Microsoft Word C039105e doc Reference number ISO/TS 21268 4 2007(E) © ISO 2007 TECHNICAL SPECIFICATION ISO/TS 21268 4 First edition 2007 11 15 Soil quality — Leaching procedures for subsequent chemica[.]
Sample size
Obtain a representative laboratory sample of at least 1 kg (dry matter) of the material Use a sample splitter
(6.12) or apply coning and quartering to split the sample
Sampling must adhere to the guidelines outlined in ISO 10381-1 to ISO 10381-5 for the preparation of a sampling plan for soil materials, ensuring the collection of representative laboratory samples.
Maintaining the appropriate L/S ratios allows for the production of larger eluate volumes necessary for ecotoxicity testing Any adjustments made to meet volume requirements must be documented in the test report.
The laboratory sample size is determined by the soil's particle size distribution, as outlined in the sampling standard Typically, the recommended sample size is sufficient; however, in certain situations where less material is available, a smaller sample may be permitted, provided the testing can still be conducted according to the specified guidelines Any deviations from the standard sample size must be documented in the test report.
Particle size reduction
Tests should ideally be conducted on the material as received, ensuring that the test portion contains at least 95% of grain size up to 4 mm If necessary, the laboratory sample must be sieved, and any oversized natural materials, such as stones or twigs, should be removed and documented If the oversized material is not naturally occurring and exceeds 5% by mass, it must be crushed using appropriate equipment, but fine grinding is prohibited All separate fractions, except for non-crushable materials, should be combined to form the test sample If the laboratory sample cannot be crushed or sieved due to moisture, it may be dried, but the drying temperature must not exceed 25 °C.
NOTE If national regulations specify other particle sizes, these can be applied
Sieving and drying at 25 °C may result in the loss of volatile components, both inorganic and organic Therefore, it is advisable to avoid particle size reduction and drying, as these processes can change the leaching characteristics.
ISO/TS 21268-4:2007(E) © ISO 2007 – All rights reserved 7
Determination of the dry matter content and of water content
The entire test sample must not be dried further if it meets the size criterion specified in section 8.2 The moisture content of the test sample is determined from a subsample at a temperature of (105 ± 5) °C, which is essential for adjusting the liquid-to-solid (L/S) ratio The dry mass of the sample is also measured at (105 ± 5) °C, following ISO 11465, and the dry matter content is calculated using the formula: \$$w_{dm} = \frac{m_D}{m_W} \times 100\$$ where \(w_{dm}\) represents the dry matter content in percent (%), \(m_D\) is the mass of the dried sample in kilograms (kg), and \(m_W\) is the mass of the non-dried sample in kilograms (kg).
The water content (w H2O in percent) is calculated in accordance with Equation (2):
If volatile or unstable compounds are present in the soil sample, this gravimetric method cannot be used for accurate determination of the water content (see ISO 11465)
If the soil sample is air-dried prior to testing, the dry matter content w dm,AD of the air-dried sample shall be determined as well.
Preparation of test portion
To ensure accurate analysis, prepare a minimum of eight test portions using a sample splitter or the coning and quartering method Depending on the sample's heterogeneity and the required eluate volume, the test portion sizes should be 15 g, 30 g, or 60 g, with a precision of ± 1 g.
Calculate the non-dried mass of the test portion, m W , to be used for the test, in accordance with Equation (3):
W D dm m 100 m = w ⋅ (3) where m D is the dried mass of the test portion (g); m W is the non-dried mass of the test portion (g); w dm is the dry matter content of the soil (%)
Contact time
The leaching procedure consists of three defined stages:
⎯ Period A (acid/base addition) from t 0 to (t 0 + 4 h) for acid/base additions in three steps;
⎯ Period B (equilibration period) from (t 0 + 4 h) to (t 0 + 44 h) equilibration period;
⎯ Period C (verification period) from (t 0 + 44 h) to (t 0 + 48 h) for verification of equilibrium condition
Measure pH in the liquid after each of these periods The total contact period (A + B + C) is 48 h.
pH-range
The comprehensive test will evaluate pH levels from 4 to 12, inclusive, encompassing eight distinct pH values, including the natural pH without any acid or base modifications Additionally, the maximum allowable difference between consecutive pH values will be limited to 1.5 pH units.
To achieve the desired pH values in a single run, prepare multiple bottles and retain only those that meet the target final pH for analysis.
The pH range for testing is often limited to values pertinent to the specific material and the issue at hand This range is influenced by the soil's properties, available data, and the objectives of the test For ecotoxicological assessments, the relevant pH range typically falls between pH 5 and 9, allowing for a more focused evaluation by potentially reducing the number of pH levels considered.
