Total Reduced Sulphur
A Brief Summary of Health Effects
Prabjit Barn, Tom Kosatsky
What is total reduced sulphur?
Total reduced sulphur (TRS) is a mixture of several compounds which contain a sulphur component in the reduced form. The most common TRS compounds are: (1) hydrogen sulphide (H2S), (2) methyl mercaptan, (3) dimethyl sulphide and (4) dimethyl disulphide.1 Much of the research on TRS has focused on H2S, which is considered to be the largest fraction and most toxic component of the mixture.1,2 Here, H2S will be used to describe TRS-related effects.
TRS and H2S are typically emitted from industrial sources, including natural gas plants, petroleum refineries and pulp and paper mills. H2S is also associated with municipal sewers and sewage treatment plants.
In BC, TRS and H2S are measured at some monitoring stations.
BC air quality guidelines
Table 1. Summary of BC quality guidelines for TRS and H2S.
|TRS||BC Level A||1-hr||7 µg/m3 (5 ppb)|
|TRS||BC Level A||24-hr||3 µg/m3 (2 ppb)|
|TRS||BC Level B||1-hr||28 µg/m3 (20 ppb)|
|TRS||BC Level B||24-hr||6 µg/m3 (4 ppb)|
|H2S||BC Level A||1-hr||7.5 -14 µg/m3 (5 ppb)|
|H2SBC Level A24-hr4 µg/m3
|H2S||BC Level B||1-hr||28 – 45 µg/m3 (20 – 32 ppb)|
|H2S||BC Level B||24-hr||6 – 7.5 µg/m3 (4 – 5 ppb)|
BC Level A = objective for new and proposed discharges and, within the limits of the best practicable technology, to existing discharges by planned staged improvements for these operations.
BC Level B = intermediate objective for all existing discharges to reach within a period of time specified by the Director, and as an immediate objective for existing discharges, which may be increased in quantity or altered in quality as a result of process expansion or modification.
+Unit conversions for TRS and H2S: 1 ppm = 1000 ppb; 1 ppm= 1.39 mg/m3; 1 mg/m3 = 1000 µg/m3
H2S Inhalation toxicity
H2S is readily absorbed across the lungs.4 Once in the body, H2S primarily acts by preventing cellular uptake of oxygen through the inhibition of cytochrome oxidase.5,6 Target organs are those with the highest oxygen demands, including the respiratory, nervous, and cardiovascular systems.5,6
H2S Health effects
Case studies in occupational settings and animal studies inform the majority of the knowledge on H2S-related health effects, particularly those related to acute exposures. A few studies have also been conducted in H2S affected communities. This information is briefly summarized below.
Acute health effects due to inhalation exposure
H2S has a characteristic “rotten egg” smell which can be detected at low levels (0.001-0.13 ppm).6 Continued exposure or exposure to higher levels (e.g. 100 pm between 2 -15 min) can lead to olfactory nerve fatigue making odor itself a poor indicator of the presence of H2S.7
Eye irritation and inflammation occur at levels above 100 ppm within a period of 2-15 minutes of exposure.6 Although eye irritation has also been reported at lower concentrations (10 ppm), it is not clear if these effects are due to H2S alone, or in combination with exposure to other gases.6 Severe irritation of the nose, throat and lungs can occur at levels at or above 100 ppm. Because of its strong smell, olfactory Pulmonary oedema (fluid accumulation in the lungs) may occur at levels above 250 ppm.6 Above 500 ppm, exposure can cause loss of consciousness, also known as “knockdown.” 8,9 At higher levels (500-1000 ppm), central nervous system depression, tissue hypoxia, cardiovascular effects, and respiratory arrest can occur, which can result in death.6,8
Long term health effects due to acute H2S exposures
A variety of long term, persistent health effects have been reported by individuals who have experienced acute exposure to H2S resulting in “knockdown” in occupational settings. Typical symptoms include neurological effects (headaches, impaired memory, problems with focusing), respiratory effects (wheeze, shortness of breath), as well as ocular dysfunction (corneal abrasions).5,8 Damage to brain structures, including to the basal ganglia and cortex, have been reported during follow-up of individuals occupationally exposed to acute levels of H2S.5
Long term health effects due to chronic exposure to low H2S levels
Occupational studies have found evidence for adverse health effects, including bronchial hyper responsiveness and mood disorders. Unfortunately, many of these studies lack accurate exposure data making it difficult to assess the actual level of exposure. 4
A few studies have investigated long-term health effects in communities exposed to short-term periods of high or long-term periods of low industrial-based emissions.10-14 These studies have found some evidence of respiratory and central nervous system- related effects in residents exposed to ambient TRS and/or H2S. Symptoms include breathlessness, cough, eye and nasal irritation and nausea. These studies have several limitations, which make it difficult to assess the level of health risk posed to community members exposed to ambient TRS and/or H2S. Due to the potential chronic nature of exposure in communities, it is difficult to separate acute and chronic exposure-related effects. Exposure classification is an issue with many of the studies. Some studies did not collect monitoring data, while others used mean daily or annual concentrations to define low and high exposures to community members which may not be representative of actual exposures. Additionally, although participants were not told which exposure period (high versus low exposure days) corresponded to collection of questionnaire data, the presence of a detectable odor very likely alerted participants to elevated levels, which consequently could have led to potential reporting bias. In studies where self-reporting of symptoms was compared between residents of an exposed versus reference community, knowledge of particular industry sources could have also led to reporting bias.
