New-Indy Catawba LLC frequently asked questions.

1. What do the daily graphs from air monitoring stations show?

The New-Indy air monitors are stationary instruments that provide data that is averaged over 30-minute periods of time. The onsite instruments measure hydrogen sulfide (H2S) down to four-tenths parts per billion (0.4 ppb). The offsite instruments measure hydrogen sulfide (H2S) down to two-tenths parts per billion (0.20 ppb). The purpose of the stationary monitors is to provide quantitative information regarding H2S concentrations at New-Indy and in the community. The red line in the graphs is set at 70 ppb, which is the 14-day Minimum Risk Level (MRL) for H2S exposure developed by the Agency for Toxic Substances and Disease Registry (ATSDR). An MRL is defined as an estimate of daily exposure to a substance (H2S) that poses a minimal risk of adverse effects to humans over a specified duration of exposure (14 days).

2. Is the community’s drinking water impacted from the New-Indy wastewater discharge?

No. The South Carolina Department of Health and Environmental Control (SC DHEC) routinely monitors public drinking water as well as the water quality of the rivers in South Carolina. The intake for drinking water systems supplying the neighborhoods in the area are UPSTREAM from the New-Indy discharge. The nearest downstream intake is 9 miles downriver. No issues related to New-Indy have been identified that are affecting drinking water quality. SC DHEC, in coordination with the Catawba Riverkeeper, conducted a special study on the river, looking at upstream and downstream locations relevant to New-Indy. The study found there were no significant impacts to the Catawba River from the New-Indy wastewater discharge. The report can be found at https://scdhec.gov/sites/default/files/media/document/CatawbaRiverStudy_Final.pdf.

3. What is the Community Engagement Group and what is its purpose?

The Community Engagement Group (CEG) provides a way for New-Indy and its neighbors to communicate directly, to form relationships with each other, and to work together to identify concerns and develop solutions. New-Indy Catawba created the CEG to improve dialogue with residents in the communities surrounding the facility and to build respect, trust and confidence with local citizens. We hope that this will help identify and resolve any concerns. New-Indy Catawba remains firmly committed to operating in a safe and sustainable manner, which will have a positive impact on the local community and South Carolina.

4. What does the foul condensate steam stripper do and why can’t New-Indy just use it to reduce odor?

The stripper treats foul condensate (foul in this instance denoting “dirty” condensate discharge) generated during the manufacture of pulp to strip hydrogen sulfide (H2S) and other non-condensable gases (NCG’s) from such condensate. The stripped H2S and NCG’s are then burned in one of the combustion boilers at the mill. At present, the stripper is not sized to treat all foul condensate generated by the mill. New-Indy is investigating several modifications that it may make to the stripper and related equipment to increase the volume of foul condensate that the stripper can process.

5. Why is New-Indy removing fiber from the aeration stabilization pond (ASB) and how much are they going to remove? What will keep the fiber from building up again and where is the material being discarded?

The layer of fiber on the ASB was the result of initial startup operations following the conversion from bleached paper to unbleached containerboard. The fiber interfered with the proper operation of the ASB and made it difficult for mill personnel to conduct preventive maintenance and repairs. As a result, several aerators in the ASB became inoperable. The situation was exacerbated by the inclement weather in January and February which prevented timely access to the ASB for heavy equipment contractors to begin the solids removal process. Beginning on March 1, 2021, New-Indy began removing fiber from the surface of the ASB. This effort has continued using various methods, including using a barge to dredge and push fiber toward the edge of the ASB. Fiber that is removed is hauled to the No. 4 sludge pond where it is processed with other similar waste. These continuing remedial measures to remove fiber have allowed personnel to reach the aerators, conduct maintenance and repairs on those aerators and return them to service, which has improved performance of the ASB and reduced related air emissions and odors.

