If you formulate or buy car wash chemistry, you have already encountered the chelant question — explicitly in product specifications, or implicitly when foam volume drops and chemical consumption rises in hard water. The four common chelants in active foam formulas — EDTA, NTA, GLDA and MGDA — perform differently on three axes that matter: chelation strength, biodegradability and cost. This guide compares them head-to-head with measurable data.
For broader context on why chelants matter in hard water regions, see our chelating agents in car shampoo for hard water guide. Here we focus on the chemistry-by-chemistry comparison.
Chelation strength — what each binds, at what pH
A chelant’s “strength” is its stability constant (log K) for binding a target metal ion. Higher = stronger.
| Chelant | log K Ca²⁺ | log K Mg²⁺ | log K Fe³⁺ | Effective pH range |
|---|---|---|---|---|
| EDTA | 10.7 | 8.7 | 25.1 | 2–14 |
| NTA | 6.4 | 5.4 | 15.9 | 5–11 |
| GLDA | 5.9 | 5.2 | 11.7 | 5–11 |
| MGDA | 7.0 | 5.8 | 16.5 | 5–13 |
| Citric acid | 4.8 | 3.4 | 11.1 | 2–6 |
Reading this in practice:
- EDTA is the strongest binder across the widest pH range — that is why it dominated for decades. Particularly strong on Fe³⁺ (rust, brake dust complexation).
- MGDA is closest to EDTA for everyday Ca²⁺/Mg²⁺ (the ions that cause hard water problems in car wash). Stable at high pH (alkaline foams up to pH 13).
- GLDA matches MGDA below pH 9, weakens slightly above. Best in eco/mild formulations (working pH 8–9).
- Citric acid is too weak for hard water chelation; useful only in mild acidic rinse products.
The takeaway: for typical car wash use (hard water Ca²⁺/Mg²⁺ at working pH 8–12), MGDA and GLDA are sufficient. EDTA’s extra strength on Fe³⁺ is irrelevant unless you wash heavily corroded vehicles.
Biodegradability — OECD 301B in 28 days
OECD 301B is the international standard for “ready biodegradability” — the percentage of test substance broken down by aerobic bacteria over 28 days under standardised conditions. EU Regulation 648/2004 requires surfactants in detergents to exceed 60% within 28 days; the same test is applied to chelants in regulatory assessments.
| Chelant | Biodegradability (OECD 301B, 28 days) | Regulatory status (2026) |
|---|---|---|
| EDTA | <10% | EU watch list, restricted in Germany industrial detergents |
| NTA | ~40% | REACH carcinogen Cat. 2 — avoided in consumer and most professional formulas |
| GLDA | >60% | Compliant — used in modern eco formulations |
| MGDA | >80% | Compliant — preferred for premium biodegradable products |
| Citric acid | >95% | Compliant — fully biodegradable |
| Phosphonates | <10% | Used in scale prevention; not as primary chelant in modern car wash chemistry |
EDTA persistence is the regulatory problem. It survives wastewater treatment, complexes heavy metals across long distances, and re-mobilises metals from sediments. The EU Water Framework Directive 2000/60/EC has placed EDTA on the watch list; national permits are tightening. Germany already restricts EDTA in industrial detergents.
For closed-loop water recycling installations, the consequence is operational, not just regulatory: EDTA does not break down between cycles, so its concentration rises with every wash. Within 4–6 months it inhibits biological treatment, interferes with UV disinfection, and re-mobilises heavy metals from oil separator sludge.
Cost per kg and per litre of working solution
Prices fluctuate with raw material costs; these are 2026 indicative ranges:
| Chelant | Price per kg (industrial bulk) | Typical dose in car wash | Cost per litre working solution |
|---|---|---|---|
| EDTA | €2.50 – €4.00 | 1–3% in concentrate | €0.025 – €0.12 (in concentrate) |
| NTA | €2.00 – €3.50 | n/a (avoided) | n/a |
| GLDA | €4.50 – €7.00 | 0.8–2.5% (higher efficiency) | €0.036 – €0.175 |
| MGDA | €6.00 – €9.00 | 0.7–2.0% | €0.042 – €0.18 |
| Citric acid | €1.50 – €3.00 | 0.5–3% (acidic rinses only) | €0.0075 – €0.09 |
| Sodium gluconate | €2.50 – €4.50 | 0.3–1.5% (co-chelant) | €0.0075 – €0.0675 |
In practice, modern GLDA/MGDA formulations use slightly less chelant per litre than legacy EDTA formulas because of better formulation. Net end-product cost difference between EDTA-based and GLDA/MGDA-based shampoo is typically 5–15%.
