Acid Neutralizing Capacity Research Articles

Acid Neutralizing Capacity of Selected Antacid Suspensions Available in the Ghanaian Market

Antacids are substances commonly used by patients to obtain fast symptomatic relief from dyspepsia. They are weak bases which neutralize excess gastric acid and subsequently raise the pH of the gastric contents. The potency of the antacids depends mainly on their acid neutralization capacity (ANC) and this can vary from one brand to another. Several dosage forms of antacids are available for use by patients. However, In Ghana, suspensions are the commonest dosage form of antacids which is preferred by patients.
 The objective of this study was to determine the acid neutralizing capacity of six (6) randomly selected brands of antacid suspensions on the Ghanaian market using potentiometric acid-base titration. The samples were coded A-F to avoid any bias in the study. All the sampled brands had more than one year to expiry as indicated on their label.
 Brand D had the highest ANC of 29.70 mEq/dose whiles brand A had the lowest ANC of 11.25 mEq/dose. From the results obtained, it can be inferred that acid neutralization can be more effective and rapidly achieved with liquid antacids containing a high amount of magnesium hydroxide and aluminium Hydroxide. Hence, for acute symptomatic relief from dyspepsia, antacids containing a higher concentration of magnesium hydroxide and aluminium hydroxide would be most beneficial to patients.

Stabilization Study of a Contaminated Soil with Metal(loid)s Adding Different Low-Grade MgO Degrees

Low-grade magnesium oxide (LG-MgO) was proposed as ordinary Portland cement (OPC) or lime substitute (CaO) for metal(loid)s remediation in contaminated soils. Some metal(loid)s precipitate at pH ≈ 9 in insoluble hydroxide form thus avoiding their leaching. LG-MgO avoids the re-dissolution of certain metal(loid)s at 9.0 < pH < 11.0 (pH-dependents), whose solubility depends on the pH. A highly contaminated soil with heavy metal(loid)s was stabilized using different LG-MgO by-products sources as stabilizing agents. Two of the three studied LG-MgOs were selected for the stabilization, by mixing 5, 10, and 15 wt.%. The effect of using LG-MgO not only depends on the size of the particles, but also on those impurities that are present in the LG-MgO samples. Particle size distribution, X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis, citric acid test, specific surface, bulk density, acid neutralization capacity, batch leaching tests (BLTs), and percolation column tests (PCTs) were techniques used to deeply characterize the different LG-MgO and the contaminated and remediated soils. The remediation’s results efficacy indicated that when the medium pH was between 9.0 and 11.0, the concentration of pH-dependent metal(loid)s decreases significantly. Although around 15 wt.% of a stabilizing agent was appropriate for the soil remediation to ensure an alkali reservoir that maintains optimal stabilization conditions for a long period, 5 wt.% of LG-MgO was enough to remedy the contaminated soil. When evaluating a polluted and decontaminated soil, both BLTs and PCTs should be complementary procedures.

Effects of volcanic parent materials on the acid buffering capacity of forest soils on Yakushima Island, Japan

ABSTRACT Soil acidification is a natural pedogenetic process in forest ecosystems, but is accelerated by acidic deposition. Soils on Yakushima Island, in southwestern Japan, are derived from granitic bedrock and volcanic parent materials influenced by eolian dust inputs. Acid deposition and low acid-neutralizing capacity (ANC) of granite-derived soils are hypothesized to be the cause of acidic stream water that has been widely observed on Yakushima. It remains unclear, however, whether ANCs are also limited in volcanic soils, which contain weatherable minerals and have high buffering capacities. To compare acidification rates between granite-derived soils and volcanic soils, we estimated changes in ANCs between granite and volcanic parent materials and the resulting soils at a pedogenetic timescale, using the mass balance of titanium. After 7300 years of soil development following the eruption of the Kikai caldera, decreased ANCs and total base reserves were observed in both granite-derived and volcanic soils, compared to their respective parent materials. No difference in soil ANC was observed between granite and volcanic parent materials. Different cations contribute to acid neutralization in soils: decreasing ANC results primarily from the loss of Al in granite-derived soils, while acidity is neutralized by the loss of base cations from volcanic soils. In granite-derived soils, resistance to weathering and K retention in 2:1 type silicate clays limit the loss of bases while increasing the accumulation of exchangeable Al. In volcanic soil profiles, base leaching and the sorption of organic acids onto short-range order minerals can neutralize acidity, although erosion and admixing of granite or eolian dust-derived materials lead to a reduction of ANC in surface soil horizons.

