Toxic metals and metalloids
In humans and mammals, the toxic effects of many metals are reported to include neurological damage, immune system suppression, foetal abnormalities and the development of cancers.
Metal contamination poses a serious threat to microorganisms, animals and plants in the environment. Several of the metals in this group are essential in trace levels in biological systems while being toxic at higher doses.
Function and use
Toxic metals are included in a wide range of materials and compounds with a range of functions, of which the most dominant are as:
- components in metal alloys for stability, workability, appearance or semiconductor properties,
- metal plating for protection or shininess,
- in catalysts
- in pigments,
- oxides having specific properties such as flame-retardance, semiconductance or insulation, biocidal or for bleaching,
- part of other inorganic compounds resulting in specific materials like silicate glass,
- part of organic compounds with specific effects such as biocides, fertilisers, catalysts or stabilisers in polymers.
Areas of application
Toxic metals and their compounds are used extensively. The most frequent uses are summarised for each metal below:
Flame retardant oxide in clothing, toys, aircraft and cars, alloy component, stabiliser/catalyst in PET production, additive, semiconductor and pigments in textile, rubber, plastics (including PET), adhesives, paints, ceramics, glass, fireworks, polystyrene and in fluorescent tubes in computer/TV screens.
Alloy component, pyrotechnics, semiconductors, wood preservation, additive in poultry and swine production and pesticides in textiles.
Lightweight metal used in aircraft and satellites, alloy component with copper or nickel, mirrors in telescopes, semiconductors, electric insulator in baseplates for high-power transistors.
Boric acid, borax and boric oxide are the most important boron compounds. These can be used in fertilisers, antiseptics, washing powders and to make Pyrex glass.
Rechargeable batteries, dyestuff and pigments for textiles.
Shiny metal in chrome plating, alloy component included in stainless steel, chromium compounds are used as mordants (to fix dye colours in fabrics), leather tanning, pigments and catalysts.
Magnetic metal, corrosion-resistant superalloy component stable at high temperatures, nickel batteries, electric car batteries, cobalt complexes as blue pigments, cobalt salts for surface treatment, as catalysts in chemical industry, in animal feeds, in fertilisers and humidity indicators.
Lead compounds may be used as pigments for pottery glazes, paints, textile and hair dyes, and lead oxide is used in lead crystal glassware.
Liquid metal in old thermometers and barometers etc., component in amalgam alloys, as compounds in preservatives and pesticides.
Corrosion-resistant metal used for plating, alloy component, nickel compounds (both organic and inorganic) are used for surface treatment, as catalysts and in batteries.
Soft metal, alloy component in bronze and with lead as solder, for plating to prevent corrosion, di-organotin compounds as stabilisers in PVC plastic, catalysts in sealants, adhesives and coatings (polyurethanes and silicones), tri-organotin compounds as biocidal agents in wood, antifouling paints and other preservatives.
As a consequence of this, organotin compounds may be found in products like food wraps and food packaging, T-shirts, soft toys, gloves (polyurethane, PVC), sanitary napkins, medical equipment, PVC plastics (water pipes, packing materials, textile products), silicone rubber (sealants, dental products, paper coatings) and polyurethanes (foam plastics, glue/sealants).
In the EU, all these metals and their compounds are restricted in the Toys directive and most of them are restricted for specific uses in REACH annex XVII. Many also appear on the REACH Candidate List.
Examples of identified alternatives to toxic metals are:
UV treatment, mechanical or enzymatic finishing
Low-impact reactive dyes and fibre-reactive dyes (are said to contain no heavy metals or other known toxic substances, and do not need mordants)
Use alternative methods for corrosion protection
Cobalt free indicating silica gel ("orange gel"), containing iron salts as indicator
Chrome rutile yellow (Chrome antimony titanium buff rutile) is reported as an alternative to lead chromate
Barium oxide, zinc oxide or potassium oxide
In crystal glass
Lead chromate or