Volatile liquid hydrocarbons in the marine environment

Abstract

Concentrations of volatile liquid hydrocarbons (VLH), C ₆- C ₁₄ hydrocarbons, were determined in coastal, shelf and open ocean surface waters of the Gulf of Mexico. Open ocean, non-petroleum polluted surface water VLH concentration were ~60 ng/1 while heavily polluted Louisiana shelf and coastal values reached ~500 ng/1. Caribbean surface samples had unusually low concentrations of ~30ng/1. An approximate linear relationship was shown to exist between anthropogenic gaseous hydrocarbons and VLH. Aromatic VLH accounted for 60-85% of the total VLH in surface waters. Cycloalkane concentrations were <1.0 ng/1 in open ocean water and increased to 60-100 ng/1 in polluted water (20% of total VLH). Total alkanes doubled from ~15 ng/1 in open ocean water to ~40ng/1 in polluted water. Determining the concentrations of five major VLH compounds (aromatics) found in water samples, benzene, toluene, ethylbezene, m, p-xylenes, and o-xylene (initialized BTX) was sufficient to predict the total VLH. The empirically determined relationship is [VLH(ng/1) = 1.42 BTX (ng/1); r= 0.96]. Sampling in the water column (at-depth) with a specifically built VLH sampler showed VLH concentrations in polluted waters at 50 meters only 35-40 ng/1 less than surface concentrations. Open ocean at-depth samples displayed very low concentrations, ~30 ng/1, at 20 meter depths. .