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API TR 406-1995: Toxicological Evaluation of Petroleum Hydrocarbon Fractions – Scope, Methods, and Regulatory Implications
A comprehensive review of the American Petroleum Institute’s technical report on the mammalian and environmental toxicity of petroleum substances
Scope and Purpose of API TR 406-1995
API Technical Report 406-1995, developed by the American Petroleum Institute, is a comprehensive toxicology report that systematically evaluates the potential health and environmental hazards associated with specific petroleum hydrocarbon fractions. Issued in 1995 under the auspices of the API Health and Environmental Sciences Department, this document serves as a foundational reference for toxicologists, industrial hygienists, and regulatory professionals working with petroleum-derived substances.
The primary scope of API TR 406-1995 includes:
- Characterization of the mammalian toxicity (acute, subchronic, and chronic) of selected petroleum streams and hydrocarbon classes.
- Evaluation of carcinogenic, mutagenic, and reproductive developmental effects of key hydrocarbon components.
- Assessment of ecotoxicity endpoints (aquatic and terrestrial) to support environmental risk assessments.
- Identification of critical dose-response relationships and derivation of health-based exposure limits (e.g., occupational exposure limits, reference doses).
The report covers a range of petroleum fractions including gasoline-range hydrocarbons, middle distillates, and heavier fuel oil components, with particular emphasis on those commonly encountered in refining, transportation, and end-use applications. It is intended to support the development of Material Safety Data Sheets (MSDS), workplace health assessments, and regulatory submissions.
Tip: API TR 406-1995 is not a standard in the prescriptive sense but a technical report that consolidates toxicological data. It is often cited as a primary source for toxicity values in EPA and OSHA risk assessments for petroleum substances.
Toxicological Methodologies and Endpoints
Mammalian Toxicity Testing
API TR 406-1995 draws upon a combination of peer‐reviewed literature, internal API-funded studies, and standard OECD/US EPA test guidelines. Acute toxicity is assessed using oral, dermal, and inhalation routes in rodent models. Subchronic (28-90 day) and chronic (2-year) studies are analyzed for target organs, with special attention to the liver, kidneys, respiratory tract, and nervous system.
Carcinogenicity and Mutagenicity
The report evaluates the weight of evidence for carcinogenicity, considering epidemiologic data, rodent bioassays, and short-term genotoxicity assays (Ames test, chromosomal aberration tests). Key findings indicate that benzene and certain polycyclic aromatic compounds (PACs) are confirmed human carcinogens, while others show limited or suggestive evidence.
Environmental Toxicology
Ecotoxicity endpoints include acute and chronic effects on freshwater and marine organisms: algae (Pseudokirchneriella subcapitata), aquatic invertebrates (Daphnia magna), and fishes (Pimephales promelas and Oncorhynchus mykiss). The report also evaluates biodegradability and bioaccumulation potential using quantitative structure-activity relationship (QSAR) models and laboratory tests.
Important: API TR 406-1995 emphasizes the need to consider the whole mixture rather than individual components, because petroleum substances are complex mixtures and toxicological interactions (e.g., synergism, antagonism) can occur.
Key Findings and Data Summary
The report presents extensive data tables, a representative excerpt of which is shown below. These values are derived from the technical report and are often used as benchmarks in hazard classification (e.g., GHS, OSHA HCS).
| Hydrocarbon Class / Substance | Acute Oral LD50 (rat) mg/kg | Acute Inhalation LC50 (rat) ppm/4h | Skin Irritation (rabbit) | Aquatic Toxicity LC50 (fish 96h) mg/L | CHronic LOEL (mg/kg-day) |
|---|---|---|---|---|---|
| Benzene | 930 | 10,000 | Mild | 5.3 | 3.2 (liver, hematologic) |
| Toluene | 5,000 | 12,000 | Mild | 42.5 | 22.0 (neurological) |
| C9–C14 Aliphatic Solvent | >2,000 | >5,000 (vapor) | Moderate | 1.8 | No observed at 250 ppm |
| Heavy Fuel Oil (IFO 380) | >5,000 | N/A (low volatility) | Moderate–Severe | 0.5–2.0 | Not established |
| Polycyclic Aromatic Hydrocarbon (PAH) Mixture | 1,100 (typical) | N/A | Severe | 0.01–0.1 | 0.1 (carcinogenic endpoint) |
Key takeaway: The data from API TR 406-1995 support the hazard classification of benzene and high-PAH streams as carcinogenic and toxic to aquatic life, while many aliphatic solvents have lower acute toxicity but may still pose chronic risks.
Implementation in Risk Assessment
API TR 406-1995 provides the essential toxicological input for quantitative risk assessments (QRAs) performed under:
- Occupational Health: Derivation of workplace exposure limits (e.g., 8‑hour TWA PELs) and risk management for refinery and downstream operations.
- Environmental Risk: Calculation of predicted no‑effect concentrations (PNECs) for water, sediment, and soil, often used in Environmental Impact Assessments (EIAs) for new projects or spills.
- Product Stewardship: Classification and labeling of petroleum substances according to the Globally Harmonized System (GHS) – the report supplies GHS hazard categories for acute toxicity, aspiration hazard, and chronic aquatic toxicity.
