170 GEHRS 



with solubility. Compounds with low boiling points generally are 

 more soluble in water and, hence, more available to be transported 

 across membranes. Legore (1974) noted a good direct relationship 

 between boiling point and relative toxicity, however. He found that 

 naphthalene, a diaromatic hydrocarbon, was considerably more toxic 

 to oyster larvae (Crassostrea gigas) than benzene, ethylbenzene, 

 b-propylbenzene, isopropylbenzene, and ortho-, meta-, and para- 

 xylenes, aromatic hydrocarbons with lower boiling points. 

 Naphthalenes have been cited as the most toxic water-soluble 

 petroleum fraction (Anderson et al., 1974). Concentrations of 

 naphthalenes in effluents are expected to be below levels reported to 

 cause acute toxicity to adult fish (15 to 25 mg/liter) (McKee and 

 Wolf, 1963). 



Chronic effects from aromatic hydrocarbon effluents are a 

 distinct possibility. Anderson et al. (1974) found increased 

 respiration rates in marine Crustacea exposed to 5 to 10 mg/liter of 

 aromatics. Soluble petroleum aromatics (0.01 to 0.1 mg/liter) 

 disrupted social behavior in the lobster (Homarus americanus) and 

 altered attraction of the snail (Nassarius obsoletus) to food at 

 concentrations as low as 0.1 /ig/liter (Bresch et al., 1972; Jacobson 

 and Boylan, 1973). 



Data on the toxicity of thiophenes (sulfur-substituted aro- 

 matic hydrocarbons) are almost nonexistent. Thiophene is 33% 

 more toxic to sunfish than benzene (Jones, 1964), and thiophene 

 and 2-methylthiophene are more toxic to mammals than their 

 benzene analogs. Since we can expect substantial quantities of 

 thiophenes in aqueous effluents from coal-conversion facilities, 

 investigations into their ecological impacts are required. 



Summarizing the data on the toxicity of the various effluent 

 classes leads to several generalities. First, insufficient data are 

 available to predict the potential for acute toxicity which might 

 result from the various effluent chemical classes, except phenols, and 

 the data that are available have resulted primarily from the testing of 

 specific compounds, not "real world" effluent mixtures. Second, the 

 information base for evaluating potential chronic effects is an abyss. 

 If we are willing to accept the inherent weaknesses of the existing 

 data base (it is sparse, does not evaluate interactions, etc.), we find 

 that two apparently opposite generalities have been formulated with 

 respect to toxicity. Moore and Dwyer (1974) suggested that the 

 toxicity of aromatic hydrocarbons is inversely associated with boiling 

 point and, hence, with solubility. Herbes, Southworth, and Gehrs 

 (1977) hypothesized a direct correlation between molecular weight 

 (which relates in a general manner to boiling point and solubility) 

 and acute toxicity within each of the various classes of compounds 



