On the occurrence and origins of hopanoids in the Chesapeake Bay (Maryland, virginia)

Analyses of surface sediment samples from the Chesapeake Bay and sediment cores from the James and the Potomac River showed that pentacyclic triterpenoids of the hopanoid skeleton were ubiquitously present in all samples. The hopanoids have been identified and quantified by gas chromatographic retention data obtained on SE-52 stationary phase, and mass spectral comparisons with the branched/cyclic fraction of a Lorraine coal extract as well as published data from authentic standards. Hopanoid acids are of extended 17(beta)(H), 21(beta)(H)-structure, ranging from C(,31) to C(,33). The 17(beta)(H), 21(beta)(H)-bishomohopanoic acid (C(,32)) is always the major acid found in the samples. All acids were present as a single epimer (22R). The 17(alpha)(H), 21(beta)(H)-hopane series is predominant in all the samples, with lesser amounts of the 17(beta)(H), 21(beta)(H)-hopane series and some hopenes also present. The extended 17(alpha)(H), 21(beta)(H)-hopanes (\u3e C(,31)) are found as mixtures of the 22R and 22S diastereomers. This indicates that there is a significant input of fossil hopanes into the Chesapeake Bay. Generally, high concentrations were found at river-mouth stations and in the northern Bay areas associated with industrial activities and intense urban development. These results are consistent with an anthropogenic source for the aromatic hydrocarbons present in the samples. Fossil hopanes appear to derive from a variety of sources including coal, crude oil, refined motor oil, asphalt particles and street dust. A comparison of hopanoid distributions in Bay sediments with possible source materials suggests that motor oil, asphalt particles and street dust are potentially important sources of fossil hopanes to the Bay. There is evidence that the input of hopanoids to surface soils is related to highway usage. These source materials and the associated fossil hopanes are reaching the Bay via natural and urban runoff, either directly or via river transport. Final accumulation in Bay sediments is evident from the elevated concentrations of fossil hopanes at river-mouth stations. These accumulations indicate that rivers are important sources of fossil hopanes to the Bay. An anomaly in the S/R ratio of the 17(alpha)(H), 21(beta)(H)-homohopane (C(,31)) in many sediment samples from the Bay is interpreted as evidence of a microbially induced isomerization of 17(beta)(H), 21(beta)(H)-C(,31) hopane (R) to 17(alpha)(H), 21(beta)(H)-C(,31) hopane (R). . . . (Author\u27s abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI