The Western Australian (WA) Department of Health (the Department) has published a report on Public health risks of methylamphetamine (meth) smoke houses (PDF 2.1MB). The report was prepared by Dr Erica Parker, a Public Health Register at the Department who has brought medical, public health and research skills to the task.
Meth contamination from smoking in homes is an ongoing public health issue, along with clandestine laboratory (clan lab) meth contamination, but poorly understood and subject currently only to interim regulatory management in WA.
Findings
Key findings from the report include:
- Meth remains the best contaminant as a basis for residue assessment and management.
- Contamination from smoking meth primarily comes from user exhalations and while surface residues are highest in the vicinity of the activity they can disperse further and persist for months and years.
- Around 2.7% of WA households (around 30,000) may have surfaces contaminated to some degree by meth smoking over the past five years and so more than 75,000 individuals (including the smokers) may have third-hand exposure via contact with these surfaces.
- From a health perspective, meth contamination from smoking is indistinguishable from contamination from manufacture, and the same health-based reference doses should apply, and likely the same action levels derived from them.
- The vast majority of suspected smokehouses have average surface meth levels less than 5µg (mean 2.7µg, median 1.5µg) per 100cm2, with ‘hotspots’ in rooms of heavy use that may reach 10-15µg/100cm2, and rarely higher.
- Meth can be absorbed into the body via dermal, oral, and inhalational routes, and subsequently act in the same physiological manner. Inhalation has not previously been considered a significant residue exposure route, and while also being modelled within this work, warrants further study.
- Although meth has a range of well documented health effects, data suggesting effects due to sustained low-dose exposure from third-hand environmental sources (such as meth smoke surface residues) are lacking.
- Modelled meth blood levels for even the worse-case exposure scenarios from meth smoke house exposure provide no indication that health effects will occur. However, the associated high levels of uncertainty prevent reliance on these calculations. As such, the current HIL is still justified.
- In conclusion, exposure to meth residues in former smokehouses based on conservative assumptions carries a low risk to public health. These residues can be managed by routine cost-efficient measures commensurate with that risk, which may include a remediation focus on ‘touchable’ living space surfaces.
Application
In 2018 the Department published an Interim Guide for Remediation of Low Level Illicit Drug Contamination (PDF 276KB) due to increasing incidents and concern about surface contamination arising from smoking meth. This guidance was unprecedented in Australia and took the approach that meth smoke residues were likely to be present at much lower levels than those from meth laboratories and could be remediated with procedures commensurate with the associated lower risk. As there was limited information to base this guidance on, it was deemed “interim”.
The above report provides substantiation to this approach and also some of the detail which will allow revision and “finalisation” of the 2018 guidance.
An ongoing problem is distinguishing meth smoke from meth manufacture surface contamination, so the appropriate remediation process can be selected. The Department has recently adopted the approach, supported by this report, that where meth contamination is suspected or investigated, any meth present should be reasonably assumed to be a result of smoking rather than manufacture, unless there is evidence or intelligence to the contrary.
This policy is supported by relevant calculations in the report. These indicate that for a 5 year period 30,000 WA households may have become impacted by meth smoke. A similar approach may be used to calculate the number of contaminated meth labs in WA over the same period based on notified police “busts” (ACIC 2021) and the assumption that only about 10% are being found (enHealth 2017). This comes to 270, which is more than 100 times less than the number of homes believed to be impacted by meth smoke.
Broader Considerations
Over much of Australia any meth contamination is treated as if it results from manufacture and so prompts a fairly rigorous and potentially expensive remediation, based on either the national clan lab guidelines, jurisdictional clan lab guidance, or industry practices.
As indicated in the report, nationally there may be 1.5% of homes (about 140,000) which may be impacted by meth smoke over the same 5 year period addressed for WA. Similar calculations can be done to work out the ratio between households impacted by smoke and manufactured meth. In this case ACIC 2021 Drug Data Report can be used for the numbers of meth labs. The rest of Australia can be determined to have a little above 2 labs per 100 smoke houses, and so more than twice the WA rate.
It is also noteworthy that all other jurisdictions predominantly have meth labs based on phosphorous methods (ACIC 2021) which are usually many more times contaminating than the dominant Nazi/Birch method used in WA (enHealth 2017).
Therefore in other jurisdictions there is likely to be a greater total risk per population from clan labs than in WA, but throughout Australia they still represent a very small proportion of impacted properties. The latter proportion is likely become more pronounced with time because although meth use seems to be falling, the numbers of meth labs have been falling faster.
In Conclusion
The Department believes that regulatory and industry effort related to testing and remediating meth impacted households should include a much greater focus on the far more common properties associated with smoke contamination and at a level commensurate with their quite low level of assessed public health risk.
References
Last reviewed: 24-11-2021
Produced by
Environmental Health Directorate