcentration at which excess cancer risk is not likely to exceed one case of cancer in a millionpersons exposed over a lifetime. The CREG is a very conservative CV that is used to estimatecancer risk. Exposure to a concentration equal to or less than the CREG is defined as aninsignificant risk and is an acceptable level of exposure over a lifetime. The risk from exposure isnot considered as a significant risk unless the exposure concentration is approximately 10 timesthe CREG and exposure occurs over several years. The EMEG is a concentration at which dailyexposure for a lifetime is unlikely to result in adverse noncancerous effects [19].

Selecting Contaminants of Concern

Contaminants of concern (COCs) are the site-specific chemical substances that the health assessorselects for further evaluation of potential health effects. Identifying contaminants of concern is aprocess that requires the assessor to examine contaminant concentrations at the site, the quality ofenvironmental sampling data, and the potential for human exposure [4]. A thorough review ofeach of these issues is required to accurately select COCs in the site-specific human exposurepathway. The following text describes the selection process.

In the first step of the COC selection process, the maximum contaminant concentrations arecompared directly to health comparison values. ATSDR considers site-specific exposure factorsto ensure selection of appropriate health comparison values. If the maximum concentrationreported for a chemical was less than the health comparison value, ATSDR concluded thatexposure to that chemical was not of public health concern; therefore, no further data review wasrequired for that chemical. However, if the maximum concentration was greater than the healthcomparison value, the chemical was selected for additional data review. In addition, any chemicalsdetected that did not have relevant health comparison values were also selected for additional datareview.

Comparison values have not been developed for some contaminants, and, based on new scientificinformation other comparison values may be determined to be inappropriate for the specific typeof exposure. In those cases, the contaminants are included as contaminants of concern if currentscientific information indicates exposure to those contaminants may be of public health concern.

The next step of the process requires a more in-depth review of data for each of the contaminantsselected. Factors used in the selection of the COCs included the number of samples withdetections above the minimum detection limit, the number of samples with detections above anacute or chronic health comparison value, and the potential for exposure at the monitoring location.


Groundwater Contaminants Detected Above ATSDR's Comparison Values

Table 1.

Groundwater Contaminants Detected in Brewton Water Works Municipality
Compound Concentration
Range (ppb)
Number of
Value (ppb)
0.5 - 1.819956/70.4CREG
00.6 - 5.419958/90.6CREG

Table 2.

Groundwater Contaminants Detected in Container Corporation's (Jefferson Smurfit) Private Well.
Compound Concentration
Range (ppb)
Number of
Value (ppb)
ppb: part per billion
CREG: Cancer Risk Evaluation Guide


Public Comments

ATSDR held a public comment period May 18-June 21, 1998 to address further questions regarding the Brewton Sites HealthConsultation. No public comments were received by ATSDR during this time period.

1For a complete description of ATSDR's health comparison values, please refer to Appendix B

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
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