Combined dynamics of mercury and terrigenous organic matter following impoundment of Churchill Falls Hydroelectric Reservoir, Labrador

Sediments from two recently (40 years) flooded lakes (Gabbro lake and Sandgirt lake) and an unflooded lake (Atikonak lake) were sampled to investigate the effects of reservoir impoundment on mercury (Hg) and terrigenous organic matter (TOM) loading in the Churchill Falls Hydroelectric complex in Labrador, Canada. Lignin biomarkers in TOM, which exclusively derive from terrestrial vegetation, were used as biomarkers for the presence and source origin of TOM—and for Hg due to their close associations—in sediments. In the two flooded Gabbro and Sandgirt lakes, we observed drastic increases in total mercury concentrations, T-[Hg], in sediments, which temporally coincided with the time of reservoir impoundment as assessed by 210Pb age dating. In the natural Atikonak lake sediments, on the other hand, T-[Hg] showed no such step-increase but gradually and slowly increased until present. T-[Hg] increases in lake sediments after flooding were also associated with a change in the nature of TOM: biomarker signatures changed to typical signatures of TOM from vegetated terrestrial landscape surrounding the lakes, and indicate a change to TOM that was much less degraded and typical of forest soil organic horizons. We conclude that T-[Hg] increase in the sediments of the two flooded reservoirs was the result of flooding of surrounding forests, whereby mainly surface organic horizons and upper soil horizons were prone to erosion and subsequent re-sedimentation in the reservoirs. The fact that T-[Hg] was still enriched 40 years after reservoir impoundment indicates prolonged response time of lake Hg and sediment loadings after reservoir impoundments

PET occupancy and competition in translational medicine and CNS drug development

Molecular imaging by single-photon emission tomography (SPECT) and positron emission tomography (PET) allows the visualization of receptor availability in a living brain. Competition from endogenous or exogenous ligands can reduce this availability. In an influential application of this principle, changes in the availability of dopamine D2/3 receptors reveal fluctuations in the interstitial concentration of dopamine. Thus benzamide ligand binding in the striatum declines after a pharmacological challenge with amphetamine, and the magnitude of this decrease is elevated in patients with schizophrenia. This paradigm has proven difficult to generalize to other neurotransmitter systems, but there is a burgeoning use of the competition paradigm to measure receptor occupancy by pharmaceuticals. Studies with antipsychotic medications established the concept of a window for therapeutic occupancy of D2/3 receptors by antipsychotic medications in the range of 60%–80%. The concept of antipsychotic atypicality is explored by PET competition studies using radioligands targeting serotonin and other receptor types. Competition studies can also quantify dose-occupancy relationships for antidepressant medications at serotonin and noradrenaline transporters in the brain. Nonsedating antihistamines show low occupancy at cerebral H1 histamine receptors relative to sedating substances like chlorpheniramine; this distinction is a matter of blood-brain barrier permeability. Recent studies consider occupancy at purinergic and nicotinic acetylcholine receptors and emphasize the pharmacodynamics of receptor occupancy after single and multiple doses.</p

Carbon sequestration in a large hydroelectric reservoir: An integrative seismic approach

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