Phillip R. Scheuerman

Teratogenic potential of atrazine and 2,4-D using FETAX.

The teratogenic potential of commercial formulations of atrazine (40.8%) and 2,4-D was evaluated using FETAX (frog embryo teratogenic assay--Xenopus). Because these herbicides have been detected in ground and surface water, this study was designed to determine the adverse effects in buffer and natural water for both herbicides. All treatments showed a significant concentration-response effect on exposed embryos, except for the 2,4-D natural water sample. Atrazine (solubility of the commercial formula used 70 mg/L at 20 degrees C), compared to 2,4-D (solubility = 311 mg/L at pH = 1 and 25 degrees C), had a significantly greater teratogenic effect in both the buffer (atrazine EC50 = 33 mg/L, LC50 = 100 mg/L, TI = 3.03; 2,4-D EC50 = 245 mg/L, LC50 = 254 mg/L, TI = 1.04) and natural water samples (atrazine EC50 < 8 mg/L, LC50 = 126 mg/L; 2,4-D EC50 and LC50 > 270 mg/L). The 2,4-D EC50 and LC50 values for the buffer were similar at 245 mg/L and 254 mg/L. These similar values and the teratogenic index (TI) of 1.04 suggested that 2,4-D was more embryotoxic than teratogenic to frog embryos at high concentrations. Atrazine in natural water demonstrated a significantly greater EC50 (100% abnormality at 8 mg/L, the lowest test concentration) to frog embryos than the buffer experiment (EC50 = 33 mg/L). The extrapolated lowest observable adverse effect concentration (LOAEC) for the natural water experiment was 1.1 mg/L. These results suggest that atrazine toxicity is enhanced by the synergistic or additive effects of some component of the water or atrazine was already present in the sample. In contrast to atrazine, 2,4-D was less toxic in natural water than buffer. These results suggest that both atrazine and 2,4-D pose little threat, since their embryotoxicity and teratogenicity to frog embryos occur at high concentrations approaching their maximum solubility levels in water.

Impacts of Select Organic Ligands on the Colloidal Stability, Dissolution Dynamics, and Toxicity of Silver Nanoparticles

Key understanding of potential transformations that may occur on silver nanoparticle (AgNP) surface upon interaction with naturally ubiquitous organic ligands (e.g., -SH (thoil), humic acid, or -COO (carboxylate)) is limited. Herein we investigated how dissolved organic carbon (DOC), -SH (in cysteine, a well-known Ag(+) chelating agent), and -COO (in trolox, a well-known antioxidant) could alter the colloidal stability, dissolution rate, and toxicity of citrate-functionalized AgNPs (citrate-AgNPs) against a keystone crustacean Daphnia magna. Cysteine, DOC, or trolox amendment of citrate-AgNPs differentially modified particle size, surface properties (charge, plasmonic spectra), and ion release dynamics, thereby attenuating (with cysteine or trolox) or promoting (with DOC) AgNP toxicity. Except with DOC amendment, the combined toxicity of AgNPs and released Ag under cysteine or trolox amendment was lower than of AgNO3 alone. The results of this study show that citrate-AgNP toxicity can be associated with oxidative stress, ion release, and the organism biology. Our evidence suggests that specific organic ligands available in the receiving waters can differentially surface modify AgNPs and alter their environmental persistence (changing dissolution dynamics) and subsequently the toxicity; hence, we caveat to generalize that surface modified nanoparticles upon environmental release may not be toxic to receptor organisms.

Use of the aquatic oligochaetes Lumbriculus variegatus and Tubifex tubifex for assessing the toxicity of copper and cadmium in a spiked-artificial-sediment toxicity test

A sediment toxicity test using the freshwater oligochaetes Lumbriculus variegatus and Tubifex tubifex was performed. We evaluated acute and chronic toxicity affects of copper and cadmium on reproduction in both species and the bioaccumulation of both metals by L. variegatus using artificial sediment. L. variegatus bioconcentrated copper 22‐fold and cadmium 16‐fold after a 14‐day exposure to spiked artificial sediments with 0.02% organic content. The EC50 for T. tubifex varied depending upon endpoint from 2.7 to 2.8 mg/L for cadmium and from 8.4 to 8.9 mg/L for copper. The EC50 for L. variegatus was 2.2 mg/L for cadmium and 3.9 mg/L for copper. Based on these results, L. variegatus appears to be more sensitive to metal toxicity in artificial sediments than T. tubifex. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 271–278, 1999

