Safety test of disinfectants on dogs and cats

Safety Testing of Disinfectants for Dogs and Cats – Comprehensive Toxicological Assessment for Veterinary, Household and Professional Use in Bulgaria

As an ISO/IEC 17025 accredited contract research laboratory, we offer specialised safety testing services for disinfectant products intended for use on or around companion animals – dogs and cats – serving Bulgarian manufacturers, veterinary clinics, pet care companies, and regulatory compliance teams. Disinfectants, including quaternary ammonium compounds, chlorine‑releasing agents, hydrogen peroxide, peracetic acid, and essential oil‑based formulations, are widely employed in kennels, catteries, veterinary surgeries, grooming salons, and homes. However, the safety of these products for animals must be rigorously established, as dogs and cats exhibit distinct sensitivities to certain chemical classes (e.g., phenols, tea tree oil, and some quaternary ammonium compounds). Our testing protocols assess dermal irritation, ocular irritation, skin sensitisation, acute oral toxicity, inhalation toxicity, and compatibility with the animal skin microbiome, following internationally accepted OECD guidelines and EU regulatory frameworks. All studies are performed in compliance with Directive 2010/63/EU, the Bulgarian Animal Welfare Act, REACH, CLP (Classification, Labelling and Packaging), and Biocidal Products Regulation (EU) 528/2012. Our reports are recognised by the Bulgarian Food Safety Agency (BFSA), the European Chemicals Agency (ECHA), and veterinary product registrars for product authorisation, hazard classification, and label development.

Disinfectant Formulations and Product Types We Evaluate

Our toxicology laboratory handles a broad spectrum of disinfectant products intended for canine and feline exposure. Typical test articles include:

• Kennel and cattery surface disinfectants – for floors, walls, and enclosures
• Veterinary clinic disinfectants – for surgical tables, instruments, and examination areas
• Paw and hoof sanitizers – for routine hygiene and infection prevention
• Grooming salon disinfectants – for baths, cages, and tools
• Household disinfectant sprays and wipes – for furniture, bedding, and floors
• Disinfectant shampoos and topical gels – for direct application to animal skin
• Concentrated liquids and ready‑to‑use formulations – varying dilution requirements
• Natural and essential‑oil based products – with declared low‑toxicity profiles

Acute Dermal Irritation and Corrosion – Skin Compatibility (OECD TG 404)

• Test system and species – We use healthy adult New Zealand White rabbits (males/females) as the standard species for dermal irritation studies, per OECD TG 404. The test substance (0.5 mL or 0.5 g) is applied to a shaved area of intact skin (approx. 6 cm²) on the dorsal surface, covered with a semi‑occlusive dressing for a 4‑hour exposure. A duplicate site may be abraded to evaluate corrosion potential.
• Observation and scoring – At 1, 24, 48, and 72 hours after patch removal, erythema (redness) and oedema (swelling) are scored on a 0‑4 scale. The Primary Irritation Index (PII) is calculated and the substance is classified as non‑irritant, mildly, moderately, or severely irritating/corrosive. For Bulgarian veterinary disinfectants intended for direct skin contact, a PII ≤ 2.0 is typically required.
• Clinical signs and reversibility – All animals are monitored for systemic toxicity (lethargy, salivation, respiratory distress) and skin reactions are followed for up to 14 days to assess reversibility; persistent reactions indicate cumulative irritation potential.
• Histopathological examination – For severe reactions, skin biopsies are taken at the end of the observation period and examined histologically to confirm the nature of tissue damage.

Acute Eye Irritation – Ocular Safety (OECD TG 405, Draize Test)

• Test system and species – New Zealand White rabbits with normal ocular surfaces are used (OECD TG 405). A single dose (0.1 mL or 100 mg) of the disinfectant (at the highest concentration intended for use) is instilled into the conjunctival sac of one eye; the contralateral eye serves as control.
• Observation and scoring – Corneal opacity, iritis, conjunctival redness, and chemosis (swelling) are evaluated at 1, 24, 48, and 72 hours, and on days 7, 14, and 21 if necessary. Each sign is scored (0‑4 for corneal opacity, 0‑3 for iritis, 0‑3 for conjunctival changes). The maximum possible score is 110. Classification: non‑irritating (≤ 15), mildly irritating (15‑25), moderately irritating (25‑50), or severely irritating (> 50).
• Reversibility assessment – If irritation persists beyond 72 hours, observations continue until resolution or until day 21; substances causing irreversible corneal damage are classified as Category 1 (Serious Eye Damage) under CLP (GHS).
• Animal welfare measures – A topical anaesthetic (proparacaine) is applied before instillation to minimise discomfort, and artificial tears are provided as supportive care after assessment.