Formulation, Development and Evaluation of Chewable Bi-layered Tablets for Treating Gastro Esophageal Reflux Disease

The purpose of this research work was to formulate raft-forming chewable bilayer tablets of sodium alginate using a raft-forming agent along with gas-generating agents. Tablets were prepared by wet granulation and evaluated for raft strength, acid neutralization capacity, weight variation, % drug content, thickness, hardness, friability and in vitro drug release. Various raft-forming agents were used in preliminary screening. The amount of sodium alginate, amount of calcium carbonate and amount sodium bicarbonate were selected as variables. Raft strength, acid neutralization capacity and drug release at 30 min were selected as responses.Tablets containing sodium alginate were having maximum raft strength as compared with other raft-forming agents. Acid neutralization capacity and in vitro drug release of all factorial batches were found to be satisfactory. Prepared tablets were found to be pharmaceutically equivalent to the marketed product. It was concluded that raft-forming chewable bilayer tablets prepared using an optimum amount of sodium alginate, calcium carbonate and sodium bicarbonate could be an efficient dosage form in the treatment of gastro oesophageal reflux diseases.
 Keywords: Chewable bilayer tablet, Sodium alginate, Raft forming agent, Acid Neutralizing capacity

Precipitation of secondary phases of iron and its role in controlling the mobility of potentially toxic elements in soils in a semiarid river basin in Northwest Mexico

Soils have the ability to retain potentially toxic elements (PTEs) through different chemical processes that promote low mobility of these elements, such as the precipitation of secondary phases of Fe, which facilitate the adsorption/co-precipitation of PTEs. The main objective of this study was to evaluate the mobility of PTEs present in an acid solution in two soils with different concentrations of calcite, understanding the role of secondary iron phases in the retention of these elements. To evaluate this phenomenon, intact soil columns of two different types of soils from the Sonora River in Northwest Mexico were exposed to an acid solution with high concentration of dissolved PTEs (mainly Fe, Al, and Cu). The Tinajas soil was free of carbonates while the Bacanuchi soil had more carbonate content than the Tinajas soil. Secondary precipitates corresponding to secondary phases of iron (mainly ferrihydrite and jarosite) were identified by X-ray diffraction. Using scanning electron microscopy, the PTEs retained in the soils were identified. The presence of calcite favored the neutral pH values in the collected leachates in the Bacanuchi soil; consequently, the mobility of the PTEs present in the acid solution was nullified. Furthermore, this process facilitated the retention of the toxic elements in the Bacanuchi soil. The retention of PTEs was 100% in the Bacanuchi soil where the natural acid-neutralizing capacity in this soil was associated with calcite. The formation of secondary phases of Fe, among them ferrihydrite, jarosite, and schwertmannite, mainly in Bacanuchi soil, promoted the retention of Al, As, Cd, Cu, Fe, Mn, and Pb (elements analyzed in this work). Results of this work can provide key insights to improve cleanup and conservation strategies in mining sites.

Phytochemical Screening and Antiulcer Activity, of Ficus thonningii (Moraceae) Aqueous Fruits Extract in Wistar Rats

