3. The chromium(VI) misconception: collective term and individual compound

Asbestos was not simply asbestos either

Asbestos was not simply asbestos either. In everyday language a distinction was made at most by colour, into white, brown and blue asbestos. Behind these lie different minerals: chrysotile, amosite and crocidolite, as well as tremolite, actinolite and anthophyllite. The European Asbestos Directive 2009/148/EC lists these six fibrous minerals individually. [62] A distinction was, however, drawn only where it was needed: in science, in engineering and later in medicine, when fibre form, durability and clinical picture had to be kept apart. On the construction site and in general usage it remained at one word. That had few consequences, because each of these minerals was a fibre and the fibre was the hazard.

The situation with “chromium(VI)” is similar, except that here even the everyday distinction is missing. The term covers industrially manufactured compounds such as chromic acid, dichromates and chromate-containing paints and primers just as much as calcium and sodium chromate, which form during operation. Anyone who hears “chromium(VI)” thinks of substances they do not use themselves and concludes from this that the issue does not concern them. Calcium and sodium chromate as reaction products of their own operations do not appear in this picture. The fact that calcium chromate is among the most potent chromates in animal studies likewise disappears behind the collective term (Sections 24 and 25).

The prefix names the reaction partner

In almost every solid finding, behind the designation “chromium(VI)” there stands a salt, a chromate or dichromate, and the prefix of that salt names its reaction partner: lead chromate, zinc chromate, strontium chromate, sodium chromate, calcium chromate. The prefix is not a formality. It is the other half of the substance and says where it comes from. Chromium trioxide and chromic acid are not salts and have no such partner. They are no less carcinogenic for that, but they belong to electroplating and surface technology, where the use is intended and declared.

The reaction partners are inconspicuous

The partners that occur in intentional use are themselves known to be hazardous: lead, zinc, strontium. The partners that lead to chromate in situ are not. As an element, calcium is the building material of bone and a constituent of milk, sodium is table salt, and both can be bought in a drugstore. The reaction partner in the insulation material, however, is not the element but the oxide. For decades chromium(III) was listed as an essential trace element in the diet; in 2014 the European Food Safety Authority concluded that evidence of essentiality is lacking and set no reference values, while in the United States an intake value continues to exist and chromium is sold as a dietary supplement. None of these three substances gives any reason to test a product for it. [76]

Inconspicuous does not mean harmless here. Calcium oxide is classified as irritating to the skin, seriously damaging to the eyes and irritating to the respiratory tract (H315, H318, H335), and Directive (EU) 2017/164 gives an indicative limit value of 1 mg/m³ as the respirable fraction. Sodium oxide forms sodium hydroxide solution with water and is correspondingly corrosive. Both, however, are not carcinogenic and not classified as CMR, and in the insulation material they are present bound in the silicate matrix. They are therefore not inconspicuous in every respect, but precisely in the one respect that matters here: anyone looking for a cancer risk has no reason to look at them. [79]

The “coating” category

Because chromium(VI) is mentally associated with paints and primers, a chromium(VI) finding is attributed to a coating, and where no coating is present, to the alloy. Both answers move the source into an area of responsibility that is already regulated. Yet it is precisely the well-known pigments that carry their partner in their name, and nobody finds that surprising. The step that is missing is the question of what applies when this partner is called calcium or sodium and nobody put it there deliberately.

The reaction partner is in the data sheet and is nevertheless not readable

The safety data sheet of a high-temperature insulation product from Morgan Advanced Materials, Ceraform 130, first issue 1 September 1990, version of 23 December 2020, lists in section 3 chromium(III) oxide at up to 3 per cent and, as the main constituent, “Refractories, Fibers, Aluminosilicate” with CAS number 142844-00-6 at 45 to 80 per cent. The service range is stated as up to 1400 °C. Which oxides lie behind this CAS number is not stated in the data sheet. ECHA’s registration dossier for the same number describes the substance as an amorphous glass fibre of silicon dioxide and aluminium oxide “and a range of oxides such as zirconia, ferric oxide, titanium oxide, magnesiumoxide, calcium oxide, other alkaline earth oxides including sodium oxide, potassium oxide, barium oxides”. Both reactants are thus declared in a single product. Section 10 of the same data sheet describes the material as stable, gives “None” under incompatible materials and lists as hazardous decomposition products only carbon oxides and traces of ammonia from the starch. [77, 78]

In addition, calcium chromate plays hardly any role in intentional use and is therefore rarely named. Legally, however, it is covered: although the REACH Authorisation List does not name it, ECHA’s restriction proposal covers the salts of chromic acid and thus also calcium chromate. The restriction therefore affects a substance that hardly anyone includes in their consideration, because it does not occur in the chemical composition of the product as delivered. It nevertheless forms thermochemically in one’s own operations, on the plant or even through the use of one’s own product. [59, 64]

Analysis: chromium(VI) content instead of compound

Once the chromate has formed and is referred to only as “chromium(VI)”, this makes root cause analysis more difficult. Standard laboratory analysis determines the chromium(VI) content, not the compound. Methods of elemental analysis, for example with inductively coupled plasma, likewise determine elements and, coupled with ion chromatography, the chromium(VI) content. They do not capture the compound itself, because the sample is dissolved for this purpose.

