Stabilization of carbon through co-addition of water treatment residuals with anaerobic digested sludge in a coarse textured soil.

Coarse textured soils have low potential to store carbon (C) due to lack of mineral oxides and have low clay content to protect C from biodegradation and leaching. This study evaluated the potential of stabilizing C by adding metal oxyhydroxide-rich water treatment residuals (WTRs) to an aeolian pure sand (<5% clay) topsoil amended with anaerobic digestate (AD) sludge. The AD sludge was applied at 5% (w/w) with aluminum based WTR (Al-WTR) and iron based WTR (Fe-WTR) co-applied at 1:1 and 2:1 WTR:AD (w/w) ratios and incubated at room temperature for 132 days. The cumulative mineralized C was normalized to the total organic C of the treatments. Co-addition with Al-WTR showed to be more effective in stabilizing C through decreased cumulative mineralized C by 48% and 57% in 1Al-WTR:1AD and 2Al-WTR:1AD, respectively, compared to AD sludge sole amendment. Co-application with Al-WTR also decreased permanganate oxidizable C by 37% and dissolved organic C by 51%. Co-application with Fe-WTR did not decrease the concentration of these labile C pools to the same extent, possibly due to the selective use of Fe-WTRs to treat organic-rich raw water. This makes it less effective in stabilizing C in a pure sand relative to Al-WTR due to chemical instability of the Fe-organic complexes. The Al-WTR provides a promising co-amendment to increase C sequestration in pure sands when co-applied with biosolids. The co-amendment approach will not only facilitate C sequestration but also contributes to waste management, aligning to the objectives of a circular economy.

Improving crop growing conditions with water treatment residual and compost co-amendments: Soil-water dynamics.

Land application of water treatment residual (WTR) in combination with phosphate-rich organic wastes, like compost or sewage sludge, in nutrient-poor soils was previously shown to promote crop growth. This WTR diversion from landfill to agriculture supports local and international mandates for waste circularity. Although soil-water dynamics-like saturated hydraulic conductivity, water retention, and hydrophobicity-are well-defined for compost and somewhat defined for WTR (except for hydrophobicity), the impacts of co-amending sandy soils with both are not well-defined. In laboratory analyses, co-amendment had an intermediate effect between individual amendments on the hydrophobic sandy soils, increasing water retention by 27% (WTR and compost both increased water retention), decreasing hydrophobicity by increasing hydraulic conductivity twofold (WTR and compost both decreased hydrophobicity), and having no effect on saturated hydraulic conductivity (decreased by WTR and increased by compost). With two positive effects and one "no effect" on soil-water dynamics in laboratory trials, the co-amendment was expected to buffer both crop water use efficiency (WUE) and nutrient availability under drought stress, for Swiss chard (Beta vulgaris L. var. cicla), co-investigated in a multifactorial pot trial. Soil nutrients, particularly phosphate, were shown more critical than soil-water dynamics to improve crop WUE. Thus, co-amended soils have significantly higher crop biomass and WUE than sandy soils. Phosphate-rich organic co-amendment is necessary for crop nutrient sufficiency and thus drought resilience in sandy soils amended with WTR. Thus, pairing wastes to soils for optimum fertility is a critical consideration in waste land application for both biomass and drought resilience.

Dissolved Mn(III) in water treatment works: Prevalence and significance.

Dissolved Mn(III) has been identified at all stages throughout a Water Treatment Works (WTW) receiving inflow from a peaty upland catchment in NE England. Ninety percent of the influent total manganese into the WTW is particulate Mn, in the form of Mn oxide (>0.2 µm). Approximately 9% (mean value, n = 22, range of 0-100%) of the dissolved (<0.2 µm) influent Mn is present as dissolved Mn(III). Mn(III) concentrations are highest (mean of 49% of total dissolved Mn; n = 26, range of 17-89%) within the WTW where water comes into contact with the organic-rich sludges which are produced as waste products in the WTW. These Mn(III)-containing wastewaters are recirculated to the head of the works and constitute a large input of Mn(III) into the WTW. This is the first report of Mn(III) being identified in a WTW. The ability of Mn(III) to act as both an oxidant and a reductant is of interest to the water industry. Understanding the formation and removal of Mn(III) within may help reduce Mn oxide deposits in pipe networks. Further understanding how the ratio of Mn(III) to Mn(II) can be used to optimise dissolved Mn removal would save the water industry significant money in reducing discoloration 'events' at the customers' tap.

