Institut Kirchhoff Berlin GmbH

Heavy metals

Date: March 2016

Arsenic

Background 

Arsenic occurs naturally in the earth’s crust. It enters animals and plants via the ground as well as ground and surface water. In food, arsenic occurs in organic form (fish and seafood) and inorganic form (rice and algae). Inorganic arsenic compounds are classified as carcinogenic for humans (IARC Group 1). Long-term intake of even low quantities can lead to skin changes and damage to blood vessels and nerves. The toxicity of organic arsenic compounds (eg arsenobetain) is largely unknown.

Rice is the main focus, as due to the particular manner it is cultivated and also the physiology of the plants in comparison to other types of grains, it demonstrates a higher content of inorganic arsenic. According to an assessment by the German Federal Institute for Risk Assessment (BfR), intake values of inorganic arsenic is relatively high in Germany, due to the consumption of rice and rice products.

On 26 June 2015, Directive (EC) 1881/2006 was amended in respect of the maximum content of inorganic arsenic stipulated by the European Commission’s Directive (EU) 2015/1006.

Milled rice0.20 mg/kg
Husked rice and parboiled riceeach 0.25 mg/kg
Rice cakes and other rice products0.30 mg/kg
Rice intended for baby food0.10 mg/kg

The directive came into force on 16 July 2015. Since 1 January 2016, the stated maximum amounts apply to inorganic arsenic.

Analysis

IPC-MS (total arsenic content)

After an acidic microwave digestion, the samples, at a suitable dilution, are atomised and ionised in an inductively coupled argon plasma. The sample’s positively charged ions are drawn from the plasma using a system of perforated sheets, then separated and detected using mass spectometry. Quantification occurs by means of an external calibration.

AAS hydrid technique (total inorganic arsenic)

Arsenic is extracted from the sample using a hydrochloric acid solution. The addition of a potassium iodate-ascorbic acid solution reduces the arsenic in the extraction solution to As3+. The conversion to volatile arsenic hydride occurs in the graphite furnace AAS, using sodium borohydride. The arsenic hydride undergoes atomic spectrometry using FIAS furnace coupling on the graphite furnace AAS, and is then quantified by means of an external calibration.

IC-ICP-MS (differenciated detection of the arsenic speciations)

The arsenic is extracted from the food samples with nitric acid solution. The species is separated to a special column and then quantified via ICP-MS by means of an external calibration.

Determination of elements

Background

Metals occur in the ground, the air and also in water. Some of them are involved in the widest variety of ways in the metabolic processes in the bodies of humans and animals, as well as in plants. Excessive intake can however lead to adverse effects with the widest variety of symptoms.

Legal classification

  • Directive (EC) 1881/2006 Appendix Paragraph 3 Maximum content of metals for: Pb, Cd, Hg, Sn, As (valid since 1 January 2016)
  • German Drinking Water Ordinance 2001 – Elements listed in Appendix 2 with limit values: Cr, Hg, Se, U, Sb, As, Pb, Cd, Ku, Ni, Fe, Mn

Analysis

After an acidic microwave digestion, the samples, at a suitable dilution, are atomised and ionised in an inductively coupled argon plasma. The sample’s positively charged ions are drawn from the plasma using a system of perforated sheets, then separated and detected using mass spectometry. Quantification occurs by means of an external calibration.

Mercury

Background

Mercury occurs naturally in the earth’s crust, but due to the industrial impact of humans it has come to be distributed in the air and in water, so that it is present in the life cycle. In food, mercury occurs especially in organic form as methylmercury in fish and seafood. Mercury contamination in inorganic form in respect of intake with food is low.

Toxicological classification

The toxicity of organic mercury relates mainly to damage to the nervous system. A chronic exposure initially leads to headaches and aching limbs, and can extend to movement disorders and paralysis, right up to a coma.

Analysis FIMS 

The sample is shut in a microwave with acid. The Hg+2 ions are stabilised by the addition of potassium permanganete, and are converted to elementary mercury in a cold vapour atom absorption spectrometer with sodium borohydrid. The mercury atoms are measured in a quartz cuvette at a wavelength of 253.7 nm and quantified by means of an external calibration.

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