Continent Development
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Etterson M.,Continent Development | Garber K.,U.S. Environmental Protection Agency | Odenkirchen E.,U.S. Environmental Protection Agency
PLoS ONE | Year: 2017

Insecticide usage in the United States is ubiquitous in urban, suburban, and rural environments. There is accumulating evidence that insecticides adversely affect non-target wildlife species, including birds, causing mortality, reproductive impairment, and indirect effects through loss of prey base, and the type and magnitude of such effects differs by chemical class, or mode of action. In evaluating data for an insecticide registration application and for registration review, scientists at the United States Environmental Protection Agency (USEPA) assess the fate of the insecticide and the risk the insecticide poses to the environment and non-target wildlife. Current USEPA risk assessments for pesticides generally rely on endpoints from laboratory based toxicity studies focused on groups of individuals and do not directly assess population-level endpoints. In this paper, we present a mechanistic model, which allows risk assessors to estimate the effects of insecticide exposure on the survival and seasonal productivity of birds known to forage in agricultural fields during their breeding season. This model relies on individual-based toxicity data and translates effects into endpoints meaningful at the population level (i.e., magnitude of mortality and reproductive impairment). The model was created from two existing USEPA avian risk assessment models, the Terrestrial Investigation Model (TIM v.3.0) and the Markov Chain Nest Productivity model (MCnest). The integrated TIM/MCnest model was used to assess the relative risk of 12 insecticides applied via aerial spray to control corn pests on a suite of 31 avian species known to forage in cornfields in agroecosystems of the Midwest, USA. We found extensive differences in risk to birds among insecticides, with chlorpyrifos and malathion (organophosphates) generally posing the greatest risk, and bifenthrin and λ-cyhalothrin (pyrethroids) posing the least risk. Comparative sensitivity analysis across the 31 species showed that ecological trait parameters related to the timing of breeding and reproductive output per nest attempt offered the greatest explanatory power for predicting the magnitude of risk. An important advantage of TIM/MCnest is that it allows risk assessors to rationally combine both acute (lethal) and chronic (reproductive) effects into a single unified measure of risk.

Diedrich D.J.,Western Washington University | Diedrich D.J.,Colorado School of Mines | Sofield R.M.,Western Washington University | Ranville J.F.,Colorado School of Mines | And 3 more authors.
Archives of Environmental Contamination and Toxicology | Year: 2015

A series of toxicity tests were conducted to investigate the role of chronological age on zinc tolerance in juvenile brown trout (Salmo trutta). Four different incubation temperatures were used to control the maturation of the juveniles before zinc exposures. These 96-h exposures used flow-through conditions and four chronological ages of fish with weights ranging from 0.148 to 1.432 g. Time-to-death (TTD) data were collected throughout the exposure along with the final mortality. The results indicate that chronological age does not play a predictable role in zinc tolerance for juvenile brown trout. However, a relationship between zinc tolerance and fish size was observed in all chronological age populations, which prompted us to conduct additional exploratory data analysis to quantify how much of an effect size had during this stage of development. The smallest fish (0.148-0.423 g) were shown to be less sensitive than the largest fish (0.639-1.432 g) with LC50 values of 868 and 354 μg Zn/L, respectively. The Kaplan-Meier product estimation method was used to determine survival functions from the TTD data and supports the LC50 results with a greater median TTD for smaller fish than larger juvenile fish. These results indicate that fish size or a related characteristic may be a significant determinant of susceptibility and should be considered in acute zinc toxicity tests with specific attention paid to the expected exposure scenario in the field. © 2015 Springer Science+Business Media.

Hill B.H.,Continent Development | Elonen C.M.,Continent Development | Anderson L.E.,Continent Development | Lehrter J.C.,National Health and Environmental Effects Research Laboratory
Aquatic Microbial Ecology | Year: 2014

Sediment chemistry (total carbon [TC], total nitrogen [TN], total phosphorus [TP]), microbial respiration (dehydrogenase activity, DHA), and ecoenzyme activity (EEA) were measured in 4 zones of similarity in the northern Gulf of Mexico (GOM). DHA and EEA reflected the differences in C and N availability associated with proximity to the discharges of the Mississippi and Atchafalaya Rivers, and EEA represented the interface between microbial demands for, and environmental supplies of, nutrients. DHA was positively correlated with β-glucosidase (BG, r = 0.30), [β-N-acetyl glucosaminidase + L-leucine amino peptidase] ([NAG + LAP], 0.65), acid phosphatase (AP, 0.17), and aryl sulfatase (SULF, 0.42). EEAs were positively correlated with each other (0.34-0.76). DHA (0.22-0.33), [NAG + LAP] (0.46-0.64), and SULF (0.17-0.56) were positively correlated with TC, TN, and TP, while BG (0.58-0.60) and AP (0.50-0.58) were correlated only with TC and TN. Carbon use efficiency (CUE) and organic C decomposition rate (M), both based on ecoenzyme models, were positively correlated with TN and TC (0.43-0.46) and TC, TN, and TP (0.24-0.60), respectively. Modeled respiration (Rm), based on M, TC, and sediment bulk density, was correlated with sediment chemistry (0.17-0.90), and with DHA (0.50). All measured chemistry, DHA, EEA, and modeled decomposition parameters exhibited significant cruise, zone, and sediment depth effects, but few significant interaction effects. Structural equation modeling (SEM) revealed a causal relationship between sediment chemistry, EEA, and DHA, explaining 46% of the variance in DHA. As such, the relative activities of the functional classes of ecoenzymes are both a measure of nutrient availability and ecosystem metabolism that may be used to assess large-scale phenomena, such as regional impacts of anthropogenic disturbances. © Inter-Research 2014.

