Costly clean-ups for ‘P’-contaminated homes have been grabbing headlines, but what are the real risks facing a family moving in?

Media have reported on figures released that show the number of state houses testing positive for methamphetamine contamination (from use or manufacturing) is increasing. There have also been a number of media reports of other homes discovered to be ex-meth labs, leading to calls for increased protection for home buyers.

The Science Media Centre collected the following expert commentary:

Dr Leo Schep, Toxicologist, National Poisons Centre, comments:

“When addressing problems associated with contaminated houses, we are dealing with two separate issues: a house where someone smoked methamphetamine, or a house that was used to manufacture methamphetamine.

“People living in a laboratory environment risk suffering adverse cardiovascular, respiratory and dermal effects following the exposure to organic solvents, acids, alkalis and other chemicals.

“However, people dwelling in a house where previous tenants had smoked methamphetamine, and there is some evidence of low concentrations on surfaces, have minimal risks of toxicity.

“The risks would be similar for people who live in a house that had previous dwellers who smoked cigarettes or marijuana. They will have exposure to these drugs but the concentrations will not be sufficiently high enough to cause either psychoactive or toxic effects to people who may have had inadvertent, and brief, dermal contact with these surfaces.”

Representatives from ESR‘s Forensic team provided the following commentary:

“It is worth pointing out that the risks associated with sites contaminated as a result of ‘P lab’ operations include exposure to methamphetamine but also to other chemicals used in/or resulting from such operations, including solvents, by-products and waste, which may have additional health implications.

“The testing that ESR undertakes gives an indication as to whether the methamphetamine was manufactured at the site, but we can’t rule out that the contamination is from methamphetamine use.

“We can’t comment on the testing that is undertaken by commercial operators for remediation purposes. Sensitivity (and specificity) may vary depending on the techniques being employed by different operators.”

Are there testing standards that commercial operators must adhere to?

“Not to our knowledge in regard to New Zealand. A number of overseas jurisdictions have promulgated testing standards. However, Standards NZ has recently established a committee that will begin looking at introducing standards for commercial operators.”

Does this industry need greater regulation?

“ESR is aware of concerns expressed in this field and supports the work initiated by Standards NZ.”

Dr Nick Kim, Senior Lecturer in Applied Environmental Chemistry, School of Public Health, Massey University, comments:

“From an industry outsider perspective it has been interesting to see almost all of the focus on removal of the methamphetamine residues themselves, e.g. this page. I don’t disagree with most of the content of that, but a wider reading of the guidelines should indicate that there are at least complementary risks around the types of other chemicals that were used in the manufacturing process.

“These chemicals vary depending on the ‘cooking’ process, so it is not safe to generalise, but a list of common known chemicals includes: hydrogen chloride, lead, iodine, mercury and volatile organic compounds. The guidelines then go on to outline which of these are regarded as the most important, in relation to exposure pathways and toxicity.

Exposure pathways inside the home

“To have a risk to people, we need an exposure pathway. Where there is no exposure pathway, there is no risk.

“For people living inside residential houses, the main potential exposure pathways are inhalation (breathing, which is dominant), and transfer to skin followed by either (a) absorption through the skin (called dermal absorption); or (b) transfer to the mouth. Dermal absorption is almost always a minor and secondary exposure pathway, because the skin (unlike the lungs) is designed to operate as a barrier.

“Inhalation relates to volatile chemicals, and these are primarily the organic solvents that were used in meth manufacture.

Organic solvents used in manufacturing methamphetamine include acetone, toluene, pyridine, ether, alcohols (methanol, isopropylalcohol), acetic anhydride, and others. Acetone and toluene are not particularly exotic solvents: acetone is commonly used in nail polish remover, and toluene is a component of petrol. Pyridine is less commonly encountered but more toxic. Ethers are so volatile that they tend not to persist.

Manufacture of methamphetamine typically causes relatively large quantities of whatever organic solvents have been used to be absorbed into soft furnishings and wall boards, or into the ceiling cavity if the solvent vapours are being vented into that. The guidelines list upholstered furniture, curtains, carpet and plasterboard as examples.

Once solvents are absorbed by these materials they gradually will re-volatilize back out into the air and be inhaled. Although some of these are solvents that we are occasionally exposed to (e.g. nail polish remover) we generally don’t want children or adults to be breathing them for extended periods, even at low concentrations.

