Dissolved and suspended mercury. species in the Wabigoon River (Ontario,Canada): seasonal and regional variations

Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH₃Hg⁺) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH₃Hg⁺, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl⁻ ions. Loadings of dissolved CH₃Hg⁺ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH₃Hg⁺ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH₃Hg⁺ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl⁻. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH₃Hg⁺ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH₃Hg⁺ and Hg²⁺ ions. CH₃Hg⁺ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl₂, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH₃Hg⁺ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H₂O₂, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (> 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl⁻ ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH₃Hg⁺ levels and CH₃Hg⁺/total Hg ratios), and was to a greater degree organically bound (H₂O₂-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH₃Hg⁺. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.     

Gating and Conduction Properties of a Sodium-activated Cation Channel from Lobster Olfactory Receptor Neurons

The gating and conduction properties of a channel activated by intracellular Na⁺ were studied by recording unitary currents in inside-out patches excised from lobster olfactory receptor neurons. Channel openings to a single conductance level of 104 pS occurred in bursts. The open probability of the channel increased with increasing concentrations of Na⁺. At 210 mm Na⁺, membrane depolarization increased the open probability e-fold per 36.6 mV. The distribution of channel open times could be fit by a single exponential with a time constant of 4.09 msec at −60 mV and 90 mm Na⁺. The open time constant was not affected by the concentration of Na⁺, but was increased by membrane depolarization. At 180 mm Na⁺ and −60 mV, the distribution of channel closed times could be fit by the sum of four exponentials with time constants of 0.20, 1.46, 8.92 and 69.9 msec, respectively. The three longer time constants decreased, while the shortest time constant did not vary with the concentration of Na⁺. Membrane depolarization decreased all four closed time constants. Burst duration was unaffected by the concentration of Na⁺, but was increased by membrane depolarization. Permeability for monovalent cations relative to that of Na⁺ (P _X /P _Na ), calculated from the reversal potential, was: Li⁺ (1.11) > Na⁺ (1.0) > K⁺ (0.54) > Rb⁺ (0.36) > Cs⁺ (0.20). Extracellular divalent cations (10 mm) blocked the inward Na⁺ current at −60 mV according to the following sequence: Mn²⁺ > Ca²⁺ > Sr²⁺ > Mg²⁺ > Ba²⁺. Relative permeabilities for divalent cations (P _Y /P _Na ) were Ca²⁺ (39.0) > Mg²⁺ (34.1) > Mn²⁺ (15.5) > Ba²⁺ (13.8) > Na⁺ (1.0). Both the reversal potential and the conductance determined in divalent cation-free mixtures of Na⁺ and Cs⁺ or Li⁺ were monotonic functions of the mole fraction, suggesting that the channel is a single-ion pore that behaves as a multi-ion pore when the current is carried exclusively by divalent cations. The properties of the channel are consistent with the channel playing a role in odor activation of these primary receptor neurons. Received: 17 September 1996/Revised: 15 November 1996     

Permafrost and fire as regulators of stream chemistry in basins of the Central Siberian Plateau

Stream chemistry in permafrost regions is regulated by a variety of drivers that affect hydrologic flowpaths and watershed carbon and nutrient dynamics. Here we examine the extent to which seasonal dynamics of soil active layer thickness and wildfires regulate solute concentration in streams of the continuous permafrost region of the Central Siberian Plateau. Samples were collected from 2006 to 2012 during the frost-free season (May–September) from sixteen watersheds with fire histories ranging from 3 to 120 years. The influence of permafrost was evident through significantly higher dissolved organic carbon (DOC) concentrations in the spring, when only the organic soil horizon was accessible to runoff. As the active layer deepened through the growing season, water was routed deeper through the underlying mineral horizon where DOC underwent adsorption and concentrations decreased. In contrast, mean concentrations of major cations (Ca²⁺ > Na⁺ > Mg²⁺ > K⁺) were significantly higher in the summer, when contact with mineral horizons in the active zone provided a source of cations. Wildfire caused significantly lower concentrations of DOC in more recently burned watersheds, due to removal of a source of DOC through combustion of the organic layer. An opposite trend was observed for dissolved inorganic carbon and major cations in more recently burned watersheds. There was also indication of talik presence in three of the larger watersheds evidenced by Cl^? concentrations that were ten times higher than those of other watersheds. Because climate change affects both fire recurrence intervals as well as rates of permafrost degradation, delineating their combined effects on solute concentration allows forecasting of the evolution of biogeochemical cycles in this region in the future.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

