Molecular Level Characterization of Diatom-Associated Biopolymers that Bind 234Th, ²³³PA, ²¹°Pb, and 7Be in Seawater: A Case Study With Phaeodactylum tricornutum

In order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides Th-234, Pa-233, Pb-210, and Be-7 during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (nonattached and attached exopolymeric substances), intracellular (ethylene diamine tetraacetic acid and sodium dodecyl sulfate extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, Uronic acids showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance analyses, the frustule BF were mainly composed of carboxyl-rich, aliphatic-phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom-associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom-related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean

Effects of Engineered Nanoparticles on the Assembly of Exopolymeric Substances from Phytoplankton

The unique properties of engineered nanoparticles (ENs) that make their industrial applications so attractive simultaneously raise questions regarding their environmental safety. ENs exhibit behaviors different from bulk materials with identical chemical compositions. Though the nanotoxicity of ENs has been studied intensively, their unintended environmental impacts remain largely unknown. Herein we report experimental results of EN interactions with exopolymeric substances (EPS) from three marine phytoplankton species: Amphora sp., Ankistrodesmus angustus and Phaeodactylum tricornutum. EPS are polysaccharide-rich anionic colloid polymers released by various microorganisms that can assemble into microgels, possibly by means of hydrophobic and ionic mechanisms. Polystyrene nanoparticles (23 nm) were used in our study as model ENs. The effects of ENs on EPS assembly were monitored with dynamic laser scattering (DLS). We found that ENs can induce significant acceleration in Amphora sp. EPS assembly; after 72 hours EN-EPS aggregation reached equilibrium, forming microscopic gels of ∼4–6 µm in size. In contrast, ENs only cause moderate assembly kinetic acceleration for A. angustus and P. tricornutum EPS samples. Our results indicate that the effects of ENs on EPS assembly kinetics mainly depend on the hydrophobic interactions of ENs with EPS polymers. The cycling mechanism of EPS is complex. Nonetheless, the change of EPS assembly kinetics induced by ENs can be considered as one potential disturbance to the marine carbon cycle

Unconventional Oil and Gas Development and Agricultural Land-use in the U.S.

The rapid development of unconventional oil and gas (UOG) has raised public concerns about its land use and competition with agriculture. Using county-level data from 1997 to 2018, we find that on average, UOG development negatively affected crop acreage in the contiguous U.S. However, there exists significant regional heterogeneity. The relationship is positive in Southwestern region, U-shaped in Great Plains, and negative in Appalachia. There is significant difference in crop acreage between counties with and without UOG after 2008 in the contiguous U.S. and Great Plains. The reduction in crop acreage after 2008 was highest in Great Plains

Unconventional Oil and Gas Development and Agricultural Land-Use in the U.S.

The rapid development of unconventional oil and gas (UOG) has raised public concerns about its land use and competition with agriculture. Using county-level data from 1997 to 2018, we find that on average, UOG development negatively affected crop acreage in the contiguous U.S. However, there exists significant regional heterogeneity. The relationship is positive in Southwestern region, U-shaped in Great Plains, and negative in Appalachia. There is significant difference in crop acreage between counties with and without UOG after 2008 in the contiguous U.S. and Great Plains. The reduction in crop acreage after 2008 was highest in Great Plains