Determination of Distribution of Microplastics in Rappahannock River, VA, and Toxicity of Polyethylene Microplastics with Interaction of Methoxychlor on Daphnia magna

Microplastics have become an emerging contaminant of concern in freshwater systems as a component of wastewater treatment plant (WWTP) effluent, household discharge, and industrial outflows. While microplastics have been detected in aquatic environments throughout the world, our knowledge regarding microplastics in the Chesapeake Bay Basin and their impacts on aquatic invertebrates combined with chemical pollutants is limited. This study consisted of two parts: a field-based assessment examining the spatial distribution of microplastics in the Rappahannock River, VA; and a lab-based analysis examining the effects of polyethylene microplastics and the pesticide methoxychlor on the viability and mobility of Daphnia magna. Microplastics were more abundant in sediment downstream of a major WWTP outfall site and equally abundant in surface waters at both sites. We suggest that residence time plays a major role in microplastic deposition and that downstream zones are at increased risk. Methoxychlor was found to decrease mobility after 48 hours, whereas microspheres alone caused no significant debilitation. Combinations of the two toxicants resulted in increased mortality rates at moderate mixture treatments and decreased mortality at the highest mixture treatment. Thus, our results suggest that level of microplastic contamination influences the degree of contact organic pollutants may have on vulnerable species

The Presence, Distribution, and Concentration of Microplastics In the Lower Basin of the Chesapeake Bay, USA Near Wastewater Treatment Plants

The Chesapeake Bay is a large estuary located along the east coast of the United States, with numerous wastewater treatment plants (WWTP) located throughout its basin. This area supports a vast diversity of aquatic biota and provides for numerous communities throughout the eastern United States. While effluent from WWTPs has been identified as a major contributor to microplastic pollution, little research has been conducted to examine microplastic contamination in the Chesapeake Bay watershed areas surrounding these effluent streams. Microplastics are unique in that their size (\u3c5mm) enables ease of ingestion by aquatic organisms, causing adverse health effects such as energy depletion and digestive tract obstructions. MPs may also biomagnify throughout trophic levels, ultimately posing a threat to human health due to unintended consumption. In this study, the presence of microplastics in major rivers in the lower basin of the Chesapeake Bay, USA was examined. Water samples and sediment samples were collected in the Potomac and Rappahannock river upstream, midstream, and downstream of WWTP outfall sites via dip sampling and grab sampling, respectively. Sediment samples were treated with a wet peroxide oxidation using Fenton’s reagent to digest natural organic matter and sodium chloride to separate MPs from the sample. Surface water samples were filtered by vacuum filtration to separate suspended particles from water. Presence, type, and quantity of MPs were assessed using light microscopy. While this project is currently ongoing, we expect to find that MPs are more abundant in samples collected at WWTP outfall locations rather than locations upstream or downstream from those sites. The results of this study will provide novel information regarding the presence, distribution, and concentrations of MPs in water and sediment samples from several areas of the Chesapeake Bay watershed due to inputs from WWTP effluent

The Influence of Polyethylene Nanoplastics on The Toxicity of Methoxychlor on D. magna

Nanoplastics (NPs), defined as plastic particles \u3c 0.1 mm, have become an emerging concern in aquatic environments due to their multiple pathways of entry into rivers and streams. NPs may originate from the manufactured beads for personal care products as well as the from the fragmentation of larger plastic items. Due to their small size they are easily ingested by aquatic organisms, resulting in detrimental health effects such as digestive tract obstructions, feeding debilitation, and energy depletion. Due to their physiochemical attributes, NPs have also been shown to sorb and mobilize organic pollutants such as pesticides, suggesting that interactions between these two types of pollutants may result in an altered biological response compared to the effects of each individual contaminant. This study assessed the potential synergistic or antagonistic effects of polyethylene nanoparticles and the organochlorine pesticide methoxychlor on the viability and mobility of Daphnia magna. Adult D. magna were exposed to either 1) virgin 10-20µm polyethylene pellets, 2) methoxychlor, or 3) various combinations of the same pellet and methoxychlor concentrations for 48 hours or 7 days using a static exposure method. Mortality and paralysis were assessed per 24 hours of exposure. Mobility was assessed after 24 hours of exposure. To assess mobility, individuals were recorded in a light-controlled behavioral chamber for 3 minutes. Footage was analyzed using ToxTrac to quantify mobile speed, acceleration, and distance traveled. While this project is currently ongoing, we expect to find a significant difference in mobility parameters and mortality rates when exposed to the combination of polyethylene pellets and methoxychlor compared to the effects from each contaminant alone. Thus far, few studies have examined the ability of NPs to influence the toxicity of organochlorine pesticides in aquatic invertebrates. This study will help explicate the impacts of plastic pollution on aquatic biota in freshwater systems

Investigations On The Properties Of Sn-8zn-3Bi Lead-Free And Sn-37Pb Eutectic Solder Alloys [TS610. D928 2005 f rb] [Microfiche 8175].

Sifat-sifat logam pateri bebas plumbum Sn-8Zn-3Bi dan logam pateri eutektik Sn-37Pb yang bersentuhan dengan substrak kuprum telah dikaji. Properties of Sn-8Zn-3Bi lead-free solder and Sn-37Pb eutectic solder in contact with copper substrates have been investigate

GraphMP: An Efficient Semi-External-Memory Big Graph Processing System on a Single Machine

Recent studies showed that single-machine graph processing systems can be as highly competitive as cluster-based approaches on large-scale problems. While several out-of-core graph processing systems and computation models have been proposed, the high disk I/O overhead could significantly reduce performance in many practical cases. In this paper, we propose GraphMP to tackle big graph analytics on a single machine. GraphMP achieves low disk I/O overhead with three techniques. First, we design a vertex-centric sliding window (VSW) computation model to avoid reading and writing vertices on disk. Second, we propose a selective scheduling method to skip loading and processing unnecessary edge shards on disk. Third, we use a compressed edge cache mechanism to fully utilize the available memory of a machine to reduce the amount of disk accesses for edges. Extensive evaluations have shown that GraphMP could outperform state-of-the-art systems such as GraphChi, X-Stream and GridGraph by 31.6x, 54.5x and 23.1x respectively, when running popular graph applications on a billion-vertex graph

GraphH: High Performance Big Graph Analytics in Small Clusters

It is common for real-world applications to analyze big graphs using distributed graph processing systems. Popular in-memory systems require an enormous amount of resources to handle big graphs. While several out-of-core approaches have been proposed for processing big graphs on disk, the high disk I/O overhead could significantly reduce performance. In this paper, we propose GraphH to enable high-performance big graph analytics in small clusters. Specifically, we design a two-stage graph partition scheme to evenly divide the input graph into partitions, and propose a GAB (Gather-Apply-Broadcast) computation model to make each worker process a partition in memory at a time. We use an edge cache mechanism to reduce the disk I/O overhead, and design a hybrid strategy to improve the communication performance. GraphH can efficiently process big graphs in small clusters or even a single commodity server. Extensive evaluations have shown that GraphH could be up to 7.8x faster compared to popular in-memory systems, such as Pregel+ and PowerGraph when processing generic graphs, and more than 100x faster than recently proposed out-of-core systems, such as GraphD and Chaos when processing big graphs

Iodine concentration calculated by dual-energy computed tomography (DECT) as a functional parameter to evaluate thyroid metabolism in patients with hyperthyroidism

学位記番号：医博甲165