Factors affecting the survival and growth of bacteria introduced into lake water

The populations of Pseudomonas sp. B4, Escherichia coli, Klebsiella pneumoniae, Micrococcus flavus, and Rhizobium leguminosarum biovar phaseoli declined rapidly in lake water. The initially rapid decline of the two pseudomonads and R. phaseoli was followed by a period of slow loss of viability, but viable cells of the other species were not found after 10 days. The rapid initial phase of decline was not a result of Bdellovibrio spp., bacteriophages, or toxins in the water since Bdellovibrio spp. were not present and passage of the lake water through filters that should not have removed bacteriophages or soluble toxins led to the elimination of the rapid phase of decline. The addition of 250 μg of cycloheximide and 30 μg of nystatin per ml eliminated viable protozoa form the lake water, and the population of Pseudomonas sp. B4 did not fall and the decline of E. coli and K. pneumoniae was delayed or slowed under these conditions. Pseudomonas sp. L2 proliferated rapidly in lake water amended with glucose, phosphate, and NH4NO3, but its numbers subsequently fell abruptly; however, in water amended with cycloheximide and nystatin, which killed indigenous protozoa, the population density was higher and the fall in numbers was delayed. Of the nutrients, the chief response was to carbon, but when glucose was added, phosphorus and nitrogen stimulated growth further. Removing other bacteria by filtering the lake water before inoculation with Pseudomonas sp. L2 suggested that competition reduced the extent of response of the pseudomonad to added nutrients. We suggest that the decline in lake water of bacteria that are resistant to starvation may be a result of protozoan grazing and that the extent of growth of introduced species may be limited by the supply of available carbon and sometimes of nitrogen and phosphorus, and by predation by indigenous protozoa.

Rapid screening of aquatic toxicity of several metal-based nanoparticles using the MetPLATE™ bioassay

Current understanding of potential toxicity of engineered nanomaterials to aquatic microorganisms is limited for risk assessment and management. Here we evaluate if the MetPLATE™ test can be used as an effective and rapid screening tool to test for potential aquatic toxicity of various metal-based nanoparticles (NPs). The MetPLATE bioassay is a heavy metal sensitive test based on β-galactosidase activity in Escherichia coli. Five different types of metal-based NPs were screened for toxicity: (1) citrate coated nAg (Citrate-nanosilver), (2) polyvinylpyrrolidone coated nAg (PVP-nAg), (3) uncoated nZnO, (4) uncoated nTiO(2) and (5) 1-Octadecylamine coated CdSe Quantum Dots (CdSe QDs); and compared with their corresponding ionic salt toxicity. Citrate-nAg was further fractionated into clean Citrate-nAg, unclean Citrate-nAg and permeate using a tangential flow filtration (TFF) system to eliminate residual ions and impurities from the stock Citrate-nAg suspension and also to differentiate between ionic- versus nano-specific toxicity. Our results showed that nAg, nZnO and CdSe QDs were less toxic than their corresponding ionic salts tested, while nano- or ionic form of TiO(2) was not toxic as high as 2.5 g L(-1) to the MetPLATE™ bacteria. Although coating-dependent toxicity was noticeable between two types of Ag NPs evaluated, particle size and surface charge were not adequate to explain the observed toxicity; hence, the toxicity appeared to be material-specific. Overall, the toxicity followed the trend: CdCl(2)>AgNO(3)>PVP-nAg>unclean Citrate-nAg>clean Citrate-nAg>ZnSO(4)>nZnO>CdSe QDs>nTiO(2)/TiO(2). These results indicate that an evaluation of β-galactosidase inhibition in MetPLATE™ E. coli can be an important consideration for rapid screening of metal-based NP toxicity, and should facilitate ecological risk assessment of these emerging contaminants.

