Effects of silver nanoparticles on zebrafish (Danio rerio) and Escherichia coli (ATCC 25922): a comparison of toxicity based on total surface area versus mass concentration of particles in a model eukaryotic and prokaryotic system

Silver nanoparticles (Ag NPs) have been classified as the most abundant NP found in commercial products. In the present study, zebrafish (Danio rerio) and bacteria (Escherichia coli; ATCC 25922) were used to test the size-dependent toxicological effects of Ag NPs, the effects of ionic silver versus Ag NPs, and Ag NP effects on mortality using mass concentration (mg/L) compared with total surface area (nm(2) /L). Several diameters of Ag NPs (20, 50, 110 nm) as well as AgNO(3) were chosen as experimental treatments. Treated zebrafish embryos exhibited anomalies of the heart, namely, slower heart rates and pericardial edema. A size-dependent response was not observed in zebrafish when viewing mortality across all Ag NP treatments, although 20 nm elicited the highest incidence of abnormal motility and induced slower development. An Ag NP dose- and size-dependent response was observed in treated bacteria using mass concentration, with 20-nm Ag NP producing the highest mortality rate. In both zebrafish and bacteria, AgNO(3) was shown to be more toxic than Ag NPs at equivalent concentrations. When total surface area of Ag NPs was used to gauge bacterial mortality, a total surface area-dependent, but not size-dependent, response was observed for all three Ag NPs used in the present study, with nearly 100% mortality observed once a total surface area of approximately 1E + 18 nm(2) /L was reached. This trend was not apparent, however, when measuring total surface area for zebrafish mortality.

The effect of particle size on the cytotoxicity, inflammation, developmental toxicity and genotoxicity of silver nanoparticles

Silver nanoparticles are of interest to be used as antimicrobial agents in wound dressings and coatings in medical devices, but potential adverse effects have been reported in the literature. The most pronounced effect of silver nanoparticles and the role of particle size in determining these effects, also in comparison to silver ions, are largely unknown. Effects of silver nanoparticles of different sizes (20, 80, 113 nm) were compared in in vitro assays for cytotoxicity, inflammation, genotoxicity and developmental toxicity. Silver nanoparticles induced effects in all endpoints studied, but effects on cellular metabolic activity and membrane damage were most pronounced. In all toxicity endpoints studied, silver nanoparticles of 20 nm were more toxic than the larger nanoparticles. In L929 fibroblasts, but not in RAW 264.7 macrophages, 20 nm silver nanoparticles were more cytotoxic than silver ions. Collectively, these results indicate that effects of silver nanoparticles on different toxic endpoints may be the consequence of their ability to inflict cell damage. In addition, the potency of silver in the form of nanoparticles to induce cell damage compared to silver ions is cell type and size-dependent.

Nanoparticle characteristics affecting environmental fate and transport through soil

Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil.

Risk assessment methodologies for exposure of great horned owls (Bubo virginianus) to PCBs on the Kalamazoo River, Michigan

Dietary exposures of great horned owls (GHO; Bubo virginianus) to polychlorinated biphenyls (PCBs) in the terrestrial food web at the Kalamazoo River, Michigan, USA, were examined. Average potential daily doses (APDD) in GHO diets were 7- to 10-fold and 3-fold greater at the more contaminated location versus a reference location for site-specific exposures quantified as total PCBs and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ(WHO-Avian)), respectively. Wetland/aquatic prey contributed significantly to PCB exposure and APDD. Estimates of risk based on comparison of modeled dietary intake (e.g., APDD) to toxicity reference values (TRVs), using a hazard quotient (HQ) methodology, varied between diet composition methods (mass basis vs numeric basis). Mass-basis compositions yielded greater HQs at all sites. Potential risks associated with dietary exposures ("bottom-up" risk assessment methodology) were less than (HQ < 1) benchmarks for effects. This result is consistent with risk estimates based on concentrations in tissues ("top-down" risk assessment methodology), and indicated PCBs posed no significant risk to terrestrial raptor species. Colocated and concurrent studies that evaluated GHO reproductive performance (nestling productivity) and relative abundance were consistent with results of the risk assessment. Measures of risk based on HQs were consistent with direct measures of ecologically relevant endpoints (reproductive fitness). Uncertainty in risk estimates is contributed during the selection of TRVs for effects in GHO based on TEQ(WHO-Avian) because of the absence of species-specific, dose-response thresholds. This evaluation indicated that a multiple-lines-of-evidence approach provided the best estimate of risk.