A PRELIMINARY LIMNOLOGICAL STUDY OF BUFFELSPOORT DAM AND ITS CATCHMENT

SUMMARY

A limnological survey of the Buffelspoort Dam and its catchment between 1973 and 1975 showed that the water of the area contained extremely low concentrations of dissolved minerals and that there was no point source of nutrient supply to the dam. The anion and cation dominance in the catchment water may be summarized as HCO3 >Cl >SO₄NO₃ and Na⁺ >Mg⁺⁺ >Ca⁺⁺ >K⁺, respectively, and this water may be classified as soft bicarbonate water. The impoundment was warm monomictic and had an extensive anaerobic hypolimnion during summer stratification. Changes in water transparency were related to the seasonal fluctuation in water content and the hydrological cycle. Nutrient concentrations in the dam displayed seasonal trends which were related to stratification, hydrological events and phytoplankton activity. On the basis of its nutrient content and chlorophyll a concentrations the impoundment can be classified as mesotrophic. The further development of holiday resorts in the catchment poses a cutrophication hazard, especially if expansion results in the installation of sewage treatment plants.     

Field and Laboratory Studies on Nile Phytoplankton in Egypt. II. Phytoplankton

Variations in chlorophyll a concentration and in qualitative and quantitative counts of Nile phytoplankton were followed at Assiut from September 1980 to September 1982. Chlorophyll a concentrations usually correlated well with phytoplankton density. The total phytoplankton exhibited higher counts in spring and summer than in autumn and winter. While diatoms exhibited the highest counts, green algae contributed more genera to the phytoplankton community.     

Glucosylglycerol-phosphate synthase: target for ion-mediated regulation of osmolyte synthesis in the cyanobacterium Synechocystis sp. strain PCC 6803

The response of cyanobacteria to a changing osmotic environment includes the accumulation of organic osmolytes such as glucosylglycerol. The activation of the enzymes involved in glucosylglycerol synthesis [glucosylglycerol-phosphate synthase (GGPS) and glucosylglycerol-phosphate phosphatase (GGPP)] in Synechocystis sp. strain PCC 6803 by various salts and salt concentrations was investigated in vitro. GGPS seemed to be the target for salt-mediated regulation of glucosylglycerol synthesis in vitro. GGPS activation was dependent on the concentration of NaCl, and a sigmoidal plot was obtained. Sensitivity to NaCl was markedly enhanced by low Mg⁺² concentrations (optimal at 4 mM), but Mg²⁺ was not absolutely necessary for the Na⁺ stimulation. As in the case of NaCl, other salts (including MgCl₂) stimulated GGPS. The relative order of GGPS activation in the presence of chloride by the cations at constant ionic strength was Li⁺ > Na⁺ > K⁺, Mg²⁺ Mn²⁺. No absolute dependence on ionic strength was observed in Mg²⁺/Na⁺-exchange experiments. The degree of activation by ions at various concentrations was positively related to the increasing destabilizing properties of the cations according to the Hofmeister rule, where chaotropic cations are most efficient. Cations were responsible for activation since chaotropic anions counteracted the activating effect of cations. Received: 10 August 1998 / Accepted: 11 November 1998     

