Estimation of emulsified and dissolved oil content in seawater

Abstract

The demand to control the amount of oil discharged to the seawater is the consequence of increasing shipping activities. Oil products enter marine environment on daily basis in the form of fuels, engine oils or crude oils. Each of them have a significant impact on marine life and the coastal water management. Oil content influences many environmental factors, like water quality and bio-optical parameters (e.g. water-leaving radiance, inherent optical properties, seawater fluorescence). It should be measured on regular basis to avoid over or underestimation of those parameters. Currently there are several methods used to estimate the total hydrocarbon content in seawater, mostly based on fluorescence measurements. We present a unique method suitable to determine the concentration of oil products in two forms: the amount of dissolved oil and the amount of oil-in-water emulsion. The method consist of several steps: seawater sampling, vacuum filtering, extracting of oil in n-hexane, fluorescence measurements and calculation of oil concentration in comparison to the reference samples, i.e. the solutions of different types of crude oil in n-hexane. The results have been measured for the samples collected in Southern Baltic Sea during several ship cruises in 2012. We discuss the advantages and disadvantages of presented method in the context of radiative transfer modelling and potential remote detection of dispersed oil.