Pet Safety / Compounds / DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211)

Is DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211) safe for dogs and cats?

Low risk for pets

Unlikely exposure.

What is dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211)?

The IUPAC name is 4,5-dichloro-2-octyl-1,2-thiazol-3-one.

Also known as: 64359-81-5, Kathon 930, dcoit, 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one.

IUPAC name
4,5-dichloro-2-octyl-1,2-thiazol-3-one
CAS number
64359-81-5
Molecular formula
C11H17Cl2NOS
Molecular weight
282.23 g/mol
SMILES
CCCCCCCCN1C(=O)C(=C(S1)Cl)Cl
PubChem CID
91688

Risk for dogs

Low risk

Unlikely exposure.

Risk for cats

Low risk

Unlikely exposure.

Regulatory consensus

3 regulatory and scientific bodies have classified DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211). The classifications differ — that's the data.

AgencyYearClassificationNotes
IMO—Listed in AFS Convention as permitted antifoulant (unlike TBT which is banned)
EU BPR—Approved for Product Type 21 (antifouling). Under review for environmental risk
Japan—Registered for antifouling use. Subject to environmental monitoring requirements

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where pets encounter dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211)

  • Marine Antifouling — Antifouling boat hull paint (Sea-Nine 211), Ship bottom coatings, Marina infrastructure protection
  • Industrial Preservatives — Paint and coating preservative (in-can), Adhesive and sealant preservative, Metalworking fluid biocide
  • Cooling Water — Industrial cooling system biocide

Safer alternatives

Lower-risk approaches that achieve a similar outcome to DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211):

  • Copper-free foul-release coatings
    Trade-offs: Zero point-of-use emissions; shifts emissions to power generation (grid-dependent); lower operating cost; higher capital cost; infrastructure requirements (charging, grid capacity); rapidly improving economics.
    Relative cost: Lower (ingredient elimination)
  • Ultrasonic antifouling
    Trade-offs: Zero point-of-use emissions; shifts emissions to power generation (grid-dependent); lower operating cost; higher capital cost; infrastructure requirements (charging, grid capacity); rapidly improving economics.
    Relative cost: 1.2-2×
  • Tralopyril
    Trade-offs: Alternative approach; specific tradeoffs depend on application context, scale, and regulatory requirements. Full hazard assessment of alternative recommended before adoption to avoid regrettable substitution.
    Relative cost: 1.2-2×

Frequently asked questions

Is dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211) safe for pets?

Unlikely exposure.

What products contain dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211)?

DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211) appears in: Antifouling boat hull paint (Sea-Nine 211) (Marine antifouling); Ship bottom coatings (Marine antifouling); Paint and coating preservative (in-can) (Industrial preservatives); Adhesive and sealant preservative (Industrial preservatives); Industrial cooling system biocide (Cooling water).

Why do regulators disagree about dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211)?

DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211) has been classified by 3 agencies including IMO, EU BPR, Japan, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.

See DCOIT (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one / Sea-Nine 211) in the pets app

Look up products containing dcoit (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one / sea-nine 211), compare to alternatives, and explore the full data record.

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Sources (1)
  1. — expert_curation

Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →