Fly Fishing

AvidDavid · Location: Long Island, NY

Misconception - Oil and water do not mix! For the most part this is true. Oil is generally less dense than water (especially salt water [more dense than fresh water]) and due to oil’s lower density, it floats on top of the water. HOWEVER, oil is slightly soluble in water (although water becomes saturated with oil at a very low concentration). Eventually, since the ocean is quite large compared to the oil spill, the oil spill will dissipate, in part by volatile components blowing away in the atmosphere (hence comments of oil smell in the air near New Orleans), in part by dissolving in the seawater and in part by some insoluble components consolidating into tar (you may have seen some washed up on beaches). Heavy oil may mix with sediments and eventually the association with sediment helps them to sink. Once it sinks, oil-laden sediment acts as a source of toxicants for years or decades to come!

Dissolution of oil aids in dissipation of the oil spill. The tiny amount of oil that dissolves in sea water (measured in parts per billion) does not appreciably diminish the amount of oil floating on the surface in the short term. With time and sufficient mixing of the seawater, more and more water may be exposed to the oil and oil will dissolve in it. Over the long term, this dissolution will lead to dissipation of the oil spill. Despite the very low concentration at which oil saturates the water, these concentrations may be high enough to be toxic! In fact, it is the oil and oil byproducts dissolved in the water that are particularly toxic to fish!

What from the oil gets in the water? Dissolved compounds are found in water equilibrated with crude oil in the laboratory. Compounds found in water after equilibration of Southern Louisiana Crude are chloroform (23.8 parts per billion [ppb]), hexane (722 ppb), benzene (816 ppb), and methanol (15 ppb) (Griffin, LF and Calder, JA (1977). Appl. Env. Microbiol. 33:1092-1096). Chloroform and benzene are human carcinogens with possible reproductive effects. Hexane is a 6 carbon alkane useful as a fuel (like propane (3 carbons), butane (4 carbons) and octane (8 carbons - the standard for rating gasoline). An MSDS for hexane indicates that it may be toxic to humans, in particular “it may be toxic to peripheral nervous system, skin, central nervous system,” and “prolonged exposure can produce target organs damage.” Methanol is wood alcohol. Anything that is toxic to humans is likely to be toxic to other species, as well. And embryos and larval forms tend to be more susceptible to toxic agents than adults.

How does an oil spill affect fish? There are at least 3 ways:

1.) Direct Contact. Fish that come in direct contact with the oil slick can develop a slimy mucous film all over their surfaces exposed to the oil (outside, inside their mouths and digestive systems, and their gills). Any oily film on the gills is likely to be quite detrimental to the fish’s ability to exchange oxygen and carbon dioxide. This can be lethal. (http://www.ehow.com/how-does_5489780_do-oil-spills-affect-fish.html ) Once the oil enters the bloodstream, it will tend to accumulate in the more oily places in their bodies (fat and cell membranes).

2.) Exposure to Oil Dissolved in the Water. Even the low concentrations of oil and crude oil extracts that occur in the water near the oil spill can be toxic to fish and especially fish embryos (developing after spawning). Acute exposure can result in death. The exposure concentration that results in death for 50% of the animals (LD50) differs for different compounds and different animals. LD50s are: chloroform (79 ppb for oyster larvae), benzene (10600 ppb for freshwater fish exposed for 24 hours), and hexane (470 ppb for fathead minnows exposed for 96 hours). Although the observed concentrations of these toxicants achievable in water are lower than these LD50s (above), The concentrations are similar in magnitude to these lethal doses! It is not unusual that longer exposures at lower doses may have other adverse effects that are not lethal. (I calculated LD50s calculations from data in MSDS’s expressed in mg/liter)

3.) Ingestion of Bacteria and Plankton Exposed to Oil Dissolved in the Water. Many fish rely on bacteria and plankton in the water as a food source (either directly or via other organisms that they eat). This ingestion of food sources that are affected by the dissolved extracts of crude oil can have detrimental effects on the fish. (http://www.ehow.com/how-does_4616883_oil-spill-affect-environment.html). Of concern is that of the crude oils tested in one study of bacteria, Southern Louisiana Crude was more toxic than crude oil from Venezuela or Florida (Griffin, LF and Calder, JA (1977). Appl. Env. Microbiol. 33:1092-1096).

An additional concern is the use of dispersants to make the floating layer of oil disappear. Dispersants are surfactants and solvents that increase the solubility of oil in water. They lead to diminution of the oil slick by mixing the oil with the water! This results in an improvement of prognosis for living things affected by the oil ON THE SURFACE (the birds and swamps/bayous/marshes). It achieves this diminution by increasing the oil dissolved in the water. Dissolved oil and dispersants affect species that live submerged in the seawater. Who is at risk for dissolved oil and dispersants? The marine animals (seafood – crabs, mussels, clams, oysters, lobsters and the myriad of finned fish). Use of dispersants speeds movement of oil (and toxic dispersants) to the bottom where the spill will more greatly affect benthic organisms (bottom fish, crustaceans and mollusks) (http://www.springerlink.com/content/kx3027l2328268tq/)

In summary, fish and seafood are particulary susceptible to the toxicity (not necessarily lethality) of the crude oil in the Gulf. Attempts to dissipate the oil by dissolution in the sea water may help the birds and decrease encroachment of oil into the bayous, but it may have disasterous effects on nearby fish, crustaceans and mollusks.[/b]

Flydude · Location: Denmark

Great post - very interesting reading
Thanks a lot.
Very Happy