Author

Delia Massey

Date of Award

5-2013

Level of Access

Campus-Only Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Jean MacRae

Third Committee Member

Sarah Nelson

Abstract

Mercury-specific diffusive gradient in thin films (DGTs) were used in laboratory microcosms as a biomonitoring tool to assess the lability of mercury (Hg) species and to develop a relationship between chemical lability and bioavailability of these species in estuarine sediments. Time-series deployment of DGTs in sediments showed that sediment-bound monomethylmercury (MeHg) is more labile than sediment-bound inorganic Hg. In subsequent experiments, DGTs were deployed simultaneously with three benthic macroinvertebrates (the estuarine amphipod, Leptocheirus plumulosus; the estuarine polychaete, Nereis virens; and the marine clam, Macoma nasuta) in sediments for up to 55 days. All organisms and their co-deployed DGTs exhibited an initial period of rapid Hg uptake followed by an apparent steady-state or slower uptake. Strong and significant correlations were generally observed between paddle-type DGTs and macroinvertebrate tissue data (R between 0.57 and 0.97). Further, %MeHg:Total Hg ratios for M. nasuta and N. virens (38.5 ± 12.2 and 19.2 ± 5.2) were similar to their corresponding ratios for the DGTs (33.1 ± 13.3 and 24.4 ± 11.0), and they were significantly higher and more variable than the same ratios for sediment (2.9 ± 0.3) and porewater (8.5 ± 4.9). The %MeHg:Total Hg ratios for L. plumulosus (68.5 ± 6.2) were significantly higher than those for the DGTs. This may be because the tissue and DGT data for this organism were not truly co-located as L. plumulosus burrows close to the sediment surface, and the DGTs sampled either the sediment surface itself or the entire 9 cm depth profile of the sediment column. Overall, the results of these experiments suggest that for benthic macroinvertebrates, (a) sediment MeHg is more bioavailable than sediment inorganic Hg, as also manifested in its higher determined with the DGTs, (b) sediment and porewater concentration measurements are not good predictors for the extent of bioaccumulation of Hg species, and (c) DGTs are an effective biomonitoring tool for the assessment of bioavailability of Hg species to benthic macroinvertebrates.

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