Leaching of heavy metals from sewage sludge through coastal plain soils

Abstract

Three types of sewage sludge are applied to the surface of soil columns of Coastal Plain soils and leached with distilled water. The Zn concentrations in leachate samples from a Sassafras loamy sand soil loaded with an industrial sludge increased with sludge loading rate. All leachate samples contained very low concentrations of Cd, Cr and Cu. Hazardous amounts of Cd, Cr, Cu and Zn would not be leached to the groundwater when recommended rates of the tested sludges are applied to Coastal Plain soils under most conditions.     

Evidence for microbial decomposition of organic acids during podzolization

Microbial aspects of podzolization were studied by percolating organic acids through sterile and non-sterile soil in columns. Six columns containing sand from a fluvioglacial sediment were percolated (90 mm d^?1) with mor extract and an oxalate-citrate solution. In three of these, sterilized soil solutions were used. Weathering was enhanced by organic acids which formed complexes with aluminium and iron. In the non-sterile soil columns weathering by organic acids was inhibited at 7–8 cm because the acids were degraded by microorganisms. Weathering was evident from colour change, contents of extractable aluminium and iron, and the micromorphology. Enhanced weathering in the sterile columns was also suggested by larger amounts of aluminium, iron, silica and base cations leached from the columns. Comparison of the output of aluminium, iron and silica from the sterile soil with that from the non-sterile soil, suggests that probably an aluminium-iron-silicate phase was formed in the deeper parts of the non-sterile columns.     

Physico-chemical and biological controls on dissolved organic matter in peat aggregate columns

We investigated the importance of physico‐chemical mechanisms responsible for the release of dissolved organic matter (DOM) from a peaty soil. Columns containing peat aggregates (embedded within a sand matrix) provided an experimental system in which both convective and diffusive processes contributed to DOM leaching. The use of aggregated peat avoided the problems associated with traditional batch equilibration experiments in which soil structure is destroyed. Biotic and abiotic processes operating in the columns were manipulated by working with two unsterilized columns (at 5°C and 22°C) and one gamma irradiation‐sterilized column (5°C). Continuous solute flows (< 80 hours) and periods of flow interruption (five interruptions of 6 hours to 384 hours) were applied to the columns (using a 1‐mm NaCl electrolyte) to investigate mechanisms of diffusion‐controlled release of DOM. For all columns, dissolved organic carbon and nitrogen (DOC and DON) effluent concentrations increased after resumption of flow and the maximum concentrations increased with increased flow‐interruption duration. Measurements of effluent UV absorbance (λ= 285 nm) showed that the DOM leached immediately after the flow interruptions contained fewer aromatic moieties of lower molecular weight than the DOM leached after periods of steady flow. The sterilized column had larger DOC and DON effluent concentration spikes than those from the unsterilized column at 5°C (38 mg C dm⁻³ and 6.5 mg N dm⁻³ versus 13 mg C dm⁻³ and 6.5 mg N dm⁻³ after the 384 hours flow interruption). This result suggested that the concentrations of DOM resulting from physico‐chemical release mechanisms (sterilized column) were attenuated by biological activity (unsterilized columns). Our results indicate that the peat’s microporous structure provides reservoirs of DOM that interact with solute in transport pores via abiotic, rate‐controlled mass transport. Hence, diffusion can influence the quantity and composition of DOM leached from peat in the field depending on intensity and duration of rainfall.     

Leaching of Metals from Oxidising Sulphide Mine Tailings with and without Sewage Sludge Application

A 20-month column experiment investigated leaching of Al, Cu, Mn, Ni, Zn, Cd and Pb during sulphide oxidation in mine tailings with and without sewage sludge (SS) amendment. Leachate pH decreased gradually in all columns during the experiment, irrespective of treatment, due to sulphide oxidation. As the degree of sulphide oxidation, and thus the pH trajectory, differed between replicates (n?=?3), running data for each column used are reported separately and the relationships between sulphide oxidation, metal leaching and treatment in each column compared. Mean pH in the columns correlated negatively with total amounts of leached SO₄ ^2-. In the beginning of the experiment the leachate concentrations of Al, Cu, Zn, Ni and Pb were higher in SS-treated columns due to high initial concentrations of dissolved organic carbon. As leaching proceeded, however, the amounts of Al, Cu, Mn and Ni leached from the columns were closely related to the degree of sulphide oxidation in each column, i.e. to its mean pH. There were no statistically significant differences between treatments regarding the total amounts of metals leached and thus addition of sewage sludge to the tailings appeared to play a minor role for metal leaching patterns. Peak concentrations of Al and Cu in the leachate from untreated tailings and of Zn in the leachate from both untreated and SS-treated tailings at pH 4 exceeded national background values for groundwater.     

