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Food-safety officials have confirmed that Coromandel honey eaten by 22 people who fell ill was contaminated with high levels of a plant toxin, and tougher controls on the honey supply are now being contemplated.

The Food Safety Authority said last night that laboratory tests had confirmed the presence, as suspected, of toxins from the tutu plant in leftover comb honey supplied by people who became sick after eating the products at Easter.

People suffered symptoms like seizures and vomiting after eating the honey produced by Projen Apiaries but no more cases have been reported. Twenty packages of potentially toxic Projen honey, branded either Wentworth Valley or Moana Point, are still unaccounted for. People who have any are urged to hand it to their nearest public health unit.

The producer, hobby beekeeper Kevin Prout of Whangamata, last night declined to comment on the test results.

The authority said a decision on whether to prosecute had not been made as the matter was still under investigation.

Honey can become contaminated with the potentially lethal toxin tutin and hyenanchin, a tutin derivative, when bees gather honeydew from the tutu plant. The honeydew is secreted by a vine-hopper insect which feeds on the plant. Periods of drought are high-risk.

Tutin and hyenanchin are thought to produce similar effects in humans, although bees are unaffected. Beekeepers are required to avoid contamination of any honey they sell for human consumption but the authority is considering stepping up controls following the food poisoning.

The authority's senior programme manager for animal products, Jim Sim, said the tests showed levels of between 30mg-50mg of tutin per kilogram of honey, and 180-300mg/kg for hyenanchin.

It was unclear how much of the toxins needed to be consumed to be harmed. There was some data on tutin and the authority was trying to obtain quantities of both toxins to ascertain their exact levels of toxicity. This could lead to regulatory maximum levels being set for honey.

Once chemical standards were available, commercial testing of honey would become viable, if it was considered necessary.

Many options for changing the management of the risks posed by the toxins were being considered by the authority, in conjunction with the honey industry.

"We want to be able to head towards setting some sort of limit," Mr Sim said.

Bee Products Standards Council chairman Jim Edwards said a viable and commercially available test would be useful.