Toxicity, bioaccumulation, and biotransformation of silver nanoparticles in marine organisms.

The toxicity, bioaccumulation, and biotransformation of citrate and polyvinylpyrrolidone (PVP) coated silver nanoparticles (NPs) (AgNP-citrate and AgNP-PVP) in marine organisms via marine sediment exposure was investigated. Results from 7-d sediment toxicity tests indicate that AgNP-citrate and AgNP-PVP did not exhibit toxicity to the amphipod (Ampelisca abdita) and mysid (Americamysis bahia) at ≤75 mg/kg dry wt. A 28-d bioaccumulation study showed that Ag was significantly accumulated in the marine polychaete Nereis virens (N. virens) in the AgNP-citrate, AgNP-PVP and a conventional salt (AgNO3) treatments. Synchrotron X-ray absorption spectroscopy (XAS) results showed the distribution of Ag species in marine sediments amended with AgNP-citrate, AgNP-PVP, and AgNO3 was AgCl (50­65%) > Ag2S (32­42%) > Ag metal (Ag0) (3­11%). In N virens, AgCl (25­59%) and Ag2S (10­31%) generally decreased and, Ag metal (32­44%) increased, relative to the sediments. The patterns of speciation in the worm were different depending upon the coating of the AgNP and both types of AgNPs were different than the AgNO3 salt. These results show that the AgNP surface capping agents influenced Ag uptake, biotransformation, and/or excretion. To our knowledge, this is the first demonstration of the bioaccumulation and speciation of AgNPs in a marine organism (N. virens).

Modern history of hypoxia in Narragansett Bay: The geochemical record.

Increased inputs of nitrogen from agricultural runoff, urbanization and suburbanization have resulted in degradation of water quality, including increased frequency and severity of hypoxia, in estuarine ecosystems. Much work has been conducted in recent years to characterize the spatial and temporal extent of hypoxia in coastal systems, but the historical record of hypoxia in such systems is much less well known. The current work examines the history of hypoxia in upper Narragansett Bay, an urbanized estuary in the northeastern U.S., through vertical profiles of geochemical markers in sediment cores. Concentrations of authigenic molybdenum indicate more frequent/ longer periods of hypoxia that are related to changes in population and anthropogenic inputs to the Bay from the surrounding watersheds. Cores from the urbanized upper bay, greatly affected by wastewater treatment facilities (WWTFs), indicate greater duration of hypoxia in the 20th century, with periods of hypoxia decreasing through mid-century and recurring thereafter. Trends of hypoxia are closely related to improvements and failures of WWTFs in surrounding communities. In Greenwich Bay, with a suburban watershed and only one WWTF, hypoxia increased substantially in parallel with growth of population in the surrounding watershed. Carbon and nitrogen concentrations and isotope values reflect increased nitrogen enrichment and productivity in the Bay in the 2nd half of the 20th century. These results can help inform study of the environmental responses to societal activities that may affect water quality.

Mapping Hypoxia Response to Estuarine Nitrogen Loading Using Molybdenum in Sediments.

Quantitative relationships between nitrogen loading and ecological effects such as hypoxia are critical to developing nitrogen (N) standards for coastal waters, but spatial and temporal variability within estuaries can make the determination of such relationships difficult. Accumulation of molybdenum (Mo) in surface sediments has been proposed as a quantitative indicator of the duration of hypoxia (defined as dissolved oxygen concentrations below 2.8 mg/L) in overlying waters, providing a metric to evaluate the relationship between varying N loads and the occurrence and duration of hypoxic conditions. Nitrogen loads were estimated for seven Rhode Island embayments based on watershed land use and normalized for embayment volume and local residence times (LRT) derived from hydrodynamic modeling. Mo was measured in surface sediments from sampling sites selected within and across the embayments to span the range of N loads. The spatial distribution of sediment Mo within the embayments closely followed that of normalized N loads, and Mo concentrations approximated a second-order relationship with normalized N loads. Sediment Mo concentrations were converted to mean annual duration of hypoxia using a previously derived linear relationship between Mo in surface sediments and annual duration of hypoxia in overlying water, and a quantitative relationship derived between normalized N loads and annual duration of hypoxia. Evaluation of that relationship provides an approach to develop standards for N loading in coastal waters.

Molybdenum accumulation in sediments: a quantitative indicator of hypoxic water conditions in Narragansett Bay, RI.

Authigenic molybdenum (Mo) accumulation in marine sediments has often been used as a qualitative indicator of hypoxic bottom water. To investigate its use as a quantitative indicator of hypoxic exposure, sediment cores were collected from water quality monitoring sites in Narragansett Bay (RI, USA) that experience varying periods of hypoxia. Total Mo concentrations in surficial (0-1 cm) sediments were determined by total digestion and ICP-MS analysis. Lithogenic contributions to total Mo concentrations were estimated by multiplying measured concentrations of aluminum (Al) by the mean crustal Mo:Al ratio and subtracting them from the total concentrations to yield the authigenic fraction. 210Pb dating was used to determine sediment accumulation rates at each site. Mean annual periods of hypoxia in bottom waters were determined from continuous monitoring data for the years coinciding with the top 1 cm of sediment. Results indicated a linear relationship between authigenic Mo concentrations and frequency of hypoxia, although the relationships differed between different sampling periods. These results demonstrate the potential of sedimentary Mo as a tool for assessing the spatial and temporal extent of hypoxia in coastal waters.

Dinoflagellate cyst records and human disturbance in two neighboring estuaries, New Bedford Harbor and Apponagansett Bay, Massachusetts (USA).

The dinoflagellate cyst records in sediments from New Bedford Harbor and Apponagansett Bay demonstrate sensitivity to environmental change caused by human activity in the watersheds over the last 500 years. Changes in the species richness, as well as absolute and relative abundance of dinoflagellate cyst taxa reflect recent periods of development around the estuaries. Cyst taxa sensitive to these changes include Dubridinium spp., Polykrikos schwartzii, Lingulodinium machaerophorum, Operculodinium israelianum and Selenopemphix quanta. The greatest changes in the dinoflagellate cyst record occur during the 20th century, when New Bedford Harbor was exposed to both toxic pollution and heavy nutrient loading from point and non-point sources. Apponagansett Bay was not subject to industrial pollution and nutrient enrichment has been lower (from non-point sources). In Apponagansett Bay there is an increase in the dinoflagellate cyst species richness while species richness first increased, then declined in New Bedford Harbor. During the same period, the total dinoflagellate cyst concentration in New Bedford Harbor fluctuated over a wide range. The decline of species richness and the large fluctuations in the total cyst abundances signal the intensified anthropogenic disturbance in the watershed, notably a high degree of eutrophication and toxic pollution.

Environmental stress and recovery: the geochemical record of human disturbance in New Bedford Harbor and Apponagansett Bay, Massachusetts (USA).

Sediments record the history of contamination to estuaries. Analysis of the concentrations of toxic organic compounds, contaminant and crustal metals, organic carbon content and isotopic composition in sediment cores from two estuarine systems in Buzzards Bay allowed reconstruction of human impacts over 350 years. Vertical distributions of the contaminants correlate with changes in the nature of watershed/estuarine activities. All contaminants were highly enriched (tens to hundreds times background) in modern New Bedford Harbor sediments. Enrichment began around the turn of the 20th century for all but PCBs, which were first synthesized in the 1930s. An increase in organic carbon content and a shift of carbon isotopes toward a more terrestrial signature illustrates increasing anthropogenic impact in New Bedford as population grew along with the industrial base. Institution of environmental protection measures in the late 20th century was reflected in decreased, although still substantially elevated, concentrations of contaminants. A lack of industrial development in Apponagansett Bay resulted in much lower concentrations of the same indicators, although specific contaminants related to the early whaling industry increased significantly above background as early as the late 18th century. The similarity of indicators in older portions of cores from NBH and unimpacted Apponagansett Bay demonstrates that cores can be used to establish reference conditions as successfully as using separate sites judged a priori to represent the reference state. The historical reconstruction approach provides the basis for establishing relationships between environmental stressors and factors that drive the stressors, as well as a framework for the assessment of ecological response(s) to environmental stressors over a range of time and/or exposure scales.

Predicting the toxicity of chromium in sediments.

Chromium exists in sediments in two oxidation states: Cr(III), which is relatively insoluble and nontoxic, and Cr(VI), which is much more soluble and toxic. Chromium(VI) is thermodynamically unstable in anoxic sediments, and acid-volatile sulfide (AVS) is formed only in anoxic sediments; therefore sediments with measurable AVS concentrations should not contain toxic Cr(VI). If this hypothesis holds true, measuring AVS could form the basis for a theoretically based guideline for Cr in sediments. Ten-day water-only and spiked sediment toxicity tests with the amphipod Ampelisca abdita were performed with Cr(VI) and Cr(III), along with sediments collected from a site contaminated with high concentrations of Cr. In sediments where AVS exceeded analytical detection limits, Cr concentrations in interstitial water were very low (<100 microg/L) and no significant toxicity to A. abdita was observed. In sediments in which AVS was not significantly greater than zero, Cr concentrations in interstitial waters increased significantly, with greater than 90% of the Cr present as Cr(VI), and mortality of A. abdita was elevated. These results demonstrate that measurements of AVS and interstitial water chromium can be useful in predicting the absence of acute effects from Cr contamination in sediments.