Metal accumulation in wild nine-banded armadillos.

Nine-banded armadillos (Dasypus novemcinctus) are widespread and abundant New World mammals with a lifestyle that entails prolonged, intimate contact with soils. Thus, armadillos would seem a promising candidate as a sentinel species to monitor chemical contamination in terrestrial ecosystems. Surprisingly, there have been virtually no toxicology studies on armadillos. Here, we provide the first analysis of metal contaminants for wild armadillos. Liver tissues were obtained from 302 armadillos collected at 6 sites in Georgia and Florida, USA that varied in their extent of human disturbance, from rural pine plantations to highly modified military/space installations. Data were stratified by age (juvenile and adult), sex, and site. Temporal (yearly) variation was examined at two of the sites that were sampled over three consecutive years. Concentrations of aluminum, cadmium, copper, nickel, lead, and zinc were measured in liver samples from each site. Although reference levels are not available for armadillos, accumulated metal concentrations were comparable to those reported for other mammals. We found no evidence of sex or age differences in the concentrations of any metal, except for Cd (age) and Pb (sex and age). However, concentrations of most metals varied substantially across sites and over time. Finally, concentrations of many metals were positively correlated with one another, suggesting that they likely co-occurred in some areas. Collectively, this study indicates the utility of armadillos as a sentinel species for studies of metal contamination in terrestrial systems, and highlights the need for further studies of other toxicants in these animals.

The influence of salinity on acute nickel toxicity to the two euryhaline fish species, Fundulus heteroclitus and Kryptolebias marmoratus.

Nickel (Ni) is a common pollutant found in aquatic environments and may be harmful at elevated concentrations. Increasing salinity has been shown to decrease the bioavailability and toxicity of other metals to aquatic organisms. In the present study, acute Ni toxicity experiments (96-h) were conducted at various salinities (0-36 ppt) to determine the effects of salinity on Ni toxicity to 2 euryhaline fish species, Kryptolebias marmoratus and Fundulus heteroclitus. Nickel concentrations causing lethality to 50% of the fish ranged from 2 mg/L in moderately hard freshwater to 66.6 mg/L in 36 ppt saltwater. Nickel toxicity to F. heteroclitus decreased linearly with increasing salinity; however, Ni toxicity to K. marmoratus was only lowered by salinities above 6 ppt, demonstrating potential physiological differences between the 2 species when they are functioning as freshwater fish. Furthermore, the authors investigated the influence of Mg(2+) , Ca(2+) , Na(+) , and Cl(-) on Ni toxicity to F. heteroclitus. Freshwater with up to 120 mg/L Ca(2+) as CaSO4 , 250 mg/L Mg(2+) as MgSO4 , or 250 mg/L Na(+) as NaHCO3 did not provide protection against Ni toxicity. Alternatively, 250 mg/L Na(+) , as NaCl, was protective against Ni toxicity; and the extent of protection was similar to that demonstrated from salt water with the same Cl(-) concentration. These results suggest that Cl(-) is the predominant ion responsible for reducing Ni toxicity to K. marmoratus and F. heteroclitus in higher salinity waters.

Toxicity of ZnO nanoparticles to the copepod Acartia tonsa, exposed through a phytoplankton diet.

