Major and Trace Elements

Major elements (Ca, Mg, Na, K, Fe, Mn and Al, Si, P, S) describe the geochemical matrix of a sample; trace elements (As, Sb, Cr, Cu, Zn, Pb, Cd, Ni, Co, U, Mo, Se) are standard markers for contamination or specific signatures. IsoFind stores these in the sample_geochem table with automatic normalization to mg/kg, supports a dozen native units, and provides dedicated visualization in the Geochemistry tab of a sample. This page describes the data structure, unit conventions, accepted analytical methods, and typical elements tracked.

Measurement Structure in sample_geochem

Each elemental measurement is a row in the sample_geochem table. It carries both the native value (as provided by the laboratory) and the normalized value in mg/kg used for calculations and inter-sample comparisons.

Field	Content
sample_id	Sample identifier (foreign key to samples)
element	Chemical symbol (stored in uppercase: CR, FE, AS, SB...)
display_value	Native value as entered or imported
display_unit	Native unit (mg/kg, mg/L, µg/L, ppm, ppb, pct...)
value_normalized	Value converted to mg/kg (or aqueous matrix equivalent)
display_uncertainty	Analytical uncertainty in mg/kg
method	Analytical method (ICP-MS, ICP-OES, AAS, XRF, IC...)
lod, loq	Detection and quantification limits specific to the measurement

The dual native and normalized value is a deliberate design choice. The native value allows for faithful reproduction of laboratory reporting in outputs, while the normalized mg/kg value is used for calculations, averages, maps, and visualizations. Users always see the unit that makes sense for their field without losing traceability.

Supported Native Units

The interface accepts the most common units in environmental geochemistry. The conversion engine recognizes standard synonyms (ppm = mg/kg for solids, mg/L for aqueous) and automatically switches to internal normalization.

Category	Accepted Units	mg/kg Equivalence
Solid matrix (soil, sediment, rock)	mg/kg, µg/g, ppm	1:1
Solid matrix (ultra-trace)	µg/kg, ng/g, ppb	÷ 1,000
Solid matrix (concentrated major)	g/kg, mg/g	× 1,000
Solid matrix (percentage)	pct, %	× 10,000
Aqueous matrix	mg/L	Maintained as mg/L equivalent
Aqueous matrix (trace)	µg/L, ppb	÷ 1,000 in mg/L equivalent
Aqueous matrix (ultra-trace)	ng/L, ppt	÷ 1,000,000

The engine logic is coded in prediction_routes.py: for each measurement, the unit is cleaned (lowercase, trim) then tested against mg, ug patterns and their synonyms. Unknown units are used as-is without conversion, preventing silent corruption of legacy or atypical data.

Percentage (pct) is common for major elements in geology (CaO 12.5 pct, Fe₂O₃ 4.8 pct). Be careful with the distinction between element percentage and oxide percentage: a result reported as "CaO 12.5%" must be converted to elemental Ca (Ca = CaO × 40.08 / 56.08 = 71.5% of the CaO). IsoFind does not perform this conversion automatically and stores the value as reported by the lab. For transfer to diagnostics, the conversion must be done prior to data entry.

Typically Tracked Major Elements

Major elements generally represent more than 0.1% (1,000 mg/kg) of the matrix. They qualify the lithological context of the sample and serve as denominators for diagnostic ratios.

Element	Typical Role	Standard Method
Ca (calcium)	Calcareous matrix, water hardness, pH buffer	ICP-OES, XRF
Mg (magnesium)	Dolomite, micas, diagnostic Ca/Mg ratio for origin	ICP-OES
Na (sodium)	Salinity, feldspars, saline contamination	ICP-OES, Flame Emission
K (potassium)	Clays, micas, potash fertilizers	ICP-OES, Flame Emission
Fe (iron)	Redox state (Fe(II) vs Fe(III)), oxyhydroxides	ICP-MS, ICP-OES, AAS
Mn (manganese)	Natural oxidant, redox couple with Fe	ICP-MS, ICP-OES
Al (aluminum)	Clays, weathering indicator	ICP-OES, XRF
Si (silicon)	Quartz, silicates, XRF reporting only	XRF (ICP difficult)
P (phosphorus)	Apatites, fertilizers, anthropogenic indicator	ICP-OES, Colorimetry
S (sulfur)	Sulfides, sulfates, redox	ICP-OES, LECO Combustion

Standard Traces in Environmental Forensics

Trace elements are preferred markers for anthropogenic contamination or specific geological signatures. Their detection thresholds range from µg/kg to ng/kg. The table below covers the elements most frequently used in IsoFind cases, their role, and their presence in the isotopic engine.