Introduction: The World Health Organization (WHO) has estimated that about 80% of the world’s population rely mostly on traditional medicine. Peptic ulcer disease (PUD) which results from an imbalance between stomach acid-pepsin and mucosal defense barriers is a chronic disease affecting up to 10% of the world’s population and represents 33% of gastroenterology consultations in Cameroon. The people in low medium incomecountries depend mostly on medicinal plants for primary healthcare since they can be accessed quickly and are affordable. Such plant is Ficus thonningii Blume, which is found abundantly in Africa and also in Cameroon. The objective of this study was to phytochemically screened the aqueous fruits extract of Ficus thonningii (AEFFt), and investigate their antiulcer activity.
 Methods: The aqueous fruits extract was phytochemically screened following standard qualitative methods. Four in vitro tests to characterize antacid properties were carried out. Ulcers were induced using an ethanol and hydrochloric acid (HCl/EtOH) solution. Ulcer preventive (anti-ulcer) activity was investigated in 6 different treatment groups: 2 conventional drugs (Maalox 100 mg/kg, Omeprazole 20 mg/kg), three doses of AEFFt at (125 mg/kg, 250 mg/kg, & 500 mg/Kg), and a vehicle treatment group (administered only the ulcerogenic agent). Histological analysis of the stomachs was carried out.
 Results: The phytochemical screening of the aqueous extract of fruits of F. thonningii showed the presence of flavonoids, mucilages, saponins, gallic tannins, betacyanins, and total polyphenols. Following the in vitro tests, we obtained a value of 7.4mEq for acid neutralization capacity (ANC) for the extract, and a pH of 4.2 for the extract following FDA test. For the in vivo tests, the aqueous extract of fruits of F. thonningii (AEFFt) showed a dose-dependent increase ulcer-preventive (gastroprotective) activity with the three treatment aqueous extracts doses.
 Conclusion: The study showed that, the aqueous extract of fruits of Ficus thonningii showed a dose-dependent ulcer-preventive activity that could be accounted for by the presence of bioactive phytochemicals like polyphenols (flavonoids, tannins).

Disruptions and re-establishment of the calcium-bicarbonate equilibrium in freshwaters

During recent decades, increasing anthropogenic activities have affected natural ionic composition, including the strongest and most common relationship between ionic concentrations in the majority of natural global freshwaters, i.e., the Ca2+-ANC (acid neutralizing capacity) equilibrium. Using long-term monitoring data and MAGIC modelling, we evaluated effects of major present environmental stressors (synthetic fertilizers, liming, acidic deposition, forest disturbances, and climate change) on the Ca2+-ANC equilibrium. We evaluated the effects for three different types of terrestrial ecosystems, a circumneutral lowland agricultural catchment, two acid sensitive mountain forest catchments differing in forest health, and one acid sensitive alpine catchment. All catchments are in a region with the world-largest changes in fertilizing rates and acidic deposition in the 20th century, with increasing impacts until the late 1980s, and their subsequent abrupt, dramatic decreases. These strong changes resulted in a substantial disruption, followed by continuing re-establishment of the Ca2+-ANC relationship in all study waters. The shape of the disruption and the following re-establishment of its new value were dependent on the intensity, duration, and combination of stressors, as well as on catchment characteristics (bedrock composition, soil amount and composition, vegetation status, and hydrology). We conclude that a new equilibrium may deviate from its natural value due to the (1) legacy of fertilizing, acidic deposition and liming, affecting the soil Ca2+ pools, (2) forest disturbances and management practices, and (3) climate change.

Recovery of phosphorus from municipal wastewater treatment sludge through bioleaching using Acidithiobacillus thiooxidans

Conventional wastewater treatment plants remove phosphorus, which is captured in sewage sludge. Increasing attention is paid to suitable process pathways that allow recovery and recycling of phosphorus. One of the processes under investigation is acid leaching and recovery of phosphorus, but this requires considerable chemical additives, which could be avoided by stimulating acidification via microbiological processes. This study investigated phosphorus leaching from sewage sludge by biogenic sulfuric acid, using Acidithiobacillus thiooxidans. Sulfur supplementation and solid to liquid ratio were varied to examine how these factors affected phosphorus leaching yield. Chemical leaching by sulfuric acid from sewage sludge and thermally-treated sludge was conducted to compare with bioleaching from sewage sludge. Sewage sludge samples were collected from wastewater treatment plants in Ghent, Belgium, and Delft, The Netherlands. Both bioleaching and chemical leaching were conducted at laboratory scale using shake flask technique, and highest phosphorus leaching yield and time was determined using one-way ANOVA statistical tests. Biogenic sulfuric acid produced by A. thiooxidans extracted phosphorus from both sludge samples. The highest phosphorus leaching yield observed was 48 ± 0% for 17 days from Ghent samples and 57 ± 4% for 27 days from Delft samples with 5.0% (w/v) sulfur supplementation and 1.0% (w/v) solid to liquid ratio. Chemical leaching took shorter than bioleaching, but the leaching yield was lower, i.e. 41 ± 1% for 4 h from Ghent samples, 44 ± 1% for 1 h from Delft samples, 48 ± 1% for 1 h from thermally-treated Ghent samples and 51 ± 2% for 4 h from thermally-treated Delft samples. During phosphorus bioleaching, pH increase was observed during the early stage which hampered the activity of A. thiooxidans and therefore increased phosphorus leaching time. This study suggests that creating conditions for A. thiooxidans to overcome acid neutralizing capacity of sewage sludge is needed to extract phosphorus effectively.

Chewable Antacid Tablets: Are Disintegration Tests Relevant?

A recently published FDA guidance on chewable tablets has addressed the quality attributes of this class of dosage forms. This study evaluated disintegration as a quality attribute for a number of commercially available chewable antacid tablets. Additionally, acid-neutralizing-capacity values were evaluated. A number of the products exhibited prolonged disintegration times-which were far longer than those of conventional immediate-release tablets. The mean disintegration times ranged from 6 to more than 60min in distilled water and from 9 to over 60min in 0.1N HCl. The products with longer disintegration times had higher breaking force and tensile strength values. Despite the range in disintegration times, all products met the criteria for acid-neutralizing capacity. These results indicate a need for patients to be aware of the need to thoroughly chew antacid tablets upon administration. Given these considerations, disintegration testing would be a useful quality control test in evaluating these dosage forms as the implicit assumption by the manufacturer that patients will chew the product sufficiently may not be met in every case.

In-vitro antiulcer activities of petal extract of Crocus sativus var. cashmerianus

Medicinal plants have been known for millennia as a rich source of traditional therapeutic agents for the prevention of diseases and ailments. The aim of the present study was performed to evaluate the antiulcer activities of hydro-alcoholic extracts of petals of Crocus sativus var. Cashmerianus by in-vitro methods viz. acid neutralizing capacity and H+/K+ - ATPase inhibition activity. In acid neutralizing capacity method, the petals extract significantly reduced acidity to 6.10 at a concentration of 1000 mg/ml as compared to 11.90 with standard 500 mg/ml of Aluminium hydroxide + Magnesium hydroxide combination. However, H+/K+ - ATPase inhibition activity method, petals extract showed maximum percentage inhibition of 70.31 % at the concentration 400µg/ml as compared to 73.82 % with a similar dose of standard Omeprazole. The IC 50 value of petals extract of C. sativus var. cashmerianus is shown 100 µg/ml in comparison with standard omeprazole of 82.5 µg/ml. The study reveals that the petals extract of C. sativus var. cashmerianus may contain compounds possessing acid neutralize and enzyme inhibition activities, thus it can be used as an alternative medicine for gastrointestinal disorders.

Effects of fertilization and water addition on soil acid neutralizing capacity in an old-field grassland

Increasing nitrogen (N) deposition results in soil acidification in grasslands. Acid buffering capacity of soil is a critical index evaluating soil acidification, the response of which to N input is regulated by precipitation and concentration of other limiting elements. To explore the responses of soil acidification to N, phosphorus (P), and water inputs, we conducted a 13-year field experiment in an old-field grassland and calculated the acid buffering capacity (ABC) and acid neutralizing capacity (ANC) at the reference of pH=5.0 (ANCpH5.0) and 4.0 (ANCpH4.0), using quadratic curve fitting model. The results showed that, without water addition, single N addition or combined with P addition significantly decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas single P addition had no significant effect on soil pH, ANCpH5.0 or ANCpH4.0. With water addition, the addition of N or combined with P decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas P addition decreased soil pH, increased ANCpH4.0, without effect on ANCpH5.0. In contrast with treatments without water addition, water addition had positive effects on soil pH, ANCpH5.0 and ANCpH4.0. For soils with different initial soil pH values, it was better to select ANC rather than ABC as an index to evaluate soil anti-acidification capacity.

