Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado.

The use of soluble PO4(3-) and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 x 2H2O). The tailings were treated with soluble PO4(3-) and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) family minerals. pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO4(3-) Pb2+, Zn2+, Cd2+, and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids.

Structural characterization of MAO and related aluminum complexes. 1. Solid-state (27)Al NMR with comparison to EFG tensors from ab initio molecular orbital calculations.

Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.

Solid-state 2H MAS NMR studies of TNT absorption in soil and clays.

The binding of TNT to a soil and soil components is studied with 2H MAS NMR. This NMR technique clearly shows different interactions for deuterated TNT with soil, quartz, and clays. Basically, this NMR method relies on the well-defined 2H MAS NMR characteristics of a deuterated methyl group attached to an aromatic ring. Stationary rings and rings executing 2- or 3-fold jump motions all yield different NMR spectra. The technique has good sensitivity; these studies were conducted at a TNT loading of 22 mmol/kg. For the soil sample studied, TNT showed binding similar to a TNT/K10-montmorillonite sample.

Randomized trial comparing dopamine and dobutamine in preterm infants.

The aim of this study was to compare the efficacy of two inotropic infusions in treating low BP in preterm neonates. Forty infants with median gestational age 27 weeks (range 23-33) were studied. At trial entry the infants, who all had a systolic BP < 40 mmHg despite receiving a colloid infusion, were randomized to receive either a dopamine or dobutamine infusion. The infusions were commenced at a rate of 5 micrograms/kg per min and, if necessary, this was increased over the 3 h study period to 15 micrograms/kg per min. There was no significant difference in the gestational or postnatal age or baseline BP of the 20 infants who received dopamine and those 20 who received dobutamine. Three hours after commencing the infusions, although there was no difference in the rate of inotrope infusion between the two groups, the infants who received dopamine had a significantly higher systolic BP, a median of 39 mmHg (range 30-58) compared to a median of 34 mmHg (range 21-46) in the dobutamine group, P < 0.05. In addition, 10 infants who received dopamine, but only 3 who received dobutamine, had a systolic BP > 40 mmHg (P < 0.05). We conclude that dopamine rather than dobutamine infusion is more efficacious in improving the BP of preterm neonates.

Assessment of non-invasive techniques for measuring blood pressure in preterm infants of birthweight less than or equal to 750 grams.

Non-invasive techniques for measuring systolic blood pressure (BP) were evaluated in 10 very preterm infants, median gestational age 24 weeks, who were all of birthweight < or = 5750 g. Systolic BP measurements were attempted in all infants using a Doppler technique (Ultrasonic Doppler Flow Detector) and two oscillometers (Sentry and EME). Using each technique five separate measurements were attempted over a 10-min period. The systolic BP measurements for each device were then compared to results obtained from intra-arterial catheters which had an undamped waveform. BP measurements were possible on all 10 infants using the Doppler technique, but only in seven using the EME oscillometer and four using the Sentry oscillometer. The mean difference in measurements from those obtained using the arterial catheter were 0.27 mmHg using the Doppler technique and, in those infants in whom measurements were possible, 1.34 mmHg using the Sentry oscillometer and 1.34 mmHg using the Sentry oscillometer. We conclude that the Doppler technique provides the most useful and reliable non-invasive method of assessment of systolic BP in immature infants of birthweight < or = 750 g.

Effect of chronic lung disease on blood pressure levels at follow up.

Thirteen preterm infants (median gestational age 28 weeks) who had developed neonatal chronic lung disease (CLD) and 13 gender- and gestational age-matched controls (without CLD) were prospectively followed. The infants were seen at monthly intervals for 6 months. At each attendance the infants were examined and their blood pressure (BP) measured using a noninvasive Doppler technique. No infant developed symptoms related to hypertension and there were no significant differences in their BP levels at follow up. Our results suggests significant BP elevation is uncommon following neonatal CLD.

Blood pressure levels of preterm infants in the first year of life.

Systolic blood pressure was measured in 36 infants with median gestational age of 29 weeks (range 24-35 weeks) and birth weight of 1160 g (range 642-1500 g). Measurements were made at 1, 6 and 12 weeks, and subsequently at 12-weekly intervals during the first year of life. No infant developed chronic lung disease. Systolic blood pressure increased over the first 24 weeks (p < 0.001) to a mean value of 95 mmHg, but did not change significantly over the next 24 weeks. These data provide a reference range of blood pressure levels during the first year of life for infants born at an early gestational age.

Efficacy of low-dose dopamine infusion.

