Photo: Rebecca Stevenson

A scientific comparison of two ways your house may be trying to kill you

While the meth testing scheme has been proven to be a rort, the dangers of lead contamination in homes is still very real. Environmental scientist Tim Muller explains.

In case you missed it, the prime minister’s chief science advisor (PMCSA) recently released a damning report into the meth testing and remediation industry. The gist is that health effects from meth residues are only a concern in houses where it’s been manufactured, not just smoked. The $100 million reportedly spent by Housing New Zealand (HNZ) combating meth contamination, plus plenty more by private homeowners, was (for most properties) wasted.

In the largely justified outrage that followed this revelation, one question has been conspicuously absent: “If we have to have a national witch hunt about house contamination, could we at least have picked a better contaminant?” The question may be a little contrived, but it is important. Spoiler alert, the answer is ‘yes’ and the contaminant is lead.

Just like half the cleaning and cosmetic products out there claim to be, lead is 100% natural. And like tigers, uranium, and many other 100% natural things, lead can kill you. While fatal lead poisoning is rare, lead can damage your kidneys and cardiovascular and nervous systems. What’s probably most concerning are lead’s effects on cognitive development, particularly IQ reductions in children.

Lead is commonly present in drinking water due to leaching from pipes and fittings (usually at very low concentrations). The Ministry of Health guidance on lead exposure advises that flushing 1-2 cups from the tap before filling your glass reduces lead concentrations to well below the drinking water standard “in almost all cases”. However, unless you have an unusual occupation or hobby like soldering or working with car batteries, the main way you might be exposed to lead is from paint.

The hazards of lead paint were recognised long ago and it was largely phased out by the mid-1980s. But before then (particularly before 1945) lead was in most paints at concentrations of up to 50%. As the paint flakes, or is sanded back during redecorating, lead builds up in house dust, and in the soil around the house. The people living in the house may then be exposed – especially children, and anyone else who appreciates the culinary delights of dirt and sucking on furniture.

There’s no level of lead that’s completely safe, but there are concentration standards for blood, soil and house dust, based on what’s considered to be acceptable risk. Because older paints are literally half lead, it doesn’t take much to cause a problem. About half a gram of paint flakes per kilogram of soil, or just under a milligram of paint dust (equivalent to maybe 10 grains of salt) per square metre of floor is enough to exceed the standards.*

My mate’s cousin, Jonathan Kennerley, found this out when he and his wife Laura bought their 1913 Mt Eden villa which a real estate agent might say had “potential” (read: it was full of car parts and left derelict for at least a decade). The exterior paint was flaking off so there was no choice but to remove it. Rather than rush in they did their research and bought a grinder with a purpose-designed vacuum extraction system, as well as wearing overalls, gloves, and respirators rated for lead dust.

Jonathan and Laura’s house, as it was when they bought it (Image: supplied)

Despite that, three-quarters of the way through, Jonathan fell sick with cold-like symptoms and stomach cramps, and a test confirmed that his blood lead concentration was three times the MoH’s level of concern (above which cognitive function can be affected). The rest of the family had no symptoms, but were tested just in case. To Laura and Jonathan’s horror even their two children, who’d only visited the house a handful of times by that stage, had blood lead concentrations around double the MoH standard.

That was in 2014, and the house and garden have been cleaned up (and done up) since then. Laura and Jonathan have their dream home, but they’ll never know for sure what it cost them.

A derelict house with flaking paint is a fairly extreme exposure scenario. But Jonathan fell ill despite the precautions taken, so it’s easy to imagine how a child crawling and licking their way through the world could get a similar level of exposure per body weight, even with much less lead dust around. And cognitive development may be impaired before blood lead concentrations get high enough to cause any observable symptoms.

The Kennerley family are just four of over 100 New Zealanders every year found to have elevated blood lead levels, mostly from non-occupational exposure. But we only know about the people who got blood tests, and the symptoms of lead poisoning are largely hidden and/or similar to other conditions. How many people would think to get a blood test if they felt sick after painting?

Number (blue) and percentage (red) of housing stock built before 1950 for each territorial authority (missing data for Stratford, Kawerau and Chatham Islands).