Leaching test
General
The following procedure applies to each of the chosen pH values to be tested.
Preparation of leachant
Identify the acid or base consumption for reaching the relevant pH values as A (mol/kg H + dry matter) or
B (mol/kg OH – dry matter) and the total volume of leachant
NOTE The acid or base consumption for the considered pH values can be derived from available information, from the preliminary procedures in Annex B, or from information in Annex C
Calculate the volume V of liquid to establish L/S = 10 ± 0,2 (l/kg) for the actual size of test portion m w (see 8.4), including the volume of acid or base, in accordance with Equation (4):
V is the total volume of the added extractant solution, in millilitres (ml); m D is the dry mass of the test portion, in grams (g) (see 8.4);
10 is the factor, in litres per kilogram (l/kg)
NOTE In relation to the L/S-ratio, V in this equation is equivalent to “L” and m D is equivalent to “S”
Calculate the amount of leachant to be added to the actual size of test portion and compensate for the water content in the test portion in accordance with Equation (5):
V is the total volume of the added extractant solution, in millilitres (ml); m D is the dry mass of the test portion, in grams (g) (see 8.4);
ISO/TS 21268-4:2007(E) © ISO 2007 – All rights reserved 9 w dm is the dry matter of the soil, in percent (%) (see 8.3);
V L is the volume of prepared leachant, in millilitres (ml)
Prepare the leachant from demineralized water (see 7.1) and acid or base (see 7.2 or 7.4) according to the acid/base consumption for the relevant pH
Prepare the acid-adjusted leachant in accordance with Equation (6) and Equation (7):
V L is the volume of prepared leachant, in millilitres (ml);
V d is the volume of demineralized water used, in millilitres (ml);
The volume of acid required is denoted as \$V_A\$ in millilitres (ml), while \$n_A\$ represents the acid consumption specific to the pH level, measured in mol/kg of hydrogen ions per dry matter Additionally, \$m_D\$ indicates the dry mass of the test portion, expressed in grams (g), as referenced in section 8.4.
C A is the concentration of the acid, in moles per litre (mol/l) (see 7.2)
Prepare the base-adjusted leachant in accordance with Equations (8) and (9):
V L is the volume of prepared leachant, in millilitres (ml);
V d is the volume of demineralized water used, in millilitres (ml);
The volume of base required is denoted as \$V_B\$ in millilitres (ml), while the base consumption for a specific pH is represented by \$n_B\$ in mol/kg OH– dry matter Additionally, the dry mass of the test portion is indicated as \$m_D\$ in grams (g), as referenced in section 8.4.
C B is the concentration of the base, in moles per litre (mol/l) (see 7.4)
Split the volume V L of leachant into three equal parts, V L /3.
Leaching procedure
Carry out the test at a temperature of (20 ± 5) °C
Select the appropriate bottle size according to the test portion size For m D = 15 g, 30 g and 60 g, this means bottle sizes of, respectively, 250 ml, 500 ml and 1 000 ml
Clean the bottle before use by filling it with 1 mol/l nitric acid (see 7.3), leaving it for at least 24 h and then rinsing it with demineralized water (see 7.1)
Place one of the test portions in the rinsed bottle
Add the leachant volume, V L /3, at three different times: a) first fraction at t 0 ; b) second fraction at t 0 + 30 min; c) third fraction at t 0 + 2 h
After sealing the bottle, shake the suspension thoroughly between each addition of leachant Prior to adding the second and third fractions, measure and document the pH If any discrepancies from the anticipated pH are noted, prepare extra bottles with adjusted acid/base additions.
When using acidic leachants, it is crucial to consider the development of carbon dioxide, as this can result in pressure build-up To manage this, the bottle should be opened periodically during the test Most gas production occurs shortly after the initial addition of acid Additionally, it is important to continue agitation for 48 hours after the final leachant addition.
NOTE 1 For the high pH values (pH > 9 ), CO 2 uptake can affect the leaching process This can be reduced by minimizing the contact time with the air during handling
Measure and record the pH at 4 hours, 44 hours, and 48 hours after the initial time (t 0) To measure the pH, stop the agitation and let the mixture settle for 5 minutes Then, insert a clean electrode into the supernatant to obtain the pH reading.
NOTE 2 The pH value at t 0 + 4 h is used for checking that sufficient pH adjustment has been obtained by the acid or base additions, respectively
Since the pH is measured directly in the suspension, rinse the pH electrode thoroughly and dry softly before and between uses in order not to contaminate the suspension
The pH value recorded at t 0 + 48 h prior to filtration will be used for the eluate analysis It is important to note that the pH is measured directly in the bottle at t 0 + 48 h, as filtration may alter the pH of the eluate.