Heavy‐metal displacement in chelate‐treated soil with sludge during phytoremediation

Heavy metals (HMs) in domestic sewage sludge, applied to land, contaminate soils. Phytoremediation is the use of plants to clean‐up toxic HMs from soil. Chelating agents are added to soil to solubilize the metals for enhanced uptake. Yet no studies report the displacement of HMs in soil with sludge following solubilization with chelates. The objective of this work was to determine the uptake or leaching of HMs due to a chelate added to a soil from a sludge farm that had received sludge for 25 y. The soil was placed in long columns (105 cm long; ?? 39 cm) in a greenhouse. Columns either had a plant (hybrid poplar; Populus deltoides Marsh. × P. nigra L.) or no plant. After the poplar seedlings had grown for 144 d, the tetrasodium salt of the chelating agent EDTA was irrigated onto the surface of the soil at a rate of 1 g per kg of soil. Drainage water, soil, and plants were analyzed for three toxic HMs (Cd, Ni, Pb) and four essential HMs (Cu, Fe, Mn, Zn). At harvest, extractable and total concentrations of each HM in the soil with EDTA were similar to those in soil without EDTA. The chelate did not affect the concentrations of HMs in the roots or leaves. With or without plants, EDTA mobilized all seven HMs and increased their concentrations in drainage water. Lower concentrations of Cd, Cu, Fe, Ni, and Zn in leachate from columns with EDTA and plants compared to columns with EDTA and no plants showed that poplars can reduce groundwater contamination by intercepting these HMs in the soil. But the poplar plants did not reduce Pb and Mn in the leachate from columns with EDTA. Concentrations of Cd and Pb in the leachate mobilized by EDTA remained above drinking‐water standards with or without plants. The results showed that a chelate (EDTA) should not be added to a soil at a sludge farm to enhance phytoremediation. The chelate mobilized HMs that leached to drainage water and contaminated it.     

Cadmium leaching from some New Zealand pasture soils

Cadmium (Cd) inputs and losses from agricultural soils are of great importance because of the potential adverse effects Cd can pose to food quality, soil health and the environment in general. One important pathway for Cd losses from soil systems is by leaching. We investigated loss of Cd from a range of contrasting New Zealand pasture soils that had received Cd predominantly from repeated applications of phosphate fertilizer. Annual leaching losses of Cd ranged between 0.27 and 0.86 g ha^–l, which are less than most losses recorded elsewhere. These losses equate to between 5 and 15% of the Cd added to soil through a typical annual application of single superphosphate, which in New Zealand contains on average 280 mg Cd kg^?1 P. It appears that Cd added to soil from phosphate fertilizer is fairly immobile and Cd tends to accumulate in the topsoil. The pH of the leachate and the total volume of drainage to some extent control the amount of Cd leached. Additional factors, such as the soil sorption capacity, are also important in controlling Cd movement in these pasture soils. The prediction of the amount of Cd leached using the measured concentrations of Cd in the soil solution and rainfall data resulted in an overestimation of Cd losses. Cadmium concentrations in drainage water are substantially less than the current maximum acceptable value of 3 µg l^?1 for drinking water in New Zealand set by the Ministry of Health.     

Degradation and Leaching of Simazine in Arctic Sandy Soils

Abstract

Degradation and leaching of ¹⁴C-labelled simazine in coarse sandy soils at 15 + 1°C were investigated using radiometric and mass-spectrometric methods. During 6 months incubation approx. 4–7% of the applied ¹⁴C-simazine was evolved as ¹⁴CO₂. 4–9% of the simazine still remained in the soil. Addition of hen manure or acidification by addition of peat did not clearly influence the rate of degradation of simazine, whereas mechanical treatment significantly increased its degradation. In a nitrogen atmosphere the rate of degradation of simazine was reduced.

9–15% of the simazine or its radioactive metabolites leached through a 33 cm sandy moraine soil column (diameter 6 cm) in ca. 1770 mm of precipitation over a 4 month period, and 2% was leached from a fine sand soil under the same conditions.     

