Biocides and fungicides are the preservatives of water-miscible metalworking fluids, making up less than 2 % by weight of a soluble-oil, semi-synthetic or synthetic concentrate (OECD ESD No. 28, 2011) and holding back the bacteria and fungi that grow in the diluted fluid. Water-miscible products hold about 80 % of the market for metalworking fluids (trade press, Lubes'n'Greases, October 2020).
This reference tracks 17 actives. On 27 October 2026, six hold an EU approval for product type 13 (PT13), two more are approved from 1 June 2027, and the approval of methylene bis-morpholine (MBM) expired on 31 March 2022.
Label doses run from 3.84 ppm active ingredient (a.i.) of CMIT/MIT as a tankside maintenance dose to 1.5 % by weight of ortho-phenylphenol in the diluted concentrate, each from one registered US product.
Standards, regulations and exposure limits are checked against their issuing bodies, product values against the named data sheet, and every figure carries its source and date; see our methodology and fact-checking.
What Do Biocides Do in Metalworking Fluids?#
Biocides keep the water phase of a metalworking fluid, an emulsion at about pH 8 to 9, from being colonized first by aerobic Gram-negative bacteria such as Pseudomonas and later by fungi (Ctgb Evaluation Manual, PT13 chapter, 2013).
Biocides are the preservative class among metalworking fluid additives. Formaldehyde is the active species of the releasers: "The actual antimicrobial agent is formaldehyde (HCHO) which is released from HHT under proper conditions" (US EPA, 2008), and release rises at lower pH and higher temperature. Isothiazolinones such as BIT and MIT react with the thiol groups of microbial proteins.
Bactericides and Fungicides: Why Many Fluids Need Both#
Fungi appeared in 5.6 % of 48,695 in-use fluid samples tested from 2014 to 2023 and in more than 50 % of 417 residue samples (Pathogens, 2024). Glycol-containing semi-synthetics are more prone to fungal than bacterial attack (Ctgb, 2013).
OIT and IPBC act as fungicides, TCMTB is described as commonly used as one, and sodium pyrithione acts on fungi and bacteria, while HHT, MBM and BIT work as bactericides. Under a heavy bacterial load, DGUV Information 209-051 advises a bactericide first, or a bactericide plus an iodocarbamate, because bacteria degrade iodocarbamates such as IPBC.
Formaldehyde Releasers, Isothiazolinones and Other Chemistries#
Formaldehyde releasers are the largest of the six chemistry groups used here, and HHT is the most common formaldehyde-condensate microbicide in metalworking fluids, according to the trade press (Lubes'n'Greases, 2020). This reference groups the 17 actives into six chemistry groups:
- Formaldehyde releasers: HHT, HPT, MBM, MBO, EDHO and DMO.
- Isothiazolinones: BIT, BBIT, MIT, CMIT/MIT and OIT.
- Phenolics: OPP, NaOPP and chlorocresol.
- Iodocarbamates: IPBC.
- Pyrithiones: sodium pyrithione.
- Benzothiazoles: TCMTB.
Which Biocide Actives Are Used in Metalworking Fluids?#
Seventeen actives appear in metalworking fluid labels, regulation and studies in this reference, from triazine (HHT) and BIT to sodium pyrithione and TCMTB, with EU statuses from approved to expired. Each label treat rate in the table belongs to one US product, named in its cell, study values are marked as studies, and no generic industry treat-rate range is verified.
The table compares the 17 actives by CAS number, label dose, fluid types, main limitation and EU PT13 status on 27 October 2026.