Urine output following administration of a low-dose dopamine infusion was assessed in 20 very immature infants (median gestational age 27 weeks). Prior to the infusion, all infants had had a period of anuria. Urine output improved significantly during the second 24 h after commencing the infusion but, at that time period, urine output was greater than 2 ml/kg/h (designated a good response) in only 13 infants. There was no significant difference in gestational age, birth weight, period of anuria or fluid input of infants who had a good or a poor response to dopamine. Although the baseline blood pressure did not differ significantly between these two groups, the increase in blood pressure resulting from dopamine administration was significantly greater in those infants with a good response in urine output (p < 0.02). We conclude that low-dose dopamine infusion can improve urine output in very immature infants. Our results suggest that there may be inter-individual variation in the sensitivity to dopamine.

Respiratory status and diuresis following treatment with dexamethasone.

The effect of dexamethasone therapy on fluid balance, lung function and requirement for respiratory support has been assessed. Ten premature infants were studied, they had a median gestational age of 28 weeks. None of the infants had any improvement in the respiratory status for 48 h prior to commencing dexamethasone. Fluid balance, pulmonary function and requirement for respiratory support were measured 12 h prior to and for 36 h after receiving dexamethasone. There were no significant changes in fluid input over the study period, but urine output increased significantly after 12 h of dexamethasone therapy (P < 0.02). Compliance of the respiratory system only significantly improved after 36 h of dexamethasone therapy (P < 0.03), this was associated with a significant change in the inspired oxygen concentration (P < 0.05). We conclude that the improvement in respiratory status resulting from dexamethasone therapy is preceded by a diuresis.

Blood pressure levels at follow-up of infants with and without chronic lung disease.

Hypertension at follow-up is a recognized association of chronic lung disease (CLD) in premature infants. The aim of this study was to assess the timing of maximum effect of the presence of CLD on blood pressure levels and the duration of its effect. Eighteen infants with CLD and 36 without CLD were recruited into the study. Measurements of systolic blood pressure were made using a Doppler technique, when the infants attended for routine premature baby follow-up. Comparison of the two groups' blood pressure revealed the infants with CLD had significantly higher blood pressure levels at 2-3 months (p < 0.001) and 4-5 months (p < 0.05) but not at 6-7 or 8-9 months. We conclude that differences in blood pressure levels between infants with and without CLD are maximum at 2-3 months and that the association of CLD and elevated blood pressure levels is a temporary one.

Effect of gender on blood pressure levels of very low birthweight infants in the first 48 hours of life.

Systolic blood pressure was measured in 98 very low birthweight (VLBW) infants in the first 48 h of life. Measurements were made on 49 male infants, median gestational age 29 weeks and 49 female infants who were matched with the male infants for gestational age. Blood pressure was measured either from an indwelling arterial line or non-invasively using a Doppler technique; measurements were made on all infants on day 1 and day 2. In both male and female infants on day 1 and day 2, blood pressure levels correlated significantly with gestational age (P < 0.01). On day 1, but not on day 2, the blood pressure of the male infants was significantly lower than the female infants. We conclude it is important to use gender appropriate regression equations for blood pressure in VLBW infants in the first 24 hours of life.

Neonatal blood pressure levels of preterm infants who did and did not develop chronic lung disease.

The aim of this study was to assess if, in the neonatal period, there were differences in the blood pressure (BP) level of infants who did and did not develop chronic lung disease. If such differences were demonstrated to exist, we also hoped to determine influencing factors. Forty infants, consecutively admitted to our unit and who remained there throughout the neonatal period were studied. Twenty infants, median gestational age 29 weeks (range 27-32), did not develop CLD (non-CLD group) and 20 infants, median gestational age 26 weeks (range 24-32), developed CLD. Systolic BP was assessed using a non-invasive Doppler technique on day one and subsequently at weekly intervals. After day one and throughout the neonatal period BP levels, corrected for birthweight, were higher in the CLD group compared to the non-CLD group, by a mean of 5 mmHg. There was no significant difference between the numbers of infants in each group receiving theophylline or pancuronium. Significantly more infants in the CLD group had an umbilical catheter inserted and their catheters remained in situ significantly longer, a median of 8 days compared to a median of one day in the non-CLD group. We conclude that even in the neonatal period infants who develop CLD may have a modest elevation of BP, this is associated with prolonged umbilical arterial catheterisation. Our results, however, suggest that significant hypertension in infants who develop CLD, occurs after the neonatal period.

Randomised controlled trial of colloid infusions in hypotensive preterm infants.

Colloid infusions are often given to treat hypotension in preterm infants. The aim of this work was to assess whether it was the amount of protein or the volume of the colloid infused which accounted for the observed increase in blood pressure. Sixty preterm infants were randomised (20 in each group) to receive 5 ml/kg 20% albumin, 15 ml/kg fresh frozen plasma, or 15 ml/kg 4.5% albumin. All infusions were given at a rate of 5 ml/kg/hour in addition to maintenance fluids. The infants were randomised when hypotensive (systolic blood pressure less than 40 mm Hg for two hours). There was no significant difference in the blood pressure of the three groups before or one hour after beginning the infusion. The mean increase in blood pressure one hour after completing the infusion, however, was significantly lower in infants receiving 20% albumin: 9% compared with 17% in the group receiving 4.5% albumin, and 19% in the group receiving fresh frozen plasma. It is concluded that the volume infused rather than albumin load is important in producing a sustained increase in blood pressure.

