Division of Spill Prevention and Response

Breadcrumbs

Tactic P-3: Understanding the Effects of Spills on the Tundra

This tactic provides a brief description of some potential spill substances and their expected effects on tundra vegetation and soils. Information was summarized recently in Tundra Spill Cleanup and Remediation Tactics: A Study of Historic Spills and Literature (Behr-Andres 2001).

This planning tactic focuses on substances that are produced, extracted, or used in the production or extraction of oil and gas in Alaska’s arctic oilfields. Substances of concern include crude oil, diesel fuel, gasoline, Therminol™, glycol (ethylene and propylene), methanol, drilling fluids and muds, produced water, seawater, and acids. Spills within the arctic oilfields commonly involve the release of more than one substance; a typical example would be a combined release of produced (saline) water and crude oil.

In tundra areas outside the oilfields, spills of diesel, gasoline, and sewage are the main potential concerns. Spills of other substances would typically be small, and would likely require the development of spill-specific treatment strategies.

In general, a rapid response to a spill will mini-mize the spread of contaminants across the tundra surface and the vertical migration of contaminants into the soil. Containment and product recovery generally must be completed as soon as possible after the spill. In winter, snow and ice help to contain contaminants and to minimize soil penetration.

Crude Oil

Crude oil contains thousands of organic and a few inorganic compounds, including natural gas, liquefied petroleum oils, resins, and asphaltenes. Hydrocarbons, which are composed only of carbon and hydrogen atoms, are the most abundant components of crude oil. Other components include sulfur, oxygen, nitrogen, and a variety of metals which are bound to organic compounds or exist as inorganic salts.

Crude oil can damage or kill plants in several ways. The light fractions are more volatile and consist of short-chain alkanes (i.e., saturates or paraffins) and aromatic (one or more rings of benzene) hydrocarbons. Light fractions cause the most severe damage by penetrating and destroying plant tissues. Heavier fractions of crude oil can coat the surface of the leaves and interfere with the exchange of oxygen and carbon dioxide, which is necessary for plant survival.

Crude oil can damage vegetation indirectly by creating hydrophobic (unwettable) soil conditions, thereby reducing the supply of water to plant roots. Crude oil can also displace the air from pore spaces in dry or moist tundra, causing the soil to become anoxic and acutely toxic to plants and soil microbes.

Several factors influence the toxic and physical effects of crude oil on tundra vegetation, including the volume spilled (Table 1), the presence of snow or surface water, weathering, and soil properties. For example, if oil is perched on top of frozen or water-saturated soils, the more toxic aromatic fractions may evaporate without penetrating the soil. This is especially important for sedges and grasses because the buds that sprout new tissue lie below ground and can escape the most damaging components of crude oil if the oil remains on the surface (Walker et al. 1978). In general, shrubs, mosses and forbs have been shown to be more sensitive to crude oil than grasses and sedges (Walker et al. 1978; Jorgenson and Cater 1992a). Dry tundra is considered to be more susceptible to crude oil damage than moist or wet tundra, because the aromatic fractions can be carried into the soil before they evaporate, damaging or killing roots and buds.

Table 1. Conversions for oiling rates, surface thickness, and soil concentrations of crude

Surface Oiling Rate

Surface Thickness

Percent Oil in Soil by Volume

Percent Oil
by Dry Weight
(soil bulk
density = 0.4 g/cm3)

Parts per Million
(ppm; mg/kg);
Dry Weight Basis

L / m2

Quarts

Gal / acre

bbl / acre

mm

Inches

Soil Oiling Depth (cm)

Soil Oiling Depth (cm)

Soil Oiling Depth (cm)

10

5

10

5

10

5

10

2-1/4

10,691

255

10

3/8

10

20

22

44

220,000

440,000

5

1

5,346

127

5

3/16

5

10

11

22

110,000

220,000

1

1/4

1,069

25

1

1/16

1

2

2.2

4.4

22,000

44,000

0.1

--

107

3

0.1

--

0.1

0.2

0.22

0.44

2,200

4,400

Diesel Fuel

Diesel fuel, also referred to as “middle distillate,” is refined from crude oil and is composed primarily of hydrocarbons with 8 to 21 carbon atoms per molecule. Refined petroleum products, including diesel, are generally more toxic to plants, microbes, and animals than is crude oil. When diesel is spilled, the volatile components (aromatic hydrocarbons such as benzene) often evaporate, changing the chemical composition of the remaining fuel. Diesel will eventually mix with water in the soil or on the tundra surface, allowing it to migrate into the surface soil and root mat. Compounds such as polynuclear aromatic hydrocarbons (PAHs) may adsorb to fine particles in tundra soil. Once adsorbed, PAHs may persist for a long time because they are unavailable to soil microbes that degrade hydrocarbons. However, the adsorption of PAH molecules by soil can reduce phytotoxicity by reducing the amount of hydrocarbons in contact with plant roots.