Element	Forensic Role	CSIA Nexus	Typical Magnitude
As (arsenic)	Mining pollution, wood treatment, legacy pesticides	Yes (δ⁷⁵As)	0.1 to 100 mg/kg soil
Sb (antimony)	Mining, munitions, flame retardants	Yes (δ¹²³Sb)	0.01 to 50 mg/kg soil
Cr (chromium)	Tannery, chrome plating, stainless steel	Yes (δ⁵³Cr)	1 to 500 mg/kg soil
Cu (copper)	Metallurgy, vineyards (Bordeaux mixture)	Yes (δ⁶⁵Cu)	1 to 200 mg/kg soil
Zn (zinc)	Galvanization, batteries, sulfide mines	Yes (δ⁶⁶Zn)	10 to 1,000 mg/kg soil
Pb (lead)	Legacy fuels, munitions, soldering	Yes (²⁰⁶/²⁰⁷/²⁰⁸ Pb ratios)	5 to 500 mg/kg soil
Cd (cadmium)	Phosphate fertilizers, Ni-Cd batteries, PVC	No (without redox)	0.1 to 20 mg/kg soil
Ni (nickel)	Stainless steel, ultrabasic rocks	No	1 to 100 mg/kg soil
Co (cobalt)	Batteries, superalloys, nickel co-products	No	0.5 to 30 mg/kg soil
U (uranium)	Nuclear industry, phosphates, natural background	Via Nexus (δ²³⁸U)	0.5 to 10 mg/kg soil
Mo (molybdenum)	Alloy steels, mines, fertilizers	Yes (δ⁹⁸Mo)	0.1 to 5 mg/kg soil
Se (selenium)	Coal, agricultural irrigation, supplements	Yes (δ⁸²Se)	0.1 to 5 mg/kg soil

Orders of magnitude are indicative benchmarks for non-contaminated to moderately contaminated soils. Beyond these, a specific assessment of the study area and local geological background is necessary to correctly interpret the values.

Recognized Analytical Methods

IsoFind does not impose a specific analytical method; the method field is a free-text string provided by the user. Recognized methods cover standard practices in specialized environmental geochemistry laboratories.

Method	Primary Usage	Typical Detection Limit
ICP-MS	Traces and ultra-traces, multi-element	0.001 to 0.1 µg/L (aqueous), µg/kg (solid)
ICP-OES (ICP-AES)	Majors and classic traces, multi-element	0.01 to 1 mg/L (aqueous), 1 to 10 mg/kg
AAS (Flame)	Single-element, historical method	0.01 to 1 mg/L depending on element
AAS (Graphite Furnace)	Metallic traces, single-element	0.1 to 10 µg/L
XRF	Solids, majors, non-destructive	10 to 100 mg/kg
Ion Chromatography (IC)	Inorganic anions in solution (NO₃⁻, SO₄²⁻, PO₄³⁻)	0.01 to 0.1 mg/L
HG-AFS / HG-AAS	Arsenic, selenium, antimony via hydride generation	0.1 µg/L
MC-ICP-MS	High-precision isotopic measurements	Specific to each isotopic system

Presentation in the Geochemistry Tab

The Geochemistry tab of a sample presents all elemental measurements in four complementary forms. Each form addresses a distinct question the user might have about the data.

Visualization	Question Answered	Format
Measurement Table	Which elements do I have for this sample?	Filterable list by element, with native and mg/kg values
Bar Chart	What are the median concentrations?	Log-scale bar chart, median concentration per element
Coverage Map	Which elements are best represented in the project?	Horizontal bars showing the number of measurements per element
Breakdown by Method	Which methods were used for these measurements?	Doughnut chart: ICP-MS / ICP-OES / AAS / others

Charts are generated using Chart.js and respond to the element filter at the top of the page. Filtering for Cr refreshes the median, count, and distribution for chromium measurements only. CSV export is available at any time via the Export button in the filter bar.

Import and Quick Entry

Geochemical measurements enter IsoFind through three primary routes. Each route passes through the universal CSV parser which recognizes the two classic orientations.

Entry Route	Expected Format	Behavior
Manual Entry	Element-by-element add modal	Form with element dropdown, value, unit, and method
Long Format CSV Import	One row per measurement (sample_id, element, value, unit)	Direct mapping, automatic detection by semantic resolver
Wide Format CSV Import	One column per element, one row per sample	Parser automatically unpivots to long format

For wide format, accepted column names are flexible: Cr, Cr_mg_kg, Cr (mg/kg), chrome, Chromium. The parser's semantic resolver identifies both the chemical symbol and the unit embedded in the column header.

For fast import, keep the CSV in wide format with clear header conventions like Cr_mg_kg, As_mg_kg, Pb_mg_kg. The parser will read both the symbol and unit simultaneously without requiring manual mapping. In case of ambiguity, the import previewer displays the proposed mapping before validation.

Quality and Control of Measurements

Quality control of elemental measurements remains the user's responsibility: IsoFind stores values as provided without validating their plausibility. A few best practices are recommended during import.

Check dimensional consistency: a chromium measurement of 10,000 mg/kg in non-industrial soil is likely a unit error (interpretation as 10 g/kg = 1 pct).
Systematically preserve laboratory LOD and LOQ: values below LOQ can appear in exports with a specific annotation.
Note the method in the method field precisely: "ICP-MS after HNO₃/HF digestion" is better than a simple "ICP".
For oxide percentage measurements (geological XRF), explicitly convert to elemental values before entry.
Avoid entering "< LOD" as a value: use zero or half the LOD depending on project convention, with a note in the notes field.

Integration with Other Views

Geochemical measurements feed into several other parts of IsoFind beyond simple display in the Geochemistry tab.

Destination	Usage of Elemental Measurements
Diagnostic Ratios	Automatic calculation of ratios from concentrations (Pb/Sr, Ca/Mg, Mn/Fe)
Redox Speciation	Total concentration used as a constraint for Cr(VI)/Cr(III) or Fe(II)/Fe(III)
3D Simulation Engine	ML prior input for Cr, isoconcentration calculation
2D Maps and Vertical Profiles	Spatial visualization of concentrations
Report Blocks	Concentration tables, element distribution charts