A review of factors influencing measurements of decadal variations in metal contamination in San Francisco Bay, California

The relationship between population attributes of the mud snail Amphibola crenata and sediment contamination: A multi-estuary assessment

This study assessed the potential of the New Zealand mud snail Amphibola crenata to act as a bioindicator of contaminated estuarine sediment. Seventeen sites with varying contaminant burdens were identified within six New Zealand regions. Attributes (population density, individual length distribution and individual dry weight condition index) were measured for field-collected A. crenata, and related to measurements of sediment trace metals and nutrients. Population density of the mud snail was relatively high in sites with elevated nutrients and organic matter. The length distribution of A. crenata showed significant regional and site-specific variations. Minimum, mean, and median shell length of A. crenata were positively correlated with sediment cadmium and zinc concentration. Overall, the sites were able to be distinguished by A. crenata population attributes and the sediment metal and nutrient content. These results suggest that A. crenata population information has potential value for assessing estuarine sediment metal and nutrient contamination.

Spatial variability of phytoplankton in a shallow tidal freshwater system reveals complex controls on abundance and community structure

Estuaries worldwide are undergoing changes to patterns of aquatic productivity because of human activities that alter flow, impact sediment delivery and thus the light field, and contribute nutrients and contaminants like pesticides and metals. These changes can influence phytoplankton communities, which in turn can alter estuarine food webs. We used multiple approaches-including high-resolution water quality mapping, synoptic sampling, productivity and nitrogen uptake rates, Lagrangian parcel tracking, enclosure experiments and bottle incubations-over a short time period to take a "spatial snapshot" of conditions in the northern region of the San Francisco Estuary (California, USA) to examine how environmental drivers like light availability, nutrients, water residence time, and contaminants affect phytoplankton abundance and community attributes like size distribution, taxonomic structure, and nutrient uptake rates. Zones characterized by longer residence time (15-60 days) had higher chlorophyll-a concentrations (9 ± 4 µg L^-1) and were comprised primarily of small phytoplankton cells (<5 µm, 74 ± 8%), lower ammonium concentrations (1 ± 0.8 µM), higher nitrate uptake rates, and higher rates of potential carbon productivity. Conversely, zones characterized by shorter residence time (1-14 days) had higher ammonium concentration (13 ± 5 µM) and lower chlorophyll-a concentration (5 ± 1 µg L^-1) with diatoms making up a larger percent contribution. Longer residence time, however, did not result in the accumulation of large (>5 µm) cells considered important to pelagic food webs. Rather, longer residence time zones had a phytoplankton community comprised primarily of small cells, particularly picocyanobacteria that made up 38 ± 17% of the chlorophyll-a - nearly double the concentration seen in shorter residence time zones (22 ± 7% picocyanobacterial of chlorophyll-a). Our results suggest that water residence time in estuaries may have an effect as large or larger than that experimentally demonstrated for light, contaminants, or nutrients.

Increases in Anthropogenic Gadolinium Anomalies and Rare Earth Element Concentrations in San Francisco Bay over a 20 Year Record

We evaluated both the spatial distribution of gadolinium (Gd) and other rare earth elements (REE) in surface waters collected in a transect of San Francisco Bay (SFB) and their temporal variations within the Bay over two decades. The REE were preconcentrated using the NOBIAS PA-1 resin prior to analysis by high-resolution inductively coupled plasma mass spectrometry. Measurements revealed a temporal increase in the Gd anomaly in SFB from the early 1990s to the present. The highest Gd anomalies were observed in the southern reach of SFB, which is surrounded by several hospitals and research centers that use Gd-based contrast agents for magnetic resonance imaging. Recent increases in that usage presumably contributed to the order of magnitude increase in anthropogenic Gd concentrations in SFB, from 8.27 to 112 pmol kg(-1) over the past two decades, and reach the northeast Pacific coastal waters. These measurements (i) show that "exotic" trace elements used in new high-tech applications, such as Gd, are emerging contaminants in San Francisco Bay and that anthropogenic Gd concentrations increased substantially over a 20 year period; (ii) substantiate proposals that REE may be used as tracers of wastewater discharges and hydrological processes; and (iii) suggest that new public policies and the development of more effective treatment technologies may be necessary to control sources and minimize future contamination by REE that are critical for the development of new technologies, which now overwhelm natural REE anomalies.

Copper Pollution Increases the Relative Importance of Predation Risk in an Aquatic Food Web

Although the cascading impact of predators depends critically on the relative role of lethal predation and predation risk, we lack an understanding of how human-caused stressors may shift this balance. Emergent evidence suggests that pollution may increase the importance of predator consumptive effects by weakening the effects of fear perceived by prey. However, this oversimplification ignores the possibility that pollution may also alter predator consumptive effects. In particular, contaminants may impair the consumptive effects of predators by altering density-dependent interactions among prey conspecifics. No study has directly compared predator consumptive and non-consumptive effects in polluted versus non-polluted settings. We addressed this issue by using laboratory mesocosms to examine the impact of sublethal doses of copper on tri-trophic interactions among estuarine predator crabs Cancer productus, carnivorous whelk prey Urosalpinx cinerea, and the basal resource barnacles Balanus glandula. We investigated crab consumptive effects (whelks culled without crab chemical cues), non-consumptive effects (whelks not culled with crab chemical cues), and total effects (whelks culled with crab chemical cues) on whelks in copper polluted and non-polluted waters. Realistic copper concentrations suppressed the effects of simulated crab lethal predation (whelk culling) by removing density-dependent feeding by whelks. Specifically, reductions in conspecific density occurring in elevated copper levels did not trigger the normal increase in whelk consumption rates of barnacles. Weakened effects of fear were only observed at extremely high copper levels, suggesting consumptive effects were more sensitive to pollution. Thus, pollution may shape communities by altering the roles of predators and interactions among prey.

Can the integration of multiple biomarkers and sediment geochemistry aid solving the complexity of sediment risk assessment? A case study with a benthic fish

Surveying toxicity of complex geochemical media as aquatic sediments often yields results that are either difficult to interpret or even contradictory to acknowledged theory. Multi-level biomarkers were investigated in a benthic fish exposed to estuarine sediments through laboratory and in situ bioassays, to evaluate their employment either in ecological risk assessment or in more mechanistic approaches to assess sediment-bound toxicity. Biomarkers reflecting lesions (such as genotoxicity or histopathology), regardless of their low or absent specificity to contaminants, are efficient in segregating exposure to contaminated from uncontaminated sediments even when classical biomarkers like CYP1A and metallothionein induction are inconclusive. Conversely, proteomics and gene transcription analyses provided information on the mechanics of toxicity and aided explaining response variation as a function of metabolic imbalance and impairment of defences against insult. In situ bioassays, although less expedite and more affected by confounding factors, produced data better correlated to overall sediment contamination.

Trend and concentrations of legacy lead (Pb) in highway runoff

This study presents the results of lead (Pb) concentrations from both highway runoff and contaminated soil along 32 and 23 highway sites, respectively. In general, the Pb concentration on topsoil (0-15 cm) along highways was much higher than the Pb concentration in subsurface soil (15-60 cm). The Pb deposited on soil appears to be anthropogenic and a strong correlation was found between the Pb concentration in surface soil and highway runoff in urban areas. The concentration of Pb measured during 1980s from highways runoff throughout the world was up to 11 times higher than the measured values in mid 1990 s and 2000s. The current Pb deposited on soil near highways appears to be a mixture of paint, tire weight balance and old leaded gasoline combustion. Overall, the Pb phase-out regulation reduced the Pb deposits in the environment and consequently lowered Pb loading into receiving waters.

Dissolved silver in the Baltic Sea

The increased use of silver as a biocide in nanoparticle formulations has heightened concern on possible environmental implications owing to its toxicity. There is however very little data on the concentration levels of silver in marine and freshwaters. Here, I report data on dissolved (<0.4 μm filter) silver concentration in the surface waters of the Baltic Sea, the first such data reported for a European coastal water body. Levels of dissolved silver in the Baltic are comparable to those reported for other American estuarine waters and range from non-detectable in the open Baltic Sea Proper (<1 pM) to 9.4 pM (1 ng/L) in the Stockholm Archipelago, with a mean of 2.8 pM (0.2 ng/L). Inputs from wastewater treatment are clearly discernable and might constitute the main source of silver to the Stockholm Archipelago and possibly the Baltic Sea Proper.

Modeled trace element concentrations and partitioning in the San Francisco estuary, based on suspended solids concentration

Although trace element (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn) and methylmercury (MeHg) concentrations have been systematically sampled 1-3 times per year throughout the San Francisco Bay estuary for more than two decades, those collections do not capture episodic events that may govern the biogeochemical cycles of these elements in the Bay and adjacent Pacific coastal waters. Analyses of the partitioning of in situ elemental concentrations between particulate and total dissolved (<0.45 microm) phases coupled with optically based measurements of suspended solids concentration (SSC) showed highly significant (p<0.001) associations between all elemental concentrations and SSC in the Bay. Predictive models were developed to estimate the distribution ratio (D), or partition coefficient (Kd), and total concentration of each element in the water column based solely on SSC measurements. Modeled predictions of total element concentrations and distribution ratios were then coupled with measured SSC to predict the concentrations of dissolved trace elements in the water column. These predicted total and dissolved concentrations of trace elements can provide both better diagnostics of biogeochemical cycling within the estuary and better estimates of fluxes to adjacent coastal waters, overcoming the limitations of the long-running but limited direct measurements of trace elements from existing sampling programs.

Metals associated with stormwater-relevant brake and tire samples

Properly apportioning the loads of metals in highway stormwater runoff to the appropriate sources requires accurate data on source composition, especially regarding constituents that help to distinguish among sources. Representative tire and brake samples were collected from privately owned vehicles and aqueous extracts were analyzed for twenty-eight elements. Correlation principal components analysis (PCA) revealed that tires were most influenced by Zn, Pb, and Cu, while brakes were best characterized by Na and Fe followed by Ba, Cu, Mg, Mn, and K; the latter three may be due to roadside soil contributions. Notably elevated Cd contributions were found in several brake samples. A targeted Cd-plated brake rotor was sampled, producing results consistent with the elevated levels found in the larger sample population. This enriched source of Cd is of particular concern due to high toxicity of Cd in aquatic ecosystems.

A review of total dissolved copper and its chemical speciation in San Francisco Bay, California

Following basin-wide contamination from industrial emissions and urban development, total dissolved copper concentrations in some regions of San Francisco Bay have exceeded national and state guidelines for water quality. In the face of dramatic improvements in wastewater treatment and point source control, persisting elevated dissolved copper concentrations in the Bay have prompted multiple studies and extensive monitoring of this estuary since 1989. Statistical analyses of monitoring data show that total dissolved copper concentrations have declined in the North (by 17%) and South (29%) San Francisco Bay as well as in the Southern Sloughs (44%) from 1993 to 2001. Concentrations remain elevated in the farthest reaches of the Bay (Delta and Estuary Interface), and in the Central Bay. Dissolved copper concentrations throughout the Bay have also been positively correlated (r = 0.632, P < 0.0005, n = 598) with dissolved organic matter, supporting results from complimentary chemical speciation studies which indicate that high-affinity copper-binding organic ligands dominate the chemical speciation of dissolved copper in the Bay. These organic ligands typically bind > 99.9% of the dissolved copper, effectively buffering the system against small changes in dissolved copper concentrations, and maintaining free Cu(2+) concentrations well below the toxicity threshold of ambient aquatic microorganisms. In response to these findings, site-specific water quality criteria for dissolved copper concentrations are now being developed by the Regional Water Quality Board to provide a more appropriate standard for copper toxicity in the Bay-one based on its chemical speciation and bioavailability.

Spatial and temporal variations in silver contamination and toxicity in San Francisco Bay

Although San Francisco Bay has a "Golden Gate", it may be argued that it is the "Silver Estuary". For at one time the Bay was reported to have the highest levels of silver in its sediments and biota, along with the only accurately measured values of silver in solution, of any estuarine system. Since then others have argued that silver contamination is higher elsewhere (e.g., New York Bight, Florida Bay, Galveston Bay) in a peculiar form of pollution machismo, while silver contamination has measurably declined in sediments, biota, and surface waters of the Bay over the past two to three decades. Documentation of those systemic temporal declines has been possible because of long-term, ongoing monitoring programs, using rigorous trace metal clean sampling and analytical techniques, of the United States Geological Survey and San Francisco Bay Regional Monitoring Program that are summarized in this report. However, recent toxicity studies with macro-invertebrates in the Bay have indicated that silver may still be adversely affecting the health of the estuarine system, and other studies have indicated that silver concentrations in the Bay may be increasing due to new industrial inputs and/or the diagenetic remobilization of silver from historically contaminated sediments being re-exposed to overlying surface waters and benthos. Consequently, the Bay may not be ready to relinquish its title as the "Silver Estuary".

