Photosynthetic efficiency predicts toxic effects of metal nanomaterials in phytoplankton.

High Throughput Screening (HTS) using in vitro assessments at the subcellular level has great promise for screening new chemicals and emerging contaminants to identify high-risk candidates, but their linkage to ecological impacts has seldom been evaluated. We tested whether a battery of subcellular HTS tests could be used to accurately predict population-level effects of engineered metal nanoparticles (ENPs) on marine phytoplankton, important primary producers that support oceanic food webs. To overcome well-known difficulties of estimating ecologically meaningful toxicity parameters, we used novel Dynamic Energy Budget and Toxicodynamic (DEBtox) modeling techniques to evaluate impacts of ENPs on population growth rates. Our results show that population growth was negatively impacted by all four ENPs tested, but the HTS tests assessing many cell/physiological functions lacked predictive power at the population level. However, declining photosynthetic efficiency, a traditional physiological endpoint for photoautotrophs, was a good predictor of population level effects in phytoplankton. DEBtox techniques provided robust estimates of EC10 for population growth rates in exponentially growing batch cultures of phytoplankton, and should be widely useful for ecotoxicological testing. Adoption of HTS approaches for ecotoxicological assessment should carefully evaluate the predictive power of specific assays to minimize the risk that effects at higher levels of biological organization may go undetected.

Dietary metal toxicity to the marine sea hare, Aplysia californica.

Metal pollution from anthropogenic inputs is a concern in many marine environments. Metals accumulate in tissue and in excess cause toxicity in marine organisms. This study investigated the accumulation and effects of dietary metals in a macroinvertebrate. The green seaweed, Ulva lactuca and the red seaweed, Agardhiella subulata were each concurrently exposed to two concentrations (100 or 1000 µg/L) of five metals (Cu, Ni, Pb, Cd, and Zn). Additionally, U. lactuca was exposed to 10 µg/L of the metal mixture as well as 10 or 100 µg/L of each metal individually for 48 h. The seaweeds were then used as food for the sea hare, Aplysia californica for two to three weeks depending on the exposure concentration. Body mass of A. californica was measured weekly, and at the end of the exposure duration, metal concentrations were quantified in dissected organs (mouth, esophagus, crop, gizzard, ovotestis, heart, hepatopancreas, gill, and the carcass). Metal distribution and accumulation in the organs of A. californica varied with the metal. A. californica fed the metal-exposed diets had significantly reduced body weight by the end of the exposure periods, as compared to controls; however, differences were observed in the extent of growth reductions, dependent on exposure concentration, duration, and exposure regime (metal mixture versus individual metal-exposed diet). Metal mixture diets decreased A. californica growth more so than comparable individual metal diets, despite more metal accumulating in the individual metal diets. Additionally, Zn- and Cu-contaminated algal diets decreased control-normalized growth of A. californica significantly more than comparable Cd-, Pb-, or Ni-contaminated diets. The seaweed diets in this study contained environmentally relevant tissue metal burdens. Therefore, these results have implications for metals in marine systems.

Accumulation and effects of metal mixtures in two seaweed species.

Metal pollution, due to various anthropogenic sources, may pose a threat to marine ecosystems. Metals can be introduced into food chains via bioaccumulation in primary producers, and may potentially lead to toxic effects. Macroalgae are used as food by a wide variety of organisms, and are therefore extremely important in aquatic systems. This study investigated the accumulation and effects of metals in two macroalgae species. The green seaweed, Ulva lactuca and the red seaweed, Agardhiella subulata were each concurrently exposed to five metals (Cu, Ni, Pb, Cd, and Zn) and U. lactuca was also exposed to each metal individually for 48 h. Metal accumulation in the seaweed was measured, and various photosynthetic parameters were assessed, using imaging pulse amplitude modulated (PAM) fluorometry. Increased metal accumulation occurred in both seaweed species after 48 h exposure to metal mixtures and each metal individually. The distribution of metals in both seaweed species changed with increasing metal exposure concentrations, resulting in higher proportions of Cu and Zn in the metal-exposed groups, as compared to respective controls. Further, U. lactuca accumulated higher concentrations of metals when exposed to each metal individually rather than in metal mixtures, suggesting interactions among metals for uptake and/or bioaccumulation. Significant impairment of photosynthetic parameters in U. lactuca was observed after exposure to 100 and 1000 µg/L metal mixtures, as well as 100 µg/L of either Cd or Cu. These results demonstrate metal bioaccumulation and toxic effects in important primary producers, and may have implications for higher trophic levels.

Cellular partitioning of nanoparticulate versus dissolved metals in marine phytoplankton.

Discharges of metal oxide nanoparticles into aquatic environments are increasing with their use in society, thereby increasing exposure risk for aquatic organisms. Separating the impacts of nanoparticle from dissolved metal pollution is critical for assessing the environmental risks of the rapidly growing nanomaterial industry, especially in terms of ecosystem effects. Metal oxides negatively affect several species of marine phytoplankton, which are responsible for most marine primary production. Whether such toxicity is generally due to nanoparticles or exposure to dissolved metals liberated from particles is uncertain. The type and severity of toxicity depends in part on whether phytoplankton cells take up and accumulate primarily nanoparticles or dissolved metal ions. We compared the responses of the marine diatom, Thalassiosira weissflogii, exposed to ZnO, AgO, and CuO nanoparticles with the responses of T. weissflogii cells exposed to the dissolved metals ZnCl2, AgNO3, and CuCl2 for 7 d. Cellular metal accumulation, metal distribution, and algal population growth were measured to elucidate differences in exposure to the different forms of metal. Concentration-dependent metal accumulation and reduced population growth were observed in T. weissflogii exposed to nanometal oxides, as well as dissolved metals. Significant effects on population growth were observed at the lowest concentrations tested for all metals, with similar toxicity for both dissolved and nanoparticulate metals. Cellular metal distribution, however, markedly differed between T. weissflogii exposed to nanometal oxides versus those exposed to dissolved metals. Metal concentrations were highest in the algal cell wall when cells were exposed to metal oxide nanoparticles, whereas algae exposed to dissolved metals had higher proportions of metal in the organelle and endoplasmic reticulum fractions. These results have implications for marine plankton communities as well as higher trophic levels, since metal may be transferred from phytoplankton through food webs vis à vis grazing by zooplankton or other pathways.

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.

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.

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.