To bridge the gap between the 1995 report and modern regulatory frameworks, practitioners are encouraged to combine the values in API TR 406-1995 with more recent dataset updates (e.g., REACH registration data) while respecting the weight-of-evidence approach laid out in the original report.
Compliance note: While API TR 406-1995 itself is a technical report and not a mandatory standard, its data are frequently incorporated into safety data sheets and regulatory summaries. Failure to consider the toxicological endpoints identified in this report may result in inadequate hazard communication and non‑compliance with OSHA’s Hazard Communication Standard (29 CFR 1910.1200) or the EU Classification, Labelling and Packaging (CLP) regulations.
Compliance Considerations and Industry Application
Regulatory Integration
In the United States, EPA’s Integrated Risk Information System (IRIS) and OSHA’s Permissible Exposure Limits (PELs) for several petroleum hydrocarbons draw on toxicological studies also cited in API TR 406-1995. Internationally, the European Chemicals Agency (ECHA) recognizes the approaches used in this report for setting Derived No-Effect Levels (DNELs) and Predicted No-Effect Concentrations (PNECs) for petroleum substances under REACH.
Updating and Gap Analysis
Since 1995, the petroleum industry has seen advances in molecular characterization and toxicological testing. API TR 406-1995 should be supplemented with more recent data from high-quality studies, especially for newer fuel formulations (e.g., biodiesel blends, ultra-low sulfur diesel). Nevertheless, the report remains a valuable baseline: its classification of hydrocarbon blocks by carbon range and aromatic content continues to be used by industry consortia for read-across approaches under REACH and similar schemes.
Training and Documentation
Industrial hygiene professionals should document how they have applied the findings of API TR 406-1995 in the development of exposure control plans. Management of change procedures should include a review of the toxicological endpoints from this report when new hydrocarbon streams are introduced.
Q: Is API TR 406-1995 a mandatory standard or a guideline?
A: It is a voluntary technical report issued by the American Petroleum Institute. While not legally binding on its own, its data and conclusions are frequently used to meet regulatory requirements for hazard communication and risk assessment in jurisdictions that adopt API consensus positions (e.g., OSHA, EPA, and international bodies like IMO and ECHA).
A: It is a voluntary technical report issued by the American Petroleum Institute. While not legally binding on its own, its data and conclusions are frequently used to meet regulatory requirements for hazard communication and risk assessment in jurisdictions that adopt API consensus positions (e.g., OSHA, EPA, and international bodies like IMO and ECHA).
Q: Can API TR 406-1995 be used to classify a petroleum stream for GHS hazard categories?
A: Yes. The report provides specific toxicity ranges and endpoints that can be mapped directly to GHS hazard categories for acute toxicity (oral, dermal, inhalation), skin irritation, aspiration hazard, and aquatic toxicity. For carcinogenicity and reproductive toxicity, users need to apply a weight‑of‑evidence approach using all available information.
A: Yes. The report provides specific toxicity ranges and endpoints that can be mapped directly to GHS hazard categories for acute toxicity (oral, dermal, inhalation), skin irritation, aspiration hazard, and aquatic toxicity. For carcinogenicity and reproductive toxicity, users need to apply a weight‑of‑evidence approach using all available information.
Q: How does API TR 406-1995 differ from more recent API reports, such as API TR 416 or API TR 423?
A: API TR 406-1995 was one of the first API toxicology reports to systematically cover a broad range of petroleum fractions. Later reports (e.g., API TR 416 on kerosene, API TR 423 on heavy fuel oils) often refine the data using more sophisticated analytical methods and extended endpoints. API TR 406-1995 remains relevant as a foundational compilation of mammalian and environmental toxicity data for the hydrocarbon classes it covers.
A: API TR 406-1995 was one of the first API toxicology reports to systematically cover a broad range of petroleum fractions. Later reports (e.g., API TR 416 on kerosene, API TR 423 on heavy fuel oils) often refine the data using more sophisticated analytical methods and extended endpoints. API TR 406-1995 remains relevant as a foundational compilation of mammalian and environmental toxicity data for the hydrocarbon classes it covers.
Q: What are the limitations of API TR 406-1995 that users should be aware of?
A: The report is based on research available up to 1995. It may not reflect the latest toxicological insights (e.g., endocrine disruption, immunotoxicity) or the composition of modern petroleum products (e.g., biofuels, synthetic paraffinic kerosene). Users should supplement with current literature and product‑specific analytical data. Additionally, the original report may not be publicly accessible; users often rely on the data as cited in secondary sources or through API’s distribution channels.
A: The report is based on research available up to 1995. It may not reflect the latest toxicological insights (e.g., endocrine disruption, immunotoxicity) or the composition of modern petroleum products (e.g., biofuels, synthetic paraffinic kerosene). Users should supplement with current literature and product‑specific analytical data. Additionally, the original report may not be publicly accessible; users often rely on the data as cited in secondary sources or through API’s distribution channels.
— This article is provided for informational purposes and reflects the technical content of API TR 406-1995 as understood in the regulatory and industrial hygiene communities. © 2026 —