| Substance | CAS | Treat rate with basis (source) | Fluid types | Key limitation | Regulatory flag (EU PT13, 2026-10-27) |
|---|---|---|---|---|---|
| Triazine (HHT) | 4719-04-4 | 0.15 % product in the use dilution, about 1,180 ppm HHT, or 3 % product in a concentrate used at 5 % (Grotan label, EPA Reg. No. 365-76) | soluble oil, semi-synthetic, synthetic (label scope) | not below pH 7; avoid prolonged exposure above 52 °C (125 °F); releases formaldehyde | under review, decision pending |
| HPT (covered on the triazine page) | 25254-50-6 (EU evaluates a UVCB without CAS) | no label rate in this reference | metalworking fluids handled by industrial or professional users (EU condition) | candidate for substitution; only Member States meeting Art. 5(2)(c) | approved from 2027-06-01 to 2032-05-31 (Impl. Reg. (EU) 2026/373) |
| Methylene bis-morpholine (MBM) | 5625-90-1 | 1,000 to 2,000 ppm product in the end-use fluid, added only through the concentrate (Contram ST-1 label, EPA Reg. No. 52484-3) | soluble oil, semi-synthetic | US label: closed or semi-enclosed machines only, no tankside use; releases formaldehyde and morpholine | approval expired 2022-03-31 |
| Oxazolidine biocides (MBO) | 66204-44-2 (EU evaluates a UVCB without CAS) | no label rate in this reference; MIC below 0.05 % against M. chelonae and M. immunogenum (Steinhauer 2008) | semi-synthetic (study) | highest mean sensitization among MWF formaldehyde releasers, 4.0 % (de Groot 2010) | approved from 2027-06-01 to 2032-05-31 (Impl. Reg. (EU) 2026/385) |
| EDHO (covered on the oxazolidines page) | 7747-35-5 | no label rate in this reference | not stated | formaldehyde releaser | under review, decision pending |
| 4,4-Dimethyloxazolidine (DMO) (covered on the oxazolidines page) | 51200-87-4 | no label rate in this reference | not stated | formaldehyde releaser | |
| Benzisothiazolinone (BIT) | 2634-33-5 | 0.05 to 0.25 % of a 20 % product in emulsions (100 to 500 ppm BIT); at most 3.0 % of that product in the concentrate, about 0.6 % BIT (Bioban BT 20 AS label, EPA Reg. No. 464-8151) | soluble oil, semi-synthetic | weaker on Pseudomonas and fungi (STLE TLT 2015) | approved 2026-10-01 to 2036-09-30 (Impl. Reg. (EU) 2025/929) |
| BBIT (covered on the BIT page) | 4299-07-4 | 50 ppm tested in a 5 % (w/w) emulsion against fungi, no label rate (Pathogens 2024) | emulsion (study) | effect limited and fluid-dependent in that study | under review, decision pending |
| Methylisothiazolinone (MIT) | 2682-20-4 | no label rate in this reference | semi-synthetic | EU: semi-automated or automated loading; difficult to stabilize in MWF (STLE TLT 2015) | approved, expiry 2029-03-31 (Impl. Dec. (EU) 2026/2127) |
| CMIT/MIT 3:1 (covered on the MIT page) | 55965-84-9 | tankside 256 ppm of a 1.5 % product (3.84 ppm a.i.) every 4 weeks; fouled systems 500 to 1,167 ppm product (7.5 to 17.5 ppm a.i.) (Kathon 886 MW 1.5 % label, EPA Reg. No. 707-134) | soluble oil, semi-synthetic | EU: not used in MWF at a concentration triggering skin-sensitizer classification (0.0015 %, 15 ppm a.i.) unless it can be demonstrated that risks can be reduced to an acceptable level by other means; quenched by organic soiling (Steinhauer 2008) | approved to 2027-06-30 (Impl. Reg. (EU) 2016/131); no renewal or postponement act in the OJ as of 2026-10-27 |
| Octylisothiazolinone (OIT) | 26530-20-1 | 55 to 167 ppm product (25 to 75 ppm OIT) in use (Kathon 893 MW label, EPA Reg. No. 707-195) | soluble oil, semi-synthetic, synthetic | label: not for foaming systems or high tramp oil | under review, decision pending |
| Iodopropynyl butylcarbamate (IPBC) | 55406-53-6 | up to 2,500 ppm product (0.25 % v/v; 2.5 L per 1,000 L, 1 US qt per 100 US gal), up to 1,000 ppm IPBC, in the use dilution (Filmguard IPBC 40 label, EPA Reg. No. 464-8124) | semi-synthetic, soluble oil | degraded by bacteria under heavy load (DGUV 209-051); EU: semi-automated or automated loading | approved, expiry 2029-05-31 (Impl. Dec. (EU) 2026/2124) |
