pH Depression Research Articles

The Aqueous and Surface Chemistry of Activation in the Flotation of Sulphide Minerals—A Review. Part II: A Surface Precipitation Model

The activation of sulphide minerals by heavy metal ions at medium to alkaline pH solutions is reviewed. The pH-dependent characteristics of adsorption are identically indicated by adsorption isotherms, surface potential and flotation responses. The mechanisms involved are explored. It is found that the initial adsorption process is controlled essentially by surface precipitation of the activator hydroxide. The real activation of flotation is obtained during the second stage—the surface conversion step. The industrial practice of activation and flotation with a highly alkaline solution highlights the proposed model and mechanisms. The mechanism underlying the intermediate pH depression of flotation of the activated mineral is discussed.

Aluminum Contamination of Groundwater: Spring Melt in Chalk River and Turkey Lakes Watersheds — Preliminary Results

Two watersheds with seasonal pH depressions in the groundwater exhibit high aluminum concentrations associated with these acidification events. The watersheds receive similar atmospheric loadings of H+ and SO42− but are covered by different surficial deposits. The aluminum is measured in four fractions by varying the pH and time conditions during analysis. The resulting classes calculated from these fractions are Class a, containing fast-reacting monomeric aluminum, predominantly inorganic Al3+ and hydroxy compounds; Class b, containing fast-reacting complex aluminum species, mainly inorganic F− complexes and simple organic complexes; Class c, containing slow-reacting amorphous and some polymeric aluminum species; and a class containing a residue of unknown aluminum species adding to the total acid-extractable aluminum. There are significant differences in the distribution of the various aluminum species between the two watersheds, both with depth and in the predominant class identified. The generally higher values measured at one watershed are consistent with the lower carbonate content of the overburden. In both locations it appears that the controlling factor is the pH of the groundwater, with all but Class c species increasing with decreasing pH. The difference between the distributions of aluminum species in groundwater and surface water is under investigation to determine the influence of groundwater-bourne aluminum on the surface water into which it flows.

Risk to Salmonids of Water Quality in the Turkey Lakes Watershed as Determined by Bioassay

Batchawana Lake, the headwater lake in the Turkey Lakes Watershed, was devoid offish. Although a number of factors could cause this fishless state, we conducted in situ studies to partially address conditions related to lake acidification. The spring pH depression did not induce significant, consistent mortality to rainbow trout (Salmo gairdneri) or lake trout (Salvelinus namaycush) caged in situ. In 1981, however, considerable mortality occurred to fish caged in Batchawana Lake during or immediately following the maximum spring pH depression. In the remaining lakes, mortality occurred later in the exposure period. Whole-body concentrations of Na+, Ca2+, and Mg2+ in rainbow trout caged (1980) in three lakes of the watershed were similar; however, K+ appeared slightly higher (but not statistically different) in fish held in the headwater lake. Static bioassays indicated that the 96-h pH-LC50 for brook trout (Salvelinus fontinalis) was 3.80–4.09, considerably lower than the lowest pH, 4.66, observed during spring. Brook trout corralled in Batchawana Lake grew slightly faster and accumulated more Pb and Hg than fish held in a downstream lake. Although pH and trace metal levels in Batchawana Lake may at times be inhospitable to fish, other factors likely contributed to the fishless condition of this lake.

Factors Affecting Survival and Cation Concentration in the Blackflies Prosimulium fuscum/mixtum and the Mayfly Leptophlebia cupida during Spring Snowmelt