Analysing the preferential transport of lead in a vegetated roadside soil using lysimeter experiments and a dual-porosity model

Lead (Pb) from the traffic accumulates in roadside soils, which are usually vegetated to control erosion. Plants release soluble organic substances that bind Pb. Root macropores also create preferential pathways through which water can flow. Both these processes may enhance Pb mobility. We used large lysimeters to investigate the transport of Pb in a contaminated (445 mg Pb kg^?1) soil under vegetation (Phacelia tanacetifolia). Despite the high soil pH (7.2), Pb leached into the drainage water during the 5‐month experiment. The fast response of the system to intense rainfall events indicated the presence of preferential flow. By comparing Pb concentrations in filtered and unfiltered leachates, we found that Pb was leaching primarily on suspended material. An increase in Pb concentration in the leachate at the end of the experiment indicated the remobilization of Pb, possibly by decaying vegetation. We parameterized the dual‐porosity MACRO model using the experimental results. The simple parameterization of MACRO used to simulate the Pb concentrations in the drainage water produced an overall model efficiency of 0.81: MACRO simulated the Pb concentrations well, but it failed to predict the observed increase of Pb in the leachate at the end of the experiment. The model gave the best prediction of Pb concentrations with a small partition coefficient (k_d= 150 cm³ g^?1). Long‐term simulations of Pb mobility showed that for our specific conditions preferential flow was the main process determining the fate of Pb.     

Wastewater Re-Use for Croton in Substrates Amended with Zeolitic Tuff

ABSTRACT

Treated wastewater was compared with tap water for irrigation of croton (Codiaeum variegatum Blume cv. ‘Petra’) in substrates consisting of 1 peat moss: 1 perlite (PP) or 1 soil: 1 sand (SS), alone or supplemented with zeolitic tuff at a ratio of 3:1 (PPZ and SSZ). Substrates were allowed to reach 80% of available water before the plants were irrigated with wastewater or tap water. Results indicated that neither water quality nor substrate affected plant width, leaf area, shoot fresh weight, or root length or weight. Wastewater increased stem diameter; node and leaf number; tissue nitrogen (N); sodium (Na); and chloride (Cl); substrate electrical conductivity (EC); phosphorus (P); Na, Cl, and leachate EC; and concentrations of Na, Cl, NO₃ ^?, and NH₄ ⁺. Root count, tissue Na, substrate potassium (K) and Na, and leachate pH were higher for zeolite-containing substrates. Shoot dry weight and tissue contents of N and P were the highest for wastewater-irrigated PP and PPZ. Wastewater-irrigated plants in PP and tap water-irrigated plants in PPZ exhibited the highest K content. The highest level of tissue Cl was recorded for SS. Tap water-irrigated PPZ had the highest pH and K concentration. Wastewater-irrigated PP, PPZ, and SS exhibited the highest contents of N, Na, and Cl, respectively. Based on the results, amendment of the substrate with zeolitic tuff is recommended to offset the adverse effect of salinity associated with wastewater.     

Glutamic acid decomposition as a sensitive measure of heavy metal pollution in soil

The effect of added heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) on the rate of decomposition of glutamic acid was studied in four Dutch soil types in order to determine if such measurements would serve as sensitive indicators of heavy metal pollution in soil. The time required to reach the maximum respiration rate (referred to as the decomposition time) with glutamic acid was linearly related to increasing concentrations of Ni in a sandy loam soil.Changes in decomposition time were measured 18 months after addition of 55, 400 or 1000 mg kg^? of Cd, Cr, Cu, Ni, Pb or Zn respectively to sand, silty loam, clay and sandy peat soils. A significant increase in the decomposition time occurred with a concentration of 55 mg kg^?1 of Cd, Cu or Zn in the sand soil. At 400mgkg^?1 adverse effects in the various soils are distinct. The sensitivity of the decomposition time of glutamic acid as a method to measure soil pollution is discussed.     

