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Exposure Investigation



The purpose of this exposure investigation is to determine whether individuals living near soil contaminated with mining wastes in the Loflin Hill neighborhood of Trinity, North Carolina are being exposed to unacceptable levels of arsenic. During the exposure investigation, an ATSDR representative collected biological (hair and urine) and environmental (indoor dust) samples to address whether increased arsenic exposure is occurring in the area.


The Loflin Gold Mine, located in Trinity, NC, operated from the mid-1800s until approximately 1910. The mine lies in an area known to have arsenic containing ore. Mining activities expanded the exposure potential to naturally occurring arsenic through excavation, crushing, treatment, and disposal of mine tailings in the area. After the mine's abandonment, the area slowly changed to residential use. Currently there are numerous mobile homes and single-family residences located on or near the old mining property.

In August 2000, the North Carolina Department of Environment and Natural Resources (NCDENR) conducted a site visit and collected three composite soil samples near these residences. Arsenic levels in these composite samples were 32, 611, and 2,024 parts per million (ppm). NCDENR referred the site to EPA Region 4 Superfund Emergency Response and Removal Branch (ERRB) following the discovery of these high arsenic levels in soil near local residences.

In November 2000, ERRB collected twelve soil samples (11 composite and 1 grab sample) to further characterize the extent of arsenic contamination in the area. This sampling indicated elevated levels near the piles of mining ore and proximate to the old mining works. In particular, elevated levels of arsenic were detected near several residences. The highest results occurred near residences on Loflin Hill Road; three samples taken near these residences detected arsenic levels of 132, 270, and 718 ppm. The other samples taken in the vicinity of the Kindley and Daniels Mobile Home Parks had arsenic levels ranging from 14.4 to 57.4 ppm. Arsenic levels typically increased with proximity to the mine tailings and trenches.


Participant recruitment focused on two specific populations who are at increased risk of exposure to arsenic contaminated soil. These groups are 1) residents in the households on Loflin Hill Road where high soil levels were previously detected and 2) children between the ages of 3-17 living in either the Kindley or Daniels Mobile Home Parks.


Prior to testing, each participant or a parent or legal guardian of each minor participant, was required to sign an informed consent/assent form. Written informed consent was also obtained for environmental testing.

An ATSDR representative distributed urine specimen cups and instructions to all participants the day prior to testing. Participants were asked to provide their first morning voided urine specimen. Urine samples were then shipped by overnight mail to the National Medical Services laboratories in Willow Grove, Pennsylvania.

An ATSDR representative collected hair samples (approximately 0.5 grams) from participants in one household following a protocol provided by National Medical Services laboratory. After collection, the hair samples were shipped by overnight mail to the National Medical Services laboratories in Willow Grove, Pennsylvania.

Environmental-indoor dust
One indoor dust sample was collected at each participating residence. Samples were collected using a HEPA vacuum to gather dust in a high traffic area of the house. Participants were asked to identify high traffic areas and all households indicated an area around their front door. A one square meter area was thoroughly vacuumed and the samples were shipped by overnight mail to DataChem Laboratories in Salt Lake City, Utah.

A brief survey was administered to each individual to gather information on risk factors for exposure to arsenic through food pathways, contact with contaminated soils, or use of other arsenic containing products. The survey was administered on initial contact with participants after an ATSDR representative explained consent/assent forms and distributed urine specimen cups.


Urine samples were analyzed for total arsenic using graphite furnace atomic absorption spectroscopy. If total arsenic levels were detected above 10 parts per billion (ppb), samples were analyzed for the inorganic arsenic fraction using atomic fluorescence spectroscopy. Test results were reported as micrograms of arsenic per liter of urine (µg/L or ppb) and in micrograms of arsenic per gram of creatinine (µg/g creatinine).

Hair samples were analyzed for total arsenic by graphite furnace atomic absorption spectroscopy. Test results were reported as micrograms of arsenic per gram of hair (µg/g).

Environmental-indoor dust
Sample collection was performed using a Nilfisk GS-80 vacuum cleaner equipped with a high efficiency particulate air (HEPA) filter. Soil and other particulate matter embedded within the carpet were collected and shipped to the laboratory for sieving and analysis.


Eight individuals participated in this EI. This group, representing four separate households in the Loflin Hill area, was comprised of four adults and four children. Urine and, in some cases, hair, were tested for arsenic. Indoor dust in each participating household was also sampled.

All eight participants provided urine samples. Total arsenic levels in urine ranged from non-detectable to 8.5 ppb. The detection limit was 1.0 ppb. The majority of the participants (75%, 6/8) did not have detectable levels of arsenic in their urine. None of the children sampled had detectable levels of arsenic in their urine. Of the two adults with detectable levels in their urine, concentrations were well below any level of concern (4.9 and 8.5 ppb).

Only two participants provided hair samples for analysis. The arsenic levels for these two hair samples were non-detectable and 0.36 µg/g.

Household dust was tested in all 4 homes. Levels of arsenic in the dust samples ranged from 6.7 to 230 µg/g of dust.


Arsenic can be measured in urine, hair, or blood to evaluate exposure. Measurement of arsenic in blood is not a reliable indicator of chronic exposure to low levels of arsenic since it is cleared from the blood within a few hours and reflects only very recent exposure. Blood arsenic levels are also difficult to interpret since the relationship between levels of exposure and blood concentrations has not been well established.