A better indicator of the scale of the problem may be the age of our housing stock. Based on aggregated age estimates for 1.1 million New Zealand houses provided by, around 20% of houses were built before 1950. In six districts, including Dunedin and Wellington cities, more than 40% of houses are that old. That amounts to over 200,000 pre-1950 houses nationwide, with almost 50,000 in Auckland alone. Houses from that era aren’t automatically a significant health risk (nor are newer houses necessarily safe). But there’s a good chance that some lead residues remain around these older houses. Even if the house has been removed, as it’s possible the garden soil could have been contaminated.

Therefore, lead contamination probably affects far more properties than methamphetamine residues, and if both are present, lead is the one to worry about (unless we’re talking about a meth lab). Simple measures like protective coatings on interior walls, covering affected soil with bark, or moving play areas and vege gardens can significantly reduce the risks, though obviously some lead remediation jobs like the Kennerleys’ are much more involved.**

It’s hard to avoid the conclusion that methamphetamine contamination got the headlines and the clean-up budgets because it plays nicely into morality politics. Plus landlords could pass the blame (and often the costs) onto tenants.

It’s not uncommon for new research to downgrade the risk of a contaminant, but it’s striking how little recent research had to be considered in the PMCSA meth report. The crux of their argument is essentially a back-of-the-envelope calculation based on (mostly) 10-year-old primary studies. That’s not a criticism of the authors, just the opposite – the back of the envelope may be the greatest scientific instrument. Instead it makes you wonder how this got so far without someone high up in the previous government asking the same questions. It’s hard to justify being ill-advised about science when you have your own personal Chief Science Advisor.

Of course, that’s easy to say with hindsight and many will say that safe is better than sorry. That impulse is perfectly understandable, but it’s the right answer to the wrong question. “Better safe than sorry” – as it’s been applied to meth remediation – only makes sense if you assume that eliminating all risk is a) possible and b) desirable. It is neither.

The global supply of risks is limitless and rising fast. Rivers might flood. Lovers might leave. Miracle building products might cause cancer. In the real world, risks are minimised, managed, insured against, begrudgingly accepted, or traded off against each other, but rarely eliminated.

The right question is: what’s the minimum total risk level that can be achieved with the resources available? So, a large property portfolio may include some former meth labs which need urgent action. Other properties where meth was only smoked will pose a negligible risk to future occupants. Somewhere in between are homes affected by other contaminants like lead (or asbestos, or toxic moulds). And properties with sub-standard insulation, ventilation or heating – issues which may pose a higher health risk than any contaminant present.

A social housing provider should also consider the health risks faced by people who need a home but can’t get one. The PMCSA report rightly states that “the risk of being in an unstable housing situation is likely to be far greater than the risk of exposure to low levels of methamphetamine residues”, and the same will often be true of lead and the other issues I’ve mentioned.

That’s not to say we shouldn’t expect HNZ and other social housing providers to be great landlords. However, sadly, the idea of all New Zealanders having access to a warm, safe, healthy home is currently a wildly aspirational goal. While we’re working on that, we need to make sure all New Zealanders at least have access to a home.

A correct application of the “better safe than sorry” principle would be to rank these potential health risks for each home, and deal with the highest risks first. In the last few years though, the principle of “better safe than sorry” has been widely interpreted as requiring clean-up of insignificant methamphetamine concentrations, sometimes at the expense of addressing real risks.

Every discussion on residential lead contamination I’ve been involved in has had more or less the same tone: yes, it’s a problem, but who’ll ever have the will to fix it? No politician wants to tell the people of Remuera and every other heritage suburb in the country their houses need testing. But if there’s one positive lesson from our national meth witch hunt, it’s that people who believe their house might be harming them will usually find the money and the means to solve the problem. Here’s hoping that works for real problems too.

* Just so I don’t get kicked out of science: these calculations are a simplification of a complex, conservative and nuanced set of standards. Those standards are intended as a trigger for further assessment, not panic and automatic remediation. That aside, I think it’s a helpful illustration. For the trainspotters, I assumed the paint is 50% lead by weight, and applied the standards for lead in typical residential conditions: 210 mg/kg for soil or 430 µg/m2 of floor area for indoor dust.

** If you’re concerned about lead at your place, the Ministry of Health and Worksafe guides are good places to start.

Tim Muller is an environmental scientist for Landpro. His specialist areas include environmental chemistry and contaminated land. Thanks to Dr David Bull and Martin Moore for their input, but all opinions expressed and any errors are the author’s.

The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.


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