Mercury Exposures from 3M Tartan Brand Floors
WESTERVILLE, FRANKLIN COUNTY, OHIO
The Health Assessment Section of the Ohio Department of Health was contacted on June 18, 2002, by Mr. Wesley Newhouse, an attorney representing Westerville Schools, regarding the presence of mercury in several of the school district's gymnasium floors. Specifically, HAS was asked to determine if this mercury had the potential to pose a health risk to the children and faculty attending the schools. During a meeting conducted at the Ohio Department of Health on November 22, 2002, HAS staff were presented with the available data collected by the school and asked to give advice and recommendations. This health consultation documents the review of the available data and the conclusions and recommendations that were given to the school district.
The 3M Tartan Brand floor covering is a solid, rubber-like polymer floor covering developed in the 1960's and promoted as a substitute for and improvement over wood flooring in gymnasiums and as a durable running surface for both indoor and outdoor track & field facilities. Westerville Schools had the material installed in eight of their schools built in the 1970's, including one of the high schools. According to 3M, mercury was used as a catalyst when mixing the polymer to form the floor covering such that the finished product typically contained 0.1 to 0.2% mercury (3M, 2002). Concerns about mercury exposure initially arose in the Westerville School District after it was determined that the school's 3M Tartan Brand gymnasium floors contained small amounts of mercury. The discovery came when a contractor removing the old flooring in one of the buildings questioned how the floors should be disposed. After having discussions with 3M and learning that the floors contained small amounts of mercury, the school chose to have the flooring analyzed utilizing the toxic characteristics leaching procedure (TCLP) test. This test is designed to identify materials that should be treated as hazardous waste by determining the amount of chemical that is likely to leach out of the material once it is placed in a landfill. A material leaching mercury in this test at a concentration above 0.2 milligrams per liter (mg/l) must be managed as a hazardous waste. The school's consultant, Gandee & Associates, collected ten samples of the 3M Tartan Brand flooring from nine schools for analysis in May 2002. Five of the nine schools' flooring samples exceeded the TCLP standard for classification as hazardous material (Gandee & Associates, 2002).
In addition to the disposal concerns, Mr. Newhouse and the school's consultant had concerns about the possibility that the mercury could be vaporizing from these floor materials into the indoor air of the schools. Supporting documentation supplied by 3M confirmed that mercury vapors have been detected in indoor air environments of other buildings containing the 3M Tartan Brand floors at levels up to 22 micrograms per cubic meter (µg/m3). Mr. Wesley contacted HAS and stated that the school had concerns about the possibility of mercury vapors being present in the school and was contemplating hiring an outside consultant to measure the mercury vapors in the indoor air of the school. HAS informed Mr. Wesley that this was a unique situation with few or no precedents and that without the additional indoor air data it would be impossible to determine if the students or faculty of the school are being exposed to elevated levels of mercury vapors at levels of health concern. HAS recommended that the school continue with their plans to monitor the indoor air of the schools for mercury to determine if students and faculty were being exposed to unacceptable levels of mercury vapor.
With guidance from HAS, Westerville Schools decided that to be protective of the health of their students and faculty it would be necessary to analyze the indoor air of the affected schools for mercury vapors. The school district obtained the services of Tetra-Tech to design and implement an indoor air sampling plan in all nine schools that had mercury containing floors. Seventeen air samples were collected and analyzed for mercury vapor concentrations in three elementary schools and one high school in the Westerville School District. In addition, Tetra-Tech conducted real-time mercury vapor air sampling using a Lumex mercury vapor analyzer Model RA-915+, in eight elementary schools and one high school. The Lumex meter is a hand-held atomic absorption unit that is capable of measuring mercury vapors in air at levels as low as 2 nanograms per cubic meter (ng/m3).
Mercury vapor air samples were collected at Annehurst, Cherrington, and Pointview Elementary Schools and Westerville North High School. The air samples were collected in the gymnasiums of each school. The mercury vapor concentration within the breathing zone of the Annehurst Elementary School gymnasium was between 1.5 and 1.6 micrograms per cubic meter (µg/m3.). The mercury vapor concentration within the breathing zone of the Cherrington Elementary School was between 1.4 and 1.6 µg/m3. The mercury vapor concentration within the breathing zone of the Pointview Elementary School gymnasium was between 0.79 and 0.94 µg/m3. The mercury vapor concentration within the breathing zone of the Westerville North High School gymnasium was between 0.86 and 0.89 µg/m3. (Tetra-Tech, 2002).