6. What is a stack test? Was it performed and what are the results of the tests?

A stack test, also referred to in EPA regulations as a performance or source test, measures the amount of a specific regulated pollutant, pollutants, or surrogates being emitted from an air emissions source, such as a stack or vent. Testing is required by a facility’s Title V Air Permit on a periodic basis. Testing the air emissions from these devices (stacks/vents) requires highly sophisticated protocols and techniques to ensure that the air quality is accurately measured and characterized. All of the stack tests required by EPA and SC DHEC have been performed, and the sampling and testing results are being analyzed to ensure data quality. This data has been submitted to SC DHEC for review and evaluation. Once approved by SC DHEC, the data will be used to generate air dispersion models to evaluate any potential offsite impact from New-Indy’s emissions.

7. Why are there fewer monitoring stations now that New-Indy is doing the monitoring?

A large amount of data has been generated by the EPA monitors, which has been helpful in pin-pointing locations where H2S levels might be elevated. As such, SC DHEC has concurred in the placement of New-Indy monitors in the areas most likely to experience elevated levels of H2S and at locations where permission was granted to install a monitor.

8. Why was New-Indy allowed to start up the plant without a foul condensate stripper?

The option to discharge the foul condensate to the wastewater treatment system instead of through the steam stripper is allowed under the federal air regulations (40 CFR Subpart S). SC DHEC approved the hard piping of the foul condensate in a revised construction permit issued on May 13, 2020. When the odor issue arose, New-Indy voluntarily decided (with SC DHEC approval) to restart the stripper on May 3, 2021.

Hydrogen Sulfide Q&A with Dr. Christopher Teaf

President & Director of Toxicology, Hazardous Substance & Waste Management Research, Inc.

1. What is hydrogen sulfide? Does hydrogen sulfide exist in nature or is it a “man-made” chemical? What are some possible sources of hydrogen sulfide?

Hydrogen sulfide (H2S) occurs naturally. H2S and related reduced sulfides, are produced when bacteria break down organic material such as plant or animal tissues where oxygen is limited (e.g., swamps, wetlands). It is not an unusual substance, and occurs in nature, as well as from some industrial sources. The World Health Organization (WHO) estimates that 75 to 250 million tons per year of H2S are released from all land and ocean sources, including natural sources, industrial petroleum processing, geothermal energy production, tanneries, and paper mills of various types.

2. How easy is it to smell hydrogen sulfide, compared to other odors? Why do people refer to “rotten eggs” as the odor associated with hydrogen sulfide?

H2S is easily detected by smell compared to other odors. The fact that you are smelling an odor does not mean that it is causing you harm. While the reported detection threshold for H2S in air for most people is in the range of 1 to 10 parts per billion (ppb), a very wide range from 0.5 to 300 ppb often is reported. Rotten eggs produce hydrogen sulfide and other reduced sulfur compounds when they decompose.

3. Can you be harmed by H2S if you cannot smell it? Is it similar to carbon monoxide?

H2S is not similar to carbon monoxide, which is a completely odorless gas. Generally, it is not possible to be harmed by H2S if you do not smell it. Even when the odor is detectable, in situations where people can move around freely, H2S is almost never a health issue. In other words, even if you do smell H2S, it does not mean that what you are smelling is harmful. Most of the time it is not.

4. How is hydrogen sulfide created? Is hydrogen sulfide always a gas? Does hydrogen sulfide exist in water? Should I be concerned that hydrogen sulfide may occur in household water?

H2S is a gas under normal circumstances. It dissolves in water, but its vapor pressure causes it to leave water quickly. There are no federal or state drinking water standards for H2S, and it is of health interest only in rare situations. If H2S taste or odor is present in water supplies, it is treated by filtration or oxidation. Occasionally, H2S is produced in homes by sulfate bacteria in electric hot water heaters. H2S is also formed as a natural product in our bodies, for example “morning breath” and intestinal gas.

5. Does hydrogen sulfide have any beneficial uses?

H2S occurs naturally, is used industrially to produce sulfuric acid and elemental sulfur and can be used to produce “heavy water” for nuclear plants. It has protective and beneficial characteristics in Alzheimer’s models and some other studies.

