Undesirable substances – more commonly known as contaminants – are defined in legislation as 'any substance or product, with the exception of pathogenic agents, which is present in and/or on the product intended for animal feed and which presents a potential danger to animal or human health or to the environment or could adversely affect livestock production'.
.Examples include arsenic, cadmium, lead, mercury, aflatoxin B1 and dioxins.
Generally, these undesirable substances are either naturally-occurring environmental contaminants that are present at low levels in feed and food products, particularly vegetable crops drawing nutrients directly from the soil, or are process contaminants that may be introduced into the feeding stuff either during or as a consequence of its treatment, manufacture and storage.
The presence of undesirable substances in feed is controlled by European Parliament and Council Directive 2002/32/EC of 7 May 2002 (as amended), which sets maximum permitted levels (MPLs) for these substances and is given effect in England by regulations 8 and 9 of the Animal Feed (England) Regulations 2010. (Separate but parallel legislation applies in Scotland, Wales and Northern Ireland.) Feed that contains a contaminant at a level above the relevant MPL is deemed to be unsafe and must be withdrawn and disposed of outside the feed and food chains, for example by sending it for alternative uses, for destruction, or returning it to the country of dispatch. (The 'blending down' of consignments of feed materials with levels of contamination above the MPL – mixing them with uncontaminated consignments in order to reduce the overall level of contamination to below the upper limit – has been prohibited since 2003.)
These controls apply to feed for both food-producing and non-food-producing animals – that is, feed for farmed livestock (including horses and rabbits), fish, pets, laboratory, zoo and circus animals, and creatures living freely in the wild.