Manfred Ehrhardt

Sunlight-induced compositional alterations in the seawater-soluble fraction of a crude oil

Abstract Oil released into the sea undergoes immediate compositional changes as a result of processes of volatilization, dissolution, particle adsorption, and microbial and photochemical decomposition. Based on our observation of the molecular composition of oil residues dissolved in subtropical ocean waters, we hypothesized photo-oxidation of alkyl-substituted polycyclic aromatic hydrocarbons (PAH) and heterocyclic aromatics in preference to their unsubstituted parent compounds. As the ratios of alkyl to parent PAH are used to assign sources to contaminant residues in environmental samples, we tested the hypothesis in a controlled experiment: membrane-filtered seawater collected near the island of Bermuda was saturated with a Nigerian crude oil and exposed to natural sunlight in a quartz flask. Comparison with a dark control under otherwise identical conditions served to differentiate between sunlight-induced and microbially mediated decreases in concentration and changes in composition. We conclude on the basis of UV fluorescence, GC-MS, and microbiological data that sunlight-induced oxidation is responsible for the rapid loss of the UV fluorescence signal for total aromatic hydrocarbons and for the preferential depletion of the alkyl-substituted PAH and heterocyclic aromatics. Structure-dependent selectivity in the photo-oxidation of dissolved oil residues may thus result in residual hydrocarbon blends which could be mistaken as originating from incomplete combustion processes.

On the sensitized photo-oxidation of alkylbenzenes in seawater

Abstract Several homologous monoalkylated benzenes were photo-oxidized as surface films on and dissolved in pure water and purified natural seawater by solar and equivalent artificial UV irradiation in the presence of anthraquinone as photo-sensitizer. The main reaction products were the 1-phenylalkanones, the corresponding secondary alcohols, benzaldehyde and, when the side chain contained four or more carbon atoms, the products of what appears to be a Norrish type II photo-degradation. The detection among the reaction products of an aldehyde with one carbon atom less than the olefin produced by the Norrish type II photo-degradation suggests a photolytic decomposition of 1-alkenes, resulting in the formation of highly reactive compounds capable of abiotic reactions in the electronic ground state with a variety of organic compounds occurring in seawater.

Hydrocarbons and related photo-oxidation products in Saudi Arabian Gulf coastal waters and hydrocarbons in underlying sediments and bioindicator bivalves

Abstract Saudi Arabian coastal waters near sandy beaches, severely contaminated with crude oil released in Kuwait during the 1991 Gulf War, as well as underlying sediments and a few bivalves, were analysed to assess concentrations and composition of petrogenic hydrocarbon mixtures and structurally related oxidation products. Concentrations of dissolved oil residues determined by UV spectrofluorometry (UVF) near oil deposits on beaches did not exceed 3.5 μg l−1; concentrations dropped to approximately 1/10th of this value a few miles offshore. Gravimetric concentrations of unfractionated lipophilic material extracted from large volumes of seawater at the same stations were up to 10 times those determined by UVF. After chromatography on silica gel, individual petroleum hydrocarbons in the low polarity fractions and oxidation products in the polar fractions were characterized by their spectra (GC/MS) and quantitated by Selected Ion Monitoring (SIM) GC/MS. Concentrations of oxidation products (ketones, aldehydes, alcohols) of aromatic hydrocarbons exceeded those of their parent compounds by more than an order of magnitude. Significant concentrations were also found of the presumably pyrogenic triplett sensitizer anthraquinone. Contributions to polar fractions of water extracts by biosynthesized lipids were negligible. UVF determinations appear to underestimate concentrations of dissolved oil residues, because many oxidation products have lower fluorescence quantum yields than the respective parent hydrocarbons. Their ecotoxicological properties are unknown. Concentrations measured in sediments by UVF ranged from 13 to 540 μg g−1 dry wt and 0.5 to 103 μg g−1 as measured by gas chromatography with flame ionization detection (FID GC). Bivalves ranged from 0.8 to 1.5 μg mg−1 extractable organic matter (EOM) by UVF, and 0.1 to 0.3 μg mg−1 EOM by GC analysis. PAHs were identified in sediment and bivalve extracts by GC/MS and quantitated by SIM GC/MS. None of the relatively water soluble alkylbenzene photo-oxidation products found in water samples nor any higher molecular weight quinones could be detected in sediment extracts. However, ion chromatograms strongly suggest the presence of numerous high molecular weight aromatics in that matrix.

