Increasing chloride in rivers of the conterminous U.S. and linkages to potential corrosivity and lead action level exceedances in drinking water.

Corrosion in water-distribution systems is a costly problem and controlling corrosion is a primary focus of efforts to reduce lead (Pb) and copper (Cu) in tap water. High chloride concentrations can increase the tendency of water to cause corrosion in distribution systems. The effects of chloride are also expressed in several indices commonly used to describe the potential corrosivity of water, the chloride-sulfate mass ratio (CSMR) and the Larson Ratio (LR). Elevated CSMR has been linked to the galvanic corrosion of Pb whereas LR is indicative of the corrosivity of water to iron and steel. Despite the known importance of chloride, CSMR, and LR to the potential corrosivity of water, monitoring of seasonal and interannual changes in these parameters is not common among water purveyors. We analyzed long-term trends (1992-2012) and the current status (2010-2015) of chloride, CSMR, and LR in order to investigate the short and long-term temporal variability in potential corrosivity of US streams and rivers. Among all sites in the trend analyses, chloride, CSMR, and LR increased slightly, with median changes of 0.9mgL-1, 0.08, and 0.01, respectively. However, urban-dominated sites had much larger increases, 46.9mgL-1, 2.50, and 0.53, respectively. Median CSMR and LR in urban streams (4.01 and 1.34, respectively) greatly exceeded thresholds found to cause corrosion in water distribution systems (0.5 and 0.3, respectively). Urbanization was strongly correlated with elevated chloride, CSMR, and LR, especially in the most snow-affected areas in the study, which are most likely to use road salt. The probability of Pb action-level exceedances (ALEs) in drinking water facilities increased along with raw surface water CSMR, indicating a statistical connection between surface water chemistry and corrosion in drinking water facilities. Optimal corrosion control will require monitoring of critical constituents reflecting the potential corrosivity in surface waters.

17 novel polymorphic microsatellite markers for the giant water bug, Abedus herberti (Belostomatidae).

The giant water bug (Abedus herberti) is a large flightless insect that is a keystone predator in aridland aquatic habitats. Extended droughts, possibly due to climate change and groundwater pumping, are causing once-perennial aquatic habitats to dry, resulting in serious conservation concern for some populations. A. herberti also exhibits exclusive male parental care, which has made it a model organism for studying mating systems evolution. Here we describe 17 novel polymorphic microsatellite loci developed for A. herberti. Number of alleles per locus ranged from 2 to 15, and average observed and expected heterozygosities were 0.579 and 0.697, respectively. These loci can successfully resolve both population genetic structure among sites separated by 3-100 km (FST = 0.08-0.21, P < 0.0001), and divergent mating strategies within local populations, making them highly useful for conservation genetics studies of this vulnerable species.

Characterization of submicrometer aqueous iron(III) colloids formed in the presence of phosphate by sedimentation field flow fractionation with multiangle laser light scattering detection.

Iron colloids play a major role in the water chemistry of natural watersheds and of engineered drinking water distribution systems. Phosphate is frequently added to distribution systems to control corrosion problems, so iron-phosphate colloids may form through reaction of iron in water pipes. In this study, sedimentation field flow fractionation (SdFFF) is coupled on-line with multiangle laser light scattering (MALLS) detection to characterize these iron colloids formed following the oxygenation of iron(II) in the presence of phosphate. The SdFFF-MALLS data were used to calculate the hydrodynamic diameter, density, and particle size distribution of these submicrometer colloids. The system was first verified with standard polystyrene beads, and the results compared well with certified values. Iron(III) colloids were formed in the presence of phosphate at a variety of pH conditions. The colloids' hydrodynamic diameters, which ranged from 218 +/- 3 (pH 7) to 208 +/- 4 nm (pH 10), did not change significantly within the 95% confidence limit. Colloid density did increase significantly from 1.12 +/- 0.01 (pH 7) to 1.36 +/- 0.02 g/mL (pH 10). Iron(III) colloids formed at pH 10 in the presence of phosphate were compared to iron(III) colloids formed without phosphate and also to iron(III) colloids formed with silicate. The iron(III) colloids formed without phosphate or silicate were 0.46 g/mL more dense than any other colloids and were >6 times more narrowly distributed than the other colloids. The data suggest competitive incorporation of respective anions into the colloid during formation.

Disturbance regimes and life-history evolution.

