The Color Coding of Oil Spills
LUIS A. ALFONZO, Research Associate
HENRY G. SCHWARTZBERG, Associate Professor
Chemical Engineering Department
New York University
New York, New York
INTRODUCTION
When an oil spill occurs it is frequently difficult to identify its source with enough
certainty to sustain legal action against the parties responsible for the spill. If the oil carried
with it a readily measurable and unique set of characteristics, similar to a person's
fingerprints, identification would be easy. Let us call such a set of characteristics a code.
A number of additives, or existing oil properties or composition factors have been
suggested for use in formulating such a code. These have included the addition of
radioactive tracers or analytically detectable trace elements or the use of trace elements
naturally found in oils. If additives are to be used they would be added to a crude oil at the
time of loading for shipment. In many instances these codes would require the use of
sophisticated analytical techniques, such as activation analysis, or the measurement of
radioactive decay patterns - techniques which are difficult to apply in any but the most up-
to-date and complete analytical laboratories. Further, in many instances, it is difficult to be
certain that the code will remain stable and unaltered as a spill weathers and ages, and as
constituents are leached from the oil during prolonged contact with water.
OIL SOLUBLE DYES
One set of code forming additives which appears attractive with respect to ease of
analysis, stability, and commercial availability is oil soluble dyes. Such dyes are virtually
insoluble in water, and thus resistant to leaching. As an oil spill weathers and case hardens,
the skin which forms should protect such dyes from oxidation by air. The opacity of the oil
should protect the dyes from deteriorative action due to sunlight. In clear solvents such as
toluene, hexane, or petroleum ether the concentration of such dyes can be readily measured
at the 0.5 to ten parts per million (ppm) level by visible light absorbtion spectrophotometry.
Because of the opacity and color of the oil it is necessary to separate the dyes from the oil
prior to spectrophotometric analysis.
CODING DENSITY
The individual dye concentrations for a combination of such dyes would constitute the
code. Using an absorbtion spectrophotometer with a 1.0 cm light path one can reliably
measure concentration levels for individual dyes with a precision of roughly 0.5 parts per
million. Thus by using dyes in the concentration range of 0 to 10 parts per million there
would be twenty distinguishable levels for each dye. By using a 2.0 cm light path the number
of distinguishable levels would be doubled.
If there are M distinguishable dyes available, and only N of these M are used, and the
number of distinguishable levels per dye is L, there are:
L    distinguishable codes.
(M-N)! N!
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