Study findings are summarized in table 2.
Exposure reduction measures
Individuals concerned about their exposures to TRS or H2S during an air quality advisory can follow some measures to help reduce exposures, including:
- Avoiding areas with known industrial emissions of TRS and/or H2S;
- For individuals experiencing symptoms like respiratory irritation, staying indoors until levels decrease; it is important to reduce indoor sources of air pollution during this time;
- Continuing to control medical conditions such as asthma and chronic respiratory disease. If symptoms continue to be bothersome, individuals should seek medical attention.
Table 2. Summary of studies investigating the health impacts of community level exposures to TRS and/or H2S
1. Ontario Ministry of the Environment. Ontario air standard for total reduce sulphur2007. Available from: http://www.ontla.on.ca/library/repository/mon/20000/277839.pdf.
2. AMEC, University of Calgary. Assessment report on reduced sulphur compounds for developing ambient air quality objectives. Edmonton, AL: prepared for Alberta Environment, Science and Standards Branch; 2004. Available from: http://environment.gov.ab.ca/info/library/6664.pdf.
3. BC Ministry of Environment. Air quality objectives and standards. 2009 [cited 2012 August 21]; Available from: http://www.bcairquality.ca/reports/pdfs/aqotable.pdf.
4. U. S. Environmental Protection Agency. Toxicological review of hydrogen sulfide. Washington, DC: U.S. Environmental Protection Agency 2003. Available from: http://www.epa.gov/iris/toxreviews/0061tr.pdf.
5. Hessel PA, Herbert FA, Melenka LS, Yoshida K, Nakaza M. Lung health in relation to hydrogen sulfide exposure in oil and gas workers in Alberta, Canada. Am J Ind Med. 1997 May;31(5):554-7.
6. Canadian Centre for Occupational Health and Safety. Hydrogen sulfide. 2012 [cited 2012 November 5]; Available from: http://www.ccohs.ca/products/databases/samples/cheminfo.html.
7. Agency for toxic substances and drug registry. Medical management guidelines for hydrogen sulfide2011. Available from: http://www.atsdr.cdc.gov/mmg/mmg.asp?id=385&tid=67.
8. Agency for toxic substances and drug registry. Toxicological profile for hydrogen sulfide2006. Available from: http://www.atsdr.cdc.gov/toxprofiles/tp114.pdf.
9. Slaughter JC, Lumley T, Sheppard L, Koenig JQ, Shapiro GG. Effects of ambient air pollution on symptom severity and medication use in children with asthma. Annals of Allergy, Asthma & Immunology. 2003;91(4):346-53.
10. Legator MS, Singleton CR, Morris DL, Philips DL. Health effects from chronic low-level exposure to hydrogen sulfide. Arch Environ Health. 2001 Mar-Apr;56(2):123-31.
11. Partti-Pellinen K, Marttila O, Vilkka V, Jaakkola JJ, Jappinen P, Haahtela T. The South Karelia Air Pollution Study: effects of low-level exposure to malodorous sulfur compounds on symptoms. Arch Environ Health. 1996 Jul-Aug;51(4):315-20.
12. Campagna D, Kathman SJ, Pierson R, Inserra SG, Phifer BL, Middleton DC, et al. Ambient hydrogen sulfide, total reduced sulfur, and hospital visits for respiratory diseases in northeast Nebraska, 1998-2000. J Expo Anal Environ Epidemiol. 2004 Mar;14(2):180-7.
13. Haahtela T, Marttila O, Vilkka V, Jappinen P, Jaakkola JJ. The South Karelia Air Pollution Study: acute health effects of malodorous sulfur air pollutants released by a pulp mill. Am J Public Health. 1992 Apr;82(4):603-5.
14. Marttila O, Jaakkola JJ, Partti-Pellinen K, Vilkka V, Haahtela T. South Karelia Air Pollution Study: daily symptom intensity in relation to exposure levels of malodorous sulfur compounds from pulp mills. Environ Res. 1995 Nov;71(2):122-7.
15. Inserra SG, Phifer BL, Anger WK, Lewin M, Hilsdon R, White MC. Neurobehavioral evaluation for a community with chronic exposure to hydrogen sulfide gas. Environ Res. 2004;95(1):53-61.