Skin Sensitisation – Allergic Contact Dermatitis (OECD TG 429, Local Lymph Node Assay – LLNA)

• Test system and species – Female CBA/J mice (8‑12 weeks old) are used for the LLNA, a validated alternative to guinea‑pig sensitisation tests. The method measures lymphocyte proliferation in draining auricular lymph nodes following dermal exposure.
• Dosing and application – The test substance (25 µL) is applied to the dorsal surface of both ears on three consecutive days. A vehicle control group receives the solvent (e.g., acetone/olive oil), and a positive control (e.g., 25 % hexyl cinnamal) is included in each run.
• Assessment of proliferation – On day 5, auricular lymph nodes are collected, single‑cell suspensions are prepared, and proliferation is measured using [³H]‑thymidine incorporation or BrdU flow cytometry. The Stimulation Index (SI) is calculated (treated/control proliferation). An SI ≥ 3.0 indicates a positive sensitisation response.
• Classification – Based on SI values, we classify the disinfectant as strong (SI ≥ 10), moderate (SI 6‑9.9), weak (SI 3‑5.9), or non‑sensitising (SI < 3). For veterinary disinfectants used in frequent contact, an SI < 3 is generally required.

Acute Oral Toxicity – LD₅₀ Determination and GHS Classification (OECD TG 423 / 425)

• Test system and species – Healthy adult Wistar or Sprague‑Dawley rats (males and females) are used for acute oral toxicity studies following the Acute Toxic Class Method (OECD TG 423) or the Up‑and‑Down Procedure (OECD TG 425).
• Dosing and observation – The test substance is administered by oral gavage in a single dose (or divided within 24 hours) at a defined starting dose (e.g., 300 mg/kg body weight). Animals are observed for 14 days for clinical signs (salivation, convulsions, tremors, diarrhoea, lethargy, respiratory changes), body weight changes, and mortality.
• LD₅₀ estimation – The median lethal dose is calculated using maximum likelihood or Probit analysis, and the confidence interval is reported. The substance is classified under GHS (CLP) into Categories 1‑5, from highly toxic (≤ 5 mg/kg) to low toxicity (2 000‑5 000 mg/kg).
• Histopathology and biochemistry – At necropsy, vital organs are examined macroscopically, and blood samples are taken for haematology and serum chemistry (ALT, AST, creatinine, BUN, glucose). Tissue samples are processed for histopathological evaluation when indicated.

Inhalation Toxicity – Acute and Repeated‑Dose Studies (OECD TG 403 / 412 / 413)

• Test system and species – Wistar rats (males and females) are used for acute (4‑hour), sub‑acute (28‑day), and sub‑chronic (90‑day) inhalation toxicity studies in whole‑body or nose‑only exposure chambers with controlled airflow, temperature (22 ± 2 °C), and humidity (50 ± 10 %).
• Test atmosphere generation – The disinfectant is aerosolised or vaporised using a nebuliser or dry‑dust generator to achieve target airborne concentrations (mg/L or ppm), monitored continuously by real‑time particle counters or gas chromatography.
• Exposure protocol – Acute studies expose animals to a single concentration (maximum achievable or at 5 mg/L limit) for 4 hours. Repeated‑dose studies expose animals for 6 hours/day, 5 days/week, for 28 or 90 days at three dose levels (low, mid, high).
• End‑point evaluation – Clinical observations (respiratory rate, cough, nasal discharge, lacrimation, salivation) are recorded daily. Body weight, food and water intake are monitored weekly. At necropsy, lung weights and bronchoalveolar lavage (BAL) fluid are assessed for total cell count, neutrophil percentage, protein content, LDH, and cytokines (IL‑1β, IL‑6, TNF‑α). Lung histopathology (H&E and Masson’s trichrome) is performed to detect bronchiolitis, fibrosis, or granulomas.
• Risk classification – Based on the No Observed Adverse Effect Level (NOAEL) and Lowest Observed Adverse Effect Level (LOAEL), we assign GHS hazard categories for respiratory toxicity (specific target organ toxicity after repeated exposure).