Evaluation of acid neutralizing and buffering capacities of selected antacids in Ghana

This study has evaluated the acid neutralizing and buffering capacities (BC) of nine selected antacid brands (“L1-L9”) in Ghana. The active acid neutralizing ingredients were recorded and the preliminary antacid test (PAT) determined with 0.5 N HCl after 10 min. The acid neutralizing capacity (ANC) was evaluated with 1 N HCl by neutralizing the excess with 0.5 N NaOH after 15 min stirring. Buffering capacity (BC) was estimated with 0.1 N HCl and titrated with 0.1 N NaOH at 5 min interval up to 50 min. All determination were at 37±3 °C using a pH meter. All brands had as part of their active ingredients dried aluminum hydroxide and magnesium hydroxide, with 67% containing simethicone as antifoam. The PAT declared all brands to be antacids with pH range of 4.38 ± 0.21–6.43 ± 0.06. The ANC of all brands were in the range 13.16 ± 0.55–20.70 ± 0.18 mEq/g with “L4” and “L9” having the lowest and highest values respectively. “L9” further demonstrated a considerably higher BC up to 40 min whiles “L6” had the least BC up to 15 min. The ability of an antacid to have a high ANC and to resist significant changes in pH (longer BC) is crucial in assuring quality and efficacy of the brand.

Safety and efficacy study of Ulsant tablet in patients with hyperacidity (Amlapitta

Hyperacidity (Amlapitta) is one of the most common disorder. It is observed by excess production of gastric acid in stomach. It is generally imbalance between offensive parameters like gastric acid and defensive factors like mucin bicarbonate secretions. Over the counter products aim at neutralizing gastric acid rather than the root cause. Ayurvedic preparations has an solution to amlapitta. It not only neutralizes acid secreted but also improves defensive properties of stomach. Once such combination is Ulsant tablets. Acid neutralizing capacity and buffering capacity was conducted in vitro. The aim of the present study was to find out safety and efficacy of Ulsant tablet. In present study total 35 patients were taken. Patients were advised with Ulsant tablet 2 tab twice a day for 45 days. Results shown significant positive results with respect to acid neutralizing capacity, buffering capacity and clinical symptoms. Keywords: Hyperacidity, Ulcer, Ayurveda, Ulsant, Natural.

Selecting the best stabilization/solidification method for the treatment of oil-contaminated soils using simple and applied best-worst multi-criteria decision-making method

Oil-contaminated soils resulted from drilling activities can cause significant damages to the environment, especially for living organisms. Treatment and management of these soils are the necessity for environmental protection. The present study investigates the field study of seven oil-contaminated soils treated by different stabilization/solidification (S/S) methods, and the selection of the best treated site and treatment method. In this study, first, the ratios of consumed binders to the contaminated soils (w/w) and the treatment times for each unit of treated soils were evaluated. The ratios of consumed binders to the contaminated soils were between 6 and 10% and the treatment times for each unit of treated soils were between 4.1 and 18.5 min/m3. Physicochemical characteristics of treated soils were also determined. Although S/S methods didn’t change the water content of treated soils, they increased the porosity of soils. Unexpectedly, the cement-based S/S methods didn’t increase the pH of the treated soils. The highest and the lowest leaching of petroleum hydrocarbons was belonging to S/S using diatomaceous earth (DE) and the combination of Portland cement, sodium silicate and DE (CS-DE), respectively. The best acid neutralization capacity was obtained for soils treated using the combination of Portland cement and sodium silicate (CS). Based on the best-worst multi-criteria decision-making method (BWM-MCDM), the soils treated using CS-DE was select as the best. The BWM-MCDM can be used as an effective tool for the selection of the best alternative in all areas of environmental decontamination.

Screening of waste materials as adjuvants for drying sewage sludge based on environmental, technical and economic criteria

Thermal drying allows the reduction of the moisture contained in the sewage sludge (SS) formed in wastewater treatment plants (WWTP) to less than 80%. The management of the dried SS is easier and may have good properties as a soil amendment (carrying organic matter and N, P nutrients). This work aims to select the most appropriate drying adjuvant for application in full-scale and produce a material adequate for agriculture soil applications by applying two multi-criteria decision making (MCDM) methods, the MOORA and TOPSIS. The criteria weights were determined using the CRITIC method. Within the circular economy framework, four industrial wastes were considered as drying adjuvants: weathered coal fly ash (CFA), green liquor dregs (GLD), eggshell (ES), and rice husk (RH). Then, small cylinders of SS were extruded with 0.15 g adjuvant g−1 SSwb and dried at a constant temperature of 70 and 130 °C. Eleven criteria were grouped into three categories (environmental, technical, and economic). Both methods MOORA and TOPSIS showed that the use of GLD at 130 °C is the best option. Moreover, ES at 130 °C and GLD at 70 °C are also good options, and the choice should consider the need for removal of pathogenic contamination. The worst alternatives were CFA and RH at 70 °C according to both MCDM methods. The most influential criteria for decision making were the removal efficiency of pathogenic microorganisms, acid neutralization capacity (ANC) and germination index (GI).

