A Monitor's Guide to Water Quality

Hydrocarbons

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What are they?

Hydrocarbons are a diverse group of organic compounds made up of hydrogen and carbon atoms. Hydrocarbons are formed from very old degraded algae, plants and other biological matter. Hydrocarbons can be gases, liquids and solids, and are generally used as a combustible fuel source.

Crude oil is a complex mixture of hydrocarbons and other constituents (like metals) that can be processed to produce various fuels, solvents, and polymers (or plastics), among other products.

Two sketches of the chemical structure of a benzene ring. The structure on the right is a shorthand version that does not illustrate the position of carbon and hydrogen atoms.

The chemical structure of a benzene ring (the structure on the right is a shorthand version). The benzene ring is present in all BTEX and PAH hydrocarbons.

Hydrocarbons with applicable Canadian Council of Ministers of the Environment (CCME) environmental guidelines.

Hydrocarbon Groups Constituents with CCME Guidelines (Water and Sediment)

BTEX

Benzene, Toluene, Ethylbenzene, Xylenes (soil only)

Polycyclic Aromatic Hydrocarbons (PAHs) or Poly­cyclic Aromatic Compounds (PACs)

2-Methylnapthalene (sediment only), Acenaphthene, Acenaphthylene (sediment only), Acridine (water only), Anthracene, Benz(a)anthracene, Benzo(a) pyrene, Chrysene (sediment only), Dibenz(a,h) anthracene (sediment only), Fluoranthene, Fluorene, Naphthalene, Phenanthrene, Pyrene, Quinoline (water only)

Hydrocarbons behave differently in the environment depending on their structure.

BTEX hydrocarbons dissolve easily in water. However, they are not very persistent over time in part because they evaporate so easily. Despite this, BTEX substances can persist in aquatic ecosystems for days or weeks, and can have negative impacts on the organisms that live in the water.

PAHs are more persistent in aquatic ecosystems, and accumulate in sediments and in some organisms. PAHs can easily attach to particles in the air, so they can be transported through the air and deposited in locations far away from their source.

Polycyclic Aromatic Hydrocarbons (PAHs) are generally released from the combustion of things like gasoline and diesel in engines, oil, coal, wood, and tobacco. They can also be released in the environment through effluents, oil spills and landfill seepage.

BTEX hydrocarbons (benzene, toluene, ethylbenzene, and xylenes) are constituents of gasoline and crude oil, and are used as solvents and to manufacture many different products (e.g., plastic, pesticides, and pharmaceuticals). BTEX are released to the air from the combustion of petroleum fuels especially in vehicle exhaust, and evaporation of solvents. They are released to water and soil through leakage from underground fuel storage tanks, spills, and pesticide application. There are also some natural sources of BTEX as well (e.g., volcanoes, forest fires).

Purple sketch of a building with steam stacks

Purple sketch of an oil rig drilling in the ground.

Purple sketch of a car with fumes coming from its exhaust.

Why do they matter?

Hydrocarbons can be harmful to aquatic ecosystems and to humans. BTEX hydrocarbons can be toxic to aquatic life if present in sufficiently high concentrations. Benzene is carcinogenic (cancer causing) in humans, and toluene is toxic to the nervous system.

Several PAHs are considered probable or possible human carcinogens and have been found to cause certain cancers, mutations and birth defects in fish and other animals.

Oil sheen over the water with long grass along the shoreline.

In some cases, a rainbow sheen can be observed at the surface of hydrocarbon-contaminated water.

How are they measured?

In aquatic ecosystems, BTEX and PAHs can be measured in water or sediments. Some can also be measured in the tissues of organisms like fish. Hydrocarbon samples must be submitted to a lab for analysis.

BTEX hydrocarbon results are usually reported individually as benzene, toluene, ethylbenzene and xylenes. There are many different PAH compounds and they can be reported individually, or grouped together according to their “parent” PAH compound (e.g., napthalene).