Cadmium Pigments Are Green

Background

BACKGROUND

Cadmium pigments are extremely insoluble compounds of calcined cadmium zinc sulphide (green-shade yellows to golden yellows) and cadmium sulphoselenide (yellow through oranges and reds to deep maroons). They give bright strong colours, which have excellent heat stability, light-fastness and chemical resistance and they do not migrate in paints and plastics.

Cadmium pigments conform to all current international requirements, meeting tight limits for acid-soluble heavy metals (Council of Europe Resolution AP (89) 1) for colourants for food-contact plastics, and TCLP waste leaching resistance in the USA. Numerous migration tests on pigmented plastics have confirmed that cadmium pigments can be safely used for toys (European Standard EN 71 part 3).

Cadmium as such is a transition heavy metal. Although a non-essential element for man, it is naturally occurring and found throughout all waters and soils. Soluble cadmium species may enter the body, and can accumulate in the kidneys, prior to excretion. Excessive intake of cadmium by man is harmful and extreme emissions to the environment could in exceptional circumstances increase cadmium to harmful levels. Cadmium pigments, however, are unlike other cadmium compounds because of their extremely insoluble nature. This results from their chemical composition, very high chemical purity and high temperature calcination. Even in acidic conditions representative of stomach acid, they impart negligible acute toxic effects.

Legislation

LEGISLATION

In the absence of definitive and accurate data about risks to man and the environment from the many different sources considered individually, the EU sought to examine the extent and relative importance of these sources (Council Resolution 88/C30/01, 25th January 1988), and proposed to replace cadmium in applications where technically viable alternatives existed.

The use of cadmium pigments has since been restricted (EC Directive 91/338) by forbidding their use in some specific polymers. More recently, the use of cadmium pigments in packaging is also being restricted (EC Directive 94/62).

Risk Assessment

RISK ASSESSMENT

In 1995, the EU recognised the lack of definitive, reliable data and DG III instituted an assessment from an independent consultant to evaluate the risk from the cradle-to-grave lifecycle of cadmium pigments. This analysis considered the manufacture of pigments and of pigmented plastic products, their use and eventual end-of-life disposal. It has been shown that emissions of cadmium to the environment and to man associated with the entire cadmium pigment lifecycle:

are negligible compared to total emissions from all known sources (<0.5%)

do not pose any significant risk to man or to the environment.

Cadmium levels in the environment from all sources have been decreasing over the last 40 years, and this trend will continue with increasing implementation of improved pollution control and recycling technologies.

Measured average cadmium intakes by man are at the lower end of the range 10 - 25 µg/day, and are much low than the tolerable daily cadmium intake of 60 - 70 µg, established by the WHO. Less than 0.1 % of this daily intake is associated with the lifecycle of cadmium pigments.

Exposure from the 2.5 % from industrial applications can be further broken down as follows:

The only potentially significant contribution from cadmium pigments to environmental emissions is from end-of-life incineration of domestic waste containing cadmium-pigmented plastics. Modern waste incinerators have air pollution capture efficiencies greater than 99 %, and the risk assessment shows that they more than adequately control emissions to safe levels. Pigmented plastics in landfills are probably the safest form of cadmium in the environment, even when compared with naturally occurring metal ores. This is because of the extremely low solubility of the cadmium pigment and its complete encapsulation in plastic.

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Alternatives

ALTERNATIVES

Cadmium pigments provide a very wide colour range (from lemon yellows, through golden yellow, orange and red to deep maroon, but not green!) and have the versatility to colour all polymers, including engineering plastics. Consequently, a very wide range of potential alternatives has to be considered.

Other inorganic pigments that are available have either toxic hazards (e.g. chromium(VI) and lead for lead chromates) or provide weak colouration, lacking the required brightness and intensity.

Some of the more complex organic pigments can provide the necessary brightness, intensity and strength needed, but are generally much more expensive, and their adoption would place the European plastics industry at a disadvantage in world markets. They often do not show adequate resistance to weathering and light and fail to produce product lifetimes matching those for cadmium pigments. Furthermore, none of the complex organic pigments has been evaluated in a total lifetime risk assessment with respect to the environment and man.

Scandinavian countries have legislated to force substitution of cadmium pigments using alternatives, and the EU is currently endeavouring to harmonise the legislation in the EU. Papers published by Finland and Sweden on their experiences in substituting for cadmium pigments show that

> the viability of substitution for cadmium pigments is neither technically proven nor commercially favourable.

> any increased substitution for cadmium pigments may actually be increasing the risk to the environment and man, because very few alternatives to cadmium pigments have been fully assessed for environmental risk.

Conclusions

CONCLUSIONS

In the light of

> no significant risk to the environment or to man from the manufacture, use and end-of-life disposal of cadmium pigments.

> insignificant emissions of cadmium to the environment associated with cadmium pigments, compared to total emissions from known sources.

> lack of technical feasibility to replace cadmium pigments with alternatives in all applications.

> no risk assessments of the alternative pigments.

> identifiable commercial and economic disadvantages associated with forced replacement of cadmium pigments with alternatives, including plant closures and redundancies.

there is no justification for any restrictions on the marketing and use of cadmium pigments.

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