National Pollutant Release Inventory overview: sulphuric acid

Every year, businesses, institutions and other facilities across Canada must report their releases and disposals of pollutants to air, water and land to the National Pollutant Release Inventory (NPRI). The publicly available information helps the government set environmental priorities and monitor environmental performance. It also provides Canadians with an opportunity to learn about pollution in their neighbourhoods.

Sulphuric acid (H₂SO₄) is part of the NPRI’s substance overview series. This substance overview explores releases, disposals and transfers of sulphuric acid that are reported to the NPRI by various industries in Canada. It also summarizes what facilities do to mitigate their environmental impacts.

Sources and uses of sulphuric acid

Sulphuric acid is a colorless, odorless liquid composed of sulphur, oxygen and hydrogen. It is the most commonly produced chemical in the world and is used in a wide variety of industries. In 2020, Canada was the largest exporter of sulphuric acid in the global market. Sulphur, needed to produce sulphuric acid, is a by-product of sulphide minerals in metal ores such as copper, lead, iron and zinc and fossil fuels such as coal, oil and natural gas. Sulphur is recovered as sulphuric acid during the oil and natural gas refining process and from metal smelting. Most of the sulphuric acid recovered this way is transferred for processing to be used in a variety of industries:

• production of phosphate fertilizer
• production of bleaching agents in pulp and paper manufacturing
• production of lead-acid batteries
• waste water processing in sewage treatment plants
• potato harvesting

Despite its myriad of uses, sulphuric acid is a highly corrosive substance that may harm environmental and human health. Therefore, facilities that manufacture, produce or otherwise use 10 tonnes or more of sulphuric acid must report to the National Pollutant Release Inventory. Sulphuric acid can enter the environment from direct industrial emissions and spills and is formed by the reaction of sulphur dioxide with water in the atmosphere. For more information on sulphur dioxide, its sources of releases and effects on the environment, please visit the NPRI report on sulphur dioxide.

Effects of sulphuric acid on health

Sulphuric acid’s highly corrosive and acidic nature can lead to severe burns when coming into contact with skin and eyes and must require immediate care. Exposure to sulphuric acid as a mist can cause irritation of the throat and lungs and high levels can cause buildup of fluid in the lungs. Strong-inorganic-acid mists containing sulphuric acid are carcinogenic to humans. Workers in industries that use or produce sulphuric acid are at risk of exposure and must follow proper handling and storage practices to prevent accidental contact. Consumers can be exposed when handling products that contain sulphuric acid such as certain cleaning products or batteries. The Canadian Centre for Occupational Health and Safety provides additional information on sulphuric acid hazards in the workplace.

Effects and fate of sulphuric acid on the environment

When released to air, the sulphuric acid droplets can dissolve in water in the atmosphere and fall to the ground through precipitation. This is called wet deposition or acid rain. Dry deposition can also occur when acidic particles directly deposit from the atmosphere onto ground surfaces such as water, vegetation and buildings. Both types of deposition can corrode surfaces, burn plants and animals, and increase the acidity of lakes and streams. Sulphuric acid is toxic to aquatic life but is not persistent or bioaccumulative. Ecosystems that do not have sufficient natural alkalinity to neutralize acidic deposits, such as areas that are part of the Canadian Shield, are more vulnerable to acid deposition. 

Facilities that report sulphuric acid releases, disposals and transfers to the NPRI

Sulphuric acid is a ubiquitous chemical with multiple uses and is found in a large variety of industrial sectors across Canada. In total, 367 facilities from various sectors reported sulphuric acid in their 2020 NPRI report. The manufacturing industry accounts for 76% of the facilities that report sulphuric acid to the NPRI, electricity-generating stations account for another 11% and various other sectors such as waste treatment, resource extraction and dry cleaning services form the remaining facilities.  In 75 of these facilities, sulphuric acid may have been consumed in the manufacture of the product, recycled, reused or neutralized, which wouldn’t trigger any releases, disposals or off-site transfers. While these facilities are still required to report since they meet the thresholds for manufacturing, producing or using the substance in sufficient quantities, they have managed not to release any amount into the environment.