Ma H.,Continent Development | Ma H.,University of Wisconsin - Milwaukee | Wallis L.K.,Continent Development | Diamond S.,NanoSafe Inc. | And 3 more authors.
Environmental Pollution | Year: 2014

The present study investigated the impact of solar UV radiation on ZnO nanoparticle toxicity through photocatalytic ROS generation and photo-induced dissolution. Toxicity of ZnO nanoparticles to Daphnia magna was examined under laboratory light versus simulated solar UV radiation (SSR). Photocatalytic ROS generation and particle dissolution were measured on a time-course basis. Two toxicity mitigation assays using CaCl2 and N-acetylcysteine were performed to differentiate the relative importance of these two modes of action. Enhanced ZnO nanoparticle toxicity under SSR was in parallel with photocatalytic ROS generation and enhanced particle dissolution. Toxicity mitigation by CaCl2 to a less extent under SSR than under lab light demonstrates the role of ROS generation in ZnO toxicity. Toxicity mitigation by N-acetylcysteine under both irradiation conditions confirms the role of particle dissolution and ROS generation. These findings demonstrate the importance of considering environmental solar UV radiation when assessing ZnO nanoparticle toxicity and risk in aquatic systems. © 2014 Elsevier Ltd. All rights reserved.

Li S.,Continent Development | Erickson R.J.,Continent Development | Wallis L.K.,Continent Development | Diamond S.A.,NanoSafe Inc. | Hoff D.J.,Continent Development
Environmental Pollution | Year: 2015

As a semiconductor with wide band gap energy, TiO2 nanoparticles (nano-TiO2) are highly photoactive, and recent efforts have demonstrated phototoxicity of nano-TiO2 to aquatic organisms. However, a dosimetry model for the phototoxicity of nanomaterials that incorporates both direct UV and photo-activated chemical toxicity has not yet been developed. In this study, a set of Hyalella azteca acute toxicity bioassays at multiple light intensities and nano-TiO2 concentrations, and with multiple diel light cycles, was conducted to assess how existing phototoxicity models should be adapted to nano-TiO2. These efforts demonstrated (a) adherence to the Bunsen-Roscoe law for the reciprocity of light intensity and time, (b) no evidence of damage repair during dark periods, (c) a lack of proportionality of effects to environmental nano-TiO2 concentrations, and (d) a need to consider the joint effects of nano-TiO2 phototoxicity and direct UV toxicity. © 2015 Elsevier Ltd. All rights reserved.

Li S.,Texas Tech University | Li S.,Continent Development | Anderson T.A.,Texas Tech University | Green M.J.,Texas Tech University | And 2 more authors.
Environmental Sciences: Processes and Impacts | Year: 2013

The batch equilibrium approach was used to examine the influence of multi-walled carbon nanotubes (MWNTs) on the sorption behaviors of polyaromatic hydrocarbons (PAHs) in soil. To the knowledge of the authors, this is the first study of PAH sorption to MWNTs in real natural soil systems. The sorption behavior of three PAHs (naphthalene, fluorene, and phenanthrene) in the presence of commercially available MWNTs in two natural soils (a sandy loam and a silt loam) and Ottawa sand was evaluated. Adsorption of PAHs by MWNTs in this study was three orders of magnitude higher than that of natural soils. Sorption coefficients of PAHs (Kd and Koc) were unchanged in the presence of 2 mg g-1 MWNTs in soil (p > 0.05). A micro-mechanics approach, termed 'the rule of mixtures' was used for predicting PAH sorption behaviors in mixtures based on sorption coefficients derived from single sorbents. The equation, KT = KMα + KN(1 - α) (K, sorption coefficients, Kd or Koc), predicted sorption coefficients in a mixture based on mixture component sorption coefficients and mass fractions. Data presented in this study could be used to fill data gaps related to the environmental fate of carbon nanotubes in soil. This journal is © The Royal Society of Chemistry.

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