Report the pH deviation between t 0 + 4 h and t 0 + 44 h
The pH difference between t 0 + 44 h and t 0 + 48 h must not exceed 0.3 pH units to indicate an equilibrium condition If this criterion is not satisfied, it should be specifically noted in the report.
If too many experimental points deviate (more than three amongst eight), the conclusion is that this test is not applicable to this material
In cases where the equilibrium condition is essential but not met during testing, the test may be extended up to 7 days for all eight selected pH values This extension helps prevent the association of results at 48 hours with those from a longer leaching period During the final 24 hours, the pH deviation should be limited to 0.3 pH units Any experimental points that do not meet these criteria will be excluded from analysis, and this will be noted in the report This specific procedure is not detailed in this document.
Allow the suspended solids to settle for (15 ± 5) min
Transfer the supernatant to centrifuge tubes (6.7)
ISO/TS 21268-4:2007(E) © ISO 2007 – All rights reserved 11
There are two options for solid-liquid separation
1) Centrifuge the eluate for 30 min at 20 000 g to 30 000 g using a high-speed centrifuge (6.6)
2) Centrifuge the eluate for 5 h at 2 000 g to 2 500 g in glass bottles using a lower speed centrifuge (6.6) Cooling shall be applied to maintain the temperature at (20 ± 5) °C (see 6.6)
NOTE 4 Based on Stoke's law, the results of both centrifugation methods are expected to be comparable
Gentle breaking shall be applied in order to avoid resuspension Deceleration time shall not exceed 20 min
After centrifugation, promptly transfer the eluate to a suitable container for pH and redox potential measurement, and store it for future chemical analysis or ecotoxicological testing.
To measure only inorganic constituents, the eluate should be filtered with suitable membrane filters and a vacuum or pressure filtration device If the specified filtration method cannot be performed promptly, alternative approaches may be necessary.
For a liquid flow rate of at least 30 ml/cm²/h, a tailored liquid-solid separation procedure must be implemented Ensure that all details are documented in the test report, and note that this procedure should be conducted without the use of additives.
For inorganic constituents, it is recommended to precentrifuge the eluate at 2,000 to 3,000 g for 20 minutes using glass bottles with screw caps and polytetrafluoroethylene inlays, or directly with the leaching bottle if feasible, before proceeding with filtration.
NOTE 5 Such a specific liquid-solid separation procedure can include settling, prefiltration on coarser filter, centrifugation, filtration on large size membrane filter, filtration at high pressure, filtration at increasing high pressure following a first period without pressure, etc
Determine the volume of eluate V E
Measure immediately the electrical conductivity (in millisiemens per metre, mS/m), temperature, DOC and pH of the eluate Measurement of turbidity and redox potential E h in millivolts (mV) is highly recommended
Analyzing Dissolved Organic Carbon (DOC) in the eluate is essential for understanding the release of both inorganic and organic substances It is crucial to treat the eluate promptly, following the guidelines outlined in Clause 10 For reference, Annex A provides a detailed example of a liquid-solid separation procedure applicable to soil samples.
Natural pH
Repeat 9.3 for a test portion without acid or base addition, when determining the volume of demineralized water to be added Measure the pH after 4 h, 44 h and 48 h, as in 9.3
Low conductivity in the eluate at natural pH can lead to colloid formation, potentially clogging filters and raising analyzed concentrations This issue can be mitigated by adding CaCl\(_2\) to the leachant at a concentration of 0.001 mol/L.
10 Eluate treatment, storage and analysis
Divide the eluate into several sub-samples for various chemical analyses Preserve these sub-samples based on the elements to be analyzed and store them according to the guidelines outlined in ISO 5667-3.
Determine the concentrations of constituents of interest using the methods of eluate analysis (e.g ISO 11047)
When using eluates for bioassays, they shall be processed as soon as possible, but storage shall not exceed
The analysis step is excluded from this section of ISO/TS 21268; therefore, the analytical methods outlined in relevant International Standards must be utilized This includes documenting the analysis date, storage conditions prior to analysis, the quantification limit of the analytical method, the laboratory's address, and the names of the operators involved.
To ensure accurate results, it is essential to conduct periodic blank tests that assess the contributions of the leachant, devices, and membrane filters throughout the entire procedure.
To create three distinct blank tests, follow the procedures outlined in section 9.3 and Clause 10, omitting the solid material For each test, add: a) the maximum quantities of acid and base to the leachant, maintaining a similar volume as used in the tests; b) acid to achieve a pH of 4; c) base to reach a pH of 12.