| Sodium pyrithione | 3811-73-2 | tankside 125 to 1,250 ppm product every 7 to 10 days; 188 to 1,250 ppm product in end use via the concentrate (Sodium Omadine 40 % label, EPA Reg. No. 6836-432) | semi-synthetic, synthetic | label footnote on concentrate use: "Not approved for use in California" | under review, decision pending |
| ortho-Phenylphenol (OPP) | 90-43-7 | 0.1 to 1.5 % by weight of the diluted concentrate, added to the emulsifiable oil concentrate during formulation (Dowicide 1E label, EPA Reg. No. 464-126) | soluble oil | EU: safe operational procedures and PPE for industrial or professional users | approved to 2027-06-30 (Impl. Reg. (EU) 2016/105); no postponement act in the OJ as of 2026-10-27 |
| Sodium o-phenylphenate (NaOPP) (covered on the OPP page) | 132-27-4 | 0.05 to 0.5 % by weight in the diluted fluid (Dowicide A label, EPA Reg. No. 464-78) | soluble oil | water-soluble salt of OPP | not available: absent from the 2022 review list |
| Chlorocresol (PCMC) | 59-50-7 | no label rate in this reference | semi-synthetic (study, Selvaraju 2011) | no verified label dose | approved 2018-05-01 to 2028-04-30 (Impl. Reg. (EU) 2016/1931) |
| TCMTB (section on this page) | 21564-17-0 | no absolute dose verified; field trials needed 2 to 4 times the lab dose where biofilm was established (Wiatr, Cribbs and French, 2026) | semi-synthetic (field trials) | non-oxidizing; described as commonly used as a fungicide |
How Much Biocide Goes Into a Metalworking Fluid?#
Labels give biocide doses as ppm of product or active in the diluted fluid, or as percent of product in the concentrate, such as 0.15 % triazine product in the use dilution, about 1,180 ppm HHT (Grotan label, EPA Reg. No. 365-76). The BIT label sets 100 to 500 ppm BIT in an emulsion (Bioban BT 20 AS label, EPA Reg. No. 464-8151). The OECD bound of less than 2 % of the concentrate is the only class-wide figure.
The table lists what each label allows in the concentrate and in the diluted fluid.
| Active and product label | Into the concentrate | Into the diluted fluid (tankside) |
|---|---|---|
| HHT, Grotan (EPA Reg. No. 365-76) | 3 % product in a concentrate used at 5 % | 0.15 % product, 1.5 L per 1,000 L (1.2 US pints per 100 US gal) |
| MBM, Contram ST-1 (52484-3) | C (ppm) = a × 100 / b for 1,000 to 2,000 ppm product in use | not permitted: "Do not apply this product directly to the end-use fluids" |
| BIT, Bioban BT 20 AS (464-8151) | at most 3.0 % of the 20 % product | 0.05 to 0.25 % of the 20 % product in emulsions |
| CMIT/MIT, Kathon 886 MW 1.5 % (707-134) | metering pump; 256 ppm product every 4 weeks, or 256 to 1,167 ppm every 8 to 12 weeks | |
| OIT, Kathon 893 MW (707-195) | enough for 55 to 167 ppm product in use | initial 55 to 167 ppm product; maintenance 11 to 67 ppm product every 4 weeks |
| IPBC, Filmguard IPBC 40 (464-8124) | 0.5 % product for 250 ppm product at 5 % dilution | up to 2,500 ppm product |
| NaPT, Sodium Omadine 40 % (6836-432) | 2.5 % for 1,250 ppm product at 5 % dilution | 125 to 1,250 ppm product every 7 to 10 days; re-dose at bacteria 10^7/mL or fungi 10^3/mL |
| OPP, Dowicide 1E (464-126) | 0.1 to 1.5 % by weight, added during formulation | |
| NaOPP, Dowicide A (464-78) | before dilution, as concentrated aqueous solution | 0.05 to 0.5 % by weight in the diluted fluid |
In the Concentrate or Tankside: Two Dosing Routes#
MBM goes only into the concentrate, at C (ppm) = a × 100 / b, where a is the target ppm in use and b the dilution in percent (Contram ST-1 label, EPA Reg. No. 52484-3). A target of 1,500 ppm at 5 % dilution needs 1,500 × 100 / 5 = 30,000 ppm (3.0 %) in the concentrate.