Dermal Absorption and Percutaneous Penetration – Topical Formulations (OECD TG 428)

• Test system and species – We use freshly excised human skin (ethically sourced) or pig skin in Franz‑type diffusion cells to measure percutaneous penetration of active ingredients from disinfectant formulations, following OECD TG 428.
• Application and collection – The test formulation (2‑5 mg/cm²) is applied to the epidermal surface. Receptor fluid (PBS with albumin and sodium azide) is sampled at intervals (0.5, 1, 2, 4, 8, 12, 24 hours) and analysed for active ingredients by HPLC‑UV, GC‑MS, or LC‑MS/MS.
• Data analysis – The cumulative absorbed amount (µg/cm²) and permeability coefficient (Kp, cm/h) are calculated, and the percentage of applied dose penetrating within 24 hours is reported. A penetration < 1 % is considered low; > 10 % indicates high systemic exposure risk.
• Margin of Safety calculation – Dermal absorption data are combined with the NOAEL from repeated‑dose oral or inhalation studies to compute the Margin of Safety, guiding safe use recommendations for animals.

Species‑Specific Assessments for Cats – Sensitivity to Phenols, Essential Oils and QACs

• Feline‑specific metabolism studies – We conduct in vitro hepatocyte assays (primary cat hepatocytes) to measure the intrinsic clearance (CLint) of phenolic compounds (e.g., thymol, eucalyptol, tea tree oil) and quaternary ammonium salts. A low CLint (≤ 0.1 mL/min/mg protein) indicates a high risk of accumulation and toxicity in cats due to reduced glucuronidation capacity.
• Acute oral toxicity in cats – when indicated – For products intended for direct use on cats, we perform a limited acute oral toxicity study (OECD TG 423) in adult domestic short‑hair cats (n=3 per dose) to confirm the LD₅₀ and identify species‑specific signs (salivation, tremors, hyperthermia, vomiting). The study is conducted under veterinary supervision with supportive care.
• Dermal tolerance in cats (patch test) – We apply the disinfectant to clipped areas (4 cm²) on the flank of adult cats for 4‑hour and 24‑hour periods, and assess erythema, oedema, and hair loss over 14 days; a score ≤ 1 (very slight erythema) is required for feline‑specific products.
• Ocular tolerance in cats (mini‑Draize) – With n=3 cats, we instil the diluted disinfectant into the conjunctival sac and evaluate corneal and conjunctival changes; products with pH outside 6.5‑8.5 or with a Draize score > 10 are considered unsuitable for direct ocular contact in cats.

Compatibility with Skin Microbiome and Cytotoxicity Assessment

• Antimicrobial activity against canine and feline commensals – We test the disinfectant’s efficacy against common skin bacteria (e.g., Staphylococcus pseudintermedius from dogs, Staphylococcus felis from cats) using broth microdilution (CLSI M07‑A11) and agar diffusion, and also assess its selectivity towards beneficial flora versus pathogenic strains.
• Cytotoxicity to primary mammalian cells – MTT assay (ISO 10993‑5) – Canine and feline primary skin fibroblasts are cultured and exposed to various disinfectant dilutions (1:10 to 1:1 000). The half‑maximal inhibitory concentration (IC₅₀) is determined; an IC₅₀ > 500 µg/mL is considered safe for repeated application.
• Skin irritation potential – in vitro Reconstructed Human Epidermis (OECD TG 439) – As a replacement for the rabbit Draize test, we use a validated RhE model (e.g., EpiSkin™) to measure tissue viability (MTT reduction) after 15‑60 minutes of exposure; viability > 50 % indicates non‑irritant classification.

Report Acceptance & Compliance with Bulgarian and EU Biocidal Regulations

All safety tests described above are conducted under our ISO/IEC 17025 accreditation and in accordance with Good Laboratory Practice (GLP) principles. Our final safety assessment reports provide a complete description of the test substance, test system, dose levels, and exposure conditions; raw data tables for all measured parameters (dermal and ocular irritation scores, LLNA SI, LD₅₀, NOAEL, dermal absorption percentages, cat‑specific results); statistical analysis (mean, SD, confidence intervals); a clear hazard classification according to CLP (GHS) and BPR (EU) 528/2012 criteria; a comprehensive risk assessment for dogs and cats (Margin of Safety, recommended precautions, and risk phrases); and a final conclusion on the suitability of the product for use on or around companion animals. These reports are accepted by the Bulgarian Food Safety Agency (BFSA), the European Chemicals Agency (ECHA), veterinary product registrars, and pet product manufacturers for product authorisation, label development, and market access. Bilingual (Bulgarian/English) versions are available to facilitate submissions to national and European regulatory bodies.