6. At what level is hydrogen sulfide dangerous to humans and pets? Does prolonged exposure to low H2S concentrations cause health issues for humans and pets? Is intermittent or occasional exposure to small to intermediate levels of hydrogen sulfide unhealthy? Are the elderly, the young and people with compromised immune systems more likely to suffer adverse health effects from either prolonged or intermittent exposure to hydrogen sulfide?

H2S typically is addressed as an odor, not a health concern. The Agency for Toxic Substances and Disease Registry (ATSDR) set a Minimal Risk Level (MRL) for H2S at 70 ppb to protect sensitive portions of our population, such as the elderly or young. H2S air levels below 70 ppb may be detectable by smell, but are not harmful to people or pets, even if exposures are common, or if brief, infrequent exceedances occur. The 70 ppb MRL does not mean that levels above 70 ppb necessarily are harmful. Rather, it is a conservative guideline for sensitive members of the population.

7. What are the health effects associated with hydrogen sulfide exposure? Do the health effects end after exposure ceases?

Exposure to concentrations of hydrogen sulfide greater than the MRL of 70 ppb in air for periods of time exceeding several weeks may cause transient and mild irritation of eyes, nose, and throat, which are reversible when exposure ceases. Individuals who are unable to smell H2S do not experience such responses.

Short-term exposures to H2S at concentrations of parts per million or higher (1 ppm = 1,000 ppb) have been reported to occasionally cause nausea, headaches, disturbed equilibrium, neurobehavioral changes, olfactory paralysis, loss of consciousness, and tremors, depending on the levels. While some persistent effects have been reported in workers exposed to H2S at high levels for long periods, effects from environmental exposures are reversible.

8. What should I do if I smell hydrogen sulfide inside my home? Outside my home?

If you are outdoors when you smell H2S, you may wish to go indoors temporarily to avoid the smell. Because it is a relatively common airborne substance, and often is associated with sewage treatment plants, sewage lift stations, decomposing vegetable matter, landfills and some industrial activities, it often is detectable near these facilities. If smells are localized indoors, ventilating the home typically is beneficial, assuming that there is not a continuing source in the home itself (e.g., hot water heater or water supply).

9. What is the most effective way to remove H2S from the home if it is entering from the outside?

Air filtration devices are available for residential applications and would be expected to help dissipate H2S odors, both existing and new.

10. Does the federal government regulate hydrogen sulfide? Is hydrogen sulfide a pollutant under federal law? Other than workplace limits imposed by the Occupational Safety and Health Administration (OSHA) has the federal government-imposed exposure limits for hydrogen sulfide? What are the exposure guidelines for hydrogen sulfide?

The workplace OSHA concentration for H2S is 20,000 ppb (20 ppm), based on a 15-minute time-weighted average. Other regulatory agencies have developed guidelines for H2S, including in occupational and environmental circumstances. There are no federal standards for air (other than for petroleum refining facilities), but protective guidelines have been recommended at the MRL of 70 ppb, which is the safe level for exposures of less than or equal to 14 days.

11. Is H2S considered a toxic substance under federal law?

H2S is not regulated by federal law according to air concentrations. There are Clean Air Act requirements related to H2S release prevention and planning. Therefore, H2S release is regulated for reporting and planning purposes beyond threshold quantities, but not by air concentration. There are also federal Permissible Exposure Limits (PELs) that apply in the workplace, but not outdoor air.

12. Is hydrogen sulfide likely to affect me or my family? If I smell “rotten eggs” am I in danger? Do I need to wear personal protective equipment if I encounter hydrogen sulfide?

In situations where people can move around freely, H2S is almost never a health issue, though the odor of H2S is easily detected. Protective equipment is not necessary except for some enclosed industrial operations.

13. Each year, how many people in the United States die from exposure to hydrogen sulfide? How many people in the U.S. each year suffer adverse health effects from exposure to hydrogen sulfide? Where do those situations typically happen?

The U.S. Bureau of Labor Statistics estimated fewer than 50 fatalities during the period from 2011 to 2017, approximately 8 per year. The cases typically are attributed to industrial accidents or entry into confined spaces containing high levels of H2S. 