某硫矿重金属分级及土柱淋溶

Fractions of various heavy metals in a sulfidic minespoil were investigated.Column leachine experiment was also conducted to simulate “acid mine drainage“(AMD) from the minespoil.The results show that leaching of heavy metals from the minespoil was extremely significant during the initial water flushing.The amounts of heavy metals leached out dramatically reduced after leaching twice.It is worthwhile to note that in this study,Zn,Mn,Fe,As and Ni in the first leachate exceeded the total amount of each corresponding water-extractable(1:5,soil:water)metal contained in the minespoil sample.This appears to suggest that 1:5 water extraction did not allow accurate estimation of water-leachable concentrations of the above heavy metals.This work has implications for the management of sulfidic minespolis.Acid drainage of great environmental concerns is likely to occur only during heavy rainfall events after substantial soluble and readily exchangeable acid and metals are accumulated in the minespoils.The slow-reacting fractions other than water-soulble and readily exchangeable fractions may pose little environmental hazards.This is particularly true for Pb,As and Ni.     

Differences in nitrogen‐assimilating enzyme activity in halophyte species are habitat‐related

The chemical form and content of available nitrogen (N) in salt marsh substrates varies considerably. On the western coast of Ireland, habitats designated as Ombrogenic Atlantic salt marshes were formed on ombrogenic peat substrate. The peat substrate in these systems has three times more ammonium than substrate from adjacent salt marsh habitats on sand and mud substrate. This study examined the extent to which the high concentration of ammonium in peat salt marsh substrate influences the N‐ assimilating enzyme activity of halophytes and the extent to which N metabolism differs between species. Specifically, this work investigated whether plants from peat salt marshes are more likely to assimilate ammonium than plants from non‐peat substrates. Four halophyte plant species—Armeria maritima, Aster tripolium, Plantago maritime, and Triglochin maritime—were sampled from various saltmarsh habitats including three sites on peat substrate and three on non‐peat substrate, comprising sand, mud and sand/mud. The activities of N‐metabolising enzymes—glutamine synthetase (GS), glutamate synthase, glutamate dehydrogenase (GDH), and nitrate reductase (NR)—were quantified in shoot and root parts. Root GS activity in Armeria maritima and shoot GS activity in Triglochin maritima were positively correlated with increasing soil ammonium levels. Root NR activity in Aster tripolium and shoot NR activity in Plantago maritima were significantly higher in plants grown on non‐peat substrates than peat substrates. The shoot : root GS activity ratio in Triglochin maritima on peat substrate was more than double the ratio on non‐peat substrates. It is concluded that all species tested displayed differences in N‐metabolising activities depending on the chemical form and/or concentration of N in the substrate, while three out of the four species were capable of taking advantage of the high levels of ammonium in peat substrates.     

Rhizodeposition of maize: Short‐term carbon budget and composition

The aim of this study was to assess differences in rhizodeposition quantity and composition from maize cropped on soil or on 1:1 (w/w) soil–sand mixture and distribution of recently assimilated C between roots, shoots, soil, soil solution, and CO₂ from root respiration. Maize was labeled in ¹⁴CO₂ atmosphere followed by subsequent simultaneous leaching and air flushing from soil. ¹⁴C was traced after 7.5 h in roots and shoots, soil, soil solution, and soil‐borne CO₂. Rhizodeposits in the leachate of the first 2 h after labeling were identified by high‐pressure liquid chromatography (HPLC) and pyrolysis–field ionization mass spectrometry (Py‐FIMS). Leachate from soil–sand contained more ¹⁴C than from soil (0.6% vs. 0.4%) and more HPLC‐detectable carboxylates (4.36 vs. 2.69 μM), especially acetate and lactate. This is either because of root response to lower nutrient concentrations in the soil–sand mixture or decreasing structural integrity of the root cells during the leaching process, or because carboxylates were more strongly sorbed to the soil compared to carbohydrates and amino acids. In contrast, Py‐FIMS total ion intensity was more than 2 times higher in leachate from soil than from soil–sand, mainly due to signals from lignin monomers. HPLC‐measured concentrations of total amino acids (1.33 μM [soil] vs. 1.03 μM [soil–sand]) and total carbohydrates (0.73 vs. 0.34 μM) and ¹⁴CO₂ from soil agreed with this pattern. Higher leachate concentrations from soil than from soil–sand for HPLC‐measured carbohydrates and amino acids and for the sum of substances detected by Py‐FIMS overcompensated the higher sorption in soil than in sand‐soil. A parallel treatment with blow‐out of the soil air but without leaching indicated that nearly all of the rhizodeposits in the treatment with leaching face decomposition to CO₂. Simultaneous application of three methods—¹⁴C‐labeling and tracing, HPLC, and Py‐FIMS—enabled us to present the budget of rhizodeposition (¹⁴C) and to analyze individual carbohydrates, carboxylates, and amino acids (HPLC) and to scan all dissolved organic substances in soil solution (Py‐FIMS) as dependent on nutrient status.     