Tankside labels dose the sump directly: CMIT/MIT by metering pump (EPA Reg. No. 707-134), sodium pyrithione every 7 to 10 days (EPA Reg. No. 6836-432). Arbitrary tankside additions carry substantial risk without supervision by a chemist familiar with the original formulation (Gresham, STLE TLT, September 2006).
When Should Biocide Be Added to Coolant?#
Add biocide only after concentration, pH, tramp oil, metal contamination, temperature, agitation and flow are corrected, then dose at a point of high turbulence (HSE MW5, 03/21). The UKLA/HSE Good Practice Guide v2.5 (February 2025) adds: dose into a full sump, record every addition, and avoid overuse, which may cause dermatitis, asthma and resistance. At 10^4 to below 10^6 CFU/mL, HSE advises adding the supplier's dose if growth continues (HSE, updated 4 December 2024).
A biocide does not restore a fluid: degraded components, metabolites and dead biomass remain, and shock dosing releases biomass that blocks filters, plus endotoxin (DGUV Information 209-051). Testing and control of bacteria in coolant come first.
Biofilm, Mycobacteria and TCMTB: Where Standard Dosing Falls Short#
Biocides dosed in the concentrate or tankside had a negligible effect on established laboratory biofilms, and Morganella morganii adapted to high MIT and BIT (von Känel et al., Life, 2025).
Mycobacterium immunogenum was 2 to 1,600 times more resistant than Pseudomonas fluorescens (Selvaraju, 2011), and triazine and methyloxazolidine reached MICs below 0.05 % against mycobacteria (Steinhauer, 2008). TCMTB was the most effective of four non-oxidizing biocides in a 72-hour laboratory challenge, yet field trials at 9 plants needed 2 to 4 times the laboratory dose where biofilm was established (Wiatr, Cribbs and French, 2026). No absolute TCMTB dose is verified here.
Which Biocide Suits Which Fluid Type and Operating Condition?#
The label and the EU approval set each active's operating window: triazine (HHT) is not for fluids below pH 7 or prolonged exposure above 52 °C (125 °F) (Grotan label, EPA Reg. No. 365-76). MBM is limited to closed or semi-enclosed machines (Contram ST-1 label), and MIT under EU PT13 needs semi-automated or automated loading.
The table matches fluid types and operating conditions to the label or EU approval.
| Condition | What the label or EU approval says | Actives concerned |
|---|---|---|
| Soluble oils | OPP added to the emulsifiable concentrate during formulation (Dowicide 1E label); BIT 100 to 500 ppm in emulsions (Bioban BT 20 AS label) | OPP, BIT |
| Semi-synthetic fluids | glycol-containing semi-synthetics lean toward fungal attack, so a fungicide is common (Ctgb, 2013) | OIT, IPBC, NaPT |
| Synthetic fluids | label scope includes synthetics; HHT pH must stay at or above 7 | HHT, OIT, NaPT |
| Fluid pH below 7 | HHT label: not suitable | HHT |
| Sump above 52 °C (125 °F) for long periods | HHT label: avoid | HHT |
| Open machines, manual tankside dosing | MBM label: closed or semi-enclosed machines only, concentrate only | MBM |
| EU, manual loading | MIT and IPBC: semi-automated or automated loading unless risks shown acceptable | MIT, IPBC |
| EU, in-use concentration of CMIT/MIT | not at a concentration triggering skin-sensitizer classification (0.0015 %, 15 ppm a.i.), unless it can be demonstrated that risks can be reduced to an acceptable level by other means | CMIT/MIT |
| Foaming system or high tramp oil | OIT label: not recommended | OIT |
| Heavy bacterial load plus fungi | bactericide first, or bactericide plus iodocarbamate (DGUV 209-051) | IPBC with a bactericide |
BIT is very stable in metalworking fluids while MIT is difficult to stabilize (STLE TLT, November 2015), and organic soiling quenches CMIT (Steinhauer, 2008). The OIT label advises against foaming systems and high tramp oil.
What Is the Approval Status of Each Biocide Active?#
On 27 October 2026, six actives hold an EU approval for PT13 (BIT, MIT, CMIT/MIT, IPBC, ortho-phenylphenol and chlorocresol), and HPT and MBO are approved from 1 June 2027.
Act-by-act detail, including US registration, sits in biocide approval for metalworking fluids. Every status below is a snapshot on 27 October 2026.
European Union: Approved, Pending and Expired PT13 Actives#
BIT is approved for PT13 from 1 October 2026 to 30 September 2036 by Implementing Regulation (EU) 2025/929. The expiry of MIT and IPBC was postponed on 24 September 2026 to 31 March 2029 and 31 May 2029 (Implementing Decisions (EU) 2026/2127 and 2026/2124). CMIT/MIT and ortho-phenylphenol are approved to 30 June 2027, and their renewal is pending. CMIT/MIT labels and safety data sheets must state no use in metalworking fluids at a concentration triggering skin-sensitizer classification, unless it can be demonstrated that risks can be reduced to an acceptable level by other means (Implementing Regulation (EU) 2016/131).
The table sets out each active's PT13 status.
| Active | Status | Act | Dates | Condition for MWF |
|---|---|---|---|---|
| BIT | approved | Impl. Reg. (EU) 2025/929 of 2025-05-21 | 2026-10-01 to 2036-09-30 | attention to professional users, surface water, sewage plants, sediment |
| MIT | approved | Impl. Reg. (EU) 2015/1726; expiry postponed by Impl. Dec. (EU) 2026/2127 of 2026-09-24 | 2016-10-01 to 2029-03-31 | automated or semi-automated loading and machines unless risks shown acceptable |
| CMIT/MIT 3:1 | approved | Impl. Reg. (EU) 2016/131 | 2017-07-01 to 2027-06-30; no renewal or postponement act in the OJ as of 2026-10-27 (pending) | labels and SDS state no use in MWF at a concentration triggering skin-sensitizer classification (0.0015 %, 15 ppm a.i.), unless it can be demonstrated that risks can be reduced to an acceptable level by other means |
| IPBC | approved | Impl. Reg. (EU) 2015/1728; expiry postponed by Impl. Dec. (EU) 2026/2124 of 2026-09-24 | 2016-12-01 to 2029-05-31 | semi-automated or automated loading unless risks shown acceptable |
| ortho-Phenylphenol | approved | Impl. Reg. (EU) 2016/105 | 2017-07-01 to 2027-06-30; no renewal or postponement act in the OJ as of 2026-10-27 (pending) | safe operational procedures and PPE for industrial or professional users |
| Chlorocresol | approved | Impl. Reg. (EU) 2016/1931 | 2018-05-01 to 2028-04-30 | attention to professional users |
| HPT (RP 1:1) | approved from 2027-06-01 | Impl. Reg. (EU) 2026/373 of 2026-02-20 | 2027-06-01 to 2032-05-31 | candidate for substitution; industrial or professional MWF only; Art. 5(2)(c) Member States |
| MBO (RP 3:2) | approved from 2027-06-01 | Impl. Reg. (EU) 2026/385 of 2026-02-20 | 2027-06-01 to 2032-05-31 | as HPT |
| HHT, OIT, sodium pyrithione, EDHO, BBIT | under review, decision pending | Del. Reg. (EU) No 1062/2014 Annex II (entries 377, 571, 365, 444, 791) | none | national Art. 89 transitional rules apply |
| MBM | expired | Impl. Reg. (EU) 2015/1981 | 2017-04-01 to 2022-03-31 | none in force |
| NaOPP | not available | absent from the 2022 Annex II list | none | none |
| MBIT | not approved | Impl. Dec. (EU) 2017/1282 | none | unacceptable environmental risks |
HPT and MBO are candidates for substitution. Five actives are under review, decision pending. Sodium o-phenylphenate is absent from the 2022 review list, and MBIT was refused by Implementing Decision (EU) 2017/1282 for unacceptable environmental risks.
Is MBM Still Approved in the EU?#
No: the PT6 and PT13 approval of formaldehyde released from N,N'-methylenebismorpholine ran from 1 April 2017 to 31 March 2022 under Implementing Regulation (EU) 2015/1981, and no renewal or postponement act appears in the Official Journal. In the US, MBM has been registered since 7 November 2011 for concentrates used in closed or semi-enclosed machines (Contram ST-1, EPA Reg. No. 52484-3).