Disturbance regimes are ecologically important, but many of their evolutionary consequences are poorly understood. A model is developed here that combines the within- and among-season dynamics of disturbances with evolutionary life-history theory. "Disturbance regime" is defined in terms of disturbance timing, frequency, predictability, and severity. The model predicts the optimal body size and time at which organisms should abandon a disturbance-prone growth habitat by maturing and moving to a disturbance-free, nongrowth habitat. The effects of both coarse-grained (those affecting the entire population synchronously) and fine-grained disturbances (those occurring in a patch dynamics setting) are explored. Several predictions are congruent with previous theory. Infrequent or temporally unpredictable disturbances should have little effect on the evolution of life-history strategies, even though they may cause high mortality. Similar to seasonal time constraints on reproduction, disturbance regimes can synchronize metamorphosis within a population, resulting in a seasonal decline in body size at maturity. Other model predictions are novel. When disturbances cause high mortality, coarse-grained disturbances have a much stronger effect on life-history strategies than fine-grained disturbances, suggesting that population structure (relative to the scale of disturbance) plays a critical evolutionary role when disturbances are severe. When within-population variance in juvenile body size is high, two consecutive seasonal declines in body size at maturity can occur, the first associated with disturbance regime and the second associated with seasonal time constraints.

Electrophoretic mobilities of Escherichia coli O157:H7 and wild-type Escherichia coli strains.

The electrophoretic mobilities (EPMs) of a number of Escherichia coli O157:H7 and wild-type E. coli strains were measured. The effects of pH and ionic strength on the EPMs were investigated. The EPMs of E. coli O157:H7 strains differed from those of wild-type strains. As the suspension pH decreased, the EPMs of both types of strains increased.

Discriminative stimulus effects of diazepam, ketamine and their mixture: ethanol substitution patterns.

When ethanol is used as a training stimulus in drug discrimination experiments, benzodiazepines (such as diazepam) as well as non-competitive N-methyl-D-aspartate (NMDA) antagonists (such as ketamine) substitute for ethanol; in contrast, when a benzodiazepine or an NMDA antagonist is used as a training drug, ethanol does not substitute reliably. In the present experiments, we trained rats to discriminate a mixture of diazepam and ketamine, to test the hypothesis that ethanol would substitute for this drug combination. Using a two-lever choice procedure with food as a reinforcer, 22 rats were trained to discriminate a mixture of diazepam (5.6 mg/kg) and ketamine (10 mg/kg) from vehicle. When administered as a mixture, diazepam and ketamine substituted for the training mixture in a dose-dependent manner. When administered separately, diazepam or ketamine substituted for the mixture with full substitution occurring at 5.6 and 17.8 mg/kg, respectively. Ethanol almost completely substituted for the mixture at 1 g/kg. There was no cross-substitution between diazepam and ketamine in rats trained to discriminate diazepam (5.6 mg/kg, n = 10) or ketamine (10 mg/kg, n = 12) from vehicle. In addition, ethanol did not substitute for the training drug in either of these discriminations. These results suggest that the simultaneous action of GABAA agonist and NMDA antagonist mechanisms produce a greater ethanol-specific discriminative stimulus than activation of either component individually.

Tolerance to the discriminative stimulus and reinforcing effects of ketamine.

In order to examine whether tolerance develops to the discriminative stimulus and reinforcing effects of ketamine, rats were trained either to discriminate ketamine (10mg/kg) from saline or to self-administer ketamine (1.1mg/kg/injection), and then treated with chronic ketamine (32mg/kg), administered i.p. every 8 hours for 7 days. No shift in the dose-response curve for either paradigm was obtained following this chronic regimen. However, following a 2-week rest period in which animals had no exposure to ketamine, the dose-response curve was shifted two-fold to the left, indicating increased sensitivity to the drug. Reinstatement of training shifted the dose-response curve back to the right in both paradigms. These results suggest that tolerance to the discriminative stimulus and reinforcing effects of ketamine develops during training. Examination of the self-administration training data support this assumption, since inter-reinforcer time decreases, reflecting an increase in ketamine intake over training sessions.

Discriminative stimulus effects of midazolam and abecarnil in rats treated chronically with diazepam or abecarnil.

