IRON OXIDE

CAS: 1332-37-2 COLOR OR COLORING ADJUNCT, SURFACE-FINISHING AGENT

Iron oxide is an inorganic color additive identified by CAS 1332-37-2, used principally for coloring and surface finishing in regulated products including foods and packaging materials.

What It Is

Iron oxide refers to mineral-based inorganic compounds composed primarily of iron and oxygen that serve as colorants and surface-finishing agents in regulated products. As a food additive, iron oxide corresponds to mixtures of iron (II) and iron (III) oxides and is recognized under food additive regulations, including provisions in U.S. color additive law and international additive registries. The additive is identified by CAS number 1332-37-2 and includes synthetic variants described in regulatory inventories. Its primary technical functions involve imparting color to food-contact materials and finished goods where pigmentation is needed. In the context of food and food-contact regulation, iron oxide is often grouped with other mineral colorants under community and national lists of permitted additives. It may appear in various color forms, including black, red, and yellow oxides, each corresponding to different iron oxide chemical forms.

How It Is Made

Iron oxide used as a color additive is manufactured through controlled oxidation and processing of iron-containing raw materials. In industrial contexts, the production of iron oxide pigments typically involves thermal or precipitation methods where iron salts or elemental iron are oxidized to produce fine particulate oxides. These processes ensure consistent color quality, particle size, and purity specifications required for use in regulated applications. To meet food additive and contact material specifications, iron oxide pigments undergo purification and testing against identity and quality criteria set forth in regulatory documents. These specifications often include limits on impurities and physical properties that could influence safety and performance. Such manufacturing controls help ensure that iron oxide meets the functional requirements for coloring and finishing without introducing unintended contaminants.

Why It Is Used In Food

Iron oxide is used in food and food-contact applications because of its stable coloring properties and compatibility with various substrates. In food-contact materials, such as packaging and coatings, iron oxide provides durable, inert pigmentation that does not easily migrate into food when applied under proper conditions. Its stability across a range of temperatures and environments makes it suitable for products that require consistent appearance and surface finish. The use of iron oxide as a colorant is driven by its ability to produce a spectrum of earthy tones, from red and brown to black, which can be desirable in certain packaging and food-contact applications. Regulatory lists often specify where and how such colorants may be applied, ensuring their use remains within established technological needs and safety assessments.

Adi Example Calculation

To illustrate how an ADI might be applied, consider an illustrative scenario based on an established ADI range for iron oxides. For a hypothetical individual with a body weight of 70 kilograms, an upper end of an ADI range might be interpreted as an amount corresponding to regulatory guidance. Using the upper bound of the historical ADI range and multiplying by body weight provides a daily intake threshold that regulatory assessments consider safe under typical conditions of exposure. This calculation does not represent a recommended intake level but rather illustrates how ADI values translate into mass-based exposure estimates for individuals of different body weights. Real-world exposures depend on actual use levels in foods and other products, which are regulated to ensure they remain consistent with safe use conditions.

Safety And Health Research

Safety and health research into iron oxide as a food additive and colorant focuses on toxicological evaluation of exposure scenarios. International reviews, including those by expert committees, have assessed national intake estimates and toxicological data associated with iron oxide use as a color additive. Such evaluations consider absorption, metabolism, and potential effects across various study types. Historical assessments by international expert bodies have established intake guidelines based on available evidence on safety endpoints. (INCHEM) Research literature also investigates properties of iron oxide pigments under artificial digestion conditions, exploring dissolution behavior and interactions at the cellular level in vitro. These studies contribute to understanding how particulate forms of iron oxide behave in biological models, complementing broader regulatory evaluations. (INCHEM) Taken together, regulatory and scientific assessments inform the conditions under which iron oxide may be used safely, acknowledging that its inert nature and limited bioavailability under common usage conditions contribute to its safety profile.

