Heavy Metals Testing by ICP-MS

Lead, arsenic, cadmium, mercury and antimony are prohibited as cosmetic ingredients in the EU and UK, and in every other regulated market. Nobody adds them. They arrive in the product as impurities in raw materials that are mined, harvested or extracted from the environment: iron oxide and ultramarine pigments, mica, kaolin and bentonite clays, talc, activated charcoal, seaweed, botanical powders, henna, mineral salts and zinc oxide. The law recognises that a trace may be unavoidable and permits it, provided it is small enough to be safe and the safety assessor has shown that it is. Showing it requires measurement.

Oxford Biosciences quantifies heavy metals in finished products and raw materials by inductively coupled plasma mass spectrometry in its own analytical laboratory. The result is reported against the limits that apply in each market, and it goes directly to the assessor writing the CPSR.

Regulatory basis

In the EU and UK, Annex II of Regulation (EC) No 1223/2009 lists the substances prohibited in cosmetic products. Lead and its compounds, arsenic and its compounds, cadmium and its compounds, mercury and its compounds (with a narrow exception for phenylmercuric salts as preservatives in eye products under Annex V), antimony and its compounds, and chromium(VI) compounds all appear on the list, and several nickel and cobalt compounds are listed through their classification as carcinogenic, mutagenic or toxic to reproduction under Article 15.

Article 17 provides that the non-intended presence of a small quantity of a prohibited substance, stemming from impurities of natural or synthetic ingredients, the manufacturing process, storage or migration from packaging, which is technically unavoidable in good manufacturing practice, is permitted provided the product remains safe under Article 3. The provision has two conditions and both must be met: the trace must be technically unavoidable, and the product must be safe with the trace in it. A measured lead content is the evidence for the second condition; a comparison with what good practice achieves for the raw material in question is the evidence for the first.

Annex I, Part A, Section 2 requires the safety information to state the purity of the substances used and, where relevant, the identification and quantity of impurities and traces, with particular reference to prohibited substances. The SCCS Notes of Guidance, in the section on impurities and traces, expects the assessor to evaluate the exposure to each trace metal and its contribution to the margin of safety, particularly for lip products, which are ingested, and for products used on children.

Neither the Regulation nor the SCCS sets numerical limits for traces. Several regulators do, and the report compares the result with each of them.

The limits applied in practice

Metal	Germany, BVL technically avoidable limits (2017), applied as the EU benchmark	Health Canada, impurity guidance	USA, FDA	ASEAN Cosmetic Directive	China, Safety and Technical Standards for Cosmetics
Lead	2 mg/kg (0.5 mg/kg in toothpaste)	10 mg/kg	10 mg/kg in lip products and externally applied cosmetics (2016 guidance); 20 mg/kg in colour additives	20 mg/kg	10 mg/kg
Arsenic	0.5 mg/kg	3 mg/kg	No general limit; 3 mg/kg in colour additives	5 mg/kg	2 mg/kg
Cadmium	0.1 mg/kg	3 mg/kg	No general limit	5 mg/kg	5 mg/kg
Mercury	0.1 mg/kg	3 mg/kg	1 mg/kg; 65 mg/kg as phenylmercuric preservative in eye products	1 mg/kg	1 mg/kg
Antimony	0.5 mg/kg	5 mg/kg	No general limit	Not specified	Not specified

All values in mg/kg, equivalent to parts per million. The German BVL limits are the strictest and are the ones the EU market surveillance authorities apply when a product is tested at the border or from the shelf; a product that meets them meets every other limit in the table. The other regulators’ figures are the limits at which a product will be refused entry or removed from sale in that market. Where a product is sold in several markets, the report assesses against the strictest and notes the rest.

For nickel, chromium and cobalt there are no statutory trace limits in cosmetics. The concern is elicitation of allergic contact dermatitis in already-sensitised consumers, and the literature threshold generally applied is 5 mg/kg for nickel, chromium and cobalt each in products in prolonged contact with the skin, with a lower figure for products used around the eyes. The report applies those thresholds and states their basis.

