Chemical characterization of organic contaminants of coal conversion processes such as gasification or liquefaction has revealed them to be a potential source of environmental hazards. The majority of these compounds may be divided into four major classes: (1) phenols, (2) aromatic hydrocarbons, (3) aromatic amines, and (4) sulfur-containing compounds. Little is known about nitrogen-substituted aromatics. The data available, however, suggest that they are toxic and, even more importantly, are resistant to structural degradation. Examination of their water solubility reveals that although they are not as soluble as low-molecular-weight phenols, arylamines are more soluble than their nonsubstituted or sulfur-containing analogs. Thus, with existing technologies there is a real possibility that nitrogen-containing aromatic compounds may be discharged from coal conversion facilities as aqueous effluent in large enough concentration to have a pemicious effect on aquatic biota. Acute toxicity thresholds of several nitrogen-containing aromatic compounds have been tabulated for aquatic organisms, but potential toxic interactions between these compounds have not been investigated.