14. What other resources are available if I would like additional information on hydrogen sulfide?

There are many sources of information regarding H2S, ranging from simple and straightforward to highly detailed and complex. These include:

ATSDR (Agency for Toxic Substances & Disease Registry). 2016a. Toxicological Profile for Hydrogen Sulfide and Carbonyl Sulfide. U.S. Department of Health and Human Services. Atlanta, GA.

ATSDR (Agency for Toxic Substances & Disease Registry). 2016b. Tox Guide for Hydrogen Sulfide (H2S). U.S. Department of Health and Human Services, Public Health Service. Atlanta, GA.  

ATSDR (Agency for Toxic Substances & Disease Registry). 2016c. Public health Statement: Hydrogen Sulfide (H2S). U.S. Department of Health and Human Services, Public Health Service. Atlanta, GA.

California ARB (California Air Resources Board). 2021. Hydrogen Sulfide & Health.

MN DOH (Minnesota Department of Health). 2019. Hydrogen Sulfide and Sulfur Bacteria in Well Water: Well Management Program. August 2019.

Wastewater Treatment System Q&A with Mike Foster

Principal Consultant, Environmental Business Specialists

1. Why does New-Indy Catawba (NICB) have such a large wastewater treatment system?

The production of pulp and paper is a water intensive process. Converting wood into paper requires a combination of physical, chemical, and thermal steps that produce fiber stock, recoverable energy, and process water that contains impurities that must be removed before it can be discharged. Fully integrated pulp and paper mills, such as NICB, employ systems that treat as much wastewater each day as a medium-sized city of over 100,000 people.

2. Can NICB recycle the water back to the mill and/or recover the impurities to use elsewhere?

The U.S. pulp and paper industry is a highly sustainable industry and has made great environmental strides over the past 20-30 years in terms of reduction in amount of water consumed per ton of paper produced, quantity of permitted components discharged, such as biochemical oxygen demand (BOD) and total suspended solids (TSS), and air emissions of hazardous air pollutants (HAPs) from wastewater collection and treatment systems. Most mills recycle significant quantities of process water, recover/refine chemicals from the wood (turpentine, soaps, and tall oil), and produce steam and electricity from such wood lignin burned in the mill’s recovery boilers.

The reality is that water can be recycled only to a certain point, after which it must be purged, collected, treated, and discharged to a receiving stream. No recovery or refining process is 100% efficient. There are practical limitations in recovering or removing all of byproducts and impurities that leave the mill, which necessitates the existence and operation of a wastewater treatment system that employs biological and physical treatment technologies.

3. What is sludge?

Sludge is the term for the biological solids generated when microbes (bacteria) degrade organic matter. As the microbes convert the organic material (BOD) into carbon dioxide and energy, they reproduce, creating additional bacterial cells. When all, or most, of the BOD is converted, the bacteria run out of “food” and the solids settle to the bottom of the ASB or #1 Holding Pond creating a layer of solids referred to as sludge. It is important that these solid particles settle somewhere in the system to avoid being discharged.

4. Can sludge be used as fertilizer?

The short answer is “maybe”. The limitations are the variability of the nutrient content in the sludge, permitting considerations, and the costs of handling, hauling, and application. NICB is continually exploring beneficial reuse opportunities for the various solid byproducts produced in their process.

5. How does NICB treat their wastewater?

The NICB wastewater is treated in a system referred to as an Aerated Stabilization Basin (ASB) and is the most common type of wastewater treatment system used by pulp and paper mills in the Southeastern United States. The term ASB generally is assigned to both the specific basin that contains the bulk of the aeration and the entire system including the settling and holding ponds. There are five steps involved in the NICB treatment process:

  1. Collection and transfer of the wastewater from the many locations throughout the mill to the wastewater treatment system via a network of sumps, pumps, and lift stations.
  2. Primary treatment – Settling of insoluble material in a primary clarifier, which removes fugitive solids such as wood fiber, boiler ash, lime mud, and general silt and sand.
  3. Reduction of BOD and other specific compounds that can be detrimental to aquatic life in the Catawba River. This occurs primarily in the ASB. The soluble BOD is converted to additional bacteria (biomass) resulting in an effluent that contains an acceptable BOD concentration under the National Pollutant Discharge Elimination System (NPDES) permit and the newly formed biomass, which must be removed by settling before discharge.
  4. Settling of solids created by the conversion of soluble organic matter (BOD) into additional bacteria (bugs) to avoid discharging solids to the river. This occurs in the #1 Holding Pond, which also serves as an equalization pond to hold water and discharge in a manner that ensures permit compliance and provides an additional layer of protection to the Catawba River.
  5. Discharge to receiving stream is monitored for numerous parameters that are listed in the NICB’s NPDES permit.
6. What is BOD?

BOD is the abbreviation for biochemical oxygen demand and is a measure of the biodegradable organic material that is in the wastewater. The bacteria in a wastewater treatment system function identically to the naturally occurring bacteria in a stream, lake, or river. The bacteria utilize available dissolved oxygen (DO) to metabolize organic matter to create additional bacteria and carbon dioxide. As related to humans, the way we measure the “strength” of our food is in calories, which is analogous to BOD for the bacteria. In both cases, the organic material is aerobically metabolized to produce energy, new cells, and carbon dioxide.

7. Why should BOD be removed before wastewater is discharged into the river?

Removal of BOD prior to discharge is critical because a “receiving stream”, i.e., a river or lake, must maintain adequate dissolved oxygen (DO) levels to support desirable aquatic life, such as game fish like bream, crappie, bass, and trout. All streams have a natural ability to handle a certain amount of organic loading from agricultural, municipal, and industrial discharges. This is called the assimilative capacity of the stream. If the total amount of BOD or other contaminants does not exceed this capacity, the receiving stream can naturally metabolize the organic material, thus maintaining a healthy environment for the aquatic life. If the assimilative capacity is consistently or excessively exceeded, the bacteria in the stream will consume more oxygen than is naturally replenished resulting in stream oxygen concentrations dipping below necessary levels to sustain aquatic organisms such as fish.

8. What is the relationship between the New-Indy ASB and hydrogen sulfide emissions?

No manufacturing facility, including NICB, has any incentive to create or release waste material that must be treated or hauled away for disposal. The components in a wastewater stream are comprised of impurities that adversely impact the quality of the paper produced and some desirable materials that the mill would prefer to capture in the process. Therefore, NICB has an incentive to minimize the loading to the ASB, which directly reduces the potential for odor formation.

When the bacteria utilize oxygen to degrade the BOD, the main byproduct is odorless carbon dioxide (CO2). However, ASBs are large non-homogenous ponds with numerous competing biological reactions occurring simultaneously. One of those competing reactions is carried out by a group of bacteria known as sulfate reducers (SRBs), which also can degrade BOD. Instead of using oxygen, SRBs use sulfate (SO4) as their “oxygen” source. The resulting byproduct is odorous H2S instead of CO2. Since sulfate is a very common, naturally occurring compound, H2S formation can occur in virtually any wastewater treatment system, as well as lift stations, sewer lines, and agricultural ponds.

Formation of H2S and other sulfides is inevitable and even desirable in an ASB, because it is the byproduct of anaerobic sludge digestion at the bottom of the basins. This reduces the volume of solids produced and is an essential component of the technology. The sulfides formed in this process are re-absorbed in the water layer of the ASB and do not leave in the air in measurable amounts. The problem occurs when the hydrogen sulfide formation rate exceeds the assimilative capacity of the water layer, resulting in H2S emissions to the atmosphere. The situation is aggravated or complicated by the dynamic nature of the treatment system and weather conditions. Therefore, New-Indy has instituted a variety of proactive and reactive steps to minimize the formation and release of odorous compounds from its wastewater treatment system. Many of these items are listed and briefly discussed below.