“A key priority in site remediation should therefore be to ensure that residual concentrations of solvents in the air are below relevant guideline levels or non-detectable. This can start with removing and replacing soft furnishings and keeping doors and windows open for an extended period, but in severe cases might require removal and replacement of the wallboards or perhaps material inside the ceiling cavity.

Most (though not all) volatile organic solvents do have an odour. As a first guide, if someone can still detect a solvent smell after a property has been remediated, there is probably still too much solvent around being released into the air from one or more unidentified reservoirs. I understand that finding the source can be tricky in some cases.

So as one priority, remediation companies should be making an effort to determine what solvents have been used in a given case, and ensure that residues of these are acceptable. Air testing is a suggested.

In some cases, inhalation may be relevant for the heavy metal mercury, if that has been used and there is a reservoir of mercury around somewhere. Mercury is a liquid at room temperature and does have an appreciable vapour pressure (a pool of mercury has mercury gas entering the air above it).

“Skin absorption relates more to chemicals that are not volatile, or semi-volatile. Although solvents (on a surface) could be absorbed through the skin, they won’t remain as a film on the surface for long and the total absorbed dose would be small.

Methamphetamine itself falls into this category. Residues of methamphetamine could exist on surfaces, and therefore transfer to skin (followed by either dermal absorption or secondary transfer to the mouth) is a potential exposure pathway. In this case inhalation is not a viable pathway, simply because methamphetamine is not particularly volatile.

This is why guideline limits for the methamphetamine itself focus on the amount left on a surface, not how much is in the air.

The approach taken in the guideline document is precautionary. We have a high level of confidence that if the guideline is met, then any exposure would be negligible.

That leaves the question of how high could methamphetamine residues get before they were no longer at a safe level? I personally don’t think it is (or will ever be) possible to accurately specify that, for several reasons. These include:

We cannot predict how much wall someone’s bare skin will come into contact with, for how long, and what proportion of the methamphetamine residues will transfer to the skin;

skin will come into contact with, for how long, and what proportion of the methamphetamine residues will transfer to the skin; We do not accurately know what proportion of the methamphetamine transferred to someone’s hand will be absorbed through their skin and over what timescale;

We cannot predict the frequency of hand washing and how this relates to the absorption timescale (hand washing will remove most of what transferred).

We cannot know the extent to which an individual will transfer methamphetamine from hand to mouth in a given case.

“We can contrast breathing and skin contact. For inhalation (breathing) we know the approximate volume or air that an adult or child breathes each day, and we know that the lungs are efficient at absorption, and we know that if a certain concentration exists in air, we can reliably estimate the inhaled and absorbed dose. We can’t do that for skin contact – there are too many unknown variables. For these reasons my own view would be that calls to specify a higher “no longer safe” level of methamphetamine are calls for something that is technically unachievable.

“However (as noted above) I am reasonably confident that the if the precautionary guideline is met, then any exposure would have to be negligible. In doing a risk assessment, we often refer to a source -> pathway -> receptor (=people) model. To have a risk, all three elements need to be in place. In a case where we are uncertain about pathway factors (as we are with skin contact here) the most reliable approach to removing risk is either to effectively remove the source (achieved here by setting a suitably low guideline value), or else remove the receptors (stop people from living there).

“Having said this my guess is that in most cases, quite high levels of (non-powder) methamphetamine on a surface may pose minimal risk because I suspect the timescale of skin absorption would be sufficiently long for the dose in general blood circulation to always be negligible (never get very high). But I can’t know.

“Traces of free methamphetamine powder would of course be a different matter.

Exposure pathways outdoors:

“In the garden where chemicals or residues may have been dumped or buried, the main potential exposure pathways are through direct ingestion (e.g. a toddler eats some contaminated soil), direct dermal contact with possibility of ingestion (the toddler comes across a discarded chemical drum). Other pathways there include potential for uptake in home grown vegetables and contamination of groundwater which might lead to a borewater supply if it is a rural property – but both of these really have limited potential to add up to any significant exposure.

“A number of chemicals that can be used in meth manufacture are corrosive (acids), directly toxic (the heavy metal mercury) or strongly alkaline (sodium hydroxide). Contact with any pools of acidic or corrosive chemicals might also cause direct effects such as chemical burns.”