United States: EPA Registration and the Product Label#
The OSHA Metalworking Fluids Best Practices Manual says biocides used in fluids and as sump-side additives should be EPA-registered for metalworking fluid use. Each registered product carries its dose on its label.
A listed registration is not a dose recommendation. MBO is registered as Stabicide 71 (EPA Reg. No. 95475-2, active since 23 July 2013), and this reference holds no statement on its metalworking fluid directions.
What Hazards Do Metalworking Fluid Biocides Carry?#
MIT (613-326-00-9), CMIT/MIT (613-167-00-5) and OIT (613-112-00-5) carry harmonized CLP lines with Acute Tox. 2 (inhalation) H330 and Skin Sens. 1A H317. IPBC (616-212-00-7) is scheduled to move from Acute Tox. 3 H331 to Acute Tox. 2 H330 on 1 February 2027 (ATP23).
Among the formaldehyde releasers, MBO shows the highest mean sensitization in metalworkers, 4.0 % (de Groot, 2010), as covered under allergic skin reactions to metalworking fluids.
The table lists the harmonized CLP lines with Annex VI index and ATP.
| Active | Annex VI index and ATP | Classification |
|---|---|---|
| MIT | 613-326-00-9 (ATP13, applicable since 2020-05-01) | Acute Tox. 2 (inhalation) H330, Acute Tox. 3 (dermal) H311, Acute Tox. 3 (oral) H301, Skin Corr. 1B H314, Eye Dam. 1 H318, Skin Sens. 1A H317 (SCL 0.0015 %), Aquatic Acute 1 H400, Aquatic Chronic 1 H410, EUH071 |
| CMIT/MIT 3:1 | 613-167-00-5 (ATP13, applicable since 2020-05-01) | Acute Tox. 2 (inhalation) H330, Acute Tox. 2 (dermal) H310, Acute Tox. 3 (oral) H301, Skin Corr. 1C H314, Eye Dam. 1 H318, Skin Sens. 1A H317 (SCL 0.0015 %), Aquatic Acute 1 H400, Aquatic Chronic 1 H410 |
| OIT | 613-112-00-5 (ATP15, applicable since 2022-03-01) | Acute Tox. 2 (inhalation) H330, Acute Tox. 3 (dermal) H311, Acute Tox. 3 (oral) H301, Skin Corr. 1 H314, Eye Dam. 1 H318, Skin Sens. 1A H317 (SCL 0.0015 %), Aquatic Acute 1 H400, Aquatic Chronic 1 H410, EUH071 |
| IPBC | 616-212-00-7 (ATP06 until 2027-01-31; ATP23 from 2027-02-01) | Acute Tox. 3 (inhalation) H331, Acute Tox. 4 (oral) H302, STOT RE 1 H372 (larynx), Eye Dam. 1 H318, Skin Sens. 1 H317, Aquatic Acute 1 H400, Aquatic Chronic 1 H410; from 2027-02-01 Acute Tox. 2 (inhalation) H330 replaces H331 |
| HHT | 613-114-00-6 (original Annex VI list, applicable since 2010-12-01) | Acute Tox. 4* H302, Skin Sens. 1 H317 (SCL 0.1 %) |
| HPT | 612-291-00-7 (ATP10, applicable since 2018-12-01) | Carc. 1B H350, Muta. 2 H341, Acute Tox. 4 H332, Acute Tox. 4 H302, STOT RE 2 H373, Skin Corr. 1C H314, Eye Dam. 1 H318, Skin Sens. 1A H317, Aquatic Chronic 2 H411, EUH071; Notes 8 and 9 |
| MBM | 607-721-00-5 (ATP10, applicable since 2018-12-01) | Carc. 1B H350, Muta. 2 H341; further codes: see the product SDS; Notes 8 and 9 |
| TCMTB | 613-119-00-3 (original Annex VI list, applicable since 2010-12-01) | Acute Tox. 2* (inhalation) H330, Acute Tox. 4* (oral) H302, Skin Irrit. 2 H315, Eye Irrit. 2 H319, Skin Sens. 1 H317, Aquatic Acute 1 H400, Aquatic Chronic 1 H410 |
| EDHO, BBIT | no Annex VI entry | see the product SDS |
HHT (613-114-00-6) carries no carcinogen class, while HPT (612-291-00-7) and MBM (607-721-00-5) are Carc. 1B H350 and Muta. 2 H341 under ATP10.
