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Human Health Risk Assesment

Velsicol conducted a human health risk assessment, which was initially submitted to TDEC as a draft in January 2005.  After an extended review process, which included  experts at TDEC, the U.S. Environmental Protection Agency (EPA), the Tennessee Department of Health and TERA (a contractor to the City of Memphis), the report was finalized and submitted to TDEC on June 29, 2006.  TDEC approved the report on July 12, 2006.  The report is entitled Revised Report, Human Health Risk Assessment and Development of Remedial Action Levels for Cypress Creek Sub-Area III, Memphis, Tennessee.  A copy of the approved report is available via this link.

What is a Human Health Risk Assessment?
A human health risk assessment is a regulatory tool used to decide if cleanup of a site is necessary. A risk assessment will not answer questions regarding an individual person’s health condition.

Scientists use a four-part process to estimate the potential that contact with chemicals from a site will harm people now or in the future. This process gives them numbers that estimate how great (or small) the risks may be.

Step 1: Data Collection & Evaluation
In the first step, scientists find out what has happened at and around the site and where chemicals may have been left. They collect samples to determine what chemicals are present and at what concentration. At Cypress Creek, the focus has been on soil sampling and testing.

Step 2: Exposure Assessment
In the next step, the data collected in the first step are used to find out how much of each chemical people may be exposed to. People must come in contact with the chemicals to be at risk. The amount of exposure depends a lot on how much of each chemical is there, who might be exposed, and how they are exposed.

Step 3: Toxicity Assessment
Toxicity Assessment is how we learn about which illnesses or other health effects may be caused by exposure to chemicals. It also says at what dose harmful health effects will occur. This is the same as saying how much of each chemical it takes to cause harm. The higher the dose, the more likely a chemical will cause harm.

Step 4: Risk Characterization
The final step of the process sums it all up. It reveals which chemicals are posing the risks and what the health risks are. It also says how sure scientists are about the results. Since some uncertainty about risk estimates is unavoidable, large margins of safety are built-in to prevent underestimation of the risks. These safeguards are intended to protect the exposed public. The risk assessment is then used to develop a cleanup plan that will make the site safe for current and future uses. We study health risks based on what people do and are likely to do on the site. Our goal is to protect everyone who could come in contact with chemicals from the site, especially children, women of childbearing age, the elderly, and others who may be at greatest risk.

How is human safety considered in the Cypress Creek Risk Assessment?
The process uses a highly protective set of assumptions that are designed to ensure that the most vulnerable individuals, ie., children, women of childbearing age, and the sick and elderly population are protected. Click here to learn more.

  • The risk assessment assumes that people live at the same home for 30 years and this period includes time spent during childhood, adolescence, and adulthood.  In fact, housing statistics show that less than 1 out of 100 of people live at a single residence during this period of their lives.  Housing statistics show that, on average, people in the south live at a single residence for less than four years.

The risk assessment considers exposure to soil/dust by incidental ingestion, inhalation, and skin contact.

    • For inhalation exposure, it assumes that people are breathing air at their home for 24 hours most every day over the entire 30 year period;
    • For skin contact, it assumes that large parts of the body (most of the arms and legs, hands and face) have a thin layer of dirt most every day during the entire 30 year period;
    • For ingestion exposure, it assumes that people eat approximately 2.8 pounds of soil during the entire 30 year period.
    • The assumption that all the soil/dust that people came into contact with comes directly from their own back yard.  Actually, much of the soil we come into contact with comes from other places we visit from day to day such as work, shopping centers, or the homes of friends or relatives.

Some assumptions are made using data from soil samples taken from 0-9 inches deep even though most contact is with soils right at the surface down to about ½ an inch deep.  We know that dieldrin degrades more rapidly when exposed to air and sunlight.  As expected, near surface samples (0-3 inch) from the study area generally have lower levels of dieldrin than deeper samples. For these reasons, use of the 0-9 inch samples overestimates exposure.

The assumption that a safe dose of dieldrin is 1000-times lower than the lowest dose that causes toxicity in animals. To put this assumption into context, it means that a person would actually need to eat over one ton of soil during the 30 year exposure period to achieve the lowest toxic dose in an animal study. Such animal studies are intentionally designed to set protective human doses.  

What is dieldrin?
Dieldrin is a pesticide that was used for many years in termite control and by farmers who used the products on certain crops.

Dieldrin does not dissolve in water very well and is therefore not found in water in high concentrations. The dieldrin in the Cypress Creek area did attach to the soil, however, and tends to stay in the soil unless it is exposed to sunlight and oxygen.

Dieldrin is the primary contaminant of concern in the Cypress Creek environmental program.

To learn more about risk assessment, click here to download a pdf from the Environmental Protection Agency (EPA) or get more information from their web site at http:///www.epa.gov.

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