Steven J. Rowland

Lost at sea: where is all the plastic?

Millions of metric tons of plastic are produced annually. Countless large items of plastic debris are accumulating in marine habitats worldwide and may persist for centuries ([ 1 ][1]–[ 4 ][2]). Here we show that microscopic plastic fragments and fibers ([Fig. 1A][3]) are also widespread in the

Transport and release of chemicals from plastics to the environment and to wildlife.

Plastics debris in the marine environment, including resin pellets, fragments and microscopic plastic fragments, contain organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, petroleum hydrocarbons, organochlorine pesticides (2,2′-bis(p-chlorophenyl)-1,1,1-trichloroethane, hexachlorinated hexanes), polybrominated diphenylethers, alkylphenols and bisphenol A, at concentrations from sub ng g–1 to µg g–1. Some of these compounds are added during plastics manufacture, while others adsorb from the surrounding seawater. Concentrations of hydrophobic contaminants adsorbed on plastics showed distinct spatial variations reflecting global pollution patterns. Model calculations and experimental observations consistently show that polyethylene accumulates more organic contaminants than other plastics such as polypropylene and polyvinyl chloride. Both a mathematical model using equilibrium partitioning and experimental data have demonstrated the transfer of contaminants from plastic to organisms. A feeding experiment indicated that PCBs could transfer from contaminated plastics to streaked shearwater chicks. Plasticizers, other plastics additives and constitutional monomers also present potential threats in terrestrial environments because they can leach from waste disposal sites into groundwater and/or surface waters. Leaching and degradation of plasticizers and polymers are complex phenomena dependent on environmental conditions in the landfill and the chemical properties of each additive. Bisphenol A concentrations in leachates from municipal waste disposal sites in tropical Asia ranged from sub µg l–1 to mg l–1 and were correlated with the level of economic development.

Biodegradation of aromatic hydrocarbons in crude oils from the Barrow Sub-basin of Western Australia

Abstract The compositions of aromatic hydrocarbon fractions isolated from four oils from the Barrow Sub-basin of Western Australia have been examined using capillary gas chromatography and gas chromatography-mass spectrometry. Each of the oils is derived from the same source rock formation, and the oils are of comparable maturity, but they contain very different distributions of aromatic hydrocarbons due to the effects of biodegradation and water washing. The susceptibility to biodegradation of the different aromatic hydrocarbon classes has been assessed and, in general, the rate of biodegradation is found to decrease with increasing number of aromatic rings and with increasing number of alkyl substituents. The rate also depends on the positions of the alkyl substituents, and it is very much lower if the aromatic hydrocarbon contains adjacent methyl substituents. Positional isomers of dimethylnaptthalenes are biodegraded at very different rates, with isomers having β-methyl substituents most susceptible to biodegradation. Ethylnaphthalenes are much less rapidly biodegraded than dimethylnaphthalenes. Trace amounts of mono- and triaromatic steroidal hydrocarbons were detected in all of the oils indicating that these compounds are ver resistant to biodegradation and thus can be used as maturity parameters even in severely biodegraded oils. There is evidence to suggest that C 21 and C 22 methyl-substituted triaromatic steroidal hydrocarbons have been removed from the severely biodegraded Mardie oil. A scale is proposed for assessing the extent to which an oil has been biodegraded based on the relative abundance of selected aromatic and saturated hydrocarbons.

The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some Ancient sediments and petroleums

Abstract The distributions of di- and trimethylnaphthalenes in two sedimentary sequences from Western Australia have been examined by capillary gas chromatography and combined gas chromatography-mass spectrometry. A general decrease was observed in the relative proportions of αα-dimethylnaphthalenes and ααβ-trimethylnaphthalenes with increasing thermal maturity. Similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories. These results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter, and the use of a number of isomer ratios is illustrated.

Enhanced desorption of persistent organic pollutants from microplastics under simulated physiological conditions

Microplastics have the potential to uptake and release persistent organic pollutants (POPs); however, subsequent transfer to marine organisms is poorly understood. Some models estimating transfer of sorbed contaminants to organisms neglect the role of gut surfactants under differing physiological conditions in the gut (varying pH and temperature), examined here. We investigated the potential for polyvinylchloride (PVC) and polyethylene (PE) to sorb and desorb (14)C-DDT, (14)C-phenanthrene (Phe), (14)C-perfluorooctanoic acid (PFOA) and (14)C-di-2-ethylhexyl phthalate (DEHP). Desorption rates of POPs were quantified in seawater and under simulated gut conditions. Influence of pH and temperature was examined in order to represent cold and warm blooded organisms. Desorption rates were faster with gut surfactant, with a further substantial increase under conditions simulating warm blooded organisms. Desorption under gut conditions could be up to 30 times greater than in seawater alone. Of the POP/plastic combinations examined Phe with PE gave the highest potential for transport to organisms.

