Date of Award

Spring 1996

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

James H Weber

Abstract

Methyltin compounds (MeSn), which are not of anthropogenic origin, are common in estuaries, particularly in the marsh grass Spartina alterniflora. During the 1989 growing season, S. alterniflora leaves collected from three locations in the Great Bay Estuary were analyzed for MeSn and inorganic tin by hydride generation/atomic absorption spectrophotometry (HG-AAS). Total MeSn concentrations showed a sharp increase early in the season, reaching a maximum on May 23, then gradually decreased. Statistical calculations verified that date was a significant contributor to the observed variance, while location was not.

Two years later the seasonal study was expanded to include below ground portions of the plant and the surrounding porewater. HG-AAS analyses on samples collected weekly at Chapman's Landing detected monomethyltin and Sn in all plant parts, with no apparent temporal trend. Concentrations of Sn and monomethyltin were generally higher in roots than in other plant parts. Additionally, there was no increase in MeSn concentration either concurrent with or following an increase in Sn concentration, indicating that Sn and MeSn are absorbed from the surrounding sediment/porewater and poorly translocated to the remainder of the plant.

Further studies examining the methylation of Sn by decaying S. alterniflora and by estuarine water were conducted to ascertain the contribution to MeSn concentrations found in the estuary. Samples of estuarine water spiked with Sn and MeSn were analyzed for Sn and MeSn periodically for four days. Overall Sn concentration decreased while total MeSn concentration increased, indicating methylation. Samples of S. alterniflora leaves in estuarine water spiked with Sn were sampled periodically for 120 h. While some conversion of MeSn species could be detected, no net methylation occurred during the time frame studied.

To further elucidate formation of MeSn in the estuary, a hydride generator was coupled to a gas chromatographic mass spectrometry (GC/MS) via cryogenic trapping and thermal desorption. Both sensitivity and precision were improved by cryogenically focusing the analytes at the head of the GC column. This method enabled sensitive and selective speciation of MeSn, and also yielded positive compound identification and the opportunity to use isotopically labeled compounds to trace methylation experiments.

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