Synthesis of long-term nickel monitoring in San Francisco Bay

The Regional Monitoring Program for Water Quality in the San Francisco Bay (RMP) has conducted annual monitoring of the San Francisco Estuary (estuary) since 1993. The RMP primarily monitors water, sediment, and bivalves, although short-term pilot and special studies on select topics are also conducted. The purpose of this article is to synthesize over 10 years of RMP nickel data and to illustrate how comprehensive monitoring data contribute to an understanding of contaminant fate. Nickel concentrations observed in water (43.7-233.7 nM) are largely a function of the geology of the watershed surrounding the estuary and inputs from wastewater treatment plants and urban runoff. The geologic formations supplying sediment to the estuary contain high concentrations of nickel (e.g., 1000-3300 microg/g). Much of the research to date on nickel speciation suggests that nickel complexes from wastewater treatment plants are not readily available for biological uptake [Bedsworth, W.W., Sedlak, D.L., 1999. Sources and environmental fate of strongly complexed nickel in estuarine waters: the role of ethylenediaminetetraacetate. Environ. Sci. Technol. 33, 926-931, Sedlak, D.L., Phinney, J.T., Bedsworth, W.W., 1997. Strongly complexed Cu and Ni in wastewater effluents and surface runoff. Environ. Sci. Technol. 31(10), 3010-3016, Donat, J.R., Lao, K.A., Bruland, K.W., 1994. Speciation of dissolved copper and nickel in South San Francisco Bay: a multi-method approach. Anal. Chim. Acta. 284, 547-571]. In addition, concentrations of nickel measured in biota by the RMP (0.905-113.0 microg/g dry weight in bivalve tissues) are well below recommended maximum tissue residue levels (220 microg/g wet weight, California state guidelines). Based on this information, regulators have reconsidered the water quality objectives developed for nickel.

Decadal mercury trends in San Francisco Estuary sediments

Monitoring sediment quality and total mercury concentrations over the period 1993-2001 at 26 stations in San Francisco Estuary has shown the seasonal cycling of mercury sediment concentrations, as well as a significant (P < 0.05) decrease in those concentrations at eight stations across the estuary. This decrease in sediment mercury concentrations is attributed to the transport of relatively cleaner sediment to the estuary from the Sacramento River and San Joaquin River watersheds. Despite the decreases observed in some parts of the estuary, no corresponding trend has been found in concurrent studies on sport fish and bivalves in the estuary.

Tidal salt marsh sediment in California, USA. Part 2: occurrence and anthropogenic input of trace metals

Surface sediment samples (0-5 cm) from 5 tidal salt marshes along the coast in California, USA were analyzed to investigate the occurrence and anthropogenic input of trace metals. Among study areas, Stege Marsh located in the central San Francisco Bay was the most contaminated marsh. Concentrations of metals in Stege Marsh sediments were higher than San Francisco Bay ambient levels. Zinc (55.3-744 microg g(-1)) was the most abundant trace metal and was followed by lead (26.6-273 microg g(-1)). Aluminum normalized enrichment factors revealed that lead was the most anthropogenically impacted metal in all marshes. Enrichment factors of lead in Stege Marsh ranged from 8 to 49 (median=16). Sediments from reference marshes also had high enrichment factors (2-8) for lead, indicating that lead contamination is ubiquitous, possibly due to continuous input from atmospherically transported lead that was previously used as a gasoline additive. Copper, silver, and zinc in Stege Marsh were also enriched by anthropogenic input. Though nickel concentrations in Stege Marsh and reference marshes exceeded sediment quality guidelines, enrichment factors indicated nickel from anthropogenic input was negligible. Presence of nickel-rich source rock such as serpentinite in the San Francisco Bay watershed can explain high levels of nickel in this area. Coefficients of variation were significantly different between anthropogenically impacted and non-impacted metals and might be used as a less conservative indicator for anthropogenic input of metals when enrichment factors are not available.