The cost of cleaning up P contaminated houses can run into the tens of thousands of dollars

Nearly a quarter of homes built for a brand new state housing development in Christchurch have already been contaminated with P less than a year later.

In most cases, the tenants were single mums with young children, including four toddlers under two.

Social Housing Minister Paula Bennett said she found the figures "shockingly high" and the age at which some children were being exposed to P, or meth, was an "extreme concern".

"Four of them are two years or younger, so wee babies. It's at a time when they are most susceptible to their environment and they need the healthiest environment they can possibly get. There are some quite serious health effects [from P] with skin and respiratory conditions. And equally you have to question if its a healthy and safe environment. "

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The new housing development only went up in June last year. Of 19 houses built, two tenants have since been evicted after tests returned positive for P and two more evictions are underway.

Police had suspicions about a further two houses but they tested negative for the drug.

Officials declined to give the location of the development but it is understood police first began investigating after reports of drug dealing and unsavoury behaviour day and night.

Bennett said there had been a dramatic escalation in the number of P contaminated houses but it was hard to know if it was a new problem, or whether it was because HNZ was testing more rigorously under its zero tolerance policy.

The most recent figures show nearly 400 HNZ properties are uninhabitable as a result of P, and clean ups can cost tens of thousands of dollars. Most are a result of P use, rather than the houses being used as P labs.

In the last six months HNZ has spent $5.8 million on testing and remediation and in the Christchurch/Marlborough/Nelson region alone the cost is $350,000.

In the same period, 279 properties have been confirmed as meth contaminated, including 33 in Christchurch, and five properties nationwide have had to be demolished.

It costs around $16,000 to demolish a small property and up to $30,000 to decontaminate a house.

Bennett said the problem was a mounting concern for Housing New Zealand, and not just because of the cost, both social and financial. It was having an impact on its waiting lists.

In Christchurch alone there were 426 people on the social housing register - the millions of dollars spent on testing and treating P houses could have bought an extra 15 properties.

HNZ has looked at options including meth testing devices but 'the science is not quite there yet", Bennett admitted.

But one option now being weighed up was testing each property in between tenancies, which would come at a heavy financial cost.

At between $600 and $1800 per test, it would add between $4 million and as much as $120 million a year to its costs.

The problem with P

* It can cause breathing problems, respiratory irritation, skin and eye irritation, headaches, nausea and dizziness.

* High exposures even for a short time can cause death or severe lung damage and skin or throat burns

* People can be exposed by breathing the air that may contain suspended contaminant particles as dust, by touching surfaces that are contaminated, by eating or drinking from contaminated dishes, or from eating or smoking after contact with contaminated areas.

* Contaminants may also linger in air filters and drains.