Aspects of petrochemical pollution in southeastern Louisiana (USA): Pre-Katrina background and source characterization

Abstract

Background petroleum pollution before Hurricane Katrina in southeastern Louisiana (USA) coastal sediments was evaluated at 320 locations in three consecutive years for polycyclic aromatic hydrocarbons (PAHs), saturated alkanes (nC9-nC35), and petroleum biomarker compounds (hopanes, steranes, pristane, and phytane). Approximately 90% of the sample locations had a total PAH concentration of less than 2.0 microg/g and total saturated alkane concentration of less than 17 microg/g, with 50% indicating a total PAH concentration of less than 200 ng/g. Upper limit or baseline high concentration for total PAHs was 1.5 microg/g, comparable to the 2.18 microg/g reported for the National Status and Trends (NST) Program of the National Oceanic and Atmospheric Administration (NOAA). Thus, 85% of sites were below the baseline high concentration. Baseline high total PAHs at 6% of the sites (described as land) was 5.1 microg/g, comparable to the 4 microg/g benchmark calculated for NST. The three-year average total PAH concentration for 95% of the sites was less than 7.5 microg/g, a defined limit of fivefold the baseline high concentration. Samples indicated petrogenic, pyrogenic, and natural/biogenic hydrocarbon inputs. Contaminant levels exceeded the state soil screening limits at only 3% of the 320 locations. Federal screening limits proposed by the NOAA for ecological effects were exceeded at only 18% of the sites (including those sites exceeding the state limit). Only 4% of the sites had concentrations exceeding the NOAA effect range-low (ER-L) in more than one collection year. At least 61% of the analytes exceeding the ER-L were pyrogenic source indicators. Source-fingerprint analysis of these selected samples showed 10 samples with notable petroleum contamination, whereas six indicated pyrogenic input. Of all samples collected, only one site showed relatively fresh/lightly weathered petroleum.