We used a transplant experiment to examine the effects of short-term pH depressions in spring on whole-body concentrations of nine metal cations (Ca, Mg, Na, Zn, Pb, Al, Mn, Cd, and Fe) and survival of two species of aquatic insects collected from two habitats with year-round differences in pH. Survival of Leptophlebia cupida and Prosimulium fuscum/mixtum was close to 100% in 4- and 10-d in situ toxicity tests prior to and during snowmelt at pH levels ranging from 6.5 to 4.2. Differences in metal concentrations (Zn, Cd, and Na) existed between mayflies collected from different streams with pH values of 6.2−5.6. Both species transplanted from pH 6.2 to 4.2 streamwater had significant decreases in whole-body concentrations of Ca, Al, and Mn. Additionally, mayflies had significant losses of Mg, Fe, and Pb, while blackflies decreased in whole-body Na and Zn concentration. Percentages of the whole-body Al concentration in the adsorbed, absorbed, and gut content fractions were 3.3, 31.7, and 65%, respectively, for L. cupida and 1.6, 56.4, and 42%, respectively, for P. fuscum/mixtum. The percent adsorbed doubled in transplanted (versus control) mayflies, but the overall whole-body Al concentration decreased.

A dosing system to vary pH, salinity and temperature

Construction of a dosing system to expose small aquatic organisms to varying pH and salinity under different temperature regimes is discussed. The design allows for three controlled pH levels and two salinity levels across three temperature regimes. The system is flexible and may be adapted for other experimental paradigms including pH depression, elevation or maintenance as well as use with various dilution media or “toxicants” other than salt.

Correlation between catecholamine release and degree of acidotic stress in trout.

Exhaustive exercise in freshwater (FW) and seawater (SW) rainbow trout resulted in a marked and acute increase of plasma catecholamines. Immediately after exercise, epinephrine and norepinephrine concentrations in FW trout were 69 and 15 times the resting level, respectively; in SW trout, they were 46 and 11 times the resting value, respectively. Over the 1st h of recovery, the magnitude of the catecholamine surge in FW animals was about twice that of their SW counterparts. Correlated with this was an extracellular pH disturbance in FW trout, which was approximately twice as severe as in SW trout. Indeed, both the magnitudes and time courses of the plasma catecholamine responses were matched to those of the acid-base disturbances. Linear correlations were found to exist between the immediate depression of blood pH and the corresponding increases in plasma epinephrine and norepinephrine. We conclude that catecholamines are released into the plasma in proportion to the magnitude of the acid-base disturbance. The higher postexercise levels of plasma catecholamines in FW trout vs. SW appear to be a response to the greater acid-base disturbance in the FW animals.

Depression of Aerobic Metabolism and Intracellular pH by Hypercapnia in Land Snails,Otala Lactea

ABSTRACTThe pulmonate land snail Otala lactea undergoes simultaneous hypercapnia, hypoxia, extracellular acidosis and metabolic depression during dormancy. We tested the effects of ambient hypercapnia and hypoxia on oxygen consumption and on extracellular and intracellular pH of active (i.e. non-dormant) individuals. Active snails reduced by 50% within 1h when exposed to 65 mmHg (1 mmHg = 133·3 Pa) ambient and by 63% in 98 mmHg. These levels of CO2 are within the range that occurs naturally in the lung and blood during dormancy. of hypercapnic snails remained below that of controls for the duration of exposure (up to 9 h) and returned to control levels within 1 h when CO2 was removed. Both pHe and whole-body pHi (measured using [14C]DMO) fell with increasing haemolymph by approximately 0·71og. Critical ( -limiting) ambient of active snails was 90 mmHg in the absence of CO2 and dropped to 50 mmHg when was reduced 45% by exposure to CO2. Estimated critical at the lower typical of dormancy is well below the typical lung of dormant Otala, suggesting that in the lung does not normally limit oxygen consumption during dormancy. These results support the hypothesis that hypercapnia or resulting respiratory acidosis depresses metabolic rate during dormancy, and argue against a limitation of by hypoxia.

