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HEALTH CONSULTATION

GREAT NORTHERN BARK COMPANY
COLUMBIA FALLS, FLATHEAD COUNTY, MONTANA


STATEMENT OF ISSUES

The Agency for Toxic Substances and Disease Registry (ATSDR) was requested to determine if airborne concentrations of volatile organic compounds (VOCs) measured near the Great Northern Bark Company could pose a public health hazard to residents of Columbia Falls, Montana.


BACKGROUND

The facility separates and classifies bark and log-yard waste into beauty bark used for landscaping. Raw material is brought in by truck from sawmills and processed through screens, hogs, and barrel trammels to separate dirt and size the bark. The processed bark is stored in outdoor storage piles and either bagged for shipment or shipped bulk. All activities except the bagging operation occur outside. An aluminum plant is one mile away from this facility. Residents who live near the facility have complained over the past two years about noxious odors, dust and numerous health problems they feel are attributable to the facility.

In December 1999, Montana Department of Environmental Quality (DEQ) collected a single air sample (Summa canister) from a bark pile at the facility. The general categories of compounds detected on 12/99 in the single air sample were: decomposition products of plant and organic matter, automobile and diesel exhaust products, and solvents products from various sources. Analysis of the results by the state laboratory did not identify elevated levels of VOCs. However, residents remained concerned. Flathead County Health Department collected air monitoring for mold spores during the summer of 2001 and detected elevated levels of mold spores in ambient air near the facility. The County Public Health Officer was directed to Centers for Disease Control (CDC) Mycotic Disease Branch for technical assistance.

Flathead County Health Department also completed a door to door (self-evaluation) health survey of residents during the summer months (2001). Analysis of the results revealed a wide range of irritant and upper-respiratory problems reported among the 196 participants. Some residents in the health survey noted odors that were described as pungent, musty, piney, strong turpentine, "penetrating unpleasant woodsy" and "pungent like the inside of a whiskey barrel". Individuals who reported the odor said it was worse from evening until morning. Many individuals also commented on the "red dust" which covered their furniture, penetrated windows to coat windowsills and furniture and was tracked in on carpets [1].

State DEQ records indicate that the facility was in compliance with their current State DEQ issued air permit. A community meeting with representatives of the state, county and the Environmental Protection Agency (EPA) was held in August 2001 at the request of Senator Conrad Burns (R-MT) to facilitate resolution of local health concerns. ATSDR assistance was initially requested (during this meeting) by the EPA/Montana Office Director to evaluate the results of the Health Survey conducted by the Flathead County Health Department. The Chief Medical Officer for the Montana Department of Health has agreed to conduct a focused epidemiological evaluation of the Health Survey.

State DEQ and Flathead County Health officials met and determined that additional air sampling information would be necessary to effectively eliminate/identify airborne chemical contaminants as a possible cause of health problems. State DEQ provided funding sufficient to allow for an additional air analysis using four Summa Canisters. The Flathead County Health Department developed a sampling plan and requested the ATSDR review the plan to ensure that the sampling plan would provide useful screening information necessary to resolve residential chemical exposure concerns associated with the Great Northern Bark Company in Columbia Falls, Montana. The ATSDR response to this request was provided through the Strike Team via an Agency Record of Activity (AROA) dated 10/18/01. The Flathead County Health Department has received the validated analysis of the air sampling and requested the ATSDR to assist in interpreting the sample analysis results.


RESULTS

A total of four (4) Summa canisters sampled air for one hour at two different locations at the perimeter of the facility on 7/10/02. Samples were taken at the same locations in the daytime (2 PM) and evening (9 PM) to compare air quality conditions. The winds were calm. Reports from the health survey indicated that most health complaints occurred when there was little wind and usually in the evening.

The samples were analyzed by combined gas chromatography/mass spectrometry (GS/MS) for tentatively identified compounds. The analyses were performed according to EPA Method TO-15. The Hewlett Packard Model 5972 GC/MS/DS interfaced to a Tekmar Auto Can Elite whole air inlet system/cryogenic concentrator was used for analysis. A 100% dimethylpolysiloxane capillary column was used for chromatographic separation.


