3. RESULTS AND DISCUSSION 



3.1 Overall Findings 



Several general trends in the data presented in the following 

 sections should be noted here along with several considerations of the 

 use of marker compounds as "fingerprints" to trace aged AMOCO CADIZ oil 

 in environmental samples. 



3.1.1 Weathering of AMOCO CADIZ Oil 



The chemical composition of spilled oil from the tanker changed 

 markedly over the first days to weeks, both at sea and once associated 

 with sediment (Atlas et al., 1981; Calder and Boehm, 1981; Boehm et 

 al., 1981). The changes are well documented in Figures 3.1 and 3.2 and 

 are summarized in Table 3A. For comparison, the background saturated 

 and aromatic hydrocarbon composition of sediment samples is illustrated. 

 The non-impacted sediments contain: 1) an unresolved complex mixture 

 (UCM) of hydrocarbon material in both fractions, 2) terrigenous n- 

 alkanes (odd chain) in the saturated fraction, and 3) pyrogenic PAH 

 compounds in the aromatic fraction. Weathered AMOCO CADIZ oil is 

 identified as such in the sections that follow based on the following: 



1) The presence of large UCM in f^ and f 2 fractions with residual 

 triterpenoid peaks. 



2) The presence of isolated isoprenoid hydrocarbon compounds in 

 the resolved (peak) part of the GC trace (in samples during 

 the first year post-spill only) . 



3) The dominance of alkylated phenanthrene (C 2 , C3, C4) , di- 

 benzothiophene, naphthalene, and fluorene (in earlier samples) 

 compounds in the aromatic fraction and a dominance of these 

 aromatics versus pyrogenic PAH (i.e. fluoranthene, pyrene, 

 benzanthracene, chrysene, benzopyrenes, etc.). 



3.1.2 Persistence of Marker Compounds 



The most persistent compounds in the saturated (f^) fraction are 

 the pentacyclic triterpanes (PCT) ; in the aromatic (f2) fraction the 

 alkylated phenanthr enes (P) and dibenzothiophenes (DBT) are most 

 persistent. To examine the PCT compound distribution, GC/MS analysis 

 of the f^ fraction was necessary (e.g. Figs. 3.3 and 3.4). This 

 results in a "terpanogram" yielding information on the relative concen- 

 tration of eight PCT compounds used by several investigators as indica- 

 tors of presence and origin of petroleum (e.g. Dastillung and Albrecht 

 1976; Pym et al., 1975) . 



Two PCT time series (Fig. 3.5) reveal that the PCT fingerprint is 

 rather constant throughout the December 1978 to March 1980 time period 



43 