Airborne transport of sulphur: Impacts on chemical composition of rivers on north shore of the St. Lawrence River (Québec)

The St. Lawrence North Shore region (Quebec) is subject to acid precipitation entailing sulphate deposition (17 to 22 kg SO4 2− ha−1 yr−1) which poses a threat to sensitive aquatic ecosystems. Physicochemical surveys conducted in 1982–1983 revealed the extreme sensitivity of the region owing to weak mineralization of the waters (mean alkalinity of 55 μeq L−1 and conductivity of 17 μS cm−1). Calculation of the annual loads of S discharged from 21 rivers throughout the region shows atmospheric deposition as the principal source of sulphate. A decreasing west-east gradient in the concentration is interpreted in terms of the impact of long-range airborne transport, although certain local sources of S emission are not to be overlooked. Analysis of the seasonal variation in the sulphate load balance, conducted in a small drainage basin (40 km2), revealed that the sulphate anion plays a part in lowering the water pH in spring. The spring pH depression is apparently intensified by an additional input of sulphate stemming from the release of this element subsequent to accumulation in the drainage basin during summer and fall. Organic acids play a measurable role in the chemical equilibrium of surface waters in the region, particularly in the eastern sector where there is less S fallout. Low pH levels in this sector (5.5 to 6.0) point to some degree of organic acidification.

Band application reduces soil acidification by nitrogen fertilizers

Abstract The objectives of this study were to establish the amount of soil acidification caused by nitrogen fertilizer; and to ascertain whether banding, “nest” placement, or using nitrification inhibitors lessened the effect. Field experiments were placed at 10 sites and were conducted for 1 or 3 years. Barley was grown after annual fertilizer application, and in the fall the crop was harvested, the soil cultivated and the soil sampled. The main experiment was at 3 sites: a Gray Luvisol, a Dark Brown Solod and a Black Chernozem. Fertilizers were ammonium nitrate (A.N.), ammonium sulphate (A.S.) or urea. Soil pH (0–15 cm depth) was lowered 0.2 to 0.3 units after 3 years on the Luvisol with the annual rate of 67 kg N/ha A.N. or urea. The effect was greater with A.S. The 202 kg N/ha rate resulted in marked pH depression with incorporation of A.S. or urea on soils (average pH reduction of 0.9 and 0.5 units, respectively). Banding resulted in only half as much pH depression. In the second experiment 56 kg N/h...

Acidification of Shallow Groundwaters During the Spring Melt Period

During the spring of 1985 shallow recharge area groundwaters at depths less than one metre in the Turkey Lakes watershed were observed to undergo short term (1 to 10 days) pH and alkalinity depressions associated with both rain and snow melt events. At the same time the concentrations of K+ in the groundwater increased. Observations suggest that, if, during an individual loading event, the loading rate of Hydrogen ions (H+) exceeds the rate at which alkalinity is made available through carbonate weathering reactions, increased alumino-silicate alteration can occur. Thus alumino-silicate alteration may occur in groundwater systems with measurable carbonate alkalinity.

Nonmutagenicity of maleic acid and its sodium salts in Salmonella assays

Maleic acid ( cis -butenedioic acid) and its mono- and disodium salts are shown to be non-mutagenic in the standard Ames Salmonella/mammalian microsome assay in the absence and presence of Aroclor-1254-induced rat liver S9. This lack of activity occurred despite depression of top agar pH in accordance with the degree of protonation of this polybasic acid. These results indicate that when chemical compounds which are maleate salts show activity in this assay, the effect is attributable to the base moiety rather than maleate or pH depression per se.

Nonmutagenicity of maleic acid and its sodium salts in Salmonella assays

Maleic acid ( cis-butenedioic acid) and its mono- and disodium salts are shown to be non-mutagenic in the standard Ames Salmonella/mammalian microsome assay in the absence and presence of Aroclor-1254-induced rat liver S9. This lack of activity occurred despite depression of top agar pH in accordance with the degree of protonation of this polybasic acid. These results indicate that when chemical compounds which are maleate salts show activity in this assay, the effect is attributable to the base moiety rather than maleate or pH depression per se.

Anaerobic fluidized-bed treatment of hazardous wastes.