DISCUSSION

The potential health effects from inhaling chemical compounds depend on the type and amount of contaminants, the amount of air inhaled, and the duration of inhalation. ATSDR provides public health advice on the basis of a review of the toxicological literature, a comparison of levels of contaminants in air to published standards, an evaluation of the exposure duration, and the population exposed. ATSDR uses different comparison values (i.e., chemical-specific, health-based standards and guidelines) derived by various government agencies to identify contaminants that require further evaluation for possible health effects.

ATSDR used the following comparison values for this health consultation: ATSDR's environmental media evaluation guidelines (EMEG), EPA Reference Concentration (RfCs), or EPA Risk Based Concentrations (RBCs). The glossary provides a summary of ATSDR Comparison Values and definitions. These levels are many (typically 10 to 100) times lower than levels known to be safe. ATSDR uses these comparison values as a means of identifying compounds that are present at safe levels and do not require further evaluation for potential public health implications.

When no standards exist for ambient air in non-occupational settings, the next source of comparison is usually standards that are used in the work place. The American Conference of Governmental Industrial Hygienists (ACGIH) publishes exposure limits (Threshold Limit Values or TLVs) for a total of 40 hours/week, and up to 10 hours a day. The National Institute of Occupational Safety and Health (NIOSH) also develops occupational health standards for substances using recommended exposure limits (RELs) and permissible exposure limits (PELs). The Occupational Safety and Health Administration (OSHA) sets and enforces health and safety standards in the workplace. OSHA has regulatory authority in the workplace setting. Although TLVs and PELs are not directly applicable to 24-hour inhalation exposures in the general environment, these values reflect the best information available from professional toxicologists. These values are clearly not appropriate for some of the listed compounds, since exposure to ambient air in non-occupational settings is often continuous. Still, they are useful numbers in situations where no other standards exist.

Alcohols

Ethanol and 2-Ethyl-1-hexanol are alcohol compounds detected in the air samples. In general, the alcohols are slight irritants at high concentrations, but they are far less irritating than aldehydes or ketones [5]. Ethanol has a mild rather pleasant odor, like wine or whiskey [2]. Ethanol is present in solvents, medicines, consumer products, and alcoholic beverages [2]. It naturally occurs as a plant volatile. 2-Ethyl-1-Hexanol has a rose-like odor (mild, sweet and slightly floral) [2]. 2-Ethyl-1-Hexanol is present as a solvent in dyes, resins, and oils. It is present in inks, rubber, paper, paints and lubricants. It can be emitted from carpets and from some plastics. It is also a naturally occurring plant volatile and can be found in a variety of fruits.

NIOSH has a 10-hour REL of 1,000 parts per million (ppm) (1.9 x 106 µg/m3) for workers who are exposed to ethanol. This level of ethanol is more than 19,000 times higher than the maximum level (100 µg/m3) of ethanol detected near the facility.

The higher the molecular weight, the less irritating the alcohol [5]. 2-Ethyl-1-hexanol has more than twice the molecular weight of ethanol. Therefore, it is even less irritating than ethanol. Occupational and non-occupational standards do not exist for 2-ethyl-1-hexanol. In the absence of standards for 2-ethyl-1-hexanol, the available ethanol standard is used here as a conservative surrogate value. 2-Ethyl-1-Hexanol was detected twice near the facility with a maximum concentration of 200 µg/m3. This is still below the NIOSH 10-hour REL. Therefore, ethanol and 2-ethyl-1-hexanol levels are not present at levels that are likely to cause adverse health effects.

Ketones

Ketones, in general, do not present serious health concern, because they have effective warning properties [5]. Ketones cause CNS depression at high concentrations. Toxic properties increase with increasing molecular weight and unsaturated compounds are more toxic than the saturated compounds. The molecular weight of acetone is approximately half of 3-heptanone. They are equally saturated compounds. Therefore, 3-heptanone is more toxic than acetone based on molecular weight.

