Timothy J. Shaw

Cellular Uptake and Cytotoxicity of Gold Nanorods: Molecular Origin of Cytotoxicity and Surface Effects

Gold nanorods of different aspect ratios are prepared using the growth-directing surfactant, cetyltrimethylammonium bromide (CTAB), which forms a bilayer on the gold nanorod surface. Toxicological assays of CTAB-capped nanorod solutions with human colon carcinoma cells (HT-29) reveal that the apparent cytotoxicity is caused by free CTAB in solution. Overcoating the nanorods with polymers substantially reduces cytotoxicity. The number of nanorods taken up per cell, for the different surface coatings, is quantitated by inductively coupled plasma mass spectrometry on washed cells; the number of nanorods per cell varies from 50 to 2300, depending on the surface chemistry. Serum proteins from the biological media, most likely bovine serum albumin, adsorb to gold nanorods, leading to all nanorod samples bearing the same effective charge, regardless of the initial nanorod surface charge. The results suggest that physiochemical surface properties of nanomaterials change substantially after coming into contact with biological media. Such changes should be taken into consideration when examining the biological properties or environmental impact of nanoparticles.

Transfer of gold nanoparticles from the water column to the estuarine food web.

Within the next five years the manufacture of large quantities of nanomaterials may lead to unintended contamination of terrestrial and aquatic ecosystems. The unique physical, chemical and electronic properties of nanomaterials allow new modes of interaction with environmental systems that can have unexpected impacts. Here, we show that gold nanorods can readily pass from the water column to the marine food web in three laboratory-constructed estuarine mesocosms containing sea water, sediment, sea grass, microbes, biofilms, snails, clams, shrimp and fish. A single dose of gold nanorods (65 nm length x 15 nm diameter) was added to each mesocosm and their distribution in the aqueous and sediment phases monitored over 12 days. Nanorods partitioned between biofilms, sediments, plants, animals and sea water with a recovery of 84.4%. Clams and biofilms accumulated the most nanoparticles on a per mass basis, suggesting that gold nanorods can readily pass from the water column to the marine food web.

The flux of barium to the coastal waters of the southeastern USA: the importance of submarine groundwater discharge

Dissolved Ba concentrations in the inner shelf waters of the South Atlantic Bight (SAB) are two- to three-fold enriched in Ba when compared to Atlantic surface water. We determined that river input could account for about 25% of the observed enrichment. However, salty groundwaters are enriched in Ba by as much as an order of magnitude over calculated river water endmembers. The resultant input of Ba to the coastal environment, via enriched groundwater, is the likely source for the observed Ba enrichment on the inner shelf. The flux of Ba from the inner shelf to the ocean is 70 × 103 moles per day. The flux of Ba reaching the inner shelf from salty groundwaters ranges from 25 to 100 × 103 moles of Ba per day. Groundwater input of Ba appears to be much more important than river input for the Southeastern coast of the US.

Chemical signals from submarine fluid advection onto the continental shelf

We report unambiguous signals of subsurface fluid input on the continental shelf 40–80 km from shore in water depths of 20–45 m. The site of this input is near the continental shelf break off the South Carolina coast between 32°–33°N and 78.5°–79.5°W. Repeated transects over this area reveal enrichments of 226Ra, 228Ra, and Ba by factors of 3–4 above ambient ocean concentrations. The short-lived 223Ra and 224Ra are enriched by over an order of magnitude. The Ra and Ba enrichments are not caused by up welling of deep water as no such 226Ra or Ba concentrations occur in the upper 2000 m of the Atlantic Ocean. Sediments in the region are largely relic sand and do not offer a viable source for 226Ra, 228Ra, and Ba enrichments. We conclude that the source is the discharge of submarine fluids enriched in 226Ra, 228Ra, and Ba. The salinity of water in the Ra-Ba-enriched zone is diluted by 0.2–0.6‰ relative to water at the same depth farther offshore. Pronounced salinity and density anomalies characterize one site of active discharge. Estimates of 226Ra and Ba concentrations in the fluids and the replacement time of water in the enriched zone suggest the fluid flux is similar to the summertime flow of major rivers in the area. The region of Ra-Ba enrichment is also characterized by a strong fluorescence signal, indicating high concentrations of chlorophyll in the water. It is probable that the leaking fluids supply nutrients that stimulate productivity in the bottom waters which are within the photic zone. Because the fluorescence signal is restricted to depths greater than 20 m, it is unlikely that the signal could be recognized by satellite or aircraft sensors.