Leaching of Nitrate,Ammonium, and Phosphate From Compost Amended Soil Columns

Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha^?1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha^?1 rate and leached with deionized water (300 ml day^?1, for five days; equivalent to 34 cm rainfall). The concentrations of NO₃-N, NH₄-N, and PO₄-P in leachate reached as high as 246, 29, and 7 mg L^?1, respectively. The amount of N and P leached accounted for 3.3-15.8 percent of total N and 0.2-2.8 percent of total P in the compost. The leaching peaks of NO₃-N occurred following the application of only 300-400 ml water (equivalent to 6.8-9.1 cm rainfall).     

The properties, genesis and significance of a man-made iron pan podzol near Castletownbere, Ireland

Beneath a layer of artificially deposited peat debris, an eluvial E horizon and thin iron pan (Bsm) has developed in the upper part of the A_p horizon of a brown podzolic soil (Haplorthod) near Castletownbere, Ireland. The thickness of the E horizon and the depth of the pan are directly related to the thickness of the layer of peat debris. The original soil (Haplorthod) was strongly podzolized with a significant accumulation of organic carbon, iron and aluminium in the spodic Bs. The iron pan of the upper sequum, on the other hand, is rich in iron. This iron pan seems to have developed as a result of reduction of iron in the E horizon, transport of divalent Fe²⁺ cations and precipitation in the Bsm as Fe₂(OH)₃, after the peat layer was deposited. We conclude that podzolization and iron pan development were fundamentally different processes. The study suggests a fundamental change in the iron pan-blanket peat development sequence previously postulated by palaeoenvironmentalists in Ireland.     

Modern and paleolimnological evidence for accelerated leaching and metal accumulation in soils in New England,caused by atmospheric deposition

Empirical field evidence for changing chemical processes in soils caused by atmospheric deposition of pollutants consists of: (1) Long-term water quality data including total dissolved solids, concentrations of specific metals (e.g. Ca), and conductivity; (2) Cation exchange capacity and base saturation values for soils located on precipitation pH gradients; (3) Lysimeter studies; and (4) Chemical analysis of organic soils on precipitation pH and metal gradients. For well-drained organic soils, as precipitation pH decreases, metals are differentially leached at an accelerated rate (Mn>Ca>Mg≥Zn>Cd and Na>Al). Experimental field and laboratory lysimeter studies on soil columns yield similar results, with increases in leaching rates for soil solutions with pH=3 up to 100 × values for soil solutions with pH=5. Nearly 100% of the Pb from precipitation is accumulating in the organic soil layer or sediments. Zn is accumulating in soils and sediments where the pH's of precipitation, soil solutions, and surface waters are generally above 5 to 5.5. At lower pH values Zn and other chemically similar elements are desorbed/leached (net) at an accelerated rate. Chemical analyses of dated sediment cores from high and low altitude lakes, with drainage basins relatively undisturbed for the last 200+ yr, reveal that increased deposition of metals on a regional scale started in the northeastern United States as early as 1880, consistent with increased fossil fuel consumption. This suggests acidified precipitation as early as 1880. Cores from historically acidified lakes (pH<≈5.3 to 5.5) indicate that, as acidification of surface waters occurs (caused by acidic deposition), concentrations of Zn, Mn, and Ca decrease in the sediment. Apparently the metals are leached from the detritus prior to sedimentation. This conclusion results from data from experimental acidification of sediment cores and the general observation that precipitation pH is generally ≥0.5 pH units lower than lake water pH. Accelerated leaching of soil in New England dates to earlier than 1900.     