Acetone

Acetone has a sweet odor. It's odor threshold in air is 13-20 ppm (31- 57 mg/m3) [3]. Acetone is a solvent with low toxicity and is naturally produced by the human body [2]. Acetone also occurs naturally as a byproduct of plants and animals and from fires. Acetone is used as a solvent for fats, oils, waxes, rubbers, plastics, drugs, paints, nail polish remover, and cements [2].

Acetone degrades in the atmosphere. Its half-life in the air is estimated to be between 71 to 80 days [2]. Acetone in indoor air was detected in a new building at 28 ppb (6.6 x 10-2 mg/m3) in Oregon [3]. Acute exposures of humans to atmospheric concentrations have been reported to produce either no gross toxic effects or minor transient effects, such as eye irritation [2]. People unaccustomed to acetone may experience eye irritation at 500 ppm (1190 mg/m3) [5].

Acetone was detected four times near the facility; the maximum concentration was 40 µg/m3. ATSDR's chronic EMEG for acetone in air is 13 ppm (31 mg/m3), which includes a 100-fold safety factor for neurological effects. This level is 775 times higher than the maximum level (40 µg/m3) detected near the facility. Therefore, it is not a contaminant of concern.

3-Heptanone

3-Heptanone is a natural constituent of beef flavor [2]. It is released from diesel engines, and from waste treatment facilities and textile finishing plants [2]. It can cause mild irritation to the eye, nose, throat, and skin at sufficiently high concentrations [2]. 3-Heptanone was detected once near this facility, at a level of 7 µg/m3. The NIOSH REL for 10 hr TWA is 50 ppm (233,040 µg/m3). This level is 33,291 times higher than the maximum level (7 µg/m3) detected near the facility. Therefore, it is not a contaminant of concern.

Hydrocarbons

The compounds listed below are similar in structure. Occupational and non-occupational standards do not exist. Therefore, the analysis of these compounds will be based on the structural similarity and relative toxicity to similar and more toxic compounds.

Cyclic Hydrocarbons

Alpha and beta pinene, and camphene are cyclic, unsaturated compounds which occur naturally in the essential oils of certain plants and are often used in perfumes and flavorings. In the sap of certain trees, they offer important protection from insects and mites, but are relatively non-toxic to mammals, especially at the levels that occur in ambient air. Although there are no comparison values available for these compounds, none of the concentrations detected in the samples collected near the Great Northern Bark Company on July 10, 2002 exceeded EPA's Reference Concentration (RfC) of 200 µg/m3 for n-hexane, a much more toxic compound. Therefore, there is no reason to expect that pinene or camphene in the ambient air could pose a public health problem at this site.

Long-chain Hydrocarbons

N-undecane, nonanal (the aldehyde of nonane), decanal, n-decanal (the aldehyde of decane), n-dodecane are C9-C24 alkanes (i.e. saturated straight-chained hydrocarbons 9 to 24 carbons long) of low toxicity relative to the C-6 compound, n-hexane. Since the toxicity of saturated hydrocarbons tends to decrease with increasing chain length, all of these alkanes are expected to be less toxic than hexane. All of the concentrations of these C9-C24 alkanes were lower than the RfC for n-hexane (200 µg/m3), therefore all of these concentrations are not of public health concern.

Aldehydes

Aldehydes cause primary irritation of the skin, eyes and upper respiratory tract. The lower the molecular weight of the compound the more irritating the aldehyde. The aldehydes, from lowest to highest molecular weight, are listed as follows: acetaldehyde < benzaldehyde < heptanal < octanal < 2-ethylhexanal < cinnamaldehyde. Therefore, acetaldehyde is the most irritating among the aldehydes detected in the air, because it has the lowest molecular weight.