EDHO and BBIT have no Annex VI entry; the product SDS governs. Symptoms in a worker are a matter for an occupational physician.
Formaldehyde Release and the Carc. 1B Mixture Rule#
Notes 8 and 9 on the Annex VI entries of MBM, MBO and HPT lift the Carc. 1B classification only below 0.1 % releasable formaldehyde in the mixture, and Muta. 2 only below 1 % (Delegated Regulation (EU) 2017/776). The notes apply since 1 December 2018, and the HHT entry carries none. Test and limits for formaldehyde-releasing biocides have their own page.
The OSHA manual advises considering the avoidance of formaldehyde-release biocides in fluid selection. MBM also releases morpholine, a secondary amine relevant to German nitrosamine rules (TRGS 611).
What Are the Alternatives to Conventional Biocides?#
Biostable fluids, bioconcept fluids, ozone treatment and nutrient limitation are the documented alternatives to dosing biocides, each with its own trade-off. Biostable fluids carry a premium of up to 10 %, which, per the same source, is recovered in most cases (Enright, STLE TLT, November 2015).
Bioconcept fluids hold "non-pathogenic waterborne bacteria", contain no biocide and need closely managed pH and concentration (HSE, updated 23 December 2024). Ozone cut viable microorganisms in a band-saw fluid by more than 95 %, while pH fell from 9 to 8 (Materials, 2025).
Lanthanum oxide above 0.08 % w/w stopped growth in a laboratory fluid, from 1.4 × 10^7 CFU/mL to zero (PubMed 28426217).
How Are Biocides Specified and Sourced for a Formulation?#
A biocide specification names the active and its content, the dosing route, the fluid type and the market of sale, because the EU approves actives by product type and the US registers each product. Its five items are listed below.
- Active and content, for example a 20 % BIT or 1.5 % CMIT/MIT product.
- Dosing route: concentrate or tankside.
- Fluid type and dilution.
- Market: EU PT13 status, US EPA Reg. No.
- Test basis: the ASTM E2169 selection practice and the ASTM E2275 bioresistance test.
ASTM E2275-24 results compare products within one test series and do not predict field performance; E2169-22 is the selection practice. EU authorization accepts robust in-house methods instead of ASTM (Ctgb, 2013).
Where Do Biocides Sit Among Metalworking Fluid Additives?#
Biocides are the preservative class among metalworking fluid additives, held below 2 % of the concentrate, and the only class whose actives need an EU product-type approval or a US pesticide registration.
This reference groups metalworking fluid additives into classes, and biocides are the one that acts on organisms rather than on metal or emulsion. Several of the same actives also preserve water and process fluids in other industries, which this reference does not cover.
Metalworking Fluid Biocides: Frequently Asked Questions#
The four questions below cover what machine shops and formulators ask most about biocides in metalworking fluids.
What Is a Tankside Additive?#
A tankside additive is dosed into the diluted fluid in the sump rather than into the concentrate; STLE names biocides and anti-mist agents for this route. Unsupervised additions carry substantial risk (Gresham, STLE TLT, 2006).
What Can Be Added to CNC Coolant to Stop Bacteria?#
Correct concentration, pH and tramp oil first (HSE MW5, 03/21), then dose a biocide registered or approved for metalworking fluids at its label rate. One example is 256 ppm of a 1.5 % CMIT/MIT product every 4 weeks (Kathon 886 MW 1.5 % label, EPA Reg. No. 707-134). The OSHA manual treats odor as a cause to address, not to mask.
Does a Biocide Fix Rancid Coolant?#
No: a biocide leaves degraded components, metabolites and dead biomass in the fluid (DGUV Information 209-051). At 10^6 CFU/mL or more, HSE calls for immediate action, normally draining and cleaning.
Do MQL Oils Need a Biocide?#
No: microbes grow only in an aqueous phase, so minimum quantity lubrication oils need no biocide (DGUV Information 209-024).
Consumption and systems of minimum quantity lubrication (MQL) oils follow from that oil-only design.