The oxidation of acid azo dye AY 36 by a manganese oxide containing mine waste.

The oxidative breakdown of acid azo dye acid yellow 36 (AY 36) by a Mn oxide containing mine tailings is demonstrated. The oxidation reaction is pH dependent with the rate of decolorization increasing with decreasing pH. The oxidation reaction mechanism is initiated at the amino moiety and proceeds via successive, one electron transfers from the dye to the Mn oxide minerals. The reaction pathway involves the formation of a number of colorless intermediate products, some of which hydrolyze in a Mn oxide-independent step. Decolorization of the dye is rapid and is observed before the cleavage of the azo-bond, which is a slower process. The terminal oxidation products were observed to be p-benzoquinone and 3-hydroxybenzenesulfonate. The reaction order of the initial decolorization was determined to be pseudo fractional order with respect to pH and pseudo first order with respect to dye concentration and Mn tailings' surface area.

Oxidative decolorization of acid azo dyes by a Mn oxide containing waste.

A Mn oxide containing mine tailings, generated in the Kalahari Mn fields, has been shown to oxidatively breakdown acid azo dyes acid orange (AO) 7, acid red 88, acid red 151 and acid yellow 36 but not acid yellow 9. The total reducible Mn content of the tailings is 33%, of which 3% is hydroquinone extractable and thus easily reducible. The net oxidation state of the Mn within the tailings is 3+. Decolorization of AO 7 by the Mn tailings increases with decreasing pH. The decolorization mechanism is initiated on the hydroxyl group of AO 7 and proceeds via successive electron transfers from the dye molecule to the oxide surface resulting in the asymmetric cleavage of the azo bond. The reaction products have been identified as 1,2-naphthoquinone, 4-hydroxybenzenesulfonate, and coupling products involving 1,2-naphthoquinone and benzenesulfonate radicals. The AO 7: Mn(III) reaction stoichiometry has been tentatively calculated to be 1:3. The reaction shows longevity with 95% decolorization still observed after 60 days of dye replenishment. Further breakdown of 1,2-naphthoquinone and 4-hydroxybenzenesulfonate was not observed, thus these compounds are considered to be the terminal reaction products of the AO 7- Mn tailings reaction.

The M1P1 loop of TASK3 K2P channels apposes the selectivity filter and influences channel function.

Channels of the two-pore domain potassium (K2P) family contain two pore domains rather than one and an unusually long pre-pore extracellular linker called the M1P1 loop. The TASK (TASK1, TASK3, and TASK5) subfamily of K2P channels is regulated by a number of different pharmacological and physiological mediators. At pH 7.4 TASK3 channels are selectively blocked by zinc in a manner that is both pH(o)- and [K](o)(-)dependent. Mutation of both the Glu-70 residue in the M1P1 loop and the His-98 residue in the pore region abolished block, suggesting the two residues may contribute to a zinc binding site. Mutation of one Glu-70 residue and one His-98 residue to cysteine in TASK3 fixed concatamer channels gave currents that were enhanced by dithiothreitol and then potently blocked by cadmium, suggesting that spontaneous disulfide bridges could be formed between these two residues. Swapping the M1P1 loops of TASK1 and TASK3 channels showed that the M1P1 loop is also involved in channel regulation by pH. Therefore, the TASK3 M1P1 loop lies close to the pore, regulating TASK3 channel activity.

Zinc and copper: pharmacological probes and endogenous modulators of neuronal excitability.