Ion Permeation and Block of P2X2 Purinoceptors: Single Channel Recordings

P2X₂ purinoceptors are cation-selective channels activated by ATP and its analogues. Using single channel measurements we studied the channel's selectivity for the alkali metal ions and organic monovalent cations NMDG⁺, Tris⁺, TMA⁺, and TEA⁺. The selectivity sequence for currents carried by alkali metal ions is: K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺, which is Eisenman sequence IV. This is different from the mobility sequence of the ions in free solution suggesting there is weak interaction between the ions and the channel interior. The relative conductance for alkali ions increases linearly in relation to the Stokes radius. The organic ions NMDG⁺, Tris⁺, TMA⁺ and TEA⁺ were virtually impermeant. The divalent ions (Mn²⁺, Mg²⁺, Ca²⁺ and Ba²⁺) induced a fast block visible as a reduction in amplitude of the unitary currents. Using a single-site binding model, the divalent ions exhibited an equilibrium affinity sequence of Mn²⁺ > Mg²⁺ > Ca²⁺ > Ba²⁺. Received: 3 May 1999/Revised: 23 August 1999     

Short communication. Selectivity of the fast activating vacuolar cation channel

The FV channel dominates the ion conductance of the vacuolar membrane at physiological Ca²⁺ concentrations. Patch-clamp measurements on whole barley (Hordeum vulgare) mesophyll vacuoles and on excised tonoplast patches showed small differences in a selectivity sequence NH4⁺ > K⁺ Rb⁺ Cs⁺ >Na⁺ >Li⁺. Less permeant cations decreased the open probability. The FV channel allows the uptake of small monovalent cations especially NH4⁺ into the vacuole.     

Physical and kinetic properties of sheep liver pyridoxine kinase

Pyridoxine kinase purified from sheep liver was found to consist of a single polypeptide chain with a molecular weight of 60,000 as determined by gel filtration, sedimentation equilibrium ultracentrifugation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoelectric pH of the enzyme was 5.1, and the pH optimum was between 5.5 and 6.0. The enzyme required divalent cations for activity. At cation concentrations of 80 μm, the enzyme activity with each cation was in the order of Zn²⁺ > Mn²⁺ > Mg²⁺. At cation concentrations of 400 μm, the enzyme activity with each cation was in the order of Mn²⁺ > Zn²⁺ > Mg²⁺. Excess free divalent cation inhibited the enzyme. Pyridoxine kinase also required monovalent cations. The enzyme activation was greatest with K⁺, then Rb⁺ and NH₄⁺, whereas the enzyme had very little activity with Na⁺, Li⁺, or Cs⁺. Na⁺ did not interfere with the activation by K⁺. The activation of the kinase by K⁺, NH₄⁺, and Rb⁺ followed Michaelis-Menten kinetics, and the apparent K_m values for the cations were 8.9, 3.7, and 5.3 mm, respectively. Increasing the potassium concentration lowered the apparent K_m value of the enzyme for pyridoxine and had little or no effect on the K_m for ZnATP^2? or the V of the kinase-catalyzed reaction.     

Cation binding to brain plasma membranes: An evaluation of the use of anionic fluorescent probes

Cation binding to brain plasma membranes has been studied using anionic sulfonate fluorescent probes. Ion affinity sequences follow the order Mg²⁺ > Ca²⁺ ? K⁺ > Cs⁺ > Na⁺ > Li⁺. The order of effectiveness, in increasing probe fluorescence, is the reverse of the affinity sequence for ions of the same charge. The affinity orders for erythrocyte membranes and dipalmitoyl lecithin are Mg²⁺ > Ca²⁺ ? Cs⁺ > K⁺ > Na⁺ > Li⁺ and Mg²⁺ > Ca²⁺ ? Li⁺ > Na⁺ > K⁺ > Cs⁺. These sequence variations are related to the differences in the nature of the ion binding sites. Heterogeneity in ion binding sites is demonstrated. Evidence is presented for the role of proteins in binding hydrophobic probes. The problem of separating specific conformational effects on ion binding from nonspecific charge neutralization effects is discussed. Pyrene excimer fluoresence rules out the possibility of extensive changes in mobility in the lipid phase on cation binding. Tetrodotoxin has been shown to inhibit Li⁺-, Na⁺-, and K⁺-induced fluorescence enancements of 1-anilino-8-naphthalene sulfonate bound to brain membranes.     