Which products need testing

The need is driven by the raw materials, not the product type. A cream made entirely from synthetic ingredients of pharmaceutical grade has no plausible route for a heavy metal trace and does not require testing; the CPSR says so and explains why. The products that do require testing are those containing:

• Mineral pigments and fillers: iron oxides (CI 77491, 77492, 77499), ultramarines (CI 77007), chromium oxide greens (CI 77288, 77289), manganese violet (CI 77742), mica (CI 77019), titanium dioxide, zinc oxide, talc, kaolin, bismuth oxychloride. Every colour cosmetic, every mineral sunscreen and every powder falls here. Lip products are the highest priority because the consumer ingests them.
• Clays and earths: kaolin, bentonite, rhassoul, French green clay, fuller’s earth, and any product marketed on the mineral content of a particular deposit.
• Charcoal and ash: activated charcoal, bamboo charcoal, wood ash in traditional soaps.
• Marine and botanical raw materials: seaweed and algae extracts and powders, which concentrate arsenic and cadmium; rice bran and rice-derived ingredients, which concentrate arsenic; cocoa and cocoa butter, which can carry cadmium; herbal powders, particularly those of Ayurvedic or traditional Chinese origin, where lead and mercury have been found as both contaminants and deliberate additions in the source material.
• Henna, indigo and other plant dyes, which have been found adulterated with lead and other metallic salts to alter the colour.
• Kohl, kajal and surma, traditional eye cosmetics in which galena, lead sulphide, was historically the principal ingredient and in which lead has been found at percentage levels in products imported into the EU and UK.
• Toothpastes, mouthwashes and lip products, because of the oral exposure route, and products for children under three, because of the SCCS’s specific attention to that group.
• Any product whose raw material comes with a certificate of analysis that is missing, incomplete, undated or unconvincing.

How the analysis is done

1. Sample preparation and digestion

Heavy metals in a cosmetic are bound in an organic matrix of oils, waxes, polymers and pigment particles that the instrument cannot analyse directly. The matrix has to be destroyed and the metals brought into solution. A weighed portion of the product, typically 0.25 to 0.5 g, is placed in a PTFE vessel with concentrated nitric acid and, for silicate-rich materials such as clays and mica, hydrofluoric acid or a nitric-hydrochloric acid mixture, and digested under microwave heating at temperatures up to 200 °C and elevated pressure. Closed-vessel microwave digestion is used rather than open hot-plate digestion because mercury and arsenic are volatile and would be lost from an open vessel, giving a falsely low result. The digestate is diluted to volume with ultrapure water. A method blank of acid alone is digested alongside every batch to account for any metal contributed by the reagents, and a certified reference material of similar matrix is digested and analysed with every batch to confirm that the digestion recovered the metals completely.

2. Inductively coupled plasma

The diluted digestate is nebulised into an argon plasma sustained by radio-frequency induction at a temperature of 6,000 to 10,000 K. At that temperature the sample is completely atomised and the atoms are ionised, so that each element enters the mass spectrometer as a stream of singly charged positive ions.

3. Mass spectrometry

The ions are extracted through a sampling cone and skimmer into the vacuum of the mass spectrometer and separated by a quadrupole mass filter according to their mass-to-charge ratio. Each element is measured at one or more of its isotopes: lead at masses 206, 207 and 208, arsenic at 75, cadmium at 111 and 114, mercury at 202, antimony at 121, nickel at 60, chromium at 52 and cobalt at 59.

Arsenic and chromium present a particular problem. Arsenic has a single isotope at mass 75, and the plasma also produces the polyatomic ion argon chloride, ⁴⁰Ar³⁵Cl⁺, at the same mass whenever chloride is present, which in a cosmetic digestate it always is. Chromium at mass 52 suffers similarly from ⁴⁰Ar¹²C⁺. Without correction, both elements read high. The instrument therefore passes the ion beam through a collision cell filled with helium before the quadrupole: the polyatomic ions, being larger, collide more often and lose energy, and a kinetic energy barrier at the cell exit rejects them while the smaller elemental ions pass. Every result on the standard panel is acquired with the collision cell active.