Releases of sulphuric acid

The primary sources of sulphuric acid emissions are manufacturing, coal-fired power plants, petroleum and coal product refining and non-conventional oil extraction (including oil sands). These emissions are mostly to the air, with total air releases of 3485 tonnes in 2020. Electric power facilities, the manufacturing industry and pulp and paper plants discharged a combined 71 tonnes to water in 2020. A combined 16 tonnes of sulphuric acid was released to land from the mining and manufacturing industries. When burned, the sulphur content in fossil fuels is mostly converted into sulphur dioxide (SO₂), which can further oxidize into sulphur trioxide (SO₃) and then react with water to form sulphuric acid.

Total releases of sulphuric acid have decreased since 1995. This is in part due to the closure of coal-fired power plants across Canada as well as the implementation of pollution prevention infrastructure and technologies at fossil fuel power plants and metals manufacturing and refining facilities. Ontario eliminated coal-fired electricity production by 2014, and the federal government announced regulations in 2018 to phase out traditional coal-fired electricity by 2030. In 2020, 3577 tonnes of sulphuric acid were released as reported to the NPRI, a reduction of 52% since 1995.

Disposals and transfers of sulphuric acid

In 2020, 134,919 tonnes of sulphuric acid were reported as eliminated or transferred, including 125,006 tonnes transferred for acid recovery. The amount transferred represents nearly 90% of the sulphuric acid reported to the NPRI. Sulphuric acid can often be recuperated and reused or sent off-site for recovery or treatment. While sulphuric acid is occasionally disposed through underground injection, the vast majority is sent off-site for the recovery of acid.

Transfers of sulphuric acid

NPRI facilities must report the destination of off-site transfers for treatment prior to final disposal, recycling and energy recovery. The majority (93%) of sulphuric acid off-site transfers in 2020 were reported as the recovery of acids and bases. Certain facilities, such as petroleum refineries, will recover sulphur content of fossil fuels by turning it into sulphuric acid. Sulphur dioxide is converted into sulphur trioxide through catalytic oxidation. The sulphur trioxide is then absorbed in a strong sulphuric acid solution. The recuperated acid is sent to processing facilities to be used in a variety of industries.

Pollution prevention

An important step in reducing the amount of sulphuric acid from entering the environment is by reducing the releases of sulphur dioxide. A number of technologies have been implemented within facilities to prevent these releases at the source. Emissions of sulphuric acid and sulphur oxides from flue gas can be abated through different methods such as wet scrubbers, electrostatic precipitators, air heaters and others methods. For example, a coal power plant may spray limestone slurry in a flue gas desulphurization unit to convert sulphur oxides into gypsum, a material used for drywall. Alternatively, reductions in sulphur dioxide and sulphuric acid have been achieved by closing fossil fuel electricity generating stations and replacing electricity production with cleaner methods.  

Facilities that handle, use, store or emit sulphuric acid can also incorporate Pollution Prevention activities to reduce the chances of accidental spills and reduce waste. Examples of pollution prevention activities from NPRI facilities include:

• employee environmental awareness training
• responsible waste management programs
• leak detection and repair
• good operating practices

The government has also set regulations to help protect the environment from hazardous substances. The Environmental Emergency Regulations, 2019 is designed to reduce the frequency and severity of accidental releases of hazardous substances into the environment, including fuming sulphuric acid, sulphur trioxide and sulphur dioxide, which are considered an inhalation hazard. Facilities that have these substances and meet the concentration, quantity and/or container capacity thresholds must report any environmental emergency and may require an environmental emergency plan to better prepare, respond and recover from an emergency.

Pollution in your neighborhood

You can identify the facilities and pollutants in your community by exploring the various data products located on the NPRI webpage.

For further analysis, check out other NPRI maps and datasets. You can also use NPRI data to do your own analysis.