Formation and weathering assessment of oil-suspended sediment aggregates through a laboratory investigation

Abstract

Formation of oil-suspended sediment aggregates (OSAs) is believed to be one of the natural cleaning processes in the marine environment. In this study, we have investigated the formation processes of OSAs under different mixing periods (continuous mixing and with the addition of sediments in between), oil-sediment ratios (1:1, 1:2 and 2:1) and crude oils (Arabian Light (AL), Kuwait (KW) and Murban (MB)). The results revealed that size of OSAs significantly increased (up to ≈ 1.41 mm) with the addition of sediments. Aggregates (total 36) were extracted for n-alkanes and polycyclic aromatic hydrocarbons to quantify and assess their weathering and toxic levels. The maximum n-alkane depletion was 84% (111-02), 94% (212-02) and 84% (321-02) and PAH depletion was ≈ 72% (111-02), 79% (212-02) and 81% (311-03) for the OSAs of AL, KW and MB crude oils, respectively, for the different samples considered, indicating that n-alkanes were depleted relatively higher than the PAHs. The highest depletion of both n-alkane and PAHs has occurred in OSAs of 10-h continuous mixing. The depletion of both n-alkane and PAHs reduced after the addition of sediments, however, escalated the growth of OSAs, resulting in bigger size OSAs. The concentration of PAHs of all 36 OSAs is greater than 5000 ng/g, indicating very high PAH pollution. Though the formation of OSAs helps in cleaning the spill sites, the carcinogenic threat to the marine ecosystem caused by these OSAs cannot be ignored.

Formation and sedimentation of oil–mineral aggregates in the presence of chemical dispersant

“…8,9 The long-term persistence of these oil-bearing aggregates in the benthic environment results in excess petroleum hydrocarbon contaminants, particularly, polycyclic aromatic hydrocarbons. 10,11…”

“…8,9 The longterm persistence of these oil-bearing aggregates in the benthic environment results in excess petroleum hydrocarbon contaminants, particularly, polycyclic aromatic hydrocarbons. 10,11 The dispersion of the spilled oil is a prerequisite for oilmineral aggregation. This increases the available surface area of the oil and the chances of collisions with suspended minerals.…”

Effects of chemical dispersant on the surface properties of kaolin and aggregation with spilled oil

“…Under appropriate conditions, up to 20% of the spilled oil can interact with particulate matter, and the oil content of the formed OMA after spraying oil dispersant accounts for 65% of the total spilled oil (Bandara et al, 2011). As polycyclic aromatic hydrocarbons (PAHs) persist much longer in the sediment phase than at the sea surface (Harayama et al, 1999), these oil-bearing aggregates will exist on the seabed for a long time, resulting in excessive petroleum hydrocarbon contaminant, especially toxic PAHs, posing a serious threat to both the benthic communities and marine environment (Gao et al, 2019;Qi et al, 2021;Suneel et al, 2021). Common oil spill responses are mostly applicable to the oating oil but ineffective for the sunken oil (IMO, 2012; Usher, 2009).…”