Stereochemical studies of acyclic isoprenoids—XII. Lipids of methanogenic bacteria and possible contributions to sediments☆

Abstract Abundant volatile lipids of Methanobacterium thermoautotrophicum and Methanosarcina barkeri include isoprenoid hydrocarbons (≤ C30), and C15, C20 and C25 isoprenoid alcohols. M. barkeri contains 2,6,10,15,19-pentamethyleicosane, whose relative stereochemistry is the same as found in marine sediments, indicating that it is a marker of methanogenic activity. The C20, C30 and C25 alkenes in M. thermoautotrophicum also have a preferred sterochemistry; the latter have the 2,6,10,14,18-pentamethyleicosanyl skeleton, suggesting that the alkane in marine sediments may derive from methanogens. The stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens; in contrast, the stereochemistry of pristane in M. thermoautotrophicum indicates a fossil fuel contaminant origin, suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin. There is, therefore, little evidence at present that the pristane in immature marine sediments originates in methanogens. The C15 and C20 saturated alcohols in M. thermoautotrophicum have mainly the all-R configuration. If this is generally true for methanogens, the C20 alcohol in the Messel shale may originate mainly from methanogens, whereas that in the Green River shale may originate mainly from photosynthetic organisms.

Diamonds in the rough: Identification of individual naphthenic acids in oil sands process water

Expansion of the oil sands industry of Canada has seen a concomitant increase in the amount of process water produced and stored in large lagoons known as tailings ponds. Concerns have been raised, particularly about the toxic complex mixtures of water-soluble naphthenic acids (NA) in the process water. To date, no individual NA have been identified, despite numerous attempts, and while the toxicity of broad classes of acids is of interest, toxicity is often structure-specific, so identification of individual acids may also be very important. Here we describe the chromatographic resolution and mass spectral identification of some individual NA from oil sands process water. We conclude that the presence of tricyclic diamondoid acids, never before even considered as NA, suggests an unprecedented degree of biodegradation of some of the oil in the oil sands. The identifications reported should now be followed by quantitative studies, and these used to direct toxicity assays of relevant NA and the method used to identify further NA to establish which, or whether all NA, are toxic. The two-dimensional comprehensive gas chromatography-mass spectrometry method described may also be important for helping to better focus reclamation/remediation strategies for NA as well as in facilitating the identification of the sources of NA in contaminated surface waters.

The widespread occurrence of highly branched acyclic C20, C25 and C30 hydrocarbons in recent sediments and biota—A review

Abstract The occurrence of widely distributed acyclic isoprenoid hydrocarbons (C2O, C25 and C30) with highly branched structures, in sediments and biota is reviewed. The compounds occur as alkanes and alkenes with from one to at least four double bonds in young aquatic (both marine and lacustrine) sediments from many parts of the globe (e.g. Peru, Antarctica, Gulf of Suez, North Sea, Atlantic) sometimes in high concentrations (e.g. 40 μg g−1 sediment) relative to other hydrocarbons. However, the compounds rapidly disappear in older sediments, possibly due to biodegradation and reaction with sedimentary sulphur. These and other factors are discussed. The sources of this fascinating group of hydrocarbons remain largely unknown, though evidence points to algae (possibly diatoms) as one possibility. The recent identification of related sulphur-containing compounds in a crude oil promises to extend the number of reports of these compounds still further, and to increase their importance as environmental biological markers.

Microbial degradation of aromatic components of crude oils: A comparison of laboratory and field observations

Abstract Small aliquots of crude oil (Brent, North Sea) were incubated aerobically for periods of up to 14 days with an inoculum of recent sediment. The saturated and aromatic hydrocarbon components were then isolated, and the latter were compared, by capillary gas chromatography, with similar fractions isolated from four oils from the Barrow Sub-basin of Western Australia which had experienced different degrees of biodegradation. Biodegradation of the aromatic hydrocarbons of Brent oil produced a series of altered oils whose compositions were comparable to those of the naturally reservoir-degraded oils. Compounds such as naphthalene, phenanthrene and alkylated homologues of these hydrocarbons were oxidised but individual isomers were oxidised to different extents.

Highly branched isoprenoids (HBIs): identification of the most common and abundant sedimentary isomers

Abstract Tri- and tetraunsaturated highly branched isoprenoid (HBI) alkenes are widespread sedimentary geochemicals but few have been isolated from sediments in sufficient quantities for rigorous identification. However, two C25 trienes, four C25 tetraenes and two C25 pentaenes have now been isolated from the diatom Pleurosigma intermedium following bulk scale culture, and these have been purified by column chromatography and fully characterised by NMR spectroscopy and mass spectrometry. The compounds have been used to identify the previously unknown, but common and abundant HBIs found previously in many studies of sediments, particles and biota from around the world. These HBIs are structurally different to those reported from other diatoms. For example, unlike HBIs from the diatoms Haslea ostrearia and Rhizosolenia setigera, the alkenes in P. intermedium are unsaturated at the major branch point of the carbon skeleton and E/Z isomerism is observed for one of the trisubstituted double bonds. There is no evidence for the presence of configurational diastereoisomerism. The distributions of HBIs in P. intermedium (including the E/Z ratios) also show a dependence on the growth conditions within the five cultures studied. The positions of the double bonds in the HBIs of P. intermedium, and by inference, of the sediments, are consistent with the positions of sulphur incorporation in some of the HBI thiolanes and thiophenes which have been reported previously in some sediments and oils.