Metal cation toxicity in the alga Gracilaria domingensis as evaluated by the daily growth rates in synthetic seawater

Macroalgae of the genus Gracilaria have considerable economic importance as raw material for agar production and belong to an important group of organisms that are tolerant of high concentrations of metal. The median inhibitory concentration (IC₅₀) values obtained by measuring the ratio of fresh mass variation (i.e., daily growth rates) of the red macroalga Gracilaria domingensis during a 48-h aquatic toxicity assay are reported here. The alga was exposed to 14 different metal cations as well as the molybdate anion in synthetic seawater. The actual concentrations of these ionic species (at IC₅₀ values) and the proportion of free ions (aqueous complexes) were determined by inductively coupled plasma atomic emission spectroscopy and the Environmental Protection Agency-recommended software, MINTEQA2, respectively. Based on the free IC₅₀ values (IC₅₀ ^F), the ions were ranked in terms of toxicity: Cd²⁺???Cu²⁺???Pb²⁺???Zn²⁺???Ni²⁺?>?Co²⁺?>?La³⁺???Mn²⁺?>?Ca²⁺?~?Li⁺???MoO₄ ^2????Sr²⁺?>?Mg²⁺???K⁺?>?Na⁺. As a member of the first trophic level in the marine food chain, G. domingensis is an appropriate target organism both for the development of toxicological assays and as a bioindicator of marine degradation.     

Characteristics of glutamic acid transport by rabbit intestinal brush-border membrane vesicles. Effects of Na+-, K+-and H+-gradients

In the presence of a Na⁺-gradient (out > in), l-glutamic acid and l-and d-aspartic acids were equally well concentrated inside the vesicles, while no transport above simple diffusion levels was seen by replacement of Na⁺ by K⁺. Equilibrium uptake values were found inversely proportional to the medium osmolarity, thus demonstrating uptake into an osmotically sensitive intravesicular space. The extrapolation of these lines to infinite medium osmolarity (zero space) showed only a small binding component in acidic amino-acid transport. When the same experiment was performed at saturating substrate concentrations, linear relationships extrapolating through the origin but showing smaller slope values were recorded, thus indicating that the binding component could be more important than suspected above. However, binding to the membrane was neglected in our studies as it was absent from initial rate measurements. Na⁺-dependent uphill transport of l-glutamic acid was stimulated by K⁺ present on the intravesicular side only but maximal stimulation was recorded under conditions of an outward K⁺-gradient (in > out). Quantitative and qualitative differences in the K⁺ effect were noted between pH 6.0 and 8.0. Initial uptake rates showed pH dependency in $\text{Na}{}^{\mathrm{+}}\text{-(out > in) + K}{}^{\mathrm{+}}\text{-(in > out)}$ gradient conditions only with a physiological pH optimum between 7.0 and 7.5. It was also found that a pH-gradient (acidic outside) could stimulate both the Na⁺-gradient and the Na⁺ + K⁺-gradient-dependent transport of l-glutamic acid. However, pH- or K⁺-gradient alone were ineffective in stimulating uptake above simple diffusion level. Finally, it was found that increased rates of efflux were always observed with an acidic pH outside, whatever the conditions inside the vesicles. From these results, we propose a channel-type mechanism of l-glutamic acid transport in which Na⁺ and K⁺ effects are modulated by the surrounding pH. The model proposes a carrier with high or low affinity for Na⁺ in the protonated or unprotonated forms, respectively. We also propose that K⁺ binding occurs only to the unprotonated carrier and allows its fast recycling as compared to the free form of the carrier. Such a model would be maximally active and effective in the intestine in the in vivo physiological situations.     

Assessment of ability of endangered Caspian brown trout, <Emphasis Type="Italic">Salmo trutta caspius</Emphasis> (Salmonidae) in production of semen with desirable quality

To assay the effects of stripping frequency on semen characteristics of Caspian brown trout, Salmo trutta caspius, the chemical composition of seminal fluid, sperm production (semen volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were investigated over four times stripping during the spawning season. According to data, semen volume, sperm density, osmolality and the concentrations of Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺ and total protein gradually decreased by increasing of stripping frequency. The values of glucose and triglyceride had no significant changes over four times stripping. Also, the values of semen pH, the percentage (5 s after activation) and duration of motility were statistically stable until third stripping but a decrease was recorded for these parameters in the fourth stripping. As well as, significant positive correlations were found for sperm density vs. K⁺, Cl⁻, Na⁺, Ca²⁺, Mg²⁺, total protein, spermatocrit; the percentage of motile spermatozoa vs. Ca²⁺, Mg²⁺, K⁺, Cl⁻, Na⁺, total protein, and also the duration of motility vs. K⁺, Cl⁻, total protein and pH. In text, specific objectives of this study have been expressed.     

