ARROW Oil Spill, 1970–90: Persistence of 20-yr Weathered Bunker C Fuel Oil

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Abstract
A full range of weathered petroleum residues persist in two beach sites in Chedabucto Bay, Nova Scotia, 20 yr after the ARROW Bunker C spill. Both sites contained ARROW bunker fuel residues (pentacyclic triterpane characterization). Residues from "tar pavement" and a tar deposit within a cobble spit retained many components of original ARROW Bunker C fuel. Results indicate that long-term persistence is a direct function of beach sediment permeability, and of the depth to which entrapped tar residues penetrate; persistence is an inverse function of the frequency and depth of sediment reworking during tidal incursions. Cobble beaches represent an extreme example, with the interstices acting as low-energy sinks for spilled oil. A revised model for oil stranding and fate proposes two distinct environmental reservoirs of stranded oil residue in these medium-grained beaches: the interstitual residue as the major long-term source and surface-stranded residue as the minor source, each with its own weathering rate, history, and persistence. Such in-beach sequestered oils undergo much slower weathering than surface-stranded residues, persist longer, and continue to be remobilized. However, actual transfer of hydrocarbons from such deposits to tidal waters is very low (ppb).

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