Petroleum-derived dissolved organic compounds concentrated from inshore waters in Bermuda

Abstract In conjunction with the IOC/GEEP Workshop of September 1988, lipophilic dissolved organic material was concentrated from Bermuda inshore waters by liquid-solid adsorption on Amberlite XAD-2. Water samplers were moored at depths of 1–2 m on the reef platform and in inland seawater basins (Hamilton Harbour, Castle Harbour). Sample volumes were 221–4351. The adsorbed material was eluted from the resin with refluxing aqueous acetone in a specially designed apparatus. Fractions containing aliphatic and aromatic hydrocarbons were obtained by liquid chromatography on silica gel. Single compounds were identified and quantified by capillary GC/MS. Alkylated PAH with minor contributions of unsubstituted parent compounds were detected in the basins, strongly suggesting a fossil fuel origin. Concentrations diminishing steeply over a short distance between contaminated harbour water and a control station suggest a source of limited spatial extension for unsubstituted PAH. An even steeper concentration gradient of alkyl substituted PAH may indicate their more rapid environmental alteration. Thus, predominance of unsubstituted over substituted PAH in environmental samples could have two causes: a significant contribution of pyrolysis products or easier conversion/degradability of substituted PAH. Photochemically generated hydroxyl and carbonyl derivatives of alkylbenzenes were also measured. Concentrations of hydroxyl derivatives exceeded those of carbonyl derivatives in harbour water with a high load of dissolved organic material, as indicated by total lipid weight and UV fluorescence measurements. In waters with lower organic carbon load, concentrations of carbonyl derivatives were essentially similar but concentrations of hydroxyl derivatives dropped below the detection limit. We propose that the total concentration of dissolved organic material in the water influences the degree of oxidation and thus the composition of products formed. Combined concentrations of specific photo-oxidation products such as alkylacetophenones, alkylbenzaldehydes, quinones, alkylbenzyl alcohols, alkylphenylethanols were up to more than seven times higher than those of the parent hydrocarbons, indicating rapid conversion rates in this subtropical environment. These results support the need for further assessment of the relative toxicities of the reaction products in addition to those of the parent hydrocarbon contaminants in marine ecosystems.

The sensitized photo-oxidation of n-pentadecane as a model for abiotic decomposition of aliphatic hydrocarbons in seawater

Abstract n -Pentadecane was photo-oxidized, as a surface film, on purified natural seawater under simulated environmental conditions with anthraquinone as sensitizer. Initial attack by hydrogen abstraction from carbon atoms within the chain is followed by reaction of the alkyl radicals thus generated with molecular oxygen. The stable reaction products identified by GC-MS strongly suggest that alkoxy radicals produced by cleavage of the peroxide bond are key intermediates in the decomposition of the original alkane. The alkoxy radicals stabilize themselves either as ketones by reaction with molecular oxygen which is transformed into HO 2 or, if μ-hydrogen atoms are available, by cyclic electron rearrangements similar to a Norrish type II photo-decomposition. The products of the electron rearrangements are 1-alkenes and daughter alkoxy radicals. The latter either yield methyl ketones and HO 2 radicals upon reaction with molecular oxygen or undergo further decomposition as long as γ-hydrogen atoms are available. The generation of acetone and HO 2 radicals, inferred by the proposed reaction mechanism as products of many such degradation sequences, offers a plausible explanation for their occurrence in seawater in addition to those already advanced.

Organic and trace metal contaminants in sediments, seawater and organisms from two Bermudan harbours

Abstract This paper presents the results of chemical analyses of sediments, seawater and selected organisms collected during an IOC/GEEP Workshop held in Bermuda in September 1988. The data show gradients for the trace metals Cu, Pb and Zn in sediments and for petroleum hydrocarbons in sediments and organisms related to point and nonpoint source inputs to the local harbour waters. Evidence for local sources of PAH combustion products and PCBs is presented, although no obvious point sources could be identified. Methods of the organic analyses were expanded to provide an estimate of the relative abundance of hydrocarbon oxidation products compared to the parent hydrocarbon contaminants. Water samples confirmed that the harbours receive inputs of low boiling fuel products in addition to deposition of fossil fuel combustion products. However, in the islands subtropical environment, processes of evaporation, tidal flushing and photo-degradation are rapid enough to prevent significant accumulation of light hydrocarbons in the calcareous sand sediments. Hydrocarbons in sediments were medium and high molecular weight residues, while the bivalve and holothurian “indicator” organisms concentrated the more soluble lighter hydrocarbon and PCB components. Arca zebra displayed bioaccumulation patterns for organic contaminants similar to those known for Mytilus edulis and Perna viridis. The data base was too small to determine the full potential of the benthic feeding holothurians as indicators of contamination, although they accumulated some organic contaminants. Significant proportions of the hydrocarbon residues in all samples were present as oxygenated reaction products, highlighting the need for further research on the bioaccumulation and relative bioactivities of the oxidation products.