Zinc oxide (ZnO) nanoparticles are being increasingly utilized in a variety of products and applications and are therefore commonly discharged into aquatic environments, increasing exposure and potentially impacting aquatic organisms. Zinc oxide nanoparticles can depress growth of some marine phytoplankton, and several examples of nanoparticle trophic transfer have been documented, although not within planktonic communities. The authors test whether feeding on ZnO-exposed phytoplankton could cause toxic effects in a widespread and ecologically important marine grazer, the copepod Acartia tonsa. The authors exposed the diatom Thalassiosira weissflogii to ZnO nanoparticles for 7 d and measured growth, zinc accumulation, and zinc distribution within the algal cells to elucidate bioavailability to grazing copepods. Thalassiosira weissflogii cultured with nano-ZnO were continuously fed to A. tonsa for 7 d, and reproduction and survival were quantified. A dose-dependent growth reduction was observed in T. weissflogii exposed to nano-ZnO, with a 20% effective concentration (EC20) of 70 µg/L Zn and a lowest observed effect concentration (LOEC) of 99 µg/L Zn. Zinc accumulation in the algae occurred dose-dependently over time, with the majority of the zinc partitioning into the cell wall fraction. Feeding on ZnO-exposed diatoms led to a decrease in copepod survival and reproduction. The EC20s corresponding to the dissolved zinc concentration in the T. weissflogii exposure media were 112 µg/L (13 µg/g dry wt) and 143 µg/L (16 µg/g dry wt), and the LOECs were 168 µg/L (17 µg/g dry wt) and 263 µg/L (21 µg/g dry wt) for copepod survival and reproduction, respectively. These results provide evidence of trophic transfer of metal contaminants associated with metal oxide nanomaterials within a marine plankton community, leading to a reduction in individual demographic performance of an important coastal marine grazer.

The effects of salinity on acute toxicity of zinc to two euryhaline species of fish, Fundulus heteroclitus and Kryptolebias marmoratus.

It is well known that the toxicity of zinc (Zn) varies with water chemistry and that its bioavailability is controlled by ligand interactions and competing ions. Zn toxicity in freshwaters with varying water chemistry has been well characterized; however, far less attention has been paid to the toxicity of Zn in estuarine and marine systems. We performed experiments using two euryhaline species of killifish, Fundulus heteroclitus and Kryptolebias marmoratus, to investigate the effects of changing salinity on acute toxicity of Zn. Larvae (7- to 8-days old) of each species were exposed to various concentrations of Zn for 96 h at salinities ranging from 0 to 36 ppt and survival was monitored. As salinity increased, Zn toxicity decreased in both fish species, and at salinities above 10 ppt, K. marmoratus larvae were generally more sensitive to Zn than were those of F. heteroclitus. The protection of salinity against Zn toxicity in F. heteroclitus was further investigated to determine the role of Ca(2+). Increased Ca(2+) in freshwater protected against Zn toxicity to the same extent as did saline waters with an equal Ca(2+) concentration up to ∼200 mg/L Ca for F. heteroclitus and ∼400 mg/L Ca for K. marmoratus. These results suggest that these two species may have differing Ca(2+) requirements and/or rates of Ca(2+) uptake in water of intermediate to full-strength salinity (∼200-400 mg/L Ca(2+)) and thus differ in their sensitivity to Zn. The overall goal of this study was to better understand Zn toxicity in waters of different salinity and to generate data on acute Zn toxicity from multiple species over a range of salinities, ultimately for use in development of estuarine and marine biotic ligand models.

Metal accumulation from dietary exposure in the sea urchin, Strongylocentrotus droebachiensis.

Metal contamination is a common problem in aquatic environments and may result in metal bioaccumulation and toxicity in aquatic biota. Recent studies have reported the significance of dietary metal accumulation in aquatic food chains, particularly in species of lower trophic levels. This research investigated the accumulation and effects of dietary metals in a macroinvertebrate. The seaweed species Ulva lactuca and Enteromorpha prolifera were concurrently exposed to five metals (copper, nickel, lead, cadmium, and zinc) and then individually fed to the green sea urchin Strongylocentrotus droebachiensis for a period of 2 weeks. Body mass, test length, total length, and coelomic fluid ion concentration and osmolality were measured. The sea urchins were also dissected and their organs (esophagus, stomach, intestine, gonads, and rectum) digested and analyzed for metals. The results demonstrated that metal accumulation and distribution varied between seaweed species and among metals. In general, there were greater concentrations of metals within the sea urchins fed E. prolifera compared with those fed U. lactuca. All of the metals accumulated within at least one organ of S. droebachiensis, with Cu being most significant. These results indicate that E. prolifera may accumulate metals in a more bioavailable form than within U. lactuca, which could impact the grazer. In this study, no significant differences in body length, growth, or coelomic fluid ion concentration and osmolality were detected between the control and metal-exposed sea urchins after the 2-week testing period. This research presents new data concerning metal accumulation in a marine herbivore after dietary metal exposure.

