The class of contaminants called petroleum hydrocarbons (PHCs), also known as fossil fuels, have great benefit to society by providing fuel for transportation and heating our homes, as well as many plastic products. But their extraction from the earth, production and consumer usage is a significant environmental issue in Canada and globally. PHCs are comprised of a broad range of thousands of different chemical compounds that originate from naturally occurring geological sources including crude oil, bitumen, natural gas and coal.
Contamination from PHCs is one of the most common types of soil and groundwater pollution in Canada. Mixtures of PHCs contain a wide range of chemical structures and properties, which can impact the environment in different ways. They can vary in their potential for distribution, bioavailability, toxicity and persistence.
What are petroleum hydrocarbons (PHCs)?
PHCs (petroleum hydrobcarbons), also commonly known as fossil fuels, originate from naturally occurring geological sources such as crude oil, bitumen and coal. These petroleum sources were formed when organic materials of previously living things underwent anaerobic decay and were subjected to heat and pressure in the earth’s crust over millions of years. They include a broad range of thousands of organic chemical compounds of various mixtures and proportions but most contain carbon and hydrogen with smaller quantities of nitrogen, sulphur and oxygen. Petroleum hydrocarbons are found in numerous everyday products such as fuel, including gasoline for cars, jet fuel and for heating our homes. They are also used in creating materials like plastic, computers and MRI scanners.
Mobility and fate of PHCs in the environment
Contamination from PHCs is one of the most common types of soil and groundwater pollution in Canada and can impair both terrestrial and aquatic systems, especially if contamination is not addressed [Canadian Council of Ministers of the Environment (CCME), 2014]. Due to the frequency and extent of this type of contamination, coupled with requirements to investigate and remediate, PHC pollution is a multibillion dollar problem in Canada.
The overall releases of petroleum from incomplete combustion in the engines of cars and trucks for example, is relatively small compared to releases to the environment from spills, leaks and volatilization to the atmosphere during storage, transport and distribution [Agency for Toxic Substances and Disease Registry (ATSDR), 1999].
In terms of frequency more petroleum spills occur in inland water bodies, including rivers, lakes and bays as compared to oceanic spills from tanker ships. Because much attention has been paid to marine spills and their prevention, large spills in Canadian sea waters are rare (Clear Seas, 2018). In terms of amount, smaller spills occur much more frequently but large spills still dominate in terms of total quantity even though they occur much less often. There have been large oil spills from pipelines in Alberta in recent years, for example, 5 million litres of bitumen-water-sand emulsion reportedly leaked from a pipeline south of Fort McMurray in 2015 (CBC News, 2015).
Mixtures of PHCs can contain various constituents with a wide range of chemical structures and properties and these will dictate their impacts on the environment, including their distribution, bioavailability, toxicity and ability to persist (CCME, 2008c). PHCs in the environment are problematic for a number of reasons:
PHCs have a chemically reactive nature and lighter PHCs are volatile and can present a fire or explosion hazard especially when vapours are not able to dissipate in open air (such as in a confined space).
- Soil processes like water retention and nutrient cycling can become impaired with PHC contamination.
- Lighter hydrocarbons can be transported through the environment and therefore can cause issues far from their release point.
- Larger and branched-chain hydrocarbons are persistent in the environment.
- PHCs can be transported between environmental compartments, often starting in soil and moving to the atmosphere or aquatic systems, such that more organisms are exposed to potential toxic effects.
- A number of Polycyclic Aromatic Hydrocarbons (PAHs), a by-product from the burning of PHCs, are carcinogenic. Where PAH contamination occurs there is often a mixture of carcinogenic and non-carcinogenic PAHs of varying concentration and potency (CCME, 2008a).
- Aesthetic issues can also occur, including offensive odour, taste or appearance in water and air.
Bacteria and other microorganisms can break down some PHCs and are considered for use in bioremediation of contaminated sites. Plants and bacteria in combination can enhance remediation because the plants improve conditions for bacteria, such as soil porosity, and plant-associated bacteria improve conditions for the plants, such as enhancing soil nutrient cycling (Gkorezis et al., 2016).