Effect of dexamethasone on blood pressure--relationship to postnatal age.

The relationship of the change in blood pressure levels of very preterm infants treated with dexamethasone to postnatal age was investigated. Sixteen infants, median gestational age 26 weeks (range 23-33) (early treatment group), and 15 infants, median gestational age 26 weeks (range 24-32) (late treatment group) were recruited. Dexamethasone was administered at a median postnatal age of 17 days (range 3-26) and 50 days (range 29-112), respectively. The systolic blood pressure at the start of treatment and the maximum systolic blood pressure achieved during therapy were both significantly lower (P less than 0.01) in the early rather than the late treatment group. The change in blood pressure, however, that is, from the pre-treatment level to the maximum systolic blood pressure achieved during therapy, was similar in the two groups (median 38 mmHg, range 23-59 early treatment group and median 34 mmHg, range 16-66 late treatment group). We conclude that, even in the first 4 weeks of life, dexamethasone can cause a marked elevation of systolic blood pressure. As a consequence, regardless of the postnatal age at which dexamethasone is administered, blood pressure levels must be measured regularly.

Dexamethasone and hypertension in preterm infants.

The magnitude and duration of the effect of dexamethasone on systolic blood pressure has been examined in 13 very preterm infants (median gestational age 25 weeks). All had chronic lung disease (CLD). To exclude any effect of CLD on blood pressure each infant acted as his or her own control. Systolic blood pressure increased in all infants (P less than 0.01) and remained elevated for at least 48h following cessation of therapy. The median maximum increase in blood pressure was 24 mmHg (range 13-49 mmHg) and occurred on day 4 (median, range 2-10) of treatment. One infant developed hypertensive encephalopathy. These results demonstrate the need to monitor infants with CLD throughout steroid therapy and preferably for some days after it has ceased.

Non-invasive blood pressure monitoring in preterm infants receiving intensive care.

It is essential to have regular, accurate blood pressure (BP) monitoring of sick preterm infants. Invasive direct arterial BP measurements are often recommended, but it was our clinical experience that such measurements may not be possible in all infants. We therefore assessed the proportion of infants receiving neonatal intensive care in whom reliable arterial BP measurements could be made, the accuracy of a non-invasive method (Doppler technique) and established a reference range of BP results related to postnatal age using this non-invasive technique. Arterial catheters were established in 44 infants (study population) of the 45 in whom access was attempted. Median gestational age was 27 weeks and birth weight 949 g. Over the 1st week, however, arterial catheters had to be removed because of complications or improving respiratory status. From those catheters that remained in situ, accurate measurements were not always possible because of damping; by day 7 only 22 catheters remained in situ and 14% of the arterial waveforms were damped. Doppler systolic BP measurements correlated well with the accurate (non-damped) arterial results (r = 0.96, P less than 0.01). Systolic blood pressure was measured on all 44 infants daily for the 1st week using the Doppler technique and increased linearly with increasing postnatal age (r = 0.92, P less than 0.01) from a mean of 41.7 mmHg on day 1 to 49.3 on day 7. We conclude that Doppler non-invasive BP monitoring is a useful method for regular monitoring of sick preterm neonates as it can be applied accurately, unlike direct arterial monitoring, to all patients.

Salbutamol infusion to treat neonatal hyperkalaemia.

Salbutamol infusion, 4 micrograms/kg in 5 ml of water infused for 20 minutes, was given to treat hyperkalaemia (potassium level > 6.0 mmol/l) in 10 critically ill preterm infants (median gestational age 26 weeks). Seven infants had acute renal failure, two had persistent metabolic acidosis without renal failure and the remaining infant had a combination of acute renal failure and persistent metabolic acidosis. No infant developed a tachycardia or became hyperglycaemic in response to the infusion. Seven of the 10 infants ultimately died but this was at a mean of 9 days following the infusion and as a consequence of complications due to their extreme prematurity or major congenital abnormality. In response to the infusion the potassium level fell in 7 infants with acute renal failure by a median of 1.1 mmol/l (range 0.7-1.8) at one hour but in the three infants with a persistent metabolic acidosis, the potassium level continued to rise. We conclude that salbutamol infusion achieves, without side-effects, at least a temporary reduction in hyperkalaemia in preterm infants with renal failure, but not metabolic acidosis. Its effect is of sufficient duration to allow ample time for definitive therapy to be instituted and thus may be a useful alternative for infants in whom the possible hypoglycaemic side-effects of glucose and insulin should be avoided.