Acetaldehyde

Acetaldehyde has a pungent suffocating odor, but at dilute concentrations it has a fruity and pleasant odor. The odor threshold of acetaldehyde is 0.05 ppm (0.09 mg/m3) [6, 7]. Acetaldehyde is used to manufacture acetic acid, synthetic flavors (orange, apple or butter flavors), plastics, drugs, dyes, and disinfectants. It can also be found in perfumes, antioxidants, varnishes, vinegar, and yeast [3]. It is naturally present in plant juices, essential oils, roasted coffee, and tobacco smoke [3]. It is present in all ripe fruits that have tart tastes before ripening [2]. Acetaldehyde is degraded in the atmosphere. It's half-life in air is estimated to be 24 hours [2]. At levels between 50 to 200 ppm (90 to 360 mg/m3 ) it can cause eye irritation and upper respiratory discomfort [3]. The median concentration in the general environment is 2.4 - 2.7 µg/m3 [8,9]. OSHA's 8 hour Time Weighted Average (TWA) Permissible Exposure Limit (PEL) for acetaldehyde is 200 ppm (360 mg/m3 or 360,000 µg/m3).

Acetaldehyde was detected only once near the facility at a concentration of 8 µg/m3. EPA's chronic RfC for acetaldehyde is 9 µg/m3. This safe level is higher than the 8 µg/m3 detected near the facility and contains a 1,000-fold built-in safety factor. Therefore, acetaldehyde is not likely to be a health concern.

Benzaldehyde

Benzaldehyde is found in dyes, drugs, perfumes and flavoring agents. It is found in the oil of bitter almond and therefore, has a bitter almond odor [3]. It is present in hickory smoke and gasoline exhaust. It occurs naturally as a volatile plant product, like cranberry aroma. It is a byproduct of toluene degradation in the atmosphere [2]. It degrades in the atmosphere with an estimated half-life of 29.8 hours [2]. It can be a skin irritant if applied directly to the skin in concentrated doses. Benzaldehyde vapors can cause eye irritation [2]. Benzaldehyde was detected twice near the facility. The maximum concentration was 10 µg/m3 near the facility. The EPA RBC for benzaldehyde is 370 µg/m3 [2]. This level is 37 times higher than the maximum level (10 µg/m3) detected near the facility. Therefore, it is not a contaminant of concern.

Cinnamaldehyde

Cinnamaldehyde is a constituent of cinnamon and therefore, has a cinnamon odor. It is a common ingredient in deodorizers, detergents, soaps, and cosmetics. It is often used as a flavoring agent in mouthwashes, gum, ice cream, meats, and baked goods [3]. When applied directly to the skin in a very concentrated form, it can cause skin irritation in some people [2]. Occupational and non-occupational standards do not exist. Cinnamaldehyde was detected twice near the facility; the maximum concentration was 20 µg/m3 in air. It's toxicity is minimal via the air exposure pathway, therefore, it is of little toxicological significance and is not a contaminant of concern.

2-Ethylhexanal

2-Ethylhexanal has a mild odor. It is used in perfumes and disinfectants [2]. It is a volatile component of baked potatoes [2]. It is emitted from particle board [2]. It degrades in the atmosphere; it has a half-life of 11 hours [2]. At sufficiently high doses, it can irritate the eyes and upper respiratory tract [2]. However, it is apparently not toxic enough to warrant any occupational and non-occupational standards. 2-Ethylhexanal was detected twice near the facility; the maximum concentration was 20 µg/m3 in air. It's toxicity is minimal compared to acetaldehyde, therefore, it is of little toxicological significance and is not a contaminant of concern.

Heptanal (synonym: N-Heptanal)

Heptanal has been described as fatty, pungent odor or a penetrating fruity odor [2]. Heptanal is a plant and microbial volatile, it is present in food and widespread in the atmosphere. It is present in a variety of fruits, food additives, perfumes and soaps [2]. In the atmosphere, it degrades with an estimated half-life of 12.7 hours [2]. In high concentrations, it can be irritating to the eyes, nose and oral passages of the upper respiratory tract. The concentration of heptanal in indoor air has been recorded has high as 504 µg/m3 in new homes [2]. Occupational and non-occupational standards do not exist. Heptanal was detected once near the facility; the concentration was 6 µg/m3. This amount of heptanal is not expected to be of any toxicological significance.