Effects of roof and rainwater characteristics on copper concentrations in roof runoff.

Copper sheeting is a common roofing material used in many parts of the world. However, copper dissolved from roof sheeting represents a source of copper ions to watersheds. Researchers have studied and recently developed a simple and efficient model to predict copper runoff rates. Important input parameters include precipitation amount, rain pH, and roof angle. We hypothesized that the length of a roof also positively correlates with copper concentration (thus, runoff rates) on the basis that runoff concentrations should positively correlate with contact time between acidic rain and the copper sheet. In this study, a novel system was designed to test and model the effects of roof length (length of roof from crown to the drip edge) on runoff copper concentrations relative to rain pH and roof angle. The system consisted of a flat-bottom copper trough mounted on an apparatus that allowed run length and slope to be varied. Water of known chemistry was trickled down the trough at a constant rate and sampled at the bottom. Consistent with other studies, as pH of the synthetic rainwater decreased, runoff copper concentrations increased. At all pH values tested, these results indicated that run length was more important in explaining variability in copper concentrations than was the roof slope. The regression equation with log-transformed data (R(2) = 0.873) accounted for slightly more variability than the equation with untransformed data (R(2) = 0.834). In log-transformed data, roof angle was not significant in predicting copper concentrations.

Validation study of the acute biotic ligand model for silver.

An important final step in development of an acute biotic ligand model for silver is to validate predictive capabilities of the biotic ligand model developed for fish and invertebrates. To accomplish this, eight natural waters, collected from across North America, were characterized with respect to ionic composition, pH, dissolved organic carbon, and sulfide. Tests were conducted with the cladoceran Ceriodaphnia dubia (48-h static) and the fish Pimephales promelas (96-h static renewal) to determine the concentrations causing lethality to 50% of the organisms (LC50s) for silver in each of these waters. Overall, the biotic ligand model adequately predicted silver toxicity to C. dubia; however, in some cases, predicted LC50 values exceeded measured values. The accuracy of the biotic ligand model predictions was less convincing for silver toxicity to P. promelas with pronounced problems in low-ionic strength waters. Another issue was the use of acclimated organisms in toxicity studies because the biotic ligand model has been developed with the use of a mix of studies with acclimated and nonacclimated test organisms of varying ages and sizes. To evaluate whether effects of acclimation to test waters influence biotic ligand model predictions, a subset of the natural waters were also tested with P. promelas that had been acclimated to the natural water for 7 d before testing. These experiments revealed no differences in toxicity between acclimated and nonacclimated P. promelas. To determine the influence of organism size, which has been previously correlated to Na(+) turnover and acute silver toxicity across multiple species, Na(+) and Cl(-) influx rates were measured in P. promelas of different sizes. Our results show that Na(+) and Cl(-) influx rates were inversely related to fish mass and positively correlated with silver sensitivity.

Toxicity of silver, zinc, copper, and nickel to the copepod Acartia tonsa exposed via a phytoplankton diet.

Toxicity tests were conducted with the marine copepod Acartia tonsa to assess the effects of dietary metal exposure. The diatom Thalassiosira pseudonana was cultured with Ag, Zn, Cu, or Ni and used as diets for adult A. tonsa over a 7-d exposure, and copepod survival and reproduction were measured throughout the exposure period. For all metals, reproduction was the most sensitive endpoint, with 20% effect concentrations (EC(20)s) corresponding to exposures of T. pseudonana to 0.64, 0.3, 1.2, and 2.4 microg/L for Ag, Zn, Cu, and Ni, respectively. The corresponding metal concentrations in the algae added to copepod test solutions (EC(20)s) were 5.44, 0.55, 22.3, and 15.3 microg/g for Ag, Zn, Cu, and Ni, respectively. None of the applied metal concentrations influenced algal growth. The results of this study have potential implications for water quality criteria considering that the estimated EC(20)s fall below the current criteria of 3, 86, 3, and 8.3 microg/L for Ag, Zn, Cu, and Ni, respectively.

