National Pollutant Releases Inventory: total reduced sulphur

Every year since 1993, the Government of Canada, has collected data from Canadian facilities on pollutant releases to water, air and soil through the National Pollutant Release Inventory (NPRI). Facilities that meet the reporting thresholds or that carry out certain activities are required to report the quantities of each substance released. This overview explores the reported quantities of total reduced sulphur (TRS).

Although there are natural sources of TRS, such as marshes, bogs, lakes and coastal regions, TRS is most often the result of industrial processes. These processes must be monitored in order to ensure that concentrations remain below a safe threshold for health and the environment and that they decline each year. The map below shows TRS releases reported to the NPRI in 2019.

TRS releases reported to the NPRI in 2019

From this overview on TRS, you will learn about:

• the effects of TRS on human health and the environment
• TRS releases to air, disposals and transfers off site for recycling
• the pollution reduction and mitigation measures taken by industry and the Government of Canada

Background

Total reduced sulphur (TRS) is a gaseous mixture of pollutants that contain sulphur (S) in its reduced state. There are many TRS compounds, but for the purposes of reporting to the NPRI, TRS refers to the following substances:

• hydrogen sulphide (H₂S)
• carbon disulphide (CS₂)
• carbonyl sulphide (COS)
• dimethyl sulphide (C₂H₆S)
• methyl mercaptan (CH₄S)
• dimethyl disulphide (C₂H₆S₂)

TRS was added to the NPRI substance list in 2007. In order to compare reports of TRS from facility to facility, the individual quantities reported for each pollutant (i.e., H₂S, CS₂, COS, C₂H₆S, CH₄S, C₂H₆S₂) are converted to a single unit (tonnes of H₂S) using a mathematical formula and equivalency factors.

Three TRS compounds are tracked individually in the NPRI:

• hydrogen sulphide (H₂S)
• carbonyl sulphide (COS)
• carbon disulphide (CS₂)

These compounds have more significant effects on human health. In the case of CS₂, even very small releases must be declared to NPRI (< 1 tonne/year).

The map below shows the location of facilities that have reported individual TRS compounds to the NPRI in the past 10 years.

Individual TRS releases reported to the NPRI over the last 10 years

H₂S was added to the NPRI substance list in 1999. In the figure below, we see that the trend in H₂S releases declined from 2002 to 2011, with few facilities reporting large releases. In 2011, there was an increase in the trend as a function of the number of reporting facilities, followed by return to a downward trend.

COS was added to the NPRI substance list in 2003. The graph shows an upward trend in COS releases and reporting facilities until 2011. Since then, there has been a downward trend in releases and number of reporting facilities.

CS₂ was added to the NPRI substance list in 1996. Few facilities report individual CS₂ releases. The graph below shows a declining trend in CS₂ releases since 2009, despite an increase in the number of reporting facilities.

Releases across Canada

In 2019, 278 Canadian facilities reported TRS releases to air. As shown in the map on the right with 2019 data, and in the figure below, the provinces of Quebec, Alberta, Manitoba and British Columbia reported the largest TRS releases to air. The figure below shows the reported releases in tonnes by province in 2019, along with the number of facilities.

TRS releases reported to the NPRI in 2019

Quebec accounted for 28% of total TRS releases reported to the NPRI, Alberta for 25%, Manitoba for 18% and British Columbia for 14%. There were no reported releases of TRS in Yukon, Northwest Territories or Prince Edward Island.

The map show that the largest TRS releases reported to the NPRI are generally outside large urban centres. In 2019, the following cities had the highest TRS releases:

• The Pas (Manitoba)
• Sept-Îles (Quebec)
• Caroline (Alberta)
• Alma (Quebec)

Reporting sectors

The industrial sectors that have the largest TRS releases are petroleum refining, pulp and paper manufacturing, aluminium production, landfilling and wastewater treatment. The figure below shows the breakdown of TRS releases by sector in 2019. The pulp and paper, aluminium, and oil and gas sectors accounted for 86% of total TRS releases reported to the NPRI in 2019.

Recent trends

Both maps below illustrates the TRS releases reported between 2012 and 2016. We see that the largest releases and the majority of reporting facilities are in the province of Alberta.

Since 2009, there has been a downward trend in TRS releases, despite the increase in the number of reporting facilities.

TRS releases reported to the NPRI in 2012

TRS releases reported to the NPRI in 2016

In the figure below, we see an increase in TRS releases between 2007 and 2010, due to growth in the oil and gas sector. From 2010 to 2011, total TRS releases declined significantly following changes in the estimation methods and emission factors used by several oil and gas extraction facilities. Releases further declined in 2014 following the closure of a facility in British Columbia and a decrease in releases reported by another facility in the same province. Reported quantities have since remained relatively stable.

In 2014, a change was made to the NPRI reporting criteria, restricting the reporting requirement for TRS to air releases only. This change excludes releases to water and soil and transfers off site for purposes of recycling in order to avoid double counting of substances. For example, it used to be possible for the individual TRS compounds to be reported to the NPRI as total TRS and also as disposals, releases to water, underground injection disposals or transfers for recycling.

