ISO 19730:2008

Overview

ISO 19730:2008 - Soil quality - Extraction of trace elements from soil using ammonium nitrate solution - specifies a standardized laboratory method to extract easily soluble trace elements from soils using a 1 mol/l ammonium nitrate (NH4NO3) solution. The method produces reproducible extracts for routine soil testing and site investigations, enabling comparison of extractable element concentrations across locations and times.

Key Topics and Technical Requirements

• Extractant and concentration: 1 mol/l ammonium nitrate (NH4NO3).
• Sample fraction: use soil fraction < 2 mm after pretreatment (see ISO 11464).
• Soil-to-solution ratio: mass:volume = 1:2.5 (typically 10.00 ± 0.01 g soil with 25.0 ml NH4NO3).
• Extraction conditions: 120 ± 5 minutes at (20 ± 2) °C on an end-over-end shaker at (20 ± 2) r/min.
• Phase separation & filtration: centrifuge (~1 000 g for 10 min), filter through 0.45 µm (or 0.2 µm if colloids present) in-line membrane filter.
• Stabilization: acidify extracts with ~1% (v/v) nitric acid (HNO3) before analysis.
• Analytical methods: suitable for AAS (flame, electrothermal, hydride generation), ICP-AES, ICP-MS or equivalent techniques.
• Quality controls: include reagent blanks, determine water content per ISO 11465, and follow specific handling for organic or reductomorphic horizons (Annexes A & C).
• Calculation: convert blank-corrected extract concentrations to extractable element mass fraction (µg/kg dry matter) using the standard’s calculation procedure.

Applications and Users

ISO 19730 is widely used for:

• Environmental monitoring and baseline studies of trace element mobility.
• Contaminated land assessment and site investigation to estimate the easily soluble fraction of metals and metalloids.
• Agricultural soil testing where soluble trace element fractions inform management decisions.
• Routine analytical laboratories performing standardized soil extraction for regulatory compliance or research.

Typical users include soil scientists, environmental consultants, analytical laboratories, land remediation professionals, and regulatory agencies.

Limitations and Practical Notes

• Results indicate easily soluble fractions, not direct measures of biological availability or total concentrations. Site-specific factors (pH, redox, soil moisture, depth) influence migration and bioavailability.
• Organic-rich or poorly aerated (hydromorphic) soils require special sampling/handling described in the standard.
• Advantages: broad applicability, environmentally friendly spent solution, and low interference in subsequent elemental analysis.

Related Standards

• ISO 11464 - Soil quality - Pretreatment of samples for physico-chemical analyses
• ISO 11465 - Soil quality - Determination of dry matter and water content - Gravimetric method
• ISO 3696 - Water for analytical laboratory use

Keywords: ISO 19730:2008, soil quality, ammonium nitrate extraction, trace elements, extractable metals, soil testing, environmental assessment.