The anaerobic attached film process consists of a columnar reactor containing a packing medium that serves as an attachment surface for the retention of anaerobic microorganisms that metabolize the organic constituents of a waste. The wastewater is usually applied in an upflow mode in order to submerge completely the unit and maintain an anaerobic environment (21). Anaerobic reactors have been operated in both the packed-bed and the expanded-bed modes. When operated in the expanded-bed or fluidized-bed mode, effluent recycle is often practiced to fluidize the bed and thereby establish close to completely mixed-flow conditions. Although the kinetics of substrate removal are generally lower in this type of reactor than in a “once-flow-through” reactor, dilution of the incoming waste can often enhance treatment by reducing inhibition. Dilution of the concentration of degradable inhibitory compounds in the feed, and the prevention of pH depression by suppressing the rapid buildup of volatile fatty acids at the inlet sections of the reactor, are two advantages attributed to effluent recycle (4). In addition, recycle minimizes problems with bed-plugging, leads to improved flow distribution, and allows for the entrapment of small particles within the bed, thus enhancing their degradation. Fluidization also reduces the thickness of the hydrodynamic boundary layer, thus decreasing resistance to mass transport.

Evidence of Acidification Effects on Stream Insect Communities in Central Ontario Between 1937 and 1985

Aquatic insect surveys were conducted in two low-alkalinity streams in Algonquin Provincial Park, Ontario, Canada, that were first studied 48 yrs ago (1937–42). At a site where current spring pH fluctuations are small (pH 6.4–6.1), most of the same taxa that were present in 1984–85 were observed during the original surveys. However, at sites where large spring pH depressions are currently observed (pH 6.4–4.9), many mayfly and stonefly taxa that were present 48 yr ago and that are known to be intolerant of low pH (pH <5) were not recorded in 1984–85. An invasion of acid-tolerant mayfly and stonefly taxa occurred at sites with large pH depressions. Species replacements from acid-sensitive to acid-tolerant insects suggest that poorly buffered surface waters in this region have acidified sometime within the last five decades.

Acidification and anadromous fish of Atlantic estuaries

The Hudson River Foundation convened a conference to evaluate evidence pertaining to the roles played by acid deposition and stream acidification in the decline of anadromous fish populations along the Atlantic coastal plain. The stimuli for the conference were that (1) some populations of Atlantic salmon, American shad, hickory shad, alewives, blueback herring and striped bass as well as a few species resident in coastal streams (yellow perch and white perch) are in a state of severe decline along portions of the east coast of North America; (2) several of these species have declined more or less simultaneously since about 1970; and (3) severe episodic pH depressions are observed in some streams of the Chesapeake Bay system. For example, the pH of Lyons Creek decreased from 7.0 to 5.9 in 1 hr during a rain event, returning to 7.0 a day later. After discussing several possible mechanisms for these observations, the conferees agreed that a combination of factors including stream and river acidification, toxic metals and organic compounds, eutrophication and overfishing appears to be contributing to the reduction in fish stocks. The essential point resulting from the conference is that the acid deposition hypotheses for stream acidification and declines of anadromous fish populations, a potential mechanism that has received very little attention heretofore, was shown to be viable for these coastal areas. Specific recommendations for research were agreed upon by the conferees.

Acid particles and the tracheobronchial region of the respiratory system--an "irritation-signaling" model for possible health effects.

This paper explores some detailed mechanistic hypotheses for the possible action of acid particles on the tracheobronchial region of the human respiratory system. Because of the buffering capacity and volume of mucus produced per day it appears doubtful that ordinary ambient exposures to acid particles could markedly change the overall pH of tracheobronchial mucus considered as a whole. However, it is possible that individual acidic particles could contain enough acid to deliver localized irritant signals that could be the triggers for enhanced mucus secretion and cell division in sensitive portions of the bronchial tree, and thereby contribute to the processes involved in chronic bronchitis. Depending on the exact pH depression required for a signal to be perceived by the tracheobronchial epithelium, the acid content of the incoming particles per unit weight, and the effect of neutralization by ammonia in the upper respiratory tract, the minimum size of an acidic particle required to deliver a perceptible signal might range from about 0.4 to 0.7 microns for portions of the epithelium that are frequently swept by 4-micron mucus droplets. Since particle number per unit weight declines dramatically with increasing particle size, the most potent fraction of particles in terms of signals deliveredmore » per /sup +/g/m/sup 3/ is likely to be just above the minimum size that is needed to produce an effective signal. The model developed here makes predictions of the relative potency of particles of different size and acid delivery capacity that could be tested in both experimental animal systems and human epidemiological studies.« less