Urine arsenic is the most reliable method for measuring arsenic exposure, particularly exposures occurring within a few days of the specimen collection. Although a 24-hour urine collection is considered an optimal sample due to fluctuations in excretion rates, most exposure studies use a first morning void or a random sample due to ease of collection. The first morning void urine results correlate well with 24-hour results. Speciated urinary arsenic distinguishes between exposure to inorganic arsenic and its metabolites and the relatively non-toxic forms of organic arsenic commonly found in seafood.

Individuals in this exposure investigation had their urine tested for total arsenic (which could come from all sources--food, water, air, soil and dust). Total urinary arsenic is comprised mostly of organic arsenic from food sources, a much less toxic form than inorganic arsenic. If participant's total urinary arsenic levels were greater than 10 ppb in this exposure investigation, samples were speciated to determine the contributions of organic and inorganic fractions to the total arsenic level. However, none of the urine samples in this EI had total urine arsenic levels greater than 10 ppb.

Participation in this exposure investigation was extremely low. Approximately 25 households were offered free biologic and environmental arsenic sampling, yet only 4 households chose to participate. However, all participating households are in one of the two predefined, high risk groups since they 1) are located in areas with the highest soil arsenic levels or 2) include children who are at increased risk of exposure to contaminated soil through outdoor activities.

The urine arsenic levels in this exposure investigation show very low levels of exposure. These levels are not expected to cause any health problems. Only two of the individuals tested had detectable levels ofarsenic (1 ppb or higher) in their urine, with levels of 4.9 and 8.5 ppb. These values all decreased when correcting for creatinine to standardize urine concentrations. The creatinine corrected values for these two individuals were 2.5 and 4.3 ppb, respectively. Both individuals with detectable levels of arsenic in their urine were adults. It is not clear whether the low arsenic concentrations in these two adults are related to arsenic contamination in soil or dust or are associated with other sources of arsenic in food and cigarette smoke. The individual with the highest total arsenic level of 8.5 ppb reported frequent yard work and gardening activities. It is notable that this individual's household dust level was also the highest in the investigation. Health effects are not expected in an adult with these urine levels. However, two caveats should be kept in mind: 1) These levels may not represent the maximum exposure to this individual over the course of a year, and 2) It is prudent public health practice to encourage individuals to decrease exposures both inside and outside the home.

Since a small amount of internal arsenic is incorporated into the hair as it grows, measurement of arsenic in hair can be used to evaluate potential exposures occurring during the time of hair growth. Theoretically, this could indicate exposures occurring over several months depending on the length of the hair. However, external arsenic found in water and dust particles can adsorb strongly to the hair surface and are not easily washed off even by laboratory methods. Thus, it is difficult to distinguish whether arsenic measured in hair samples is the result of internal absorption or toxicologically insignificant deposition of dust on the hair surface. Nevertheless, measuring hair arsenic levels may be of some value. A hair arsenic level in the normal range indicates that unusual exposure has not occurred. However, if the hair arsenic level is elevated, it is not possible to unequivocally determine whether the person has been exposed to arsenic, or whether the arsenic is just external contamination.

Hair arsenic testing allows us to look at arsenic exposure during the past months or years (depending on the length of the hair). Two individuals had their hair arsenic levels tested and had results of non-detectable and 0.36 µg/g. The detection level was 0.03 µg/g hair. Levels below 1 µg/g hair usually indicate no significant exposure. The participant with the detectable level of arsenic in their hair also exhibited the highest urinary arsenic result. In summary, the hair arsenic levels show very low levels of exposure and these levels are not expected to cause any health problems.

Household dust was tested in all participants' residences. Levels of arsenic ranged from 6.7 to 230 µg/g of dust. The average was 72.7 µg/g of dust. The detection limit ranged from 0.3 to 0.5 µg/g of dust, depending on the mass of the sample. These household dust samples indicate that arsenic contamination is found within some residences in the Loflin Hill area. However, the health significance of these values is not clear. It is evident from hair and urine testing that these dust levels do not appear to be causing elevated arsenic levels in the participants. The findings do suggest that yard soil contaminated with arsenic may be tracked into homes and could increase the potential for exposure. Residents should therefore be mindful of decreasing contact with contaminated soil while working and playing outdoors and should focus on minimizing the tracking of soil into their homes.


  1. Urine and hair arsenic testing show very low or non-detectable levels of arsenic exposure in the sampled population.

  2. These levels are not expected to cause health problems.

  3. Arsenic is present in the dust of households in the Loflin Hill area. However, no significant levels of arsenic were found in biological sampling of residents of households where arsenic was detected in the indoor dust.


  1. Thorough and consistent cleaning of homes (using wet mopping techniques instead of vacuuming) and a focus on decreasing the amount of tracked-in soil from the yard.

  2. Careful attention to using practices and techniques which decrease inhalation and ingestion of soil particles while working in the yard and garden.


Steve Dearwent
Epidemiologist, Exposure Investigations Section
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation

Reviewed by:

Susan Metcalf, M.D.
Chief, Exposure Investigations Section
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation


  1. ATSDR; Toxicological Profile for Arsenic (Update); September 2000.

  2. Kalman DA, et al. The Effect of Variable Environmental Arsenic Contamination on Urinary Concentrations of Arsenic Species. Environmental Health Perspectives, Vol. 89, pp. 145-151, 1990.

  3. National Research Council (NRC). Arsenic in Drinking Water. Washington, DC: National Academy Press, 1999.

  4. National Medical Services, Product Services Manual, 2001.

  5. Weston Inc. CERCLA Removal Assessment, Letter Report, January, 2001.

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