REACH classification and worker safety
| Chelant | REACH classification | Worker safety highlights |
|---|---|---|
| EDTA | Eye irritant Cat. 2; aquatic chronic Cat. 3 | Standard PPE; avoid contact with eyes |
| NTA | Carcinogen Cat. 2; aquatic chronic Cat. 3 | Avoided in modern formulations |
| GLDA | Eye irritant Cat. 2 | Standard PPE; lowest hazard profile of the four |
| MGDA | Eye irritant Cat. 2; skin irritant Cat. 2 | Standard PPE; chronic toxicity studies clean |
| Citric acid | Eye irritant Cat. 2 | Standard PPE |
NTA’s carcinogen classification (REACH Cat. 2 since 2008 update) is why no responsible formulator uses it in 2026. It is the cheapest of the four but the regulatory and reputational risk is unmanageable.
Closed-loop compatibility — chelant accumulation analysis
In a closed-loop water recycling system, 80–90% of process water returns to the wash bays. Chelant introduced with each dose of shampoo partially recirculates. Over many cycles, persistent chelants accumulate.
| Chelant | Cycles to 90% degradation | Accumulation behaviour | Closed-loop verdict |
|---|---|---|---|
| EDTA | >90 cycles (>3 months at typical throughput) | Severe — concentration rises monotonically | Not recommended |
| NTA | ~30 cycles | Moderate accumulation | Avoided (REACH) |
| GLDA | ~10 cycles | Mild — reaches steady state quickly | Compatible |
| MGDA | ~5–8 cycles | Minimal — biodegrades faster than recirculation | Preferred |
| Citric acid | ~2–3 cycles | None — fully degraded | Compatible (mild rinses) |
Bottom line for closed-loop: MGDA-dominant or GLDA-dominant formulations only. EDTA is incompatible operationally, regardless of regulatory status.
What modern formulations actually use
A summary of chelant choice across product tiers in the EU 2026 car wash chemistry market:
| Product type | Primary chelant | Secondary | Working pH |
|---|---|---|---|
| Premium alkaline (touchless, portal) | MGDA | Sodium gluconate | 11–12 |
| Mid-tier alkaline | MGDA or GLDA | Sodium gluconate | 10–11 |
| Eco / detailing-grade | GLDA | Citric acid | 8–9 |
| Acidic rinse | Citric acid | (standalone) | 2–4 |
| Legacy budget | EDTA | (none) | 9–13 |
Fortis Foam PRO (alkaline, working pH 11.7–12) uses MGDA-dominant chelation with sodium gluconate as a co-chelant for iron and trace metals. Fortis Foam ECO (mild, working pH 8.3–8.5) uses GLDA-dominant chelation with citric acid as a mild secondary chelant. Both are EDTA-free, NTA-free and phosphate-free. Full chelant declaration is on the Safety Data Sheet.
Summary
- EDTA is the strongest chelant but persists in the environment (<10% biodegradation). Phasing out under EU regulations and incompatible with closed-loop water recycling.
- NTA has REACH carcinogen classification — avoided in modern formulations.
- GLDA is a renewable-feedstock aminocarboxylate, biodegradable >60%, optimal at neutral-to-mild-alkaline pH (5–9). The chelant of choice in eco/detailing formulations.
- MGDA is synthetic but biodegrades >80% in 28 days, stable at high pH (>11). The chelant of choice in alkaline touchless and portal car wash formulas.
- Citric acid is a mild fully-biodegradable secondary chelant for acidic rinses; not a hard-water solution on its own.
For practical guidance on chelant selection by water hardness, see chelating agents in car shampoo for hard water guide. For closed-loop ROI calculation including chemistry compatibility, see closed-loop wash water recycling system ROI.
Need the full chelant breakdown for Fortis Foam PRO or Fortis Foam ECO? Request the Safety Data Sheet via our contact form — full declaration sent the same business day.