Human health effects

Of the various TRS compounds, hydrogen sulphide (H₂S), carbonyl sulphide (COS) and carbon disulphide (CS₂) are the most likely to cause human health effects because they are quickly absorbed into the body when inhaled. Exposure to TRS is associated with irritation of the mucous membranes (i.e., eyes, nose, throat, respiratory system). Long and repeated exposure to TRS can also cause long-term health effects, such as:

• Nausea
• Fatigue
• Vertigo
• Conjunctivitis
• Loss of smell
• Visual impairment
• Memory loss
• Headaches
• Severe neurological effects

Sensitivity to these pollutants varies from person to person. According to a 2017 Health Canada report that found that current levels of H₂S in ambient air did not pose a risk to the health of Canadians. However, H₂S could pose significant health risks if levels were to increase, primarily for employees exposed to it in the workplace. For that reason, workers who are in close contact with TRS compounds must wear proper personal protective equipment (PPE), be aware of the risks posed by these substances and wear a gas monitor at all times.

Environmental effects

When released to the air, TRS can also have harmful environmental impacts. It contributes to the formation of acid rain, which has devastating effects on vegetation and stream health. Acid rain affects the growth of vegetation and is harmful to aquatic organisms. TRS can also contribute to physical damage, such as premature metal corrosion and paint discoloration.

All TRS compounds can be easily detected in ambient air even at very low concentrations because they have a distinct odour similar to rotten eggs or boiled cabbage. Even at concentrations as low as 1 to 5 ppb (parts per billion), TRS can produce an unpleasant odour. For example, carbon disulphide (CS₂) can remain in the atmosphere for 11 days. The odour can travel long distances and can become a nuisance to neighbouring areas, depending on wind speed and weather conditions.

Industries located near residential areas must closely monitor their TRS emissions to avoid odour complaints from residents. Some cities and provinces have chosen to set ambient air quality criteria for TRS. For example, Hamilton, Ontario and Pictou, Nova Scotia have established odour targets and measure ambient air TRS concentrations to more effectively control industrial releases and limit nuisance odours in communities. See Clean Air Hamilton and Pictou TRS Hourly data for more information.

Persistent odours can increase stress in communities by preventing residents from enjoying outdoor activities or forcing them to close their windows. TRS releases to air can significantly reduce Canadians’ quality of life. See Indicator supporting the Federal Sustainable Development Strategy for more information.

Disposals and transfers for recycling

Between 2007 and 2013, 99% of disposals and transfers for recycling consisted of underground injection, either on-site (69%) or off-site (30%). On-site tailings management and transfers off-site for recycling for the reuse or refining of used oil accounted for less than 1%.

TRS compounds are generally recovered and incinerated on site with other odorous or toxic gases for disposal.

Environmental management measures

Although the trend in TRS releases to air has declined since 2007, some facilities still report high TRS releases. For example, one Canadian facility released a total of 958 tonnes of TRS in 2019, which accounts for an annual average of 2.62 tonnes per day. The NPRI reporting threshold for TRS is 10 tonnes annually (H₂S equivalent), which means that that particular facility exceeded that threshold after just four days.

In an effort to offset TRS releases, a number of  initiatives have been introduced by the provincial governments to encourage Canadian facilities to reduce or mitigate TRS concentrations in the air. For example, some facilities create buffer zones by planting trees, whereas others improve gas treatment through the capture of new sources of emissions or incineration of gases.

Although TRS is not regulated by the Government of Canada, some provincial environment ministries have chosen to use their own monitoring and regulatory mechanisms to set ambient air quality standards for TRS. For example:

• in Quebec, the air quality standard for H₂S is a limit of 6 micrograms (µg)/m³ in four minutes and an annual average of 2 µg/m³
• the Alberta air quality health index provides information on the risks posed by various pollutants to human health so that they can adapt their activities accordingly. For H₂S and the TRS compounds, a threshold of 1 part per million (ppm) has been set to identify a high or very high risk for outdoor activities. In addition, an odour threshold of 10 parts per billion (ppb) has been set for H₂S and TRS
• the British Columbia air quality health index provides real-time ambient air quality and meteorological data from monitoring stations in various air zones. One example is the Northeast Air Zone, which measures TRS and H₂S concentrations in ppb

Provincial governments can also impose additional operating conditions on facilities if they exceed the air quality standards.  For example:

• operating conditions: The facility has a maximum daily production or a maximum daily concentration of TRS;
• mitigation measures:  The facility must incinerate gases from emission sources that release directly into outdoor air (i.e., uncaptured);
• monitoring: The facility must operate its own ambient air monitoring station to communicate, on request, measured concentrations to its provincial environmental ministry;
• environmental assessment upon acceptance of project applications: sampling of sources of releases to air.

Facilities reporting to the NPRI can also implement pollution prevention measures to reduce their TRS emissions.

For more information

As a result of the measures put in place by the Government of Canada, the provinces and industry, TRS releases to air are declining. However, it is imperative to continue to monitor annual reporting by facilities to detect any change in trends or processes to better protect the environment.

To do your own analysis of TRS or any other substance tracked by the NRPI, you can download the NPRI datasets containing the pollutant quantities reported since 1994. You can also consult NPRI maps. Additional substance overviews are also available on the NPRI website.