Natural water chemistry (dissolved organic carbon, pH, and hardness) modulates colloidal stability, dissolution, and antimicrobial activity of citrate functionalized silver nanoparticles

Knowledge about whether/how natural water chemistry influences the fate, dissolution, and toxicity of silver nanoparticles (AgNPs) should contribute to ecological risk assessment and informed decision making. The effects of three critical water chemistry parameters – dissolved organic carbon (DOC), pH, and hardness – were investigated on the colloidal stability, dissolution dynamics, and antimicrobial activity of citrate-functionalized AgNPs (citrate–AgNPs) against Escherichia coli. Toxicities of citrate–AgNPs and AgNO3 were also determined in the river water samples collected across three seasons (for seven months). Detectable changes in hydrodynamic diameter, surface charge, and plasmonic resonance revealed the modulating effects of the water chemistry parameters on the colloidal stability of citrate–AgNPs. Although, overall Ag release from citrate–AgNPs was low (0.33–3.62%), it increased with increasing DOC concentrations (0–20 mg L−1) but decreased with increasing pH (5–7.5) or hardness (150–280 mg L−1). Citrate–AgNP toxicity was 3–44 fold lower than of AgNO3 (Ag mass basis). Notably, higher DOC or pH conferred protection to E. coli against citrate–AgNPs or AgNO3; increasing solution hardness tended to enhance toxicity, however. Citrate–AgNPs or AgNO3 toxicity in the river water matrix revealed no seasonality. Generalized linear models developed, by parameterizing particle properties, could fairly predict empirically-derived nanotoxicity. Our results show that particle size, surface properties, ion release kinetics, and toxicity of citrate–AgNPs can be modified upon release into aquatic environments, suggesting potential implications to ecosystem health and functions.

Laboratory studies of virus survival during aerobic and anaerobic digestion of sewage sludge

The survival of three enteroviruses (polio 1, coxsackie B3 and echo 1) and a rotavirus (SA-11) was studied under laboratory conditions. The effects of temperature, dissolved oxygen, detention time, sludge source and virus type on virus inactivation were determined. Temperature was the single most important factor influencing the rate of virus inactivation. No significant differences were found for virus inactivation rates at dissolved oxygen levels between 0.9 and 5.8 mg/l. However, the inactivation rate of the viruses under aerobic conditions was found to be significantly greater than the inactivation rate under anaerobic conditions (−0.77log10/day vs −0.33 log10/day). Sludge source, detention time and virus type did not significantly influence the rate of virus inactivation.

Application of multivariate statistical methodology to model factors influencing fate and transport of fecal pollution in surface waters.

The increasing number of polluted watersheds and water bodies with total maximum daily loads (TMDLs) has resulted in increased research to find methods that effectively and universally identify fecal pollution sources. A fundamental requirement to identify such methods is understanding the microbial and chemical processes that influence fate and transport of fecal indicators from various sources to receiving streams. Using the Watauga River watershed in northeast Tennessee as a model to better understand these processes, multivariate statistical analyses were conducted on data collected from four creeks that have or are expected to have pathogen TMDLs. The application of canonical correlation and discriminant analyses revealed spatial and temporal variability in the microbial and chemical parameters influencing water quality, suggesting that these creeks differ in terms of the nature and extent of fecal pollution. The identification of creeks within a watershed that have similar sources of fecal pollution using this data analysis approach could change prioritization of best management practices selection and placement. Furthermore, this suggests that TMDL development may require multiyear and multisite data using a targeted sampling approach instead of a 30-d geometric mean in large, complex watersheds. This technique may facilitate the choice between watershed TMDLs and single segment or stream TMDLs.

Evaluation of Experimental Design Options in Environmental Nano-Science Research

Evaluation of Experimental Design Options in Environmental Nano-Science Research As an experimental research design plays a pivotal role in executing a research problem, it is imperative of a researcher to develop a suitable and sound research design. Utilizing robust statistical methods can further enhance the study power and thus allow drawing a logical conclusion. The same holds true for basic environmental science research, including research related to the effects of engineered nanomaterials in the environment.

Development of a method for the recovery of enteroviruses from aerobically digested wastewater sludges

Abstract A method was developed for virus recovery from aerobically digested sludge. This method, hereafter named the TCA-lysine procedure, consists of eluting virus from sludge with sodium trichloroacetate + lysine at pH 9.0. The eluates are further processed by two successive concentration steps. Comparison of this procedure was made to other methods. This procedure recovered 82% of added poliovirus from aerobic sludges. The range for the other procedures tested ranged from 1.1 to 66% recovery. Recovery of indigenous enteroviruses was found to be equal to or greater than other methods tested for both aerobically and anaerobically digested sludges. The TCA-lysine procedure is potentially more sensitive and cost effective than other methods tested due to the smaller concentration volume. In addition bacterial contamination of cell cultures used for viral assays was not as severe as with other procedures tested.