Influence of mound construction by red and hybrid imported fire ants on soil chemical properties and turfgrass in a sod production agroecosystem

Mound construction by imported fire ants (Solenopsis spp.) actively modify the biogeochemical and physical properties of soil; however, their influence on nutrient levels in surrounding vegetation is poorly understood. Aside from the reported persistence of elevated available P and K levels in clay-rich soils one year after mound abandonment, the relative stability of nutrient concentrations from one season to the next is largely unknown. Nutrient concentrations were concurrently analysed from ant mounds and undisturbed soils as well as plant samples collected from warm-season turfgrass in a commercial sod production agroecosystem. Initial collection of soil and turfgrass samples coincided with peak annual biomass (September 2006); the second soil sample collection occurred over twelve weeks later during turfgrass dormancy and ant brood minimum (December 2006). Total C, C/N ratios, organic matter (OM), and Zn²⁺ concentrations as well as pH of ant mound soils were significantly higher than control plot soils; these trends persisted across seasons. Turfgrass harvested from ant mound perimeters in September exhibited elevated N, P, Ca²⁺, S, Cu²⁺, Fe²⁺, and Na⁺ concentrations. Evaluation of the relative stability of soil parameters across seasons revealed a significant drop in ant nest pH from September to December 2006. Total N of mound soils was distinctively greater than control soil counterparts during September only. Soil P, K⁺, Ca²⁺, Mg²⁺ and S (all macronutrients), as well as Na⁺ concentrations from ant mound soils were substantially elevated during the late Autumn to Winter transition compared to control soil locations, whereas Fe²⁺ and Mn²⁺ levels (both micronutrients) were significantly lower in ant mound soils versus control soil environments. Continuous pedoturbation by imported fire ants as well as seasonal shifts in mound soil chemistry resulting from changes in assimilation/dissimilation among mound biota may influence the site-specific effectiveness of microfaunal pathogens (e.g., Thelohania solenopsae) or parasites (e.g., Orasema spp.) identified as classical biological control agents of non-native Solenopsis spp. Therefore, further study of the intrinsic complexities of soil ecosystem dynamics of imported fire ant mounds across several seasons is warranted. Received 10 September 2007; revised 23 April 2008; accepted 1 May 2008.     

Genetic engineering of sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.) for resistance to necrosis disease through deployment of the TSV coat protein gene

Nitrogen is a major driver of plant growth and the nitrogen source can be critical to good growth in vitro. A response surface methodology mixture-component design and a data mining algorithm were applied to nitrogen (N) nutrition for improving the micropropagation of Prunus armeniaca Lam. Data taken on shoot cultures included a subjective quality rating, shoot number, shoot length, leaf characteristics and physiological disorders. Data were analyzed using the Classification and Regression Tree data mining algorithm. The best overall shoot quality as well as leaf color were on medium with NO₃^??>?25 mM and NH₄⁺/Ca⁺ >?0.8. Improving shoot length to15 mm required 25?<?NO₃^? ≤?35 mM with NH₄⁺/Ca²⁺ ≤?2.33. The most shoots (11.6) were produced with NO₃^? >?25 mM and NH₄⁺/Ca²⁺ ≤ 0.8, but there were 5–10 shoots at other NO₃^? concentrations regardless of NH₄⁺/Ca²⁺ proportion. Leaves increased in size with higher NO₃^? concentrations (>?55 mM). Physiological disorders were also influenced by the nitrogen components. Shoot tip necrosis was rarely present with NO₃^? > 45 mM. Callus production decreased somewhat with NH₄⁺/Ca²⁺ >?2.33. Suggested concentrations for an improved medium considering all of these growth characteristics would be 25?<?NO₃^? ≤?35 mM and NH₄⁺/Ca⁺ ≤ 0.8. Validation experiments comparing WPM and three trial media showed improvements in several shoot growth parameters on medium with optimized mesos and optimized nitrogen components.     

