Levels of arsenic and lead in a contaminated Thames subdivision are so high that a handful of soil could prove fatal if ingested by a small child, a toxicologist has claimed.
But Health Waikato says the soil would only make the child ill and is sticking to its warnings to supervise young children living at Moanataiari to make sure they do not eat any dirt.
Mike Fitzpatrick, a former arsenic chemist, said a lethal dose of arsenic for a toddler weighing 10kg, usually about 12 to 18 months old, was 10mg.
The highest surface soil level of arsenic at the 1970s suburb, which houses 200 properties, two preschools and a primary school, was 670mg a kilogram.
"Eating a small handful of it would kill a child," said Dr Fitzpatrick. "It would be acutely toxic."
Dr Fitzpatrick, now a medical researcher, recommended Health Waikato test residents to check their exposure to the deadly metals.
In November, it was revealed parts of the subdivision had arsenic levels up to 235 times higher than the national soil contaminant standard of 20mg/kg of dirt. Last week, further tests by Thames-Coromandel District Council showed high amounts of lead and other metals.
Contamination at the site is understood to be from tailings from old goldmines which were dumped there.
Dr Fitzpatrick dropped leaflets to residents in the subdivision warning them not to be complacent and offering a free assessment of their soil results.
So far only one resident has contacted him for the assessment.
Waikato District Health Board medical officer of health Dr Dell Hood admitted there was a "real concern" for very young children but did not believe a handful of the soil could kill a toddler.
"Dr Fitzpatrick's information is theoretically correct in some situations but the contamination is patchy," Dr Hood said.
"It would make them sick. The probability that a child would ingest a hazardous amount of lead or arsenic to the extent of poisoning themselves is therefore reasonably low."
She said no child anywhere should be eating dirt because all soil was full of health hazards.
Dr Hood said Thames Hospital and GPs in the town were prepared for possible arsenic or lead poisoning cases.
Long-term exposure was of more concern, Dr Hood said, but so far there was no evidence of lead exposure. Arsenic exposure was harder to measure.
"We have evidence of children not presenting with raised lead levels ... they're not over-represented at all in the Thames community.
"But because there is the potential for the lower level long-term exposure, starting before birth potentially during pregnancy, we want the community to know about this and be vigilant more than usual."
Health warnings included preventing children from playing in or ingesting the soil, not eating homegrown vegetables or fruit unless the soil is clean fill, washing hands after contact with soil, and removing footwear before going indoors.
Since the arsenic was discovered in October last year, the council has held weekly meetings to update residents.
It also removed exposed soil at the school and preschools and is to look at management of the situation and remediation options - which could include replacing exposed top soil - in May.
Meanwhile, Dr Fitzpatrick's father-in-law, Gordon Rogers, who lives in Moanataiari, said he wanted to move out of the subdivision. "We've been here seven years ... but we're selling our house to get away from the area."
The 71-year-old said he had moved to Thames from Auckland but would never have bought a house in Moanataiari had he known about the contamination.
"It's not good. There's people coming from other areas to buy a house at a very cheap rate."
Mr Rogers said one buyer offered him $200,000 for the house, which had a capital valuation of around $300,000, and Mr Rogers put its market value at $350,000.
"They want to rent it out, they're not prepared to live here. But we're not going to give it away."