Using the Lumex, real-time mercury vapor concentrations in the indoor air of all schools were measured from non-detectable levels to a high of 1.43 µg/m3 in Annehurst Elementary School (Tetra-Tech, 2002).
In addition to measuring the mercury vapors in indoor air, Tetra-Tech also placed gym equipment, including athletic balls, rubber floor matts, and stage curtains in plastic bags and measured the amount of mercury vapor volatilizing into the air. These objects also were found to contain mercury and were degassing vapors at maximum levels of 2-9 µg/m3. These levels, while generally higher than the indoor air values obtained for the gymnasium area as a whole, are still below the 10 µg/m3 action level ATSDR has established as safe enough to allow for the return of mercury-contaminated personal property (ATSDR, 2000).
To date, flooring has been removed from Annehurst, Cherrington, and Pointview elementary schools where both total leachable mercury and mercury vapor exposures were the highest. Mercury vapor levels in these three schools have dropped to nearly non-detectable levels following the removal actions. No decision has been made as to whether the gymnasium floor in the Westerville North High School will be removed. Mercury vapor levels in the high school are generally lower than in the other schools sampled. In addition the Tartan floor in the North High School has been covered by a wooden floor which might reduce potential exposures.
When evaluating exposures to mercury vapor, HAS generally compares detected levels of mercury to the Agency for Toxic Substances and Disease Registry's (ATSDR) Minimum Risk Level (MRL). This level is the amount of mercury vapor in the air that is unlikely to produce adverse health effects based on a continuous exposure over a person's lifetime. The MRL does not indicate a threshold level above which toxic effects are likely to occur, but rather provides a trigger or screening level to suggest to public health officials that a closer examination of the potential exposure may be warranted.
MRLs are acknowledged to have a level of uncertainty about them, and represent the conservative boundary of that uncertainty. It is generally accepted that MRLs are thought to be protective of all populations including sensitive populations such as children and pregnant women.
ATSDR's chronic inhalation MRL for mercury vapor is 0.2 µg/m3. The United States Environmental Protection Agency's (EPA) reference concentration (RfC) is 0.3 µg/m3. They are both based on the same study (Fawer et al., 1983), an occupational study in which workers were exposed to an average airborne mercury concentration of 26 µg/m3 for an average length of 15.3 years experienced subtle neurologic effects (electrophysiologically-measured fine motor tremors measured during mechanical stress). To calculate the MRL, the 26 µg/m3 was adjusted from the 8 hour per day, 5 day per week occupational exposure in which it was measured to a 24 hour per day, 7 day per week exposure scenario. The calculated value was then divided by an uncertainty factor of 30 [10 to account for the variability within the human population and 3 to account for the use of the lowest observed adverse effect level (LOAEL) rather than a "no observed adverse effect level" (NOAEL) in the derivation process].
The small difference between the MRL and RfC is due to slightly different assumptions in calculating the final "safe level," and is not considered to be biologically significant. Thus, ATSDR considers EPA's RfC to also be a safe level for up to a lifetime of exposure for all populations.
Given the limitations in the level of precision of current mercury vapor monitoring equipment, and the necessarily conservative approach to the derivation of the MRL and RfC, ATSDR typically considers mercury vapor concentrations of 1 µg/m3 to satisfy the safety requirements for airborne mercury exposure in a residential scenario. Confidence that the 1 µg/m3 value is safe is provided by the fact that there are no credible studies that indicate or suggest that health effects due to inhalation of mercury vapor might occur at air mercury concentrations less than 10 µg/m3 (ATSDR, 1997).
Westerville School Exposures
The highest level of mercury vapor detected in the indoor air of any of the Westerville school gymnasiums was 1.6 µg/m3 in the Annehurst and Cherrington Elementary Schools. Both of the Tartan brand floors in these schools have been removed. The level of mercury detected in the schools is slightly above the ATSDR recommended screening level of 1 µg/m3. It is unlikely that children and staff exposed to these levels would be expected to develop adverse health effects because of the relatively short periods of time spent in the gymnasium and the fact that students are only enrolled at the schools in question for a limited number of years.
Equipment tested in the schools was found to contain mercury vapor concentrations of 2-9 µg/m3. ATSDR has established a screening level of 10 µg/m3 for returning personal property after mercury contamination. Westerville Schools took it upon themselves to replace all of the equipment in the elementary schools found to be contaminated with mercury.