Direct exposure to diesel will kill leaves, and can kill the entire plant if roots and buds are also exposed. As explained above (see Crude Oil), spills to dry or moist tundra are potentially more damaging than similar spills to wet tundra. This is partly due to protective effects of water-saturated soil, and partly to characteristics of the dominant plant growth forms in the different tundra types.

Gasoline

Gasoline is a highly volatile and flammable refined petroleum product that spreads rapidly to a thin sheen on water or wet soil. Evaporation rates are very high, as gasoline contains a larger percentage of volatile aromatic compounds than either diesel or crude oil.

Like diesel, gasoline is generally more damaging to vegetation, microbes, and animals than is crude oil. Direct contact of plant leaves, buds or roots with gasoline will often kill the entire plant. In wet tundra, saturated soil may initially provide some protection from gasoline spills, as explained above (Crude Oil). However, like diesel, gasoline will eventually mix with water, allowing it to migrate into the surface soil and root mat. Moist and dry tundra are highly susceptible to the effects of gasoline for the same reasons they are readily damaged by diesel spills—rapid penetration of the soil and trapping of the aromatic fractions in the rooting zone, where they can be toxic to vegetation. Many of the harmful aromatic fractions of gasoline, however, may evaporate before penetrating tundra soils.

Saline Waters and Substances

Seawater and brine are used on the North Slope as part of enhanced oil recovery processes and are transported by pipeline and truck. Produced water is generally separated from the oil stream and reinjected at well heads. The salt in seawater, brine, and produced water consists mainly of sodium chloride, which can negatively affect plant growth and survival at relatively low concentrations. These effects may be persistent since, unlike hydrocarbons, salts are not broken down by chemical or biological processes in soil. Low precipitation and hydrologic gradients typical of the North Slope may prevent salts from being flushed from soils as quickly as they would be in many other areas. Soil amendments (e.g., gypsum) may ameliorate the negative effects of salt spills (Tactic TR-13).

High levels of salts in soil increase the
osmotic potential of soil water, making water uptake difficult for most tundra plants.
Depending on salt concentrations, salt-affected vegetation may wilt, become discolored, drop leaves, or die within hours or days of contact with foliage or roots (Barker 1985). Jorgenson et al. (1987) found that damage to tundra vegetation was absent at soil salinity levels below 2–3 mmhos/cm, moderate between 2–3 and 6–10 mmhos/cm, and severe above 6–10 mmhos/cm. Simmons et al. (1983) made controlled releases of seawater to tundra at 8 sites in the Prudhoe Bay, Alaska area. They found that wet tundra was affected much less than moist and dry tundra, reflecting different physiological tolerances of the dominant species, as well as dilution of salts in soils with high water content.

Many spills involve mixtures of crude oil and saline water, and initial cleanup efforts usually emphasize recovery of the crude oil. However, salts can also be harmful to vegetation at relatively low concentrations, and the effects are usually longer lasting since salts are not broken down in soil. Some recent spill responses have focused on the simultaneous recovery of both contaminants.

Drilling Mud and Fluids

Drilling muds and fluids are generally variable and complex mixtures designed to meet oil-well drilling needs. Many current mixtures are water-based, and often contain bentonite clay (barium sulfate), and saline substances (e.g., potassium chloride). Mixtures may also be oil-based, which often include denatured diesel fuel (i.e., mineral oil). Drilling mud spills often include varying amounts of crude oil and saline water. Drilling muds and fluids can affect tundra plants by changing soil salinity and alkalinity, as well as smothering due to burial.

Synthetic Fluids

Methanol. Also known as wood alcohol or methyl alcohol, methanol is a highly flammable, volatile solvent used in oilfield operations. Methanol is a clear, colorless liquid with a pungent odor, and is completely soluble in water. Methanol evaporates quickly from soil and water when exposed to air. This chemical is highly toxic to wildlife, but its toxicity to plants is not well known.

Glycols. Ethylene and propylene glycol are synthetic liquids that mix with water. They are used as antifreeze for vehicles, in heating systems, and in industrial applications. Glycols are clear, odorless liquids that mix completely with water and have low vapor pressures. Abiotic transformations in soil or water are not significant except that glycols are subject to photo-oxidation by the sun. Little information is available on the toxicity of glycols to plants. Ethylene glycol is highly toxic to animals, so initial responses to spills of this compound should focus on wildlife protection, followed by containment and recovery.

Therminol. An insoluble organic liquid commonly used as a heat transfer fluid for pump stations and well houses. In its raw form, it is a clear yellow liquid with a mild hydrocarbon odor and is viscous even at below-freezing temperatures. Little is known about the environmental toxicity of Therminol, but test results suggest that it is resistant to biodegradation (Solutia MSDS).


Updated: 12/20/2010