Pretreating landfill leachate with peat to remove metals

In this investigation, the capacity of peat to treat two different landfill leachates was determined. Freundlich isotherms showed that, for the tested metals (Cd, Cr, Cu, and Pb), an increased time of contact increased the level of adsorption over the entire range of influent values studied. In addition, metal interaction may play an important role in the adsorption of metals from leachate, as the various metal ions compete for the available adsorption sites on the peat. Column studies using two leachates, one from a municipal refuse fill (Al, Ca, Cd, Fe, Mg, Na, and Pb), and one from a fill which receives mainly oil and fly ash (Al, Ca, Cr, Fe, Mg, Mn, Na, Pb, and V), were conducted to establish design parameters for full-scale design. The efficiency of treatment was evaluated as a function of factors important for developing filter design criteria. Further considerations were given to filter longevity and ease of replacement, as well as for the ultimate disposal of the peat from the filters. For the municipal leachate a compaction density of 0.12 g mL^?1 gave the best results as clogging occurred at higher densities, whereas 0.18 g mL^?1 provided the best removal for the industrial leachate. While peat is incapable of adequately removing metals to acceptable levels for direct discharge, peat can provide substantial removal as a pretreatment process at low hydraulic loadings. Desorption of up to 50% was found when deionized water was applied to spent columns so ultimate disposal of the peat would require a dry environment.     

Toxicity of arsenic in relation to soil properties: implications to regulatory purposes

Purpose

The present work evaluates the influence of different soil properties and constituents on As solubility in laboratory-contaminated soils, with the aim of assessing the toxicity of this element from the use of bioassays to evaluate the soil leachate toxicity and thereby propose soil guideline values for studies of environmental risk assessment in soil contamination.

Materials and methods

Seven soils with contrasting properties were artificially contaminated in laboratory with increasing concentrations of As. Samples were incubated for 4 weeks, and afterwards, soil solution (1:1) was obtained after shaking for 24 h. The soil leachate toxicity was assessed with two commonly used bioassays (seed germination test with Lactuca sativa and Microtox ® test with Vibrio fischeri).

Results and discussion

The relationship between soluble As and soil properties indicated that iron oxides and organic matter content were the variables most closely related to the reduction of the As solubility, while pH and CaCO₃ increased As solubility in the soil solutions. Toxicity bioassays showed significant differences between soils depending on their properties, with a reduction of the toxicity in the iron-rich soil (no observed effect concentration (NOEC)?=?150 mg kg^?1) and a significant increase in the highly carbonate samples (NOEC between 15 and 25 mg kg^?1).

Conclusions

Soil guideline values for regulatory purposes usually set a single value for large areas (regions or countries) which can produce over- or underestimation of efforts in soil remediation actions. These values should consider different levels according to the main soil properties controlling arsenic mobility and the soil leachate toxicity.     

Limited downward migration of pollutant metals (Cu,Zn, Ni,and Pb) in acidic virgin peat soils near a smelter

The distribution of pollutant heavy metals (Cu, Zn, Ni, Cd, and Pb) was determined in 11 acidic virgin peat profiles located along two transects moving away from a smelter plant in the Noranda region of Quebec. The levels of all five metals were found highest in the 0 to 15 cm layer at site near the smelter, and decreased progressively with the distance from the smelter, up to 42 km. Copper had the highest concentrations (5525 μg g^?1) followed by Pb and Zn. The maximum levels of total metals built up in the peat surface near the smelter were high, approximately reaching the threshold limits for phytotoxicity in peat soils. The amounts of heavy metals moving down and accumulating in the anaerobic zone of the peat profiles were limited. The distribution and enrichment ratios in the profiles showed that Cu, Zn, and Cd would have relatively higher mobility than Pb.     

Integrated Flow-based System Displaying an In-line Mini Soil Column to Monitor Iron Species in Soils Leachates

ABSTRACT

Contamination of ground water as a consequence of soil leaching processes is an issue of major concern. In this context, a simulation of the soil leaching process was designed. A sequential injection (SI) method to monitor the soil leaching of iron complexes with in-line rain simulation for leachate production is described. The developed methodology comprises the SI determination of both iron(III) and 3-hydroxy-4-pyridinones iron(III) complexes, coupled to a mini soil column (mSC) for displaying in-line rain simulations. The described SI method enabled iron(III) determination within the range 2.0–35 µmol L^?1, with a detection limit of 0.42 µmol L^?1, and determination of iron(III) complexes in the range 1.0–45 µmol L^?1. It was successfully applied to leachates from laboratory scale soil columns (LSSC), with good precision for both iron(III) and iron complexes determinations: calculated relative standard deviation (RSD) of 5% and 6%, respectively. A step further in automation and miniaturization was attained with the incorporation of a mini soil column for the in-line leachate production. The system enabled the soil leachate production and assessment in less than 5 min, including determinations in triplicate.