Note: Hydrogen sulfide (H2S) and its similarly odiferous cousins, such as methyl mercaptan and dimethyl sulfide, have many potential sources beyond ASBs and sewage treatment. In fact, mercaptans such as dimethyl sulfide are added to odorless natural gas for safety reasons. Hydrogen sulfide is commonly an issue for municipal wastewater collection system due to low flow, anaerobic conditions in collection systems and lift stations. Lastly, marsh gas, also known as swamp gas, is a mixture of methane, hydrogen sulfide, carbon dioxide, and trace phosphine produced naturally within some marshes, swamps, and bogs.

9. What are some tools and strategies for monitoring, controlling, and minimizing H2S formation and emissions in a wastewater treatment system?

As discussed previously, minimizing mill losses and process upsets is the first place to start, and best management practices in pulp and paper mills generally include continually investigating and evaluating potential improvements from this perspective. This answer will focus on the wastewater treatment system, which is tasked with handling what leaves the mill and protecting the environment.

Optimizing the aerobic treatment component of the ASB is priority one. This includes:

  • Maintaining sufficient aeration in the aerated portion of the ASB to ensure that undesirable H2S formation in the ASB is minimized1,
  • Installing a unique biosensor probe technology to provide real-time data regarding the health and performance of the ASB1,
  • Strategically dredging solids1 to maintain adequate hydraulic retention time for treatment and prevent stagnant areas that can produce H2S, and
  • Evaluating supplemental nutrient and/or bacteria addition2 to further optimize BOD treatment and reduce the potential for H2S formation in the #1 Holding Pond.

In addition to the aeration basin efforts above, the mill is taking or evaluating steps to eliminate H2S emissions from the mill site. These include:

  • Installation of additional aerators in the #1 Holding Pond to reduce stagnant locations and maintain an aerobic environment prior to discharge2,
  • Using chemical additives (calcium nitrate, hydrogen peroxide, and ferric sulfate) individually or in combination to prevent/eliminate H2S in the #1 Holding Pond1, and
  • Evaluating the applicability of in-pond monitors to better apply the above-mentioned chemical to prevent and/or remediate H2S formation.3

1 Currently in use
2 Evaluation or installation planned
3 Under consideration

Methyl Mercaptan Q&A with Dr. Christopher Teaf

President & Director of Toxicology, Hazardous Substance & Waste Management Research, Inc.

1. What is methyl mercaptan?

Methyl mercaptan (also called methanethiol) occurs naturally in human and other animal tissues, as well as in certain foods such as nuts, cheeses, and wines. It may be released from decaying organic matter in swampy areas and is added to natural gas to help people detect gas leaks.

2. Does New-Indy Catawba put the community at risk of exposure to methyl mercaptan?
No. Based on recent studies conducted at New-Indy Catawba, methyl mercaptan was not detected in air sampling data collected over four consecutive weeks in April of 2022. This data was collected from three air monitoring locations along the fence line at the facility. Samples were collected and provided them to state and federal regulators. They contained no indication that operations at New-Indy Catawba produce methyl mercaptan emissions that would pose any health risk to the surrounding community.
3. How easy is it to smell methyl mercaptan compared to other odors?

Easy. Methyl mercaptan has a low odor threshold of 0.002 parts per million (ppm) in air, which is 250 times lower than the 0.5 ppm NIOSH Recommended Exposure Limit and 5,000 times lower than the 10 ppm OSHA Permissible Exposure Limit. Methyl mercaptan has an unpleasant odor that resembles rotten cabbage or garlic.

4. Can methyl mercaptan be harmful if you cannot smell it? Is it similar to carbon monoxide (CO)?

Methyl mercaptan is not similar to CO, which is a completely odorless gas. Generally, it is not possible to be harmed by methyl mercaptan if you do not smell it. For most people, the methyl mercaptan odor threshold is low enough that it provides a good warning to avoid possible harmful exposures. Even if you do smell methyl mercaptan, it does not mean that it is harmful.

5. Is methyl mercaptan always a gas? Does it exist in household water?

Methyl mercaptan is a gas under normal circumstances. It occurs in outdoor air in mostly low concentrations. It has not been reported as a drinking water contaminant. There are no federal or state drinking water standards for methyl mercaptan, and it is of health interest only in rare airborne situations.