Life Stage and Population Variation in Resistance and Tolerance ofHyalella azteca(Amphipoda) to Low pH

Lethality experiments revealed that resistance of Hyalella azteca (Amphipoda) to low pH was directly related to size and developmental stage. Exposure of adults to water below pH 5.0 during pulses of acid snowmelt, or of juveniles to below pH 5.5 through gradual lake acidification, could result in population decline. Hyalella azteca from moderately acidic Ontario lakes (pH 5.6–5.7) survived longer at lethal pH than did amphipods from circumneutral lakes (pH 6.4–7.2) where spring pH depressions do not occur. Resistance and tolerance to low pH was neither readily lost by tolerant amphipods exposed to neutral water for 10 d nor readily gained by nontolerant amphipods exposed to sublethal low pH for a similar duration. This absence of physiological plasticity of individual H. azteca suggests that population differences in acid tolerance may result from processes of selective mortality with or without a genetic basis.

A theoretical consideration of the implications of cell clustering for the prediction of nitrification in soil

The time course of nitrate production is different in different soils; in some soils, nitrate is produced at a constant rate while in others, this rate increases with time, often exponentially. Mechanistic models, based on the Monod equations, cannot account for a constant rate of nitrification. All such mechanistic models make the implicit assumption that the nitrifying organisms are distributed uniformly as single cells throughout the soil volume, while in reality, the cells might be expected to occur in small clusters formed by repeated cell division. This paper examines the effects of allowing the ammonium oxidising cells to occur in evenly distributed clusters of cells of equal volume. One effect of clustering would be the lowering of soil pH around the cluster, caused by differences in the rates of acid production and diffusion. The effects of this pH depression were examined using a mathematical model.

Winter and Spring pH Depressions in Northern Wisconsin Lakes Caused by Increases in pCO2

Seasonal variation in pH in six clearwater northern Wisconsin lakes (mean pH 5.9–7.8; mean total alkalinity 9–830 μeq∙L−1) encompasses an annual range of 1.0–1.5 units in each lake, with lowest values characteristically occurring during the late winter and early spring. In detailed investigations of one lake, we evaluated strong acid inputs, shifts in pCO2, and changes in organic acids as possible mechanisms for pH depression. Our results indicate that seasonal pH depressions are caused largely by pCO2 increases under the ice. Despite an acidic snowpack the pH depression could not be attributed to input of acid meltwater because total alkalinity did not change in the lake. Our results emphasize the importance of using measurements other than pH in investigating the causes of acid dynamics of natural waters.

Lack of bioaccumulation of metals by Elliptio complanata (Bivalvia) during acidic snowmelt in three south-central Ontario streams.

Depression of pH and elevation of metals during spring snowmelt may be widespread. However, because of the episodic nature of these events they are very difficult to measure or even detect. Sampling of snowmelt at regular intervals of only a few days, may not be adequate to detect short-term variations in pH and metal concentrations. The objective of the present study was to determine the feasibility of using biomonitoring to detect short-term changes in concentration or bioavailability of metals (Al, Zn, Cd) during spring snowmelt. Unionid clams, (Elliptio complanata) were held in three south-central Ontario streams during the spring snowmelt period of 1982. The gill tissues accumulate metals more readily than other tissues and thus are better biomonitors of available metals than whole body concentrations of these elements. Therefore, the concentration of metals in soft tissues (gill, body, foot) were compared separately to the stream water chemistry during snowmelt.