Ask H&H: grazing

Q: I have been offered grazing for my horses on an old landfill site that has now been laid to grass. The soil was tested and is contaminated with heavy metals (including lead). I understand that the grass is safe for animals to eat, but I do not want to risk my horses becoming ill if they consume a small amount of soil. Are these fields safe for them?
CP, Essex

WE asked the reader’s local council, Epping Forest, for its advice.

“You don’t mention the levels at which the metals were found,” replied Dr Paul Baccarini, of the council’s environmental health department.

“Many people see metals such as lead, copper and zinc as contaminants. However, while elevated levels are usually a result of a pollution, metals do exist naturally in soils and plants — some are essential micronutrients.

“Many factors will influence the toxicity of metals to your horses. For example, what form of metal exists in the soil? Is it available for uptake into plants?”

According to Dr Baccarini, all animals tolerate metals that are present naturally but, where there are extremely high levels of a certain metal, acute toxicity symptoms may be seen.

“In horses, lead exposure symptoms include breathing difficulties, stiffness, clumsiness, enlarged joints, facial paralysis, muscular weakness and poor appetite,” he said.

“At lower levels, no such symptoms may be seen but the metal may interfere with the uptake and distribution through the animal’s body of natural nutrients.

“You should contact a vet with your concerns,” advised Dr Baccarini.

“If they consider there to be a low risk, you may wish to keep the grazing intensity low to reduce the likelihood of consumption of soil and roots, keep a regular check on the health of your animals and don’t use the grass to make hay. In the case of lead, blood levels are a good measure of exposure, and your vet may advise you on a screening programme.”

H&H also asked Nick Lepp, professor of plant science at Liverpool John Moores University (JMU), for his advice on the ingestion of heavy metals.

“There are two main potential ‘exposure pathways’ for horses,” he explained.

“The first is year-round ingestion of grass that is contaminated with metals. The second is direct ingestion of soil in the winter months, when the grass is growing slowly, or not at all.

“In an acid soil, heavy metals are more soluble and plant-available, while arsenic is more mobile in an alkaline soil. Lead, copper and arsenic are fixed to organic matter — dead plant remains — and may stay close to the soil surface, making them potentially more dangerous to grazing animals in terms of direct soil ingestion.”

INFORMATION

Liverpool JMU www.livjm.ac.uk

This Q&A was first published in Horse & Hound (3 April, ’08)