As well as being key structural components of many proteins, increasing evidence suggests that zinc and copper ions function as signaling molecules in the nervous system and are released from the synaptic terminals of certain neurons. In this review, we consider the actions of these two ions on proteins that regulate neuronal excitability. In addition to the established actions of zinc, and to a lesser degree copper, on excitatory and inhibitory ligand-gated ion channels, we show that both ions have a number of actions on selected members of the voltage-gated-like ion channel superfamily. For example, zinc is a much more effective blocker of one subtype of tetrodotoxin (TTX)-insensitive sodium (Na+) channel (NaV1.5) than other Na+ channels, whereas a certain T-type calcium (Ca2+) channel subunit (CaV3.2) is particularly sensitive to zinc. For potassium (K+) channels, zinc can have profound effects on the gating of certain KV channels whereas zinc and copper have distinct actions on closely related members of the 2 pore domain potassium channel (K2P) channel family. In addition to direct actions on these proteins, zinc is able to permeate a number of membrane proteins such as (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors, Ca2+ channels and some transient receptor potential (trp) channels. There are a number of important physiological and pathophysiological consequences of these many actions of zinc and copper on membrane proteins, in terms of regulation of neuronal excitability and neurotoxicity. Furthermore, the concentration of free zinc and copper either in the synaptic cleft or neuronal cytoplasm may contribute to the etiology of certain disease states such as Alzheimer's disease (AD) and epilepsy.

Selective block of the human 2-P domain potassium channel, TASK-3, and the native leak potassium current, IKSO, by zinc.

Background potassium channels control the resting membrane potential of neurones and regulate their excitability. Two-pore-domain potassium (2-PK) channels have been shown to underlie a number of such neuronal background currents. Currents through human TASK-1, TASK-2 and TASK-3 channels expressed in Xenopus oocytes were inhibited by extracellular acidification. For TASK-3, mutation of histidine 98 to aspartate or alanine considerably reduced this effect of pH. Zinc was found to be a selective blocker of TASK-3 with virtually no effect on TASK-1 or TASK-2. Zinc had an IC(50) of 19.8 microM for TASK-3, at +80 mV, with little voltage dependence associated with this inhibition. TASK-3 H98A had a much reduced sensitivity to zinc suggesting this site is important for zinc block. Surprisingly, TASK-1 also has histidine in position 98 but is insensitive to zinc block. TASK-3 and TASK-1 differ at position 70 with glutamate for TASK-3 and lysine for TASK-1. TASK-3 E70K also had a much reduced sensitivity to zinc while the corresponding reverse mutation in TASK-1, K70E, induced zinc sensitivity. A TASK-3-TASK-1 concatamer channel was comparatively zinc insensitive. For TASK-3, it is concluded that positions E70 and H98 are both critical for zinc block. The native cerebellar granule neurone (CGN) leak current, IK(SO), is sensitive to block by zinc, with current reduced to 0.58 of control values in the presence of 100 microM zinc. This suggests that TASK-3 channels underlie a major component of IK(SO). It has recently been suggested that zinc is released from inhibitory synapses onto CGNs. Therefore it is possible that inhibition of IK(SO) in cerebellar granule cells by synaptically released zinc may have important physiological consequences.

Molecular basis of slow activation of the human ether-a-go-go related gene potassium channel.

The human ether-á-go-go related gene (HERG) encodes the pore forming alpha-subunit of the rapid delayed rectifier K(+) channel which is central to the repolarization phase of the cardiac action potential. HERG K(+) channels have unusual kinetics characterized by slow activation and deactivation, yet rapid inactivation. The fourth transmembrane domain (S4) of HERG, like other voltage-gated K(+) channels, contains multiple positive charges and is the voltage sensor for activation. In this study, we mutated each of the positively charged residues in this region to glutamine (Q), expressed the mutant and wild-type (WT) channels in Xenopus laevis oocytes and studied them using two-electrode voltage clamp methods. K525Q channels activated at more hyperpolarized potentials than WT, whereas all the other mutant channels activated at more depolarized potentials. All mutants except for R531Q also had a reduction in apparent gating charge associated with activation. Mutation of K525 to cysteine (C) resulted in a less dramatic phenotype than K525Q. The addition of the positively charged MTSET to K525C altered the phenotype to one more similar to K525Q than to WT. Therefore it is not charge per se, but the specific lysine side chain at position 525, that is crucial for stabilizing the closed state. When rates of activation and deactivation for WT and mutant channels were compared at equivalent total (chemical + electrostatic) driving forces, K525Q and R528Q accelerated activation but had no effect on deactivation, R531Q slowed activation and deactivation, R534Q accelerated activation but slowed deactivation and R537Q accelerated deactivation but had no effect on activation. The main conclusions we can draw from these data are that in WT channels K525 stabilizes the closed state, R531 stabilizes the open state and R534 participates in interactions that stabilize pre-open closed states.

