A Hazard Ranking of Organic Contaminants in Refinery Effluents

Abstract

An environmental hazard ranking model (benchmark ranking model) has been developed and used for the ranking of organic compounds likely to be found in petroleum refinery effluents. The hazardfunction is essentially a multiplication of variables for toxicity (as LC50), octanol-water ratio (Kow), soil adsorption (Koc), solubility (S), and half-life (T1/2). The final score is obtained by taking the logarithm of the hazard and normalizing the values from 1-10. It is a benchmark ranking (BR) approach in the sense that the hazard for chemicals with essentially unknown environmental behaviors may be compared with the hazard for chemicals with well-known behaviors. In general, debates on water pollution have focused on non-polar (hydrophobic) compounds whereas polar (water soluble) compounds have attracted much less attention and regulation. This study focuses on a number of the polar compounds (methyl-tertiary butyl-ether [MTBE], morpholine, metanolamine and others) since there are indications that some of these may cause environmental damage. While non-polar compounds receive the highest score in the study, the combination of frequently large volumes, low biodegradability, low treatability, and analytical detection problems suggest caution when neglecting polar compounds in waste minimization pursuits and in the assessment of environmental hazard and damage. The ranking results are compared to those obtained by using three regulatory systems for the screening and classification of chemicals from the USA and Western Europe. Only the environmental dimension, not the human health dimension, is incorporated in the comparisons and final scores. Although there is good agreement, the number of compounds that get a low score (1-3 on the 1-10 scale) are fewer in the BR system than in the other systems, partly due to the weight of degradation as T½ in the function. The lack of accurate input data, in particular for biodegradation, is a major problem in the ranking. Data for biological oxygen demand (BOD), or from major biodegradation models such as BIODEG and AERUD, give little or no distinction between compounds that biodegrade in four months or forty years.