Which chromate phase is present is clarified only by phase analysis such as X-ray diffraction (XRD), with which Sayano et al. identified CaCrO₄ and Na₂CrO₄. It is not part of routine analysis and covers only a small portion of the sample and only crystalline phases above its detection limit. It does not provide a statement about the entire surface of a component or an insulation. [11]

For occupational safety and health, this results not in uncertainty but in a clear requirement: if a carcinogenic chromium(VI) compound cannot be reliably ruled out, its presence is to be assumed. The German TRGS 561 expressly requires the protective measures under sections 4.1 and 4.2 as soon as chromium(VI) exposure cannot be ruled out. [19]

In many companies, dismantling comes first and testing afterwards, often only with unreliable rapid tests (Section 19). Occupational safety and health requires the reverse order: the situation is to be assessed in the risk assessment before the work begins. The German TRGS 561 requires the protective measures as soon as chromium(VI) exposure cannot be ruled out; a negative test does not remove this situation of suspicion, especially as chromates can also form inside the insulation elements. [11, 19, 36]

Classification: group and individual compound

For occupational and environmental protection, the exact compound is not decisive. The harmonised European classification covers chromium(VI) compounds as a group as carcinogenic category 1B, with the exception of barium chromate and the compounds specified elsewhere; calcium chromate is itself separately classified as carcinogenic category 1B. The assessment criteria under the German TRGS 910 relate to the elemental content of chromium, not to the compound. Here one can again speak of chromium(VI) in general, just as with asbestos. [63, 64, 71]

The German Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) lists the routes of uptake for chromium(VI) compounds as “inhalation, skin absorption”. For non-threshold carcinogens there is no dose without risk; a chromate is neither only slightly carcinogenic nor only slightly absorbed through the skin. [71]

Differences exist in the other classifications. Sodium chromate is additionally classified as germ cell mutagenic and toxic to reproduction category 1B, and also, among other things, as acutely toxic, corrosive and sensitising. It is on the Candidate List of substances of very high concern (SVHC) and in Annex XIV of the REACH Regulation; its use is subject to authorisation. Calcium chromate is on neither list, although its classification as carcinogenic category 1B alone would suffice for identification as an SVHC (Article 57(a) REACH). [64-67]

With the planned restriction, the chromium(VI) substances are transferred from authorisation to Annex XVII of the REACH Regulation, that is, to the same Annex that lists asbestos fibres under entry 6. According to the available summaries, the proposal covers the salts of chromic and dichromic acid and thus also calcium chromate; the three lead chromate entries are exempted. [59, 66, 68]

Sodium chromate in insulation materials: the question of use

In sodium-containing insulation materials such as mineral wool, the formation of sodium chromate cannot be ruled out; Sayano et al. identified Na₂CrO₄ at the interface between metal and sodium-containing insulation material. The dust of such insulation is a mixture; chromate formed is present loosely as a substance in its own right. Neither is an article within the meaning of Article 3(3) of the REACH Regulation, as neither has a specific shape. As a substance of very high concern, sodium chromate is already listed today in Annex XIV of the REACH Regulation; its use is subject to authorisation. If such insulation is removed, stored and reused, it is not waste. Is this not already today a use subject to authorisation? For occupational safety and health, this question does not arise: here the requirement of the German TRGS 561 applies, which demands protective measures as soon as chromium(VI) exposure cannot be ruled out. [11, 19, 60, 66]

Sodium chromate in ashes: waste classification

Sodium chromate cannot be ruled out in chromate-containing ashes either; the question of use does not arise there. Whether a waste is hazardous is determined by Annex III of the European Waste Framework Directive 2008/98/EC and thus by the CLP classification of the substances contained, not by their SVHC status. From 0.1%, both chromates lead to classification as hazardous waste via criterion HP7 (carcinogenic). Sodium chromate additionally meets HP11 (germ cell mutagenic, from 0.1%) and HP10 (toxic to reproduction, from 0.3%), without lowering the decisive threshold. [69]

What is measured is the Cr(VI) content, but the threshold applies to the compound. Chromium accounts for about 33% of the mass of calcium chromate and about 32% of that of sodium chromate; 0.1% chromate thus corresponds to around 0.03% Cr(VI). Here too, the question of which chromate is present is practically irrelevant. This is relevant above all for grate ash, for which the European List of Waste provides a hazardous and a non-hazardous entry (19 01 11* and 19 01 12). Does the assessment in the individual case capture the Cr(VI) content, and does it convert it to the compound? [70]

Maternity protection

The consequence extends as far as maternity protection. Under section 11(1) of the German Maternity Protection Act (Mutterschutzgesetz, MuSchG), an unacceptable hazard for pregnant women exists, among other things, in the case of substances classified as carcinogenic, germ cell mutagenic or toxic to reproduction of categories 1A or 1B, or as acutely toxic of categories 1 to 3. Calcium chromate meets this as carcinogenic category 1B, sodium chromate additionally as germ cell mutagenic, toxic to reproduction and acutely toxic. The exception where the occupational exposure limit is complied with does not apply, since no such limit value exists for chromium(VI) compounds, but rather a risk-based assessment criterion under the German TRGS 910. [63, 71, 73]

If the presence of one of these chromates cannot be ruled out, pregnant women may not carry out activities such as maintenance, removal, inspection, cleaning or ash handling in these areas. For breastfeeding women, the IFA recommends as a precaution that no exposure to carcinogenic substances of categories 1A and 1B be permitted either. Under section 10 MuSchG, the hazard must be assessed for every activity to which a woman is or may be exposed. [72, 73]