Mercury adheres to the surfaces of the sample introduction system and washes out slowly, so that a low sample measured after a high one reads falsely high. A gold solution is added to the rinse and to the samples to keep mercury in solution, and extended rinse times and mercury-specific blanks are run between samples.

4. Calibration and quality control

The instrument is calibrated for each element with a series of standards prepared from certified single-element or multi-element reference solutions traceable to national standards, matrix-matched to the acid concentration of the digestates. An internal standard mixture of elements not present in cosmetics, typically scandium, germanium, rhodium, indium and bismuth, is added to every solution and used to correct for drift in the instrument and for suppression of the signal by the sample matrix. Each analytical batch includes a method blank, a calibration check standard, a duplicate digestion, a spiked sample to confirm recovery, and the certified reference material. Results are accepted only when every control falls within its limit.

5. Reporting limits

The limit of quantification for each metal in the product is typically 0.01 to 0.05 mg/kg, depending on the sample mass and dilution, which is between ten and a hundred times below the strictest limit in the table above. A result below the limit of quantification is reported as such, not as zero, and the limit is stated on the report so that the assessor can see that a negative result is a meaningful one.

Chromium speciation

Total chromium by ICP-MS cannot distinguish chromium(III), which is present in the green pigments chromium oxide (CI 77288) and chromium hydroxide (CI 77289) and is of low toxicity, from chromium(VI), which is prohibited, carcinogenic and a potent sensitiser. The purity criteria for the two green pigments in Annex IV require that they be free of chromate ion, and a product containing them cannot demonstrate that with a total chromium figure. Where a product contains either pigment, or where total chromium is found in a product with no obvious source, chromium(VI) is determined separately by alkaline extraction and either ion chromatography coupled to ICP-MS or the diphenylcarbazide colorimetric method, and reported as a separate figure.

Interpreting the result

A result above the strictest limit is not the end of the analysis. The report identifies the likely source in the formulation by comparing the finished product result with the raw material certificates, the concentrations of the mineral ingredients, and where necessary by analysing the raw material itself. A trace of lead at 3 mg/kg in a lipstick is a raw material problem in the pigment, and the resolution is a different pigment lot or supplier, not a reformulation. The report also calculates the exposure: for a lip product, the daily amount applied, the fraction ingested, the lead content, and the resulting daily intake against the reference value, so that the CPSR can state whether the product is safe under Article 3 with the trace present, which is the question Article 17 asks.

What the report contains

• Sample identification, form, batch and date of receipt
• Metals determined, digestion method and instrumental method summary
• Result for each metal in mg/kg, with the limit of quantification
• Quality control summary: blank, recovery, duplicate and certified reference material results
• Comparison with the trace limits of each market the product is sold in
• Where a result requires it, the likely source and the exposure calculation
• Signature of the analyst and the Head of Laboratory Sciences

What to send

10 g or mL of finished product, or 5 g of raw material, in a clean container that has not been used for anything else. Glass or polypropylene is preferred; avoid metal-lined closures. The formulation with percentages and the supplier certificates of analysis for all mineral, clay, charcoal, marine and botanical ingredients are needed so that the panel can be matched to the raw materials and a result traced to its source.

How it fits with the CPSR

The heavy metals result populates the impurities and traces section of Annex I, Part A, Section 2 and supports the Article 17 reasoning and the toxicological assessment in Part B. Where we prepare the CPSR, the analysis is ordered by the assessor for the raw materials that need it and the assessment is written from the data. Where a client brings a certificate from a raw material supplier, we check the method, the limits and the date, and we advise when the certificate does not cover the metal, the batch or the market that matters.