Microelectrode studies of organic carbon degradation and calcite dissolution at a California Continental rise site

Fine scale porewater profiles of resistivity, O2, pH, and pCO2 were measured in situ with microelectrodes at a site on the California continental rise. They are reported here with more traditional measurements of shipboard porewater NO3−, alkalinity and TCO2, and sediment organic C and CaCO3 profiles. A numerical model encompassing diffusion, advection, and multiple reaction terms is applied to these data to characterize organic carbon degradation and CaCO3 dissolution processes near the sediment-water interface. A benthic O2 flux of 58 μmol cm−2 yr−1 over the top 1 mm sediment is estimated based on one measured sub-mm depth scale O2 profile. The numerical model indicates that this high O2 consumption rate is related to a very labile fraction of organic C which has a degradation rate constant of approximately 4.5 × 10−8 s−1 (1.4 yr−1 ), and which is not mixed downward by biological mixing. Seasonality in the benthic O2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic C. Degradation rate constants of the bulk organic C by oxygen reduction and by nitrate reduction are estimated to be about the same (1 × 10−9 s−1 ). The organic C rain rate responsible for the bulk organic C is estimated to be 53 μmol cm−2 yr−1 . This estimate exceeds the average rain rate determined by sediment trap collections at this site. Saturation state profiles, calculated from the in situ pH and pCO2 data and from modelling the in situ O2 and pH data, both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm. The dissolution rate constant of calcite in this CaCO3-poor station is determined to be 5–10% day−1 (assuming the reaction order is 4.5 ), which is close to the minimum estimates for environments richer in calcite. A uniform calcite dissolution rate constant, therefore, may be adequate for representing carbonate dissolution in global-scale models of ocean chemistry.

Acute toxicity of five sediment-associated metals, individually and in a mixture, to the estuarine meiobenthic harpacticoid copepod Amphiascus tenuiremis.

The acute effects of many individual, seawater-solubilized metals on meiobenthic copepods and nematodes are well known. In sediments, however, metals most often occur as mixtures, and it is not known whether such mixtures exhibit simple additive toxicity to meiobenthos. The estuarine meiobenthic copepod Amphiascus tenuiremis was tested in four acute (96-h) sediment bioassays to determine sediment and pore-water LC50s for single-metal exposures to copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn). Laboratory-cultured copepods were exposed to clean 98% silt:clay sediments spiked with metal chloride solutions to yield five exposure concentrations plus a control. Trimmed Spearman-Karber analysis gave sediment 96-h LC50 values of 4.4 mumole Cu/g, 5.7 mumole Ni/g, 11.9 mumole Pb/g, 10.3 mumole Zn/g, and pore-water 96-h LC50 values of 2 mumole/l, 11.7 mumole/l, and 5.7 mumole/l for Cu, Ni, and Zn, respectively. Male survival after exposure to Cu, Pb, and Ni was significantly less than female survival (alpha = 0.05). Toxicity of a combined USEPA priority metal mixture to A. tenuiremis was assessed using sediment spiked equitoxically with Cd, Cu, Ni, Pb, and Zn. The sum toxic unit that produced a median lethal dose was 0.72. The mixture had a significantly greater than additive effect on A. tenuiremis survival, with the mixture being 1.4x more toxic than that expected by simple additivity.

The Mobility of Rare Earth Elements and Redox Sensitive Elements in the Groundwater/Seawater Mixing Zone of a Shallow Coastal Aquifer

The concentrations of Rare Earth Elements (REE) and Redox Sensitive Elements (RSE) were measured in groundwaters along a transect of the forest-marsh interface of a surficial aquifer system in North Inlet, SC. The well transect extended from a forest recharge area across the marsh and tidal creek to a tidal recharge area of beach ridge. The concentrations of the RSE (Fe, Mn, and U) were consistent with reducing conditions through the transect. Fe was present at concentrations ranging from a few micromolar to greater than one hundred micromolar in most wells. U was depleted with respect to salinity predicted concentrations, indicating removal with respect to the seawater endmember. Dissolved Mn concentrations were generally low in all wells, indicating no significant solid source of Mn (as MnOx) in this system. When extrapolated to a global scale, estimates of U removal during seawater exchange with the aquifer solids equaled 10–20% of the total riverine dissolved U input flux. REE concentrations in the forest recharge area were high in shallow wells, and showed a light enriched fractionation pattern, characteristic of soil leaching by Natural Organic Matter (NOM) rich waters. A decrease in REE concentration with depth in the forest wells coupled with a trend towards Heavy REE (HREE) enriched fractionation pattern indicated removal of the REE coincident with NOM and Dissolved Organic Carbon (DOC) removal. The saline waters of the beach ridge wells show a Light REE (LREE) enriched fractionation pattern and have the highest overall concentrations of the REE, indicating a significant REE source to the seawater endmember waters. The concentration gradients along the beach ridge flow path indicate a large source in the deep wells, and net export of dissolved REE to the tidal creek system and the coastal ocean. Ultrafiltration experiments indicate a transition from a colloidal dominated reservoir for the REE in the forest wells to a colloidal and dissolved reservoir in the beach ridge wells. The ultrafiltration data coupled with a correlation with Dissolved Inorganic Carbon (DIC) release suggest that there is diagenetic mobilization of an REE rich organic carbon phase in the saline endmember wells. We suggest here that degradation of this relic terrestrial organic carbon and REE rich phase results in the export of dissolved REE equal to or exceeding river inputs in this region.