Structure of the HERG K+ channel S5P extracellular linker: role of an amphipathic alpha-helix in C-type inactivation.

The HERG K+ channel has very unusual kinetic behavior that includes slow activation but rapid inactivation. These features are critical for normal cardiac repolarization as well as in preventing lethal ventricular arrhythmias. Mutagenesis studies have shown that the extracellular peptide linker joining the fifth transmembrane domain to the pore helix is critical for rapid inactivation of the HERG K+ channel. This peptide linker is also considerably longer in HERG K+ channels, 40 amino acids, than in most other voltage-gated K+ channels. In this study we show that a synthetic 42-residue peptide corresponding to this linker region of the HERG K+ channel does not have defined structural elements in aqueous solution; however, it displays two well defined helical regions when in the presence of SDS micelles. The helices correspond to Trp585-Ile593 and Gly604-Tyr611 of the channel. The Trp585-Ile593 helix has distinct hydrophilic and hydrophobic surfaces. The Gly604-Tyr611 helix corresponds to an N-terminal extension of the pore helix. Electrophysiological studies of HERG currents following application of exogenous S5P peptides show that the amphipathic helix in the S5P linker interacts with the pore region of the channel in a voltage-dependent manner.

What are the roles of the many different types of potassium channel expressed in cerebellar granule cells?

Potassium (K) channels have a key role in the regulation of neuronal excitability. Over a hundred different subunits encoding distinct K channel subtypes have been identified so far. A major challenge is to relate these many different channel subunits to the functional K currents observed in native neurons. In this review, we have concentrated on cerebellar granule neurons (CGNs). We have considered each of the three principal super families of K channels in turn, namely, the six transmembrane domain, voltage-gated super family, the two transmembrane domain, inward-rectifier super family and the four transmembrane domain, leak channel super family. For each super family, we have identified the subunits that are expressed in CGNs and related the properties of these expressed channel subunits to the functional currents seen in electrophysiological recordings from these neurons. In some cases, there are strong molecular candidates for proteins underlying observed currents. In other cases the correlation is less clear. We show that at least 26 potassium channel alpha subunits are moderately or strongly expressed in CGNs. Nevertheless, a good empirical model of CGN function has been obtained with just six distinct K conductances. The transient KA current in CGNs, seems due to expression of Kv4.2 channels or Kv4.2/4.3 heteromers, while the KCa current is due to expression of large-conductance slo channels. The G-protein activated KIR current is probably due to heteromeric expression of KIR3.1 and KIR3.2. Perhaps KIR2.2 subunits underlie the KIR current when it is constitutively active. The leak conductance can be attributed to TASK-1 and or TASK-3 channels. With less certainty, the IK-slow current may be due to expression of one or more members of the KCNQ or EAG family. Lastly, the delayed-rectifier Kv current has as many as six different potential contributors from the extensive Kv family of alpha subunits. Since many of these subunits are highly regulated by neurotransmitters, physiological regulators and, often, auxiliary subunits, the resulting electrical properties of CGNs may be highly dynamic and subject to constant fine-tuning.

Cloning and functional expression of a human orthologue of rat vanilloid receptor-1.

Capsaicin, resiniferatoxin, protons or heat have been shown to activate an ion channel, termed the rat vanilloid receptor-1 (rVR1), originally isolated by expression cloning for a capsaicin sensitive phenotype. Here we describe the cloning of a human vanilloid receptor-1 (hVR1) cDNA containing a 2517 bp open reading frame that encodes a protein with 92% homology to the rat vanilloid receptor-1. Oocytes or mammalian cells expressing this cDNA respond to capsaicin, pH and temperature by generating inward membrane currents. Mammalian cells transfected with human VR1 respond to capsaicin with an increase in intracellular calcium. The human VR1 has a chromosomal location of 17p13 and is expressed in human dorsal root ganglia and also at low levels throughout a wide range of CNS and peripheral tissues. Together the sequence homology, similar expression profile and functional properties confirm that the cloned cDNA represents the human orthologue of rat VR1.