Spatiotemporal variability, source apportionment, and acid-neutralizing capacity of atmospheric wet base-cation deposition in China

Atmospheric wet deposition of base cations (BCs) plays a significant role in providing plant nutrients and buffering acidification. However, the temporal dynamic of wet BC deposition in China during the past two decades remain unclear. Here, we used long-term monitoring and literature data since 2000 to assess the temporal dynamics (seasonal and inter-annual variation), spatial patterns, main influencing factors, source apportionment, and capacity to neutralize the acidity of wet BC depositions at site, regional, and national scales. The results showed that total wet deposition of BCs was, on average, 2.12 keq ha−1 yr−1, where Ca2+ accounted for 65.57% of the total deposition, followed by Na+ (13.21%), Mg2+ (13.68%), and K+ (7.55%). Qinghai-Tibet had significantly lower BC deposition fluxes than northern, southern, and central China, as well as Inner Mongolia. Exchangeable BCs in soil, PM10 in the atmosphere, energy consumption, and cement production are significantly related to wet BC deposition, which account for 79.17% of the variation in the spatial deposition of BC. Influenced by the strategies to control acid rain and particulate matter in China, interannual variations showed a stabilization trend after a continuous decline from 2000 to 2017, which can be explained by inter-annual changes in PM10, energy consumption and cement production. Statistical methods confirmed that 45.95% of wet BC deposition was derived from crustal contributions, 27.78% from sea salt sources, and 26.27% from anthropogenic sources. Furthermore, we found that wet deposition of BCs neutralized 84.85% of the acidity due to NO3− and SO42− depositions. Under the emissions reduction strategy, there has been a decrease in the deposition of BC. However, SO42− and NO3− depositions decreased faster than BC deposition, which buffered a higher proportion of acidic depositions. Our findings contribute to an improved understanding of wet BC deposition in China, an evaluation of their capacity to neutralize acidity, and important parameters for acidification models.

Kraft pulp mill dregs and grits as permeable reactive barrier for removal of copper and sulfate in acid mine drainage

Mining is an essential human activity, but results in several environmental impacts, notably the contamination of ground and surface water through the presence of toxic substances such as metals and sulfates in mine drainage. Permeable reactive barriers (PRB) have been applied to remediate this environmental impact, but the high costs associated with the maintenance of this system are still a challenge. The main objective of this study was to evaluate the use of kraft pulp mill alkaline residues, known as dregs and grits, as material for PRB, and to determine their capacity for retaining copper and sulfate. The work was carried out in laboratory adsorption kinetics assays, batch assays and column tests. Tests for elemental characterization, point of zero charge, acid neutralization capacity, total porosity, bulk density and moisture of the dregs and grits were conducted. The results showed high retention of Cu due to a chemical precipitation mechanism, notably for dregs (99%) at 5 min in adsorption kinetics. The grits presented similar results after 180 min for the same assay. Sulfate retention was effective at pH below 5, with an efficiency of 79% and 89% for dregs and grits, respectively. Dregs presented the best results for acid drainage remediation, notably with a solid:liquid (S:L) ratio of 1:10.

Contribution of bacterially-induced oxidation of Fe-silicates in iron-rich ore to laterite formation, Salobo IOCG mine, Brazil