Octanal (synonym: 1-Octanal)

Octanal has a sharp, fatty, fruity odor [2]. It is used as a food additive in baked goods, candy, and gelatins. It is found in perfumes, detergents. It is the natural and major component of rose and citrus oils [2 ]. In high concentrations, it can be irritating to the eyes, nose and oral passages of the upper respiratory tract [2]. Occupational and non-occupational standards do not exist. Octanal was detected three times near the facility; the maximum concentration was 30 µg/m3. This amount of octanal detected is of no toxicological significance. Therefore, it is not a contaminant of concern.

Terpenes

Unidentified terpene

Terpenes are a group of unsaturated aliphatic cyclic hydrocarbons that are derived from plants [4]. The best known substances in this group are pine oil, turpentine, and camphor oil [4]. Turpentine is used as a solvent for oils, resins, varnishes, and paints. It is also used in perfumes and deodorizers [2]. All terpenes are local irritants [4]. Terpenes were detected 4 times near the facility; the maximum concentration was 100 µg/m3. Turpentine will be used as a comparison value for unidentified terpenes. The ACGIH 8-hour TWA for turpentine is 100 ppm (560 mg/m3). This level is 5,600 times higher than the maximum level (100 µg/m3) detected near the facility. Therefore, it is not likely to be a contaminant of health concern.

Isoprene

Isoprene has a mild and aromatic odor [2]. Isoprene is ubiquitous in nature and it is released into the environment from vegetables. It has been found in car exhaust and cigarette smoke [2]. It is used in the production of synthetic rubber [2]. The half-life of isoprene in air is estimated at 4 hours [2]. It can be irritating to the eyes, nose and throat, in high concentrations [2].Isoprene was detected twice near the facility; the maximum concentration was 20 ug/m3. The ACGIH TWA for a 8 hours is 50 ppm (139,020 µg/m3). This level is 6,951 times higher than the maximum level (20 µg/m3) detected near the facility. The amount of isoprene detected has little toxicological significance. Therefore, it is not a contaminant of concern.

Beta-phellandrene

Beta-phellandrene is a naturally occurring terpene of essential oils of leaves and flowers.

Other Compounds

Acetic Acid

Acetic acid has a sour, vinegar like odor or pungent odor [2]. Vinegar can contain up to 4 -10% acetic acid [2]. It is found throughout nature as a normal metabolite of both plants and animals [2]. Because it is ubiquitous in the environment, the general public is continuously exposed to this compound [2]. It is an additive for pickles, fish, meat, and candy. It is used in the textile and dye industries [2]. It is used in a fungicide and is widely used in commercial organic synthesis [2]. Unacclimatized humans can experience eye and nasal irritation at concentrations in excess of 25 ppm [2]. Acetic acid is degraded in air; the half-life is estimated at 22 days [2]. Acetic acid was detected once near the facility, at 20 ug/m3. The ACGIH TWA for acetic acid is 10 ppm (24,551 ug/m3). This level is 1,225 times higher than the maximum level (20 ug/m3) detected near the facility. Therefore, it is not a contaminant of concern.

Toluene

Toluene has a sweet odor. It's odor threshold in air is 8 ppm [3]. Toluene is a solvent used for paints, lacquers, gums, resins and as an additive to gasoline. It is used in cements, spot removers, cosmetics, antifreezes and inks. It is released in the atmosphere from cigarette smoke and car exhaust. [2]. It is produced naturally during forest fires [2]. At levels of 100 ppm (370 mg/m3) of toluene in air, humans can experience eye and respiratory irritation [3]. Toluene is a common indoor air pollutant that averages about 30 µg/m3 (8 ppb) [3]. Toluene was detected once near the facility, at 6 µg/m3. The ATSDR chronic inhalation EMEG for toluene is 80 ppb (300 µg/m3) in ambient air. This level is 50 times higher than the maximum level (6 ug/m3) detected near the facility. Therefore, it is not a contaminant of concern.

Odors and Dust

  • Many of the health complaints noted in the self-reported survey include: odor, dust, and upper respiratory complaints. The upper respiratory health concerns can be caused by many factors, such as infections and allergies. It is not possible from a survey to identify the cause of a specific health concern.