Many petroleum components have densities lower than water, causing them to form thin surface films that float (ATSDR, 1999). Due to this property, a very small amount of oil can spread over a large surface water area. Though weathering processes may dissipate or degrade an oil slick in a relatively short time (i.e., days to weeks), there is potential during that time to cause damage to fish and wildlife, contamination to groundwater, and impacts to shoreline or riparian areas. For example, when feathers of waterfowl become oiled, preening can cause toxicity and insulation problems can cause hypothermia (CCME, 2008c). This type of situation is considered to involve “free-phase” PHCs, such as what might occur when a spill is released close- or direct-to a water body. Otherwise PHC contamination would generally involve introduction into soil media that would negatively affect the ecological integrity of an area by causing problems for plant roots, soil invertebrates and microorganisms to function effectively.
Some components of the heavier petroleum fractions, including PAHs, are heavier than water and may accumulate in river and lake sediments, causing stresses for benthic macroinvertebrates, shellfish and bottom feeding fish (ATSDR, 1999). PAHs and BTEX (benzene, toluene, ethylbenzene and xylene) are known toxins with guidelines for the protection of aquatic life available for various individual chemical components [pyrene, for example; CCME, 1999; Ministry of the Environment and Climate Change (MOECC), 2016].
Most PHC constituents have some level of toxicity associated with them, but determining thresholds or developing guidelines to protect ecological receptors (e.g., aquatic life) is not straight-forward due to the complexity of PHC mixtures and their behaviour in the environment (CCME, 2008b and 2008c). PHC mixtures typically have hundreds of components and it is impractical and impossible to measure them all and determine their toxicity potential. Instead, guidelines for soil have been developed based on PHC fractions (CCME, 2008c; characterized by carbon numbers and boiling points as described in the next section; see Regulation section for more details of the guidelines). Water and sediment guidelines are not currently available, but soil guidelines are developed with intent to also protect aquatic life in nearby waterways.
Note on measurement of PHCs in environmental samples
Due to varying proportions and mixtures of petrochemical compounds in a given sample, PHCs are considered as part of four broad physico-chemical fractions during laboratory analysis, each having a specified range of carbons in the molecular structure (CCME, 2001). Some of the potential components of each fraction are listed below, but because the separation of fractions is based on carbon count and boiling point, some petroleum products can be found in more than one fraction due to their PHC mixture. Furthermore, these tests do not identify individual chemical make-up (aside from PAHs and BTEX).
- Fraction 1 (containing molecules with 6-10 carbons) represents the volatile fraction of most hydrocarbon mixtures including gasoline from motor vehicles and its BTEX.
- Fraction 2 contains the range of carbons from 10-16 and can contain a variety of products including kerosene, creosote and diesel.
- Fraction 3 contains 16-34 carbons, and these can include diesel and oil range organics and PAHs. Sometimes naturally occurring hydrocarbons that are not derived from petroleum sources (such as hydrocarbons derived from plants; O’Sullivan et al., 2010) can be erroneously measured in this fraction, inflating the quantity of measured PHCs.
- Fraction 4 encompasses compounds with 34-50 carbons that can include lubricating and heavy fuel oils (viscous oil used in industrial plants and power stations). After analysis of fraction 4 in the laboratory, an additional fraction (4G) is measured if the test indicates heavier hydrocarbons (50+ carbon chain length) are present. Petroleum hydrocarbons found in fractions 4 and 4G are considered to be of low mobility (due to low volatility and solubility) and might include asphalts and pitch.
PHCs in the Lake Simcoe watershed
Studies were carried-out in 2004 and 2015 to identify levels of PHCs in water and sediment of the various Lake Simcoe tributaries and areas of lake itself. Sample locations were selected to assess impact of various land uses on sediment PHC content, including naturalized, agricultural, urbanized or mixed land uses (LSRCA, 2006; LSRCA, 2019). While these studies help identify PHC occurrence it is not possible to assess significance of the recorded levels due to the absence of guidelines for sediment and water (see “Impacts to aquatic ecosystems” above). In 2004, only one water sample from an urbanized tributary site (Tannery Creek in Aurora) had a detectable concentration of PHCs. In 2015, PHCs were not reported above the analytical detection limits in any water samples from tributaries, the lake or lake-level river sites (i.e., sites in the lower Holland River that are at or near the elevation and water level of the lake).