The eluates from blank tests must meet the criterion that the concentration of each element is less than 10% of its concentration in the eluate If an element's concentration is below the detection limit of the analytical method used, the blank test will be considered compliant if it also falls below this detection limit Failure to meet these requirements necessitates efforts to reduce contamination.
The most recent blank test results shall be available
Do not subtract the results of the blank test determination from the test results
The leaching test analysis reveals the concentrations of constituents in the eluate, measured in milligrams per litre (mg/l) Ultimately, the results indicate the amount of each constituent leached, expressed as milligrams per kilogram (mg/kg) of dry matter relative to the total mass of the sample.
Calculate the quantity of a constituent leached from the material, based on the dry mass of the original material, from Equation (10):
( )X 1 ( ) (X L D ) ( H O 2 100) w =ρ ⋅⎡⎢⎣V m + w ⎤⎥⎦ (10) where w(X) is the release of a constituent X at a L/S = 10, in milligrams per kilogram (mg/kg of dry matter); ρ 1 (X) is the analyte concentration, in milligrams per litre (mg/l);
V L is the volume of leachant used, in litres (l); w H2O is the water content, as calculated in Equation (2); m D is the mass of the dried test portion, in kilograms (kg)
ISO/TS 21268-4:2007(E) © ISO 2007 – All rights reserved 13
The test report must adhere to ISO/TS 21268 and include essential details such as complete sample identification, the test results, and any optional information or deviations from the specifications, along with any factors that may have influenced the results.
When this part of ISO/TS 21268 was adopted by ISO, the test specified in this document was not validated and no data were available on robustness, repeatability and reproducibility
Example of a specific liquid-solid separation procedure for soil sample
Leaching tests primarily focus on solid substances with significant dissolved salt content, but their effectiveness is limited when assessing soil samples, especially regarding oxidized, adsorbed, or organically-bound heavy metals, which tend to be less soluble Despite their low solubility, heavy metals pose significant environmental concerns In contaminated soil samples, the lower the "pure" solubility of these metals, the greater the impact of colloidal particles in the eluate on the final results.
In fine-textured soil samples rich in humus but low in electrolytes, the resulting filter cake during filtration has very fine pores, leading to minimal colloid passage through the membrane filter This filter cake significantly influences the solubility of heavy metals, as measured by this method To ensure comparable results, it is essential to identify the factors that affect the height of the filter cake, which is primarily influenced by the filter diameter and the volume of the eluate, in addition to the specific properties of the sample.
A.2.1 Pressure filtration unit for membrane filter (diameter 142 mm)
A.2.2 Membrane filter of pore size 0,45 àm
When using a different filter size, the volume to be filtered must be adjusted based on the filter surface area It is crucial to maintain the relationship between the volume and the filter surface, which is approximately 1 liter of volume for every 158 cm² of filter surface (equivalent to a diameter of 142 mm).
A.2.3 Media-guiding material (in contact with extracts), in polytetrafluoroethylene
For sedimentation of the larger particles, allow the suspension to stand for 15 min after shaking
Decant almost completely the supernatant liquid into a centrifuge tube or bottle device
Almost complete decanting of supernatant liquid into the membrane pressure filter apparatus
Apply, after 5 min of filtration without pressure, a pressure of 100 kPa (1 bar) to accelerate filtration If after
15 min less than two thirds of the eluate have passed through the filter, increase the pressure to 200 kPa
Increase the pressure to a maximum of 350 kPa (3.5 bar) if needed after 30 minutes Continue filtration until all supernatant from centrifugation has passed through the filter If filtration remains incomplete after 2 hours, cease the process, collect the incomplete filtrate, and prepare it for analysis.
This procedure significantly minimizes potential errors related to the proportions of colloidal and dissolved heavy metals in the filtrate Therefore, it is prohibited to decant the initial portion of the filtrate and reintroduce it to the filter, a practice commonly observed in many laboratories.
ISO/TS 21268-4:2007(E) © ISO 2007 – All rights reserved 15
Operation and uses of the test: influence of pH on the leaching behaviour
B.1 Comparison of the mode of operation of the test with the pH continuous control mode — Influence of pH on the leaching behaviour
Both modes are aimed at determining the influence of pH on the release of the inorganic and organic constituents from a soil sample (check in the whole document)
This document outlines a test that establishes an equilibrium condition at various pH levels through the reaction of specific amounts of acid or base with soil samples To expedite the attainment of this equilibrium, size reduction of the soil is implemented.
The continuous pH control test, as outlined in CEN/TS 14997, effectively assesses the impact of pH on leaching, particularly for materials with low buffer capacity This method is ideal for evaluating leaching behavior at specific pH levels, where even minor pH fluctuations can significantly alter the release of substances.