Ecological risk screen for PAHs in sediments near two produced water discharges at coastal production platforms in the Gulf of Mexico Page: 4 of 12

Results

At Delacroix Island total and individual PAH concentrations exceeded ERL criteria at the
discharge and 100 m stations (Table 2). Acenapthene exceeded the ERL Value at the
300 m and 500 m stations of the northwest transect. No criteria values were exceeded
at 1000 m and reference stations, and no PAHs exceeded ERM values at any stations.
At Bay de Chene only the discharge station samples exceeded ERM criteria for total
and individual PAHs (Table 3). Total and individual PAH concentrations exceeded ERL
criteria at the discharge, 100 m, and 300 m stations (Table 4). High concentrations at
100 m NE probably reflect the influence of the abandoned loading dock.
Discussion
Before cessation of operations, PAH levels in surface sediments were generally
elevated above ERL criteria, up to 100 m in radius around the two discharges. At Bay
de Chene, ERL criteria were also exceeded at 300 m, particularly on the NE transect.
This could reflect a combination of factors: a rate of produced water discharge that was
approximately double the rate at Delacroix Island (Table 1); greater chance for
distribution of the discharge because of turbulence (see discussion below); and the
presence of a channel; and residual sediment contamination from the abandoned dock
at the 100 m station in that channel. Nevertheless, sediment samples from the Bay de
Chene discharge station were the only ones that exceeded ERM criteria for PAHs.
If sediment PAH concentrations are a determining factor, one could predict from our
screening results that benthic biota would be adversely affected within a 100 m radius
from open bay discharges of produced waters. The pre-termination sediment PAH
concentration data were supplied to us by Steimle & Associates, Inc. These data are
part of a report by Mullino et al. 1995 on the USDOE field study. They reported
depressions of numbers of species (amphipod, gastropod, bivalve, and polychaete)
and/or individuals at less than 100 m from the discharges. These field observations
agree with other observations on open coastal bays off Louisiana (Neff et al. 1992;
Rabalais et al. 1992).
The pre-termination benthic effects were greater at the Delacroix Island discharge
station than at the comparable Bay de Chene station. Mullino et al. explained this as a
result of hydrology of the environment. Although the Delacroix discharge was
approximately half that at Bay de Chene, there was less opportunity for turbulent mixing
and dilution of the discharge, because the Delacroix environment was semi-enclosed. It
was suggested that the Delacroix discharge was more likely to produce a hypersaline
nonoxygenated layer on the bottom, as supported by data, from the 2 sites, on the
chlorinity of pore water (Mullino et al. 1995).
The effects of hypersalinity and other contaminants can't be separated from those of
PAHs. Mullino et al. 1995 reported that multiple regression analyses identified sediment
concentrations of dibenzothiophenes (not listed in the criteria values) at the stations as
negatively correlated to numbers of individuals around both sites. Dibenzothiophenes
and fluoranthenes were negatively correlated with numbers of individuals and numbers
of species at Bay de Chene.

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Holtzman, S.; Meinhold, A.F. & DePhillips, M.P. Ecological risk screen for PAHs in sediments near two produced water discharges at coastal production platforms in the Gulf of Mexico, article, December 1, 1995; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc624273/m1/4/ocr/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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