Regulatory Status Worldwide

Iron oxide is specifically d in U.S. color additive regulations governing permitted colorants for regulated products. Under Title 21 of the Code of Federal Regulations, iron oxides listed by CAS number 1332-37-2 must meet defined identity and specification requirements and are exempt from batch certification for certain uses, such as in contact lenses, when utilized within regulatory limits. This listing reflects a defined regulatory status for iron oxide in U.S. contexts. In the European Union, iron oxides and hydroxides are included in the Union list of food additives and permitted for use in foods at levels consistent with good manufacturing practice and technological necessity. EU food additive regulations establish the framework under which such additives may be authorized, emphasizing safety evaluation and adherence to specifications. (EUR-Lex) On the international stage, expert committees such as the Joint FAO/WHO Expert Committee on Food Additives have evaluated iron oxides as food colorants. Historical evaluations have set acceptable intake guidelines based on available toxicological data, reflecting a global consideration of safety and exposure. Such evaluations inform national and regional regulatory decisions without prescribing identical conditions across all jurisdictions.

Taste And Functional Properties

Iron oxide itself does not contribute a detectable taste when used in compliant quantities and applications. Functionally, the additive is valued for its color stability — it resists significant change under standard processing conditions, including moderate heat and exposure to light. Its particulate form also allows it to provide uniform pigmentation when dispersed in inks, coatings, and packaging materials. Because iron oxide is insoluble in water and most food matrices, it remains localized where applied, minimizing alteration of the product’s sensory attributes beyond color. These properties contribute to its continued use in regulated coloring applications where functional stability is essential.

Acceptable Daily Intake Explained

An acceptable daily intake (ADI) is a regulatory concept used to express the amount of a substance that can be consumed daily over a lifetime without appreciable health risk. For iron oxides evaluated by international expert committees, historical assessments have described an ADI range based on toxicological data and intake estimates. This range reflects the level at which long-term exposure is not expected to pose safety concerns when the additive is used in accordance with good manufacturing practice. (INCHEM) It is important to understand that the ADI is a safety benchmark rather than a dietary recommendation. It is derived through analysis of available data and the application of uncertainty factors to account for variability in human responses. As such, it provides a regulatory reference point that supports safe use conditions for food additives.

Comparison With Similar Additives

Iron oxide can be compared with other color additives that serve similar functional roles. For example, titanium dioxide is another mineral-based white pigment widely used in food and food-contact applications, valued for its high opacity and brightness. Regulatory evaluations for titanium dioxide differ by jurisdiction, reflecting varying approaches to safety and exposure assessment. In contrast, iron oxide pigments provide earth-tone color options and often remain exempt from certification requirements under certain regulations when used appropriately. Other colorants such as annatto extract, derived from plant sources, offer natural yellow-orange hues and are regulated under different criteria given their botanical origin. Compared to organic plant-derived colorants, iron oxides are inorganic mineral pigments with distinct stability and performance characteristics that influence their selection in specific applications.

Regsafety Not Reachable By Search

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Common Food Applications Narrative

Iron oxide pigments are used in a range of applications where stable, inert coloring is required. In packaging materials and coatings, iron oxide-based pigments provide visual qualities that complement product design while meeting technological needs. For example, printed elements on packaging films may use iron oxide pigments in inks and surface treatments to achieve desired visual effects. Specialty applications such as colored casings and coated materials also integrate iron oxide pigments under defined conditions of use. These applications benefit from the stability of iron oxide across processing and storage conditions, contributing to consistent appearance without affecting the sensory qualities of the finished food product. Across such applications, the role of iron oxide remains focused on coloration and surface finishing rather than altering flavor or nutritional content. Regulatory frameworks in various regions specify the contexts in which iron oxide pigments can be used, aligning technological purpose with safety evaluations.

Safety & Regulations

FDA

  • Approved: True
  • Regulation: 21 CFR 73.3125

EFSA

  • Notes: EFSA has not allocated a numeric ADI in available evaluations
  • Approved: True
  • E Number: E172

JECFA

  • Year: 1999
  • Ins Number: 172
  • Adi Display: 0-0.5 mg/kg bw
  • Adi Mg Per Kg: 0.5

Sources

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