  • Many of the compounds detected emit odors similar to those described in the self-reported health survey. At the levels detected, these compounds do not pose a health hazard. However, some of these odors could constitute a nuisance to some people.

  • The compounds measured are not associated with dust emissions. Dust problems were mentioned in the self-reported health survey, however, no particulate sampling data was available for review with this consultation. Although, the concentrations of the compounds measured do not pose a health hazard, the odors and dust could conceivably produce symptoms in some people. Asthmatics and those with chronic respiratory disorders are especially sensitive to dust and sometimes to odors.

  • If past or future particulate sampling data is needed for review, ATSDR will evaluate this data if requested.

DATA LIMITATIONS AND UNCERTAINTIES

The following limitations for this analysis are noted.

  • The data analysis pertains to current exposure levels only. No conclusions can be drawn about past exposure.

  • There were no blank samples (or samples that are known to be absent of VOCs) and therefore, no way to be certain that all the VOCs detected were actually present.

  • ATSDR cannot evaluate the 2 days of monitoring data provided and produce a meaningful public health implication for chronic exposures. A valid evaluation of health risks, such as cancer, that are traditionally associated with chronic (i.e., greater than 1 year) exposures requires data to be representative over the full range of seasons and conditions present.

Limitations of Environmental Sample collection

The total uncertainty is based on sampling uncertainty and analytical uncertainty. Because of the small number of samples, the sampling uncertainty is the more limiting factor. Because of the sampling uncertainty the data should be used for screening purposes only.

Air Sampling

Air is a variable matrix. Values vary by factors of 10 and 100 due to wind direction, wind speed and other atmospheric phenomena. Typical procedures are to collect an 8-24 hour sample for several days to evaluate intermediate or long term exposures. Shorter term samples should be used to evaluate peak exposures, and they also may be used to evaluate if longer-term samples should be collected. Protocol requires that one blank sample (or unused sample) be sent to the laboratory with each day that other samples are collected, with the total number of blanks exceeding 10% of the samples.

Laboratory Analysis

Air samples were analyzed for VOCs and several SVOCs according to EPA method T0-15. Light weight hydrocarbons were analyzed with a full scan by GC/MS, however they have a lower level of quality assurance. The Tier 1 method used by this contractor reports only those compounds which are detected to the level of quality assurance and quality control required of tentatively identified compounds (TICs).

Identification and quantification of the chemicals occurs with a gas chromatography and mass spectrum analysis. This method separates the specific chemicals and quantifies by measuring the mass charge. It is very specific and very sensitive. However, tentatively identified compounds may not be the exact chemical reported, but rather, chemicals that are similar.


PUBLIC HEALTH IMPLICATIONS

Question to ATSDR: Do the contaminants found in the air pose a public health hazard hazard?


CONCLUSIONS

  • Based on the sampling limitations, there is no apparent public health hazard posed by the measured air contaminants to the general population.

  • The odors and dust can produce irritant symptoms in some people but seldom at levels as low as those detected at this site. Asthmatics and those with chronic respiratory disorders are especially sensitive to dust and sometimes to odors.

  • The chemicals measured are not associated with the dust emissions.

  • The chemicals detected are consistent with wood decomposition.

RECOMMENDATIONS

  • Form smaller piles. Smaller piles ferment slowly, producing less odor.

  • Further investigate dust emissions.

  • Further reduce dust emissions with smart management practices.

    • Smaller piles receive less wind erosion.
    • Silt fences reduce migration.

REFERENCES

  1. Letter from the Flathead City-County Health Department, "Health Survey Analysis". August 24, 2001.

  2. HSDS: Hazardous Substances Database. Bethesda, MD: Updated May 2002. Accessed September 2002. National Library of Medicine, National Toxicology Program. Available from URL: http://toxnet.nlm.nih.gov

  3. Sullivan JB and Krieger GR (eds.). Clinical and Environmental Health and Toxic Exposures, 2nd edition. Philadelphia: Lippincott Williams & Wilkins, 2001.

