Partitioning of chemicals—important factors in exposure assessment of offshore discharges

The CHARM (chemical hazard assessment and risk management) model was developed to give operators, chemical suppliers, and environmental authorities a scientific framework for analyzing the environmental hazard and risk of offshore chemicals used and discharged to the marine environment. This paper presents results from an R and D project carried out on partitioning of typical offshore chemicals where the objective was to validate the partitioning algorithms in CHARM. The work included further development and verification of the HPLC (OECD 117) method for determining oil/water partitioning, or fraction released of production chemicals, for evaluation of the applicability of the Shake Flask method (OECD 107) and modification of the sediment/water partitioning test methods, as well as establishment of a calculation method for determining the weighted average log Pow for chemical mixtures of homologs. The calculation method was recommended adopted in CHARM. Based on the experimental partitioning results, the CHARM partitioning algorithms were evaluated. The test results showed that the HPLC technique is a “robust” method for determining the Pow, but has limitations for surfactants and chemicals with high log Pow-values, which are typical offshore chemicals. The traditional correlations reported between Pow, the BCF, the fraction of a chemical released with produced water, and the Psw is not valid for typical surfactants. Another approach is therefore used in CHARM, which also was evaluated in this project. There is, however, a need for further validation of the CHARM partitioning algorithms.