While it is unlikely that students or faculty would have been expected to experience adverse health effects from exposure to the mercury detected in the gymnasiums in question, HAS agrees with the decision to remove and replace the Tartan brand gym floors. There are several factors that make replacing the flooring a favorable option; 1) the Tartan brand floor material is a source of long-term release of mercury vapor to the environment; 2) the full extent of human health effects from long-term exposure to low levels of mercury vapor in indoor air are not fully understood; 3) children playing in the gymnasium are likely exerting themselves and thus are breathing heavier and most likely would have a greater exposure than a sedentary person; 4) the polymer flooring material breaks down with age, possibly leading to the release of increasing levels of mercury vapor into the air through time; and 5) data from 3M (1971) has suggested that mercury vapor levels associated with this flooring might reach levels as high a 22 µg/m3.
HAS and ATSDR understand that when it comes to exposure to toxic chemicals that children are at a greater risk that adults. Children have developing body systems that are more easily impacted by exposure to hazardous chemicals. This is especially the case with mercury. Children under six and pregnant women would be at the most risk when exposed to mercury vapor due to their developing nervous systems. Children playing in the gymnasiums are likely to have increased exposures due to the fact that they are exerting themselves and are breathing heavier. To take the most conservative approach, HAS assumed that children under six were being exposed when writing conclusions and making recommendations.
The levels of mercury vapor detected in the Westerville Schools posed "no apparent health hazard" to the students and faculty attending the schools. Based on the relatively low levels of mercury vapor detected and the fact that the length of exposure is likely to be short, it is unlikely that anyone exposed to the mercury vapors would suffer from adverse health effects. Westerville Schools has taken a preemptive approach to reduce possible exposures by removing the floors with the highest mercury vapor concentrations, thereby eliminating the mercury source.
HAS agrees with Westerville's decision to remove the flooring based on the potential for the flooring to emit higher levels of mercury vapor in the future.
It is likely that 3M Tartan Brand floors are present in a large number of school gymnasiums in Ohio and across the country. There are many uncertainties with regard to a public health threat posed by the flooring and 3M's own data has shown that mercury vapor levels in the flooring have reached levels as high as 22 µg/m3. Based on the uncertainty involved with the material, the Ohio Department of Health has begun to attempt to identify other schools in Ohio that may contain the 3M Tartan flooring. We are working with U.S. EPA to locate some schools that are willing to participate in a pilot study to determine a range of mercury vapors associated with the flooring and also if mercury vapor levels are stable or if they change based on usage conditions of the flooring. We also hope to develop an investigation and removal standard operating procedure to provide to schools so that there is a universal approach to investigating the flooring. We hope to be able to build a better understanding of the ability of the flooring to leach mercury vapor in hopes to make a statewide recommendation on how or whether schools should proceed with an investigation of their synthetic flooring.
Eric Yates, environmental specialist
Robert Frey, Ph.D., principal investigator
Agency for Toxic Substances and Disease Registry. Suggested Action Levels for Indoor Mercury Vapors in Homes or Businesses with Indoor Gas Regulators. December 2000.
Agency for Toxic Substances and Disease Registry. Toxicological Profile for Mercury. U.S. Department of Health and Human Services. September 1997.
Fawer RF, DeRibaupierre Y, Guillemin M, et al. 1983. Measurement of hand tremor induced by industrial exposure to metallic mercury. Br J Ind Med 40:204-208.
Gandee & Associates. Toxic Characteristic Leaching Procedure laboratory results from Westerville Schools. June 18, 2002.
Tetra Tech EM Inc. Letter RE: Mercury Vapor Air Monitoring - Westerville Elementary Schools. July 19, 2002.
3M Environmental Technology and Services. Letter from Eric A. Reiner to Jeff Wright of Westerville Schools disclosing the mercury content of the Tartan Brand flooring and the proper ways to dispose of the material. July 26, 2002.
This Westerville Schools Public Health Consultation was prepared by the Ohio Department of Health under the a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the public health consultation was initiated.
Alan W. Yarbrough
Technical Project Officer, SPS, SSAB, DHAC, ATSDR
The Division of Health Assessment and Consultation, ATSDR, has reviewed this Public Health Consultation and concurs with its findings.
Chief, State Programs Section, SSAB, DHAC, ATSDR