Reproductive success of passerines exposed to polychlorinated biphenyls through the terrestrial food web of the Kalamazoo River

The eastern bluebird (Sialia sialis) and the house wren (Troglodytes aedon) were identified as ecological receptors of concern due to exposure and potential effects stemming from polychlorinated biphenyl (PCB) contamination in floodplain soils of the Kalamazoo River Superfund Site, Michigan, USA. Measures of population health were compared at a contaminated and a less-contaminated reference location. During this 3-year study, productivity of bluebirds was significantly less at the downstream location than at the reference location. Hatching success, clutch size, and predicted brood size were significantly less in early clutches of house wrens at the more contaminated location than at the upstream reference location, but fledging success was significantly greater at the contaminated location. Studies concurrent to the study presented here reported that concentrations of PCBs in the tissues and diets of the passerine birds were less than the predicted threshold for adverse effects. The results of our study, taken along with the measured exposure data, suggest that other factors in addition to PCB exposure such as habitat, prey availability, small sample size, and cocontaminants were likely causes of the differences that were observed at the two locations.

Accumulation of polychlorinated biphenyls from floodplain soils by passerine birds

Eggs, nestlings, and adults of the eastern bluebird (Sialia sialis) and house wren (Troglodytes aedon) were collected at a polychlorinated biphenyl (PCB)-contaminated site and a reference location on the Kalamazoo River (MI, USA). Eggs and nestlings of eastern bluebirds at the more contaminated location contained concentrations of 8.3 and 1.3 mg/kg, respectively, of total PCBs and 77 and 6.3 ng/kg, respectively, of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs). Eggs, nestlings, and adults of house wrens from the contaminated location contained 6.3, 0.77, and 3.2 mg/kg, respectively, of PCBs and 400, 63, and 110 ng/kg, respectively, of TEQs. Concentrations of total PCBs and TEQs in tissues at the more contaminated location were significantly greater than concentrations in tissues at the reference site for all tissue types of both species. Exposures of the two species studied were different, which suggests that terrestrial-based insectivorous passerine species, foraging in the same area, may have differential exposure to PCBs depending on specific foraging techniques and the insect orders that are targeted. Despite the greater accumulation of PCBs at the more contaminated location, the risk of exposure to PCBs did not exceed the threshold for adverse effects at either location.

Productivity of tree swallows (Tachycineta bicolor) exposed to PCBs at the Kalamazoo River superfund site

A 123-km stretch of the Kalamazoo River in Michigan, was designated a Superfund site in 1990 due to historical releases of effluent containing polychlorinated biphenyl (PCB)-contaminated paper waste. Risk to bird species in the river ecosystem was evaluated using the tree swallow (Tachycineta bicolor) as a monitor for possible effects due to PCB exposure at two nesting locations, one in the Superfund site and one in an upstream reference location that is less contaminated with PCBs. In 2 of the 3 years of the study, clutch size at the contaminated location was 3.7 +/- 1.4 and 4.8 +/- 0.73 eggs per nest (mean +/- SD), which was significantly less than the clutch size at the reference location (5.0 +/- 1.1 and 5.3 +/- 1.1 eggs per nest). However, there were no statistically significant differences in fledging success, predicted brood size, predicted number of fledglings, or growth of nestlings between the Kalamazoo River Superfund site and an upstream reference location with lesser concentrations of PCBs in the sediments and riparian soils. Productivity and hatching success comparisons between these same sites were also not significantly different; however, the power of these conclusions was less (p < .10). The reduction in clutch size at the co-contaminated location could not be attributed to PCBs due to a number of confounding factors, including Co-cocontaminants, habitat structure, and food availability. Other reproductive parameters were not significantly impaired, and the size of the newly established colony at the Kalamazoo River Superfund site continued to grow over the period of the study. These site-specific observations, combined with multiple lines of evidence approach that considered results reported for the effects of both total PCBs and 2,3,7,8 tetrachlorodibenzo-p-dioxin equivalents (TEQ) on tree swallows at other locations, suggest that there were no significant population-level effects of PCBs on tree swallows at the Kalamazoo River Superfund site.