Aromatic ketones concentrated from Baltic Sea water

Abstract Aromatic ketones were concentrated from filtered Baltic Sea water by liquid—solid adsorption. After wet-chemical separation from acidic and basic components, the neutral fraction was column chromatographed to yield sub-fractions of increasing polarity. A subfraction eluted from silica gel with cyclopentane/diethyl ether contained a number of compounds which were identified by GC and GC—MS techniques as fluorenone, anthraquinone, benzanthrone, and benzene derivatives carrying an oxo group in the α-position relative to the aromatic ring. Formation and abiotic chemical reactions of these compounds in seawater are discussed.

On the composition of dissolved and particle-associated fossil fuel residues in Mediterranean surface water

Gas chromatography-mass spectrometry (GC-MS) analyses of organic concentrates from eastern Mediterranean surface water show that dissolved fossil fuel residues are dominated by unsubstituted aromatic hydrocarbons and heterocyclic aromatics and thus resemble products of incomplete combustion. Deviating from this interpretation, preferential photochemical oxidation of alkyl-substituted aromatics is suggested as the principal causative mechanism, although, especially near land-based sources. the influence of combustion-derived unsubstituted aromatics is not defined. Total concentrations of dissolved aromatics as determined by GC-FID (flame ionization detection) and GC-MS from a limited data subset were in reasonable agreement with UV fluorescence measurements of dissolved/dispersed oil residues. The same preponderance of unsubstituted aromatics over their alkyl derivatives was found in extracts of the particulate phase, but concentrations were small relative to alkanes and/or alkenes of recent marine biosynthetic origin. CPI (carbon preference index) values of higher molecular weight n-alkanes indicated varying contributions of plant waxes to the particulate hydrocarbon pool. CPI values of corresponding dissolved n-alkanes were found to be near unity, indicating fossil fuel origin. Despite differences in higher molecular weight n-alkane CPI values and the predominance of recent biosynthetic aliphatics, the similarity of dissolved and particulate aromatic fractions suggests limited adsorption by particles of fossil fuel derived hydrocarbons and heterocyclics.

Dissolved/dispersed Hydrocarbons, Tarballs and the Surface Microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December, 1984

Abstract An intercomparison exercise was conducted at the Bermuda Biological Station for Research, Inc, Bermuda on 1–15 December 1984. It primarily involved the testing of the IOC Manual for monitoring oil and dissolved/dispersed petroleum hydrocarbons (DDPH) in marine waters and on beaches (IOC, Manuals and Guides, No. 13). An additional exercise sought to intercompare methodologies for the collection of sea surface microlayer samples. DDPH measurements in the inshore waters of Bermuda resulted in a mean concentration of 0.057 μg l−1 of (n = 30) chrysene equivalents with a 60% relative standard deviation (RSD). Open ocean samples yielded a mean concentration of 0.011 μg l−1 (n = 44) with a 65% RSD. These concentrations are extremely low and the results indicate that the method described in the Manual is sufficiently sensitive for the detection of ‘hot spots’ The collection of beach tar using the method outlined in the Manual indicated that the data, when expresed as per metre of linear beach length, are an extremely good measure of oil contamination. The mean of 42 collections was 23.1 ± 14.4 g m−1 in the first sampling period and the mean of 39 transects was 40.6 ± 17.7 g m−1 on the second sampling period. Although 14 individuals took part in the sampling the results of individuals were consistent enough to demonstrate that beach tar collections are indeed valuable tools for monitoring contamination by petroleum in the marine environment. The operational manual for the sampling of the sea surface microlayer (IOC Manuals and Guides, No. 15), was also tested. The results indicated that this method collects reproduceable volumes of elevated concentrations of materials from the sea surface suitable at least for qualitative analyses. However, the spatial distribution and stability of surface films may render quantitative analyses less meaningful.

Photo-oxidation products of fossil fuel components in the water of hamilton harbour, Bermuda

Abstract A number of aromatic alcohols, aldehydes and ketones were found in organic concentrates obtained by liquid-solid adsorption from the waters of Hamilton Harbour, Bermuda. The compounds were characterized and identified using authentic reference materials by their mass spectra and relative retention indices. The origins of the aromatic alcohols, aldehydes and ketones, theoretically deduced from the results of earlier model experiments involving the sensitized photo-oxidation of alkylbenzenes, were demonstrated to be gasoline components. Sensitized photooxidation of a seawater solution of gasoline yielded oxidation products identical to those found in the water of Hamilton Harbour.