Part 4. Trace metals studies in sediment and fauna
Abstract
From the Abstract: “In 1978 and 1979, a multidisciplinary study of the effects of offshore petroleum production platforms on the marine environment was funded through the Bureau of Land Management and done by Southwest Research Institute. Twenty platforms in the Gulf of Mexico offshore Louisiana and west of the Mississippi River delta were studied. Four Primary Platforms and four Control Sites were visited in each of three seasons; May 1978 (Cruise I), August-September 1978 (Cruise II), and January 1979 (Cruise III), and 16 Secondary Platforms were sampled during Cruise II . Trace metal research examined surficial sediments, downcore sediments and selected biological samples collected up to 2000 m from these platforms. Concentrations of Cd, Cr, Cu, Fe, Ni, Pb, and Zn were determined in these samples by atomic absorption spectrophotometry; Ba and V were determined by neutron activation analysis.
Surficial sediment trace metal concentrations did not show strong evidence of contamination from the platforms. However, at 100 m of some platforms there were elevated concentrations of metals (Ba, Cr, Cu, Pb, and Zn) that were not related to natural geochemical processes. These elevated concentrations of metals were not correlated with the age of the platforms, the quantity of petroleum production, or the number of wells on the platforms. Sediment flow from the Mississippi River is thought to "mask" any trace metal sediment concentrations around the platforms.
Unsuccessful attempts to determine the chronological age of downcore sediments by Pb-210 dating techniques are thought to be due to one or more of the following:
(1) excessive levels of Ra-226 supported Pb-210
(2) high sedimentation rates
(3) sediment reworking
(4) the possibility of sediment mixing during sample collection (piston coring).
Downcore sediment trace metal concentrations were relatively constant with depth. However, concentrations of Ba, Cd, and Zn showed an increase with depth.
Concentrations of Cr, Cu, Fe, and Ni in sheepshead (Archosargus probatocephalus), spadefish (Chaetodipterus faber), and red snapper (Lutjanus campechanus) associated with the platform structures suggest a relationship with surficial sediment concentrations . No evidence of bioaccumulation was observed.”