Identifying key factors of groundwater chemistry in three diverse Landscapes of Central Mexico

In order to understand the hydrogeochemical pattern, ground (n = 23) and surface water (n = 2) samples were collected from three different landscapes (mountain, plain, valley) of Hidalgo State, Central Mexico. Physicochemical characteristics (pH, electrical conductivity, total hardness, alkalinity, total acidity, total solids, total dissolved solids, total suspended solids, CO₂; cations (Ca²⁺, Mg²⁺, Na⁺), anions (NO₃^?, Cl^?, PO₄^3?and SO₄^2?) and dissolved geochemical elements (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd and As) were analyzed. Results illustrated they are neutral to slightly alkaline due to the dissolution of carbonates. Average concentrations of anions and cations presented an order of (in mg/l): Na⁺ (273) > Ca²⁺ (206) > SO₄^2? (181) > Cl^? (163) > Mg²⁺ (115) > NO₃^? (11.07) > PO₄^3? (0.12) revealing the local geogenic and anthropogenic influences. High mean concentrations of dissolved trace metals (0.052 mg/l) in the mountains is attributed to their diverse geochemical environment of the terrain and climatic variability. Concentrations of Cr, Cu, Ni and Zn were below the permissible limits set forth by WHO and the Mexican Government. Piper trilinear diagram revealed that they are mainly of Ca-Mg-HCO₃ and Ca-Mg-SO₄ type. Sodium Absorption Ratio (SAR) indicated that nearly 96% are of excellent quality, while Magnesium Adsorption Ratio (MAR) showed that 68% of them are unsuitable for irrigation purposes.     

Nutrient couplings between on-site sewage disposal systems, groundwaters, and nearshore surface waters of the Florida Keys

We performed a one-year study to determine the effects of on-site sewage disposal systems (OSDS, septic tanks) on the nutrient relations of limestone groundwaters and nearshore surface waters of the Florida Keys. Monitor wells were installed on canal residences with OSDS and a control site in the Key Deer National Wildlife Refuge on Big Pine Key. Groundwater and surface water samples were collected monthly during 1987 and analyzed for concentrations of dissolved inorganic nitrogen (DIN = NO_f3/sup- + NO_f2/sup- + NH_4/su+), soluble reactive phosphate (SRP), temperature and salinity. Significant nutrient enrichment (up to 5000-fold) occurred in groundwaters contiguous to OSDS; DIN was enriched an average of 400-fold and SRP some 70-fold compared to control groundwaters. Ammonium was the dominant nitrogenous species and its concentration ranged from a low of 0.77 μM in control wells to 2.75 mM in OSDS-enriched groundwaters. Concentrations of nitrate plus nitrite were also highly enriched and ranged from 0.05 μM in control wells to 2.89 mM in enriched groundwaters. Relative to DIN, concentrations of SRP were low and ranged from 30 nM in control wells to 107 μM in enriched groundwaters. N : P ratios of enriched groundwaters were consistently > 100 and increased with increasing distance from the OSDS, suggesting significant, but incomplete, adsorption of SRP by subsurface flow through carbonate substrata. Nutrient concentrations of groundwaters also varied seasonally and were approximately two-fold higher during the winter (DIN = 1035 μM; SRP = 10.3 μM) compared to summer (DIN = 470 μM; SRP = 4.0 μM). In contrast, surface water nutrient concentrations were two-fold higher during the summer (DIN = 5.0 μM; SRP = 0.50 μM) compared to winter (DIN = 2.5 μM; SRP = 0.15 μM). Direct measurement of subsurface groundwater flow rate indicated that tides and increased groundwater recharge enhanced flow some two-fold and six-fold, respectively. Accordingly, the observed seasonal coupling of OSDS-derived nutrients from groundwaters to surface waters is maximum during summer because of seasonally maximum tides and increased hydraulic head during the summer wet season. The yearly average benthic flux of anthropogenic DIN into contiguous canal surface waters is 55 mmol m^-2 day^-1, a value some five-fold greater than the highest rate of benthic N-fixation measured in carbonate-rich tropical marine waters.     