Abecarnil (ABC) is a beta-carboline that acts as an agonist at benzodiazepine (BZD) receptors. It possesses anxiolytic and anticonvulsant properties, but produces little sedation and is without muscle relaxant effects. To explain this unusual profile of activity, two hypotheses have been advanced: either 1) ABC acts as a partial agonist or 2) ABC acts as a full agonist, but only at a sub-population of BZD receptors. The present experiment used cross-tolerance profiles between BZDs and ABC to differentiate these hypotheses based upon predictions of receptor theory: tolerance produced to a full agonist should confer even greater cross-tolerance to a partial agonsit. Rats were trained in a three-choice drug discrimination procedure to detect the benzodiazepine, midazolam (MDZ, 1.0 mg/kg) from pentylenetetrazole (PTZ, 20 mg/kg) from saline. Tested acutely, MDZ and ABC substituted for MDZ with similar potencies. Following chronic treatment with the BZD-agonist diazepam (DZP; 20 mg/kg per 8 h for 7 days), both the MDZ and ABC dose-effect curves were significantly shifted to the right, and both drugs showed a comparable three-fold decrease in potency. The chronic administration of ABC (4.0 mg/kg per 8 h for 7 days) produced a different spectrum of results. No significant shift occurred in the MDZ dose-effect curve, but there was a significant seven-fold shift to the right of the ABC dose-effect curve. Throughout all test, PTZ-lever responding rarely occurred and did not account for more than 20% of lever selections for any individual test. These data support the hypothesis that ABC acts as a full agonist at a sub-population of BZD receptors, which mediate its substitution for MDZ.

Discrimination of ethanol and of diazepam: differential cross-tolerance.

These experiments tested the hypothesis that cross-tolerance between ethanol (EtOH) and diazepam would occur in a drug discrimination paradigm. One group of rats (n = 28) was trained to discriminate EtOH (1.0g/kg, i.p.) from vehicle; another group of rats (n = 10) was trained to discriminate diazepam (5.6mg/kg, i.p.) from vehicle. Subjects were trained using a two-lever choice procedure where food was delivered under a fixed-ratio 10 schedule of reinforcement. In rats trained to detect EtOH, both EtOH (0.1-1.78g/kg) and diazepam (0.32-10mg/kg) dose dependently substituted for EtOH. Chronic administration of EtOH (6.8g/kg/12h for 7 days) resulted in 3-fold tolerance to EtOH and 6-fold cross-tolerance to the ability of diazepam to substitute for EtOH; chronic administration of diazepam (20mg/kg/8h for 7 days) failed to confer cross-tolerance to EtOH nor did it produce tolerance to the ability of diazepam to substitute for EtOH. In rats trained to detect diazepam, diazepam (0.56-10mg/kg) but not EtOH (0.1-1.78g/kg) substituted for diazepam. Chronic administration of diazepam (20mg/kg/8h for 7 days) produced 3-fold tolerance to diazepam; in contrast, chronic administration of EtOH (6.8g/kg/12h for 7 days) failed to confer cross-tolerance to diazepam. The dissociation of the cross-substitution and cross-tolerance patterns between EtOH and diazepam suggests that the population of benzodiazepine receptors that mediates substitution of diazepam for EtOH differs from the population of benzodiazepine receptors that mediates substitution of diazepam for diazepam.

Conflicting evidence regarding the efficacy of ondansetron in benzodiazepine withdrawal.

These experiments tested the efficacy of the 5-hydroxytryptamine3 antagonist ondansetron (OND) in reversing various aspects of benzodiazepine withdrawal in rats. Three tests were used in which the benzodiazepine antagonist flumazenil was administered to rats receiving chronic administration of chlordiazepoxide. In one test, the elevated plus-maze, flumazenil produced a reduction in time spent in the open arms of the maze; OND completely reversed this effect of flumazenil in a dose-related fashion. However, OND failed to block the effects of the anxiogenic drug pentylenetetrazole (PTZ) in the elevated plus-maze. In a second test, rats were trained to discriminate PTZ. After chlordiazepoxide, flumazenil substituted for PTZ; OND failed to block flumazenil. In a third test, rats maintained on a chronic base line of chlordiazepoxide were trained to discriminate flumazenil from vehicle. In this discrimination, PTZ substituted for flumazenil, and pentobarbital blocked the flumazenil stimulus; OND, however, failed to block the flumazenil stimulus. In a separate set of experiments, OND also failed to reverse the suppression of responding produced in a conditioned emotional response paradigm. Thus, some data from the elevated plus-maze are consistent with the hypothesis that benzodiazepine withdrawal shares common effects with other stimuli known to be anxiogenic, and that OND blocks this aspect of withdrawal. However, all other data are inconsistent with the hypotheses that OND is anxiolytic or has efficacy in reversing benzodiazepine withdrawal. We suggest that ondansetron is likely to have minimal efficacy in humans for the treatment of sedative-hypnotic withdrawal.