A team from Flinders University has investigated the levels of residual methamphetamine potentially left on soft, porous surfaces such as carpet, air-filters, and clothes.
The literature review, published 12 December 2022 in Toxics, highlighted that even after an extensive clean-up of surfaces in dwellings used to manufacture methamphetamine, or where meth had been used in the past, samples still contained elevated levels of the drug which could pose a threat to other people.
The team reported residue levels equivalent to consuming as much as 15g per day of methamphetamine at former drug labs, months after they were shut down, with re-emission detected from carpets, air-conditioning, soft toys, underwear, and cotton-based clothes.
Lead author and Flinders PhD candidate, Ms Gemma Kerry, from the Forensic and Analytical Science research group, explained that methamphetamine is manufactured or ‘cooked’ in clandestine laboratories by a variety of methods commonly using precursors such as ephedrine, pseudoephedrine, 1-phenyl-2-propanone (P-2-P), and P-2-P precursors.
During the manufacturing process and after smoking the drug, methamphetamine residues, airborne particles, gases, and volatile organic compounds (VOCs) are released into the surrounding environment.
“A methamphetamine contaminated property could pose a third-hand exposure risk to individuals from skin contact, ingestion, and inhalation exposure routes,” Ms Kerry said.
“Those living or working in contaminated properties have experienced adverse health effects including respiratory irritation, eye irritation, nausea, headaches, behavioural issues, and sleep issues.”
Typically, soft furnishings and clothing are discarded from contaminated properties as they can be difficult to decontaminate and can re-emit residues, and wipe sampling of hard, non-porous surfaces is commonly performed to determine surface methamphetamine concentrations on contaminated items.
In Australia, current guidelines for indoor surface methamphetamine residues are at 0.5 μg of methamphetamine per 100 cm2 and 10 μg/100 cm2 for residential and commercial properties, respectively, however there are no recommendations for sampling and analysing indoor airborne methamphetamine.
“These guidelines are based on dermal transfer and oral intake and do not take into consideration inhalation intake; and as such, these guidelines could significantly underestimate the overall environmental exposure,” Ms Kerry said.
“There is a lack of information on the transfer processes of methamphetamine from indoor air and clothing that could contribute to potential health risks from potential re-emission, direct skin contact and ingestion from hand-to mouth activity in these areas.”
For example, one study from 2021 found that air samples taken from a ‘cook house’, suggested that the total methamphetamine intake by young children and adults could be 0.01 mg/kg/day and 0.001 mg/kg/day respectively, from oral, dermal, and inhalation exposure – with total intake from inhalation comprising 20% for young children, and up to 80% for adults.
Similarly, methamphetamine was detected at low levels from the air-conditioning system at another former drug lab, several months after it was shut down, and based on assumptions in breathing rate and exposure time, the authors determined that the potential inhalation dose from this site would be 15g/day of methamphetamine.
Fabric materials with a large surface area such as carpeting fabrics were also found to act as a sink and contaminant source, with vacuum samples of carpet prior to methamphetamine manufacture revealing levels between 2.7 to 5.5g/m2.
“Typically, solvent extraction or SPME followed by GC-MS or LC-MS analysis is used for compound analysis on fabrics,” Ms Kerry explained.
“But again, there are no universally recommended guidelines for extracting methamphetamine from textile materials – even though research has shown that chemicals related to third-hand tobacco smoke can sorb to clothing and reemit.”
Subsequent surface sampling and bulk analysis of carpet sections gave concentrations in the range of 5.4 to 70g/100 cm2 and 27 to 460g/100 cm2, and compared to linoleum and drywall, the carpet appeared to readily absorb methamphetamine resulting in higher surface contamination.
Soft toys obtained from a contaminated property also revealed methamphetamine concentrations ranging from 1.1 to 12g/g for bulk analysis and 0.046 to 0.3g/m3 for air sampling of the toys in a sealed bag, with the authors noting that “both liquid extraction and air sampling of soft toys showed that methamphetamine could sorb and desorb from these toy materials.”
In terms of the release and detection of airborne methamphetamine after ‘smoking’ the drug, the review found that that methamphetamine levels decreased significantly after a four-week period from the final smoking event.
However, airborne levels still ranged from 300 to 520g/m3 after a single smoke of 100mg of methamphetamine at 91% purity, with any rise in the total amount smoked further increasing the levels of airborne methamphetamine.
Another study reported that surface values of 0.25 to 2.96g/cm2 were obtained after smoking of 0.2g methamphetamine, and the drug was detected in underpants, undershirts, and pant samples from known users, with higher concentrations found in garments exposed to sweat secretion through direct skin contact.
“Furthermore, loose-weave cotton material appeared to readily desorb methamphetamine without treatment, and just five minutes after fabric-to-skin contact it was observed in skin and receptor fluid samples, indicating that fabric-to-skin drug transfer was rapid,” the authors said.
“In addition, the moistened fabric was found to have seven times greater fabric-skin transfer efficiency compared to the dry fabric after two hours of contact.”
Thankfully, the review also revealed that up to 99.9% of methamphetamine could be removed from contaminated clothing after three wash cycles.
While the AIHW reported in 2019 that 1.3% of Australians aged 14 and over reported using meth or ‘ice’, the review stressed that such figures did not include those who were impacted by other peoples’ methamphetamine through second- and/or third-hand exposure.
“The presence of methamphetamine indoors poses environmental and public health risks,” the authors concluded.
“From air sampling studies, elevated airborne methamphetamine levels were present in indoor air at suspected former clandestine laboratories, after controlled methamphetamine manufacture, and after controlled smoking.
“The scarcity of publications outlined in this review highlights that more research needs to be completed and disseminated so that the total impact of second- and third-hand exposure to methamphetamine is known by police, forensic investigators, first responders, and legal and medical practitioners.”