Comparative aquatic toxicology of aromatic hydrocarbons

Structure-toxicity relationships were investigated for six organic contaminants, representative of three chemical classes, likely to be found in coal conversion process waters and effluents. Using embryo-larval stages of the rainbow trout (Salmo gairdneri) and largemouth bass (Micropterus salmoides), continuous-flow toxicity tests were performed on hydroxylated aromatic hydrocarbons (phenol, beta-naphthol), azaarenes (quinoline, acridine), and polycyclic aromatic hydrocarbons (naphthalene, phenanthrene). Exposure was initiated at fertilization and maintained through 4 days post-hatching. Median lethal concentrations (LC50), based on combined frequencies of embryo-larval mortality and teratogenesis, were used to rank the toxicity of the compounds to each fish species. With the trout, the order of decreasing toxicity was phenanthrene (0.04 mg/L), beta-naphthol (0.07 mg/L), naphthalene (0.11 mg/L), phenol (0.15 mg/L), acridine (0.32 mg/L) and quinoline (11.0 mg/L). The toxicological ranking with the bass was phenanthrene (0.18 mg/L), naphthalene (0.51 mg/L), acridine (1.02 mg/L), beta-naphthol (1.77 mg/L), phenol (2.80 mg/L) and quinoline (7.50 mg/L). For each class of compounds, the chemical with the greater number of aromatic rings always exerted the greater toxicity. In tests with both fish species, beta-naphthol (two rings) was about twice as toxic as phenol (one ring), and phenanthrene (three rings) was nearly three times more toxic than naphthalene (two rings). Acridine (three rings) was seven times more toxic to bass and 34 times more toxic to trout than was quinoline (two rings). This relationship between ring number and toxicity was in excellent agreement with results from acute tests on the same compounds. Furthermore, a close correlation existed between toxicity and n-octanol:water partition coefficients within each class of compounds.