Responses of hybrid striped bass to waterborne and dietary copper in freshwater and saltwater.

Mechanisms of copper toxicity and consequences of exposure vary due to uptake route and ionoregulatory status. The goal of this research was to develop a model fish system to assess the influence of different Cu exposure routes (waterborne or dietary) on bioavailability, uptake, and effects in hybrid striped bass (Morone chrysops x Morone saxatilis) acclimated to fresh- or saltwater. Initially, hybrid striped bass were exposed to dietary Cu concentrations of 571, 785, and 1013 mug Cu/g, along with a control (approximately 5 microg Cu/g), for 14 days in saltwater. Intestinal and liver Cu accumulated in a dose-dependent manner in fish exposed to increasing levels of dietary Cu. Chronic (42 days) experiments were then conducted to determine sub-lethal effects of aqueous, dietary, and combined aqueous and dietary Cu exposures to both freshwater- and saltwater-acclimated hybrid striped bass. Growth and Cu accumulation in the gill, intestine, and liver were measured. Although no significant effects were observed in fish exposed to waterborne Cu, those exposed through the diet accumulated significant liver and intestinal Cu but showed no significant change in growth. Overall, these results suggest that at the levels tested, exposure to elevated waterborne Cu did not cause significant long-term tissue Cu accumulation, whereas dietary Cu exposure caused significant liver and intestinal Cu accumulation in hybrid striped bass which was comparable in both freshwater and saltwater (15 g/L).

Changes in water quality after addition of sea salts to fresh water: implications during toxicity testing.

Sea salts (seven brands from six commercially-available sources) were dissolved in water to develop 30 g/l solutions, and selected water quality characteristics were then monitored for 96 h. One or more water quality characteristics changed significantly during the 96 h period in six of the reconstituted sea salts. Measured characteristics of sea water diluted to 30 g/l demonstrated no changes during the observation period. The sea salts from different sources also demonstrated differences in absolute concentrations of some characteristics measured. Application of the Biotic Ligand Model to predict copper toxicity to the bivalve Mytilus edulis in solutions of the salts tested yielded 96-h median-lethal concentrations that ranged from 2 to 13 microg/l. Since water quality affects toxicity of many environmental pollutants, the source of the sea salt and equilibration time should be considered when planning toxicity tests.

Effects of ligand-bound silver on Ceriodaphnia dubia.

In aqueous media, ionic silver concentrations are low and transport occurs in the colloidal phase. In the aquatic environment, silver forms 1:1 complexes with thiol-containing compounds such as cysteine and glutathione. In order to quantitatively characterize the risk associated with silver in aquatic ecosystems, the bioavailabilities and toxicities of silver cysteinate and silver glutathionate were characterized. Static renewal bioassays were conducted with Ceriodaphnia dubia to estimate chronic toxicity, using mortality and reproduction as endpoints. Silver nitrate was the most lethal compound, with a median lethal concentration (8-d LC50) of 0.32 microg Ag/L (95% confidence interval [CI] = 0.19-0.54). The 48-h LC50 for AgNO3 was 0.5 microg/L and did not change significantly through 8 d. The presence of food in the bioassay did not change the 48-h LC50 for AgNO3. Silver glutathionate (AgGSH) and silver cysteinate (AgCys) induced less mortality during the 8-d bioassay. Silver cysteinate appeared to have the greatest effect on fecundity, with a no-observable-effect concentration (NOEC) less than 0.001 microg/L. Silver nitrate and AgGSH had lowest-observable-effect concentration (LOEC) values (nominal concentrations) of 0.01 and 0.6 microg/L, respectively. Results indicate that the ligand-bound silver in these laboratory studies is bioavailable and impairs reproduction of C. dubia at low aqueous concentrations.