6. Does methyl mercaptan have any beneficial uses?

Yes. Methyl mercaptan is used in preparing animal feed and as a chemical used in pesticides, fungicides, and plastics. It is used as an odorant in natural gas supplies, although other mercaptans and sulfide compounds are also commonly used for this application.

7. At what level is methyl mercaptan dangerous to humans and pets? Does prolonged exposure to low concentrations cause health issues for humans and pets? Is intermittent or occasional exposure to small to intermediate levels of methyl mercaptan unhealthy? Are the elderly, the young, and people with compromised immune systems more likely to suffer adverse health effects from either prolonged or intermittent exposure to methyl mercaptan?

Occupational guidelines are available for methyl mercaptan in worker air space (REL and PEL), and the National Advisory Committee has established emergency response guidelines for methyl mercaptan for the public during, for example, chemical spills (Acute Exposure Guideline Levels or AEGLs), but methyl mercaptan generally is of interest with respect to odor control rather than health considerations. No information was found regarding potential adverse effects specifically to pets, children, or the elderly. Animal studies show adverse health effects starting at concentrations in the low ppm range. Occupational studies report central nervous system effects, such as headache, at long term daily exposures in the 15-ppm range.

8. What are the health effects associated with methyl mercaptan exposure? Do the health effects end after exposure ceases?

Due to the low odor threshold acting as a warning, human exposures to harmful levels of methyl mercaptan are rare. It is only through occupational exposures that health effects are reported. Worker exposures to unspecified “lower levels” of methyl mercaptan have resulted in reported respiratory, eye, and mucous membrane irritation, dizziness, nausea, and vomiting. The irritant effects cease when exposure ends. A few reports of death were found from exposure to greater than 10,000 ppm.

9. Does the federal or state government regulate methyl mercaptan? Is methyl mercaptan a pollutant under state or federal law? Other than workplace limits from OSHA, has the state or federal government-imposed exposure limits for methyl mercaptan? What are the exposure guidelines for methyl mercaptan?

South Carolina regulates methyl mercaptan under SC Reg. 61-62.5 Standard No. 8. Certain air emission sources that are regulated under Standard No. 8 are required to complete ambient air dispersion modeling to demonstrate that their air emissions do not exceed the maximum allowable 24-hour average concentrations (MAAC) identified in Standard No. 8, including for methyl mercaptan.

Exposure guidelines for the public (Acute Exposure Guideline Levels or AEGLs) are available for use under emergency response situations like chemical spills. The one-hour and eight-hour AEGLs are 23 ppm and 7.3 ppm, respectively.

10. Is methyl mercaptan considered a toxic substance under federal law?

No. But it is regulated by OSHA and NIOSH for workplace exposures. The workplace Permissible Exposure Limit (PEL) enforced by OSHA is 10 ppm, and the NIOSH Recommended Exposure Limit (REL) is 0.5 ppm.

11. What are some source materials with technical information about methyl mercaptan?

ATSDR (Agency for Toxic Substances & Disease Registry). 1992. Public Health Statement: Methyl Mercaptan. DHHS. Atlanta, GA.

ATSDR (Agency for Toxic Substances & Disease Registry). 1992. Toxicological Profile for Methyl Mercaptan. U.S. DHHS. Atlanta, GA. September 1992.

ATSDR (Agency for Toxic Substances & Disease Registry). 2014. Addendum to the Toxicological Profile for Methyl Mercaptan. U.S. DHHS. Atlanta, GA. October 2014.

NRC (National Research Council). 2013. Methyl Mercaptan Acute Exposure Guideline Levels. Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 15. Washington DC. September 26, 2013.

SCDHEC (South Carolina Department of Health and Environmental Control). 2019. Regulation 61-62 Air Pollution Control Regulations and Standards. January 25, 2019.

USEPA (U.S. Environmental Protection Agency). 2004. Provisional Peer Reviewed Toxicity Values for Methyl Mercaptan. USEPA National Center for Environmental Assessment Office of Research and Development. Cincinnati, OH. December 20, 2004.