Tree swallow (Tachycineta bicolor) exposure to polychlorinated biphenyls at the Kalamazoo River superfund site, Michigan, USA

In 1990, a portion of the Kalamazoo River in Michigan, USA, was designated a Superfund site because of the presence of polychlorinated biphenyls (PCBs) in the sediment and floodplain soils. During a four-year period from 2000 to 2003, several avian species were monitored for reproductive effects and concentrations of PCBs in tissues attributed to food chain transfer from contaminated sediments. The tree swallow (Tachycineta bicolor) was chosen as a model receptor for contamination of passerine species. A top-down methodology was used to evaluate the bioaccumulation of PCBs, including non-ortho and mono-ortho congeners, in tree swallow eggs, nestlings, and adults at the Kalamazoo River area of concern (KRAOC) and at an upstream reference site. Generally, a sixfold difference in tissue concentrations of total PCBs was observed between the two sites with concentrations in eggs and nestlings at the KRAOC ranging from 0.95 to 15 microg PCB/g wet weight. Concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQsWHO Avian) for PCBs, based on bird-specific World Health Organization toxic equivalence factors, were 10- to 30-fold greater in the KRAOC than at the reference location. Egg and nestling TEQsWHO-Avian ranged from 0.21 to 2.4 ng TEQ/g wet weight at the KRAOC. Hazard quotients calculated from literature-derived toxicity reference values were below 1.0 at both the target and the reference site based on the no-observed-adverse-effect level and the lowest-observed-adverse-effect level.

Differential accumulation of polychlorinated biphenyl congeners in the aquatic food web at the Kalamazoo River Superfund site, Michigan

A series of field studies were conducted to gain a better understanding of the bioaccumulation and dynamics of polychlorinated biphenyl (PCB) congeners in the aquatic food web of the Kalamazoo River flood plain. Representative species of passerine birds, mammals, fish, aquatic plants, invertebrates, and colocated sediments were collected from areas located within submerged portions of the former Trowbridge impoundment and also from areas located at an upstream reference location. In most matrixes, total concentrations of PCBs were significantly greater in the downstream study area compared to the upstream reference location. Patterns of PCB congeners varied among trophic levels due to selective bioaccumulation of more chlorinated congeners in upper trophic level organisms. There were no statistically significant differences in total PCB concentrations among sampling grids within either site or temporally among three sampling seasons between May and September. The greatest total PCB concentrations were detected in adult tree swallows (mean = 8.7 mg/kg wet weight (ww)) and fish (mean = 4.4 mg/ kg ww) collected from the former Trowbridge impoundment. Concentrations of total 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) were greatest in egg, nestling, and adult tree swallows collected from the former Trowbridge impoundment. There was not a significant correlation between concentrations of total PCBs and TEQs at either site in the mammalian or avian food webs. The relative potency of the mixture of PCBs, expressed as the ratio of TEQs to total PCBs, increased with trophic position in the avian and mammalian aquatic food webs located within the former Trowbridge impoundment.

Differential accumulation of polychlorinated biphenyl congeners in the terrestrial food web of the Kalamazoo River Superfund site, Michigan

A series of field studies was conducted to determine the bioaccumulation of polychlorinated biphenyl (PCB) congeners in the terrestrial food web of the Kalamazoo River flood plain. Samples included colocated soils, native plants likely to be consumed by wildlife, several taxa of terrestrial invertebrates, small mammals, passerine bird eggs, nestlings, and adults, and great horned owl plasma and eggs. Mean concentrations of total PCBs in samples from the former Trowbridge impoundment were 6.5 mg/kg dry weight for soils and 0.023, 0.13, 1.3, 1.3, 1.6, and 8.2 mg/kg wet weight for plants, small herbivorous mammals, depurated earthworms, shrews, great horned owl eggs, and house wren eggs, respectively. Historical data from the Kalamazoo River have reported Aroclor-equivalent total PCB concentrations in the terrestrial food web; however, the degree of environmental weathering of the parent PCB mixtures was unknown. In this study, earthworms and composite samples of coleoptera exhibited PCB congener patterns that were similar to patterns in colocated soils. However, in plants, less chlorinated PCBs (e.g., mono-, di-, tri-, and tetrachlorinated biphenyls) were predominant, and in small mammals, there was a notable enrichment of PCBs 153, 180, 138, 118, and 99. In general, concentrations of PCBs were lower in most biota than in soil from the Kalamazoo River Area of Concern (KRAOC) although there was a modest biomagnification of PCBs from lower trophic level biota to highertrophic levels. As a consequence of environmental weathering of PCBs in the terrestrial food web of the KRAOC, the relative potency of the PCBs (expressed as mg TEQs/kg PCBs) decreased from soil to most biota. While there was a general trend, as expected, in which concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) increased with total PCBs, this relationship was rather poor (R2 = 0.13). Taken together, these data suggest that the differential accumulation of PCB congeners in the terrestrial food web can be explained by congener-specific differences in bioavailability from soil, exposure pathways, and metabolic potential of each of the food web components.