Experimental determination of trace element partition coefficients in cultured benthic foraminifera

Abstract We present the first trace metal partition coefficients obtained from reproducing cultures of deep-sea benthic foraminifera. Paleoceanographically important species, including juvenile Bulimina marginata , Cibicidoides pachyderma , and Uvigerina peregrina , were maintained in sediment microcosms at 10°C, 35 psu, and pH 8 for 1–3 years. Juvenile foraminifera were separated, cleaned, and dissolved under clean conditions for determination of trace metal partition coefficients on recently deposited (1–3 months) foraminiferal calcite. In addition to the deep-sea species, we analyzed a shallow water benthic foraminifer, Ammonia beccarii . Overlying water samples were collected from the microcosms concurrent to the period of calcification (3 months prior to separation). Ba/Ca partition coefficients ( D Ba ) were measured in replicate for benthic foraminifera species Bulimina marginata (0.24 ± 0.07), Uvigerina peregrina (0.24 ± 0.06, Ammonia beccarii (0.20 ± 0.04). The D Ba for Bulimina marginata and Uvigerina peregrina were found to closely match the range from the Ontong Java Plateau. Sample size limitations allowed for only one analysis of D Ba for Cibicidoides pachyderma . However, our nonreplicated D Ba of 0.5 ± 0.1 falls within the accepted range of core top samples (0.37 ± 0.06). We report a D Cd for Ammonia of 1.0 ± 0.5, for Cibicidoides of 4 ± 2, for Bulimina of 3 ± 1, and for Uvigerina 2 ± 1 which all fall within the ranges reported for core top calibrations. The large uncertainties in D Cd reflect variation in dissolved Cd concentration in the artificial seawater reservoir due to loss and replacement of Cd during the course of the experiment. The variability between species is probably the result of variability in pore water Cd in the sediment culture system and may reflect habitat effects.

The Carbon and Oxygen Stable Isotopic Composition of Cultured Benthic Foraminifera

Abstract Laboratory cultures of several species of benthic foraminifera were grown under controlled physical and chemical conditions during months-long experiments carried out at the University of South Carolina in 2001 and 2002. A dozen experimental culture chambers contained a c. 1–3 mm layer of trace-metal free silica substrate, and were continuously flushed with water from a large (1600 L) seawater reservoir with known, constant temperature and composition (δ18O(water), carbonate system chemistry, and trace element concentrations). Each year, in most of the culture chambers, one or more species reproduced, producing hundreds of juveniles which grew into size classes ranging from 100 to 500 microns. Bulimina aculeata was the most successful species in the 2001 cultures, and both B. aculeata and Rosalina vilardeboana were abundant in 2002. We determined the shell C and O isotopic composition of the cultured foraminifera, and compared these isotopic values with the water chemistry of the culture chambers, and also with the shell chemistry of field specimens collected from sites on the North Carolina and South Carolina (USA) continental margin. The cultured foraminifera showed substantial offsets from the δ13C of system water dissolved inorganic carbon (−0.5 to −2.5‰, depending on species) and smaller offsets (0 to −0.5‰) from the predicted δ18O of calcite in equilibrium with the culture system water at the growth temperature. These offsets reflect at least three factors: species-dependent vital effects; ontogenetic variations in shell chemistry; and the aqueous carbonate chemistry ([CO3−] or pH) of the experimental system.

Icebergs as Unique Lagrangian Ecosystems in Polar Seas

Global warming and its disproportionate impact on polar regions have led to increased iceberg populations. Southern Ocean studies in the northwest Weddell Sea have verified substantial delivery of terrestrial material accompanied by increased primary production and faunal abundance associated with free-drifting icebergs. It is hypothesized that input and utilization of macro- and micronutrients are promoted by conditions unique to free-drifting icebergs, leading to increased production, grazing, and export of organic carbon. In Arctic regions, increased freshwater input from meltwater acts to stratify and stabilize the upper water column. As has been observed in the Southern Ocean, Arctic-region icebergs should drive turbulent upwelling and reduce stratification, potentially leading to increased nitrate delivery to the local ecosystem. Increasing populations of icebergs in polar regions can potentially be important in mediating the drawdown and sequestration of CO(2) and can thus impact the oceanic carbon cycle.