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
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
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
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
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.