  4. Marcus S and Karkkevandian E. Toxicity, Terpene. E-medicine, Last updated 8/31/01. Accessed September 2002. Available from URL: http://www.emedicine.com/emerg/topic572.htm

  5. Williams PL and Burson JL (eds.). Industrial Toxicology: Safety and Health Applications in the Workplace. New York: Van Nostrand Reinhold, 1985.

  6. U.S. Environmental Protection Agency. Health Assessment Document for Acetaldehyde. EPA/600/8-86-015A. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Research Triangle Park, NC. 1987.

  7. J.E. Amoore and E. Hautala. Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology, 3(6):272-290. 1983.

  8. Shah and Singh, VOCs, Engineering Science and Technology, 2(12) 1381-1388, 1988.

  9. Kelley et al, Outdoor VOCs, Engineering Science and Technology, 28(8): 378A-387A, 1994.

LIST OF ABBREVIATIONS AND ACRONYMS

ACGIH: American Conference of Governmental Industrial Hygienists established standards for occupational settings for five, 8-hour days per week.

ACGIH TLV: The Threshold Limit Value refers to airborne concentrations of substances and represents conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse effect.

ACGIH TLV-TWA: The Threshold Limit Value for a Time Weighted Average concentration is for a normal 8-hour workday, and a 40-hour work week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.

EMEGs: Environmental Media Evaluation Guides are concentrations that are calculated from ATSDR minimal risk levels by factoring in default body weights and ingestion rates.

EPA RBC: Risk-Based Concentrations (RBC) are media-specific concentrations derived by Region III of the Environmental Protection Agency (EPA) They represent concentrations of a contaminant ambient air that are considered unlikely to cause adverse health effects over a lifetime of chronic exposure. RBCs are based either on cancer ("c") or noncancer ("n") effects.

EPA RfC: The EPA Reference Concentration is an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to humans, including sensitive subgroups, that is likely to be without appreciable risks of deleterious effects during a lifetime.

MRL: Minimal Risk Levels are estimates of daily human exposure to a chemical (doses expressed in mg/kg/day) that are unlikely to be associated with any appreciable risk of deleterious noncancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are reported for acute ( 14 days), intermediate (15-364 days), and chronic ( 365 days) exposures. MRLs are published in ATSDR Toxicological Profiles for specific chemicals.

NIOSH: National Institute of Occupational Safety and Health establishes standards for occupational settings.

NIOSH REL: Recommended Exposure Limit is the highest allowable airborne concentration that is not expected to injure a worker; expressed as a ceiling limit or TWA for an 8- to 10-hour workday.

OSHA TWA-PEL: The Occupational Safety and Health Administration sets permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances. PELs are regulatory limits on the amount or concentration of a substance in the air. OSHA PELs are based on an 8-hour time weighted average (TWA) exposure.

RMEG: Reference Dose Media Evaluation Guides are concentrations of a contaminant in air that are unlikely to be associated with any appreciable risk of deleterious non-cancer effects over a specified duration of exposure. RMEGs are derived from EPAs Reference Dose or Reference Concentration, and are for chronic exposures.

Listed below are the abbreviations for the most common units of measure and comparison values.

EMEG= Environmental Media Evaluation Guides
RMEG= Reference Dose Media Evaluation Guide
MCL = Maximum Contaminant Level
ppm = Parts Per Million, e.g., mg/L or mg/kg
ppb = Parts Per Billion, e.g., µg/L or µg/kg
kg = Kilogram (1,000 grams)
mg = Milligram (0.001 grams)
µg = Microgram (0.000001 grams)
L = Liter
m3 = Cubic Meter (used in reference to a volume of air equal to 1,000 liters)


PREPARERS OF REPORT

Ketna Mistry, M.D., F.A.A.P.
Medical Officer
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry

Greg Zarus
Atmospheric Scientist
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry


Reviewed by:

Frank Schnell, Ph.D.
Toxicologist
Petitions Section
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry

Dan Strausbaugh, M.P.H.
Regional Representative
Office of Regional Operations, Region VIII
Agency for Toxic Substances and Disease Registry

Don Joe, PE
Acting Deputy Branch Chief
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry



Table of Contents

  
 
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