Effects of chronic exposure to ammonia concentrations on brain monoamines and ATPases of Nile tilapia (Oreochromis niloticus)

The effects of chronic exposure to total ammonia nitrogen (TAN) concentrations on the brain monoamines and ATPases of Nile tilapia, Oreochromis niloticus fingerlings, were studied. The period of exposure was 70 consecutive days, and the initial weight of the fingerlings was 18 ± 2.1 g. In addition to the control, three treatment groups exposed to 2.5 (low), 5 (medium), and 10 (high) mg TAN L^?1 concentrations were tested. The unionized ammonia nitrogen (NH₃) levels calculated in mg L^?1 were 0.059, 0.185, and 0.575 in aquaria at 26 °C. The brain monoamines were serotonin (5-HT), dopamine (DA), and norepinephrine (NE), as well as their derivatives, 5-hydroxyindoleacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC). Compared with the controls, the levels of brain monoamines and Na⁺/K⁺- and Ca²⁺-ATPase activities were not significantly altered in fish exposed to low TAN concentration. However, there was a significant decrease in 5-HT, DA, and NE levels, and a significant increase in both serotonergic (5-HIAA/5-HT) and dopaminergic (DOPAC/DA) activities of fish exposed to medium TAN and high TAN concentrations. The activities of brain Na⁺/K⁺- and Ca²⁺-ATPases of fish exposed to medium TAN and high TAN concentrations significantly increased, while Mg²⁺-ATPase did not significantly change compared with that of the controls. The quantity of the detected alterations increased in fish exposed to high TAN concentration.     

Mitochondrial Ca influx and efflux rates in guinea pig cardiac mitochondria:Low and high affinity effects of cyclosporine A

Ca²⁺ plays a central role in energy supply and demand matching in cardiomyocytes by transmitting changes in excitation-contraction coupling to mitochondrial oxidative phosphorylation. Matrix Ca²⁺ is controlled primarily by the mitochondrial Ca²⁺ uniporter and the mitochondrial Na⁺/Ca²⁺ exchanger, influencing NADH production through Ca²⁺-sensitive dehydrogenases in the Krebs cycle. In addition to the well-accepted role of the Ca²⁺-triggered mitochondrial permeability transition pore in cell death, it has been proposed that the permeability transition pore might also contribute to physiological mitochondrial Ca²⁺ release. Here we selectively measure Ca²⁺ influx rate through the mitochondrial Ca²⁺ uniporter and Ca²⁺ efflux rates through Na⁺-dependent and Na⁺-independent pathways in isolated guinea pig heart mitochondria in the presence or absence of inhibitors of mitochondrial Na⁺/Ca²⁺ exchanger (CGP 37157) or the permeability transition pore (cyclosporine A). cyclosporine A suppressed the negative bioenergetic consequences (ΔΨ_m loss, Ca²⁺ release, NADH oxidation, swelling) of high extramitochondrial Ca²⁺ additions, allowing mitochondria to tolerate total mitochondrial Ca²⁺ loads of > 400 nmol/mg protein. For Ca²⁺ pulses up to 15 μM, Na⁺-independent Ca²⁺ efflux through the permeability transition pore accounted for ~ 5% of the total Ca²⁺ efflux rate compared to that mediated by the mitochondrial Na⁺/Ca²⁺ exchanger (in 5 mM Na⁺). Unexpectedly, we also observed that cyclosporine A inhibited mitochondrial Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ efflux at higher concentrations (IC₅₀ = 2 μM) than those required to inhibit the permeability transition pore, with a maximal inhibition of ~ 40% at 10 μM cyclosporine A, while having no effect on the mitochondrial Ca²⁺ uniporter. The results suggest a possible alternative mechanism by which cyclosporine A could affect mitochondrial Ca²⁺ load in cardiomyocytes, potentially explaining the paradoxical toxic effects of cyclosporine A at high concentrations. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.