Our fundamental understanding of the nature of petroleum toxicity has developed 

 from laboratory studies of acute toxicity. A generally accepted method of expressing 

 acute toxicity of a given pollutant is the 96-hr LC50. The LCs ( , value of a pollutant is 

 the concentration of the toxicant required to kill 50 percent of the test organisms 

 within 96 hours. Three variables are immediately obvious in the determination of an 

 LCmi for petroleum: (1) the oil tested. (2) the form of oil presented (water-soluble 

 fraction or dispersion), and (3) the organism and life stage tested. Each of these vari- 

 ables affect the LC50 value obtained and thus partially explains the wide range of 

 values reported in the literature. Table 2 presents a compilation of LC50 data largely 

 obtained with water-soluble fractions (WSF) of oils or pure compounds. The data of 

 Table 2 indicate fuel oils are generally more toxic than crude oils to a wide variety of 

 organisms. Fuel oils (No. 2 and No. 6) contain larger percentages of toxic naphtha- 

 lenes and phenanthrenes than do crude oils. Rossi et al. (1976) found two fuel oils 

 more toxic to the polychaete Neanthes arenaceodentata than two crude fuel oils. The 

 higher toxicity of the fuel oils was attributed to their higher content of naphthalenes. 

 Tissues from animals exposed to WSF from No. 2 fuel oil contained a higher concen- 

 tration of naphthalenes than animals exposed to WSF from crude oil. Crude oil- 

 exposed animals had higher tissue levels of alkyl benzenes. Accumulation of naph- 

 thalenes in organs of Fundulus similus exposed to WSF of No. 2 fuel oil has been 

 documented by Dixit and Anderson ( 1977). Concentrations of total naphthalenes in 

 excess of 200 ppm in the brain were found to correlate with loss of locomotor and 

 regulatory capabilities. Affected fish placed in clean water returned to normal swim- 

 ming behavior within 3.5 hours, and brain levels of naphthalenes were found to be 

 about 200 ppm. Winters and Parker ( 1977) have reported that WSF of fuel oils also 

 contain higher concentrations of phenols, anilines, indoles, and quinolines than do 

 crude oils. Some of these one- and two-ring aromatic compounds containing oxygen 

 or nitrogen may be formed during catalytic cracking and reforming of crude oil in 

 refinery processes. The differences in toxicities of No. 2 fuel oils to microalgae have 

 been demonstrated to depend upon differences in concentration of these minor com- 

 ponents. Winters et al. ( 1976) tested the toxicity of WSF from four No. 2 fuel oils on 

 the growth of microalgae. Water-soluble fractions from two of the oils were lethal to 

 the two blue-green algae tested. The observed toxicity to blue-greens was due to a 

 higher concentration of anilines in these oils. Para-toluidine. a methyl aniline, was 

 found to be toxic to Agmenellum quadruplicatum at a concentration of 100 ^g 1. 

 Similarly in another study, perinaphthenone was found to be largely responsible for 

 the high toxicity of WSF of a No. 2 fuel oil to green algae (Winters et al.. 1977). Peri- 

 naphthenone, a three-ring aromatic ketone, was present at a concentration of 200 

 Hg: 1 in the WSF. Toxicity of the pure compound alone was demonstrated at a con- 

 centration of 250 /ig 1. Crude oils also exhibit a wide range of toxicities in bioassays, 

 no doubt owing to their diverse chemical and physical properties. 



Oil has generally been presented to test organisms as an oil-in-water dispersion 

 (OWD) or as a water-soluble fraction prepared from the oil. Neither method pro- 

 duces a stable concentration of oil in seawater. The stability of an OWD depends 

 upon the size of droplets, specific gravity of the oil, and seawater circulation within 

 the test chamber. Evaporation of volatile components quickly decreases the concen- 

 tration of WSF even in nonaerated aquaria (Winters and Parker, 1977). Mainte- 

 nance of constant concentrations of oil in seawater during exposure is greatly facili- 

 tated by use of flow-through test chambers. Flow-through systems provide addi- 

 tional advantages such as maintaining dissolved oxygen concentration with less or 

 no aeration, minimizing problems associated with bacterial contamination, and 

 removing waste products from test animals. 



The toxicities of individual compounds known to occur in petroleum have also 

 been tested (Neff et al.. 1976). Generally, toxicity of naphthalenes was greater than 

 that of benzenes and increased with degree of alkyl substitution of a given aromatic 

 ring system (Table 2). Neff et al. ( 1976) found phenanthrenes more toxic than naph- 

 thalenes to a species of polychaete worm. 



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