A diverse array of microorganisms, found within the uppermost lithosphere, can mediate the dissolution and precipitation of minerals and therefore contribute to the formation of laterites. The Salobo iron-oxide copper gold (IOCG) mine in Brazil is an ideal environment to examine the specific interaction between iron-oxidising bacteria and ferrous iron-bearing minerals during formation of a ~60 m thick laterite weathering profile. We identified bacteria using DNA extracted from samples in active weathering zones. Many of the identified species are capable of oxidising the ferrous iron and/or reduced sulphur that occurred in minerals associated with the unweathered rocks of the deposit. Fe-bearing phyllosilicates have been variably altered to clays along cleavage planes by bacterial iron oxidation. Accelerated weathering of fresh rocks in laboratory-scale leaching column experiments was conducted using an endemic Acidithiobacillus ferrooxidans ssp. previously cultured from the Salobo mine. There were strong similarities between field samples from the Salobo laterite zone, and experimental leachate chemistry, associated precipitates, and fossilised bacteria remnants, particularly with respect to ferric (oxyhydr)oxide formation. Groundwaters in the Salobo laterite zone have circumneutral pH, whereas some iron-oxidising bacteria thrive in, and locally create, more acidic conditions (~pH 3). The leaching experiments showed that bacterially-facilitated silicate weathering, and bornite (Cu5FeS4) oxidation, can consume acid generated by bacterial oxidation reactions, creating an effective equilibrium with ferric (oxyhydr)oxide precipitation. However, the current acid neutralisation capacity of the ferricrete horizon at the top of the laterite zone was minimal. While bacterial activity promoted mineral oxidation and decomposition within the thick laterite at the Salobo mine, related iron mobility is restricted to the micrometre scale by essentially instantaneous precipitation of ferric (oxyhydr)oxide that eventually transforms via inorganic dehydration to goethite and hematite. Similar processes to those described in this study have likely occurred during the formation of many other iron-rich laterites.

Rapid Recent Recovery from Acidic Deposition in Central Ontario Lakes

In many regions, chemical recovery in lakes from acidic deposition has been generally slower than expected due to a variety of factors, including continued soil acidification, climate-induced sulphate (SO4) loading to lakes and increases in organic acidity. In central Ontario, Canada, atmospheric sulphur (S) deposition decreased by approximately two-thirds between 1982 and 2015, with half of this reduction occurring between 2005 and 2015. Chemical recovery in the seven lakes was limited prior to 2005, with only small increases in pH, Gran alkalinity and charge-balance ANC (acid-neutralizing capacity). This was because lake SO4 concentrations closely followed changes in S deposition, and decreases in base cation concentration closely matched declines in SO4. However, decreases in S deposition and lake SO4 were more pronounced post-2005, and much smaller decreases in lake base cation concentrations relative to SO4 resulted in large and rapid increases in pH, alkalinity and ANC. Dissolved organic carbon concentrations in lakes increased over the study period, but had a limited effect on lake recovery. Clear chemical recovery of these lakes only occurred after 2005, coinciding with a period of dramatic declines in S deposition.

The response of stream ecosystems in the Adirondack region of New York to historical and future changes in atmospheric deposition of sulfur and nitrogen

The present-day acid-base chemistry of surface waters can be directly linked to contemporary observations of acid deposition; however, pre-industrial conditions are key to predicting the potential future recovery of stream ecosystems under decreasing loads of atmospheric sulfur (S) and nitrogen (N) deposition. The integrated biogeochemical model PnET-BGC was applied to 25 forest watersheds that represent a range of acid sensitivity in the Adirondack region of New York, USA to simulate the response of streams to past and future changes in atmospheric S and N deposition, and calculate the target loads of acidity for protecting and restoring stream water quality and ecosystem health. Using measured data, the model was calibrated and applied to simulate soil and stream chemistry at all study sites. Model hindcasts indicate that historically stream water chemistry in the Adirondacks was variable, but inherently sensitive to acid deposition. The median model-simulated acid neutralizing capacity (ANC) of the streams was projected to be 55 μeq L-1 before the advent of anthropogenic acid deposition (~1850), decreasing to minimum values of 10 μeq L-1 around the year 2000. The median simulated ANC increased to 13 μeq L-1 by 2015 in response to decreases in acid deposition that have occurred over recent decades. Model projections suggest that simultaneous decreases in sulfate, nitrate and ammonium deposition are more effective in restoring stream ANC than individual decreases in sulfur or nitrogen deposition. However, the increases in stream ANC per unit equivalent decrease in S deposition is greater compared to decreases in N deposition. Using empirical algorithms, fish community density and biomass are projected to increase under several deposition-control scenarios that coincide with increases in stream ANC. Model projections suggest that even under the most aggressive deposition-reduction scenarios, stream chemistry and fisheries will not fully recover from historical acidification by 2200.