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Gasoline

Petroleum is a type of oil found deep within the geologic formations of the earth and is formed from the decomposition of dead marine organisms, like algae or plankton. This precious oil has been drilled and used worldwide, with its two main uses being for fuel (heating, automobiles) and the synthesis of organic chemical compounds (petrochemicals). Commercially important chemical compounds synthesized from petroleum include gasoline and kerosine. Gasoline can be sourced from petroleum refineries, cars, and storage containers for gasoline stations, of which each source can be a potential input into the environment. With gasoline being less dense than water, it is able to float on top of water bodies (lakes, streams) or above the groundwater table.

Groundwater Table: Beneath the soil surface is a large reservoir of freshwater referred to as “groundwater”, in which the groundwater table is the interface between this reservoir and the drier layer of soil above

Therefore, gasoline can be characterized as an LNAPL (Light Non Aqueous Phase Liquid) and when spilled overtop of soil in the environment it will sink until it reaches the groundwater table interface and remain in this general area.

Light Non Aqueous Phase Liquid (LNAPL): "Light" – The contaminant is less dense than water and will float. "Non Aqueous Phase" – The contaminant will not mix with water. "Liquid"– The contaminant is in a liquid state.

However, groundwater is not stagnant within the soil and can therefore transport the gasoline contaminant to different locations within the soil. Similarly, if gasoline is spilled overtop of a water body, it can be transported with the movement of water. Furthermore, gasoline has a high vapor pressure, allowing it to emit harmful chemical compounds in the form of gases, making gasoline a Volatile Organic Compound (VOC).

Vapor pressure: The pressure above a liquid that is formed due to the evaporation of constituents within the liquid, in which the liquid is in an equilibrium state.

VOCs are problematic when there are spills or leaks because the gaseous chemicals emitted can build up in soils or in buildings. For example, if there were a gasoline leak below a household, then there could be a build up of harmful gaseous chemicals in the basement, causing health issues for the home owner, or alternatively become an explosion hazard. The emissions from gasoline use as a fuel are major contributors to climate change and contain greenhouse gases (refer to air pollutants for more information) such as NO₂, CO, and CO₂, in which the continual use of gasoline in automobiles has caused potentially irreversible impacts to our climate. Additionally, gasoline vapor exposure to humans in high concentrations can cause health problems, such as irritation of the lungs or induce dizziness and headaches. In more extreme cases it can even cause respiratory arrest or a coma.

PFAS

PFAS stands for Per- and Polyfluoalkyl Substances and are a class of chemicals used as surfactants (assist with mixing of oils, water, soaps), lubricants, and repellents (repels dirt, water, oils). PFAS substances can be found in a wide variety of industrial and commercial goods such as food packaging, Teflon pots and pans, firefighting foams, waterproof clothing, fabrics, and electronics. The US Environmental Protection Agency has catalogued over 8000 different PFAS molecules, of which around 600 are currently estimated to be in use commercially. PFAS has become an increasing concern over the years due to its resilient chemical properties and has obtained the nickname “forever chemicals” because they are extremely resistant to being broken down in the environment. They are easily transported throughout different environments and have been detected in tap water, rain water, snow, groundwater, and the air worldwide.

There is concern among governments regarding the use of PFAS in products and regulating the amount of exposure to the public. In 2007, the estimated total daily intake of PFAS in Canadians was 410 nanograms/day. This is equivalent to about 0.001% of the caffeine concentration you would get from 1 cup of coffee with 40mg of caffeine in it. Furthermore, about

‍98% of the Canadian population and 99% of the American population are estimated to have PFAS within their bloodstream!

There are also concerns regarding the bioaccumulation of PFAS in animals, which is the ingestion of a pollutant/ contaminant by an animal that remains lodged within their body over time. Other organisms that eat these animals then also ingest the contaminant, causing an accumulation of the contaminant throughout the food chain. PFAS has been linked to various human health impacts such as cancer, liver damage, and hormone disruption. However, it is challenging to determine the associated risk of certain human health impacts to PFAS exposure since cancer, as an example, is only observed in areas where individuals have had extremely high PFAS exposure. Additionally, relating PFAS exposure to human health is challenging since many companies withhold PFAS product concentration information and treat it as confidential. However, many studies have observed a deterioration in the immune system due to PFAS, particularly in children. Overall, exposure to PFAS has shown an increased number of health effects on humans as compared to other chemical classes, elevating the need to pay attention to its exposure to the public.

TCE

Trichloroethylene (TCE) is a solvent that is used as a degreaser for industrial operations, dry cleaning, food processing for inks and paints, and in pharmaceutical drugs. TCE can be released into the environment due to storage leaks/spills or its disposal.

TCE can be transported in the environment through water (groundwater, streams, lakes) and soil systems and additionally has a high molecular weight, making it a fairly dense chemical liquid in the environment (DNAPL).

Dense Non Aquenous Phase Liquid (DNAPL): "Dense" - The contaminant is heavier than water and will sink. "Non Aqueous Phase" - The contaminant will not mix with liquid water. "Liquid" - The contaminant is in a liquid state

Due to its dense properties, TCE will sink when added to water, making remediation and clean up of this chemical challenging to deal with. If TCE were to be spilled overtop of soil, in a field as an example, it would leach into the soil and sink below groundwater levels due to its high density. However, the speed at which it travels through the soil would be dependent on different soil characteristics. The TCE chemical compound has the potential to be broken down into smaller molecules when passing through soils, due to microbes and bacteria within the soil interacting with it (Biodegradation). This can be potentially good and acts as a method of remediation, however, dependent on biodegradation processes and the types of microbes interacting with the chemical, the resultant smaller chemical products of TCE can be equally as harmful to the environment.

TCE is known to be a group 1 carcinogen, meaning that based on research there is sufficient evidence that the chemical compound causes cancer. More specifically, TCE may increase the likelihood of kidney, cervix, or liver cancer in humans. Additionally, TCE has been found to cause endocrine disrupting effects (hormone disruptions/ changes). Consequently, TCE has been listed as a priority pollutant by the US Environmental Protection Agency and the European commission.

PCBs

PCB stands for Polychlorinated Biphenyls and are chemicals that were used commercially from 1929 to 1977. PCBs were commonly used as an oily fluid in capacitors and electrical transformers due to their electrical insulating properties. They were additionally used as hydraulic fluids, lubricating oils, paint additives, and in sealants and plastics. However, PCBs were found to be endocrine disrupting chemicals and affected both human and animal immune, neurological, developmental, behavioural, and genetic systems.

Generally, PCBS were found to largely affect the level of hormones with individuals and animals due to their similar chemical structure to hormones, which in turn can cause harmful effects such as fertility issues, deformities in select organs, cancer, respiratory issues, and mood disorders.

PCBs were therefore banned in 1977 in Canada and the U.S. and exposure rates have decreased since this time,

however, due to their highly persistent properties in the environment it is estimated that 30% of the historical production is still in aquatic environments. PCBs can be input to aquatic environments by atmospheric deposition (PCB dust settles into a water body) and be ingested by aquatic organisms. Once ingested, bioaccumulation can then occur, which is the transport of a contaminant throughout the food chain due to other animals ingesting contaminated organisms, or coming in contact with them. For example, a fish that ingests a soil grain with a PCB contaminant can then be eaten by a human, therefore transferring the contaminant to the individual.