In 2015, there were PHCs observed in sediments within, adjacent to or downstream of three vegetable polders (Holland Marsh, Bradford Marsh and Colbar Marsh) and these sites were near various types of roadways (Highway 400, for example). The PHCs detected were in fraction 3, indicating that the source of these could be diesel-fuelled vehicles for farming or on the highway, or perhaps these PHCs could be plant derived hydrocarbons occurring from the moist, marsh-vegetated soils (O’Sullivan, et al., 2010) that originated in this area. Similarly, PHCs from fraction 3 were the predominant form in three overlapping sites in and around the Holland Marsh in 2004, but in two of these sites PHCs from fraction 4 were observed also. This fraction generally contains heavier industrial oils.
Tributary sites near more urban and industrial areas, including the cities of Newmarket and Aurora, Barrie, Orillia and Innisfil, contained a greater amount of overall PHCs (that is, the sum of all fractions) in sediment. The PHCs detected were primarily in fraction 3, as well as the heaviest fractions (fractions 4 and 4G) which can include crude oil and petroleum products that are less mobile. Sediment PHCs levels were low or not detected in more naturalized systems (Hawkestone Creek), agricultural systems aside from polders (Maskinonge River), in moderately urbanized areas (Leonards Creek) and in urbanized areas that are not as industrialized (Lovers Creek). The 2015 results were generally similar to 2004 results, for overlapping sites.
Lake and lake-level river sites typically reflected what was observed in the tributaries, such that PHCs were detected in sediment downstream of highly urbanized or intensive agricultural areas including Newmarket, Aurora, Barrie, Orillia and the polders. All of these sites had PHCs in fraction 3 but sites in Kempenfelt Bay, adjacent to Barrie, and a site in the East Holland River had higher overall PHCs including PHCs in fractions 4 and 4G.
Actions to reduce PHCs in the environment
The properties of PHC mixtures vary with the petroleum source, soil composition, amount of processing (crude, blended, refined) and the extent of weathering from environmental exposure. The assessment of adverse impacts of PHCs to the environment is complicated because of the variety of sources and mixtures of PHCs and site-specific conditions.
Regulatory agencies across Canada have attempted to address PHC contamination but due to the complex nature of PHCs there was a lack of consistency of information across jurisdictions. The Canada-Wide Standards for PHC in Soil is a scientifically-based remedial standard that provides consistent methods and outcomes for regulators and the public for assessment and management of potentially contaminated sites across Canada, even with regional differences (CCME, 2008b). The guidelines were developed based upon the protection of ecological functioning (through the protection of plants, invertebrates and soil processes), aquatic life in water bodies adjacent to contaminated sites and livestock exposure from drinking or eating from contaminated media (CCME, 2008b and 2008c).
Ontario passed the Record of Site Condition Regulation (O. Reg. 153/04, Environmental Protection Act Part XV.1; MOECC, 2017) in 2004 which essentially used standards from CCME though there were some differences. Through revisions of both the CCME protocol and Ontario’s regulation, they are more in line currently (CCME, 2014).
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Canadian Council of Ministers of the Environment (CCME). 1999. Canadian sediment quality guidelines for the protection of aquatic life: Polycyclic aromatic hydrocarbons (PAHs). In: Canadian environmental quality guidelines. Winnipeg, Manitoba: CCME.
CCME. 2001. Reference method for the Canada-wide standard for petroleum hydrocarbons in soil – Tier 1 method. Winnipeg, Manitoba: CCME.
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Ministry of the Environment and Climate Change (MOECC). 2016, July 28. Soil, ground water and sediment standards for use under Part XV.1 of the Environmental Protection Act (EPA). Retrieved from: https://www.ontario.ca/page/soil-ground-water-and-sediment-standards-use-under-part-xv1-environmental-protection-act
MOECC. 2017, July 28. O. Reg. 153/04: Records of Site Condition – Part XV.1 of EPA, R.S.O. 1990, chapter E. 19. Toronto, Ontario: Queen’s Printer for Ontario.
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